Somatosensory

Question 1

Why is somatosensory system important?

Answer 1

The somatosensory system provides a crucial line of communication between us & outside world

Question 2

What conditions occur when you damage peripheral or central components of somatosensory system?

Answer 2

Damage to peripheral or central components results in conditions such as neuropathy, neuralgia, phantom pain

Question 3

What are the 4 main classess of somatosensory receptors?

Answer 3

Tactile
Proprioception
Thermal sensations
Nociceptive (painful) sensations

Question 4

What receptors are involved in Tactile sensation?

Answer 4

mediated by low threshold Mechanoreceptors, Merkel, Ruffini, Meissner & Pacinian types

Question 5

What is Tactile sensation?

Answer 5

Not harm ful sensation to light touch

Question 6

What mediates proprioception?

Answer 6

Mediated by muscle (spindle) & joint (Golgi tendon) receptors, some inputs from cutaneous mechanoreceptors

Question 7

Thermal sensation is mediated by what?

Answer 7

Mediated by thermoreceptors localized to discrete zones that exhibit hot & cold sensitivity

Question 8

What mediates Mociceptive (painful) sensation?

Answer 8

Mediated by mechanical, thermal & polymodal nociceptors

Question 9

What are the different sensory receptors of the skin?

Answer 9

Free nerve endings
Meckels disks
Meissners corpuscle
Pacinian corpuscle
Ruffini's corpuscles

Question 10

What are the 3 layers of the skin?

Answer 10

Epidermis
Dermis
Subcutis/hypodermis

Question 11

Where are each of the sensory receptors of the skin found?

Answer 11

Meissners and Merkel are found just beneath the epidermis. Meissners sit between the dermal pupillae and Merkels are aligned with the pupillae.

Ruffini’s corpuscles located deep in dermis, long axis of the corpuscle is orientated parallel to the skin.

Pacinian corpuscles are large encapsulated endings located in the subcutaneous tissue.

Question 12

What is the morphology of cutaneous skin receptors?

Answer 12

A. Meissners Corpuscles - looping axonal terminals that inter-twine supporting cells

B. Merkel’s - dome structure atop axon terminals

C. Pacinian Corpuscles - sensory axon surrounded by fluid filled capsule, onion-shaped appearance

D. Ruffini endings - nerve terminals intertwined with collagen fibrils

E. Nociceptors - free nerve endings that penetrate epithelial cells, no morphological specialization

Question 13

What is the area, function and speed of adapatibility of merkel cells?

Answer 13

Dermo-epidermal boundary
Slow adapting
Pressure form, texture
Small receptive field size

Question 14

What is the area, function and speed of adapatibility of meissner corpuscle?

Answer 14

Papillary dermis
Rapidly adapting
Flutter, motion
Small receptive field size

Question 15

What is the area, function and speed of adapatibility of Pacinian corpuscle?

Answer 15

Deep in subcutis
Rapidly adapting
Vibration –> mechanical distortion
Large receptive field size

Question 16

What is the area, function and speed of adapatibility of Ruffini corupuscle?

Answer 16

Dermis
Slow adapting
Stretching and shearing of skin
Large receptive field size

Question 17

What is the fiber type of all the skin reecptors?

Answer 17

Ab

Question 18

How do you test the receptive field of cutaneous sensory receptors?

Answer 18

Testing the receptive field of sensory receptors using a stimulus probe on the hand, and recording action potentials from a single median nerve axon.

Results for main types of cutaneous sensory receptors.

Question 19

Is two point discrimiation same across the whole body?

Answer 19

Two point discrimination thresholds vary across body surface
Sensitivity is correlated with density of sensory innervation

Question 20

What areas have high and low two point discrimination?

Answer 20

Areas of high sensitivity – fingertips , face

Areas of low sensitivity – torso, limbs

Question 21

What is the range of temperatures sensory fibres can response to?

Answer 21

cold pain
cold
warm
hot pain

Question 22

What family of receptors are activated by temperature?

Answer 22

Trp family of receptors

Question 23

What is the methanol receptor?

Answer 23

Trpm8 and is a cold receptor

Question 24

What is the Capsaicin receptor ?

Answer 24

TRPV1/VR1 –> heat receptor

Question 25

Where is capsaicin found?

Answer 25

Extract of chilli peppers

Question 26

What chemical group does capsaicin belong? to?

Answer 26

Vanilloids

Question 27

What receptor does Capsaicin act on and what is the consequence?

Answer 27

Act on thermal receptor that produces an inward Ca current.

Question 28

What is the function of muscle spindles?

Answer 28

Muscle spindles provide sensory feedback from muscle fibres on body position and movement.

Question 29

What is the function of golgi tendons?

Answer 29

Golgi tendon organs regulate muscle tension or force of contraction, and prevent muscle overloading.

Question 30

What is the general principle for large diameter receptors?

Answer 30

Rapidly conducting afferents (I/II) associated with low threshold mechanoreceptors.

Question 31

What is the general principle for small diameter receptors?

Answer 31

Slow conducting afferents (III/IV) associated with nociceptors and thermoreceptors.

Question 32

What is the conduction velocity positively correlated with?

Answer 32

Conduction velocity is positively correlated with axon diameter

Question 33

What does dermatome represent?

Answer 33

Each dermatome represents that area of skin innervated by the left and right dorsal roots of a single spinal segment

Question 34

What do dorsal roots contain?

Answer 34

Dorsal roots contain sensory afferents innervating receptors of peripheral targets e.g. in skin & muscle

Question 35

Are dermatome boundaries absolute?

