Human Physiology Test 2 Study Guide
Human Physiology Test 2 Study Guide BIOL 3160
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This 40 page Study Guide was uploaded by MBattito on Tuesday February 23, 2016. The Study Guide belongs to BIOL 3160 at Clemson University taught by Dr. Tamara McNutt-Scott in Fall 2015. Since its upload, it has received 151 views. For similar materials see Human Physiology in Biological Sciences at Clemson University.
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Date Created: 02/23/16
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 tube 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 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 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 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 involved in sense of smell In humans: neurons generated here migrate to the striatum 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 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 volume 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 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 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 NREM 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) 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 left hemisphere dominant o Hemispheres function complementary to each other (neither subordinate) o Cerebral lateralization: specialization of function in one hemisphere 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 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 tongue, lips, larynx, etc. are unaffected o Wernicke’s Aphasia: Results in speech that is rapid and fluid but without meaning 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 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 information 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 “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 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 Magnesium 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 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 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 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 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 neurotransmitters 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 preganglionic neuron autonomic ganglion postsynaptic neuron 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 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 parasympathetic ganglia are either on or next to effector organ Mass activation: stimulates sympathetic nerves to “rev up” organs 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 st 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 Gustation- Taste Chemical sense chemoR; exteroceptor Evoked by receptors that consist of barrel shaped taste buds o Each taste bud is located on the dorsal surface of the tongue and consist of 50-100 specialized epithelial cells with long microvilli that extend to the external surface o Are not neurons but behave like them become depolarized, do not produce action potentials, and release neurotransmitters that stimulate sensory neurons Classified as neuroepithelial cells Gustation follows along Cranial Nerves 7 and 9 (facial and glossopharyngeal) carries taste information to the medulla oblongata carried to the thalamus directed to the cerebral cortex 5 tastes o Salty o Sour o Sweet o Umami o Bitter Taste cells: specialized epithelial cells of the taste bud o All taste buds are sensitive to each category of taste but each particular taste cell is only sensitive to one category Taste is influenced by the temperature and texture of food Tastes: Salty: o Due to presence of sodium ions that activate specific receptor cells for the salty taste o The sodium passes into the sensitive receptor cells calcium ion gated channels open depolarizing the cell, causing them to release a neurotransmitter o The anion associated with Na+ modifies the perceived saltiness NaCl tastes much saltier than other sodium salts Sour: o Due to the presence of H+ ions via ion movement through the membrane channels o H+ ions enter the cell calcium ion gated channels open cells is depolarized and releases neurotransmitter o All acids taste sour The more acidic pH, the more sour it will taste The remaining three: sweet, bitter and umami involve interactions of the taste molecules with membrane receptors couples to G-proteins o Ability of sweet receptors to respond to a wide variety of organic molecules is due to the presence of multiple ligand binding sites in the receptor proteins o G-protein-coupled umami receptors are activated only by the binding of the amino acids L-glutamate and L-asparate Evokes a savory, “meaty” taste o Bitter taste serves to warn against toxins more sensitive to low concentrations of their ligand Able to detect a wide variety of toxins but are not able to distinguish between them The most acute sensation Utilizes membrane receptors and second messenger system Releases Calcium from endoplasmic