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

What do the dorsal roots contain?

Answer 12

→ Sensory afferents

Question 13

What do the ventral roots contain?

Answer 13

→ Motor efferents (somatic)

→ Autonomic effererents

Question 14

What do dorsal and ventral roots unite to form?

Answer 14

→ Spinal nerve

Question 15

What does white matter contain?

Answer 15

→ Ascending and descending axon tracts

Question 16

What does grey matter contain?

Answer 16

→ Cell bodies
→ Dendrites

→ Synapses

Question 17

Where do the spinal nerves pass through?

Answer 17

→ Intervertebral foramina

Question 18

What do dorsal root ganglia contain?

Answer 18

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

Question 19

What do large fibres sense?

Answer 19

→ tactile and proprioceptive

Question 20

What do small fibres sense?

Answer 20

→ Temperature
→ pain

→ itch
→ crude touch

Question 21

What are dorsal root ganglia neurons called and why?

Answer 21

→ pseudo unipolar neurons
→ they have a single process

→ gives rise to an axon in both directions

Question 22

What kind of adaptation does a Merkel disc have?

Answer 22

→ Slow adapting

Question 23

How many large fibre afferents are there in the skin?

Answer 23

→ 4

Question 24

What kind of touch are Merkels discs sensitive to?

Answer 24

→ Light touch and pressure

Question 25

Where are Meissners corpuscles and Merkels discs located?

Answer 25

→ between the dermis and the epidermis

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

What are the cutaneous tactile afferents?

Answer 28

→ Meissners corpuscles | → Merkels discs

Question 29

What are the deep tactile afferents?

Answer 29

→ Ruffini | → Pacinian

Question 30

What type of fibre are tactile afferents?

Answer 30

→ A beta | large diameter, myelinated, 2nd fastest conducting

Question 31

What do Pacinian corpuscles respond to?

Answer 31

→ Vibration

Question 32

What do Ruffini corpuscles respond to?

Answer 32

→ Slipping | → Non slipping

Question 33

What are fast adapting afferents?

Answer 33

→ Meissner | → Pacinian

Question 34

What are slow adapting afferents?

Answer 34

→ Ruffini | → Merkel

Question 35

What do muscle spindles detect?

Answer 35

→ Changes in muscle length

Question 36

What fibres detect change in length in muscles?

Answer 36

→ Large fibre systems | →A-alpha afferents

Question 37

What senses muscle tension?

Answer 37

→ Golgi tendon organs

Question 38

What is muscle length a cue for?

Answer 38

→ Proprioception

Question 39

What type of neuron is a normal motor neuron?

Answer 39

→ Alpha

Question 40

What are A delta fibres like?

Answer 40

→ thin | → myelinated

Question 41

What are C fibres like?

Answer 41

→ Thin | → unmyelinated

Question 42

What does a small receptive field mean?

Answer 42

→ THe stimulus is localised

Question 43

What are the two major somatosensory pathways?

Answer 43

→ Dorsal column - medial lemniscal system | → Spinothalamic tract

Question 44

What does the dorsal column sense?

Answer 44

→ Mediates discriminative touch → vibration →Inputs from A-β and A-α afferent fibres → proprioception

Question 45

What does the spinothalamic tract sense?

Answer 45

→ Coarse touch → temperature →coarse touch, temperature, pain Inputs from A-δ and C fibres → pain

Question 46

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

Answer 46

→ 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 axons from cells of the dorsal column nuclei arch toward the ventral and medial medulla, and decussate → the 2nd order neuron travels up the medial lemniscal tract of the brainstem to the VPL thalamus → 2nd order neuron synapses at the VP thalamus with a 3rd order neuron which carries it to the somatosensory cortex

Question 47

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

Answer 47

→ Cuneate - upper body | → Gracile - lower body

Question 48

What inputs come to the ventral posterior medial nucleus?

Answer 48

→ Sensory inputs of the head and face

Question 49

What inputs come to the ventral posterior lateral nucleus?

Answer 49

→ Sensory inputs from the body

Question 50

Where is the somatosensory cortex?

Answer 50

→ Front of the parietal lobe

Question 51

What are A-beta afferents?

Answer 51

large diameter, myelinated, | →2nd fastest conducting

Question 52

Where are small receptive fields found?

Answer 52

→ tips of fingers

Question 53

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

Answer 53

→ large diameter mechanosensory receptors from face picked by trigeminal ganglion → synapses onto the principal ipsilateral nucleus of trigeminal complex →the 2nd order neuron decussates at the midline → the 2nd order neuron travels up the medial lemniscal tract of the brainstem to the VP thalamus →relayed to somatosensory cortex

Question 54

What is one difference between VPL and VPM?

Answer 54

→VPM- face | →VPL sensory info from the body

Question 55

What are areas 1, 2,3 in the postcentral gyrus?

Answer 55

→ primary somatosensory cortex

Question 56

What is area 4 in the central sulcus?

Answer 56

motor cortex

Question 57

How are regional cortical differences identified?

Answer 57

→ relative thickness → cell size →density

Question 58

How are somatotopic maps duplicated?

Answer 58

duplicates 4 times each in the Browman’s area

Question 59

Where does secondary somatosensory info go to?

Answer 59

→ to amygdala and hippocampus

Question 60

Where does parietal somatosensory info go?

Answer 60

→ to motor and premotor cortical areas

Question 61

What is the only sensory information which does not first synapse in the thalamus?

Answer 61

olfactory

Question 62

What is the difference between muscle spindle and Golgi tendon organ?

Answer 62

The function of the GTO can be considered opposite of the muscle spindle, which serves to produce muscle contraction. When a GTO is stimulated, it causes its associated muscle to relax by interrupting its contraction.​