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CHP 9, 10, 11, 12

by: Emma Myhre

CHP 9, 10, 11, 12 Anat 204

Emma Myhre
GPA 2.791

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CHP 9, 10, 11, 12
Anatomy for Paramedical Personnel
Mr. Berge
Study Guide
UND, anatomy
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This 43 page Study Guide was uploaded by Emma Myhre on Sunday February 28, 2016. The Study Guide belongs to Anat 204 at University of North Dakota taught by Mr. Berge in Winter 2016. Since its upload, it has received 72 views. For similar materials see Anatomy for Paramedical Personnel in Anatomy at University of North Dakota.


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Date Created: 02/28/16
Chapter 10: Nervous System I: Basic Structure and Function  Introduction  The nervous system is composed predominately of nervous tissue but also includes some blood vessels and connective tissue.  Two cell types of nervous tissue are neurons and neuroglial cells.  Neurons are specialized to react to physical and chemical changes in their surroundings.  Dendrites are small cellular processes that receive input.  Axons are long cellular processes that carry information away from neurons.  Impulses are bioelectric signals produced by neurons.  Bundles of axons are called nerves.  Small space between a neuron and the cell(s) with which it communicates is called a synapse.  Neurotransmitters are biological messengers produced by neurons.  The central nervous system contains the brain and spinal cord.  The peripheral nervous system contains cranial and spinal nerves.  General Functions of the Nervous System  Three general functions of the nervous system are sensory, integrative, and motor.  Sensory receptors are located at the ends of peripheral neurons and provide the sensory function of the nervous system.  Receptors gather information.  Receptors convert their information into nerve impulses, which are then transmitted over peripheral nerves to the central nervous system.  In the central nervous system, the signals are integrated.  Following integration, decisions are made and acted upon by means of motor functions.  The motor functions of the nervous system use neurons to carry impulses from the central nervous system to effectors.  Examples of effectors are muscles and glands.  The two divisions of the motor division are somatic and autonomic.  The somatic nervous system is involved in conscious activities.  The autonomic nervous system is involved in unconscious activities.  The nervous system can detect changes in the body, make decisions, and stimulate muscles or glands to respond.  Description of Cells of the Nervous System  The three parts all neurons have are cell body, axon, and dendrites.  A neuron’s cell body contains granular cytoplasm, mitochondria, lysosomes, a golgi apparatus, and many microtubules. It also contains a large nucleus, chromatophilic substance, and cytoplasmic inclusions.  Neurofibrils are fine threads that extend into axons.  Chromatophilic substance is membranous sacs that contain rough endoplasmic reticulum.  Mature neurons generally do not divide but neural stem cells do.  Dendrites are usually highly branched to provide receptive surfaces to which processes from other neurons communicate.  Dendritic spines are tiny, thornlike spines on the surface of dendrites.  A neuron may have many dendrites but will have only one axon.  An axonal hillock is the initial portion of an axon closest to the cell body.  An axon is specialized to carry nerve impulses away from the cell body.  The cytoplasm of an axon includes mitochondria, microtubules, and neruofibrils.  Collaterals are branches of axons.  A synaptic knob is a specialized ending of an axon.  A synaptic cleft is the space between a synaptic knob and the receptive surface of another cell.  Axonal transport is the process an axon uses to convey biochemicals that are produced in the neuron cell body.  Schwann cells produce myelin.  Myelin is a lipid-rich substance.  A myelin sheath is a coating produced by Schwann cells that is wrapped around an axon.  A neurilemma is a portion of a Schwann cell outside of the myelin sheath.  A node of Ranvier is a narrow gap between myelin sheaths.  Myelinated axons have myelin sheaths.  Unmyelinated axons have no myelin sheaths.  W. White matter is composed of myelinated axons.  X. Gray matter is composed of unmyelinated axons, dendrites, and cell bodies of neurons.  Classification of Neurons and Neuroglia  Classification of Neurons  The three major classifications of neurons based on structural differences are bipolar, multipolar, and unipolar.  Bipolar neurons have two processes; one process is a dendrite and the other an axon.  Bipolar neurons are found within the eyes, ears, and nose.  Unipolar neurons have one process which functions as an axon.  The peripheral process of a unipolar neuron is associated with dendrites near a peripheral body part and the central process enters the brain or spinal cord.  Unipolar neurons are located in ganglia.  Multipolar neurons have multiple dendrites and one axon.  Multipolar neurons are located in the brain and spinal cord.  The three classes of neurons based on functional differences are sensory, motor, and interneurons.  Sensory neurons carry nerve impulses from peripheral body parts into the brain or spinal cord.  Sensory neurons have specialized sensory receptors at the distal ends of their dendrites.  Most sensory neurons are unipolar but some are bipolar.  Interneurons are located in the brain and spinal cord.  Interneurons are multipolar and form links between other neurons.  Motor neurons carry nerve impulses from the brain and spinal cord to effectors.  Motor neurons that control skeletal muscle are under voluntary control.  Motor neurons that control glands, smooth muscle and cardiac muscle are under involuntary control.  Classification of Neuroglial Cells  In the embryo, neuroglial cells guide neurons to their positions and may stimulate them to grow.  Neuroglial cells also produce growth factors that nourish neurons.  The four neuroglial cells of the central nervous system are astrocytes, oligodendrocytes, microglial cells, and ependymal cells.  Astrocytes are star shaped and are commonly found between neurons and blood vessels.  Astrocytes provide support and hold structures together.  Astrocytes aid metabolism of glucose.  Astrocytes respond to injury of brain tissue and form a special type of scar tissue.  Astrocytes play a role in the blood-brain barrier, which restricts movement of substances between the blood and CNS.  Oligodendrocytes occur in rows along myelinated axons and form myelin in the brain and spinal cord.  Unlike Schwann cells, oligodendrocytes do not form neurilemma.  Microglia function to support neurons and phagocytize bacterial cells and cellular debris.  Ependyma form the inner lining of the central canal of the spinal cord and ventricles of the brain.  Gap junctions join ependymal cells together.  Ependymal cells form a porous layer through which substances diffuse freely between the interstitial fluid of the brain tissues and the fluid within the ventricles.  