Somatosensory system

Question 1

What are the functions of the somatosensory pathways? What does it generally consider?

Answer 1

Ability to interpret bodily sensation
Mechanical, thermal, proprioceptive, nociceptive (anything negative)
Consists of skin, tissue, joints, nerves, spinal cord and brain

Question 2

What are the different somatosensory modilities?

Answer 2

Mechanical, Thermal, Proprioceptive, Nociceptive

Modalities mean each of these different nerves

Question 3

What do the terminals of sensory nerves look like?

Answer 3

Modifed nerve endings - free nerve endings-thermoreceptors and nociceptors
Enclosed nerve ending-mechanorecptors

Question 4

What are the 3 main classes of sensory neurons

Answer 4

Aalpha-motor
Abeta-smaller than Aa but faster than res, mechanoreceptors of skin (large and fast), myelinated increase speed (m/sec)
Reaches CNS before pain
Agamma-nociceptors and mechanical stimuli (smaller than Ab)
C-Unmyelinated, smaller- slower-pain temperature, itch

Question 5

Define receptor. What types of thermoreceptors are they?

Answer 5

Receptors are transducers that convert energy from the environement to Action potential
Themroreceptors-Agamma, C fibres-sensitive via membrane. Very sensitive, but not evenly distributed
Free nerve endings
Temp ability depends of what receptors (TRP ion channels)-4heat activated ion channels (TRPV1-4), 2 cold activated-TRPM8/A1 (activated by wasabi)
MEchanoreceptors

Question 6

Define the 5 main mechanoreceptors

Answer 6

Meissners corpuscules (fine discriminative, low frequency vibration)
Merkel cells-light souch, superficial oressure
Pacinian corpuscule-deep pressure, high frequency vibration
Ruffini endings-continous pressure and stretch
ALL are Abeta type fibres

Question 7

Define stimulus threshold

Answer 7

Point of intensity where a person can detect the stimulus 50% of the time (like microfilaments-which thickness)

Question 8

Define stimulus intensity

Answer 8

Define by how much a neuron fires above its threshold-with longer/stronger timulus, more AP leading to increased sensrory

Question 9

What are tonic receptors?

Answer 9

Detect continous stimulus strength- but adapt very slowly/dont adapt
fire all the time of the stimulus-keeps brain informed
MERKEL cells are a type of that

Question 10

What is adaptation?

Answer 10

Detection of continous stimulus strength-your body wont keep telling you about it if nothing changes (like a hand on a table for long)-only stimlus at start and end

Question 11

What are Phasic receptors?

Answer 11

They detect change in stimulus strengtgh-only fire when there is a change-adapt fast
Pacinian recepot-fire start and end of pressure, not in between

Question 12

What is a receptive field>

Answer 12

Region of the skin which activates only 1 sensory neuron
Different sizes in places
Upper arm have large ones-so cant differciate too much
Fingers have timy ones, which allows very precise
Back is super large-reduced precision

Question 13

What is two point discrimination?

Answer 13

Minimun distance at which 2 points are considered diferent
Usually dependent on the size of the receptive field
Vary wildly between body-hand is 4/5mm, but back/calf is over 45mm

Question 14

What are somatosensory dermatomes?

Answer 14

area of skin innvervated by a sigle spinal nerve
Each nerve has a ventral and dorsal root
Provide a mapping system to see where sensory is going
C5-clavicule, C6 (6 shooter)-thumb. T4 is nipples, T10 is belly body

Question 15

Where are the cell bodies for neurons in body and face?

Answer 15

body dorsal root ganglia in body, and trigeminal ganglia for face
Legs go up gracile fasciculutus, and arms go up the cuneate fasciculutus -cross over in the medulla to thalamus
(gracile more medial than cuneate)
Trigeminal go directly via pons to trigeminal nucleus, then to thalamus

Question 16

What are the two neuron types in the dorsal horn>

Answer 16

Those that prokect to brain (projection neurons)-
And interneurons that remain in spinal cord
Thermo and noci (Adelta/C fibre-are more superficial)
Ab are deeper in the dorsal horn

Question 17

What is lateral inhbition?

