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Neuroscience I Test 3 > Basic Sensory and Motor Mechanisms and Pathway > Flashcards

Basic Sensory and Motor Mechanisms and Pathway Flashcards

1
Q

basic components to a reflex arc

A
  1. receptor–free N endings for pain sensation
  2. afferent neuron–dorsal root ganglion neuron
  3. interneuron
    • may terminate directly or indirectly upon motor neurons
    • processes may ascend/descend/cross in SC
    • KEY component in formation of reflex patterns
  4. efferent neuron–alpha or gamma motor neurons in motor nuclei or columns
  5. effector–motor end plate at a NMJ
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2
Q

interneuron

A
  • terminates directly or indirectly (via another interneuron) upon a ventral horn cell
  • course and termination of an interneuron determines the pattern of reflex response
  • KEY component in formation of reflex patterns
  • 3 types: intrasegmental reflex, intersegmental reflex, contralateral crossed reflexes
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3
Q

intrasegmental reflex

A
  • type of interneuron

- occur within the same level as the afferent stimulus

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4
Q

intersegmental reflex

A
  • type of interneuron
  • extend the influence of incoming info among more than one spinal segment
  • major fiber bundle associated with intersegmental reflexes is the fascicles proprius
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5
Q

fascicles proprius

A
  • distributed around the periphery of the gray matter of SC
  • continuous superiorly with the reticular formation
  • complex diffuse fascicles is comprised of ascending and descending processes of interneurons
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6
Q

contralateral (crossed) reflex

A
  • type of interneuron
  • reflex may be conveyed to the other side by way of a commissural neuron
  • may be intra or inter segmental depending upon the type, quality, quantity of stimulus
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7
Q

pathways from SC go to the brainstem and then sensory info goes to…

A

the tectum which is made up of the superior and inferior colliculus
-auditory and visual info goes here

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8
Q

monosynaptic reflex

A
  • comprise a 2 neuron reflex arc with only one synapse
  • no interneuron
  • ex: myotatic reflex–tested with jaw jerk or knee jerk reflex
    • stimulus: rapid stretching of muscle
    • response: contraction of the corresponding M
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9
Q

polysynaptic reflex

A

-involve interneurons to elicit stereotypical response patterns to a particular type of stimulus

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10
Q

pain reflex

A
  • type of polysynaptic reflex
    • stimulus: noxious stimulus (pain)
    • response: withdrawal from stimulus
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11
Q

autogenic inhibition reflex

A
  • type of polysynaptic reflex
    • stimulus: excessive tension on the tendon
    • response: relaxation of the corresponding M
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12
Q

reciprocal inhibition reflex

A
  • type of polysynaptic reflex
    • stimulus: contraction of agonist M
    • response: relaxation of the antagonist M
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13
Q

primary neuron

A
  • pseudounipolar neuron whose cell body is located in the spinal ganglion
  • peripheral process (dendrite) courses in a peripheral N & the ending is assoc with some type of R
    • central process enters CNS and bifurcates to ascend and descend a variable # of segments
    • along its course it sends off collaterals to interneurons for reflexes
    • primary sensory fiber eventually terminates upon a secondary neuron
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14
Q

secondary neuron

A
  • located in the SC (pain/temp path) or medulla (proprioceptive path)
    1. collaterals from 2ndary axon also terminate directly or indirectly via interneurons upon motor neurons for various reflexes
    2. in a conscious sensory pathway the secondary axon:
    • always decussates and ascends as a lemniscus
    • terminates upon a tertiary neuron in dorsal thalamus
    • sends collateral fibers to reticular formation and tectum
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15
Q

tertiary neuron

A
  • soma of the neuron is located in a specific nucleus of dorsal thalamus
  • projects to the primary somesthetic cortex via the thalamic radiations of the posterior limb of internal capsule and corona radiata
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16
Q

primary somesthetic cortex

A
  • post central gyrus

- plays role in the perception and discrimination of sensory stimuli

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17
Q

association cortex

A

-involved in the integration, modification, and interpretation of sensory info

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18
Q

lemniscal systems

A

-secondary axons in a conscious sensory pathway that have already crossed midline so relay info from the contralateral side