Covering the choroid plexus, ependymal cells also regulate the composition of the cerebrospinal fluid.  Schwann cells and Satellite cells are the two types of neuroglia cells found in the peripheral nervous system.  Schwann cells produce the myelin found on peripheral myelinated neurons.  Satellite cells support clusters of neuron cell bodies called ganglia, found in the PNS.  Neuroglia and axonal regeneration  Injury to a neuron cell body usually kills the neuron but damaged peripheral axons usually regenerate.  If a peripheral axon is separated from its cell body, the distal portion of the axon deteriorates, but the proximal end of the axon develops sprouts shortly after injury.  Growth of a regenerating axon is slow but eventually the new axon may reestablish the former connection.  Axons within the central nervous system do not regenerate because there is no tube of sheath cells to guide it.  The Synapse  Introduction  Synapses are the places where impulses are passed from one neuron to another or to other cells.  A presynaptic neuron is the neuron that brings the impulse to the synapse.  A postsynaptic neuron is the neuron that is stimulated by the presynaptic neuron.  Synaptic transmission is the process by which the impulse in the presynaptic neuron signals the postsynaptic neuron.  An impulse travels along an axon to the axon terminals.  The synaptic knobs of axons contain sacs called synaptic vesicles.  Synaptic vesicles contain neurotransmitters.  When an impulse reaches a synaptic knob, calcium diffuses inward from the extracellular fluid.  The calcium inside the synaptic knob initiates a series of events that causes the synaptic vesicles to fuse with the cell membrane, releasing the neurotransmitter by exocytosis.  Cell Membrane Potential  Introduction  Polarized means electrically charged.  When a cell membrane is polarized, the inside is negatively charged with respect to the outside.  The polarization of a cell membrane is due to an unequal distribution of positive and negative ions on either side of the membrane.  Distribution of Ions  Potassium ions are the major intracellular positive ion and sodium ions are the major extracellular cation.  The distribution of potassium and sodium is largely created by the sodium- potassium pump.  The passage of potassium and sodium ions through the cell membrane depends on the presence of channels.  Resting Potential  A resting nerve cell is not being stimulated to send a nerve impulse.  At rest, a cell membrane gets a slight surplus of positive charges outside, and inside reflects a slight negative surplus of impermeable negatively charged ions because the cell membrane is more permeable to potassium ions than sodium ions. Also the cell may contain anions and proteins that are negatively charged that cannot diffuse out of the cell.  The cell uses ATP to actively transport sodium and potassium ions in opposite directions.  Volts are the electrical differences between two points.  A volt is called a potential difference because it represents stored electrical energy that can be used to do work.  The membrane potential is the potential difference across the cell membrane and is measured in millivolts.  Resting potential is the membrane potential of a resting neuron and has a value of –70 millivolts.  The negative sign of a resting membrane potential is relative to the inside of the cell and is due to the excess negative charges on the inside of the cell membrane.  Local Potential Changes  Neurons are described as excitable because they can respond to the changes in their surroundings.  Stimuli on neurons usually affect the membrane potential in the region of the membranes exposed to the stimulus.  The stimulus affects the membrane potential of a neuron by opening a gated ion channel.  A membrane is hyperpolarized if the membrane potential becomes more negative than the resting potential.  A membrane is depolarized if the membrane becomes less negative than the resting potential.  Local potential changes are graded meaning that the degree of change in the membrane potential is directly proportional to the intensity of the stimulation.  A threshold potential is sufficient depolarization that triggers an action potential.  Action Potentials  The trigger zone of an axon is the first part or initial segment of an axon.  The trigger zone contains many voltage-gated sodium channels.  At the resting membrane potential, sodium channels are closed but when threshold is reached, sodium channels open.  As sodium ions rush into the cell, the membrane potential changes and temporarily becomes positive on the inside.  When sodium channels close and potassium channels open, potassium diffuses out across the membrane and the inside of the membrane becomes negatively charged again.  Repolarized means the membrane is polar again or returned to its original resting state.  Axons are capable of action potentials but the cell body and dendrites are not.  A nerve impulse is the propagation of action potentials along an axon.  All-or-None Response  A nerve impulse is an all-or-nothing response, meaning if a neuron responds at all to a nerve impulse, it responds completely.  A greater intensity of stimulation on the neuron produces more impulses per second, but not a stronger impulse.  Refractory Period  The refractory period is the period in which a threshold stimulus will not trigger another impulse on an axon.  An absolute refractory period is the period when an axon’s membrane cannot be stimulated and is the first part of the refractory period.  A relative refractory period is the period in which a stronger stimulus can trigger an impulse.  The refractory period limits how many action potentials may be generated in a neuron in a given time.  Impulse Conduction  Myelin serves as an insulator.  Saltatory conduction is the type of nerve impulse conduction that occurs only at nodes.  Myelinated axons exhibit saltatory conduction.  Myelinated axons send nerve impulses faster than unmyelinated axons.  The diameter of an axon also affects the speed of a nerve impulse.  Synaptic Transmission  Synaptic Transmission  Released neurotransmitters diffuse across the synaptic cleft and react with specific molecules that form structures called receptors in or on the postsynaptic neuron membrane.  Some neurotransmitters cause ion channels to open; some cause ion channels to close.  Synaptic potentials are local potentials created by changes in chemically gated ion channels.  Synaptic Potentials  Synaptic potentials can depolarize or hyperpolarize the receiving cell membrane.  An excitatory postsynaptic potential is a type of membrane change in which the receiving cell membrane is depolarized.  An inhibitory postsynaptic potential is a type of membrane change in which the receiving cell membrane is hyperpolarized.  Within the brain and spinal cord, each neuron may receive the synaptic knobs of a thousand or more axons on its cell body and dendrites.  The integrated sum of EPSPs and IPSPs determines whether an action potential results.  