Simple reflexes

Question 1

Neural reflexes

Answer 1

Stereotyped, involuntary reactions of the CNS to specific sensory input. Produce a rapid response, without conscious thought. They may be somatic (skeletal muscles) or autonomic (smooth muscles/glands).

Question 2

Example of an autonomic reflex

Answer 2

Pupillary reflex

Question 3

Example of a somatic reflex

Answer 3

Deep tendon reflex

Question 4

Function of reflexes

Answer 4

1) protection eg. limb withdrawal, cough reflex, skeletal muscle damage
2) postural control eg. walking
3) homeostasis eg. blood pressure

1 and 2 are mainly SNS reflexes, while 3 are mainly ANS reflexes.

Question 5

Reflex arc

Answer 5

sensory receptor–>afferent–>integration (CNS)–>efferent–>effector

Question 6

Integration

Answer 6

Interneurones are found in the CNS (or enteric NS) and integrate information by adjusting the inputs and outputs of the reflex arc.

Question 7

Simple stretch reflexes (myotatic)

Answer 7

Control posture by adjusting the degree of skeletal muscle contraction. Proprioceptors monitor the state and position of muscles and joints, and can be:

• muscle spindles
• golgi tendon organs

Question 8

Muscle spindles

Answer 8

Specialised sets of skeletal muscle fibres, innervated by myelinated sensory (afferent) neurones whose axons wrap around the spindle. They synapse directly with lower motor (efferent) neurones in the spinal cord (monosynaptic).

Question 9

Knee jerk reflex

Answer 9

Antagonistic muscle pairs react differently to the same stimulus, communicated by a single sensory neurone. In the knee jerk reflex, one a-motoneurone excites the quadricep muscle causing contraction, while another a-motoneurone inhibits the hamstring, causing relaxation.

Question 10

Golgi tendon organs

Answer 10

Sensory neurone endings within tendons, which detect the stretching of collagen fibres. When the golgi tendon organs are compressed, the sensory neurone is activated, depolarising an interneurone within the CNS (polysynaptic) which inhibits the related motor neurone.

Question 11

Crossed extensor reflex

Answer 11

Involves the integration of information carried by one sensory neurone to multiple excitatory and inhibitory interneurones within the CNS. A stimulus detected on one side of the body can translate into a response on the other/both sides, as the neural circuity crosses over within the brain or spinal cord.