L59. Reflexes

Question 1

Reflexes are involuntary movements controlled by which nerves?

Answer 1

Spinal nerves and cranial nerves

Question 2

Give the basic motor pathway:

________ -> ___________ -> ___________

Answer 2

Motor cortex -> Brainstem/spinal cord -> muscle

Question 3

Which 2 regions activate motor neurons?

Answer 3

Brain regions (cortex)
Peripheral receptors (reflexes)

Question 4

Give the motor pathway for reflexes

Answer 4

Receptor reflexes -> brainstem/spinal cord -> muscle

Question 5

Which section of the spinal cord in grey matter?

Answer 5

Inner portion of spinal cord is grey matter.

Question 6

Which portion of the spinal cord is white matter?

Answer 6

Outer portion of the spinal cord is white matter.

Question 7

Describe the position and shape of the dorsal horn.

Answer 7

The dorsal horn is at the back and is thinner.

Question 8

Describe the location and shape of the intermediate horn.

Answer 8

The intermediate horn sits in between the dorsal and ventral horn.

Question 9

Describe the position and location of the ventral horn.

Answer 9

The ventral horn is at the front and is thicker than the dorsal horn.

Question 10

Where do sensory afferents travel to?

Answer 10

Dorsal horn

Question 11

Ventral signals travel via _______ _____________.

Answer 11

Motor efferents

Question 12

Name the 2 types of somatic reflexes.

Answer 12

Tendon - jerk

Cutaneous reflex

Question 13

Give the path of a monosynaptic reflex arc.

Answer 13

Arrow 1 : Receptor to Ventral horn (via dorsal horn)
SYNAPSE 1
Arrow 2 : Ventral horn to effector

Question 14

Fill in the following for a reflex pathway :

1. Hammer tap to muscle
2. ___________________________________
3. Action potentials are _________________________________________
4. Monosynaptic activation of motor neurons
5. Axon potentials ________________________________________
6. Muscles contract

Answer 14

1. Hammer tap to muscle
2. Muscle spindles stretch
3. Action potentials are conducted along group 1a muscle afferents to the brainstem.
4. Monosynaptic activation of motor neurons
5. Axon potentials travel along A-alpha motor axon.
6. Muscles contract

Question 15

Describe the anatomical benefit of the reflex pathway.

Answer 15

A digestive aid, eg gag reflex.

Question 16

Describe the route of a disynaptic pathway.

Answer 16

Stimulus receptor to dorsal horn
SYNAPSE
Dorsal horn to ventral horn (interneuron)
SYNAPSE
Ventral horn to muscle effector

Question 17

During muscle loading, how is the receptor activated?

Answer 17

Stretch and contraction

Question 18

Describe the anatomy behind muscle loading reflexes, and why this is of benefit.

Answer 18

Afferent signals cause the inhibition of motor neuron activation.

• > inverse stretch reflex
• > Group 1b muscle afferents

This prevents the overloading of muscles.

Question 19

Biting force is controlled by load. Describe the effect of the muscle loading reflex on jaw muscles.

Answer 19

When hit, afferents inhibit jaw elevator muscle motor neurons (so jaw opens slightly to counteract the load)

Question 20

Describe how the pharyngeal reflex is activated.

Answer 20

Activated by mechanoreceptor afferents in the posterior part of the tongue / soft palate.

Question 21

Describe the path from stimulus to gag reflex.

Answer 21

Stimulus for gag reflex
->
Lower medulla
->
Upper medulla
->
Bilateral contraction of posterior oral and pharyngeal muscles.

Question 22

Describe what onsets a salivary stimulus.

Answer 22

Gustatory (taste)

chewing forces