Neurotransmitters  The nervous system produces at least thirty different kinds of neurotransmitters.  Acetylcholine stimulates skeletal muscle contractions.  Examples of monoamines are epinephrine, norepinephrine, dopamine, and serotonin.  Examples of unmodified amino acids that act as neurotransmitters are glycine, glutamic acid, aspartic acid, and GABA.  Examples of peptides are enkephalins and substance P.  Peptide neurotransmitters are synthesized in the rough endoplasmic reticulum of the neuron cell bodies and transported in vesicles down the axon to the nerve terminal.  The more calcium that enters the synaptic knob, the more neurotransmitters that are released.  After a vesicle releases its neurotransmitter, it becomes part of the cell membrane.  The enzyme acetlycholinesterase functions to break down acetylcholine.  The process of reuptake is when neurotransmitters are transported back into the synaptic knobs of the presynaptic neurons.  Monoamine oxidase functions to inactivate epinephrine and norepinephrine after reuptake.  Neuropeptides  Neuropeptides are substances that alter a neuron’s response to a neurotransmitter or block the release of a neurotransmitter.  Three examples of neuropeptides are enkephalins, beta endorphin, and substance P.  Enkephalins function to relieve pain sensations.  Endorphins function to relieve pain.  The function of substance P is to transmit pain impulses into the spinal cord and on to the brain.  Impulse Processing  Neuronal Pools  Neuronal pools are groups of neurons that make synaptic connections with each other and work together to perform a common function.  Neuronal pools may have excitatory or inhibitory effects on other pools or on peripheral effectors.  Facilitation is a condition created in which a neuron is brought closer to threshold.  Convergence  Axons originating from different parts of the nervous system leading to the same neuron exhibit convergence.  Convergence allows the nervous system to collect, process, and respond to information.  Divergence  Axons may branch at several points.  Impulses leaving a neuron of a neuronal pool may exhibit divergence by reaching several other neurons.  Diverging axons can amplify an impulse. Chapter 11: Nervous System II: Divisions of the Nervous System  Introduction  Introduction  The central nervous system consists of the brain and spinal cord.  The brain is the largest and most complex part of the nervous system.  The brain includes two cerebral hemispheres, the diencephalon, the brainstem, and the cerebellum.  The brainstem connects the brain and spinal cord and allows two-way communication between them.  The spinal cord provides two-way communication between the central nervous system and the peripheral nervous system.  The brain lies within the cranial cavity of the skull and the spinal cord occupies the vertebral canal.  Meninges are located between the bone and the soft tissues of the nervous system and protect the brain and spinal cord.  Meninges  The meninges have three layers.  The outermost layer is the dura mater and is composed of tough, white, dense connective tissue.  Dural sinuses are channels in dura mater.  Denticulate ligaments are bands of pia mater that attach spinal cord to dura mater.  The epidural space is between the dural sheath and the bony walls and contains blood vessels.  The arachnoid mater is a thin, weblike membrane that lacks blood vessels and is located between the dura and pia maters.  The subarachnoid space is between the arachnoid and pia maters and contains a fluid called cerebrospinal fluid.  The pia mater is very thin and contains many nerves and blood vessels.  The pia matter is attached to the surfaces of the brain and spinal cord.  Ventricles and Cerebrospinal Fluid  Introduction  Ventricles are interconnected cavities and are located within the cerebral hemispheres and brain stem.  The ventricles are continuous with the central canal of the spinal cord and are filled with cerebrospinal fluid.  The largest ventricles are the lateral ventricles which are located in the cerebral hemispheres.  The third ventricle is located in the midline of the brain beneath the corpus callosum.  The fourth ventricle is located in the brainstem just in front of the cerebellum.  The cerebral aqueduct is a connection between the third and fourth ventricles.  The choroid plexus is a specialized mass of capillaries and functions to secrete cerebrospinal fluid.  Most of the cerebrospinal fluid arises in the lateral ventricles and circulates into the third ventricle, fourth ventricle, the central canal of the spinal cord, and the subarachnoid space.  Cerebrospinal fluid is continuously absorbed into the blood.  Arachnoid granulations are tiny, fingerlike structures that project from the subarachnoid space into the dural sinuses.  Cerebrospinal fluid is different from blood in that it contains a greater concentration of sodium and lesser concentrations of glucose and potassium.  The functions of cerebrospinal fluid are to help maintain a stable ionic concentration in the CNS, and provide a pathway to the blood for wastes.  Because cerebrospinal fluid completely surrounds the brain and spinal cord, it protects them by absorbing forces that might otherwise jar and damage them.  Spinal Cord  Introduction  The spinal cord is continuous with the brain and extends downward through the vertebral canal.  The spinal cord begins at the level of the foramen magnum and terminates near the intervertebral disc that separates the first and second lumbar vertebrae.  Structure of the Spinal Cord  The spinal cord consists of thirty-one segments, each of which gives rise to a pair of spinal nerves.  The two enlargements of the spinal cord are the cervical enlargement and the lumbar enlargement.  The cervical enlargement supplies nerves to the upper limbs.  The lumbar enlargement supplies nerves to the lower limbs.  The conus medullaris is the tapered end of the spinal cord.  The filum terminale is a thin cord of connective tissue that anchors the spinal cord to the upper surface of the coccyx.  The cauda equina is a group of spinal nerves below the conus medullaris.  Two grooves that extend the length of the spinal cord are the anterior median fissure and a posterior median sulcus.  In a cross section of the spinal cord, white matter surrounds gray matter.  Each side of the gray matter is divided into the following three horns: posterior horn, anterior horn, and lateral horn.  Motor neurons are located in the anterior horns.  The gray commissure is a horizontal bar of gray matter in the middle of the spinal cord.  The central canal is a canal running through the center of the gray commissure down the entire length of the spinal cord.  Three regions of the white matter are posterior funiculi, anterior funiculi, and lateral funiculi.  Tracts are groups of myelinated nerve fibers in the CNS.  Functions of the Spinal Cord  Reflex Arcs  Reflex arcs carry out reflexes.  A reflex arc begins with a receptor at the dendritic end of the a sensory neuron.  