reticulum o Sweet and Umami: Utilizes membrane receptors and second messenger system Closes potassium gate to depolarize and releases neurotransmitter Gustducin: G-proteins involved with taste o Dissociation of the Gustducin G-protein subunit activates a second-messenger system depolarizes the cell activates the sensory neuron associated with the taste o Second-messenger systems activated by G-protein depend on the molecule tasted In the sweet taste of sugars: G-proteins activate cAMP produces depolarization by closing potassium channels In the sweet taste of artificial sweeteners: Involve activation of membrane enzyme that produces IP3 and DAG Olfaction – smell Chemical sense chemoR; extercoceptor Genes for about 300 different olfactory receptor proteins with 1 receptor type expressed per bipolar neuron, yet we can identify over 10,000 different odors Brains must somehow integrate information from many different receptor inputs and then interpret the pattern as a characteristic fingerprint for a particular odor Olfactory apparatus: o Olfactory receptor cells: bipolar neurons o Supporting (sustenacular) cells: epithelial cells rich in enzymes Oxidize hydrophobic molecules making them less lipid-soluble, and thus less able to penetrate membrane and enter the brain o Basal stem cells: generate new receptor cells every 1-2 months to replace damaged neurons Only place in the human body that has neuron turnover Odorant stimulated G-protein second messenger system – strong depolarization o Odorant binds to its receptor G-protein subunits dissociate and enter the plasma membrane to activate adenylate cyclase converts ATP to cAMP opens ion channels allowing Na+ and Ca2+ to diffuse in produces a graded depolarization produces an action potential Second messenger is an amplification process – accounts for the extreme sensitivity of the sense of smell Sense of smell is transmitted directly to the cerebral cortex, NOT first sent to the thalamus Vestibular Apparatus and Equilibrium: Sense of equilibrium provides orientation with respect to gravity due to function of the vestibular apparatus Inner ear is composed of the: o Cochlea: snail-shaped structure involved with hearing o Vestibular apparatus: consists of 2 parts Macula: include the utricle and saccule Semicircular canals Movements of the head cause fluid within these structures to bend extensions of sensory hair cells resulting in the production of action potentials Membranous labyrinth: where the sensory structures of the vestibular apparatus and cochlea are located o Filled with endolymph: fluid with a high K+ concentration o Located in the bony labyrinth a bony cavity within the skull Perilymph located between the membranous labyrinth and the bone (fairly typical extracellular fluid) Sensory Hair Cells of the Vestibular Apparatus Utricle and Saccule: provide information about linear acceleration o Utricle: horizontal o Saccule: vertical Semilunar canals: crista ampularis provide information about rotational acceleration Hair cells: modified epithelial cells; receptors for equilibrium o Gives off a steady frequency of action potentials o Contains 20-50 hair-like extensions o Sterocilia: modified microvilli arranged in rows of increasing height o Kinocilum: taller true cilium touching the stereocilia of the tallest row o When the stereocilia are bent in the direction of the kilocilium, the plasma membrane is depressed and K+ ion channels open, allowing K+ to enter and depolarize the cell release neurotransmitter o When the stereocilia are bent in the opposite direction, it causes hyperpolarization releases less synaptic transmitter The ears and hearing: Sound causes movements of the tympanic membrane and middle-ear ossicles that are transmitted into the cochlea causes a bending of the hair cells produces action potentials interpreted by the brain as sound Sound waves are characterized by their frequency and intensity o Pitch is directly related to frequency: the greater the frequency the higher the pitch Each sound frequency produces vibrations at a different region of the basilar membrane pitch discrimination Intensity (loudness) of a sound is directly related to amplitude Outer Ear: Formed by the pinna (auricle) and external auditory meatus External auditory meatus channels sound waves to the eardrum (tympanic membrane) Middle Ear: Cavity between the tympanic membrane and cochlea 3 middle ear ossicles o Malleus o Incus o Stapes Malleus is attached to the tympanic membrane – vibrations are transmitted from the tympanic membrane to malleus, incus and then stapes The stages transmits vibrations to the oval window (a membrane in the cochlea) o Observe muscles in the middle ear that contract when sound is too loud to protect our ear Cochlea: Snail shaped organ within the temporal bone Composes the inner ear along with the vestibular apparatus 3 chambers within it: o Scala vestibuli: upper chamber Part of the bony labyrinth Vibrations of the stapes and oval window displace perilymph fluid within it – causes pressure waves o Scala