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19
Q

general conscious sensory pathway

A
  1. receptor
  2. primary neuron with cell body in the ganglion cell and central process terminating in the CNS at the secondary neuron
  3. secondary neuron decussates and ascends as a lemniscus and terminates on a tertiary neuron in the dorsal thalamus
    • also sends fibers to the reticular formation and tectum
  4. tertiary neuron in the dorsal thalamus projects to primary somesthetic cortex in the internal capsule
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20
Q

lesion of primary neuron

A

results in ipsilateral deficits

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21
Q

lesion of the tertiary neuron/lemniscus

A

results in contralateral deficits

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22
Q

fast pain/temperature pathway

A
  1. primary neuron: spinal ganglion
  2. conveyed by: dorsolateral fasciculus
  3. secondary neuron: substantia gelatinosa
  4. conveyed by: spinal lemniscus and lateral spinothalamic tract
  5. tertiary neuron: ventral posterior lateral nucleus (VPL)
  6. cerebral cortex: primary somesthetic cortex in posterior limb of internal capsule
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23
Q

crude tactile pathway

A
  1. primary neuron: spinal ganglion
  2. conveyed by: short ascending fibers in posterior columns
  3. secondary neuron: nucleus proprius intermediate gray
  4. conveyed by: ventral spinothalamic tract
  5. tertiary neuron: ventral posterior lateral nucleus (VPL)
  6. cerebral cortex: primary somesthetic cortex in posterior limb of internal capsule
24
Q

proprioception/2 point tactile pathway

A
  1. primary neuron: spinal ganglion
  2. conveyed by: long ascending fibers in posterior columns, fasciculus gracilis, fasciculus cuneatus
  3. secondary neuron: nucleus gracilis (lower limb), and nucleus cuneatus (upper limb)
  4. conveyed by: medial leminiscus
  5. tertiary neuron: ventral posterior lateral nucleus (VPL)
  6. cerebral cortex: primary somesthetic cortex in posterior limb of internal capsule
25
Q

VPL vs VPM

A
  • VPL: ventral posterior lateral nucleus–sensory info from body
  • VPM: ventral posterior medial nucleus–sensory info from face
26
Q

lower motor neurons

A
  • final common pathway b/c they synapse directly with striated skeletal muscle so allows the motor response
    • final effectors of the motor system
  • cell bodies located in one of the craniospinal motor nuclei
  • processes form the motor Ns that innervate skeletal Ms
  • 2 types: alpha and gamma
27
Q

alpha motor neurons

A
  • type of LMN

- innervate extrafusal or skeletal M fibers

28
Q

gamma motor neurons

A
  • type of LMN
  • innervate the modified muscle cells (intrafusal fibers) that form part of the proprioceptive neuromuscular spindles
  • activating them inc muscle tension and muscle tone
29
Q

somatotropic organization of the anterior horn

A
  • lateral portion–distal upper extremities
  • proximal upper extremities are more medially
  • trunk is in the midline
  • neurons in the anterior funicular affect the axial M bilaterally
30
Q

SVE Nuclei:

  1. trigeminal motor nucleus
  2. facial motor nucleus
  3. nucleus ambiguus
  4. accessory nucleus
A
  1. mastication Ms
  2. mimetic Ms
  3. laryngeal and pharyngeal Ms
  4. trapezius and SCM
31
Q

GSE Nuclei:

  1. oculomotor nucleus
  2. trochlear nucleus
  3. abducens nucleus
  4. hypoglossal nucleus
  5. phrenic nucleus
  6. medial motor cell column
  7. lateral motor cell column
A
  1. LPS, medial rectus, superior rectus, inferior rectus, inferior oblique
  2. superior oblique
  3. lateral rectus
  4. intrinsic Ms of the tongue
  5. diaphragm
  6. axial postural Ms
  7. limb Ms
32
Q

LMN paralysis

A
  • paralyzed, no reflexes

- results from destruction of the motor neurons or axons of one or more of the cranial or spinal motor nuclei

33
Q

flaccid paralysis

A
  • atonic and areflexic
  • M is completely limp and no resistance to passive movement
  • results from destruction to LMN
34
Q

areflexia

A
  • loss of efferent component of the reflex arc to a M results in the absence of the assoc M reflex
  • results from destruction of LMN
35
Q

atonia

A
  • destruction of gamma motor neurons or their axons results in absence of M tone
  • results from destruction of LMN
36
Q

atrophy

A
  • denervated M atrophies due to the loss of stimulation from motor neurons
  • results from destruction of LMN
37
Q

fasciculations

A

-“twitching” of denervated M, probably due to hypersensitivity of the motor end plate

38
Q

poliomyelitis

A
  • involves the motor neurons of the anterior (ventral) horns and the cranial N motor nuclei
  • 1st: severe inflammation, vasodilation, edema, and macrophage activity
  • 2nd: neurons die and significant astrocytic gliosis
  • onset of this viral disease lasts b/w 2-4 days with symptoms which are characteristic of acute viral meningitis–fever, headache, vomiting, neck stiffness, pain in back and limbs
    • sympatoms may subside and pt completely recovers result in varying degrees of paralysis
39
Q

corticospinal tract

A

-arises from large pyramidally shaped neurons located in the primary motor and premotor cortices