Nerve impulses on the sensory neurons enter the CNS and constitute a sensory or afferent limb of the reflex.  The CNS is a processing center.  Afferent neurons or interneurons ultimately connect with motor neurons, whose fibers pass outward from the CNS to effectors.  Reflex Behavior  Reflexes are automatic, subconscious responses to changes within or outside the body.  Reflexes function to maintain homeostasis by controlling many involuntary processes such as heart rate, breathing rate, etc.  The knee-jerk reflex is an example of a simple monosynaptic reflex because it only uses two neurons.  The knee-jerk reflex is initiated by striking the patellar tendon.  When the tendon is struck, the quadriceps muscle is pulled.  When the muscle is pulled, stretch receptors are stimulated.  The receptors generate a nervous impulse that enters the spinal cord on an axon; the axon synapses with a motor neuron.  The axon of the motor neuron synapses with the quadriceps muscle and the muscle responds by contracting.  The knee-jerk reflex helps maintain posture.  The withdrawal reflex occurs when a person touches something painful.  In the withdrawal reflex, muscles on the affected side contract and the flexor muscles on the unaffected side are inhibited.  The extensor muscles on the unaffected side contract, helping to support the body weight that has been shifted.  A crossed extensor reflex is due to interneuron pathways within the reflex center of the spinal cord that allow sensory impulses arriving on one side of the cord to pass across to the other side and produce an opposite effect.  A withdrawal reflex protects because it prevents or limits tissue damage when a body part touches something potentially harmful.  Ascending and Descending Tracts  Ascending tracts conduct sensory impulses to the brain.  Descending tracts conduct motor impulses away from the brain.  The names that identify nerve tracts often reflect the origin and termination of the tract.  Four major ascending tracts of the spinal cord are fasciculus gracilis, fasciculus cuneatus, spinothalamic tracts, and spinocerebellar tracts.  The fasciculus gracilis and fasciculus cuneatus are located in posterior funiculi.  The fibers of fasciculus gracilis and fasciculus cuneatus conduct sensory impulses associated with the senses of touch, pressure, and body movement from skin, muscles, tendons, and joints to the brain.  The spinothalamic tracts are located in lateral and anterior funiculi.  The lateral spinothalamic tracts conduct impulses from various body regions to the brain and give rise to sensations of pain and temperature.  The anterior spinothalamic tract’s impulses are interpreted as touch and pressure.  Spinocerebellar tracts are located in lateral funiculi.  Impulses on the spinocerebellar tracts originate in the muscles of the lower limbs and trunk and travel to the cerebellum.  Three major descending tracts of the spinal cord are corticospinal tracts, reticulospinal tracts, and rubrospinal tracts.  Corticospinal tracts are located in lateral and anterior funiculi.  The corticospinal tracts conduct motor impulses associated with voluntary movements from the brain to skeletal muscles.  The pyramidal tracts are the corticospinal tracts and the extrapyramidal tracts are all other descending spinal tracts.  Reticulospinal tracts are located in lateral and anterior funiculi.  Motor impulses of the reticulospinal tracts control muscular tone and activity of sweat glands.  Rubrospinal tracts are located in lateral funiculi.  Rubrospinal tracts carry motor impulses that coordinate muscles and control posture.  Brain  Introduction  The brain contains nerve centers associated with sensory functions and is responsible for sensations and perceptions.  The other functions of the brain include control of motor functions and higher mental functions such as memory; it also provides characteristics such as personality.  Brain Development  The brain begins as a neural tube.  The portion of the neural tube that becomes the brain has the following three major cavities: forebrain, midbrain, and hindbrain.  The forebrain divides into the telencephalon and the diencephalon.  The hindbrain partially divides into the metencephalon and myelencephalon.  The wall of the anterior potion of the forebrain gives rise to the cerebrum and basal nuclei.  The posterior portion of the forebrain gives rise to the diencephalon.  The midbrain is called midbrain in the adult and the hindbrain gives rise to the cerebellum, pons, and medulla oblongata.  Structure of the Cerebrum  The cerebrum is the largest part of the adult brain.  The cerebrum consists of two hemispheres.  The corpus callosum is a bridge of nerve fibers that connects the two cerebral hemispheres.  Convolutions are ridges.  Sulci are grooves between ridges.  A fissure is a deep groove.  The longitudinal fissure separates the left and right cerebral hemispheres.  The transverse fissure separates the cerebrum from the cerebellum.  The 5 lobes of the cerebral hemispheres are frontal, parietal, occipital, temporal and insular.  The most anterior lobe is the frontal.  The frontal lobe is bordered posteriorly by the central sulcus and inferiorly by a lateral sulcus.  The parietal lobe is separated from the frontal lobe by the central sulcus.  The temporal lobe lies inferior to the frontal and parietal lobes and is separated from them by the lateral sulcus.  The most posterior lobe is the occipital lobe.  The tentorium cerebelli is an extension of the dura mater between the occipital lobe and cerebellum.  The insula is located deep within the lateral fissure.  The cerebral cortex is an outer, thin layer of gray matter and contains nearly 75% of all the neuron cell bodies in the nervous system.  Just beneath the cerebral cortex is white matter.  Functions of the Cerebrum  Functional Regions of the Cortex  The cerebral cortex is divided into the following three major sections: sensory, association areas, and motor areas.  Sensory Areas  Sensory areas interpret impulses from sensory receptors.  Sensations on the skin are interpreted in the anterior portions of the parietal lobes along the central sulcus.  Visual sensations are interpreted in the occipital lobe.  Auditory sensations are interpreted in the temporal lobe.  Taste sensations are interpreted in the bases of the central sulci along the lateral sulci.  Like motor fibers, sensory fibers cross over in the spinal cord or brainstem.  Association Areas  Association areas are not primarily sensory or motor in function.  Association areas analyze and interpret sensory experiences and help provide memory, reasoning, verbalizing, judgment, and emotions.  The association areas of the frontal lobe provide higher intellectual processes.  The prefrontal areas control emotional behavior and produce awareness of the possible consequences of behavior.  The parietal lobes have association areas that help interpret sensory information and aid in understanding speech and choosing words to express thoughts and feeling.  The association areas of the temporal lobes interpret complex sensory experiences, such as those needed to understand speech and to read.  