FINISH lecture 21 - nervous system1: skin sensation

Question 1

what is the somatosensory system?

Answer 1

the neural sense concerned with body sensations

Question 2

what are the 3 divisions of the somatosensory system?

Answer 2

cutaneous (skin) sensations

visceral - internal organs and deep tissues

proprioception - position of the limbs and body in space
• without it movement is impossible

Question 3

functions of the somatosensory system

Answer 3

recognition - perception doesn’t always correspond to reality

exploration - control of movement

communication - close, social and intimate

Question 4

why do all sensory systems require receptors?

Answer 4

to convert stimulus energy

converted into a receptor/generator potential

size depends on stimulus strength

isn’t an AP as its graded

Question 5

what happens when a receptor potential exceeds threshold?

Answer 5

nerve fibres fire an AP

stimulus strength coded by firing rate or by pattern of firing

this is called sensory transduction

Question 6

where can cutaneous receptors be found?

Answer 6

in the skin - eg. hair receptors

underneath the skin:
• superficial - just below the epidermis
• deep - in subcutaneous fat

some have capsules around them but some of them are free nerve endings

Question 7

superficial cutaneous receptors

Answer 7

• Merkels disk
• epidermal-dermal border
• free nerve endings
• Meissners corpuscle

Merkels disk and Meissners corpuscle are capsulated receptors

Question 8

deep cutaneous receptors

Answer 8

• pacinian corpuscle

* Ruffinis corpuscle

Question 9

how are cutaneous receptors distinguished?

Answer 9

• appearance
• location - deep or superficial
• size of receptive fields
• physiological properties - rapidly or slow adapting

Question 10

what fibres are associated with cutaneous receptors?

Answer 10

served either by:
• large (A-beta) myelinated fibres
• small (A-delta) myelinated fibres

C fibres are unmyelinated fibres

Question 11

what is a receptive field?

Answer 11

area of skin over which a stimulus activates a single nerve fibre

Question 12

what are anerve fibres?

Answer 12

a bundle of nerve fibres

Question 13

how do receptive fields differ in cutaneous receptors?

Answer 13

Meissners corpuscle and Merkels disk have feil small receptive fields

pacinian corpuscle has large receptive field

Ruffinis corpuscle prefers movement across the receptive field in a certain way

deep receptors have larger receptive fields

Question 14

what is receptor adaptation?

Answer 14

when sensory receptors change their sensitivity to a stimulus

you get slow and rapidly adapting receptors

Question 15

slowly adapting receptors

Answer 15

tonic receptors

when you apply stimulus, you initially get a generator response that is maintained

maintained firing of AP throughout duration of stimulus

Question 16

rapidly adapting receptors

Answer 16

phasic receptors

AP at onset and offset of stimulus but no other

highlights when the stimulus changes - important for detecting threats and opportunities

Question 17

why is rapidly adapting receptors more useful?

Answer 17

only processes the start and the end of the stimulus

this reduces computational load

doesn’t use as much energy

Question 18

temperature receptors

Answer 18

warm - free nerve endings
• C fibres: unmyelinated

cold - free nerve endings
• A-delta fibres

detect temperature in discrete spots - cold sensation only felt at specific locations

Question 19

noxious receptors

Answer 19

respond to noxious or painful stimuli

• mechanical - crushing, pricking
• thermal - painfully hot or cold

small unmyelinated fibres (A-delta): first pain - initial sharp sensation

unmyelinated C fibres: second pain - nagging pain that follows first pain

Question 20

what cutaneous receptors are slow adapting?

Answer 20

Ruffini

Merkel

Question 21

what cutaneous receptors are fast adapting?

Answer 21

Meissner
Pacinian
hair follicles

Question 22

rapid adaptation of the pacinian corpuscle

Answer 22

depends on its mechanical properties - comes from the capsule around the nerve fibre

capsule present - rapid adaptation of receptor potential

capsule removed - much less adaptation of receptor potential

Question 23

what 2 pathways transmit somatosensory information in the spinal cord?

Answer 23

dorsal column

spinothalamic pathways

Question 24

what are the 2 components of the spinal cord?

Answer 24

grey matter - butterfly shape and made of neurones

white matter - consists of nerve fibres covered in myelin
• fattiness gives the white colour