BIOL 5600 Week 6 Notes
BIOL 5600 Week 6 Notes BIOL 5600
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This 12 page Class Notes was uploaded by Madissen Patterson on Monday September 26, 2016. The Class Notes belongs to BIOL 5600 at Auburn University taught by Jeffery Goessling in Fall 2016. Since its upload, it has received 2 views. For similar materials see Biomedical Physiology in Biology at Auburn University.
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Date Created: 09/26/16
9/20 Review: Brain: central integrator of CNS Forebrain: anterior most regions; cerebrum, cerebral cortex, thalamus, & hypothalamus Midbrain: basal ganglia (in forebrain in textbook, not perfectly defined), corpora quadrigemina, reticular formation, & cerebral peduncles o Basal ganglia: somatic inhibitory effect: what filters efferent signals; control what signals leave CNS so that skeletal muscle contraction is deliberate and controlled; thalamus is central circuit going to & from cerebrum so basal ganglia has imp afferent & efferent tracts going to thalamus; cerebrum sends afferent signal to basal ganglia, basal ganglia sends efferent signal so contraction can happen o Corpora quadrigemina: 2 sets of ridges/bumps- generally related to somatosensory reflexes (visual or auditory) o Reticular formation: not well defined single structure; network; cluster signals within different components of brain; main role is prodding/arousing cortex; filter for afferent signals that are relevant to wake up cortex; imp in regulation of sleep/wake cycles; aroused cortex increases consciousness & keeps you awake Have diff set of nuclei related to autonomic regulation- stretch reflexes, skeletal muscle tone, coordinates breathing Modulates pain- controls what stimuli reaches brain Pain is response to stimulus; CNS receives signal & processes it as neg stimulus o Cerebral peduncles: large nerve fibers that carry afferent/efferent info between cerebrum & spinal cord New Material Still Brain Most posterior aspect of brain: Hindbrain Cerebellum: largest component o Like smaller version of cerebrum o Integrating CNS organ o Much smaller than cerebrum bc cerebrum is so large; cerebellum has almost equal volume as cerebrum in amphibians, etc., not as evolved species as humans o Relatively complex structure; structures of cerebellum: Vermis: runs longitudinally down center of cerebellum; shaped like worm; how cerebellum maintains contact with the rest of the CNS Nodulus/Flocculus- form Vestibulocerebellum: most inferior aspect of cerebellum Cerebrocerebellum: "wings of cerebellum" Spinocerebellum Arbor vitae ****: provide connections within cerebellum & between cerebellum & other components of CNS o imp regulatory component of CNS o Ultimate goal is to coordinate movements in space & in time; integrator for taking signal & making action happen o Vestibulocerebellum: Responsible for balance Connect nerve fibers to inner ear vestibular system; inner ear has cells that perceive movement & send signal to vestibulocerebellum Don’t need to know other name for it Receives info from visual cortex; if visual cortex is sending afferent signal to vestibulocerebellum that is in conflict with info from vestibular system (inner ear), vestibulocerebellum gets confused- results in symptoms of motion sickness o Spinocerebellum Movement: executes signal into movement Unique bc it can predict where appendages/body will be- described as having feed forward mechanism: receive info as to what next movement will be Receives afferent signals (like vestibulocerebellum); has to know where you are now to predict where you will move; gets signals from visual & auditory complexes Transmits efferent signals through reticular formation o Cerebrocerebellum Planning: not same process as feed forward, instead is direct contact with cerebrum deciding what to do; have to decide with this first before spinocerebellum can make movement happen Purely cognitive (other 2 aren't): main function is contacting cerebellum directly to make decision about process/movement that will occur Pons o "bridge"; physical bridge that connects spinal cord or other distal or inferior components of CNS to central part of CNS (fore- and midbrain) o Relatively small but extremely imp for autonomic regulation o Receives afferent input related to somatosensory effects (hearing, equilibrium- vestibular system, taste, touch, & pain) o Associated with reticular formation o Tegmentum: within pons Center of centers; center= nucleus, clustering of cell bodies Contains centers for several cranial nerves, for other nerves/components related to regulation of ventilation Pneumotaxic Apneustic Both located within tegmentum; directly regulation/modulate ventilation- how long you inhale, how deep your breath is, how frequently you breathe If we removed or damaged cell bodies for these centers, negative feedback loop that maintains ventilation would become inhibited Medulla Oblongata o Posterior/inferior most component of CNS o Medulla: center/core o Oblongata: stretched/oblong o Name= core/center regulatory process for autonomic NS o Where CNS transitions from brain to spinal cord SC o Imp clusters of cell bodies (centers) for other cranial nerves Cranial nerve X (10): vagus cell bodies for this nerve are in medulla oblongata Vagus: center for BP regulation, some regulation for ventilation; source for regulating heart beat independently of whatever other functions are happening, vagus being centered here is reason for it being so important for life Pyramids/Medullary pyramids o At end of medulla; inferior most portion of medulla o Where myelinated axons leave medulla & enter SC- this is where brain ends & SC begins o Imp bc it's where many neurons cross in space; contralateral- sensing info from left side of body on right side of brain or vice versa, pyramids are where crossing occurs o Decussation: process of axons crossing from one side of brain to other side; not every neuron decussates (cross) at pyramids If neuron does cross it is decussate Other important nuclei located within medulla oblongata; relatively near pyramids: generally receive info about proprioception or fine touch. (still hindbrain) o Nucleus gracilis; cell body for afferent signal Located dorso lateral relative to cuneatus- not that imp Receives info generally from lower body Afferent signals of fine touch coming in from lower body o Nucleus cuneatus; cell body for afferent signal Related to proprioception or fine touch from upper body/face/upper extremities Located ventro medial to gracilis- not that imp, function more imp Regional Distinction of brain comes from embryological development Terminology dividing regions Forebrain Telencephalon= cerebral cortex o Tele: most distal/removed o Most distal component of brain- cerebral cortex- conscious though, higher processing o Component of forebrain Diencephalon= thalamus & hypothalamus o Forebrain o Furthest component of brain within head o Much more subconscious regulation o Other components related to thalamus are also diencephalon- thalamus derivatives Mesencephalon= midbrain- already described o Mes-: middle Hindbrain Metencephalon= Pons & Cerebellum o Meta: after o Posterior to middle/mesencephalon o Somewhat connected/related functions with autonomic regulation, balance, & movement Myelencephalon= Medulla Oblongata- already described End of Brain, Start of Spinal Cord Spinal Cord Closely related functions to brain: send afferent/efferent signals, integrator, in direct circulation with brain Bathed in cerebrospinal fluid (CSF)- keep pathogens from getting to brain Spinal nerves: divided regionally by vertebra that they enter or exit spine o Total of 31 afferent/efferent- 1 branches out to left & 1 to right: why they are pairs o 8 cervical o 12 thoracic- rib cage, encloses lungs o 5 lumbar- lower back o 1 coccygeal: tailbone Tip of spinal cord- conus medullaris o Posterior most aspect of spinal cord o Floating between vertebrae, has to be anchored down so long filament anchors conus medullaris- provides rigidity so tip isn't moving around- filum terminale Derived from tissue called pia mater- surrounds & nourishes spinal cord & brain o Components of spinal cord extend further than length of spinal cord; terminal nerves are bunched together; where nerves are bundled together is cauda equina Posterior to spinal cord Begins at conus medullaris First spinal nerve included is L2; includes L2-coccygeal nerve 9/21 Spinal Cord Interneuron: neurons that are in-between other neurons; complete circuitry between other neurons; only found in CNS Receive info from presyn & dumps response on it's own postsyn; strictly neuro-neuronal synapses Most abundant neuron type within CNS Cross Section of Spinal Cord Figure Butterfly shape 2 diff structures going into spinal cord o Dorsal structure (on back) o Ventral structure (facing toward abdomen) Within cross section of spinal cord itself is grey matter o Clustering of nerve/neuron cell bodies Lateral to grey matter is white matter o Myelinated axons o If those myelinated axons are within CNS & are carrying afferent info, we have a different term- ascending signal o If it is motor (efferent signal) coming out of CNS traveling down SC, it's a descending signal Interneuron connects dorsal horn to ventral horn; completes reflex arc Neurons are commonly divergent Dorsal horn: receives afferent signal; creates ascending signal **don’t have to know as much detail as book has here** Dermatome: total region/area of skin innervated by a signal spinal afferent nerve o 31 total pairs of spinal nerves o 29 total dermatomes o Means of breaking down body/skin to specific region, specific nerve o C1 and coccygeal don’t have dermatomes o If there is specific region of skin not receiving afferent signal, can look at map of dermatomes to see where that disease is located o Infection by herpes zoster (virus that causes shingles) can be localized to dermatomes Virus can lie dormant in cell bodies innervating single dermatome; no symptoms during dormancy Virus can travel through afferent axons to cause symptoms we're used to Dorsal horn made of psuedounipolar cell body o Clustering of cell bodies (ganglion) is dorsal group ganglion- corresponds directly to a spinal nerve that is regionally relevant Ventral horn o Sends out efferent signal to effector tissue (muscular or glandular) o 1 multipolar cell body; located within grey matter o As axons are leaving spinal cord, don’t have root ganglion like dorsal root has; described just as ventral root Spinal nerve formed from ventral axons & dorsal root ??