The association areas of the occipital lobes are important for analyzing visual patterns and combining visual images with other sensory experiences.  The general interpretative area is located where the parietal, temporal, and occipital association areas join and functions to make it possible for a person to recognize words and arrange them to express a thought, and to read.  Motor Areas  The primary motor areas are located in the frontal lobes just in front of the central sulcus and in the anterior wall of this sulcus.  Impulses transmitted from the primary motor cortex are responsible for fine movements in skeletal muscles.  Broca’s area is located just anterior to the primary motor cortex and superior to the lateral sulcus and is responsible for coordinating complex muscular movements of the mouth, tongue, and larynx for speech.  Broca’s area is usually found in the left hemisphere.  The frontal eye field is located above Broca’s area and is responsible for controlling voluntary movements of the eyes and eyelids.  Hemisphere Dominance  In most people the left hemisphere is dominant.  The dominant hemisphere controls language-related activities of speech, writing, and reading. It also controls complex intellectual functions requiring verbal, analytical, and computational skills.  The nondominant hemisphere controls nonverbal functions, such as motor tasks that require orientation of the body in space, understanding and interpreting musical patterns and visual experiences. It also provides emotional and intuitive thought processes.  Nerve fibers of the corpus callosum enable the dominant hemisphere to control the motor cortex of the nondominant hemisphere.  Memory  Memory is the consequence of learning.  Two types of memory are short-term and long-term.  Short-term memories are electrical in nature.  When the electrical impulse of a short-term memory ceases, the memory goes away.  Long-term memory changes the structure or function of neurons in ways that enhance synaptic transmission.  Memory consolidation is the way the brain encodes memories and how short-term memories are converted to long-term memories.  Basal Nuclei  The basal nuclei are masses of gray matter deep within the cerebral hemispheres and are called caudate nucleus, the putamen, and globus pallidus.  The basal nuclei relay motor impulses originating in the cerebral cortex and passing into the brainstem and spinal cord.  The basal nuclei produce most of the dopamine in the nervous system.  Impulses from the basal nuclei function to control muscular activities.  Diencephalon  The diencephalon is located between the cerebral hemispheres and above the brainstem.  The various parts of the diencephalon are the thalamus, hypothalamus, optic tracts, the infundibulum, posterior pituitary gland, mammillary bodies, and the pineal gland.  The thalamus is a selective gateway for sensory impulses ascending from other parts of the nervous system to the cerebral cortex.  The thalamus receives most sensory impulses and channels them to appropriate parts of the cortex for interpretation.  The hypothalamus regulates heart rate, arterial blood pressure, body temperature, water and electrolyte balance, control of hunger and body weight, control of movements and glandular secretions of the stomach and intestine, produces hormones, and controls sleep and wakefulness.  The limbic system consists of portions of the cerebral cortex, thalamus, hypothalamus, basal nuclei, and other deep nuclei and controls emotional experience and expression and can modify the way a person acts.  Brain Stem  Introduction  The brain stem connects the brain and spinal cord.  The brain stem consists of the midbrain, pons, and medulla oblongata.  Nuclei of the brain stem are masses of gray matter.  Midbrain  The midbrain is between the diencephalon and the pons.  The cerebral aqueduct is a connection between the third ventricle and fourth ventricle.  Corpora quadrigemina are two pairs of rounded knobs on the superior surface of the midbrain.  The superior colliculi contain centers for visual reflexes.  The inferior colliculi contain centers for auditory reflexes.  The red nucleus is at the center of the midbrain and is important for controlling reflexes that maintain posture.  Pons  The pons is located on the underside of the brainstem between the midbrain and medulla oblongata.  The dorsal portion of the pons largely consists of fibers that relay impulses to and from the medulla oblongata and the cerebrum.  The ventral portion consists of fibers that relay impulses from the cerebrum to centers within the cerebellum.  Several nuclei of the pons relay sensory information to higher brain centers.  The pons also regulates rate and depth of breathing.  Medulla Oblongata  The medulla oblongata is located between the spinal cord and pons.  The olive of the medulla oblongata is a bulge where bundles of fibers originate and pass to the cerebellum.  The visceral activities controlled by the medulla oblongata are heart rate, vasoconstriction, vasodilation, and breathing.  Nonvital reflexes regulated by the medulla oblongata are coughing, sneezing, swallowing, and vomiting.  Reticular Formation  The reticular formation is a complex network of fibers that extend throughout the brainstem and diencephalon and connects with centers of the hypothalamus, cerebrum, cerebellum, and basal nuclei.  The reticular formation activates the cerebral cortex into a state of wakefulness.  Decreased activity of the reticular formation results in sleep.  The reticular formation also filters incoming sensory impulses.  The reticular formation also regulates motor activities so that various skeletal muscles move together evenly, and it inhibits or enhances certain spinal reflexes.  Types of Sleep  The two types of sleep are slow wave and rapid eye movement.  Slow-wave sleep occurs when a person is very tired and it reflects decreasing activity of the reticular formation.  Slow-wave sleep is accompanied by reduced blood pressure and respiratory rate.  REM sleep is the type of sleep in which dreaming occurs and heart rate and respiratory rates are irregular.  Cerebellum  The cerebellum is located inferior to the occipital lobes of the cerebrum and posterior to the pons and medulla oblongata.  The falx cerebelli is a layer of dura mater that partially separates the cerebellar hemispheres.  The vermis is a structure that connects the cerebellar hemispheres at the midline.  The cerebellar cortex is an outer, thin layer of gray matter.  The arbor vitae is a treelike pattern of white matter in the cerebellum.  The largest and most important nucleus of the cerebellum is the dentate nucleus.  Cerebellar peduncles are nerve tracts.  Inferior peduncles bring sensory information concerning the actual position of body parts such as limbs and joints to the cerebellum.  The middle peduncles transmit impulses from the cerebral cortex about the desired position of body parts to the cerebellum.  The superior peduncles send correcting impulses to the midbrain.  