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C1 Modules > Somatosensory system > Flashcards

Somatosensory system Flashcards

1
Q

What are 3 functions of somatosensory system?

A
  1. Proprioception
  2. Exteroception
  3. Interoception
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2
Q

What is proprioception?

A

Receptors are in the skeletal muscle, joint capsule and the skin

Enables us to have conscious awareness of posture and movement of our own body, particularly 4 limbs + head

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3
Q

What happens when there is no sensory feedback from proprioceptors?

A

The movement are often clumsy, poorly coordinated and inadequately adapted to complex tasks, particularly if visual guidance is absent

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4
Q

What is exteroception?

A

Sense of direct interaction with external world as it impacts on body

Receptors are located in the skin (mechanoreceptors, thermoreceptors + nociceptors)

Touch + pain mediated by different pathways

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5
Q

What are examples of exteroception?

A
  1. Touch [contact, pressure, stroking motion, vibration]

2. Temperature + pain [nociception]

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6
Q

What is Interoception?

A

Sense of function of major organ systems of body and its internal state

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7
Q

For transmission, what are all somatic senses mediated by?

A

one class of sensory neurons - dorsal root ganglion neurons

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8
Q

What do axons of primary afferent fibres have?

A

2 branches, one projecting to periphery and one projecting to CNS

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9
Q

What does axons of each dorsal root ganglion cells serve as?

A

single transmission line with one polarity between the receptor terminal and CNS

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10
Q

How are DRG guided?

A

Through development to a specific location in body via various trophic factors

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11
Q

What do peripheral nerve also include?

A

Motor axon innervating nearby muscles, blood vessels, glands or viscera

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12
Q

What do individual neurons in DRG respond selectively to?

A

Specific type of stimuli because of morphological and molecular specialisation of peripheral terminals

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13
Q

What are receptors?

A

Transducers converting stimulus energy into electrochemical energy; receptor potential and nerve action potentials

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14
Q

What do mechanoreceptors sense?

A

Physical deformation of tissue in which they reside

  1. light touch, vibration, pressure
  2. Muscle stretch, contraction, joints angle
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15
Q

What do nociceptors and thermoceptors detect + initiate?

A

Sensation of painful stimuli + abnormal temperature

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16
Q

What is touch mediated by?

A

4 types of mechanorecptors in human hand

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17
Q

What are terminals of myelinated sensory nerve innervating hand surrounded by?

A

Specialised structures that detect contact on skin

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18
Q

What do receptors differ in?

A
  1. Morphology
  2. Innervation pattern
  3. Location in the skin
  4. Receptive field size
  5. Physiological response to touch
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19
Q

What do superificial layers contain?

A

Small receptor cells: Meissner corpuscle + Merkel cells

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20
Q

What do deep layers of skin + subcutaneous tissue contain?

A

Large receptors: Pacinian corpuscle + rufinni endings

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21
Q

What does receptive field of mechanoreceptor reflect?

A

Location + distribution of terminals in skin

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22
Q

What do spike train show?

A

Responses of each type of nerve when its receptor is activated by constant pressure against skin

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23
Q

What do RA type fibre that innervate Meisnner + pacinian corpuscle adapt to?

A

Constant stimulation

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24
Q

What do SA type nerve that innervate Merkel cell + Rufinni endings adapt ?

A

ongoing stimulation

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25
Q

What do rapidly-adapting nerve fibre send information related to?

A

Changing stimuli

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26
Q

Receptive field in human hand

A

Smallest at fingertips

27
Q

What do receptive field of receptors in superificial layers of skin encompass?

A

Spot-like patches of skin

28
Q

Where do receptors in deep layers extend across?

A

Wide region of skin

29
Q

Where are responses strongest in skin?

A

Directly over receptor (dark spot)

30
Q

What is contour map?

A

Pressure sensitivity throughout the receptive field

31
Q

What do 2-point threshold measure?

A

Minimum distance at which 2 stimuli are resolved as distinct

32
Q

Where are the greatest discriminative capacity afforded in?

