Lecture 14 Sensory Physiology Flashcards
Sensory receptors
- specialized cells that detect a specific type of stimulus
- sensory receptors are transducers that convert stimuli into changes in membrane potential
Transducer
a device that converts variations in a physical quantity, such as pressure or brightness, into an electrical signal, or vice versa.
Structural types of sensory receptors
free nerve endings
modified nerve ending
separate sensory receptor cells
Sensitivity of sensory receptors
each sensory receptor has an adequate stimulus that it responds best to
Functional classes of sensory receptors
responsive to particular sensory modalities
chemoreceptors, mechanoreceptors, photoreceptors, thermoreceptors, nociceptors
Chemoreceptors
specific chemicals (taste, olfaction), pH, O2
Mechanoreceptors
touch, pressure, stretch, vibration, sound, acceleration
photoreceptors
light
nociceptors
pain
noxious stimuli (chemical, mechanical, thermal)
*noxious is harmful, poisonous or unpleasant
Sensory transduction
sensory receptors produce graded receptor potentials in response to sensory stimuli
sensory neurons convert receptor potentials into streams of action potentials.
Stimulus -> sensory receptor(receptor potential) -> sensory neuron(action potentials) -> CNS
receptive field
area supplied by one sensory neuron
two point discrimination test
smaller receptive fields result in more sensitive discrimination
Afferent Division of PNS
Conveys APs from sensory neurons to the CNS
somatic sensory, visceral sensory, special senses
Somatic Sensory
touch, temperature, pain, proprioception (general sesnes)
Visceral Sensory
Mechanical and chemical stimuli from internal organs
special senses
vision, hearing, equilibrium, olfaction, taste
Sensory pathways in the CNS
ascending tracts in the spinal cord (somatic senses)
1st order neurons, second order neurons, third order neurons.
Cranial nerve sensory pathways
First order sensory neurons
from receptors to spinal cord or brainstem
second order neurons
from spinal cord or brainstem to thalamus
third order neurons
from thalamus to cerebral cortex
Sensory areas of the cerebral cortex
somatosensory cortex - parietal lobe
visual cortex - occipital lobe
auditory cortex - temporal lobe
CNS integration of sensory information
Properties of stimuli
modality, location, intensity, duration
Modality of stimulus indicated by
specificity of receptors and sensory neurons activated
specific neural pathways in the CNS -> specific areas in the brain (“labeled line coding”)
Location of stimulus
specific neural pathways connect receptive fields to specific locations in the cortex
sound localization uses differences in timing form R and L ears
lateral inhibition- increases contrast between adjacent receptive fields
Intensity of stimulus encoded by
number of receptors activated
frequency of action potentials in sensory neurons
Duration of stimulus
coded by duration of APs
Receptor Adaptation
decreases in response to a persistent stimulus over time
Tonic receptors and Phasic receptors
Tonic Receptors
non-adapting or slowly adapting
fairly constant response to sustained stimulus
e.g. muscle spindle stretch receptors
Phasic receptors
rapidly adapting
respond to initial change in stimulus, then decrease response
e.g. olfactory receptors
