Overview of the PNS

Question 1

What does the PNS consist of?

Answer 1

sensory and motor nerves from endings in skin/ muscle to point where they enter/ leave the spinal cord

Question 2

Where do motor nerve fibres arise from?

Answer 2

Cell bodies in spinal cord

Question 3

How is the spinal cord protected?

Answer 3

Protected in spinal canal. lamina bone laterally and spinous process dorsally.

Question 4

where do sensory neruones from peripheral nerves enter spinal cord?

Answer 4

dorsal root

Question 5

where are sensory cell bodies located?

Answer 5

outside the spinal cord in their dorsal root ganglion

Question 6

where do motor neurones exit the spinal cord?

Answer 6

ventral root

Question 7

where are motor cell bodies located?

Answer 7

grey matter in ventral horn of spinal cord

Question 8

how are spinal nerves formed?

Answer 8

fusion of dorsal and ventral roots

Question 9

where are dorsal root ganglia located?

Answer 9

in the intervertebral foramina

Question 10

how is oxygen supplied to peripheral nerves?

Answer 10

peripheral nerves have arteries within them which are branches of spinal cord arteries

Question 11

one peripheral nerve arises from _____ spinal root(s)

Answer 11

at least 2

Question 12

one root contributes to ______ peripheral nerve(s)

Answer 12

at least 2

Question 13

define dermatome

Answer 13

area of skin innervated by spinal nerve or corresponding dorsal root

Question 14

what is meant by lower motor neurone?

Answer 14

motor nerve cells which connect with skeletal muscle

Question 15

where are the cell bodies of lower motor neurons, and where do their axons project?

Answer 15

cell bodies in ventral horn

axons project out ventral root and down peripheral nerve to synapse with skeletal muscle fibres

Question 16

how many axons emerge from lower motor neuron cell body?

Answer 16

one

Question 17

define endoneurium

Answer 17

thin, protective membrane that surround individual nerve fibres

Question 18

define nerve fascicle

Answer 18

groups of functionally related nerve fibres collected together

Question 19

what surround nerve fascicle?

Answer 19

perineurium

Question 20

what does a whole peripheral nerve made up of?

Answer 20

several fascicles bundled together with blood vessels, all surrounded by epineurium

Question 21

where are the majority of skin receptors found?

Answer 21

epidermal-dermal junction

Question 22

describe the type of receptors found of glabrous skin

Answer 22

variety of receptors that respond to pressure, light touch, vibration

Question 23

describe type of receptors found on hairy skin

Answer 23

hair follicle receptors that respond to hair displacement

Question 24

how are non-voltage gated sodium channels opened on the end of sensory nerves?

Answer 24

mechanical bending

Question 25

how is action potential initiated in sensory nerve fibres (4)

Answer 25

opening of non voltage gated sodium channels produces depolarisation called receptor potential.
this causes current to flow to first node
at first node, current raises potential so node becomes depolarised.
when there is significant depolarisation, action potential is initiated.

Question 26

where does the receptor potential generally generate first action potential in sensory nerve fibres?

Answer 26

the first node of Ranvier where regenerative sodium channels start to occur normally

Question 27

What is the effect of a higher intensity of stimulus?

Answer 27

higher frequency of action potentials

Question 28

define conduction velocity

Answer 28

speed with which an action potential travels along a nerve fibre

Question 29

what is equation for conduction velocity of myelinated fibres

Answer 29

CV= 6*diameter

Question 30

what is the equation for conduction velocity of unmyelinated fibres

Answer 30

CV=diameter (approx)

Question 31

Function of A-beta fibres?

Answer 31

form variety of specialised endings in skin

Question 32

Define encapsulated mechanoreceptors?

Answer 32

Connective tissue capsule surrounding A-beta fibres which tunes them to detect different types of mechanical stimulation

Question 33

What are Meissner’s corpuscles?

Answer 33

nerve endings in the skin that detect light touch- rapidly adapting receptors

Question 34

Where are meissner’s corpuscles most concentrated?

Answer 34

thick hairless skin such as finger pads

Question 35

What are Merkel receptors?

Answer 35

mechanoreceptors which give information on light pressure and position- slowly adapting receptors

Question 36

What are Pacinian corpuscles?

Answer 36

rapidly adapting mechanoreceptors that detect high frequency vibration of the skin

Question 37

What are Ruffini corpuscles

Answer 37

slowly adapting receptors that detect heavy pressure on the skin

Question 38

Define receptive field (RF)

Answer 38

area of skin that can activate a single sensory nerve fibre

Question 39

Why does damage to a single nerve fibre not render skin anaesthetic?

Answer 39

Because receptive fields on individual nerves overlap so each skin in part of at least 2 receptive fields

Question 40

Effect of smaller receptive fields? How can this be tested?

Answer 40

Better localisation of stimuli on the skin. Two point discrimination test

Question 41

What do you cal nerve endings without a capsule?

Answer 41

free nerve endings

Question 42

What do A-gamma and C fibres detect?

Answer 42

Both movement and chemical changes in the environement. Signal temperature and pain

Question 43

Describe what happens when a peripheral nerve is cut (4)

Answer 43

distal Shwann cells unwrap themselves and divide to form continuous line of cells
proximal cut ends of nerve fibres form growth cones and grow back down inside the sheaths guided by cell adhesion molecules
Shwann cells proliferate and wrap myelin around regenerating nerve fibres
with time, nerve fibres enlarge but may never reach original diameter