neuroanatomy exam 2

Neuroectoderm derivatives including associated ventricular system structures

• telencephalon

  • cerebral hemispheres + olf. bulb + olf. cortex

  • lateral ventricles

• diencephalon

  • thalamus + hypothalamus + epithalamus

  • 3rd ventricle

• mesencephalon

  • midbrain

  • cerebral aqueduct

• metencephalon

  • pons + cerebellum

  • 4th ventricle

• myelencephalon

  • medulla oblongata

  • 4th ventricle + central canal

• neural tube

  • spinal cord

  • central canal

Which ventricular system structures are associated w/ which adult structures?

• lateral ventricle → cerebral hemisphere

• 3rd ventricle → thalamus + hypothalamus

• cerebral aqueduct → midbrain

• 4th ventricle → pons + medulla

• central canal → spinal cord

Where is the location of the choroid plexus?

lateral, 3rd, 4th ventricles

Explain the circulation of CSF from production to drainage

• CSF prod. by choroid plexus in lateral, 3rd, 4th ventricles

  • CSF prod. in lat. ventricles must drain into 3rd ventricles via interventricular foramina → then into 4th ventricles via cerebral aqueduct

• drainage:

  • 4th ventricle → lateral apertures → subarachnoid space → arachnoid villi → dorsal sagittal sinus → cerebral veins

  • 4th ventricle → central canal in spinal cord

What are the fxns of CSF?

• suspend brain in liquid:

  • reduce effective weight

  • prevention of blood supply being cut off

  • cushion CNS from mechanical trauma

• maintain CNS homeostasis

  • provide extracellular fluid

  • remove metabolic wastes of CNS

What problems are associated w/ obstruction of CSF circulation?

• obstruction of CSF circ. → inc. intracranial pressure → compression of midbrain → narrowing of cerebral aqueduct → accumulation of CSF in lateral + 3rd ventricles → further inc. intracranial pressure → cerebral edema severity compounds

• hydrocephalus = accumulation of CSF

• cerebral edema = brain tissue swelling due to fluid buildup in intracellular/extracellular space causing inc. intracranial pressure

How do spinal cord segments correspond to the vertebrae? Which vertebrae do the sacral segments lie w/i?

• 36 cord segments → 36 pairs of spinal n.

• vertebral column longer than spinal cord

• sacral segments of spinal cord lie w/i L5

• spinal segment nn. enter/exit thru IVF cranial to vertebrae of same #

  • spinal segments do not align w/ lumbar vertebrae

3 basic fxns of spinal cord?

• mediate spinal reflexes

• pathway for afferent sensory signals to the brain

• pathway for efferent motor signals to the spinal motor neurons

What is a dermotome?

• area of skin (except face) that has its sensory innervation by the dorsal root of a single spinal n.

• map of dermatomes represented in somesthetic cerebral cortex

What spinal cord segments correspond to what regions of the body?

• C1-C5 → cervical region

• C6-T1(2) → cervical enlargement = brachial plexus → thoracic limbs

• T1-L3 → trunk region

• L4-S1(2) → lumbosacral enlargement = lumbosacral plexus → pelvic limbs

What kind of tracts are in the dorsal, lateral, and ventral funiculi?

• dorsal → sensory only

• lateral → sensory + motor

• ventral → sensory + motor

Where are glia, perikarya, dendrites, and axons located in the spinal cord?

• gray matter

Where are spinal sensory + motor nuclei located in the spinal cord?

• sensory nuclei in the dorsal horn

• somatic motor nuclei in the ventral horn

What are the sensory receptors in the epidermis + dermis?

