EXAM 2 Study Guide
EXAM 2 Study Guide ASCI 141
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This 11 page Study Guide was uploaded by Katarina Fielding on Tuesday March 15, 2016. The Study Guide belongs to ASCI 141 at University of Vermont taught by Feng-Qi Zhao in Spring 2016. Since its upload, it has received 35 views. For similar materials see Anatomy and Physiology of Domestic Animals in Animal Science and Zoology at University of Vermont.
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Date Created: 03/15/16
EXAM #2 MATERIAL CHAPTER #9: NERVOUS SYSTEM Neurons and supporting cells o Neurons- basic functional units of the system, smallest pieces of the nervous system that shows basic nervous system functions Responding to stimuli, conducting impulses from one part of the cell to another High maintenance cells- very high requirement for oxygen, cannot live without it for more than a few minutes Shortly after animal is born- neurons lose their ability to reproduce but can regenerate cell processes if the cell body remains intact This is why brain injuries such as strokes are debilitating and have long lasting effects o Glial cells- structurally and functionally support and protect the neurons Outnumber neurons 10 to 1 but are not directly involved in transmitting information or impulses throughout the nervous system; important parts of infrastructure necessary for neurons to do their job o Neuron can be structurally divided into two parts- central cell body (soma or perikaryon), and the two types of processes from the cell body, dendrites and axons Dendrites- receive stimuli (impulses) from other neurons, and conduct it to the cell body Afferent process- conduct impulses toward the cell body Can be modified into sensory receptors which receive stimuli such as heat, cold, pressure, touch, stretch, or physical changes from inside or outside the body Tend to be short, numerous, and have many branches Axons- conduct nerve impulses away from the cell body toward another neuron or effector cell Efferent processes- conduct impulses away from the cell body Single process which can be very long Can also be called nerve fibers- usually used only when talk about bundles of axons Covered by a sheath of a fatty substance called myelin- appears white- tissue containing many myelinated axons referred to as white matter Myelin sheath made of cell membranes of oligodendrocytes in the brain and the spinal cord; Schwann cells in nerves outside brain and spinal cord o The cells wrap around the axon like a thin pancake wrapped around a hotdog o Take multiple Schwann cells or oligodendrocytes lined end to end to cover the entire length of the axon Between adjacent cells are small gaps known as nodes of Ranvier Nodes of Ranvier and myelin sheath work together to enhance the speed of conduction of nerve impulses along axon Unmyelinated axons conduct slower then myelinated ones Organization of the Nervous System o Anatomic Location: CNS versus PNS Central Nervous System (CNS)- anatomically composed of the brain and the spinal cord, found along the central axis of the body Peripheral Nervous System (PNS)- “to the side” or “away from the center” , made up of components of the nervous system that extend away from the central axis, pointed towards the periphery of the body Cranial nerves are few in PNS that originate from the brain directly Most PNS nerves- spinal nerves emerging from the spinal cord o Direction of Impulses: Afferent and Efferent Afferent nerve fibers- conduct nerve impulses towards the CNS Called sensory nerve fibers- due to conducting sensations from sensory receptors in skin and other body locations to the CNS Efferent nerve fibers- conduct nerve impulses away from the CNS Impulses from CNS to muscles and other organs; cause skeletal muscle contraction and movement and therefore are usually called motor neurons Cranial and spinal nerves in PNS and bundles of axons in the CNS may be made up of nerve fibers which are sensory or motor, or a combination of both Nerve containing only sensory nerve fibers is called sensory nerve Nerve containing only motor nerve fibers is called motor nerve Nerves containing both are mixed nerves Most PNS nerves are mixed o Function: Autonomic versus Somatic Conscious, voluntary control of skeletal muscles is somatic nervous system function Voluntary initiation of efferent impulses and the function is classified as somatic motor function Somatic sensory function- impulses to CNS from receptors in muscles, skin, eyes or ears; perceived by the brain Unconscious, automatic functions- controlled and coordinated by the autonomic nervous system Has sensory and motor neurons- send impulses to smooth muscle, cardiac muscle, and glands to regulate a wide variety of automatic body functions Autonomic sensory nerves receive signals from sensory receptors used to automatically regulate these body functions Neuron Function: Depolarization and Repolarization o Resting state, polarization, and resting membrane potential Neuron not being stimulated= in a resting state Still working to maintain resting state Uses a sodium potassium pump o Causes higher concentrations of potassium to accumulate inside the cell; causes higher concentrations of sodium to accumulate outside the cell o This causes polarization of the cell The standard electrical difference in the cell is called the resting membrane potential o Net negative charge of millivolts- net negative charge within the cell Selectively pumping sodium out and potassium in, cell maintains negatively charged resting membrane potential o Depolarization Nerve firing is depolarization Sodium