40
Q

pyramidal decussation

A
  • corticospinal tract descends thru the corona radiate internal capsule, cerebral peduncles, pons, upper medulla
  • in lower medulla, 85-90% of corticospinal fibers decussate at pyramidal decussation and form the lateral reticulospinal tract (LCST)
  • remaining uncrossed fibers continue as the anterior corticospinal tract (ACST)
41
Q

lateral corticospinal tract (LCST)

A
  • in the SC, it descends in the lateral funiculus
  • fibers from the pyramidal decussation continue on here
  • most of the fibers terminate in neuronal pools at all levels of the SC
    • some fibers synapse directly on LMN
    • corticospinal tracts primarily terminate in LMN pools which in turn exert their collective influence upon intrinsic spinal reflex circuits
42
Q

lesions of the LCST

A

-unilateral lesions result in ipsilateral paralysis or paresis of the distal limb musculature innervated by those spinal segments below the level of the lesion

43
Q

anterior corticospinal tract

A
  • some of the corticospinal fibers that don’t cross at the decussation descend uncrossed in the anterior funicular of the cervical and upper thoracic SC
  • unilateral lesions here have minimal clinical effect
44
Q

UMN paralysis

A
  • due to interruption of the motor cortex, corticospinal or corticobulbar tracts
  • rare, but pure isolated lesions of the CST result in paresis and incoordination of the primarily distal musculature of the extremities
  • UMN paralysis is referred to as spastic paralysis of the antigravity Ms
  • signs/symptoms
    • varying degrees of spastic paresis of axial and proximal limb musculature
    • hypertonia/hyperreflexia
    • babinski sign
    • clonus
    • rigidity
    • disuse atrophy
45
Q

what happens when we lose the UMN?

A

hyperactivity of reflexes

46
Q

spinal cord injury

A

3 phases

  1. spinal shock with areflexia, atone, and flaccid paralysis
  2. after few weeks or months, return of the basic spinal reflexes indicates the pt’s recovery from spinal shock
    • reflexes due to reactivation of the intrinsic circuits of the SC distal to lesion
    • pt has some degree of spastic paresis of axial and proximal limb muscles–hyperactivity; some paresis of distal limb Ms
  3. after 1-2 yrs, affected M groups will exhibit spasms of extensors, or flexors, or remain flaccid
47
Q

spasticity

A
  • abnormal, passive resistance to movement in one direction
  • may be due to increased sensitivity of the neuromuscular spindles to the stretch of the gravity Ms, inc gamma efferent activity, loss of descending inhibition, and/or enervation hypersensitivity of LMN pools
48
Q

rigidity

A
  • abnormal passive resistance to movement in all directions

- Parkinson’s Dz

49
Q

decerebrate rigidity

A
  • characterized by spasticity of extensors of both upper and lower extremities
  • pts usually do not survive
50
Q

decorticate rigidity

A
  • characterized by spastic hemiplegia of the flexors of the upper extremity and extensors of the lower extremity
    • usually due to a lesion of the internal capsule
51
Q

characteristics of UMN lesions

A
  • paralyzes mvmts in hemiplegic, quadriplegic, or paraplegic distribution, not indiv. Ms
  • atrophy of disuse
  • hyperactive DTRs
  • clonus
  • clasp knife spasticity
  • absent abdominal cremasteric reflexes
  • Babinski sign
52
Q

characteristics of LMN lesions

A
  • paralyzes individual Ms or sets of Ms in root or peripheral N distributions
  • atrophy of denervation–early and severe
  • fasciculations and fibrillations
  • hypoactive or absent DTRs
  • hypotonia
53
Q

clinically important regions of the SC

A
  1. dorsal roots
  2. posterior columns
  3. lateral funiculus
  4. anterior funiculus
54
Q

posterior columns

A

-ascending sensory tracts for proprioception, 2 pt tactile discrimination, and vibratory sensations

55
Q

lateral funiculus

A
  • where LCST runs
  • descending UMN tracts for volitional control of limb musculature
  • descending UMN tracts for autonomic control of bladder and bowel dysfunction
56
Q

anterior funiculus

A
  • ascending sensory tracts for pain and temp, and cruse tactile sensations
  • decussating fibers in the direct pain and temp pathway
  • LMNs in the anterior ventral horn of the SC

Neuroscience I Test 3 (20 decks)

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