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Neuro 3 - MS1 > Lecture 01 Basic Sensory and Motor Mechanisms and Pathways > Flashcards

Lecture 01 Basic Sensory and Motor Mechanisms and Pathways Flashcards

1
Q

Describe interneurons in the reflex pathway

A

may terminate directly or indirectly upon motor neurons in ventral horn cells
Processes may ascend, descend or cross (commissural fibers) in the spinal cord.

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2
Q

describe efferent neurons in the reflex arcs

A

alpha or gamma motor neurons in the motor nuclei or columns

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3
Q

What are the receptors for free nerve endings?

A

interoceptors, exteroceptors and peritrichial nerve endings

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4
Q

What is the stimulus for interoceptors and exteroceptors ?

A

pain, temp and touch

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5
Q

What is the stimulus of peritrichial nerve endings ?

A

light touch

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6
Q

What are intrasegmental reflexes?

A

interneurons terminates within the same level as the afferent stimulus

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7
Q

What are intersegmental reflexes?

A

interneurons extend the influence of the incoming info among more than one spinal segment

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8
Q

What is a major fiber bundle associated with intersegmental reflexes?

A

fasiculus proprius (fasciculus spinospinalis)

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9
Q

What is the fasiculus proprius?

A

fiber bundle that is distributed around the periphery of the gray matter of spinal cord and is continuous superiorly with the reticular formation
Comprised of ascending and descending processes of interneurons

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10
Q

What are contralateral reflexes?

A

a reflex may be conveyed to the other side by way of a commissural neurons (interneuron)
this may be intra or intersegmental depending upon the type, quality and quantity of the stimulus

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11
Q

What do alpha motor neurons innervate?

A

extrafusal fibers

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12
Q

What do gamma motor neurons innervate?

A

intrafusual

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13
Q

Describe monosynaptic reflexes?

A

comprise of a two-neuron reflex arc with only one synapse

Do not have an interneuron

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14
Q

What reflex is tested during the clinical examinations of the knee-jerk or jaw-jerk reflexes?

A

myotatic reflex: rapid stretching of the muscle and contraction of the corresponding muscle
type of monosynaptic reflex

Afferent: Ia n
Efferent: alpha motor

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15
Q

What is a polysynaptic reflex ?

A

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

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16
Q

What type of reflex is the pain reflex?

A 
polysynaptic reflex
Stimulus: noxious stimulus (pain)
Response: withdrawal 
Receptor: naked nerve endings 
Efferent: alpha motor
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17
Q

What are the common features in a conscious sensory pathway?

A 
Primary neuron 
Secondary neuron 
Tertiary Neuron
Primary Somesthetic Cortex
Association Cortex
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18
Q

Describe the primary neuron features in a conscious sensory pathway

A

Pseudounipolar neuron
Cell body is located in a spinal ganglion
Dendrite courses peripheral nerve
Central process enters CNS and bifurcates to ascend and descend a variable # of segments
Sends off collaterals to interneurons for reflexes
primary sensory fiber eventually terminates upon a secondary neuron

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19
Q

Describe the common features of a secondary neuron in the conscious sensory pathway

A

located in the spinal cord (pain and temperature pathway) or in the medulla (proprioceptive pathway)
Collaterals from the secondary axon terminate directly or indirectly via interneurons upon motor neurons for various reflexes

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20
Q

What will secondary axons end in a conscious sensory pathway?

A

Always decussates and ascends as a lemniscus and terminates upon a tertiary neuron in the dorsal thalamus

also sends collateral fibers to the reticular formation and tectum

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21
Q

Describe tertiary neurons in the conscious sensory pathway

A

soma of the neuron is located in a specific nucleus of the dorsal thalamus
axon projects to the primary somesthetic cortex via the thalamic radiations of the internal capsule and corona radiata

22
Q

What does the primary somestehtic cortex play a role in the conscious sensory pathway?

A

perception and discrimination of sensory stimuli

23
Q

What is the conscious sensory pathway for fast pain and temp?

A

primary neuron: spinal ganglion
Conveyed by: dorsolateral fasciculus
Secondary Neuron: Substantia gelatinosa
Converyed by: spinal lemniscus ->Lateral spinothalamic tract
Tertiary neuron: ventral posterior lateral nuclues
Cerebral cortex: primary somesthetic cortex

24
Q

What is the crude tactile pathway in the conscious sensory pathway?

A

Primary neuron: spinal ganglion
Conveyed by: short ascending fibers in the posterior columns
Secondary Neuron: nucleus proprius intermediate gray
Conveyed by: ventral spinothalamic tract
Tertiary neuron: Ventral posterior lateral nucleus
Cerebral Cortex: ventral posterior lateral nucleus

25
Q

There are many reflex patterns, most of which are programmed by what connections?

A

interneurons

26
Q

What is the proprioception 2-pt tactile pathway in the conscious sensory pathway?