* Ascending Nerve Pathways (afferent=ascending) More complex Depending on specifics, there are a range of diff ascending & descending pathways Dorsal column series (dorsal column medial lemniscus, DCML series) o Ascending pathway has series of neurons directly contacting each other so there is series of interneurons o 1st order: 1st neuron in chain o 2nd order o 3rd order: if there is a 3rd order, there are 3 ganglia, 3 ascending neurons o Cerebrum: what is doing integrating in this series o Gracilis or cuneatus: serve as ascending fibers- lower body is gracilis, upper body is cuneatus o Series is contralateral o Transmits fine touch & proprioception; sensitive throughout body o Ganglion in medulla where decussation occurs, in medullary pyramids; left side of body to right side of CNS o Pass through pons & cerebral peduncles, makes its way to thalamus- gatekeeper bc it passes through before it goes to cerebrum (3rd order) Back to cross section of spinal cord: o Blue: sensory/ascending pathways- located dorsally within vertebral column Spinothalamic system/anterolateral system o transmits info about pain, itch, tickle, & thermal sense- not fine touch but still coming from periphery/skin o Utilizes 3 neurons- up to 3rd order o Decussation doesn’t happen at medulla or pyramids like most decussations happen o Cell body located in thalamus; 2nd order neuron receives info in spinal cord & has long axon that goes to thalamus, goes through medulla, pons, & cerebral peduncles o Difference between the orders & where decussation is occurring that distinguishes this one & DCML o More lateral & more inferior o Goes ultimately to cerebrum, passes through thalamus o Difference is that 1st order neuron is much shorter than 1st order in dorsal column o Transition from 1st to 2nd order happens almost immediately at spinal cord, in grey matter in the dorsal horn o 2nd order has cell body located in spinal cord close to 1st order where 1st order enters spinal cord o Decussation happens in spinal cord, long ascending axon that travels all the way through the spinal cord, passes through midbrain & medulla- not decussation in medulla bc it's already done it, innervate 3rd order neuron located in thalamus (this last step is same here & in dorsal column); thalamus sends it to cerebral cortex to be processed o Similar to dorsal column: capability for very fine touch; pain & temp- main afferent signals; pain sensed by same receptors that itch or tickle is Spinocerebellar tract o More simple than either of the other 2 o Only uses up to 2nd order neurons o Not cerebrum that is integrating but is cerebellum itself o Shorter tract- why it's only 2nd order o 2 ganglia located within chain o Ipsilateral instead of contralateral, no decussation o Sends info about muscle position- where in space muscles are & how stretched they are o Signal doesn’t go through thalamus, reaches cerebellum without going through it, cerebellum processes info o Crosses through medulla, but doesn’t decussate there; doesn’t decussate at all o Sends ascending signal that is ipsilateral to cerebellum o Utilizes 2 neurons: sensory (primary)- psuedounipolar just like almost all neurons coming into spinal cord; 2nd neuron sends signal through myelinated axons along same side of body; bypasses pons & goes directly to cerebellum for integration o Largely related to subconscious muscle function; cerebellum regulates muscle tone- keeps you from risking muscle injury; largely related to stretch- cerebellum has info about it's level of output; also proprioception: where in space is muscle that is trying to contract Descending Tracts: can decussate or not- contralateral or ipsilateral; if they decussate in pyramids, are known as pyramidal tracts; if they don’t decussate in pyramids they're extrapyramidal tracts o Pyramidal are more related to somatic skeletal muscle contraction o Extrapyramidal are related to autonomic regulation Pyramidal tracts- decussate in medullary pyramids Corticospinal tract- lateral o Pyramidal o Decussation happens in pyramids o 2 neurons involved- more simple pathway o Begins in brain & target is something in periphery o Nuclei are in cerebrum/cortex o Grey matter: when synapses happen in spinal cord, it happens in grey matter of SC o Largely responsible for skeletal muscle contractions o 90% of neurons decussate like diagram we've drawn - part of the lateral corticospinal path o 10% of neurons are medial corticospinal neurons; form medial corticospinal pathway; are ipsilateral o Signal initiated in cerebrum o Travels on long myelinated axon to medullary pyramids- contralateral signal so decussation occurs at pyramids o After decussation, signal travels through white matter of spinal cord where it interacts directly with motor neuron, motor neuron is 2nd order- directly innervates somatic tissue to enable contraction to occur Extrapyramidal Pathway- either don’t decussate or don’t decussate in pyramids o Rubrospinal is