Peripheral nerves and dermatomes

Question 1

What are the 2 groups that peripheral neves can be grouped into according to their function? Briefly describe them

Answer 1

Sensory neurons - free nerve endings detect sensory information in skin and axon relays this to the CNS
Motor neurons - axons send information out of CNS to the muscles

Question 2

How many cranial nerves are there?

Answer 2

12

Question 3

how many pairs of spinal nerves are there and how are they organised?

Answer 3

31
Cervical: 8
Thoracic: 12
Lumbar: 5
Sacral: 5
Coccygeal: 1

Question 4

What does one spinal segment give rise to?

Answer 4

a pair of spinal nerves

Question 5

What are the roles of the dorsal and ventral horns and where do they lie in relation to each other?

Answer 5

Dorsal: receives sensory information (POSterior)
Ventral: sends out motor output (anterior)

Question 6

What are grey and white matter made up of?

Answer 6

grey: nerve cell bodies
white: nerve cell axons

Question 7

What do pairs of spinal nerves fuse together to form?

Answer 7

A Plexus

Question 8

Describe the organisation of a perisperhal nerve

Answer 8

Axons are surrounded by a myelin sheath - which consists of several concentric layers of membrane.
A layer of connective tissue called the endoneurium surrounds axons and they bundle together to form a fascicle. Each fascicle is surrounded by a perineurium.
Bundles of fascicles are surrounded by a tough connective tissue called epineurium.

Question 9

What is the difference in roles of myelinated and unmyelinated axons?

Answer 9

Myelinated: involved in perception of touch, vibrations, cause muscle contractions

Unmyelinated: involved in perception of temperature and pain

Question 10

What type of peripheral neurones are sensory afferents?

Answer 10

Pseudo-unipolar cells

Question 11

What are the receptors called that are involved in detection of pain?

Answer 11

Nocicepters

Question 12

Describe the process of sensory fibre input

Answer 12

Skin stimulated
Action potential generated
AP is conducted centrally via dorsal root and terminates in the dorsal horn

Question 13

Describe the process of motor fibre output

Answer 13

Cell bodies are in the ventral part of the spinal cord
Axons project out and exit the spinal cord via ventral roots.
Axons ultimately terminate in the target muscles

Question 14

Where do the sensory cell bodies collect?

Answer 14

Dorsal root ganglia

Question 15

Define a myotome

Answer 15

Muscle groups supplied by distinct spinal cord segments and they corresponding spinal nerves

Question 16

Define a dermatome

Answer 16

Area of skin innervated by a distinct spinal cord segment and its corresponding spinal nerve

Question 17

What is the ASIA scale used to do?

Answer 17

To evaluate the extent and level of spinal cord injury

Question 18

BY what methods does the ASIA scale assess the severity and level of spinal cord injury

Answer 18

Assessing reflex and voluntary movement

Question 19

Define proprioception

Answer 19

Awareness of where body is in 3D space

Question 20

In what two senses can there be proprioception?

Answer 20

Movement sense: awareness of joint movement

Position sense: awareness of static joint position

Question 21

Describe the pathway for voluntary movement

Answer 21

Upper motor neurons sit in the motor cortex of Brain
Axons of UMNs project through the white matter of spinal cord to target lower motor neurons.

LMNs sit in the ventral (anterior) horn of grey matter. Their axons exit the spinal cord through dorsal roots and target muscle groups.

Question 22

How does the pathway for voluntary and reflex movement differ? Describe the pathway for reflex movement.

Answer 22

Reflex does not have an upper motor neuron component.

Reflex has 2 parts:
Lower motor neuron
Sensory inputs which originate from the same muscle group

The lower motor neuron innervates the muscle and causes it to contract. The sensory fibre which originates in the same muscle has an axon that projects along the same peripheral nerve. THE SENSORY FIBRE INNERVATES THE SAME MOTOR Neuron the caused it to contract.

Question 23

List some potential contributors to proprioceptive sensations

Answer 23

Ruffini endings in skin and joints
Muscle spindles (sensory ending in muscles) 
Tendon organs