Tympani: lower chamber Part of the bony labyrinth o Scala media: middle chamber Also called the cochlear duct Part of the membranous labyrinth Coils to form 3 turns Contains endolymph instead of perilymph Endolymph is rich in potassium Cochlear duct ends blindly causes the perilymph of the scala vestibuli and scala tympani to be continuous at the apex o Helicotrema: small space between the end of the cochlear duct and the wall of the cochlea Pressure waves in the scala vestibuli are passed to the scala tympani travels to the base of the cochlea causes displacement of the round window (membrane into the middle ear cavity) o Perilymph cannot be compressed so an inward movement of the oval window must be compensated for by an outward movement of the round window When sound frequency (pitch) is low, there is enough time for the pressure waves to travel through the helicotrema As the frequency increases there is not enough time, so it must travel through the vestibular membrane (separates the scala vestibuli and the cochlear duct) and the basilar membrane (separates the cochlear duct from the scala tympani) o The distance the pressure waves travel decreases as the sound frequency increases o Displacement of the basilar membrane is central to pitch discrimination o Sounds of higher frequency cause maximum vibrations of the basilar membrane closer to the stapes o Greater displacement of the basilar membrane, the greater the amount of neurotransmitter released, leading to greater receptor potential produced in afferent neuron and a louder sound The Spiral Organ (Organ of Corti) Organ for hearing within the cochlea Sensory hair cells located on the basilar membrane project into the endolymph of the cochlear duct o Stereocilia arranged in bundles that increase in size stepwise similar to the vestibular apparatus – different from apparatus because they lack kinocilia Inner hair cells: about 3500 per cochlea o Form one row that extend the length of the basilar membrane o Mechanosensory: transform sound waves into nerve impulses o Stereocilia are interconnected near their tips with filaments that are coupled to mechanotransduction channels in the plasma membrane o Channels open when bundles are bent toward the tallest one allow movement of potassium Since [K+] is so high in the endolymph it has an amazingly high positive potential (+100mV) This plus the negative resting membrane potential of the hair cells produces a steep electrochemical gradient favoring the entry of K+ into the hair cells depolarizes hair cells and stimulates them to release glutamate, which stimulates the associated sensory neuron The K+ can move passively out through channels in the basal surface o Middle of the basilar membrane has the greatest number of synapses and the highest sensitivity to sound Outer hair cells: about 11000 o Arranged in multiple rows 3 rows in the basilar turn 4 rows in the middle turn 5 rows in the apical turn o Innervated primarily by motor neurons originated in the medulla Cause outer hair cells to depolarize or hyperpolarize get shorter when depolarized Aid the function of the inner hair cells Tectorial membrane: overhangs the hair cells in the cochlear duct, embedding the stereocilia Spiral organ composed of tectorial membrane, basilar membrane and inner hair cells with sensory fibers Eyes and Vision: Eyes transduce energy in electromagnetic radiation into nerve impulses Very limited portion of vast spectrum Light passes from a medium of one density to a medium of a different density and is bent, or refracted Light refraction is the mechanism which allows us to focus on an image on retina Accommodation: ability to keep image focused on retina as the distance between eyes and object varies; results from ciliary muscle contraction Cornea curvature is constant but can adjust lens curvature therefore refractive properties of lens can provide fine control for focusing light o Sometimes the lens cannot focus correctly – leads to farsightedness or nearsightedness Farsightedness: hyperopia Focus behind retina Need a convex lens to correct it Nearsightedness: myopia Focus before retina Need a concave lens to correct it Retina: Consists of: o Single layer of pigment epithelium that functions in: Phagocytosis of the shed outer segments of the photoreceptors Absorption of scattered light in the retina by melanin pigment Delivery of nutrients from the blood to the photoreceptors Suppression of an immune attack of the retina retina is immunologically privileged Conversion of visual pigment from the photoreceptors into its active form Stabilization of the ion composition surrounding the photoreceptors – helps them respond appropriately to light o Photoreceptor cells Rods and cones Composed of inner and outer segment Inner segment contains most of the organelles Outer segment contains discs – discs contain photopigment molecules, which respond to light only receptive area o Neural layer Forward extension of the brain Optic nerve can be considered a tract Face outward toward incoming light – so