Somatosensory system

Question 1

What are the properties of primary sensory neurones?

Answer 1

all excitatory - Using glutamate

Ability to generate action potentials from free nerve endings

All their cell bodies are located in the dorsal root ganglion.

Question 2

What are the different classifications of primary sensory nerve fibres depending on their function?

Answer 2

A alpha
A beta
A delta
C

(in order of diameter largest-smallest and speed of conduction smallest - highest)

Question 3

What are A alpha afferent fibres used for?

Answer 3

Proprioceptors of skeletal muscles

Question 4

What are A beta afferent fibres used for?

Answer 4

Mechanoreceptors of skin

Question 5

What are A delta afferent fibres used for?

Answer 5

Pain/temperature

Question 6

What are C afferent fibres used for?

Answer 6

Temperature
Pain
Itch

Question 7

What are receptive field properties?

Answer 7

Axons have distinct receptive fields where each axon innervates a specific receptive field in its dermatome.

Question 8

What is a dermatome?

Answer 8

Area of skin innervated by nerve fibres from a single nerve

Question 9

What determines the size of a receptive field?

Answer 9

2 point discrimination

Receptive field sizes vary depending on the precision of localisation

Question 10

Why does the precision of sensory localisation vary greatly across the body?

Answer 10

Related to the area of the cerebral cortex devoted to each region.

Question 11

What is an adequate (prefered) stimulus?

Answer 11

The right stimulus for a neurone that will cause a response

Question 12

What are some general properties of sensory receptors?

Answer 12

Adequate stimulus depends on the nerve ending

Threshold for signal depends on the nerve ending

Firing rate is proportional to the stimulus strength.

Question 13

How is a signla transduced form sensory receptors?

Answer 13

The stimulus causes transduction channel opening.

Graded receptor potential if threshold is passed causing an action potential

Question 14

What are some adaptations of sensory receptors?

Answer 14

Phasic or tonic receptors

Question 15

What is a phasic receptor?

Answer 15

Fast adapting receptor:
Detects how fast a stimulus can change.
Therefore is useful when attntion to a stimulus is no longer required (such as wearing clothes)

Question 16

What is a tonic receptor?

Answer 16

Slow/non-adapting:
Stimulus is only detected whilst it is being maintained.
Important when maintaining information about a stimulus such as amount of pain.

Question 17

What are the major cutanous senory receptors?

Answer 17

Mechanorecepotrs - Touch/pressure/vibrations

Thermoreceptors - Hot/cold (temperature)

Nociceptors - Noxious stimuluation (pain)

Question 18

What are some properties of cutaneous mechanoreceptors?

Answer 18

A beta fibres - Detect tactile touch

nerve ending has specialised sensory apparatus (organ)

Apparatus comprises of a specialised cell - Structure determines function => function determines location.

Question 19

What are the 4 main types of mechanoreceptor and where are they found in the skin?

Answer 19

Foundin superficial skin layers:
Merkels Receptor
Meissners Corpuscles

Found in deeper skin layers:
Ruffinies’ corpuscle
Pacinian corpuscle

Question 20

What are the Meissners copruscles?

Answer 20

Found in papillary dermis
Rapidly adapting
Detect light touch and vibrations

Question 21

What would meissners corpuscles be used for?

Answer 21

Adjustment of grip whilst holding objects

Putting on clothes but not wearing them.

Question 22

What are merkels receptors?

Answer 22

High density in the epidermis of digits and around the mouth
Slow adapting
Detect sustained light touch
Apparatus is a specialised keratocyte
Perception of form and texture

Question 23

What are ruffinis’ corpuscles?

Answer 23

Respond to lateral movement or stretching of the skin
Detect deep touch
Apparatus is a netwokr of collagen fibres

Question 24

What are pacinian corpuscles?

Answer 24

Found in deep layers of the dermis
Rapidly adapting
detect deep touch and poke
Fully encapsulated nerve ending
Onion structure deforms on distortion.

Question 25

What are hair follicle receptors?

Answer 25

Detect light touch activation in the dermis
Rapidly adapting
Nerve fibre wrapped around hair
Hair deflection detected.

Question 26

What are cutaneous thermoreceptors?

Answer 26

Bare nerve endings
Slow adapting
Two types detecting either warming or cooling
Poor indicators of absolute temperature
sense of temp comes from comparison of signals

Question 27

What are thermoreceptor channels?

Answer 27

TRP (transient receptors)
non specific cation channels.
Nerve ending sensitivity depends on the transducer expressed

Question 28

What temperature do the TRPV3/4 channels open at?

Answer 28

Warm - channels open at 29-45 degrees

Question 29

What temperature do the TRPM8 channels open at?

Answer 29

Cold - Channels open at 8-38 degrees

Question 30

What temperature do the TRPA1 channels open at?

Answer 30

Cold - <17 degrees

Question 31

What are cutaneous nociceptors?

Answer 31

Bare nerve endings
Non adapting - high threshold
Require an adequate stimulus capable of damaging tissue.

Question 32

What is proprioception?

Answer 32

Sense of 3D dimensions of the body

Detection of the mechanical status of the musculoskeletal system

Question 33

What do proprioceptors detect?

Answer 33

Joint position
Muscle length
Muscle movement
Acceleration
Tension/force
Simple reflexes

Question 34

What are the 2 proprioceptors found in muscles?

Answer 34

Muscle spindle

Golgi tendon organ

Question 35

What does the muscle spindle detect?

Answer 35

Length and acceleration of muscle

Stretch sensitive

Question 36

What fibres are found in the muscle spindle?

Answer 36

Groups of A delta afferents wrapped around a central sensory portion

Question 37

What does the golgi tendon organ detect?

Answer 37

Muscle tension
Located at the junction of muscles and tendons
Sensitive to tension generated by contraction

Question 38

What are the fibres found in the golgi tendon organ?

Answer 38

Innervated by the A beta afferents

Question 39

What sensory fibres are found in the dorsocolumn pathway and what information does it carry?

Answer 39

Large A beta fibres
Information:
Touch
Virbation
2 point discrimination
proprioception.

Question 40

What sensory fibres are found in the Spinothalamic pathway and what information does it carry?

Answer 40

Small A delta and C fibres
Information:
Pain
Temperature
Non-discriminatory touch