A

Primary neuron: spinal ganglion
Conveyed by: long ascending fibers in the posterior columns
Secondary neuron: Nucleus gracilis, nucleus cuneatus
Conveyed by: medial lemniscus
Tertiary neuron: ventral posterior lateral nucleus
Cerebral cortex: primary somesthetic cortex

27
Q

Describe lower motor neurons

A 
final common pathway 
final effectors of the motor system 
Cell bodies in craniospinal motor nuclei 
Innervate skeletal m 
Alpha and gamma
28
Q

Describe upper motor neurons

A

premotor

descending processes form the rest of the motor system

29
Q

What type of fibers innervate branciomeric mm?

A

SVE

30
Q

What type of fibers innervate myotomic mm?

A

GSE

31
Q

SVE from nucleus ambiguus go to what structures?

A

laryngeal and pharyngeal mm

32
Q

What are the clinical manifestations of LMN paralysis ?

A

Flaccid paralysis: muscles limp
Areflexia: Loss of efferent component of reflex arc
Atonia: Destruction of gamma motor neurons = absence of muscle tone
Atrophy: Denervated m due to loss of motor neurons
Fasciculations: twitching of denervated m; hypersensitivity of motor end plate

33
Q

What is poliomyelitis ?

A

Viral disease
Motor neurons of anterior horns and cranial nerve motor nuclei die due to inflammation, edema, and macrophage activity
Astrocytic gliosis
2-4 days of symptoms: fever, headache, vomit, neck stiffness, back and limb pain (similar to any acute viral meningitis)
Symptoms may subside and pt completely recover or have varying degrees of paresis or paralysis

34
Q

What is the pathway of the corticospinal tract?

A

Primary motor cortex ->descends through the corona radiata, posterior limb of internal capsule, cerebral peduncles, pons, and upper medulla
90% decussate at pyramidal decussations and form LCST
Remaining uncrossed fibers ->ACST

35
Q

What does unilateral lesions of the LCST result in?

A

ipsilateral paralysis or paresis of the distal limb musculature innervated by those spinal segments below the level of the lesion

Very rare to have pure isolated lesions of the corticospinal tract

36
Q

What is the lateral corticospinal tract primarily involved in?

A

the control of the distal limb musculature, especially precise, individualized movements of the digits

Piano

37
Q

What is UMN paralysis commonly due to?

A

interruption of the motor cortex, corticospinal and/or corticobulbar tracts

38
Q

What is an UMN paralysis classically referred to? what are the signs and symptoms ?

A 
as the spastic paralysis of the antigravity mm
Symptoms: varying degrees of spastic paresis of axial and proximal limb mm, some degree of spastic paralysis of the distal limb mm esp the upper extremity
hypertonia 
hyperrreflexia
babinski sign
clonus
rigidity
disuse atrophy
39
Q

Where does the LCST terminate?

A

it descends in the lateral funiculus and most fibers terminate in neuronal ‘pools’ (intermediate gray) at all levels of the spinal cord

40
Q

What are the three phases of physical events following UMN lesions due to spinal cord injury ?

A
  1. pt in spinal shock with areflexia, atonia, and flaccid paralysis
  2. weeks-mnts: return of basic sppinal reflexes indicates pts recovery from spinal shock
    (reflexes due to reactivation of intrinsic circuits of the spinal cord distal to lesion)pts display some degree of spastic paresis of axial and prox limb and some spastic paralysis of distal limb mm
  3. 1-2 yrs: affected m groups will exhibit spasms of extensors, or flexors or remain flaccid
41
Q

What is spasticity?

A

abnormal, passive resistance to movement in one direction due to increased sensitivity of neuromuscular spindles to the stretch of gravity mm, increased gamma efferent activity and/or denervation hypersensitivity of LMN pools

42
Q

What is rigidity ?

A

abnormal passive resistance to movement in ALL directions

43
Q

Paralyzes movements in hemiplegic, quadriplegic or paraplegic distribution, not individual mm are due to UMN or LMN lesions?

A

UMN

44
Q

Paralyzes individual mm or sets of mm in root or peripheral nerve distributions are due to UMN or LMN lesions?

A

LMN

45
Q

Atrophy of disuse only is due to UMN or LMN lesions?

A

UMN (late or slight)

46
Q

Fasiculations and fibrillation symptoms due to UMN or LMN lesions?

A

LMN

47
Q

Hyperactive deep tendon reflexes due to UMN or LMN lesions?

A

UMN

48
Q

Hypoactive or absent deep tendon reflexes due to UMN or LMN lesions?

A

LMN

49
Q

What type of tracts are found in posterior columns?

A

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

50
Q

What type of tracts are found in the lateral funiculus?

A

descending UMN tracts for volitional control of limb musculature
Descending UMN tracts for autonomic control of bladder and bowel

51
Q

What tracts are in the anterior funiculus?

A

ascending sensory tracts for pain and temp, crude (light) tactile sensations
Decussating fibers in the direct pain and temp pathway
LMN in the anterior horn of spinal cord
Lateral spinothalamic tract

Neuro 3 - MS1 (9 decks)

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