Neuroscience Week 3: Muscle Stretch Reflex

Question 1

Muscle Stretch Reflex AKA

4 Listed

Answer 1

• Monosynaptic Reflex
• Myotactic reflex
• Deep Tendon Reflex
• Tendon Jerk

Question 2

Muscle Stretch Reflex Description

Answer 2

An automatic monosynaptic reflex that involves a muscle and tendon, and produces a jerk response

Question 3

Muscle Stretch Reflex Key Mediators

5 Listed

Answer 3

• Muscle Spindles
• Spinal Neurons
• Muscle Fibers
• Interneurons
• Golgi Tendon Organs

Question 4

Innervation Ratio of Large muscle Group

Answer 4

1 motor neuron - 1,000 muscle fibers

Question 5

Innervation Ratio of Small Muscle Group

Answer 5

1 motor neuron - <10 Muscle Fibers

Question 6

Interneurons AKA

Answer 6

Renshaw Cell

Question 7

Knee Extensor Reflex: Activation

Answer 7

When the patellar tendon is activated, the muscle spindle sends an excitatory volley along the Type 1a sensory afferent, which excites the extensor motor neuron. It activates the muscle extensors, which extend the knee.

Question 8

Biceps Reflex Nerves Roots

Answer 8

C5, C6

Question 9

Triceps Reflex Nerve Roots

Answer 9

C7, C8

Question 10

Patella Reflex Nerve Roots

Answer 10

L2 - L4

Question 11

Achilles Reflex Nerve Roots

Answer 11

S1, S2

Question 12

Renshaw Cell acts through this neurotransmitter

Answer 12

Inhibitory neurotransmitter Glycine

Question 13

Flexion-Crossed Extension Reflex

Answer 13

Plantar stimulation causes in the stimulated leg

• Ankle flexion
• Knee flexion
• Hip flexion

In the unaffected leg

• Ankle extension
• Knee extension
• Hip extension

Question 14

Triple flexor Reflex in comatose patients

Answer 14

presence of the triple flexor reflex to plantar stimulation is a sign to disinhibition and is akin to the Babinski sign

Question 15

Golgi Tendon Organ uses what type of neuron

Answer 15

Type 1b sensory nerve

Question 16

Muscle spindle uses what type of neuron?

Answer 16

Type 1a sensory nerve

Question 17

Knee extensor reflex: Termination

Answer 17

Extensor muscle contraction activates the Golgi Tendon Organ

and sends an afferent signal to the Renshaw cell along Type 1b sensory nerve which i

n turn inhibits the extensor efferent neuron to the extensor and blocks excitation of the extensor muscle so that it relaxes

The Muscle spindle fires before the Golgi Tendon organ which explains the jerk response

………………………….

Golgi tendon organs are situated where the quadriceps tendon inserts into the patella. Type 1b fibers project from the Golgi tendon organs to the Renshaw interneurons. Inhibitory fibers project from the the Renshaw interneurons to the extensor motor neurons. The Type 1a and 1b fibers fire at the same rate, but the muscle spindle fibers have a much lower threshold to fire than Golgi tendon organs, thus, the muscle spindle fibers fire first, and then later the Golgi tendon organs fire, which terminates the muscle stretch reflex.

Question 18

Neurobiological influences on the relaxation of muscle contraction

Answer 18

• Myosin ATPase.
• Calcium re-accumulation into the endoplasmic reticulum.
• Symptomatic hypothyroidism causes a delay in the relaxation phase of the muscle stretch reflex (aka Woltman’s sign).

These aid in muscle contraction.

Question 19

Woltman’s sign

Answer 19

delay in the relaxation phase of the muscle stretch reflex (can be caused by symptomatic hypothyroidism)

Question 20

Key mediators of Muscle Stretch Reflex: Muscle Spindles

Answer 20

Activate via muscle stretch

Question 21

Key mediators of Muscle Stretch Reflex: Spinal Neurons

Answer 21

which receive sensory input and generate motor output.

Question 22

Key mediators of Muscle Stretch Reflex: Muscle Fibers

Answer 22

Which contract

Question 23

Key mediators of Muscle Stretch Reflex: Interneurons

Answer 23

which modulate neuronal firing

Question 24

Key mediators of Muscle Stretch Reflex: Golgi Tendon Organs

Answer 24

Which activate via muscle contraction to terminate the reflex

Question 25

Knee extensor reflex: Interneuronal Inhibition

Answer 25

Renshaw cells are interneurons that lie in the anterior horn of the gray matter of the spinal cord. When Renshaw cells are activated, they inhibit flexor motor neurons using the inhibitory neurotransmitter glycine.

Question 26

Achilles Reflex Nerve Roots

Answer 26

S1 , S2 “buckle my shoe”

Question 27

Patellar Reflex Nerve Roots

Answer 27

L3, L4 “Kick the door”

Question 28

Biceps and Brachoradialis Reflex Nerve Roots

Answer 28

C5, C6 “Pick up sticks”

Question 29

Triceps Reflex Nerve Roots

Answer 29

C7, C8 “lay them straight”

Question 30

Cremasteric Reflex Nerve Roots

Answer 30

L1, L2 “Testicles move”

Question 31

Anal wink Reflex Nerve Roots

Answer 31

S3, S4 “Winks galore”

Question 32

Primitive Reflexes Description

Answer 32

CNS reflexes that are present in a healthy infant but are absent in a neurologically intact adult.

Normally disappear within the 1st year of life

These primitive reflexes are inhibited by a mature/developing frontal lobe

they may remerge in adults following frontal lobe lesions -> loss of inhibition of these reflexes

Question 33

Moro reflex

Answer 33

Hang on for life reflex - abduct/extend the arms when startled and then draw together

Question 34

Rooting Reflex

Answer 34

Movement of head toward one side if cheek or mouth is stroked (nipple seeking)

Question 35

Sucking reflex

Answer 35

Sucking response when roof of mouth is touched

Question 36

Plantar reflex

Answer 36

Dorsiflexion of large toe and fanning of other toes with plantar stimulation

(Babinski Sign) presence of this in an adult may signify UMN lesion

Question 37

Galant Reflex

Answer 37

Stroking along one side of the spine while newborn is in ventral suspension (face down) causes lateral flexion of lower body toward the stimulated side