• epidermis

  • free nerve endings → pain, temperature, touch

• dermis

  • Meissner’s corpuscle → touch, vibration

  • Merkel’s corpuscle → touch, pressure

  • Ruffini’s corpuscle → stretching

  • hair follicle terminal → touch

Spinothalamic tract sensory receptors + modality, primary sensory neuron, location of perikarya of projection neurons + ascending tracts, destination

1) pain + temperature sensory receptors

2) primary sensory neurons: DRG neurons

3) enter spinal cord at dorsal horn

4) travel bilaterally L/R in lateral funiculus

5) thalamus → somesthetic cortical area of cerebral cortex

Fasciculus gracilis sensory receptors + modality, primary sensory neuron, location of perikarya of projection neurons + ascending tracts, destination

1) tactile sensory receptors innervating body caudal to T1

2) primary sensory neurons: DRG neurons

3) enter spinal cord at dorsal horn

4) travel unilaterally + ipsilaterally at medial aspect of dorsal funiculus

5) cross over to contralateral thalamus → somesthetic cortical area

Fasciculus cuneatus sensory receptors + modality, primary sensory neuron, location of perikarya of projection neurons + ascending tracts, destination

1) tactile sensory receptors innervating body C1-T1 (thoracic limb + neck) + conscious proprioception of thoracic limb

2) primary sensory neurons: DRG neurons

3) enter spinal cord at dorsal horn

4) travel unilaterally + ipsilaterally in lateral aspect of dorsal funiculus

5) cross over to contralateral thalamus → somesthetic cortical area of cerebral cortex

How do animals know the location of stimuli applied to the skin?

• dermatomes = area of skin supplied by a single spinal n.

• map of dermatomes represented in somesthetic area of cerebral cortex

conscious vs. subconscious proprioception

• conscious proprioception → contralateral thalamus + cerebrum

  • active awareness of where body is in space

• subconscious proprioception → ipsilateral cerebellum

  • not consciously aware like regulation of muscle tone to maintain posture

Spinocuneocerebellar tract sensory receptors + modality, primary sensory neuron, location of perikarya of projection neurons + ascending tracts, destination

1) proprioceptive receptors (m. spindle, pacinian corpuscle, golgi-tendon organ, Ruffini’s corpuscle) for subconscious proprioception of thoracic limb

2) primary sensory neurons: DRG neurons

3) enter through dorsal horn of spinal cord

4) travel unilaterally + ipsilaterally in dorsal funiculus next to fasciculus cuneatus

5) ipsilateral cerebellum

Spinomedullary tract sensory receptors + modality, primary sensory neuron, location of perikarya of projection neurons + ascending tracts, destination

1) proprioceptive receptors for conscious proprioception of pelvic limb + tail

2) primary sensory neurons: DRG neurons

3) enter at dorsal horn of spinal cord

4) travel unilaterally + ipsilaterally in dorsal funiculus briefly before reaching nucleus thoracicus in lateral funiculus

5) ascend in spinomedullary tract in lateral funiculus

6) cross over to contralateral thalamus → cerebral cortex

Dorsal spinocerebellar tract sensory receptors + modality, primary sensory neuron, location of perikarya of projection neurons + ascending tracts, destination

1) proprioceptive receptors for subconscious proprioception of pelvic limb + tail

2) primary sensory neurons: DRG neurons

3) enter at dorsal horn of spinal cord

4) travel unilaterally + ipsilaterally in dorsal funiculus briefly before reaching nucleus thoracicus in lateral funiculus

5) ascend in dorsal spinocerebellar tract tract in lateral funiculus

6) ipsilateral cerebellum

Proprioceptive positioning test what does it test, how to perform it, what functioning structures does it require?

• tests conscious proprioception

• turn paw over → animal should flip paw back over to normal position

• req:

  • spinal n. + peripheral n. (sensory + motor)

  • spinal cord

  • thalamus + cerebellum

  • somesthetic + motor cortices

How is pain, temperature, touch, and conscious/subconscious proprioception sensed in the thoracic limb?

1) sensory receptors

2) primary sensory neurons: DRG neurons

3) information enters at dorsal horn of spinal cord at cervical enlargement

4)

• pain + temperature → ascends bilaterally in spinothalamic tract in lateral funiculus → bilateral thalamus + cerebral cortex

• touch → ascends unilaterally + ipsilaterally in fasciculus cuneatus in dorsal funiculus → contralateral thalamus + cerebral cortex

• conscious proprioception → ascends unilaterally + ipsilaterally in fasciculus cuneatus in dorsal funiculus → contralateral thalamus + cerebral cortex

• subconscious proprioception → ascends unilaterally + ipsilaterally in spinocuneocerebellar tract in dorsal funiculus touch → ipsilateral cerebellum

How is pain, temperature, touch, and conscious/subconscious proprioception sensed in the pelvic limb?

