Somatic Sensory System Flashcards
What sensory receptors have encapsulated nerve endings?
meissner and pacinian corpuscles
Where are meissner corpuscles found
palms, eyes, lips
What do Meissner corpuscles detect
light touch, texture, movement
Describe Meissner corpuscles
sensitive and rapidly adapting
Where are Pacinian corpuscles located
deeper in the skin
What do pacinian corpuscles detect
deep pressure, stretch
Describe Pacinian corpuscles
sensitive, rapidly adapting
Which sensory receptors have un-encapsulated nerve endings
Merkel discs, free nerve endings, Ruffini corpuscles
Where are ruffini corpuscles located
dermis, subcutaneous tissue
What do Ruffini corpuscles detect
heavy touch, pressure
Describe Ruffini corpuscles
slow adapting, proprioreceptor
Where are Merkel discs located
skin
What do Merkel discs detect
light touch, texture
Describe Merkel discs
slowly adapting
Where are free nerve ending located
epithelia, connective tissues
What do free nerve endings detect
pain, heat and cold
Describe hair follicles
varied sensory receptors - rapid and slow
Where are hair follicles located
epithelia
What type of receptors are sensory receptors
CELLULAR
How do rapidly adapting receptors respond
fire immediately - rapidly stop
What do rapidly adapting receptors give information about
changes in the stimulus
What do slowly adapting receptors give information about
persistence of stimulus
How do slowly adapting receptors respond
fire slowly - continue to fire if stimulus present
How are primary afferent axon subtypes classified
conduction velocity
Where is sensory information organised
spinal cord dorsal horn
Function of medial lemniscal tracts
carries mechanoreceptive, proprioceptive signals to the thalamus
function of spinothalamic tract
carries pain, temperature signals to thalamus
What are the two main somatosensory routes
medial lemniscal tracts, spinothalamic tract
How many neurons does sensory information travel through
3
Function of first order neurons
detect stimulus, transmit it to spinal cord
Function of second order neurons
relay signal to the thalamus, gateway to the cortex
Which order neurons are commissural?
second order
Function of third order neurons
relay from thalamus to cortex
How are axons of the medial lemniscal pathway organised?
Topologically
Describe the pathways of first order neurons from the upper and lower body in the Medial Lemniscal system
upper body - lateral
lower body - medial
What do first order axons from the lower body in the MSL synapse onto
neurons in gracile nucleus
What do first order neurons from upper body in MLS synapse onto
neurons in cuneate nucleus
What happens to second order neurons in the MLS
cross the midline
What do second order neurons in the MLS ascend in to
medial lemniscus
What is the lower body pathway
medial
What is the upper body pathway
lateral
What is a dermatome
specific domain of the body
What are somites
iterated structures
What do somites give rise to
musculature and skeleton
What do sensory ganglions associate with in the embryo
specific somite
What is the area of the cortex dedicated to each area of the body proportional to
density of innervation in that area
Describe the cortical map
highly plastic - change overtime depending on usage
