Basic Sensory and Motor Mechanisms and Pathway Flashcards
1
Q
basic components to a reflex arc
A
- receptor–free N endings for pain sensation
- afferent neuron–dorsal root ganglion neuron
- interneuron
- may terminate directly or indirectly upon motor neurons
- processes may ascend/descend/cross in SC
- KEY component in formation of reflex patterns
- efferent neuron–alpha or gamma motor neurons in motor nuclei or columns
- effector–motor end plate at a NMJ
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
3
Q
intrasegmental reflex
A
- type of interneuron
- occur within the same level as the afferent stimulus
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
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
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
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
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
9
Q
polysynaptic reflex
A
-involve interneurons to elicit stereotypical response patterns to a particular type of stimulus
10
Q
pain reflex
A
- type of polysynaptic reflex
- stimulus: noxious stimulus (pain)
- response: withdrawal from stimulus
11
Q
autogenic inhibition reflex
A
- type of polysynaptic reflex
- stimulus: excessive tension on the tendon
- response: relaxation of the corresponding M
12
Q
reciprocal inhibition reflex
A
- type of polysynaptic reflex
- stimulus: contraction of agonist M
- response: relaxation of the antagonist M
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
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
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
16
Q
primary somesthetic cortex
A
- post central gyrus
- plays role in the perception and discrimination of sensory stimuli
17
Q
association cortex
A
-involved in the integration, modification, and interpretation of sensory info
18
Q
lemniscal systems
A
-secondary axons in a conscious sensory pathway that have already crossed midline so relay info from the contralateral side
19
Q
general conscious sensory pathway
A
- receptor
- primary neuron with cell body in the ganglion cell and central process terminating in the CNS at the secondary neuron
- 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
- tertiary neuron in the dorsal thalamus projects to primary somesthetic cortex in the internal capsule
20
Q
lesion of primary neuron
A
results in ipsilateral deficits
21
Q
lesion of the tertiary neuron/lemniscus
A
results in contralateral deficits
22
Q
fast pain/temperature pathway
A
- primary neuron: spinal ganglion
- conveyed by: dorsolateral fasciculus
- secondary neuron: substantia gelatinosa
- conveyed by: spinal lemniscus and lateral spinothalamic tract
- tertiary neuron: ventral posterior lateral nucleus (VPL)
- cerebral cortex: primary somesthetic cortex in posterior limb of internal capsule
23
Q
crude tactile pathway
A
- primary neuron: spinal ganglion
- conveyed by: short ascending fibers in posterior columns
- secondary neuron: nucleus proprius intermediate gray
- conveyed by: ventral spinothalamic tract
- tertiary neuron: ventral posterior lateral nucleus (VPL)
- cerebral cortex: primary somesthetic cortex in posterior limb of internal capsule
24
Q
proprioception/2 point tactile pathway
A
- primary neuron: spinal ganglion
- conveyed by: long ascending fibers in posterior columns, fasciculus gracilis, fasciculus cuneatus
- secondary neuron: nucleus gracilis (lower limb), and nucleus cuneatus (upper limb)
- conveyed by: medial leminiscus
- tertiary neuron: ventral posterior lateral nucleus (VPL)
- 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:
- trigeminal motor nucleus
- facial motor nucleus
- nucleus ambiguus
- accessory nucleus
A
- mastication Ms
- mimetic Ms
- laryngeal and pharyngeal Ms
- trapezius and SCM
31
Q
GSE Nuclei:
- oculomotor nucleus
- trochlear nucleus
- abducens nucleus
- hypoglossal nucleus
- phrenic nucleus
- medial motor cell column
- lateral motor cell column
A
- LPS, medial rectus, superior rectus, inferior rectus, inferior oblique
- superior oblique
- lateral rectus
- intrinsic Ms of the tongue
- diaphragm
- axial postural Ms
- 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
- spinal shock with areflexia, atone, and flaccid paralysis
- 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
- 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
- dorsal roots
- posterior columns
- lateral funiculus
- 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
