Human Physiology Notes 2/1 - 2/12
Human Physiology Notes 2/1 - 2/12 BIOL 3160
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This 15 page Class Notes was uploaded by MBattito on Monday February 15, 2016. The Class Notes belongs to BIOL 3160 at Clemson University taught by Dr. Tamara McNutt-Scott in Fall 2015. Since its upload, it has received 82 views. For similar materials see Human Physiology in Biological Sciences at Clemson University.
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Date Created: 02/15/16
Chapter 8: Central Nervous System The central nervous system (CNS) is comprised of brain and spinal cord • Functions to: o Receive input information from sesnsory neurons o Direct activity of motor neurons that innervate muscles and glands o Association, or interneurons, within brain and spinal cord serve to “associate” appropriate motor responses with sensory stimuli, thus maintaining homeostasis During development: • Ectoderm: embryonic tissue layer on the surface of an early embryo o Eventually will form the epidermis of the skin • A groove develops in the ectoderm along the dorsal midline of the embryo’s body o Groove deepens and forms the neural tubeà neural tube becomes the CNS • Neural crest: part of the ectoderm where the fusion of the neural tube occurs o Located between the neural tube and the surface ectoderm o Neural crest (among other structures) becomes the ganglia of the peripheral nervous system • Anterior portion of neural tube becomes brain, folds form 3 distinct regions o Forebrain (prosencephalon) § At fifth week of development differentiates to form telencephalon and diencephalon § Telencephalon grows disproportionately in humans à forms the two enormous cerebral hemispheres o Midbrain (mesencephalon) o Hindbrain (rhombencephalon) § At fifth week of development differentiates to form metencephalon and myelencephalon • Ventricles: cavities that maintain “hollow” morphology à filled with cerebrospinal fluid o Central canal: cavity in the spinal cord; also filled with cerebrospinal fluid § Cerebrospinal fluid: formed by choroid plexuses • Constant composition • Slightly hypertonic • Differs from plasma in its concentrations of various ions • Moves by pulsations in the choroid plexuses CNS comprised of gray and white matter • Grey matter: contains neuron cell bodies and dendrites o Found in the cortex of the brain and deeper within the brain in aggregations known as nuclei • White matter: myelinated axon tracts o Underlie the cortex and surround the nuclei Brain: • 3-‐35 lbs • receives about 15% total blood flow to body per minute à due to high metabolic requirements • Involvement in learning and memory – permits behavior to be modified by experience o Benefits survival • Along with perceptions, emotions and self-‐awareness forms basis oc consciousness • Neural stem cells develop into neurons and glial cells o Neurogenesis: formation of new neurons from neural stem cells; observed in 2 locations: § Subventricular zone: thin layer adjacent to the ependymaa that lines the lateral ventricles • In mammals (other than humans) the neurons generated here migrate to the olfactory bulbs à involved in sense of smell • In humans: neurons generated here migrate to the striatum à regulates motor control and cognitive functions § Subgranular zone: in the hippocampus • Form interneurons that function within the hippocampus to aid learning and memory • Brain creations: o Not a “singular event” Cerebrum • Largest portion of the brain • Region primarily responsible for higher brain functions • Divided into left and right hemispheres o Connected internally via large fiber tract à corpus callosum § Corpus callosum: major tract of axons that functionally interconnects the hemispheres • Cerebral cortex § 2-‐4mm of gray matter form the outer surface – underlying white matter o Anatomic construction increases area for neurons but does not increase volumeà convolutions § Gyri: elevated folds of convolutions § Sulci: depressed grooves of convolutions o Most complex integrating area of nervous system 5 lobes of the cerebrum and their functions • Frontal: voluntary motor control of skeletal muscles; personality; higher intellectual processes; verbal communication • Parietal: somatesthetic interpretation; understanding speech and formulating words to express thoughts and emotions; interpretation of textures and shapes • Temporal: interpretation of auditory sensations; storage (memory) of auditory and visual experiences • Occipital: integration of movements in focusing the eye; correlation of visual images with previous visual experiences and other sensory stimuli; conscious perception of vision • Insula: memory; sensory (principally pain) and visceral integration • Cortex is mapped by regions of body – somatotopy o Note that body part size does not correspond with amount of cortical area used à body regions with the highest densities of receptors are represented by the largest areas of the sensory cortex and the body regions with the greatest number of motor innervations are represented by the largest areas of motor cortex § The hands and face are served by a larger area than the rest of the body Electroencephalogram • Synaptic potentials produced by cell bodies and dendrites in cerebral cortex create electrical currents that can be measured by electrodes placed on the scalp à termed electroencephalogram (EEG) • Deviations from normal EEG patterns can be used clinically to diagnose epilepsy and other abnormal states o Abnormal synchronized discharges of cerebral neuron o Electrical storm within a short circuit, occurs at small spot within brain – focus – causes waves of electrical activity to spread throughout brain • Absence of EEG signifies brain death • 4 type of EEG patterns: o Alpha waves: best recorded from parietal and occipital regions while a person is awake and relaxed with eyes closed § Rhythmic oscillations of 10-‐12 cycles/second o Beta waves: strongest near frontal lobes § Evoked activity: produced by visual stimuli and mental activity § 13-‐25 cycles/second o Theta waves: emitted from temporal and occipital lobes § Common in infants and sleeping adults § Increase in awake adults during tasks the require attention and memory, sleep deprivation, and severe emotional stress § 5-‐8cycles/seconds o Delta waves: emitted in a general pattern from the cerebral cortex § Common during sleeping adults and awake infants § 1-‐5cycles/second § Presence in an awake adult indicates brain damage Sleep • EEG patterns change with sleep o REM sleep: when you dream § Theta waves § Limbic system is active during REM sleep § Higher total brain metabolism and higher blood flow § Irregular breathing o Non-‐REM (NREM) sleep: remainder of time during sleep § Resting sleep § Decreased energy metabolism and blood flow § Regular breathing and heart rate § Subjects allowed to have NREM sleep after a learning trial displayed improved performance to those not allowed NREM sleep § 4 stages of NREMà stages 3-‐4 are known as slow-‐wave sleep • delta waves • Observe cycles with subject going through stages of NREM seep, then ascend back through to REM, followed by stages of NREM o Cycle ~ 90 minutes o 4-‐5 REM to NREM cycles per night o Typically wake up from REM sleep Basal Nuclei • Masses of gray matter deep within white matter of cerebrum composed of neuron cell bodies • Play important role in movement and posture as well as complex aspects of behavior • Corpus striatum: most prominent basal nuclei o Composed of the caudate and lentiform (consisting of putamen and globus pallidus portions) nuclei o Function in the control of voluntary movement • Substantia nigra and subthalamic nuclei o Functionally associated with basal nuclei • Motor circuit: o Motor cortex sends signals to basal nuclei o Putamen in basal nuclei sends signals to other BN areas o GP and SN send signals to thalamus o Thalamus then sends signals to motor cortex o Allows intended movements while inhibiting unintended movements Cerebral/Hemispheric lateralization • Cerebral hemispheres appear symmetrical, but each has anatomic chemical and functional specializations • Information entering brain decussates (crosses over) à thus the right side of the brain controls the left side of the body and vise versa o Communication via corpus callosum keeps each hemisphere appraised of “total” body function • Through experimentation, found that each hemisphere is good at certain categories of tasks and poor at others o Lead to concept of cerebral dominance § Handedness: people generally have a greater motor competence with one hand than with the other • Right-‐handed à left hemisphere dominant o Hemispheres function complementary to each other (neither subordinate) o Cerebral lateralization: specialization of function in one hemisphere à now preferred over cerebral dominance • Speculate that creative ability may be related to interaction of information between hemispheres o Proportion of left-‐handed art students is much higher than right-‐ handed Language • Potential for development of language specific mechanism in left hemisphere is present at birth, yet assignment is flexible in early years of life à after, success rates decline • Language is a complex code that includes the acts of listening, seeing, reading and speaking with each aspect of language dealt with by different regions • Knowledge gained through study of aphasias: speech and language disorders caused by damage to the brain through