Basic Sensory and Motor Mechanisms and Pathway Flashcards Preview

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

Flashcards in Basic Sensory and Motor Mechanisms and Pathway Deck (56):

basic components to a reflex arc

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



-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


intrasegmental reflex

-type of interneuron
-occur within the same level as the afferent stimulus


intersegmental reflex

-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


fascicles proprius

-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


contralateral (crossed) reflex

-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


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

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


monosynaptic reflex

-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


polysynaptic reflex

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


pain reflex

-type of polysynaptic reflex
-stimulus: noxious stimulus (pain)
-response: withdrawal from stimulus


autogenic inhibition reflex

-type of polysynaptic reflex
-stimulus: excessive tension on the tendon
-response: relaxation of the corresponding M


reciprocal inhibition reflex

-type of polysynaptic reflex
-stimulus: contraction of agonist M
-response: relaxation of the antagonist M


primary neuron

-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


secondary neuron

-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


tertiary neuron

-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


primary somesthetic cortex

-post central gyrus
-plays role in the perception and discrimination of sensory stimuli


association cortex

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


lemniscal systems

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


general conscious sensory pathway

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


lesion of primary neuron

results in ipsilateral deficits


lesion of the tertiary neuron/lemniscus

results in contralateral deficits


fast pain/temperature pathway

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


crude tactile pathway

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


proprioception/2 point tactile pathway

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



-VPL: ventral posterior lateral nucleus--sensory info from body
-VPM: ventral posterior medial nucleus--sensory info from face


lower motor neurons

-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


alpha motor neurons

-type of LMN
-innervate extrafusal or skeletal M fibers


gamma motor neurons

-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


somatotropic organization of the anterior horn

-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


SVE Nuclei:
1. trigeminal motor nucleus
2. facial motor nucleus
3. nucleus ambiguus
4. accessory nucleus

1. mastication Ms
2. mimetic Ms
3. laryngeal and pharyngeal Ms
4. trapezius and SCM


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

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


LMN paralysis

-paralyzed, no reflexes
-results from destruction of the motor neurons or axons of one or more of the cranial or spinal motor nuclei


flaccid paralysis

-atonic and areflexic
-M is completely limp and no resistance to passive movement
-results from destruction to LMN



-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



-destruction of gamma motor neurons or their axons results in absence of M tone
-results from destruction of LMN



-denervated M atrophies due to the loss of stimulation from motor neurons
-results from destruction of LMN



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



-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


corticospinal tract

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


pyramidal decussation

-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)


lateral corticospinal tract (LCST)

-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


lesions of the LCST

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


anterior corticospinal tract

-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


UMN paralysis

-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
-varying degrees of spastic paresis of axial and proximal limb musculature
-babinski sign
-disuse atrophy


what happens when we lose the UMN?

hyperactivity of reflexes


spinal cord injury

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



-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



-abnormal passive resistance to movement in all directions
-Parkinson's Dz


decerebrate rigidity

-characterized by spasticity of extensors of both upper and lower extremities
-pts usually do not survive


decorticate rigidity

-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


characteristics of UMN lesions

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


characteristics of LMN lesions

-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


clinically important regions of the SC

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


posterior columns

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


lateral funiculus

-where LCST runs
-descending UMN tracts for volitional control of limb musculature
-descending UMN tracts for autonomic control of bladder and bowel dysfunction


anterior funiculus

-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