Hirsch study guide 19 PDF

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Exam questions are: 1) Fill in the blank 2) Multiple choice (sometimes you will need to circle several options for full credit and –and just so you don’t circle everything – deductions for wrong answers). The lowest number of points you can get on a single question is 0, not a negative number. 3) True False Questions will range from 2-4 points each. I will give you one 4pt wildcard question. You choose one 4pt question to cross out Some parts of the guide are redundant, but all will help you prepare for the exam. Questions on the exam will derive from the material here, though the format of the questions will likely differ from the format here. Questions sometimes span more than one lecture. I have also posted an old exam on blackboard. https://www.fictionpress.com/s/3215838/3/Neurobiology https://nba.uth.tmc.edu/neuroscience/m/s3/chapter01.html

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BRAIN STRUCTURE Know the three main divisions of the brain and be able to associate large structures with each 1. Forebrain: cerebral cortex, basal ganglia, thalamus, hypothalamus 2. Midbrain: tectum 3. Hindbrain: cerebellum, pons, medulla oblongata Know the names of the four lobes of the cerebral cortex and where they are in relation to one another. 1. Frontal 2. Temporal 3. Parietal 4. Occipital Know the three planes of section: Coronal, Sagittal and Horizontal. - Coronal: “frontal” - Sagittal: left/right - Horizontal: ‘transverse” If I slice your brain so that I cut through your frontal and occipital lobe – have I cut? a) A coronal section b) A horizontal section c) A sagittal section d) A coronal or horizontal section e) A coronal or sagittal section f) A sagittal or horizontal section Divisons of CNS and PNS CNS: brainstem, spinal cord, cerebrum, cerebellum PNS: somatic (voluntary) and visceral (autonomic) Know which parts of the brain developed from which embryonic divisions.

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SPINAL CORD AND MOTOR SYSTEM

What is the difference between an upper and lower motor neuron (think about which type synapses with muscle)? - Upper: in brain stem and cortex. Descending system - Lower: in spinal cord or brainstem. Synapses with skeletal muslces What is the difference between a motor pool and motor unit? - motor pool: group of motor neurons that innervate a single muscle. o The motor pool can comprise more than one type of motor unit. - motor unit: The group of muscle fibers that receive input from a single motor neuron. Are larger or smaller motor units associated with muscles that generate fine movements (eyes, lips and fingers) - fine movements involve small motor units and coarse forceful movements involve large motor units. Spinal Cord Arrangement Dorsal Horn: inputs from sensory cells, contains somas of local circuit neurons, but doesn’t have LMN. Sends signals out Dorsal roots ganglia: contain somas of sensory neurons whose axons travel out to peripheral sensory receptors and into the cord via roots. The axons travelling in are afferents Lateral white matter: carries fibers (axons) from motor cortex Ventral Horn: somas of lower motor neurons .synapse with skeletal muscle Ventral Roots: contain axons of lower motor neurons that travel out (efferent) towards muscles Medial White Matter: carries axons from brainstem. More for posture. Which region of the spinal cord houses motor neurons? - Ventral Horn has somas and ventral roots have their axons Types of Motor Neurons innervate Different fiber types 1. Small (slow): alpha motor neurons conduct slowly and innervate fibers for posture/lasting contractions. Usually small motor unit

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2. Large (FF: Fast Fatigue): ): alpha motor neurons innervate large groups of muscles that make large forces. conduct quickly and fatigue fast. Larger motor units to turn on many muscle fibers at once. 3. Intermediate (FR: fatigue resistant): ~intermediate~ Which type of muscle do you think would be more resistant to fatigue? A muscle involved in maintaining posture or one involved in movements associated with attack or escape? Think about the different types of muscle fibers. - Posture muscles fatigue less bc they are innervated by small alpha motor neurons. (soleus) - In leg majority of motor pool is fast fatigable. Two types of muscle fibers in spindles: intrafusal and extrasfusal. Arranged in parallel Alpha motor neurons innervate: extrafusal muscle fibers. (outside spindle) Gamma motor neurons innervate: intrafusal muscle fibers (inside spindle) - They regulate sensitivity of muscle spindle and stretching ends of bag and chain fibers When are gamma motor neurons likely to fire? See the animation for help answering this. - When a muscle is contracted and it need to be pulled out muscle spindles to get back in sensitive range o Contracts at the ends and stretches the region where afferents are located Which might trigger the reflex that involves muscle spindles? - Agonist muscle is stretched  1a fires.  length needs to be restored via alpha MN  contraction  inhib interneuron to relax alpha MN that innervates the antagonist - Tension/force  Ib fires and inhibits alpha motorneurons  decreased muscle contraction and tension Group 1a and group II fibers carry information from which types of intrafusal muscle fibers? - Group Ia sensory afferents: wrap around the bag and chain intrafusal fibers. (Most active when muscle length changes, i.e. when the muscle is stretching.) Group II sensory afferents: wrap around the chain intrafusal fibers only. (Most active when muscle is stretched.) What kind of information does each provide (e.g. length and/or velocity)? - Nuclear bag fibers: sensitive to rate of change in muscle length (velocity). - Nuclear chain fibers: sensitive to muscle length. What sort of information does the Golgi tendon organ convey, via which type of afferent? - Sends info about force and the state of muscles. Afferent activity is high when muscle contracts - Incase Group 1B afferents that wrap around collagen fibrils. - Location of golgi tendon organs: embedded in tendons (muscle to bone) Be able to draw the spinal reflex arc-from input from the muscle spindles to the cord to actions on lower motor neurons (the simple version illustrated in the slide and animation – not as illustrated in the book).

