Wednesday, 4-20-Motor Control: Reflexes (Karius)

Question 1

the placing and hopping reaction are ___ reflexes

vestibular, righting reflex, suckling, yawning, and eye/head movement are __ reflexes

stretch (myotatic), Golgi tendo reflex, and crossed extensor are __ reflexes

Answer 1

cortical

brainstem/midbrain

spinal

Question 2

Precise motions in response to afferent stimuli that is mediated at all levels of the CNS, has rapid initiation, and may be elicited during unconsciousness are descriptive of ___ activity

Answer 2

reflex

Question 3

___ activity originates in cortical areas associated with judgement, initiative, and motor control. It has a longer onset latency due to processing and requires conscious awareness

Answer 3

volitional

Question 4

This reflex is a contraction (shortening) of a stretched muscle. It is to protect the muscle from tearing due to stretch, is initiated by a muscle spindle, and is a monosynaptic, segmental reflex

Answer 4

myotatic

Question 5

The __ fibers of the muscle spindle have both MOTOR and SENSORY components

Answer 5

intrafusal

Question 6

this part of the muscle spindle is not contractile, is the portion sensitive to length, and has 2 sensors: nuclear bag and nuclear chain fibers

Answer 6

sensory portion

Question 7

what are the 2 sensors of the sensory portion of a muscle spindle?

Answer 7

nuclear bag fiber

nuclear chain fiber

Question 8

this fiber innervates both the nuclear bag and nuclear chain. It is a large, myelinated fiber that is sensitive to the length of the muscle and how fast the length is changing

Answer 8

Primary afferent, Group Ia fiber

Question 9

This fiber innervates only the nuclear chain fiber, is smaller and myelinated, and sensitive only to the length of the muscle

Answer 9

Secondary afferent, Group II fiber

Question 10

The motor portion of the muscle spindle consists of the ___ elements

Answer 10

intrafusal contractile

Question 11

The motor portion of the muscle spindle is innervated by a ___ motorneuron and controls the length of the sensory portion

Answer 11

gamma

Question 12

These motor neurons are large, heavily myelinated fibers. They innervate (via NMJ) skeletal muscle, are responsible for activating muscle, and activity directly leads to motion

Answer 12

Alpha

Question 13

These motor neurons are slightly smaller, innervate the contractile component of the muscle spindle via NMJ, its activity causes contraction, controls the sensitivity of the muscle spindle, and its activity does NOT directly lead to motion

Answer 13

gamma

Question 14

When eliciting the stretch reflex in a muscle group, the antagonist muscle group has a decrease in activity of the alpha motor neurons innervating it which allows the antagonist to relax and lengthen. This is an example of ___

Answer 14

reciprocal inhibition

Question 15

This reflex appears to be a sudden (abrupt) relaxation of a contracted muscle, protects muscle from damage due to excessive force, is polysynaptic and a segmental reflex

Answer 15

Golgi tendon reflex

Question 16

what is the afferent fiber in a Golgi tendon reflex?

What is the efferent fibers in a Golgi tendon reflex?

Answer 16

afferent–> Ib afferent from Golgi tendon

efferent –> alpha-motor neuron

Question 17

recovery from spinal shock is believed to result from:

Answer 17

• axonal sprouting below the level of a transection

- expression of receptor phenotypes that are self-activating (5-HTC receptor)

Question 18

___ results from loss of structures rostral to the pons

Answer 18

decerebrate posturing

Question 19

In decerebrate posturing, ___ is resisted motion in all directions, results from maintained muscle contraction and continual activation of alpha-motor neurons (not due to reflexes)

Answer 19

rigidity

Question 20

in decerebrate posturing, ___ is resisted motion in a given direction, there is a hyperactive myotatic reflex, and continual activation of gamma motor neurons –> contracts intrafusal muscle, lengthens nuclear bag/chain fibers

Answer 20

spasticity

Question 21

in decerebrate posturing:

Spasticity results from continual activation of ___ motorneurons

Rigidity results from continual activation of ___ motorneurons

Answer 21

gamma

alpha

Question 22

Regarding spasticity in decerebrate posturing: By activating the gamma-motorneurons, muscle spindles become more sensitive and there is spontaneous activation of this region: ___

Answer 22

brainstem facilitatory region

Question 23

Regarding spasticity in decerebrate posturing: This region inhibits gamma motorneurons, making muscle spindle less sensitive. This region requires activation from cortical regions

Answer 23

Brainstem inhibitory region

Question 24

What happens to the brainstem inhibitory region and brainstem facilitatory region when there is loss of the cortex (spasticity)?

Answer 24

With loss of the cortex, the brainstem inhibitory region is NOT activated, leaving the brainstem facilitatory region to dominate

The end result of the uncontrolled brainstem facilitatory region is stretch reflexes that fight any passive motion–> Spasticity

Question 25

__ is caused by a loss of cortical influence that inhibits a medullary input to the alpha motor neurons

Answer 25

rigidity

Question 26

___ is caused by damage to the cortex that abolishes activation of the brainstem inhibitory region (brain arousal systems)

Answer 26

spasticity

Question 27

describe the characteristics of Decorticate posturing (rigidity):

Answer 27

• Flexion of UL joints
• Extension of LL;s
• Dependent on head position

Question 28

Unilateral decorticate posturing results from strokes in the vicinity of the ___

Answer 28

internal capsule –> relatively common site for a stroke

Question 29

In decorticate posturing, rotation of the head to the right will cause flexion of which limb?

Answer 29

flexion of the left upper limb

Question 30

__ is due to transection of the SC, characterized by all reflexes being abolished even if the circuit is intact. It is due to hyperpolarization of spinal neurons due to loss of excitatory input from the cortex

Answer 30

spinal shock

Question 31

___ is a contraction of all anti-gravity muscles (arms in extension), loss of input from all structures rostral to the pons, and is usually bilateral and indicative of severe brain injury

Answer 31

decerebrate posture