What is the sensory (afferent) root also known as?
Dorsal root
The dorsal root enters the gray matter of the spinal cord.
What type of neurons do some afferents synapse directly on?
Interneurons
Interneurons can connect to motor neurons or ascend to higher centers.
What is the function of the motor (efferent) root?
Carries output to muscle
The motor root is also referred to as the ventral root.
What do alpha motor neurons innervate?
Extrafusal fibers
Alpha motor neurons are responsible for main skeletal muscle contraction.
What do gamma motor neurons innervate?
Intrafusal fibers of muscle spindles
Gamma motor neurons maintain muscle tone and spindle sensitivity.
What is the role of gamma-dynamic (γd) motor neurons?
Respond to rate of stretch
These are a subtype of gamma motor neurons.
What do muscle spindles detect?
Muscle length & rate of change
Muscle spindles contain primary (Ia) and secondary (II) afferents.
What is the function of Golgi tendon organs (GTOs)?
Detect tension & rate of tension change in tendons
GTOs inhibit contraction of overstressed muscles to prevent damage.
What is the stretch reflex also known as?
Myotatic reflex
This reflex helps provide smooth contraction and posture stability.
What occurs during reciprocal inhibition?
Agonist contracts, antagonist is inhibited
This mechanism helps coordinate muscle actions.
What triggers the flexor (withdrawal) reflex?
Pain stimulus
This reflex involves interneurons that excite flexors and inhibit extensors.
What is the crossed extensor reflex?
Pain in one limb causes contralateral extension
This supports body weight during the withdrawal reflex.
What do postural/locomotor reflexes help with?
Maintain balance
These reflexes are largely mediated by the spinal cord.
What is the scratch reflex triggered by?
Localized cutaneous stimulation
This reflex results in rhythmic scratching.
What causes muscle cramps?
Local irritation leading to reflex contraction
This creates a positive feedback contraction through spindle/GTO signals.
What is the difference in function between alpha and gamma motor neurons?
Alpha = extrafusal contraction, Gamma = intrafusal tone
This distinction is crucial for understanding muscle control.
Fill in the blank: Spindles sense _______ while GTOs sense tension.
Length
Spindles and GTOs play different roles in muscle sensing.
List the types of reflexes mentioned.
- Stretch reflex
- Withdrawal reflex
- Crossed extensor reflex
- Postural reflex
- Stepping reflex
- Scratch reflex
These reflexes serve various functions in muscle response.
True or False: Cramps and spasms are pathologic positive feedback reflex loops.
True
These conditions result from abnormal reflex activity.
Where are spinal reflexes processed?
In the spinal cord—they do not require brain or brainstem input.
What is the basic spinal reflex pathway?
Sensory input enters the dorsal horn → may synapse on interneurons → motor output exits via the ventral horn.
Where are alpha motor neuron cell bodies located?
In the anterior horn of the spinal cord gray matter.
What is the role of interneurons in reflexes?
They connect sensory and motor neurons and can be excitatory or inhibitory; some reflexes are monosynaptic and don’t need them.
What are the four main spinal reflex types?
Stretch reflex, tendon (Golgi tendon) reflex, withdrawal (flexor) reflex, and crossed extensor reflex.