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What cortical regions supply the fibers that descend trough the corticospinal and corticobulbar tracts? - Both from premotor cortex - corticobulbar tract is uncrossed. Ends in brainstem What is the main functional difference between the anterior and lateral corticospinal tracts? Is there a difference in where they cross, as per the lecture? -

Lateral corticospinal tract crosses at the midline (pyramidal decussation at medulla and terminate on lateral motor neurons for fine movements (toes, fingers)) . Ends in spinal cord Anterior corticospinal tract: crosses at the spinal cord and makes bilateral/polysynaptic connections with medial Motor neurons  maintains posture.

What is a main difference between motor and premotor cortex? - Pre-Motor: movement planning - Motor: movement execution BASAL GANGLIA - Includes Caudate, Putamen, and Globus Pallidus Know the direct and indirect pathways in the basal ganglia! Memorize the block diagrams, remember which regions send excitatory projections to their targets and which send inhibitory projections

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- excitatory regions (glutamate): cortex, subthalamic nucleus, VA/VL thalamus - inhibitory regions (gaba): striatum (putamen and caudate), glob pal ext, glob pal int Connections regarding Basal Ganglia: - Spiny Motor neurons: Silent unless excited o they are Gabergic o Get input from cortex. Dopaminergic neurons can excite or inhibit them o Located in caudate and putamen. o Its axons wrap around Globus Pallidus or substantia nigra neurons - Globus Pallidus or substantia nigra pars reticulata neurons: Cells fire unless inhibited o Also gabergic o The output of basal ganglia How does each pathway accelerate or brake movements? These are motor loops that regulate upper motor neurons to help coordinate voluntary movements - Indirect pathway: brake  Parkingsons - Direct pathway: accelerator  Huntingtons -indicate which structures are inhibitory and which are excitatory, pick out a mistake, predict what symptoms a patient might have (e.g. inability to initiate movement vs. inability to control or restrain movement) if a particular region were damaged. How can structures become more active? - directly, by the actions of an excitatory transmitter - indirectly-- by means of disinhibition. Loss of dopamine correlates with which disease, Huntington’s or Parkinson’s? - Parkinson’s Loss of striatal neurons results in which disease, Huntington’s or Parkinson’s? - Huntingtons o Loss of putamen in indirect pathway cause reduced inhibition of glob pal ext. o Glob pal ext is sends more inhibitory signal  more inhibited sub thal nuc  less excited glob pal int  less inhibited thalamus / heightened cortical activity

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What are the actions of D1 and D2 receptors on different populations of striatal neurons? Which receptor is associated with which pathway? - D1: direct, excitatory input to the D1 receptors in the putamen, where spiny neurons are that project to Glob Pal INT - D2: indirect, dopamine inhibits the D2 receptors in the putamen, where spiny neurons are that project to Glob Pal EXT What is the movement deficit associated with loss of dopamine - Can’t perform smooth movements. Very jerky - From loss of the substantia nigra pars compacta which makes dopamine Does the loss of dopamine affect only one pathway or both? - Both. D1/D2 affected Why do you think that hemiballismus affects only one side of the body? - Hemiballismus: lesion in the indirect pathway. Usually of sub thal nuc. Would lead to excitation in motor thalamus bc glob pal ext slightly inhibits glo pal int. which sends too little inhibition to Thalamus. - Affects one side of the body bc the lesion is usually on one side. Very excited cortex.