one ex- more imp extrapyramidal pathway Rubro: red Initiated in red nucleus within midbrain o Originates in red nucleus: located in midbrain- more diffuse & function isn't as cut & dry o Descending signal immediately decussates; doesn’t happen in medullary pyramids o Transmits some contralateral signal o Overall function is to help regulate other descending signals, receives info from corticospinal pathway Bc it receives info in parallel, it receives info about what is desired & about what is happening Modulates the function- fine tunes or adjusts contractions that are happening o Close contact with cerebellum o Important source of memory related to skeletal muscle contractions; muscle memory; whatever brain has picked up as most efficient means of contraction o Contralateral o Immediately decussates as signal leaves red nucleus o Simple tract- don’t have to be able to diagram o In humans, function is unknown; know it's related to optimizing/learning best way of contracting skeletal muscles; directly receives info from cerebellum; as cerebellum gets ascending info about contraction, where muscles are in space, tension, etc., rubrospinal tract modifies output signal- can still directly affect skeletal muscle but isn't primary effector Thought to be failsafe or backup for other tracts in case injury occurs to those tracts; can increase it's ability to compensate for damage/loss More important in other mammals 9/22 Different Spinal & Cranial Nerve Types General Somatic Afferent Nerves (GSA) Not consciously firing, but info is coming in via a somatic tract Ex: burning sensation o Extreme physical damage to soma/tissues are sent to CNS via GSA nerves Included in cranial & spinal nerves General Somatic Efferent (GSE) nerves Send signals out to skeletal muscle tissue that generate somatic motor contractions Nerve: bundle of axons/many neurons; nerve can serve both GSA & GSE function; function can be both afferent or efferent along single nerve type bc there are diff neurons within that axon General Visceral Afferent (GVA) Nerves/Neuron Sense autonomic conditions within body Afferent signal coming from viscera Things related to digestive state or other regulatory states- BP, ventilation, osmotic balance General Visceral Efferent (GVE) Nerves Visceral effectors; effect output via GVE nerve Both cranial & spinal nerves can be broken down by all 4 of these ^ Cranial Specializations More channelized, related to special senses or very specific task Special Somatic Afferent Special Somatic Efferent Both related to nerves about hearing & sound; special senses within head; not spinal nerve Special Visceral Efferent Efferent- cause some contractile type response Control chewing; subconscious for the most part Receptor Physiology Diversity of receptor types, functions All receptors: receptor receives info about extracellular environment; special senses-external environment; get light or temp or sound info; not action potential; not ionotropic signal; receives info of any type of information, has to physically transduce signal into ionotropic signal, ultimately into action potential; diversity of receptors matches diversity of signal types Mechanoreceptors Sense shape change from outside of the cell, respond to some mechanical/physical disturbance to their cell membrane/integrity Physical pressure changes Na permeability, stimulus must be intense enough to get cell above threshold so in response AP can fire from receptor cell Ex: Organ of Corti: cell type located within ears; as sound waves enter ears, cause physical vibration that is amplified through ear, effects Na permeability in cells, causes AP that make their way to brain Receptors typically receives signal similar to graded pot; response typically proportional to strength of stimulus it's receiving o Receptors alter force of signal or respond proportionately is by increasing frequency by which they fire o Potential generated by receptor cells; as graded pot propagates it's either supra or subthreshold & causes AP- all or none; can't increase intensity of AP; receptors have control of afferent signal bc it graded pot reaches suprathreshold quickly enough, it reaches AP more quickly; if stimulus remains, continuously fires high intensity AP, increase frequency by which some neuron/cell in brain receives signal Thermoreceptors Sensitive to changes in temperature Relatively diverse Can either be central or peripheral o Central located deep within CNS; respond/send afferent signals about core body temp; hypothalamus is an imp regulator of core body temp (if we have fever it's bc hypothalamus wants us to have one); hypothalamus in contact with these receptors o Periphery: receptors scattered about our periphery; send afferent/ascending signals that go to hypothalamus o Similar in function, differ in neuron network by which they make signals known to hypothalamus Can be polymodal: responding to more than one sensory modality o Modality: mechanism by which you measure something about environment o Can respond to change in temp & other chemical changes as well o Send AP completely independent of temp Can send signals that seem like pain stimulus Vanilloid receptor o Within