Somatic Sensory System Flashcards

1
Q

somatic sesnory system =

A

representation of body in the brain

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2
Q

2 major inputs

A

mechanical stimuli

painful stimuli and tempertautre

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3
Q

input and interpretation enables us to…..

A

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

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4
Q

sensory receptors

A

golgi tendon organ

muscle spindles

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5
Q

sensory receptors

meissner (tactile) corpuscles

A

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

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6
Q

sensory receptors

pacinian (lamellated) corpuscles

A

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

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7
Q

encapsulated nerve endings

A

meissener
pacinian
Ruffini

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8
Q

sensory receptors

ruffini corpuscles

A

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

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9
Q

sensory receptors

merkel (tactile) discs

A

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

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10
Q

sensory receptors

free nerve endings

A

location - widespread in epithelia and connective tissues

modality - pain, heat, cold

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11
Q

unencapsulated nerve endings

A

merkel

free nerve endings

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12
Q

sensory receptors

hair follices

A

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

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13
Q

cellular vs molecular receptors

A
molecular = molecule on surface to detect other molecules
cellular = group of cells organised to form receptor - detect pain, temp etc
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14
Q

sensory receptors = not always neurons

A

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

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15
Q

classes of mechanoreceptor response

A

phasic

tonic

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16
Q

phasic response

A

rapidly adapting

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

17
Q

tonic

A

slow adapting

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

18
Q

primary afferent sub types

A

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

19
Q

axons coming from skin

A

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

20
Q

axons coming from muscles

A

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

21
Q

organisation of sensory info

A

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

22
Q

somatosensory projections

2 routes to brain

A

medial lemniscal tract

spinothalamic tract

23
Q

medial lemniscal tract

A

cary mechanoreceptive and proprioceptive signals to thalamus

24
Q

spinothalamic tract

A

carries pain and temperature signals to thalamus

25
3 types of neurons
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
26
medial lemniscal system | 1st orders
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
27
medial lemniscal system | 2nd orders
2nd order acons cross midline and ascend in medial lemniscus topology is reversed, relative to midline, so lower body axons are lateral
28
medial lemniscal system | 3rd orders
again reverse topology so lower body axons are medial again and upper are lateral
29
somatotropic order in brain
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
30
dermatones
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
31
topographic map
larger areas in cortex = reflects behavioural significance
32
receptive fields
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
33
sensory modality in cortex
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
34
cortical map plasticity
cut off monkeys finger | = area in cortex disappeared and other areas grew larger