CEREBELLUM - compares motor plans with physical execution - makes adjustments to keep movements, coordinated, fluid and on target. - involved in motor learning Gross anatomy of the cerebellum

What are the functional differences of the 3 divisions of the cerebellum and their inputs/outputs 1. Cerebrocerebellum (neocerebellum): regulates complex movements and speech a. INPUT: from contralateral cerebral cortex b. OUTPUT: Sends output to Dentate i. Dentate projects to the contralateral premotor cortex and association cortices of the frontal lobe involved in planning movement 2. Spinocerebellum: median regulates proximal muscles, paramedian regulates distal muscles a. INPUT: from spinal cord b. OUTPUT: i. sends output to interposed deep cerebellar nuclei. Which Projects to the contralateral motor cortex to aid in executing movement. ii. sends output to Fastigial deep cerebellar nuclei. Which projects to upper motor neurons in the ipsilateral brainstem to aid in executing movement 3. Vestibulocerebellum: ‘ancient’ regulates posture and balance, some eye movements a. INPUT: vestibular nuclei b. OUTPUT: vestibular nuclei. No deep cerebellar nuclei Know the peduncles through which inputs and outputs travel. (efferent exits peduncle, afferent arrives) - Superior peduncles o Efferent pathway (mainly) o made of fibers exiting from the deep cerebellar nuclei. - Middle peduncles (really big) o Afferent pathway o made of fibers carrying information from the cortex (via the pons)

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Inferior peduncles: mixed o Afferent fibers from brainstem and spinal cord o Efferent fibers from the vestibulocerebellum

Do all the deep nuclei project out of the cerebellum through a peduncle? - Yes Do all regions of the cerebellar cortex project to a deep nucleus? - No, not the Vestibulocerebellum Do all peduncles carry afferent or efferent information or is one or more “mixed”? - One is mixed (inferior peduncle) What if I have damage to the left cerebellum but not the right? Which side of the body is most gravely affected? - Opposite side (right) is more affected. (cerebellar cortex  deep cerebellar nuclei  CROSS MIDLINE  thalamus  primary/pre motor cortex Which side of the body would a deficit in the left motor cortex affect most severely? - Same side (left) is more affected because Fastigial projects to upper motor neurons in the ipsilateral brainstem What is special about climbing fibers? What form of plasticity do they mediate (e.g. calibrating movement – with the VOR as an example)? - Climbing fibers: convey input from inferior olive (which receives input from the cerebral cortex, spinal cord and red nucleus), Each Purkinje cell receives input from a single climbing fiber. Purkinje cell fires a complex spike in response to input from a climbing fiber. - Climbing fiber loop: to detect errors and correct them over the longer term --this is the "learning" loop. What are symptoms that would indicate loss of the cerebellum? - Difficulty walking, taking, moving eyes Cortical pathway (from the perspective of the left neocortex)    

Left premotor and motor neocortex  left pontine nuclei.  right cerebrocerebellum  right dentate nucleusleft motor thalamus left cortex. Remember that this pathway is mainly involved with planning and coordination The spinocerebellum (output is via interposed + fastigial nuclei) also participates in the neocortical pathway; its contributions involve motor execution Crosses midline at pons?

Brainstem (including vestibular) pathways    

Inferior olive, spinal cord, vestibular nuclei  spinocerebellum  interposed + fastigial nuclei  brainstem including vestibular nuclei and spinal cord. this pathway is involved in motor execution Vestibular nuclei  vestibulocerebellum  vestibular nuclei. this evolutionarily ancient pathway is largely involved with motor adjustment and balance.

EYE MOVEMENTS What are 6 muscles that move the eye?