1) sensory receptors

2) primary sensory neurons: DRG neurons

3) enter at dorsal horn of spinal cord at lumbosacral enlargement

4)

• pain + temperature → ascends bilaterally in spinothalamic tract in lateral funiculus → bilateral thalamus + cerebral cortex

• touch → ascends unilaterally + ipsilaterally in fasciculus gracilis in dorsal funiculus → contralateral thalamus + cerebral cortex

• conscious proprioception → starts in dorsal funiculus → nucleus thoracicus → ascends unilaterally + ipsilaterally in spinomedullary tract in lateral funiculus → contralateral thalamus + cerebral cortex

• subconscious proprioception → starts in dorsal funiculus → nucleus thoracicus → ascends unilaterally + ipsilaterally in dorsal spinocerebellar tract → ipsilateral cerebellum

Corticospinal tract origin, pathway, location in spinal cord, fxn, lesion

• origin + pathway: cerebral motor cortex (postcruciate gyrus + rostral suprasylvian gyrus) → internal capsule → crus cerebri → pyramid → pyramidal decussation → lateral corticospinal tract + ventral corticospinal tract in spinal cord

• location:

  • majority corticospinal fibers cross over at pyramidal decussation → become lateral corticospinal tract → descend in lateral funiculus

  • rest travel ipsilaterally as ventral corticospinal tract → ventral funiculus → do eventually cross contralaterally at enlargements

• fxn:

  • UMN

  • precise + refined voluntary control of extremities

• lesion:

Rubrospinal tract origin, pathway, location in spinal cord, fxn, lesion

• origin + pathway: red nucleus → axons cross over → descend contralaterallay as rubrospinal tract in spinal cord

• location: lateral funiculus

• fxn:

  • key voluntary motor tract in dog

  • UMN

  • excite flexors

• lesion:

Medullary reticulospinal tract origin, pathway, location in spinal cord, fxn, lesion

• origin + pathway: medullary RF → descend ipsilaterally as medullary reticulospinal tract in spinal cord

• location: lateral funiculus

• fxn:

  • UMN

  • excite flexors

  • inhibit extensors

  • maintain m. tone necessary for supporting body against gravity, postural adjustments, synergistic mvmt

• lesion:

  • decrease of excitation of flexors on the same side of the body

Pontine reticulospinal tract origin, pathway, location in spinal cord, fxn, lesion

• origin + pathway: pontine RF → descend ipsilaterally as pontine reticulospinal tract in spinal cord

• location: ventral funiculus

• fxn:

  • UMN

  • excite extensors = anti-gravity mm.

  • inhibit flexors

  • maintain m. tone necessary for supporting body against gravity, postural adjustments, synergistic mvmt

• lesion:

  • decrease of excitation of extensors on the same side of the body

Vestibulospinal tracts origin, pathway, location in spinal cord, fxn, lesion

• origin + pathway: vestibular nuclei → descend ipsilaterally in spinal cord as lateral + medial vestibulospinal tracts

• location: ventral funiculus

• fxn:

  • UMN

  • excite extensors

  • help maintain normal standing posture

• lesion:

  • decreased excitation of extensors on the same side of the body

Describe how UMN + LMN work

• UMN

  • CNS

  • cell bodies in brain? + axons in spinal cord

  • synapse on other neurons

  • always excitatory

  • excite inhibitory or excitatory interneurons

• interneurons

  • CNS

  • cell bodies + axons in gray matter of spinal cord

  • innervate LMN

  • either excitatory OR inhibitory

• LMN

  • CNS

  • cell bodies in ventral horn of spinal cord

  • alpha motor neuron → inn. skeletal m.

    • ALWAYS excitatory

  • visceral motor neuron → inn. smooth + cardiac mm.

