Lecture 01 Basic Sensory and Motor Mechanisms and Pathways

Question 1

Describe interneurons in the reflex pathway

Answer 1

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

Question 2

describe efferent neurons in the reflex arcs

Answer 2

alpha or gamma motor neurons in the motor nuclei or columns

Question 3

What are the receptors for free nerve endings?

Answer 3

interoceptors, exteroceptors and peritrichial nerve endings

Question 4

What is the stimulus for interoceptors and exteroceptors ?

Answer 4

pain, temp and touch

Question 5

What is the stimulus of peritrichial nerve endings ?

Answer 5

light touch

Question 6

What are intrasegmental reflexes?

Answer 6

interneurons terminates within the same level as the afferent stimulus

Question 7

What are intersegmental reflexes?

Answer 7

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

Question 8

What is a major fiber bundle associated with intersegmental reflexes?

Answer 8

fasiculus proprius (fasciculus spinospinalis)

Question 9

What is the fasiculus proprius?

Answer 9

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

Question 10

What are contralateral reflexes?

Answer 10

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

Question 11

What do alpha motor neurons innervate?

Answer 11

extrafusal fibers

Question 12

What do gamma motor neurons innervate?

Answer 12

intrafusual

Question 13

Describe monosynaptic reflexes?

Answer 13

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

Do not have an interneuron

Question 14

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

Answer 14

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

Afferent: Ia n
Efferent: alpha motor

Question 15

What is a polysynaptic reflex ?

Answer 15

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

Question 16

What type of reflex is the pain reflex?

Answer 16

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

Question 17

What are the common features in a conscious sensory pathway?

Answer 17

Primary neuron 
Secondary neuron 
Tertiary Neuron
Primary Somesthetic Cortex
Association Cortex

Question 18

Describe the primary neuron features in a conscious sensory pathway

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What will secondary axons end in a conscious sensory pathway?

Answer 20

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

Question 21

Describe tertiary neurons in the conscious sensory pathway

Answer 21

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

Question 22

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

Answer 22

perception and discrimination of sensory stimuli

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

interneurons

Question 26

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

Answer 26

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

Question 27

Describe lower motor neurons

Answer 27

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

Question 28

Describe upper motor neurons

Answer 28

premotor | descending processes form the rest of the motor system

Question 29

What type of fibers innervate branciomeric mm?

Answer 29

SVE

Question 30

What type of fibers innervate myotomic mm?

Answer 30

GSE

Question 31

SVE from nucleus ambiguus go to what structures?

Answer 31

laryngeal and pharyngeal mm

Question 32

What are the clinical manifestations of LMN paralysis ?

Answer 32

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

Question 33

What is poliomyelitis ?

Answer 33

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

Question 34

What is the pathway of the corticospinal tract?

Answer 34

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

Question 35

What does unilateral lesions of the LCST result in?

Answer 35

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

Question 36

What is the lateral corticospinal tract primarily involved in?

Answer 36

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

Question 37

What is UMN paralysis commonly due to?

Answer 37

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

Question 38

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

Answer 38

``` 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 ```

Question 39

Where does the LCST terminate?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

What is spasticity?

Answer 41

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

Question 42

What is rigidity ?

Answer 42

abnormal passive resistance to movement in ALL directions

Question 43

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

Answer 43

UMN

Question 44

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

Answer 44

LMN

Question 45

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

Answer 45

UMN (late or slight)

Question 46

Fasiculations and fibrillation symptoms due to UMN or LMN lesions?

Answer 46

LMN

Question 47

Hyperactive deep tendon reflexes due to UMN or LMN lesions?

Answer 47

UMN

Question 48

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

Answer 48

LMN

Question 49

What type of tracts are found in posterior columns?

Answer 49

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

Question 50

What type of tracts are found in the lateral funiculus?

Answer 50

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

Question 51

What tracts are in the anterior funiculus?

Answer 51

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