Download muscle spindles

Muscle Excitation-Contraction
• 1)Action Potential in Motor
Axon
• 2) End Plate Potential at
Neuromuscular Junction
• 3) Action Potential in Muscle
Fiber.
• 4) The AP induces, after a small
latency, a twitch in the muscle
fiber
• Twitch - transient all-or-none
contraction
1. spindle stretch activates sensory neuron.
2. sensory neuron synapses on ventral cord
motor neurons and interneurons
3. increase in motor neuron activity
innervates same and synergistic muscles.
4. inhibits motor neurons that innervate
antagonistic muscles
Stretch reflex
Types of motor neurons
• a motor neurons- innervate the extrafusal muscle
fibers that generate the forces needed for
movement and posture.
• g motor neurons - innervate muscle spindles in
intrafusal muscle fibers. These fibers regulate the
sensory input from spindles by setting the muscle
fibers to an appropriate length.
g motor Neuron Activity Affects Reponses of Muscle Spindles
Gamma neurons
regulate excitation
of spindles so they
can activate the
muscle indirectly
through the stretch
reflex.
Golgi tendon organ
• Encapsulated afferent nerve endings located at the junction of
the muscle and tendon.
• Fire when muscle contracts and are less sensitive (not
completely insensitive) to passive stretch of the muscle.
• axons from Golgi tendon organs inhibit neurons in the spinal
cord that synapse with the a motor neurons that innervate
the same muscle.
• Helps prevent fatigue
• Protects muscle from large forces
• Maintains steady level of muscle force
Golgi Tendon Organs
Comparison of the Function of Muscle
Spindles and Golgi Tendon Organs
Comparison of the Function of Muscle
Spindles and Golgi Tendon Organs
Negative Feedback Regulation of Muscle Tension By Golgi
Tendon Organs
Negative feedback by
Golgi tendon organs
When muscle contracts, feedback
inhibits additional contractions –
prevents damage and fatigue.
Flexion reflex
• Reflexes that compensate posture when one withdraws
from pain.
• involves several synaptic links
• excitation of nociceptor leads to ipsilateral and
contralateral responses.
• flexion reflex. Stimulation of cutaneous receptors in
the foot leads to activation of spinal cord local circuits
that withdrawal stimulated (pained) side and extend
other side to provide compensatory support.
Spinal Cord Circuitry Responsible for the
Flexion Reflex