Somatosensory system

Question 1

What are 3 functions of somatosensory system?

Answer 1

1. Proprioception
2. Exteroception
3. Interoception

Question 2

What is proprioception?

Answer 2

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

Question 3

What happens when there is no sensory feedback from proprioceptors?

Answer 3

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

Question 4

What is exteroception?

Answer 4

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

Question 5

What are examples of exteroception?

Answer 5

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

2. Temperature + pain [nociception]

Question 6

What is Interoception?

Answer 6

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

Question 7

For transmission, what are all somatic senses mediated by?

Answer 7

one class of sensory neurons - dorsal root ganglion neurons

Question 8

What do axons of primary afferent fibres have?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

How are DRG guided?

Answer 10

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

Question 11

What do peripheral nerve also include?

Answer 11

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

Question 12

What do individual neurons in DRG respond selectively to?

Answer 12

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

Question 13

What are receptors?

Answer 13

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

Question 14

What do mechanoreceptors sense?

Answer 14

Physical deformation of tissue in which they reside

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

Question 15

What do nociceptors and thermoceptors detect + initiate?

Answer 15

Sensation of painful stimuli + abnormal temperature

Question 16

What is touch mediated by?

Answer 16

4 types of mechanorecptors in human hand

Question 17

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

Answer 17

Specialised structures that detect contact on skin

Question 18

What do receptors differ in?

Answer 18

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

Question 19

What do superificial layers contain?

Answer 19

Small receptor cells: Meissner corpuscle + Merkel cells

Question 20

What do deep layers of skin + subcutaneous tissue contain?

Answer 20

Large receptors: Pacinian corpuscle + rufinni endings

Question 21

What does receptive field of mechanoreceptor reflect?

Answer 21

Location + distribution of terminals in skin

Question 22

What do spike train show?

Answer 22

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

Question 23

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

Answer 23

Constant stimulation

Question 24

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

Answer 24

ongoing stimulation

Question 25

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

Answer 25

Changing stimuli

Question 26

Receptive field in human hand

Answer 26

Smallest at fingertips

Question 27

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

Answer 27

Spot-like patches of skin

Question 28

Where do receptors in deep layers extend across?

Answer 28

Wide region of skin

Question 29

Where are responses strongest in skin?

Answer 29

Directly over receptor (dark spot)

Question 30

What is contour map?

Answer 30

Pressure sensitivity throughout the receptive field

Question 31

What do 2-point threshold measure?

Answer 31

Minimum distance at which 2 stimuli are resolved as distinct

Question 32

Where are the greatest discriminative capacity afforded in?

Answer 32

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

Question 33

Where is tactile acuity in human hand highest in?

Answer 33

Fingertip

Question 34

What constitutes a dermatome?

Answer 34

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

Question 35

What do the 4 mechanoreceptors detect?

Answer 35

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)

Question 36

What does a single dorsal root ganglion contain?

Answer 36

around 100,000 neurons

Question 37

where does incoming afferent information travel

Answer 37

Dorsal root

Question 38

What do dorsal horn contain?

Answer 38

Orderly arrangement of sensory relay neuron that receive input from periphery

Question 39

What do ventral horn contain?

Answer 39

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

Question 40

What does white matter contain?

Answer 40

rostral-caudal ascending and descending tract of myelinated axons

Question 41

What does ascending pathway carry?

Answer 41

Sensory information to brain

Question 42

What does descending pathway carry ?

Answer 42

motor command + modulatory signal from brain to muscles

Question 43

What does the sensory division carry?

Answer 43

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

Question 44

What do different classes of axon within dorsal root convey?

Answer 44

Pain, temperature, touch and visceral sensory information

Question 45

What do motor division (ventral root) do?

Answer 45

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

Question 46

What do ventral root from certain levels of SC include?

Answer 46

sympathetic and parasympathetic axon

Question 47

What do motor neuron of spinal cord comprise

Answer 47

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

Question 48

Define referred pain

Answer 48

Disorder of internal organ is sometime perceived as cutaneous pain

Question 49

What is most common clinical example of referred pain?

Answer 49

Anginal pain

Question 50

What are 2 main pathways transmitting and processing somatosensory input?

Answer 50

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

Question 51

What are part of spinothalamic pathway?

Answer 51

protopathic, pain and temperature

Question 52

What is the role of dorsolateral tract?

Answer 52

Convery somatosensory information from lower half of body to cerebellum

Question 53

What does Dorsal-column medial lemniscus pathway mediate?

Answer 53

Light touch, pressure and proprioception

Question 54

How do many primary afferent travel ?

Answer 54

In a highly-ordered, somatotopic manner in dorsal column

Question 55

What do dorsal column consist of?

Answer 55

Cuneate = upper limb Gracile = lower limb tracts

Question 56

Where do DCML pathway terminate in?

Answer 56

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

Question 57

Where do thalamus somatopically project to?

Answer 57

primary somatosensory cortex (S1)

Question 58

What does the spinothalamic pathway mediate?

Answer 58

Crude touch, pain and temperature

Question 59

Where does the spinothalamic pathway terminate in?

Answer 59

Thalamus (Ventroposterior lateral nucleus) Third order thalamic neuron project to somatosensory cortex

Question 60

Why are there no clear centre for pain?

Answer 60

widely distributed over many cortical/sub-cortical sites

Question 61

What is brown-sequard syndrome?

Answer 61

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

Question 62

who mapped the sensory homunculus?

Answer 62

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

Question 63

Where is clear somatotopic map found on?

Answer 63

Face on most lateral surface and lower limb on medial surface

Question 64

How is receptor density reflected ?

Answer 64

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