Neuroscience Week 3: Muscle Stretch Reflex Flashcards
Muscle Stretch Reflex AKA
4 Listed
- Monosynaptic Reflex
- Myotactic reflex
- Deep Tendon Reflex
- Tendon Jerk
Muscle Stretch Reflex Description
An automatic monosynaptic reflex that involves a muscle and tendon, and produces a jerk response
Muscle Stretch Reflex Key Mediators
5 Listed
- Muscle Spindles
- Spinal Neurons
- Muscle Fibers
- Interneurons
- Golgi Tendon Organs
Innervation Ratio of Large muscle Group
1 motor neuron - 1,000 muscle fibers
Innervation Ratio of Small Muscle Group
1 motor neuron - <10 Muscle Fibers
Interneurons AKA
Renshaw Cell
Knee Extensor Reflex: Activation
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.
Biceps Reflex Nerves Roots
C5, C6
Triceps Reflex Nerve Roots
C7, C8
Patella Reflex Nerve Roots
L2 - L4
Achilles Reflex Nerve Roots
S1, S2
Renshaw Cell acts through this neurotransmitter
Inhibitory neurotransmitter Glycine
Flexion-Crossed Extension Reflex
Plantar stimulation causes in the stimulated leg
- Ankle flexion
- Knee flexion
- Hip flexion
In the unaffected leg
- Ankle extension
- Knee extension
- Hip extension
Triple flexor Reflex in comatose patients
presence of the triple flexor reflex to plantar stimulation is a sign to disinhibition and is akin to the Babinski sign
Golgi Tendon Organ uses what type of neuron
Type 1b sensory nerve
Muscle spindle uses what type of neuron?
Type 1a sensory nerve
Knee extensor reflex: Termination
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.
Neurobiological influences on the relaxation of muscle contraction
- 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.
Woltman’s sign
delay in the relaxation phase of the muscle stretch reflex (can be caused by symptomatic hypothyroidism)
Key mediators of Muscle Stretch Reflex: Muscle Spindles
Activate via muscle stretch
Key mediators of Muscle Stretch Reflex: Spinal Neurons
which receive sensory input and generate motor output.
Key mediators of Muscle Stretch Reflex: Muscle Fibers
Which contract
Key mediators of Muscle Stretch Reflex: Interneurons
which modulate neuronal firing
Key mediators of Muscle Stretch Reflex: Golgi Tendon Organs
Which activate via muscle contraction to terminate the reflex
Knee extensor reflex: Interneuronal Inhibition
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.
Achilles Reflex Nerve Roots
S1 , S2 “buckle my shoe”
Patellar Reflex Nerve Roots
L3, L4 “Kick the door”
Biceps and Brachoradialis Reflex Nerve Roots
C5, C6 “Pick up sticks”
Triceps Reflex Nerve Roots
C7, C8 “lay them straight”
Cremasteric Reflex Nerve Roots
L1, L2 “Testicles move”
Anal wink Reflex Nerve Roots
S3, S4 “Winks galore”
Primitive Reflexes Description
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
Moro reflex
Hang on for life reflex - abduct/extend the arms when startled and then draw together
Rooting Reflex
Movement of head toward one side if cheek or mouth is stroked (nipple seeking)
Sucking reflex
Sucking response when roof of mouth is touched
Plantar reflex
Dorsiflexion of large toe and fanning of other toes with plantar stimulation
(Babinski Sign) presence of this in an adult may signify UMN lesion
Galant Reflex
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
