Nervous System Physiology Part 8 Flashcards
Where are anterior motor neurons located?
In the anterior horns of the spinal cord gray matter.
What are the two types of anterior motor neurons?
Alpha motor neurons and gamma motor neurons.
What do alpha motor neurons innervate?
Extrafusal muscle fibers.
What do gamma motor neurons innervate?
Intrafusal muscle fibers.
What are muscle spindles?
Encapsulated muscle fibers scattered throughout striated muscle.
How do anterior motor neurons compare in size to other neurons?
They are 50 to 100 percent larger.
What is the function of the ventral horn in the spinal cord?
It contains motor neurons responsible for movement.
What do alpha (α) motor neurons innervate?
Extrafusal skeletal muscle fibers.
What is a motor unit?
An alpha motor neuron and the muscle fibers that it innervates.
Why are alpha motor neurons called the “final common pathway” out of Central Nervous System ?
Because all neural influences on skeletal muscle converge on them, and they are the only route through which the CNS can affect skeletal muscle.
What do gamma (γ) motor neurons innervate?
Specialized intrafusal muscle fibers, which are part of muscle spindles.
What is the function of the muscle spindle?
To sense muscle length.
What is the function of gamma motor neurons?
To adjust the sensitivity of the muscle spindles.
What do gamma (γ) motor neurons innervate?
The polar regions of intrafusal fibers
What happens when gamma motor neurons are activated?
The central receptor region of the intrafusal fibers is stretched.
Where are muscle spindles located?
Throughout the belly of the muscle.
What do muscle spindles do?
They send information to the nervous system about muscle length or rate of change of length.
What is alpha-gamma coactivation
The simultaneous activation of gamma and alpha motor neurons to maintain tension in the muscle spindle during contraction.
Why is alpha-gamma coactivation important?
: It prevents the central region of the muscle spindle from going slack during a shortening contraction, allowing continued sensory feedback.
Where are Golgi tendon organs located?
: In the muscle tendons near their junction with the muscle.
What do Golgi tendon organs detect?
Tendon tension or the rate of change of tension.
What wraps around the collagen bundles in tendons?
Afferent nerve fibers from Golgi tendon organs.
What activates the Golgi tendon organs?
Tension from muscle stretching or contraction that straightens collagen bundles and distorts receptor endings.
When is the tendon stretched more: active contraction or passive stretch?
Tendon is stretched more during active contraction of the muscle.
What are spinal reflexes?
Somatic reflexes mediated by the spinal cord, often without higher brain involvement.
Name the three types of spinal reflexes.
1.The Stretch Reflex
2. The Tendon Reflex
3. The Withdrawal Reflex and Crossed-extensor Reflex
How do Golgi tendon organs work?
Afferent nerve endings wrap around collagen bundles; when tension is applied, the collagen straightens and distorts the endings, activating the receptors.
Does the brain play any role in spinal reflexes?
Yes, the brain is “advised” of most spinal reflex activity and can facilitate, inhibit, or adapt it.
What triggers the stretch reflex?
Stretching of muscle spindles activates sensory neurons, which send signals to the spinal cord.
What happens when sensory neurons of the stretch reflex reach the spinal cord?
They synapse with motor neurons that excite the extrafusal muscle fibers of the stretched muscle, causing contraction.
What is the function of the stretch reflex?
: It causes reflexive muscle contraction to resist further stretching.
What initiates the knee-jerk reflex?
Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles.
What does a positive knee-jerk reflex indicate?
That sensory and motor pathways between the muscle and spinal cord are intact and it shows spinal cord excitability.
What happens during the knee-jerk reflex after the quadriceps are stretched?
Afferent impulses travel to the spinal cord.
2. Motor neurons send activating impulses to quadriceps (causing contraction).
3. Interneurons inhibit motor neurons to hamstrings (preventing resistance to movement).
How does the state of spinal motor neurons affect the reflex response?
Highly facilitated neurons cause a strong reflex, while high inhibitory input may prevent the reflex entirely.