injury or stroke • Key regions of particular importance in the production of aphasia: Broca’s area and Wernicke’s area o Broca’s Aphasia: § Weakness in the right arm and right side of face § Those affected are reluctant to speak § Speech is slow and poorly articulated § Comprehension of speech is unimpaired § Not due to motor control à tongue, lips, larynx, etc. are unaffected o Wernicke’s Aphasia: § Results in speech that is rapid and fluid but without meaning à word salad § Language comprehension is destroyed – cannot understand spoken or written language § Wernicke’s area: concept of words originates here • Arcuate fasciculus: fiber tract that communicates between Broca’s area and Wernicke’s area o To speak intelligibly, the concept of words originated in Wernicke’s area must be communicated to Broca’s area o Broca’s area sends fibers to the motor cortex à directly controls musculature of speech o Conduction aphasia: damage to the arcuate fasciculus § Produces fluent but nonsensical speech • Angular gyrus: located at the junction of the parietal, temporal and occipital lobe o Believed to be the center for the integration of auditory, visual and somatesthetic information o Damage to it produces aphasias—suggests it projects into Wernicke’s area PET scans • Increased blood flow to specific lobes of brain during various language-‐based activities Limbic System and Emotion • Hypothalamus and limbic system are important brain regions for neural element of emotional states • Limbic system: consists of a group of forebrain nuclei and fiber tracts that for a ring around the brain stem o Initially called “smell brain” because it is involved in the central processing of olfactory informationà primary function in lower vertebrates o The center for emotional drives and derived early in course of vertebrate evolution o Few synaptic connections between the cerebral cortex and limbic system – explains why we have so little conscious control over our emotions • Involved in: o Aggression: stimulation of certain areas of the amygdala and hypothalamus produce rage and aggression o Fear: amygdala is needed for fear conditioning o Feeding: hypothalamus contains both feeding center and satiety center § Stimulation of the feeding center results in overeating § Stimulation of the satiety center will stop feeding behavior o Sex: limbic system and hypothalamus important in regulation of sex drive and behavior § In lower animals: cerebral cortex is important in sex drive § In humans: cerebrum is more important in sex drive o Goal-‐oriented behavior: center of reward/punishment system • Papez circuit: Closed circuit that information flows through between the limbic system and the thalamus and hypothalamus o Hippocampal/mammillothalamic tract o Found to be involved in consolidation of memories à “passes through circuit” Learning and Memory • Learning: acquisition and stoage of information as a consequence of experience o Measured by increase in likelihood of a particular behavioral response to a stimulus o Rewards/punishments crucial ingredients in learning • Memory: relatively permanent storage form of learned information o Not single, unitary phenomenon § Bra processes, stores and retrieves information in different ways to suit different needs Memory • Several different brain regions involved with storage and retrieval o Amnesia: loss of memory § Result with damage to several different areas § Suggests the presence of several different systems of information storage available in brain • Different categories o Short-‐term or working memory: § Registers and retains incoming information for a short time • Retention: seconds-‐minutes § New memories not instantly permanent and susceptible to modification • Require protein synthesis before becoming stable § Stored differently dependent on type of information to be stored – involves prefrontal lobe o Long Term memory: § Store for days to years § Depends on the synthesis of mRNA and protein § Memory consolidation: conversion of short-‐term memories, recalled at a later time • Requires the activation of genes, the production of new proteins, and the formation of new synapses § Classified as: • Non-‐declarative (implicit) memory: memory of simple skills and conditions (ex. How to tie a shoelace) • Declarative (explicit) memory: retention and recall of conscious experiences that can be verbalized; people with amnesia have impaired declarative memory o Sematic (fact) memory: remembering the names of the bones o Episodic (event) memory: remembering the experience of taking a practical exam on the skeletal system • Removal of the left medial temporal lobe impairs the consolidation of verbal memories while removal of the right medial temporal lobe impairs the