Somatosensory System FINAL

Question 1

Mechanoreceptors function

Answer 1

Detect touch and proprioception

Question 2

Sensory neuron types fastest to slowest and uses of each

Answer 2

ABeta- Innoucuous mechanical stimulation
ADelta- Noxious mechanical and thermal stimulation
C fibres- Noxious mechanical, thermal and chemical stimulation

Question 3

Features of ABeta,ADelta and Cfibres that affect its speed

Answer 3

ABeta- Largest diameter +myelinated
ADelta- smaller diameter +myelinated
C fibres - smallest diamater and not myelinated

Question 4

Sensory Receptor:

Answer 4

Transducer that converts energy from environment into neuronal action potential

Question 5

Receptors with Free endings

Answer 5

Nocioceptor and thermoceptors

Question 6

Receptors with enclosed endings

Answer 6

Mechanoreceptors

Question 7

Thermoreceptors are what type of fibres

Express what on their neurons

Answer 7

Adelta and C fibres

Express TRP -Transient Receptor Potential ion channels

Question 8

Heat activated TRP

Cold activated TRP

Answer 8

TRP1,2,3,4

TRPM8, TRPA1

Question 9

Mechanoreceptors are what sort of fibres

Answer 9

AB fibres

Question 10

5 types of mechanoreceptors and functions

Answer 10

1) Meissner’s corpuscle
2) Merkel Cells
3) Pacinian Corpuscle
4) Ruffini endings
5) Hair follicle receptors

1) Meissner’s-Discrimnative touch
2) Merkel Cells-light and superficial pressure
3) Pacinian corpuscle-High frequency vibration
4) Ruffini endings-continous pressure/touch and stretch
5) Hair follicle receptors: light touch

Question 11

Nociceptors are what fibres

Answer 11

Adelta and C fibres like thermoceptors

Question 12

Stimulus threshold:

Answer 12

Point of intensity at which person can JUST detect the presence of a stimulus 50% of the time– absolute threshold

Question 13

Stimulus Intensity

Answer 13

Increased stimulus strength and duration=increased neurotransmitter release=greater intensity
> encoded by how quickly neurons fire

Question 14

Adaption: what are the 2 types

What is sensory adaption

Answer 14

1) Tonic receptors
2) Phasic Receptors

Change with time in responsiveness of a sensory receptor to a stimulus

Question 15

Mechanism of tonic receptors

E.g of tonic receptor

Answer 15

1) Detect continuous stimulus strength
2) Fire quickly at point of stimulation and slow down after
3) Continue to transmit impulses to brain as long as stimulus is present
4) Keeps brain constantly informed

Merkel cell
–>Slowly adapt, allowing for superficial pressure and fine touch to be percieved

Question 16

Mechanism of phasic receptors

E.g

Answer 16

1) Detect change in stimulus strength
2) Transmit impulse at start and end of stimulus

Pacinian Corpuscle

• Sudden pressure excites receptor
• Transmits signal again when pressure is released

Question 17

Receptive fields

Answer 17

Region of skin which causes activation of a SINGLE sensory neuron when activated

Question 18

Small receptive fields

Answer 18

Precise perception- allow for detection of fine detail over small area

Question 19

Large receptive fields

Answer 19

Less precise, allow cell to detect changes over a wider area

Question 20

Two point discrimnation

Answer 20

min distance at which 2 points are perceived as separate

->related to size of receptive fields

Question 21

Where are the dermatomes C5, T4

Answer 21

c5- Clavicle, t4= nipple

Question 22

Where are cell bodies found in body and in the face

Answer 22

In body–dorsal root ganglia

In face- Trigeminal ganglia

Question 23

Info from upper and lower bodies received at what level of spine

Answer 23

Upper= Cervical

Lower=Lumbar

Question 24

Where are gracilis and cuneatus fasciulus located

Answer 24

In spinal cord

Question 25

Where are secondary (internal arcuate fibres) from and reach where

Answer 25

From gracilis and cuneatus in spinal cord to thalamus

Question 26

Secondary neurons cross over where and form

Answer 26

Cross over at medulla | Medial leminiscus tract

Question 27

Secondary neurons axons synapse on neurons in

Answer 27

Ventral nuclear group

Question 28

Tertiary neurons from where to where

Answer 28

Thalamus to primary motor cortex

Question 29

Somatosensory function from face: Enters brain at Where do primary neurons synapse

Answer 29

Pons Trigeminal nucleus

Question 30

2 main types of dorsal horn neurons

Answer 30

1) Projection neurons-Neurons with axons that project to brain 2) Interneurons- Neurons with axons that remain in spinal cord

