Nervous system Part 2 Flashcards
What does the somatosensory system do?
mediates a diverse range of senstations
touch, pressure, limb position, vibration, temp, pain
where are the receptors located for the somatosensory system?
skin, muscle and tendons
tranmitted to CNS
What are the three sub-sytems of the somatosensory system and their function?
Cutaneous mechanoreceptors- touch, vibration, pressure
Proprioception- Muscles, tendons, joints, limb postion, load on joint
Pain and temperature
What is the somatosensory pathway?
Through the dorsal root ganglia and cranial nerve ganglia
What is a Dermatome?
the territory innervated from a singal dorsal root ganglion and its spinal nerve is called a dermatome
area of skin associated with spin
How many pairs of cervical nerves?
8
Transduction of mechanosensory afferent:
what does a stimulus do?
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
how do somatosensory afferent differ ?
axonal diameter and conduction velocities
how does the size of the receptor field vary?
two point discrimination- dependent on area (ie. fingers(3mm) have much smaller than arm(40mm))
Somatosensory afferents Attributes
:What is Temporal dynamics
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
Mechanoreceptors in the skin:
what is different about the afferent fiber’s?
encapsulated by specialized receptor cells
Mechanoreceptors
Mechanoreceptors in the skin:
What do mechanoreceptors do?
help fine tune fiber to somatic stimulation features
Mechanoreceptors in the skin:
what are the afferent fibers that lack specialized receptor cells?
free nerve ending- pain sensation
Mechanoreceptors in the skin:
what do afferents with encapsulated endings do?
Lowers threshold for initiating AP
more sensitive to sensory stimulation than free nerve endings
Mechanoreceptors in the skin:
what are 4 characteristics anout Merkel cell afferent?
highest spatial resolution (0.5mm)
slowly adapting
enriched in fingerprints
sensitive to points, edges, curvanture, process info anout form and texture.
Mechanoreceptors in the skin:
what are 6 characteristics about meissner afferent?
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)
Mechanoreceptors in the skin:
5 characteristics of Pacinian afferent
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
Mechanoreceptors in the skin:
4 characteristics of Ruffini afferent
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
pathway of mechanosensory
- 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
proprioceptors:
what do they do?
give continuous info on limb position and other body parts in space
proprioceptors:
Muscle spindles
where are they found/ made of?
in skeletal muscles; consist of specialized intrafusal muscle fibers
proprioceptors:
muscle spindles
characteristics of their sensory afferents?
coiled around intrafusal fibers
consist of group 1a and group 2 afferents
proprioceptors:
muscle spindles
what does group 1a do?
movement of limbs
proprioceptors:
muscle spindles
what does group 2 do?
static limb position
proprioceptors:
muscle spindles what do they do?
encode info on muscle length changes
proprioceptors:
Golgi tendon organs
which group is afferent>
1b is afferent
proprioceptors:
Golgi tendon organs
how are they distributed?
among collagen fibers of the tendon
proprioceptors:
Golgi tendon organs
what do they provide?
information on the tension on the muscle
what is the Proprioceptive Pathway?
-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
Primary somatosensory cortex:
Where does the mechanosensitive and propriceptive info arise from?
from ventral posterior complex of thalamus project to layer 4 of the primary somatosensory cortex
Primary somatosensory cortex:
what brodmann’s areas
3a, 3b, 1, 2
