Somatic Sensory System

Question 1

what does the somatic sensory system give us?

Answer 1

body sense - the representation of the body in the brain.

Question 2

what are to major input components of the somatic sensory system? (basic)

Answer 2

mechanical stimuli - touch / pressure,

pain stimuli / temp.

Question 3

what do these basic input components of the somatic sensory system allow us to do?

Answer 3

identify shape and texture,
monitor internal and external forces on the body,
detect harmful circumstances,
have a sense of ourselves within our environment.

Question 4

what are 8 types of sensory receptors in the somatic sensory system?

Answer 4

Meisner corpuscles,
Pacinian corpuscles,
Ruffini corpuscles,
Merkel discs,
free nerve endings,
hair follicles,
muscle spindles,
Golgi tendon organs.

Question 5

what are Meisner corpuscles?

Answer 5

located in the dermal papillae of the skin, especially in the palms, eyelids, lips, and tongue.
they detect light touch and texture,
they are rapidly adapting,
sensitive to 30-50Hz.

Question 6

what are Pacinian corpuscles?

Answer 6

located deeper in the dermis, joint capsules, and viscera.
they are sensitive to deep pressure, stretch, vibration, and tickle.
they are rapidly adapting,
sensitive to 250-350Hz.

Question 7

what are Ruffini corpuscles?

Answer 7

located in dermis, joint capsules, and subcutaneous tissue.
they detect heavy touch, pressure, skin stretch, and joint movements.
they are slowly adapting.

Question 8

what are Merkel discs?

Answer 8

located in the epidermis and superficial layers of the skin.
they are sensitive to light touch, texture, edges, and shapes.
they are slowly adapting.

Question 9

what are free nerve endings?

Answer 9

they are widespread in the epithelia and connective tissue.

they detect heat, pain, and cold.

Question 10

what are rapidly adapting / phasic receptors?

Answer 10

after a stimulus is applied, this type of receptor will initially respond but then stop firing even if the stimulus is still there,
gives us info about changes in the stimulus.

Question 11

what are slowly adapting / tonic receptors?

Answer 11

respond to a stimulus and then stay active / on / continue to respond to the stimulus,
give us info about the persistence of a stimulus.

Question 12

how are primary afferent axons classified?

Answer 12

according to conduction velocity (which also reflect diameter).

Question 13

axons from the skin are classified by letters:

Answer 13

A,B,C
A = the fastest / largest,
C = the slowest / smallest.

Question 14

the A category of axons from the skin is broken down my Greek characters:

Answer 14

α, β, δ
α = fastest,
δ = slowest.

Question 15

axons coming from the muscles are classified by roman numerals:

Answer 15

I, II, III, IV
I = fastest,
IV = slowest.

Question 16

how is sensory information relayed to the brain ?

Answer 16

cell bodies of sensory neurons are grouped in the dorsal root ganglion,
their projections are organised into different layers of the dorsal horn.

Question 17

how do mechanoreceptive and proprioceptive signals reach the brain?

Answer 17

the medial lemniscal tracts carry signals to the thalamus.

Question 18

how do pain and temperature signals reach the brain?

Answer 18

the spinothalamic tract carries signals to the thalamus.

Question 19

what are the three neurons that sensory info travels through to reach higher centres?

Answer 19

first-order neurons,
second-order neurons,
third-order neurons.

Question 20

what do the first-order neurons in the somatic sensory system do?

Answer 20

detect the stimulus and transmits it to the spinal cord.

Question 21

what do the second-order neurons in the somatic sensory system do?

Answer 21

relay the signals to the thalamus,

they also cross the midline / commissural.

Question 22

what do the third-order neurons in the somatic sensory system do?

Answer 22

carry signals from the thalamus to the cortex.

Question 23

what does this mean:

axons in the medial lemniscal pathway are topologically organised.

Answer 23

the spatial arrangement of the objects are relative to one another.

Question 24

what pathway do the first-order neurons from the upper body in the somatic sensory system follow?

Answer 24

the lateral pathway and synapse on to second-order neurons in the cuneate nucleus.

Question 25

what pathway do the first-order neurons from the lower body in the somatic sensory system follow?

Answer 25

a more medial pathway and synapse on to neurons in the gracile nucleus.

Question 26

what pathway do second-order neurons in the somatic sensory system follow?

Answer 26

they cross the midline and ascend in the medial lemniscus.

Question 27

the topological projection forms a map of the cortex…

Answer 27

it is very fine,

reflects that each dorsal root ganglion innervates a specific domain of the body called a dermatome.

Question 28

what influences the size of a receptive field?

Answer 28

where it is in the body as some regions will have denser innervation than others.

Question 29

how can the size of a receptive field of the somatic sensory system be measured?

Answer 29

assessing the ability to discriminate 2 sharp points set apart at different distances,
if the subject can feel the 2 points then the distance between them is larger than the receptive field.

Question 30

how can the size of a receptive field of the somatic sensory system be measured?

Answer 30

assessing the ability to discriminate 2 sharp points set apart at different distances,
if the subject can feel the 2 points then the distance between them is larger than the receptive field.

Question 31

what is discrimination like when receptive fields are large?

Answer 31

large receptive field = low discrimination,

arms and legs.

Question 32

what is discrimination like when the receptive fields are small?

Answer 32

small receptive field = high discrimination,

hands.