Answer 17

Explain how receptive fields can overlap with other-difficult to distinguish
In the dorsal horn, inhbitory interneuron stop from adjacent neurons from being activated too, increasing perception

Question 18

Describe the touch and proprioception tract

Answer 18

Ab fibres via dorsal horn to dorsal columjn pathays
Via fasciculutus gracilis(under T6)/Cuneatus (above T6)
On the SAME SIDE (ipsilateral) and cross over (dessecate) in medulla
Do fine discriminative touch and vibration
1st order neuron to medulla each synapse within cuneate/gracilis nuclei in medulla
2nd order go to caudal medulla -form contralateal lemniscus tract
2nd order neurons teperminate in ventral posteror lateral nuctleus of thalamis (VPL)
3rd order neurons terminate in somatosensory cortex-size of area in brain depends on densirty of fibres from that area (hand massive)

Question 19

Describe the ascending pathway for pain, temperature and crude touch

Answer 19

Carried in SPINOTHALAMIC pathway (pain/temp-lateral, Crude touch in the anterior)
CROSS OVER at the same level as they enter (immediate), then go up to thalamus/somatosensory cortex
1st order terminate in spinal cord/dorsal horn
2nd orderneuron cross over and to thalamus to ventral posterio lateral nucleus (VPL)

Question 20

What is the clincal relevance of 2 point discrimination test

Answer 20

Called psychophysical assessment-depends on patients a lot
Tests the integrity of acending-can test sensation. pain, discrimation (dorsal column)
In anterior spinal artery damge-lose spinothalamuc tract below lesion-BUT dorsal part is intact (light touch, vibration, 2point discrimation)

Question 21

Define pain rohgly

Answer 21

Unpleasent sensory and emotional experience associated with actual or potential tissue damage

Question 22

Describe Nociceptors types and roles

Answer 22

Adelta fibres-type 1 noxious mechanical, noxious heat-fast sharp pain
C fibres mediate the dull/aching pain

Question 23

What is the neurotransmitter used in pain processing?

Answer 23

Glutamate released as an answer to the stimuli, to the dorsal root then can go to several levels-physical and emotion/learning

Question 24

How is pain carried to the brain

Answer 24

Sensroy is carried via lateral spinothalamic tract, but spinoreticular tract carries the emotion component
In the brain, involves incredible amounts of part (frontal, amygdala, cerebellumn brainstem, etc

Question 25

Explain how nociceptor input can be gated by CNS

Answer 25

Gate control theory-Inhbition of primary afferent inputs before they are transmitted to brain
Like rubbing elbow after hitting it-activating Ab fibers to activate inhbitory neurons, stopping C Fibre info from passing to brain
Also descending control pathways-strong emotions can inhbit pain-involved periaqueductal grey-facilitation and inhbition of nociceptive precessing. Use serotonin/noradrenaline (opiods similar)
Placebo seems to do that

Question 26

What are the main mechanisms of chronic pain?

Answer 26

Pain that last over 3 month-
Can be nociceptive pain-skin, msucle, ligaments, etc (arthirits) or neuropathic pain (sciatica, trauma, diabete)c
Also mixed pain-lower back pain, osteoarthiritis

Question 27

What is peripheral sensitisation?

Answer 27

As an area is damaged, create a inflmatory soup-create inflamation, but also modulate nociceptors or the area
make it more sensitive (reduce threshold but peripherally and centrally (via plasticity of projection neuron of dorsal horn)

Question 28

Define Allodynia and hyperalgesia

Answer 28

Allodynia-Pain due to stimulus that doesnt normally provoke pain
Hyperalgesia-increased pain from normally painful stimuli (primary-at the area of damge, secondary-around) -pretty much reduce stimulus threshold needed

Question 29

How do you diagnose neuropathic pain?

Answer 29

Very filtered-has to have neurological damage. Symptoms have to match. Have to have sensory lose or gain
Usually start with questionnaires, but not diagnostic

Question 30

What are the 3 main neuropathic pain cluster types

Answer 30

Sensory loss, Thermal hyperalgesia and mechanical hyperalgesia