Somatosensation I

Question 1

What are the 5 functions of the somatosensory pathway?

Answer 1

→ Conveying sensation from the body
→ touch
→ proprioception ( sense of body position) 
→ Heat and cold
→ pain and itch

Question 2

How many pairs of spinal nerves do we have?

Answer 2

→ 31 pairs

Question 3

How is the CNS connected to the body?

Answer 3

→ Spinal and cranial nerves

Question 4

What is a nerve?

Answer 4

→ a bunch of fascicles

Question 5

What do fascicles consist of?

Answer 5

→ Individual myelinated axons

Question 6

What is the membrane of the fasciles called?

Answer 6

→ perineurium

Question 7

What is the membrane of the spinal nerve called?

Answer 7

→ Epineurium

Question 8

What is the membrane of each individual axon called?

Answer 8

→ Endoneurium

Question 9

What do the 8 spinal nerves and the top of the thoracic nerves form?

Answer 9

→ Brachial plexus

→ Cervical plexus

Question 10

What is the function of spinal nerves?

Answer 10

→ Carry information between the CNS and the periphery

Question 11

How many pairs of nerves does the cervical region contain?

Answer 11

→ 8

Question 12

How many pairs of nerves does the thoracic region contain?

Answer 12

→ 12

Question 13

How many pairs of nerves does the lumbar region have?

Answer 13

→ 5

Question 14

How many pairs of nerves does the sacral region have?

Answer 14

→ 5

Question 15

How many pairs of nerves does the coccygeal region have?

Answer 15

→ 1

Question 16

What do the dorsal roots contain?

Answer 16

→ Sensory afferents

Question 17

What do the ventral roots contain?

Answer 17

→ Motor efferents (somatic)

→ Autonomic effererents

Question 18

What do dorsal and ventral roots unite to form?

Answer 18

→ Spinal nerve

Question 19

What does white matter contain?

Answer 19

→ Ascending and descending axon tracts

Question 20

What does grey matter contain?

Answer 20

→ Cell bodies
→ Dendrites
→ Synapses

Question 21

Where do the spinal nerves pass through?

Answer 21

→ Intervertebral foramina

Question 22

What do dorsal root ganglia contain?

Answer 22

→ All the cell bodies of all the sensory neurons of the somatosensory system

Question 23

What do large fibres sense?

Answer 23

→ tactile and proprioceptive

Question 24

What do small fibres sense?

Answer 24

→ Temperature
→ pain
→ itch
→ crude touch

Question 25

What are dorsal root ganglia neurons called and why?

Answer 25

→ pseudo unipolar neurons → they have a single process → gives rise to an axon in both directions

Question 26

What kind of adaptation does a Merkel disc have?

Answer 26

→ Slow adapting

Question 27

How many large fibre afferents are there in the skin?

Answer 27

→ 4

Question 28

What kind of touch are Merkels discs sensitive to?

Answer 28

→ Light touch and pressure

Question 29

Where are Meissners corpuscles and Merkels discs located?

Answer 29

→ between the dermis and the epidermis

Question 30

What happens to a Merkels disc if a stimulus is applied and maintained?

Answer 30

→ Action potentials fire | →if the stimulus is maintained then the action potentials continue to fire

Question 31

What happens to a Meissners corpuscle if a stimulus is applied and maintained?

Answer 31

→ action potentials fire | → if the stimulus is maintained the action potentials drop to 0

Question 32

What are the cutaneous tactile afferents?

Answer 32

→ Meissners corpuscles | → Merkels discs

Question 33

What are the deep tactile afferents?

Answer 33

→ Ruffini | → Pacinian

Question 34

What type of fibre are tactile afferents?

Answer 34

→ A beta

Question 35

What do Pacinian corpuscles respond to?

Answer 35

→ Vibration

Question 36

What do Ruffini corpuscles respond to?

Answer 36

→ Slipping | → Non slipping

Question 37

What are fast adapting afferents?

Answer 37

→ Meissner | → Pacinian

Question 38

What are slow adapting afferents?

Answer 38

→ Ruffini | → Merkel

Question 39

What do muscle spindles detect?

Answer 39

→ Changes in muscle length

Question 40

What fibres detect change in length in muscles?

Answer 40

→ Large fibre systems

Question 41

What senses muscle tension?

Answer 41

→ Golgi tendon organs

Question 42

What is muscle length a cue for?

Answer 42

→ Proprioception

Question 43

What type of neuron is a normal motor neuron?

Answer 43

→ Alpha

Question 44

What are A delta fibres like?

Answer 44

→ thin | → myelinated

Question 45

What are C fibres like?

Answer 45

→ Thin | → unmyelinated

Question 46

What does a small receptive field mean?

Answer 46

→ THe stimulus is localised

Question 47

What are the two major somatosensory pathways?

Answer 47

→ Dorsal column - medial lemniscal system | → Spinothalamic tract

Question 48

What does the dorsal column sense?

Answer 48

→ Mediates discriminative touch → vibration → proprioception

Question 49

What does the spinothalamic tract sense?

Answer 49

→ Coarse touch → temperature → pain

Question 50

Describe the pathway from a tactile afferent in the upper body to the somatosensory cortex

Answer 50

→ Stimulus from the Merkel, Ruffini, Pacinian or Meissners occurs → The stimulus travels via 1st order neurons to the dorsal column (cuneatus) → the 1st order neuron travels up to the medulla (nucleus cuneatus) where it synapses with a 2nd order neuron → the 2nd order neuron decussates at the midline → the 2nd order neuron travels up the medial lemniscal tract of the brainstem to the thalamus → 2nd order neuron synapses at the thalamus with a 3rd order neuron which carries it to the somatosensory cortex

Question 51

What is the difference between the Cuneate and Gracile dorsal column?

Answer 51

→ Cuneate - upper body | → Gracile - lower body

Question 52

What inputs come to the ventral posterior medial nucleus?

Answer 52

→ Sensory inputs of the head and face

Question 53

What inputs come to the ventral posterior lateral nucleus?

Answer 53

→ Sensory inputs from the body

Question 54

Where is the somatosensory cortex?

Answer 54

→ Front of the parietal lobe