Answer 35

Boundaries are not absolute | Overlap between adjacent dermatomes

Question 36

What is the process of developing shingles?

Answer 36

Herpes Zoster Virus (Chickenpox) Virus lurks in primary sensory neurons Can re-activate as Shingles Inflammation & blistering on skin area of affected dorsal root/sensory neuron (e.g. L4)

Question 37

Via what pathway does innocous snesitivies ascend?

Answer 37

Via the dorsal column pathway

Question 38

Via what pathway does Noxious and thermal sensitivity ascend?

Answer 38

Spinothalamic pathway

Question 39

Where is primary somatosensroy cortex (S1) found? What is its function?

Answer 39

Localized to postcentral gyrus and flanked by the central sulcus and the postcentral sulcus Receives strong somatosensory inputs from thalamus

Question 40

Where is secondary somatosensroy cortex (S2) found? What is its function?

Answer 40

Lies adjacent to S1 along the lateral sulcus Plays a key role in sensory and motor integration Receives corpus callosum inputs to form ‘joined -up’ body image Build info from multiple body areas, body image

Question 41

What is the function of sensory assoication areas?

Answer 41

Localized to posterior parietal cortex | Plays role in integration of multimodal senses

Question 42

Who produced the idea of sensory and motor homunculus?

Answer 42

Dr Wilder Penfield

Question 43

What neurological disorders can occur due to sensory asosication area ( posteirorparietal cortex)?

Answer 43

Astereoagnosia Neglect Agnosia

Question 44

What is asteroeangosia?

Answer 44

The inability to identify objects on basis of touch alone but can recognize object by sight or sound

Question 45

What is neglect syndrome?

Answer 45

Body part or visual field is disregarded.

Question 46

Damage to what hemisphere usually causes neglect syndrome and what is the prognosis?

Answer 46

Most common after damage to the right hemispere, and usually improve or disappear with time

Question 47

What is agnosia?

Answer 47

Inability to recognise objects despite normal sensory functioning

Question 48

What are the common symptoms of lateral medullary syndrome?

Answer 48

Loss of pain and temperature on the ipsilateral side of the face but contralateral side of the body

Question 49

What causes lateral medullary syndrome?

Answer 49

little stroke in the medulla

Question 50

Why do you also get Rapidly developed vertigo, unsteadiness, hoarse voice and difficulty swallowing ?

Answer 50

The lower cranial nerves and sympathetic nerves come out of the medulla so these get damage too

Question 51

In what part of the circle of willis does a stroke occur to cause lateral medulalry syndrome?

Answer 51

Posterior inferior cerebellar artery

Question 52

What caues Anterior spinal syndrome?

Answer 52

The anterior spinal artery is occluded so lack of blood supply to the motor area and spinothalamic area of the spinal cord

Question 53

What surgical procedure can cause Anterior spinal syndrome?

Answer 53

Clamping the aorta

Question 54

What is the outcome of Anterior spinal syndrome?

Answer 54

Loss of both motor innervation and pain and temperature sensation. Vibration and proprioception is preserved

Question 55

What would be the outcome of a lacunar stroke of the thalamus?

Answer 55

Can get sudden onset loss of sensation of the single side of the whole body including the face. Loss of sensation to all modalities

Question 56

What is lacunar stroke associated with?

Answer 56

Usually associated with smoking, high blood pressure or diabetes

Question 57

What are the symtpoms of Syringomyelia?

Answer 57

Gradually develop loss of pain and temperature sensation in both hands and across her body in a cape like distribution. Also get wasting in small muscles of the hands and weakness in the legs.

Question 58

What is Syringomyelia?

Answer 58

Rare expansion of spinal canal

Question 59

What does Syringomyelia effect?

Answer 59

Affects crossing fibres first Pain and temperature sensation Later can cause paraparesis and root lesions (wasted hands)

Question 60

How is Syringomyelia treated?

Answer 60

Surgically

Question 61

What is peripheral neuropathy?

Answer 61

all the nerve endings are damaged of the peripheral nerves

Question 62

What are the causes of peripheral neuropathy?

Answer 62

``` Diabetes mellitus Autoimmune (Guillain-Barre, CIDP, vasculitis) Toxic (including drugs) Vitamin deficiency Paraneoplastic Chronic kidney, liver disease Inherited (Charcot-marie-Tooth disease) ```

Question 63

What is the cause of Subacute combined degeneration?

Answer 63

Caused by B12 deficiency

Question 64

What degeneration do you get in Subacute combined degeneration?

Answer 64

Degeneration of dorsal column but the rest of the cord is still intact so still feel things

Question 65

Why is dorsal column pathway effected but not spinothalamic pathway in subacute combined degeneration?

Answer 65

B12 is used to make myelin so axons that don’t have myelin such as spinothalamic are actually protected by this

Question 66

What antibody is subacute combined degeneration assoicated with and what is the consequence?

Answer 66

Usually associated with Anti-parietal cell antibodies--> these destroy the parietal cells that absorb B12 even though they are taking in B12

Question 67

What is complications of subacute combined degeneration ?

Answer 67

Cause also a peripheral neuropathy or dementia

Question 68

Why is it important to treat subacute combined degeneration qucikly?

Answer 68

The treatment will stop the degeneration but won't reverse it so the effects are done.

Question 69

What is the treatment of subactute combined degeneration?

Answer 69

You cannot take B12 tablets because you can’t absorb it but you can use B12 injection