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Lateral Rectus: abduction away from the nose Medial Rectus: adduction towards the nose Superior Rectus: elevation Inferior Rectus: depression Superior Oblique: intorsion (top of the eye towards the nose) Inferior Oblique: extorsion (top of the eye away from the nose Which brainstem nuclei innervate the muscles? Medial Rectus: cranial nerve III via oculomotor nucleus Superior Rectus: cranial nerve III Inferior Rectus: cranial nerve III Inferior Oblique: cranial nerve III Superior Oblique: cranial nerve IV via trochlea nucleus Lateral Rectus: cranial nerve VI via abducens nucleus What is the circuit used to drive eyes to the right or the left? Be able to apply principles to hypothetical circuits - abducens nucleus innervates the lateral rectus muscle on the ipsilateral side via cranial nerve 6 - trochlear nucleus innervates superior oblique contralaterally via cranial nerve 4 - Oculomotor nucleus innervates the other 4 muscles ipsilaterally via cranial nerve 3 What is the difference between saccades and smooth pursuit? - Both move eyes to direct gaze to targets of interest or track those targets as they move. - Called conjugate movement: eyes move in the same direction - Saccades: ballistic movement, once you start you can’t stop. Ex looking at the bird - Smooth pursuit: slower. Ex. following pointer or bird flying Do vergence movements involve conjugate or disconjugate eye movements? - Vergence movement is a type of disconjugate movements. o When something between your eyes move closer/further - They help move to help align the fovea of each eye on the target of interest when the distances between each eye and the target are different. - Disconjugate: eyes move in different directions. What happens to eye movements when the superior colliculus is damaged? - impedes the ability to make very rapid saccades. - Superior colliculus: gets info from eye, ear, and skin. Has a map of space, audition, and vision. Uses all to guide the eyes What happens when the frontal cortex (frontal eye fields) is damaged? - impairs the ability to make voluntary movements away from a salient stimulus in the visual field or movements towards “remembered” positions. Need neocortex for this. - Frontal eye field indirectly (via superior colic) or directly communicates with PPRF for redundancy What happens if both structures are damaged? - lesions to both lead to a permanent loss of the ability to make saccades. - If only one has lesion, there is short-term but not long-term loss in the ability to make saccades. What, in a nutshell, does the horizontal gaze center do? (PPRF) - Sends commands to 2 cells o To alpha motor neuron to right abducen nucleus that innervates right lateral rectus muscle and leads to its contraction

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At same time, Medial longitudinal fasciculus helps send signal to contralateral side of brain (bundle of axons of internuclear neurons) Excitation to alpha MN of right abducen nucleus and excitatory neuron that travels to contralateral side of brain to innervate left occulomotor nucleus. Alpha MN here innervate left medial rectus muscles and are turned on Both eyes make conjugate movement to right Also, inhibition of neurons on opposite side of body to relax muscles

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PPRF gets projections from superior colliculus, frontal eye fields (thinking heavy eye field), and the motor cortex

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Do we need to know map of superior colliculus?

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VISCERAL NERVOUS SYSTEM - Visceral is the autonomic nervous system. Its motor (effector) neurons are in the PNS and these effector neurons have diffuse connections (systemic) o Divided into  Sympathetic nervous system: fight or flight  Parasympathetic: rest and digest.  Enteric motor system Preganglionic cells of Sympathetic: - In the CNS, output to ganglia, have mylenated axons and are tonically active and fast - Reach sympathetic chain ganglia via white communicating rami - Location In sympathetic: lateral horn of thoracic and lumbar spinal cord - Axons exit through ventral root (also where alpha MN exit) and enter sympathetic chain through white communicating rami - Some axon collaterals travel outside to link to neighboring ganglia and others exit through the spinal nerves to reach the prevertebral ganglia. - 1 preganglionic sympathetic axon will synapse onto many postganganglionic sympathetic neurons. Preganglionic cells of Paraysmpathetic: - In the CNS, output to ganglia, - Location in parasympathetic: brainstem, sacral spinal cord - In the brainstem, they project out along the cranial nerves - In the cord, they project from lateral horn via the ventral root and splanchnic nerve to the postganglionic cells o One preganglionic parasympathetic axons will synapse onto few postganglionic neurons o Sacral cord controls: bladder, gun, genitals Postganglionic cells of Sympathetic: sympathetic ganglia: have unmylenated axons o most in the paravetebral (aka sympathetic chain/trunk)  send axons via gray communicating rami to effectors o remaining are in prevertebral ganglia tucked between the cord and effector organs Postganglionic cells of Paraysmpathetic: in various parasymathetic ganglia (plexes, etc.) that are near or even within the effector sites (organs), unlike the sympathetic division. What happens to heart rate when baroreceptors send signals that blood pressure is too high? Where do the sensory afferents project? What signals are sent to the para- vs. sympathetic nervous system? What happens to heart rate as a consequence of this reflex? - Baroreceptors: live in the aortic arch signal pressure. Tell that pressure is too high/low

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o Pressure receptors in heart, bladder, gut etc. Chemoreceptors in the carotid bodies signal blood gas levels (e.g. hypoxia, pH). Tell to beat slower/faster When pressure is high: baroreceptors afferents in aortic arch send impulses to the brainstem which excites the parasympathetic. preganglionic cells (nucleus ambiguous) that project via the vagus to the cardiac plexus—> squirts ACh through nicotinic receptors on heart to slow heart down. (directly)

Same baroreceptors afferents initiate an inhibitory signal to the preganglionic symp...