A

Fingertips, lips + tongues, which have the smallest receptive field

33
Q

Where is tactile acuity in human hand highest in?

A

Fingertip

34
Q

What constitutes a dermatome?

A

The skin + deeper tissues innervated by afferent fibres of a single spinal nerve

35
Q

What do the 4 mechanoreceptors detect?

A
  1. Grip forces (SA1, merkel)
  2. Hand posture ( SA2, Rufinni)
  3. Force rate (RA1, Meissner)
  4. Vibrations at hand contact, lift-off, table contact + release of grasp (RA2, pacinian)
36
Q

What does a single dorsal root ganglion contain?

A

around 100,000 neurons

37
Q

where does incoming afferent information travel

A

Dorsal root

38
Q

What do dorsal horn contain?

A

Orderly arrangement of sensory relay neuron that receive input from periphery

39
Q

What do ventral horn contain?

A

Group of motor neurons and interneurons that regulate motor neuronal firing patterns

40
Q

What does white matter contain?

A

rostral-caudal ascending and descending tract of myelinated axons

41
Q

What does ascending pathway carry?

A

Sensory information to brain

42
Q

What does descending pathway carry ?

A

motor command + modulatory signal from brain to muscles

43
Q

What does the sensory division carry?

A

Information from muscles + skin into spinal cord + terminate in dorsal aspect of cord

44
Q

What do different classes of axon within dorsal root convey?

A

Pain, temperature, touch and visceral sensory information

45
Q

What do motor division (ventral root) do?

A

Emerge from ventral aspect of cord and comprises the axon of motor neuron that innervate muscle

46
Q

What do ventral root from certain levels of SC include?

A

sympathetic and parasympathetic axon

47
Q

What do motor neuron of spinal cord comprise

A

final common pathway through which all higher brain levels controlling motor activity must act

48
Q

Define referred pain

A

Disorder of internal organ is sometime perceived as cutaneous pain

49
Q

What is most common clinical example of referred pain?

A

Anginal pain

50
Q

What are 2 main pathways transmitting and processing somatosensory input?

A
  1. epicritic sensation - high resolution, light touch = DCMLP
  2. protophatic sensation - poorly localised, pain + temp
51
Q

What are part of spinothalamic pathway?

A

protopathic, pain and temperature

52
Q

What is the role of dorsolateral tract?

A

Convery somatosensory information from lower half of body to cerebellum

53
Q

What does Dorsal-column medial lemniscus pathway mediate?

A

Light touch, pressure and proprioception

54
Q

How do many primary afferent travel ?

A

In a highly-ordered, somatotopic manner in dorsal column

55
Q

What do dorsal column consist of?

A

Cuneate = upper limb
Gracile = lower limb
tracts

56
Q

Where do DCML pathway terminate in?

A

Cuneate + Gracile nuclei
Axons of second order neuron decussate + project through brainstem as medial lemniscus to thalamus ( ventro-posterior nucleus)

57
Q

Where do thalamus somatopically project to?

A

primary somatosensory cortex (S1)

58
Q

What does the spinothalamic pathway mediate?

A

Crude touch, pain and temperature

59
Q

Where does the spinothalamic pathway terminate in?

A

Thalamus
(Ventroposterior lateral nucleus)

Third order thalamic neuron project to somatosensory cortex

60
Q

Why are there no clear centre for pain?

A

widely distributed over many cortical/sub-cortical sites

61
Q

What is brown-sequard syndrome?

A

Dissociated sensory loss following a spinal cord hemisection at 10th thoracic level on left side + motor weakness on same side as lesion

62
Q

who mapped the sensory homunculus?

A

Penfield (1930’s)
Electrical stimulation of brain
Patient being operated for epilepsy

63
Q

Where is clear somatotopic map found on?

A

Face on most lateral surface and lower limb on medial surface

64
Q

How is receptor density reflected ?

A

Disproportionately large representation of distal extremities (lips, digits + toes)

C1 Modules (20 decks)

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