Spinal Reflexes

Question 1

Define reflex

Answer 1

rapid (synapses involved), involuntary, yet stereotyped (suggesting simple underlying circuitry) and co-ordinated response to a sensory stimulus
Usually involve muscle contraction (can include glandular response)

Extensor muscle - causing limb to extend
Flexor muscle - causing limb to flex/bend

Question 2

Relate the structure of the spinal cord to physiological reflexes.

Answer 2

Reflexes are mediated by the spinal cord
spinal cord organised so reflexes can be elicited from specific segments of the cord, which are responsible for controlling different parts of the body

When a muscle is stretched, sensory neurons in the muscle spindle within the muscle send a signal to the spinal cord. The sensory neuron synapses with a motor neuron in the spinal cord, which in turn stimulates the muscle to contract, causing the limb to move

Somatic reflexes also called spinal reflexes

Question 3

Differentiate between spinal and cranial reflexes, and between mono- and poly-synaptic reflexes.

Answer 3

Spinal reflexes occur within the spinal cord and involve the processing of sensory information and motor responses. These reflexes are typically simple and fast, and do not involve conscious control

Cranial reflexes occur in the brainstem and involve the processing of sensory information and motor responses. These reflexes are often more complex and may involve conscious control.

Mono-synaptic reflexes involve a single synapse between the sensory and motor neurons
Poly-synaptic reflexes involve multiple synapses and interneurons

Question 4

Give examples of each type of reflex.

Answer 4

Monosynaptic reflex & spinal reflex
E.g. knee-jerk reflex

Polysynaptic reflex
E.g. touching a hot stove

Crossed extensor reflex
E.g. stepping on a nail with the left food, the body shifts weight to the right

Cranial reflex
E.g. gag reflex

Question 5

Note how simple reflexes may be used in behaviours such as locomotion.

Answer 5

In individual limbs, extensors and flexors are alternatively activated

Activity of these muscles in different limbs is also coordinated between the limbs so legs alternate

Presence of local circuits that can generate the pattern of alternating flexion and extension implied as this activity continues even if spinal cord connections to the brain are severed = known as central pattern generators

Critical feature of the cellular basis of pattern generators is that there is inhibition across the midline

A molecule that can directly detect body movement is a critical part of proprioception