channel opens when point of stimulus occurs on the neuron Allows only sodium ions to pass through, sodium readily flows in due to higher concentration outside of the cell and moves by passive diffusion , also attracted to the net negative charge inside the cell Depolarization- opening of sodium channels and sudden influx of many sodium ions into the cell Sodium influx results in the loss of two distinct poles of sodium and potassium on either side of the membrane Significant change in electric charge from negative to positive is also referred to as an action potential o Repolarization Almost simultaneously after depolarization, specialized potassium pumps open up in the cell membrane Potassium passively diffuses out of the cell propelled by the concentration gradient and the strong positive charge brought into the cell by the influx of sodium ions Exodus of potassium ions from the neuron causes the charge inside the cell to swing back in the negative direction Cell said to be repolarized because the sodium and potassium ions are once again on opposite sides of the cell membrane Only difference between the resting and repolarization state is that sodium and potassium ions are on the opposite sides from where they began In order to replace to original status, sodium potassium pump allows for the replacement o Depolarization threshold, nerve impulse conduction, and all-or-nothing principle When stimulus is strong enough to cause complete depolarization- said to have reached threshold and causes cell to fire or depolarize Stimulus of sufficient intensity to generate a nerve impulse- threshold stimulus Wave of sodium channels opening to allow sodium influx- wave of depolarization Can alos be called conduction of action potential because the strong influx of sodium ions during depolarization Nerve impulse- conduction of action potential and wave of depolarization Regardless how strong the initial stimulus is, if sufficient enough to achieve threshold for a neuron to fire, the nerve impulse would be generated and conducted along the entire neuron with uniform strength- all-or-nothing principle because either the neuron polarized completely to maximum strength or does not polarize at all Sensory nerve impulses go to a certain areas of the brain where they are interpreted as the appropriate sensation Motor nerve impulses go to effector organs, which are stimulated to perform particular actions o Refractory Period Very brief period during and after a neuron has generated a nerve impulse, it cannot generate another which is known as the refractory period Cells in depolarization and late repolarization phases are already in the process of executing the depolarization-repolarization cycle, that they cannot depolarize again until the cycle is finished Any stimulus received during the cycle would die out Refractory period= insensitive to new stimuli until it recovers from the previous nerve impulse Period of sodium influx and early potassium outflow is the part of the refractory period during which no stimulus not matter how strong can cause the cell to depolarize again- called the absolute refractory period During refractory period, cell many depolarized again if stimulus is stronger than normal- relative refractory period o How myelinated axons conduct action potentials quicker: saltatory conduction Depolarization in myelinated axons can only take place at the gaps in the myelin sheath that occur at the nodes of Ranvier Skips from one node of Ranvier to the next greatly accelerating the rate at which the depolarization wave moves from the neuron cell body to the other end of the axon Saltatory conduction- rapid means of conducting an action potential; make processes such as vision and fine motor control possible in large aniamsl such a humans and many other domesticated species; effects of demyelinating disease can be seen in multiple sclerosis How neurons communicate: the synapse o Synapse- junction between two neurons or a neuron and a target cell Consists of a physical gap between the two cells- synaptic cleft Presynaptic neuron- neuron bringing nerve impulse to the synapse and releasing the chemical to stimulate the next cell Neurotransmitter- chemical signal released by presynaptic neuron Post synaptic cell- neuron which contains the receptors that receive the neurotransmitter Telodendron (slightly branched structure) which ends with the synaptic knob- Synaptic knobs contain many mitochondria that provide energy for the processes that occur there and vesicles which contain the neurotransmitter Wave of depolarization reaches the synaptic knob: calcium channels open in the knobs membranes and the influx of calcium causes the vesicles containing neurotransmitters to fuse with the knobs membrane and dump the contents into the synaptic cleft Synaptic transmission is very specific and only certain neurotransmitters will with in the receptors and cause the receptor to trigger cellular changes- only effective if receptors to the neurotransmitter exist on the postsynaptic cell’s membrane Types of neurotransmitters and their effect on postsynaptic membranes o Two classes of neurotransmitters: excitatory and inhibitory Excitatory have a excitatory effect on the postsynaptic when they combine with specific receptors Usually cause an influx of sodium so postsynaptic membrane can move towards the threshold Inhibitory neurotransmitters hyperpolarize the postsynaptic making the inside of the cell more negative and moving the charge within the postsynaptic cell farther away from the threshold Negatively charged chloride ions enter the postsynaptic cell and allows positively charged