thermoreceptor group of proteins o Send afferent signal o Responds to increase in temp or binding of ligand o Ligand can be capsaicin: what makes spicy things spicy; capsaicin binds to vanilloid receptors & tricks body into thinking surface is hot; polymodal- transmits pain signal too- not only hot but painfully hot o Menthol Responds to menthol Menthol targets similar vanilloid receptor that sends signal of being cold; opposite of capsaicin Nociceptors Pain- not stimulus but is response to some stimulus Subtypes that respond to extreme temp, pressure (severe mechanical disturbance), & certain chemicals Receptor types not mutually exclusive of each other; thermoreceptors can have nociceptor properties "Sleeping" receptors: not sending signal under normal context but if you injure yourself (break leg), receptors will awaken & signal that pain; heighten pain sensation in that area; as pain progresses, this receptor type is increases level to which they are excitable; after they're fired, certain hormones & neurotrans make them more sensitive Electromagnetic Receptors Respond to change in Earth's electromagnetic field Generally located in eyes of vertebrates; capable of seeing electromag. radiation similar to light One in humans but is essentially dysfunctional Other vertebrate animals have sensitive electromag receptors- how birds can migrate, turtles do too, many reptiles Chemoreceptors Not mutually exclusive Respond to change in chemical Not necessarily on skin, may be in mucosal surfaces: taste is some chemoreception Are central: either in CNS or close to heart o Way we centrally are able to regulate homeostatic conditions of our body o Sense CO2- single most imp thing our body measures Related to BP- measure Na concentration in plasma Measure external body stimuli too but central body stimuli more imp Photoreceptors Only in retina on posterior margin of eye in humans Respond to change in photons- unit of light Give us sight Opsin, retinal- proteins that make up backbone of photoreception o Photon of appropriate wavelength targets these proteins, hits cell, causes cell to change membrane polarity, sends afferent signal into brain o Fusion of these are rhodopsin- different ones respond to diff wavelengths- how we see diff colors o Right combination of sensory proteins responding to right wavelength are how some animals see UV radiation Osmoreceptor Specific type of chemoreceptor Senses plasma osmolarity Imp for BP regulation Imp clustering of these within kidney- can sense & respond to stimulus Olfactory Type of chemoreceptor Sense smell/olfaction Relatively generic- utilize G protein system o Not direct chemically gated Na channel that cause AP o G protein coupled receptor is generic; if any one of broad class of chemicals binds, signal transduction cascade that alters neuron Any given chemical may stimulate range of receptors Unifying concepts in receptor physiology Operate by Weber-Fechner Principle/Law: reason we can perceive sensory info in graded manner; AP all or none but can perceive stimulus as altering in intensity o Not perfectly linear; log base relationship between stimulus intensity & perceived response/reception of stimulus; any change in stimulus intensity to be detected has to be increased by relatively large proportional magnitude Receptors can adapt to stimulus Adaptations o Phasic: enable you to ignore stimulus after certain amount of time; get used to presence of stimulus; afferent signal to CNS gets shut down so you aren't constantly processing stimulus; Ex: putting on clothes; not thinking about feeling of clothes on skin even though it is o Tonic: stimulus is constantly being perceived, not shutting down signal going to CNS; don’t get used to, not adapting, still some CNS processing as long as stimulus is present; degree of integration can decrease but still aware of it Ex: walking down steps; need to know where each step is; need to perceive steps & distance to not fall down steps; awareness may decrease slightly but still receiving signal from CNS Anatomy of CNS CNS is discrete unit of neurons acting together Barrier that separates CNS from rest of periphery, keeps pathogens & such out of CNS Extremely energetically demanding (brain) Needs to be in isolation but also needs to be well nourished Brain covered in series of membranes that nourish & protect; membranes known as meninges Cross section of brain o Skin, bone o 2 layered meninge: most external meninge: Dura mater- tough/fibrous mater Mater: protecting, defending CNS Dura: tough, thick, heavy Embedded within dura mater are large pocketings of blood called sinuses- collectively sinuses are known as dural sinuses Sinus: collective term for low pressure collection of blood o Arachnoid mater: below dura mater Arachnoid: either looks like spider web or looks like spider legs Web like membrane located just below dura mater Enables cerebrospinal fluid in direct contact with CNS to exit CNS & make way into dural sinuses Has outpocketings that project through dural mater into dural sinuses; called arachnoid villi- 1 way valve that CSF drains into venous circulatory system
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