  • gamma motor neuron → inn. muscle spindle

How do motor units fxn in voluntary mvmts? Are they activated all at the same time or in sequence? How is appropriate force generated?

• motor unit = a motor neuron coming from ventral horn spinal cord + all the m. fibers it innervates

  • voluntary mvmt → alpha motor neuron bc they inn. skeletal m.

• activated in sequence PRN to gen. more force

• appropriate force generated by activating more motor units until enough force is generated for any given task

• motor units are on/off

4 basic aspects of a reflex

• sensory component

• motor component = LMN

• local

• do NOT depend on UMN

  • tho UMN have a net inhib. effect on the body

Limbs affected, touch, pain, proprioception, motor fxn, reflexes, muscle tone in L side complete hemisection C1-C5

• limbs: L thoracic + pelvic

• touch: absent in L thoracic + pelvic limbs

• pain: present in both L limbs

• proprioception: absent in both L limbs

• motor fxn: absent in both L limbs

• reflex: present in both L limbs

Limbs affected, touch, pain, proprioception, motor fxn, reflexes, muscle tone in 1 side complete hemisection C6-T1 cervicothoracic enlargement

Limbs affected, touch, pain, proprioception, motor fxn, reflexes, muscle tone in 1 side complete hemisection T2-L3

Limbs affected, touch, pain, proprioception, motor fxn, reflexes, muscle tone in L side complete hemisection L4-S1 lumbosacral enlargement

• limbs: L pelvic

• touch: absent in L pelvic limb

• pain: absent in L pelvic limb

• proprioception: absent in L pelvic limb

• motor fxn: absent in L pelvic limb

• reflex: absent in L pelvic limb

• this is bc no sensory info from the limb can enter in a complete lesion of an enlargement

Monosynaptic vs. polysynaptic reflexes w/ an example of each

Myotatic (stretch) reflex pathway using quadriceps reflex as example

Golgi tendon reflex pathway

crossed extensor reflex pathway

Perineal reflex pathway

Flexor reflex pathway

UMN disease effect on spinal reflexes, muscle tone, paralysis, and muscle atrophy

• spinal reflexes: present to exaggerated

  • hyperreflexia bc loss of opposing Golgi tendon reflex means loss of the general inhib. effect from UMN

    • ex) Parkinson’s is an UMN disease and patients shake bc loss of inhibition on shaking

• muscle tone: present to increased

  • hypertonic

• paralysis: present

• muscle atrophy: present

LMN disease effect on spinal reflexes, muscle tone, paralysis, and muscle atrophy

• spinal reflexes: decreased to absent

  • hyporeflexia to areflexia

• muscle tone: decreased to absent

  • hypotonia to atonia

• paralysis: yes

• muscle atrophy: yes

Name these RF structures + their significance

• RF neuron has many collaterals comparatively →

  • allow monitoring of various ascending + descending tracts

    • receive input from thousands of cells to monitor entire state of body

Explain the role of the RF in consciousness + list the structures involved. Explain using waking up to the sound of an alarm as an example

• structures involved in staying awake:

  • ARAS = ascending reticular activating system

    • rostral RF (in midbrain)

    • thalamus

    • cortex

• ARAS wakes up cortex via thalamus

  • sensory receptors →

    • rostral RF → (via ARAS) nonspecific thalamic nuclei → cortex + specific thalamic nuclei → primary cortical area(s)

    • specific thalamic nuclei → primary cortical area(s)

• ex) alarm clock rings

  • cochlear receptors →

    • rostral RF → nonspecific thalamic nuclei → cortex + medial geniculate nucleus → primary auditory area

    • medial geniculate nucleus in thalamus → primary auditory area in cortex

Explain the role of the RF in unconsciousness. What do anesthetic drugs usually target and why isn’t it the RF?