Overall, the cerebellum functions to integrate sensory information concerning the position of body parts and coordinated skeletal muscle activity and maintains posture.  Peripheral Nervous System  Introduction  The peripheral nervous system consists of nerves that branch from the central nervous system.  The somatic nervous system consists of the cranial and spinal nerve fibers that connect the CNS to the skin and skeletal muscles.  The autonomic nervous system consists of fibers that connect the CNS to viscera and various glands.  Structure of Peripheral Nerves  A peripheral nerve consists of connective tissue surrounding bundles of nerve fibers.  Epineurium is the outermost layer of connective tissue of a nerve.  Perineurium is a sleeve of connective tissue that surrounds a nerve fascicle.  Endoneurium is loose connective tissue that surrounds individual nerve fibers.  Nerve Fiber Classification  Sensory nerves are nerves that have only fibers of sensory neurons, conducting impulses into the brain or spinal cord.  Motor nerves are nerves that have only fibers involved in motor control.  Mixed nerves are nerves that include both sensory and motor fibers.  Cranial nerves are nerves that originate from the brain.  Spinal nerves are nerves that originate from the spinal cord.  General somatic efferent fibers carry motor impulses outward from the brain or spinal cord to skeletal muscles and stimulate them to contract.  General visceral efferent fibers carry motor impulses outward from the brain or spinal cord to various smooth muscles and glands associated with internal organs, causing certain muscles to contract or glands to secrete.  General somatic afferent fibers carry sensory impulses inward to the brain or spinal cord from receptors in the skin and skeletal muscles.  General visceral afferent fibers carry sensory impulses to the central nervous system from blood vessels and internal organs.  Special somatic efferent fibers carry motor impulses outward from the brain to the muscles used in chewing, swallowing, speaking, and forming facial expressions.  Special visceral afferent fibers carry sensory impulses inward to the brain from the olfactory and taste receptors.  Special somatic afferent fibers carry sensory impulses inward to the brain from the receptors of sight, hearing, and equilibrium.  Cranial Nerves  Cranial nerves arise from the underside of the brain.  Cranial nerves are designated by numbers or name.  The olfactory nerve functions to transmit sensory impulses associated with smell.  The optic nerve functions to transmit sensory impulses associated with sight.  The oculomotor nerve functions to transmit impulses to muscles that raise the eyelids, move the eyes, adjust the amount of light entering the eyes, and focus the lenses. It also transmits sensory impulses associated with proprioceptors.  The trochlear nerve functions to transmit impulses to muscles that move the eyes. It also transmits sensory impulses associated with proprioceptors.  The three divisions of the trigeminal nerve are ophthalmic, maxillary, and mandibular.  The ophthalmic division functions to transmit sensory impulses from the surface of the eyes, tear glands, scalp, forehead, and upper eyelids.  The maxillary division functions to transmit impulses from the upper teeth, upper gum, upper lip, lining of the palate, and skin of the face.  The mandibular division functions to transmit sensory impulses from the scalp, skin of the jaw, lower teeth, lower gum, and lower lip. It also transmits motor impulses to muscles of mastication and to muscles in the floor of the mouth.  The abducens nerve functions to transmit motor impulses to muscles that move the eyes. It also transmits sensory impulses associated with proprioceptors.  The facial nerve functions to transmit sensory impulses associated with taste receptors of the anterior tongue. It also transmits motor impulses to muscles of facial expression, tear glands, and salivary glands.  The two branches of the vestibulocochlear nerve are the vestibular branch and the cochlear branch.  The vestibular branch functions to transmit sensory impulses associated with the sense of equilibrium.  The cochlear branch functions to transmit sensory impulses associated with hearing.  The glossopharyngeal nerve functions to transmit sensory impulses for the pharynx, tonsils, posterior tongue, and carotid arteries. It also transmits motor impulses to salivary glands and to muscles of the pharynx used in swallowing.  The vagus nerve functions to transmit motor impulses to muscles associated with speech and swallowing, and to viscera of the thorax and abdomen. It also transmits sensory impulses from the pharynx, larynx, esophagus, and viscera of the thorax and abdomen.  The branches of the accessory nerve are the cranial branch and spinal branch.  The cranial branch functions to transmit motor impulses to muscles of the soft palate, pharynx, and larynx.  The spinal branch functions to transmit motor impulses to muscles of the neck and back.  The hypoglossal nerve functions to transmit motor impulses to muscles that move the tongue.  Spinal Nerves  Introduction  There are thirty-one pairs of spinal nerves.  All spinal nerves are mixed nerves and they provide two-way communication between the spinal cord and parts of the upper and lower limbs, neck and trunk.  There are 8 pairs of cervical nerves.  There are 12 pairs of thoracic nerves.  There are 5 pairs of lumbar nerves.  There are 5 pairs of sacral nerves.  There is 1 pair of coccygeal nerves.  The adult spinal cord ends at the level of the first or second lumbar vertebrae.  The cauda equina is a collection of spinal nerves at the end of the spinal cord.  Each spinal nerve emerges from the cord by roots.  The dorsal root ganglion contains the cell bodies of the sensory neurons whose dendrites conduct impulses from the peripheral body parts.  The axons of neurons in dorsal root ganglia extend through the dorsal root.  A dermatome is an area of skin that the sensory nerve fibers of a particular spinal nerve innervate.  The ventral root consists of axons from the motor neurons whose cell bodies are located within the gray matter of the cord.  A ventral root and dorsal root unite to form a spinal nerve.  A meningeal branch of a spinal nerve supplies the meninges and blood vessels of the spinal cord, as well as the intervertebral ligaments and the vertebrae.  A posterior branch of a spinal nerve supplies the muscles and skin of the back.  An anterior branch of a spinal nerve supplies muscles and skin on the front and sides of the trunk and limbs.  A plexus is a complex network of anterior branches of spinal nerves.  In a plexus, fibers of various spinal nerves are sorted and recombined, so fibers associated with a particular peripheral body part reach it in the same nerve, even though the fibers originate from different spinal nerves.  Cervical Plexuses  The cervical plexus is located deep in the neck on either side.  The cervical plexus is formed by the anterior branches of the first four cervical nerves.  Fibers from the cervical plexus supply the muscles and skin of the neck and contribute to the phrenic nerve.  