potassium ions to leave the cell making the inside of the cell more negative Some neurotransmitters can have an excitatory effect on some cells and an inhibitory effect on others Acetylcholine- can be either excitatory or inhibitory depending on its location in the body Excitatory- between somatic motor neurons and the muscles that they supply o Stimulates muscle fibers to contract Inhibitory- parasympathetic nerves synapse with the heart o Slows the heart rate Catecholamines- norepinephrine, epinephrine, and dopamine Norepinephrine- associated with arousal and flight-or-fight reactions of the sympathetic nervous system Epinephrine- released from adrenal medulla; hormone in the flight-or-fight response Dopamine- found in brain; involved with autonomic functions and muscle control Inhibitory- Gamma-aminobutyric acid (GABA) and glycine GABA- found in the brain; effects by inhibiting activity in the brain and producing tranquilization (reduced anxiety) with sedation (drowsiness) Glycine- found in the spinal cord By having both inhibitory and excitatory neurotransmitters can selectively increase or decrease the activity of specific parts of the brain or spinal cord Drugs or poisons imitating the inhibitory or excitatory neurotransmitters can cause CNS depression or increased CNS activity o Stopping and recycling the neurotransmitter Body must have a way of stopping the effect of the neurotransmitter quickly so that the postsynaptic cell does not continue to be excited or inhibited Acetylcholine- broken down quickly by an enzyme found on postsynaptic membrane called acetylcholinesterase Norepinephrine – rapidly taken back into the synaptic knob and where it is broken down into its components by enzyme monoamine oxidase (MAO); any not absorbed is degraded by another enzyme called catechol-O-methyl transferase (COMT) COMT and MAO is slower than the effects of acetylcholinesterase and explains the effects of excitatory neurotransmitters lingering for a while after their release The Central nervous system- brain and spinal cord o Central nervous system main components- neuron cell bodies, myelinated and unmyelinated nerve fibers and glial cells Gray matter- thinking part of the CNS; contains most of the neuron cell bodies and appears dark-brownish gray color White matter- contains most of myelinated nerve fibers an appears white because all of myelin; wiring that connects various components of the brain; makes up a network of some 100,000 miles of nerve fibers o Brain is divided into four parts: the cerebrum, cerebellum, diencephalon, and brainstem Each section has its own particular function and disease in each part produces different clinical signs Brainstem and diencephalon- more primitive parts; both do not have clearly visible layers of gray matter and white matter Diencephalon- serves as a nervous system passageway between the primitive brainstem and the cerebrum; commonly called the between brain o Thalamus- relay station for regulating sensory inputs to the cerebrum o Hypothalamus- interface between the nervous and endocrine system o Pituitary- endocrine “master gland” that regulates production and release of hormones throughout the body Brainstem- connection between the rest of the brain and the spinal cord; most primitive part of the brain which includes the medulla oblongata, pons, and the midbrain o Maintains the basic support functions of the body; operates subconsciously; heavily involved in autonomic control functions related to heart, respiration, blood vessel diameter, swallowing and vomiting o May cranial nerves originate here; damage to the brainstem can result in animal dying rapidly from respiratory failure or cardiovascular collapse Cerebellum- coordinates motor control Second largest component of brain, caudal to the cerebrum Allows body to have coordinated movement, balance, posture and complex reflexes o Compares the movement the body intends to make with the actual position of muscles and joints to determine whether the intentions of the cerebellum are being carried out; if not, cerebellum fine tunes the movements by inhibiting or stimulating muscles Uses same sensory feedback from muscles to maintain posture and balance Hypermetria- voluntary movements become jerky and exaggerated- occurs when there id damage or disease to cerebellum: seen as pigs with cerebellar disease Cerebrum- centers of higher learning and intelligence Made up of gray matter in the cerebral cortex (most superficial layer of the brain) and white matter beneath the cortex with the corpus callosum ( set of fibers which connects the two halves of the cerebral cortex) Largest part of brain in domestic animals and constitutes area of brain responsible for those functions most commonly associated with higher-order behaviors (learning, reasoning, and intelligence) Receives and interprets sensory information, initiates voluntary nerve impulses to skeletal muscles, and integrates neuron activity associated with communication, expression of emotional responses, learning, memory and recall Gyri are folds, gyri are separated by deep grooves called fissures and shallow grooves called sulci o Longitudinal fissure- divides cerebrum into right and left cerebral hemispheres o Each hemisphere is divided into lobes by sulci, lobes specialize in certain functions If neurons of certain lobes being to fire spontaneously, animal can exhibit spontaneous movements, seizure activity, abnormal behaviors, or hallucinations depending on the affected lobe If parts of cerebrum become damaged/nonfunctional due to lack of oxygen, poisonous substances, or strokes, animal may lose perception of