• dec. ARAS activity + dec. thalamus activity → sleep

• anesthetic drugs usually target thalamic neurons

  • targeting RF riskier bc RF has many jobs

  • thalamus only job = keep us awake + make sure sensory info gets to the right place

Explain the role of the RF in swallowing

• CN 9, 10, 11

• swallowing center = central pattern generators that work tgt to cause swallowing

• nuc of solitary tract in medullary RF receives sensory input from CN 9 + 10 (pharyngeal mucosa senses bolus) → sends sensory info to swallowing center → facilitates via nuc ambiguus in medullary RF to coordinate motor outputs to CN 9 + 10 + 11

  • soft palate contracts → pharynx pulled fwd + larynx closes → pharyngeal peristalsis → esophageal peristalsis

What are central pattern generators + their importance to RF?

• dedicated network of neurons that act tgt to produce a specific sequence of events

  • multiple different CPG networks in RF to regulate visceromotor fxns

Explain the role of the RF in vomiting

• vomiting center = CPGs in medullary RF

  • receive inputs from:

    • chemical trigger zone

    • vestibular receptors

    • stomach + small intestine

    • cortical centers

  • outputs: (don’t need to know exact)

    • salivation

    • inspiration then inhibition of breathing

    • peristalsis in small intestine

    • relax pyloric + esophageal sphincters

    • contract ab. mm.

    • jaw opens

    • eject vomitus

Explain the role of the RF in motor fxn

• origin of:

  • pontine reticulospinal tract

    • ipsilateral

    • ventral funiculus

    • UMNs that excite extensors (anti-gravity mm.) + inhibit flexors

  • medullary reticulospinal tract

    • mostly ipsilateral

    • lateral funiculus

    • UMNs that excite flexors + inhibit extensors

Explain the 4 categories of inputs to the vomiting center

1) chemical trigger zone

• located in area postrema = wall of ventricle adjacent to obex

• incomplete blood-brain barrier → allows sampling of blood to monitor for bad stuff we may have ingested → input to vomiting center

• commonly triggered by anesthetics, opioids, uremia, hypoxia, emetic drugs, chemo drugs

2) vestibular receptors

• vestibular receptors sense abnorm. motion → input to vomiting center

• mechanism for motion sickness

3) stomach + small intestine

• receptors sense irritation/distention → send afferent signals via vagus n. → nuc solitary tract → input to vomiting center

4) cortical centers

• fear/smell/sight/trauma processed by cortical centers → input to vomiting center

Describe the general organization + overall fxn of the vestibular system

• bilateral vestibular organ senses change in head position → sends afferent signals via vestibular n. of CN 9 → cerebellum + vestibular nuclei

  • cerebellum → vestibular nuclei

  • bilateral vestibular nuclei →

    • vestibulospinal tract → skeletal mm. → change body position

    • medial longitudinal fasciculus → motor nuclei of CN 3, 4, 6 → change eye position

• fxn = reflexively control eye + body position in response to change in head position

Where will head tilt, body circle, and eyes move in normally functioning vestibular sys

• head tilt → twd side w/ more activity

• body circle → twd side w/ more activity

• eyes move → opp. head mvmt

Where will head tilt, body circle, and eyes move in unilateral vestibular sys lesion?

• head tilt → twd lesion

• body circle → twd lesion

• eye mvmt →

  • quick phase away from lesion

  • slow phase twd lesion

Structures of the vestibular organ?

• located inside petrous portion of temporal bone

  • membranous labyrinth

  • osseous labyrinth

• 3 structural units

  • 3 semicircular ducts w/ ampulla at 1 end → crista ampullaris

  • utricle → macula

  • saccule → macula

What are the sensory cells of the vestibular organ + how do they work? Describe the signal transduction

• ampulla → crista ampullaris = sensory epithelium

  • sensory cells lined w/ kinocilium + stereocilia

    • kinocilium

    • stereocilia

  • supporting cells

• utricle → macula = sensory epi.

  • sensory cells

  • supporting cells

• saccule → macula = sensory epi.

  • sensory cell

  • supporting cells

• signal transduction

  • stereocilia deflected TWDS kinocilium → inc. firing rate → depolarized

  • stereocilia deflected AWAY from kinocilium → dec. firing rate → hyperpolarized