The phrenic nerve conducts impulses to the diaphragm.  Brachial Plexuses  The brachial plexus is located deep within the shoulders between the neck and axillae.  The brachial plexus is formed by the anterior branches of the lower four cervical nerves and the first thoracic nerve.  The major branches emerging from the brachial plexus are the musculocutaneous, ulnar, median, radial, and axillary.  The musculocutaneous nerves supply muscles of the arms on the anterior sides and the skin of the forearms.  The ulnar nerves supply muscles of the forearms and hands and the skin of the hands.  The radial nerves supply muscles of the arms on the posterior sides and the skin of the forearms and hands.  The median nerves supply muscles of the forearms and muscles and skin of the hands.  The axillary nerves supply muscles and skin of the anterior, lateral, and posterior regions of the arm.  Lumbosacral Plexuses  The lumbosacral plexus is located in the lumbar and pelvic regions.  The lumbosacral plexus is formed by anterior branches of the last thoracic nerve and lumbar, sacral , and coccygeal nerves.  The major branches of the lumbosacral plexus are obturator, femoral, and sciatic nerves.  The obturator nerves supply the adductor muscles of the thighs.  The femoral nerves supply motor impulses to muscles of the anterior thigh and receive sensory impulses from the skin of the thighs and legs.  The sciatic nerves supply muscles and skin of the thighs, legs, and feet.  The anterior branches of thoracic spinal nerves do not enter a plexus; instead these branches become intercostal nerves that supply motor impulses to the intercostal muscles and the upper abdominal wall muscles.  Autonomic Nervous System  Introduction  The autonomic nervous system controls visceral activities by regulating the actions of smooth muscles, cardiac muscles, and various glands.  The autonomic nervous system functions without conscious effort.  General Characteristics  The two divisions of the autonomic nervous system are sympathetic and parasympathetic.  The sympathetic division prepares the body for energy-expending, stressful, or emergency situations.  The parasympathetic division is most active during ordinary, restful, peaceful conditions.  Autonomic Nerve Fibers  All nerve neurons of the autonomic nervous system are motor neurons.  In the autonomic system, motor pathways include two neurons.  A preganglionic fiber is an axon of a preganglionic neuron.  A postganglionic fiber is an axon of a postganglionic neuron.  A preganglionic fiber synapses with a postganglionic neuron.  A postganglionic fiber synapses with a visceral effector, such as a gland.  Sympathetic Division  In the sympathetic division, the preganglionic fibers originate from neurons within the lateral horns of the spinal cord. These neurons are in the thoracic and lumbar regions of the spinal cord.  In the sympathetic division, the preganglionic fibers leave the spinal nerves through white rami and enter sympathetic ganglia.  Paravertebral ganglia are located in chains along the sides of the vertebral column.  The sympathetic trunks are Paravertebral ganglia and the fibers that connect the ganglia.  The collateral ganglia are located within the abdomen, closely associated with certain large blood vessels.  Typically a preganglionic axon of the sympathetic nervous system synapses with several other neurons within a sympathetic ganglion.  In the sympathetic division, the postganglionic fibers extend from the sympathetic ganglia to visceral effectors.  Gray rami are branches that contain unmyelinated postganglionic axons.  Parasympathetic Division  The preganglionic fibers of the parasympathetic division arise from neurons in the midbrain, pons, medulla oblongata, and from part of the sacral region of the spinal cord.  The preganglionic fibers of the parasympathetic division lead to ganglia that are located near or within various organs.  The short postganglionic fibers of the parasympathetic division lead to specific muscles or glands within visceral organs.  Parasympathetic preganglionic fibers are usually myelinated and the postganglionic fibers are usually unmyelinated.  Autonomic Neurotransmitters  The different postganglionic neurotransmitters are responsible for the different effects that the sympathetic and parasympathetic divisions have on organs.  The preganglionic neurons of the sympathetic and parasympathetic divisions secrete acetylcholine and are called cholinergic.  The parasympathetic postganglionic neurons are cholinergic.  Most sympathetic postganglionic neurons secrete norepinephrine and are called adrenergic.  Sympathetic tone is a state of constant partial contraction of smooth muscles in the wall of blood vessels caused by sympathetic innervation.  Actions of Autonomic Neurotransmitters  The actions of autonomic neurotransmitters result from their binding to protein receptors in the membrane of effector cells.  Two types of cholinergic receptors are muscarinic and nicotinic.  Muscarinic receptors are located in the membranes of effector cells at the ends of all postganglionic parasympathetic nerve fibers and at the ends of the cholinergic sympathetic fibers.  Nicotinic receptors are located in the synapses between the preganglionic and postganglionic neurons of the parasympathetic and sympathetic pathways.  Responses from muscarinic receptors are excitatory and slow.  Responses from nicotinic receptors are excitatory and rapid.  The two major types of adrenergic receptors are alpha and beta receptors.  Acetylcholinesterase decomposes acetylcholine.  Control of Autonomic Activity  The autonomic nervous system is largely controlled by the brain and spinal cord.  The limbic system and cerebral cortex control the autonomic nervous system during emotional stress.  Life-Span Changes  Apoptosis is a form of programmed cell death and first occurs during development.  By age thirty, the die-off of neurons accelerates.  Over an average lifetime, the brain shrinks by about 10%.  With aging, the numbers of dendritic branches and amounts of neurotransmitters decrease.  Noticeable signs of a normally aging nervous system include fading memory and slowed responses and reflexes.  Decline in function of the sympathetic nervous system may cause transient drops in blood pressure.  Changes in sleep patterns reflect the functioning of the reticular activating system. Chapter 12: Nervous System III: Senses  Introduction  Introduction  The general senses are those with receptors widely distributed throughout the body, including the skin, various organs, and joints.  The special senses have more specialized receptors and are confined to structures in the head, such as the eyes and ears.  Sensory receptors collect information from the environment and send impulses along sensory fibers to the brain.  The cerebral cortex forms perceptions  Receptors, Sensation and Perception  Receptor Types  Five types of sensory receptors are chemoreceptors, pain receptors, thermoreceptors, mechanoreceptors, and photoreceptors.  