specific sensations, loss of voluntary movement, or may be unable to retain or recall information (unable to learn) o Other clinically important structures of the brain Meninges- set of connective tissue layers that surround the brain and spinal cord Three layers of meninges from outside to innermost: tough fibrous dura matter, spiderweb-like arachnoid matter and very thin pia matter laying directly on the surface of the brain and spinal cord Contain a rich network of blood vessels that supply nutrients and oxygen to the superficial tissues of the brain and spinal cord Fat, fluid, and connective tissue between the layers of meninges provide cushioning and distribution of the nutrients for the CNS Cerebrospinal fluid- circulates between layers of meninges and through cavities inside the brain and the spinal cord CSF’s chemical composition may be involved in the regulation of certain autonomic functions (respiration and vomiting) Blood-Brain barrier- functional barrier separating the capillaries in the brain from the nervous tissue itself No fenestrations in capillaries- small openings between cells of capillary walls Capillaries in the brain are covered by the cell membranes of glial cells; results in a cellular barrier that prevents many drugs, proteins, ions, and other molecules from readily passing from the blood into the brain Protects the brain from many poisons circulating the bloodstream; prevents drugs that we administer from penetrating into the brain Cranial nerves- special set of 12 nerve pairs in the peripheral nervous system that originate directly from the brain May contain axons of motor neurons, axons of sensory neurons, or combinations of both Numb Name Type Key functions er I Olfactory Sensor Smell y II Optic Sensor Vision y III Oculomotor Motor Eye movement, pupil size, focusing lens IV Trachlear Motor Eye movement V Trigeminal Both Sensations from the head and teeth, chewing VI Abducent Motor Eye movement VII Facial Both Face and scalp movement, salivation, tears, taste VIII Vestibulocochl Sensor Balance, hearing ear y IX Glossopharyn Both Tongue movement, geal swallowing, salivation, taste X Vagus(wander Both Sensory from er) gastrointestinal tract and respiratory tree; motor to the larynx, pharynx, parasympathetic; motor to the abdominal and thoracic organs XI Accessory Motor Head movement, accessory motor with vagus XII Hypoglossal Motor Tongue movement Spinal cord-caudal continuation of the brainstem outside of the skull that continues down the bony spinal canal formed by the vertebrae Conducts sensory information and motor instructions between the brain and the periphery of the body Contains many neuron cell bodies( in gray matter) and extensive synapses between ascending nerve fibers conducting sensory information toward the brain and descending nerve fibers conducting motor information to muscles and other organs Gray matter is located on the inside of the spinal cord while the white matter is on the outside Between each pair of adjacent vertebrae, the spinal cord sends off dorsal and ventral nerve roots from each side that combine to form left and right spinal nerves; link with spinal cord to make peripheral nerves o Dorsal nerve roots- contain sensory( afferent) fibers o Ventral nerve roots- contain motor (efferent) fibers o Sensory information comes into the spinal cord via the dorsal nerve roots and motor instructions go out the body via ventral nerve roots Autonomic Nervous System o Formed from two divisions: parasympathetic and sympathetic nervous system Generally have opposite effects on organs or tissues o Structure Nerves for the sympathetic nervous system emerge from the thoracic and lumbar vertebral regions in the back Nerves for the parasympathetic nervous system merges from the brain and the sacral vertebral regions Efferent motor nerves of both systems are composed of a sequence of two neurons; first neuron has cell body in the brain or spinal cord, and extends axon out from the CNS to the autonomic ganglion First neuron- preganglionic neuron; second neuron- postganglionic neuron Sympathetic preganglionic neuron originates in the thoracic and lumbar segments of the spinal column; extends out from the spinal cord and either synapses with a neuron within the ganglion chain or passes through the ganglionic chain and synapses with a neuron located beyond the sympathetic chain Explains why sympathetic nervous system responses are usually spread throughout the body an involve several organs simultaneously Sympathetic postganglionic neuron extends the remaining distance to the target organ; much longer than the preganglionic neuron Parasympathetic preganglionic neuron is quite long and originates from the nuclei of several cranial nerves and from the sacral region of the spinal cord Parasympathetic preganglionic neuron travels directly from the CNS to its target organ; synapses with a short postganglionic neuron in the target organ Parasympathetic preganglionic neuron is relatively long compared to the short postganglionic neuron o General Functions Sympathetic Parasympathetic System Effect System Effect Heart Rate Increases Decreases Force of heart Increases Decreases contraction Diameter of Increases (dilates) Decreases (constricts) bronchioles Diameter of pupil Increases (dilates) Decreases (constricts) Gastrointestinal Decreases Increases motility, secretions, and blood flow Diameter of skin Decreases No significant effect blood vessels Diameter of Increases No significant effect muscle blood vessels Diameter of Decreases No significant effect blood vessels to kidneys o
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