Nervous system Part 2

Question 1

What does the somatosensory system do?

Answer 1

mediates a diverse range of senstations

touch, pressure, limb position, vibration, temp, pain

Question 2

where are the receptors located for the somatosensory system?

Answer 2

skin, muscle and tendons

tranmitted to CNS

Question 3

What are the three sub-sytems of the somatosensory system and their function?

Answer 3

Cutaneous mechanoreceptors- touch, vibration, pressure

Proprioception- Muscles, tendons, joints, limb postion, load on joint

Pain and temperature

Question 4

What is the somatosensory pathway?

Answer 4

Through the dorsal root ganglia and cranial nerve ganglia

Question 5

What is a Dermatome?

Answer 5

the territory innervated from a singal dorsal root ganglion and its spinal nerve is called a dermatome

area of skin associated with spin

Question 6

How many pairs of cervical nerves?

Answer 6

8

Question 7

Transduction of mechanosensory afferent:

what does a stimulus do?

Answer 7

alters the permeability of cation channels in the afferent nerve endings

will generate depolarizing current- generator or receptor potential

if large enough in magnitude- threshold reached and AP initieaded

firing is proportional to magnitude of depolarization or strength of stimulus

Question 8

how do somatosensory afferent differ ?

Answer 8

axonal diameter and conduction velocities

Question 9

how does the size of the receptor field vary?

Answer 9

two point discrimination- dependent on area (ie. fingers(3mm) have much smaller than arm(40mm))

Question 10

Somatosensory afferents Attributes

:What is Temporal dynamics

Answer 10

rapidly adapting afferents- AP become quiescent with continued stimulation; encodes movement

Slowly adapting aferents- contimue to respond with AP for the duration of the stimulus; size and shape

Question 11

Mechanoreceptors in the skin:

what is different about the afferent fiber’s?

Answer 11

encapsulated by specialized receptor cells

Mechanoreceptors

Question 12

Mechanoreceptors in the skin:

What do mechanoreceptors do?

Answer 12

help fine tune fiber to somatic stimulation features

Question 13

Mechanoreceptors in the skin:

what are the afferent fibers that lack specialized receptor cells?

Answer 13

free nerve ending- pain sensation

Question 14

Mechanoreceptors in the skin:

what do afferents with encapsulated endings do?

Answer 14

Lowers threshold for initiating AP

more sensitive to sensory stimulation than free nerve endings

Question 15

Mechanoreceptors in the skin:

what are 4 characteristics anout Merkel cell afferent?

Answer 15

highest spatial resolution (0.5mm)

slowly adapting

enriched in fingerprints

sensitive to points, edges, curvanture, process info anout form and texture.

Question 16

Mechanoreceptors in the skin:

what are 6 characteristics about meissner afferent?

Answer 16

high spatial resolution (3mm)

rapidly adapting

low frequency vibrations

high innervation of hand, closest to skin surface

4 times more sensitive than markel afferents, close to surface

transduced info when textured objects move across skin (Grip)

Question 17

Mechanoreceptors in the skin:

5 characteristics of Pacinian afferent

Answer 17

Located deep in dermin, rapdly adapting

the most sensitive of all mechanoreceptors

low spatial resolution > 10mm

activated by high frequency 5-1000 hz

detect vibrations though an object

Question 18

Mechanoreceptors in the skin:

4 characteristics of Ruffini afferent

Answer 18

located depp in the skin, slowly adapting

low spacial resolution >7mm

responsive to internally generated stimuli ie movement of fingers

accurate info on fingers position and hand conformation

Question 19

pathway of mechanosensory

Answer 19

• cutaneous info into dorsal root
• ipsilateral up dorsal column (gracile or cuneate tracts)
• synapse in caudal medula in gracile or cuneate nuclei
• cross over via internal arcuate fibers goes up medial lemiscus tract
• synapses onto ventral posterior lateral nucleus of thalamus
• projects to somatosensory cortex

Question 20

proprioceptors:

what do they do?

Answer 20

give continuous info on limb position and other body parts in space

Question 21

proprioceptors:

Muscle spindles

where are they found/ made of?

Answer 21

in skeletal muscles; consist of specialized intrafusal muscle fibers

Question 22

proprioceptors:

muscle spindles

characteristics of their sensory afferents?

Answer 22

coiled around intrafusal fibers

consist of group 1a and group 2 afferents

Question 23

proprioceptors:

muscle spindles

what does group 1a do?

Answer 23

movement of limbs

Question 24

proprioceptors:

muscle spindles

what does group 2 do?

Answer 24

static limb position

Question 25

proprioceptors:

muscle spindles what do they do?

Answer 25

encode info on muscle length changes

Question 26

proprioceptors:

Golgi tendon organs

which group is afferent>

Answer 26

1b is afferent

Question 27

proprioceptors:

Golgi tendon organs

how are they distributed?

Answer 27

among collagen fibers of the tendon

Question 28

proprioceptors:

Golgi tendon organs

what do they provide?

Answer 28

information on the tension on the muscle

Question 29

what is the Proprioceptive Pathway?

Answer 29

-lower body proprioception dorsal root and up dorsal colum
-synapse to Clarke’s nucleus, project up dorsospinocerebellar tract
-sends colaterals ipsilaterally to cerebellum and other collaterals cross caudal medulla
-medial lemiscus synapses to ventral posterior lateral nucleus of thalamus
-projects to somatosensory cortex
-upper body info goes same path as mechanosensory but also sends collaterals ipsilaterally to
cerebellum

Question 30

Primary somatosensory cortex:

Where does the mechanosensitive and propriceptive info arise from?

Answer 30

from ventral posterior complex of thalamus project to layer 4 of the primary somatosensory cortex

Question 31

Primary somatosensory cortex:

what brodmann’s areas

Answer 31

3a, 3b, 1, 2