Chemoreceptors respond to changes in chemical concentrations.  Pain receptors respond to tissue damage.  Thermoreceptors respond to temperature changes.  Mechanoreceptors respond to mechanical forces.  Proprioceptors sense changes in the tension of muscles and tendons.  Baroreceptors detect changes in blood pressure.  Stretch receptors respond to stretch.  Photoreceptors respond to light energy.  Sensory Impulses  Sensory receptors can be ends of neurons or other kinds of cells located close to them.  Stimulation of sensory receptors causes local changes in their membrane potential, generating a graded electric current that reflects the intensity of stimulation.  If a receptor is a neuron and the change in membrane potential reaches threshold, an action potential is generated.  If the receptor is another type of cell, its receptor potential must be transferred to a neuron to trigger an action potential.  Sensation and Perception  A sensation is a feeling that occurs when the brain interprets sensory impulses.  Sensations depend on which region of the cerebral cortex receives the impulse.  Projection is a process in which the cerebral cortex projects a sensation back to its apparent source.  Sensory Adaptation  Sensory adaptation is the ability to ignore unimportant stimuli.  An example of sensory adaptation is background noise in a room.  General Senses  Introduction  General senses are those whose sensory receptors are associated with the skin, muscles, joints, and viscera.  Three groups of somatic senses are exteroceptive senses, proprioceptive senses, and visceroceptive senses.  Exteroceptive senses include senses of touch, pressure, temperature, and pain.  Proprioceptive senses include senses associated with changes in muscles and tendons and in body position.  Visceroceptive senses include senses associated with changes in viscera.  Touch and Pressure Senses  Three kinds of touch and pressure receptors are free nerve endings, Meissner’s corpuscles, and Pacinian corpuscles.  Free nerve endings are located in epithelial tissues and are responsible for the sensation of itching.  Meissner’s corpuscles are located in hairless portions of skin and are involved in fine touch, as in distinguishing between two points on the skin.  Pacinian corpuscles are located in deeper subcutaneous tissues of the hands, feet, penis, clitoris, urethra, breasts, and tendons and ligaments, and are associated with heavier pressure, stretch, and vibrations.  Temperature Senses  Two types of temperature receptors are warm and cold receptors.  Warm receptors respond to temperatures between 25 C and 45 C. o  Cold receptors respond to temperatures between 10 C and 20 C. o  Temperatures above 45 C and below 10 C activate pain receptors.  Sense of Pain  Introduction  Pain receptors consist of free nerve endings.  Pain receptors are distributed widely throughout the skin and internal tissues, except in the nervous tissue of the brain.  Pain receptors can be stimulated by damaged tissue.  Pain receptors adapt very little, if at all.  Visceral Pain  Visceral pain receptors respond differently to stimulation than those of surface tissues.  Pain in visceral organs result from stimulation of mechanoreceptors and from decreased blood flow accompanied by lower tissue oxygen levels and accumulation of pain-stimulating chemicals.  Referred pain is a phenomenon is which visceral pain may feel as if it is coming from some part of the body other than the part being stimulated.  Referred pain may come from common nerve pathways that sensory impulses coming both from skin areas and from internal organs use.  During a heart attack, the cerebral cortex may incorrectly interpret the source of the impulses as coming from the left arm.  Pain Nerve Pathways  Two main types of pain fibers are acute pain fibers and chronic pain fibers.  Acute pain fibers are thin, myelinated nerve fibers and conduct impulses rapidly at velocities up to 30 meters per second.  Acute pain fibers are associated with the sensation of sharp pain.  Chronic pain fibers are thin, unmyelinated nerve fibers that conduct impulses more slowly.  Impulses from chronic pain fibers cause dull, aching pain  sensations.  Acute pain is usually sensed as being from a local area of skin and chronic pain is likely to be felt in deeper tissues as well as the skin.  Pain impulses that originate from tissues of the head reach the brain on sensory fibers of fifth, seventh, ninth, and tenth cranial nerves.  All other pain impulses travel on sensory fibers of spinal nerves and they pass into the spinal cord by way of dorsal roots.  Upon reaching the spinal cord, pain impulses enter the gray matter of the posterior horn, where they are processed.  Within the brain, most pain fibers terminate in the reticular formation and from there are conducted on fibers to the thalamus, hypothalamus, and cerebral cortex.  Regulation of Pain Impulses  Awareness of pain occurs when pain impulses reach the level of the thalamus.  The cerebral cortex judges the intensity of pain and locates its source.  Enkephalins and serotonin can suppress pain impulses.  Endorphins are natural pain controlling substances in the pituitary gland and hypothalamus.  Proprioception  Proprioceptors are mechanoreceptors that send information to the spinal cord and brain concerning the lengths and tensions of skeletal muscles.  Two main kinds of stretch receptors are muscle spindles and Golgi tendon organs.  Muscle spindles are located in skeletal muscles near their junctions with tendons and function to detect stretch.  Golgi tendon organs are located in tendons close to their attachments to muscles and function to detect increased tension.  The stretch reflex is an action that opposes the lengthening of a muscle and helps maintain the desired position of a limb in spite of gravitational or other forces tending to move it.  Special Senses  Introduction  Examples of special senses are sight, smell, hearing, and taste.  Special senses are those whose sensory receptors are within sensory organs of the head.  Sense of Smell  Olfactory Receptors  Olfactory receptors are used to sense smell and are chemoreceptors.  Olfactory receptors are similar to those for taste in that they are both chemoreceptors sensitive to chemicals dissolved in liquids.  Taste is a combination of smell and taste sensations.  Olfactory Organs  Olfactory organs contain the olfactory receptors.  Olfactory organs are located in the upper pars of the nasal cavity, the superior nasal conchae, and a portion of the nasal septum.  The olfactory receptor cells are bipolar neurons surrounded by columnar epithelial cells.  Cilia of olfactory receptor cells project into the nasal cavity.  Smell impulses are generated when odorants enter the nasal cavity, dissolve in fluids, and bind to receptor proteins on cilia that are part of the cell membranes of the olfactory receptor cells.  Olfactory Pathways  Once olfactory receptors are stimulated, nerve impulses travel along their axons to synapse with neurons in the olfactory bulbs.


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