Chp 13.15-.13.20 Flashcards
receptive field
area monitored by a singer receptor cell
the larger the receptive field, the poorer the ability to localize a stimulus
ex: receptive fields on the tongue or fingertips much smaller than on the skin of the abdomen
4 events along SENSORY pathways
- depolarization of receptor
- action potential generation
- propagation over labeled line
- CNS processing
- depolarization of receptor
physical or chemical stimulus results in graded changed in membrane potential of receptor cell
transduction
transduction
conversion of stimulus to a change in membrane potential
- action potential generation
if receptor cell depolarized to threshold, action potential develops in the initial segment
greater degree of depolarization=greater frequency of action potential
- propagation over labeled line
a labeled line consists of axons carrying information about one type of stimulus
CNS interprets stimulus according to the nature of the axon on which it arrives
- CNS processing
occurs at every synapse along the labeled line
line may branch repeatedly, distributing sensory information to multiple nuclei and centers in spinal cord and brain
events long MOTOR pathways from CNS processing
involuntary motor pathways and voluntary motor pathways
involuntary motor pathways
immediate involuntary response
respond before sensations reach cerebral cortex
ex: reflex response
voluntary motor pathways
1% of arriving sensations relayed to primary sensory cortex where perception occurs
voluntary response is not immediate
functional classes of free nerve endings
nociceptors, thermoreceptors, chemorecpetors, mechanoreceptors
2 axon types of nociceptors
type A fibers and type C fibers
nociceptors
pain receptors
free nerve endings with large receptive fields and broad sensitivity
type A fibers
FAST PAIN
ex: deep cut or injection
sensations quickly reach the CNS and trigger somatic reflexes
relayed to primary sensory cortex for conscious attention
can usually localize the stimulus within a few centimeters
type C fibers
SLOW PAIN
ex: burning and aching pain
cause a generalized activation of reticular formation and thalamus
individual is aware of the pain but has only a general idea of the area affected
thermoreceptors
temperature
free nerve endings
located in dermis, skeletal muscles, liver, hypothalamus
cold receptors 3-4 times more numerous than warm
chemoreceptors
respond to water-soluble and lipid-soluble substances that are dissolved in body fluids
mechanoreceptors
sensitive to stimuli that distort their plasma membranes
membranes contain mechanically gated ion channels
stretching, compression, twisting
gates open or close in response to:
3 mechanoreceptors
proprioceptors, baroreceptors, tactile receptors
proprioceptors
monitor position of joints and muscles
most complex
ex: muscle spindle
baroreceptors
detect pressure changes in walls of blood vessels and portions of digestive, respiratory and urinary tracts
tactile receptors
provide sensations of touch, pressure, and vibration
fine touch and pressure receptors
give detailed information about a stimulation
crude touch and pressure receptors
provide poor localization and give little information
tonic receptors
ALWAYS ACTIVE
frequency of generated action potentials reflects level of stimulation
increased stimulus=increased frequency
phasic receptors
NORMALLY INACTIVE
become active for a short time in response to a change in monitored conditions
peripheral adaptation, central adaptation
two types of adaptation
adaptation
reduction in sensitivity in the presence of a constant stimulus
peripheral adaption
occurs when level of receptor activity changes
receptors responds strongly at first, then activity gradually declines
central adaption
occurs along sensory pathways within the CNS
generally involves inhibition of nuclei along a sensory pathway
ex: new smell disappears after a few seconds
free nerve endings, root hair plexuses, tactile discs, tactile corpuscles, lamellated corpuscles, ruffini corpuscles
6 types of tactile receptors in the skin
free nerve endings
branching tips of sensory neurons
nonspecific
respond to touch, pressure, pain, temp
most common receptors in the skin
root hair plexus
monitor distortions and movements of hair follicle
displacements of hair distorts sensory dendrites and produces action potentials
adapt rapidly
tactile discs and Merkel cells
decect fine touch and pressure
extremely sensitive tonic receptors
very small receptive fields
each merkel cell and its nerve terminal make up a tactile disc
merkel cells
unusually large epithelial cells in stratum basale
dendritic processes from many nerve terminals branching from single mylinated afferent fiber make close contact with Merkel cells
tactile corpuscles or Meissner’s corpuscles
provide sensations of fine touch, pressure, low-frequency vibration
adapt to stimulation within a second
fairly large 100um
most abundant in eyelids, lips, fingertips, nipples
highly coiled and interwoven dendrite
lamellated corpuscles or pacinian corpuscles
sensitive to deep pressure
fast adapting
large receptors 4mm
single dendrite wrapped in layers of collagen fibers separated by intersitial fluid
found in fingers, mammary glands, superficial and deep fasciae and join capsules, viscera
ruffini corpuscles
sensitive to pressure and distortion of reticular dermis
ex: stretching of the skin
tonic receptors with little adaption
capsule surrounds core of collagen fibers
