Muscle Stretch Reflex

Question 1

Define reflex arc & its components

Answer 1

It is the basic functional unit of the nervous system as it is the smallest simplest unit capable of recieving a stimulus and producing a response.
Receptor, sensory neuron, integrating center, motor neuron, effector organ

Question 2

Compare afferent & efferent fibers of myotactic reflex

Answer 2

A, type Ia rapidly conducting fibres & type II fibers
E, alpha motor neurons in spinal cord

Question 3

List clinical importance of muscle spindle reflex

Answer 3

Examination of static (muscle tone) & dynamic (deep reflex) stretch reflex
Diagnosis of site & cause of neurological diseases

Question 4

Compare nuclear bag & chain with respect, func.

Answer 4

Bag: detect the rate of change of muscle length (rate detectors, dynamic response), phasic receptors (stop discharge during maintained strech)
Chain: detect degree of change in muscle lenth (static response), tonic receptors(does not stop discharge)

Question 5

Compare 1ry & 2ry afferent endings involved in myotactic reflex

Answer 5

1ry, annulospiral ending, type Ia, around central portion of nuclear bag & chain, rapidly conducting & act with dynamic & static stimuli
2ry, flower soraycendings, type ll, around chain only, slowly conducting, static stimulation only.

Question 6

Describe efferent innervation of myotactic reflex

Answer 6

A) alpha motor neurons: innervates extrafusal fibers
B) gamma motor neurons: which are dynamic for peripheral contractile part of nuclear bag & static for peripheral contractile part of nuclear chain.

Question 7

Mention causes of stimulation of intrafusal fibers

Answer 7

Stretch of central contractile part by:
1. Lengthening of the whole skeletal muscle
2. Contraction of peripheral parts of intrafusal fibers by gamma efferents
Stronger when both occur

Question 8

Synaptic delay of myotactic reflex is …..

Answer 8

0.3-0.5 msec

Question 9

Mention inhibitors of stretch reflex

Answer 9

Active muscle contraction (silent period of muscle spindle)
Stimulation of stretch reflex of antagonist muscle
Stimulation of Golgi tendon organ reflex (inverse or negative stretch relex)

Question 10

Compare static & dynamic stretch reflex with respect, stimulus & receptor

Answer 10

S, sudden rapid stretch & central parts of nuclear bag fibers of muscle spindle (rapidly adapting)
D, maintained weak stretch & central parts of nuclear chain fibers of muscle spindle (slowly adapting)

Question 11

Explain a. & g. co-activation

Answer 11

During voluntary contraction, supraspinal facilitatory impulses activate both a & g fibers, a for extrafusal fibers & g for intrafusal fibers to keep the central sensory part sensitive & prevent unloading. If the load on the muscle increases both types of fibers are stretched. Stretching of the central receptor part of intrafusal fibers increases impulses in type Ia fibers which eventually causes increased discharge in alpha motor neurons to increase force of contraction

Question 12

What happens when muscle spindle, its afferents or efferents do not work properly with respect voluntary movements

Answer 12

Muscle contraction is jerky during the course of such a signal

Question 13

Describe the clinical value of stretch reflex

Answer 13

1. Presence of normal stretch reflex indicates all components are normal & there is balance between excitatory & inhibitory signals from higher centers.
2. Localization of site and cause of neurological disease
3. Gives an idea about tone, hypereflexia accompanies hypertonia & vice versa

Question 14

Compare facilitatory & inhibitory centers

Answer 14

F, motor area 4 & caudate nucleus act through stimulation of potine reticular formation which has intrinsic activity. Also vestibular nucleus through vestibulospinal tract.
I, cortical suppressor area 4s & 6s and lentiform nucleus act via stimulation of medullary reticular formation which has NO intrinsic ativity also red nucleus via rubrospinal tract.