Question 31

Lateral inhibition is what is the purpose How is it mediated

Answer 31

Difference between adjacent inputs is enhanced by lateral inhibtion Prevents overlap of receptive field Facilitates -pinpoint accuracy in localisation -enhanced sensory perecption inhibitory interneurons with dorsal horn of of spinal cord

Question 32

Describe the ascending pathway of touch proprioception

Answer 32

1) Innocuous mechanical stimuli: -fine discriminatory touch or vibration 2) ABeta fibres enter via dorsal horn and enter ascending dorsal column pathways 3) Info from limbs travel ipsilaterally long respective dorsal column tracts (gracilis/cuneatus) 4) Fibres in gracile tract have their first synapse in the gracile nucleus --same for cuneatus 5) 1st order neurons terminate in medulla 6) 2nd order axons decussate in medulla at caudal medulla and form contralateral medial lemniscus tract 7) 2nd order neurons terminate in thalamus at ventral posterior lateral nucleus (VPL) 8) 3rd order neurons from VPL project to somatosensory cortex of post central gyrus of parietal cortex

Question 33

Describe the ascending pathway of pain, temperature and crude touch

Answer 33

1)Pain and temperature sensations ascend within Lateral spinothalamic tract Crude touch ascends within the anterior spinothalamic tract 2)Primary afferent axons terminate upon entering spinal cord Secondary neurons decussate immediately in spinal cord and form spinothalamic tract 3) Secondary neurons terminate in VPL of thalamus

Question 34

Dorsal column Vs Spinothalamic tracts

Answer 34

Dorsal column: - Light touch - Vibration - 2 point discriminiation Spinothalamic tracts: - Pain - Temp - Crude/Coarse touch

Question 35

Meissner's corpuscle type of fibre

Answer 35

Abeta

Question 36

Crude touch uses what fibre

Answer 36

Adelta

Question 37

Nociceptors | Are what types of fibres and each mediate

Answer 37

ADelta and Cfibres ADelta Sharp, Intense first pain CFibres Dull, aching or second pain

Question 38

Describe the 2 types of Adelta fibres of nociceptors

Answer 38

Type 1 -Noxious mechanical Type 2 -Noxious heat

Question 39

Cfibres

Answer 39

Noxious thermal, mechanical and chemical stimulus

Question 40

Type of neurotransmitter released from sensory afferents in response to noxious stimuli

Answer 40

Glutamate --> Excitatory

Question 41

Pain pathway: | Sensory component through which tract?

Answer 41

Lateral spinothalamic tract

Question 42

Pain pathway: | Emotional component through which tract?

Answer 42

Spinoreticular tract

Question 43

What is the gate control theory Common behaviour that shows this

Answer 43

Inhibition of primary afferent inputs before transmitted to brain through ascending pathways Instinctive rubbing-- stimulates ABeta which blocks C fibres of pain to brain

Question 44

Descending control pathways for pain can be inhibited by? potential

Answer 44

Strong emotions can inhibit pain -Electrical analgesia Descend from somatosensory cortex P

Question 45

Key area in descending control pathway

Answer 45

PAG- periaqueductal grey

Question 46

Nociceptive processing in dorsal horn can be affected by

Answer 46

Facilitation and inhibition

Question 47

Monoamines that inhibit activity in spinothalamic tract and function of efferent C fibres

Answer 47

Serotonin--facilitate pain | Noradrenaline --inhibit pain

Question 48

Nociceptive pain e.g Neuropathic pain: e.g Mixed

Answer 48

Noxious stimulation of a nociceptor (somatic or viscera) e.g Lesion/ disease or somatosensory system e.g sciatica, diabetic, trauma Ostearthritis

Question 49

Tissue damage results in release of Result of release

Answer 49

``` Neurotransmitters Peptides Lipids Protease Cytokines Chemines ``` Produce inflammation, initiate healing, make nociceptors more sensitive by modulating their excitability

Question 50

Peripheral sensitisation Central Sensitisation

Answer 50

Reduce threshold to peripheral stimuli at site of injury Reduce threshold to peripheral stimuli at an adjacent site to injury - Expansion of receptive field - Spontaneous pain

Question 51

Allodynia

Answer 51

Pain due to a stimulus that does not normally provoke pain

Question 52

Hyperalgesia Primary Secondary

Answer 52

Increased pain from stimulus that normally provokes pain Primary- at site of stimulus Secondary- around site of stimulus