Somatic Sensory System

Question 1

somatic sesnory system =

Answer 1

representation of body in the brain

Question 2

2 major inputs

Answer 2

mechanical stimuli

painful stimuli and tempertautre

Question 3

input and interpretation enables us to…..

Answer 3

identify shape and texture
monitor internal and external forces acting on body
detect potentially harful circumstances

Question 4

sensory receptors

Answer 4

golgi tendon organ

muscle spindles

Question 5

sensory receptors

meissner (tactile) corpuscles

Answer 5

location - dermal papillae of skin, eyes, palms etc
modality - light, touch, texture (movement e.g friction)
sensitive to 30-50Hz
rapidly adapting

Question 6

sensory receptors

pacinian (lamellated) corpuscles

Answer 6

location - dermis, joint capsules, viscera
modality - deep pressure, stretch, tickle, vibration
sensitive to 250 - 350 Hz
rapidly adapting

Question 7

encapsulated nerve endings

Answer 7

meissener
pacinian
Ruffini

Question 8

sensory receptors

ruffini corpuscles

Answer 8

location - dermis, subcutaneous tissue, joint capsules
modality - heavy touch, pressure, skin stretch
slowly adapting

Question 9

sensory receptors

merkel (tactile) discs

Answer 9

location - superficial skin - epidermis
modality - light touch, texture, edges, shapes
slowly adapting

Question 10

sensory receptors

free nerve endings

Answer 10

location - widespread in epithelia and connective tissues

modality - pain, heat, cold

Question 11

unencapsulated nerve endings

Answer 11

merkel

free nerve endings

Question 12

sensory receptors

hair follices

Answer 12

location - widespread in eptihelia
modality - varied according to type
both rapid and slow adapting

Question 13

cellular vs molecular receptors

Answer 13

molecular = molecule on surface to detect other molecules
cellular = group of cells organised to form receptor - detect pain, temp etc

Question 14

sensory receptors = not always neurons

Answer 14

in above examples, cells are doing the sensing = they are the sensory neurons themselves
but, photoreceptors, auditory and vestibular hair cells are specialist cell types that synapse with sensory afferent to relay to CNS

Question 15

classes of mechanoreceptor response

Answer 15

phasic

tonic

Question 16

phasic response

Answer 16

rapidly adapting

give info about changes in the stimulus e.g. pacinian corpuscles

Question 17

tonic

Answer 17

slow adapting

continue to respond as long as stimulus is present - gives info about presence of stimulus e.g. ruffini corpuscles

Question 18

primary afferent sub types

Answer 18

according to conduction velocity which broadly reflects diameter (faster = larger diameter)

Question 19

axons coming from skin

Answer 19

labelled with letters
A = fastest/largest
can be further broken down by greek letters, alpha = fastest

Question 20

axons coming from muscles

Answer 20

Roman numerals
I = largest/fastest
Ia = faster than Ib

Question 21

organisation of sensory info

Answer 21

in layers in spinal cord dorsal horn
cell bodies of different classes of sensory neurons are grouped in DRG and their projections organised to different layers of dorsal horn

Question 22

somatosensory projections

2 routes to brain

Answer 22

medial lemniscal tract

spinothalamic tract

Question 23

medial lemniscal tract

Answer 23

cary mechanoreceptive and proprioceptive signals to thalamus

Question 24

spinothalamic tract

Answer 24

carries pain and temperature signals to thalamus

Question 25

3 types of neurons

Answer 25

first order - detect stimulus and transmit to spinal cord - from periphery to spinal cord
second order - relay signal to thalamus, gateway to cortex
third order - carry signal from thalamus to cortex

Question 26

medial lemniscal system

1st orders

Answer 26

topologically organised = spatial arrangement of objects relative to one another
1st order axons from upper body follow lateral pathway and synapse on 2nd order in cuneate nucleus
1st order from lower body follow medial pathway and synapse on neurons in gracile nucleus
both nuclei = dorsal column nuclei

Question 27

medial lemniscal system

2nd orders

Answer 27

2nd order acons cross midline and ascend in medial lemniscus
topology is reversed, relative to midline, so lower body axons are lateral

Question 28

medial lemniscal system

3rd orders

Answer 28

again reverse topology so lower body axons are medial again and upper are lateral

Question 29

somatotropic order in brain

Answer 29

results of topology projection = map of body in cortex
system is posterier to central sulcus in brain
very fine map as each DRG innervates specific domains of body = dermatone

Question 30

dermatones

Answer 30

specific region of skin innvernated by each sensory ganglion
due to dermis of each region being derived from a specific somite
somites give rise to underlying musculature and skeleton
in embryo, each DRG is associated with specific somite

Question 31

topographic map

Answer 31

larger areas in cortex = reflects behavioural significance

Question 32

receptive fields

Answer 32

each sensory neuron has a receptive field
size of field depends on where it is in body
large field = low discrimination e.g arm
small field = high discrimination e.g. fingers
higher number of ending from different neurons

Question 33

sensory modality in cortex

Answer 33

somatotopic map - preserved in coronal plane in postcentral gyrus
different sensory modalities are localised along saggital axis
e.g. texture discrimination, finger co ordination = Brodmann areas

Question 34

cortical map plasticity

Answer 34

cut off monkeys finger

= area in cortex disappeared and other areas grew larger