light must pass through several neural layers before striking the photocreptors Neural layer composed of: o Horizontal cells: interneurons that help primarily with cones mostly color vision o Bipolar cells: receive input from photoreceptors and send synaptic input to ganglion cells o Amacrine cells: interneurons that process information from the bipolar cells to the ganglion cells o Ganglion cells: outer layer of neurons that contribute axons to the optic nerve Only cells that will activate action potential Photoreceptor cells and bipolar cells will depolarize or hyperpolarize but not cause an action potential Close functional relationship between pigment epithelium and photoreceptor cells Effect of Light on Rods Photoreceptor cells activated when light produces a chemical change in the disc’s pigment molecules Rhodopsin: biological purple pigment found in the rods of retina o G-protein coupled receptor o Extremely sensitive to light enables vision in low-light conditions When light hits rhodopsin it causes components to dissociate and it becomes active opsin o Bleaching reaction: changes retinal from 11-cis to all-trans conformation – causes the dissociation o Dissociation causes changes in the ionic permeability of the rod plasma membrane and results in production of nerve impulses in the ganglion cells Visual cycle of retinal: interaction between photoreceptor cells and pigment epithelium o All-trans transported to pigment epithelium, which convers it back to 11-cis conformation Effect of light on retinal cells: Dark adaptation: gradual increase in photoreceptor sensitivity o As a light-adapted person enters a dark room they are temporarily “blinded” o Restoration of visual pigment in the rods must occur before they can “see” again Light adaptation: occurs as rhodopsin in rods is bleached by light and cones become prominent operators o As a person steps from a dark place into bright sunlight, the image they see is too bright and of poor contrast Note: The only cells in the retina that produce all-or-none action potentials are ganglion and Amacrine cells o Photoreceptor cells, horizontal cells and bipolar cells can produce graded depolarizations or hyperpolarizations Photoreceptor cells are very unique sensory cells that depolarize at rest o In the dark the photoreceptors release an inhibitory neurotransmitter that hyperpolarizes the bipolar neurons o Light inhibits the photoreceptors from releasing their inhibitory neurotransmitter and this stimulates the bipolar cells Dark current: small flow of Na+ in that occurs in the absence of light stimulation causes photoreceptors to be somewhat depolarized in the dark cGMP is needed to keep the Na+ channels open o Channels will close if cGMP is converted into GMP o Light causes that converstion and thus closes the channels Visual Acuity and Sensitivity: Rods maximize sensitivity to low levels of light at expense of visual acuity – convergence Cones provide high visual acuity but reduced sensitivity to light – no convergence Fovea centralis: area of greatest visual acuity o Contains both rods and cones but is primarily made up of cones Chapter 11: Endocrine Glands – secretion and action of hormones Endocrine glands: ductless glands which secrete hormones (biologically active molecules) into interstitial fluid and travel via blood/lymph to their target cells that contain receptor proteins for a given hormone Major Endocrine Glands: Pineal gland, pituitary gland, thyroid gland, parathyroid gland, thymus gland, adrenal glands, pancreas, ovary/testis Hypothalamus: plays an important role in both nervous and endocrine system neuroendocrine gland Discrete organs o Primary function production/secretion of hormones Do not display the anatomical continuity typical of most other organ systems Widely scattered about the body o Comprised of endocrine cells – glandular (epithelial) secretory cells Are thee the only glands/organs that secrete hormones in the human body? o No, observe nonendocrine organs with endocrine functions Hormones affect the metabolism of their target organs Norepinephrine can be a neurotransmitter but also a hormone secreted from the adrenal gland Chemical Classifications of Hormones: Hormones vary in their chemical structure Grouped into chemical classes DO NOT have to know all of them but have to understand each category Amines: o Derived from amino acids tyrosine and tryptophan o Include hormones secreted by the adrenal medulla, thyroid and pineal glands Polypeptides and Proteins: o Polypeptides are chains of amino acids o Proteins are large polypeptide chains o Ex. Antidiuretic hormone is 9 amino acids long too short to call a protein Vs. growth hormone is 191 amino acids protein Glycoproteins: o Consist of a protein bound to one or more carbohydrate groups o Ex. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) Steroids: o Derived from cholesterol after an enzyme cleaves off the side chain attached to the five carbon D ring o Include: testosterone, estradiol, progesterone and cortisol o Secreted only by adrenal cortex and gonads Corticosteroids in adrenal cortex Sex steroids in the gonads Classification in terms of their actions in a target cell can also be divided into categories of polar vs. nonpolar o Lipophilic hormones: nonpolar and thus soluble in lipids o Allows them to pass through the plasma membrane of the target cell o Include steroid hormones and thyroid hormones Thyroid hormones and steroids are similar in their small, nonpolar structure o Only active when taken orally Polypeptide and glycoprotein hormones cannot be taken orally – they would be digested before entering the blood stream o Why diabetics have to inject themselves with insulin Hormone Synthesis: Amino acid-based hormones often produce an inactive or precursor form Prohormone: polypeptide precursor that may be a longer chain that is cut and spliced together within the gland cell to make the hormone o Ex. Proinsulin produces insulin within the pancreas Prehormone (or preprohormone): prohormone precursor of an even longer chain o Ex. Preproinsulin o Prehormones can also refer to molecules that are secreted by endocrine glands but are inactive until they are converted within their target cells into an active form of hormone Ex. Thyroxine (T4) is inactive until changed into T3 Ex. Testosterone is active in its own right but in Common Aspects of Neural and Endocrine Regulation: Nervous system and endocrine system work together to regulate and maintain body homeostasis o Action is complementary o Similarities between two systems Rely on release of chemicals Share chemical messengers Regulate primarily by negative feedback mechanisms Share common goal – homeostasis By coordinating and regulating activities of cells, tissues, organs and organ systems o Regulatory molecule to function in physiological regulation Target cells contain receptor that combines with regulatory molecule Hormone-receptor causes a cellular effect Mechanism to “turn off” regulator action Changes in membrane potential is not unique to the nervous system o Action potentials involve the movement of ions down their electrochemical gradients – such movements also accompany the actions of some hormones Regulatory molecules discovered in unicellular organisms suggest they appeared early in evolution and incorporated into nervous system and endocrine system Main difference between nervous and endocrine system: o Nervous system corrects quickly and effects last for a short period of time o Endocrine system acts slower but has more long-term effect for overall homeostasis o When there is a sudden change nervous system acts immediately and endocrine system smooth it out Hormone Interactions: Hormone effects can be complex, especially when you have multiple hormones acting on the same target cell o Hormones may antagonize each other or work together to produce effects that are additive or complementary Types of hormone interactions: o Permissive: Situation where one hormone acts to enhance the responsiveness of a target organ to a second hormone or increase the activity of the second hormone Ex. Thyroid Hormone o Synergistic: Situation where two or more hormones work together to produce a particular result Additive or complementary Ex. Glucagon and epinephrine both cause liver to secrete glucose separately but secretion increases 150% when used together o Antagonistic: Situation where one hormone opposes the action of another hormone Ex. Insulin brings down blood glucose levels and glucagon brings it up Effects of hormone concentrations on tissue response Blood hormone concentration reflects rate of secretion by endocrine gland o Hormones do not generally accumulate in blood rapidly removed by target tissue and liver Hormone half-life: time required for the plasma concentration of a given amount of hormone to be reduced to half its reference level o Ranges from minutes to hours for most hormones (except thyroid hormone lasts days) Hormone concentration impacts function o Normal tissue responses are produced only when hormones present within their normal, physiological concentration range Pharmacological levels: abnormally high levels taken as a drug Have widespread and damaging side effects THUS target tissue responsiveness is not only affected by varied numbers of receptors on the target tissue but also by hormone concentration Hormone concentration variation can affect target cell responsiveness o Upregulation Priming effect Prolonged low concentrations of hormone causes an increase in sensitivity Increased numbers of receptor proteins for the hormone being primed are inserted into the plasma membrane causes a greater response o Downregulation: Prolonged exposure to high concentrations of a hormone can desensitize the target cell produces less of a response Decrease in the number of receptor proteins for a polypeptide hormone Pulsatile secretion rate: the secretion of hormones in spurts rather than continuously to prevent desensitization Hormones can up or down regulate their own r
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