Question

What is a quick description of the Achilles tendon reflex, naming the sensory neurons, motor neurons and muscles involved?

Answer 1

Achilles tendon reflex also known as ankle jerk reflex, is a type of the stretch reflex. In this, the foot is made slightly everted and dorsiflexed. Then strike is made on the Achilles tendon. This causes plantar flexion of the foot.

This is a monosynaptic reflex.

Stimulus that evokes this response is stretched to the Achilles tendon (muscle-Gastrocnemius).

Reaction time (time between the application of the stimulus and the response for the reflex) is 19-24 milliseconds.

AFFERENT LIMB:-

• Receptor is the muscle spindle. As a sensory receptor, the muscle spindle can detect the degree and rate of muscle stretch.
• Afferent nerve. Two types of nerve fibres- Group Ia and II fibres supply the muscle spindle. The afferent nerve fibres emerging from the muscle spindle travel around the spinal nerve and enter the spinal cord through the dorsal root and send the branches to every Alpha motor neuron that goes to the muscle from which the Is originated.

CENTRE

Centre for Achilles tendon reflex is the ventral grey horn area where the afferent nerve ends and synapses directly with the Alpha motor neuron. Thus, alpha motor neuron is the final common pathway, serving as both integrating centre and efferent pathway.

EFFERENT LIMB

• Efferent nerve. The axons of alpha motor neurons form the efferent nerve fibres which leave the spinal cord through the ventral root and supply the skeletal muscle fibres. (S1 and S2 segments of spinal cord).
• Effector organ is the gastrocnemius muscle which contracts and cause plantar flexion of the foot and also reciprocal inhibition is received by the extensor muscles.