consolidation of nonverbal memories • Hippocampus appears to be important component of memory system o MRIs reveal that the hippocampus is often shrunken in living amnesia patients • Emotions influence and strengthen/hinder memory formation o Amygdala improves memory when there is an emotional content (fear) • Stress hinders memory formation o Reduces ability of hippocampus to form memories § Mechanism unknown but area targeted (hippocampus and amygdala) due to presence of receptors for stress • Inferior temporal lobes: appear to be sites for the storage of long-‐term visual memories o Medial regions cannot be site of storage because destruction of these area in patients treated for epilepsy did not destroy the memory of events prior Synaptic changes: § Short-‐term memory involves establishment of recurrent/reverberating circuits o Where neurons synapse with each other to form a circular path à last neuron to be activated then stimulates the first neuron o The circuits are the neuronal basis of working memory § Consolidation involves permanent changes to the chemical structure of neurons and their synapses with protein synthesis being required o Long-‐Term Potentiation (LTP) § Type of synaptic learning § Mechanism couples frequent activity across synapse with lasting changes in signal strength across the synapse § Stimulation at high frequency exhibit subsequent increased excitability Long-‐Term Potentiation: § Induced by the activation of NMDA receptors for glutamate § At resting membrane potential the pore is blocked by Magnesiumà does not allow entry of potassium even if glutamate is present § To allow activation of NMDA receptors, the membrane must become partially depolarized to make the magnesium leave the pore o The depolarization could be caused by glutamate binding to the AMPA receptor § When glutamate can bind to its NMDA receptor, the NMDA channel opens allowing calcium to diffuse into the cell § The calcium binds to calmodulin à activates CaMKII enzyme o The CaMKII moves to the synapse and phosphorylates proteins that allow more AMPA receptors for glutamate to be inserted into the postsynaptic membrane and increase the ion conductance of each AMPA channel § Specific to that stimulated synapse § Result: synaptic transmission of that synapse is strengthened so that a given amount of glutamate produces a greater postsynaptic depolarization à EPSP § The rise in the intracellular calcium concentration also causes longer-‐term changes in the postsynaptic neuron o The long term changes activate CREB and other epigenetic changes that contribute to long-‐term memory § Most ESPS are produced on dendritic spines à LTP induces dendritic spines to enlarge and change shape o LTD dendritic spines are observed to shrink or disappear Neural stem cells § Found in hippocampus § Suggest that neurogenesis may be involved in earning and memory § Depolarization-‐induced suppression of inhibition endocannabinoid § Neurogenesis occurs in subgranular zone Diencephalon: § Represents structures around the third ventricle and are completely surrounded by the cerebral hemispheres § Comprised of: o Thalamus: primarily relay center through which all sensory information (except smell) passes to cerebrum o Epithalamus: § Contains choroid plexus: where cerebral spinal fluid is formed § Contains pineal gland: secretes melatonin to regulate circadian rhythms o Hypothalamus: collection of nuclei that are involved in a variety of homeostatic processes Brainstem § Comprised of midbrain, pons and medulla § Involved rigidly, programmed automatic behaviors necessary for survival as well as providing a pathway for fiber tracts running between higher and lower neural centers § Midbrain o Cerebral peduncles (ascending/descending fiber tracts) § Ascending axons: sensory § Descending axons: motor o Corpora quadrigemina (visual/auditory reflexes) § Tectal plate o Red nucleus (motor coordination) o Substantia nigra (movement, mood, reward, addiction) § Pons: o Passage of sensory and motor tracts o Several nuclei associated with central nervous system o Observe autonomic respiratory centers § Modifies breathing which is controlled by medulla § Medulla: o All ascending and descending tracts between spinal cord and brain pass through this region § Site of decussation o Nuclei important for motor control o House vital centers: groupings of neurons required for the regulation of breathing and of cardiovascular responses § Vasomotor center: controls autonomic innervation of blood vessels § Cardiac control center: regulates autonomic nerve control of the heart; closely associated with the vasomotor control center § Respiratory center: sets the rate and depth of breathing à modified by the pons Cerebellum: § Second