Anatomy of the Spinal Cord
What is the functional unit of the nervous system used for involuntary and stereotyped responses?
The reflex arc
Which type of motor neuron is responsible for the actual generation of force and muscle contraction?
Alpha (α) motor neurons.
What is the clinical name for the stretch reflex?
The myotatic reflex
Where is the Golgi tendon organ specifically located?
In the tendon, specifically at the interface between muscle fibers and the tendon (musculotendinous junction).
What type of stimulus triggers a flexor reflex?
A painful (nociceptive) stimulus, such as a pinprick or heat.
What is the name of the deep groove located on the anterior (front) midline of the spinal cord?
The anterior median fissure.
What is the primary function of Gamma (γ) motor neurons?
Regulation of sensory sensitivity and maintenance of muscle tone.
Which receptor in the muscle belly detects changes in muscle length and the rate of that change?
The muscle spindle
What is the primary physical property that the Golgi tendon organ measures?
The amount of tension or force exerted on a tendon.
On the Wexler reflex scale, what does a grade of 2+ represent?
An active/normal, healthy baseline response
Where are the cell bodies of sensory neurons located before their axons enter the spinal cord via the dorsal root?
In the dorsal root ganglion
How do Alpha and Gamma motor neurons differ in terms of their conduction velocity?
Alpha neurons are very fast (70–120 m/s), while Gamma neurons are slow (10–30 m/s).
Why is the stretch reflex categorized as a monosynaptic reflex?
Because the sensory fiber forms a direct synapse with the alpha motor neuron in the spinal cord without an interneuron.
Which specific sensory fiber carries information from the Golgi tendon organ to the spinal cord?
Type Ib afferent fibers.
What is reciprocal inhibition in the context of the flexor reflex?
The process where flexor muscles are excited to withdraw the limb while extensor muscles on the same side are inhibited
According to the external anatomy diagram, what are the two specific grooves located on the posterior side of the spinal cord?
The posterolateral sulcus and the posterior median fissure.
What specific type of muscle fibers do Alpha motor neurons innervate compared to Gamma motor neurons?
Alpha neurons innervate extrafusal muscle fibers (the actual muscle mass), while Gamma neurons innervate intrafusal muscle fibers (inside the muscle spindle).
When a muscle is stretched suddenly, the signal from the Ia sensory fiber splits into two branches. Where does "Branch A" travel?
It travels to the brain and cerebellum for informational purposes.
What is the role of the inhibitory interneuron in the Golgi tendon reflex?
It blocks (inhibits) the alpha motor neuron, causing the muscle to relax to prevent damage.
Describe the timing and function of the crossed extensor reflex.
It occurs 0.2–0.5 seconds after the flexor reflex; the opposite limb extends to push the body away from danger.
Based on the internal anatomy of the spinal cord, which specific cells are identified as receiving input from the sensory root before the signal reaches the motor neurons?
Solitary cells and external basal cells.
From which specific areas of the central nervous system do Gamma motor neurons primarily receive their activation?
The bulboreticular formation of the brainstem and the cortex
Why does the central region of an intrafusal fiber act as a receptor zone rather than contracting?
Because the central region has no contractile filaments, causing it to stretch and signal length changes when the muscle lengthens.
Contrast the "reflex" type of the muscle spindle versus the Golgi tendon organ.
The muscle spindle reflex is excitatory (causes contraction), while the Golgi tendon reflex is inhibitory (causes relaxation).
If a patient exhibits a reflex grade of 4+ with clonus, what is the clinical interpretation?
A definitive upper motor neuron (UMN) lesion, indicating the brain is not "braking" the reflex.