largest structure of brain § Receives input from proprioceptors and works together with basal nuclei and cerebral cortex motor area in coordination of movement o Proprioceptor: sensory receptor found in joints, tendons and muscles § Needed for motor learning and coordinating movement of different joints in movement § Required for proper timing and force required for limb movements o Ex. Cerebellum is needed to touch your finger to your nose, bring a fork of food to your mouth or find keys by touch in your pocket § Purkinje cells: specific cerebellar neurons that the functions can only operate through § Current research suggest may have other functions besides motor o Schizophrenia § Individual interprets reality abnormally § Cognitive dementia • General discoordination of sensoriomotor and mental processes o Autism § Group of developmental problems, affect child’s ability to communicate and interact with others § Smaller/abnormal area in vermis § Ataxia: lack of muscle coordination during voluntary movements o Indicative of cerebellum damage Reticular Formation and Reticular Activating System § An interconnected group of neurons that constitutes an arousal system o Reticular activating system (RAS): ascending arousal system § Promotes wakefulness when activated and sleep when inhibited • Accomplished via use of excitatory and inhibitory neurotransmittersà work in tandem like a switch § Many drugs act on the RAS, promoting sleep or wakefulness § Narcolepsy: neurological disorder where a person will fall asleep inappropriately throughout the day despite having ample sleep • Loss of LHA neurons that release polypeptide neurotransmitters that promote arousal § Hypothesis for sleep-‐wake cycles: o During waking, aminergic neurons dominate and during REM sleep cholinergic neurons are dominant § Hypothalamic neurons project to RAS and influence sleep-‐ wave cycles in regards to biological clock aligned with circadian rhythms Chapter 9: The Autonomic Nervous System Autonomic Nervous System Neurons § Innervate organs whose function typically not under voluntary control o Effectors that respond to autonomic regulation include cardiac muscle, smooth muscle and glands § Unlike somatic, have a 2-‐neuron pathway o Central nervous system à preganglionic neuron à autonomic ganglion à postsynaptic neuron à involuntary effector o Ganglion: collection of neuron cell bodies § Autonomic control is an integral part of organ systems physiology § Common features: o Resting tone (tension) in absence of nerve stimulation o Denervation hypersensitivity § Autonomic nerve damage results in an increase of target tissue sensitivity to stimulating agents • A compensatory event to nerve damage o Autonomic innervation § Target tissues display autorythmicity • Organs “independent” of their innervation § Increase or decrease target tissue activity à modulator (not simulator) Divisions of the ANS: § Parasympathetic (craniosacral) nerves: come from the brainstem and sacral region of the spinal cord o “Break” o “Rest and digest” § Sympathetic (thoracocolumbar) nerves: come from the thoracic and lumbar regions of the spinal cord o “Gas” o “Fight or flight” § Note ganglia location: for sympathetic most ganglia lie close to the spinal cord à parasympathetic ganglia are either on or next to effector organ § Mass activation: stimulates sympathetic nerves to “rev up” organs à global event Adrenergic Stimulation § Response of target tissue dependent on receptor displayed o Alpha or beta-‐adrenergic receptors § Subtypes (do not have to know subtypes) o Act via G-‐proteins § Clinical application o Drugs can be agonists or antagonists § Use of drugs that specifically stimulate/block various receptors can be used clinically to treat disease • Propanol o Hypertension o Non-‐selective beta blocker Cholinergic stimulation: § Preganglionic release is always excitatory, postganglionic release can be either excitatory or inhibitory o Response is receptor type-‐dependent § Other autonomic neurotransmitters referred to as nonadrenergic, noncholingeric fibers Organs with dual innervation § Innervated by both parasympathetic nervous system and sympathetic nervous system § Action: o Antagonistic: most common o Complementary: stimulation of either division causes similar effects o Cooperative: stimulation causes different effects by parasympathic and sympathetic nervous system that work together to promote a single action Organs without Dual innervation § Include: adrenal gland, arrector pili muscle, sweat glands and most blood vessels § Regulation achieved by increase or decrease in ton (firing rate) of sympathetic nervous system fibers Control of Autonomic nervous system by higher brain centers § Visceral functions regulated by autonomic reflexes, as sensory input to brain centers integrate and respond by modifying preganglionic neuron activity § Neural centers of medulla control autonomic nervous system activity o Responsive to hypothalamus, ie. Higher brain center § Major regulatory center for ANS § Limbic system o Visceral response to emotional states § Cerebellum Chapter 10: Sensory Physiology Sensory system: neural mechanism, which processes sensory information bringing awareness of internal and external environment Sensory Receptor Characteristics: § Muller’s Law: o Each sensory receptor response to a particular modality of environmental stimulus o Brain interprets impulses along a specific neural pathway as the stimulus § Transduces stimulus energy into electrochemical energy § Sensory unit: o Single afferent neuron and all of its receptor endings o Receptive field § Overlap o Modality and body location § Unique pathway § Specific region of sensory cortex o Acuity, or precision § Locate and discern one stimulus from another § Amount of neuronal input convergence § Each sensory nerve ending, however stimulated, gives rise to its own specific sensation o Each sensation type depends not on the nerve it travels but upon the part of the brain in which the fibers terminate Factors affecting acuity: § Sensory unit density and amount of overlap § Size of receptive field covered by a sensory unit § Greater sensory neuron response when stimulus applied center of receptive field Lateral Inhibition § Occurs in the central nervous system § Most important mechanism enabling localization of stimulus site § Receptors at edge of stimulus strongly inhibited compared to center § Sensory neuron most strongly stimulated inhibits neighboring sensory neurons Categories of sensory receptors: § Structural o Simple or complex in design o Peripheral nerve endings free (respond to pain or temperature) or encapsulated (respond to pressure) § Functional o Characterized by type of stimulus they respond to § ChemoR: chemical stimuli in environment or blood • Ex. Taste buds, olfactory epithelium and the aortic and carotid bodies § PhotoR: rods and cones in the retina of the eye § ThermoR: respond to temperature § MechanoR: stimulated by mechanical deformation of the receptor cell membrane • Ex. Touch and pressure receptors in the skin and hair cells within the inner ear § Nociceptor: pain receptors that depolarize in response to stimuli that accompany tissue damage o Type of stimulus information delivered § Proprioceptors: muscles, joints and tendons • Provide sense of body position and allow fine control of skeletal movements § Cutaneous receptors: • Touch and pressure receptors • Heat and cold receptors • Pain receptors § Special senses: • Sight • Hearing • Equilibrium • Taste • smell § Exteroceptor vs. Interoceptor o Exteroceptors: respond to external stimuli o Interoceptors: respond to internal stimuli Sensory Adaptation § Tonic receptor – slow adapting o Maintain firing frequency during application of stimulus § Phasic receptor – fast adapting o Respond with quick burst of activity when stimulus 1 applied, then firing rate decreases § Adaptation: ability to cease paying attention to constant stimuli • Ex. Shower water feels much hotter when you first step in o Quick short burst of impulses when stimulus applied, then another quick short burst of impulses when stimulus removed § “on-‐off” info Receptor (generator) Potential § In response to stimulus, sensory endings produce local graded changes in membrane potential o Depolarizations analogous to EPSPs § In sensory nerve endings, these potential changes in response to stimulation are called receptor or generator potentials o Since sensory neurons are Pseudounipolar, the action potentials produced are conducted continuously from the periphery into the central nervous system § Phasic receptor: ex. Pacinian corpuscle o When a light touch is applied to the receptor a small depolarization is produced o Increasing pressure increases the magnitude until the threshold needed for an action potential is reached o If the pressure is maintained the size of the generator potential produced quickly diminishes § Tonic receptor: o Generator potential it produces is proportional to the intensity of the stimulus o If threshold is reached, an increase in the generator potential amplitude will result in an increase in action potential frequency o Tonic receptors provide information about the relative intensity of a stimulus Cutaneous sensations § Result due to information from a variety of sensory receptors § Somatic sensations: sensation from skin, muscles, bones tendons and joints § Somatesthetic senses: conscious awareness of body
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