sensory receptors Flashcards
different kinds of sensory receptors neurons
- DRG = pseudo-unipolar
- sensory neurons in retina = rods and cones
- olfactory bulb
- auditory nerve
classification of receptors on basis of energy form
- mechanoreceptors
- photoreceptors
- thermoreceptors
- chemoreceptors
energy form
on the basis of the energy that each receptor will respond to
adequate stimulus
a type of energy form that is appropriate for that receptor
mechanoreceptors
respond to mechanical stimulation such as pressure
photo receptor
light energy
chemo receptor
chemical energy such as osmotic pressure
thermo receptor
thermal energy
classification of receptors on basis of function
- exteroceptors
- interoceptors
types of exteroceptors
- distance receptors
- contact receptors
exteroceptors
stimuli coming from outside of the body
- divided into 2 classes
distance exteroceptor receive
light, sound, etc
contact exteroceptor receive
touch, pressure, pain
types of interceptors
- equilibrium receptors
- proprioceptors (position and movement of muscles and joints)
- visceroceptors
equilibrium receptors
position in space, in the inner ear
proprioceptors
unconscious sensation of the body
visceroceptors
chem, glucose, pH, oxygen receptors
structural classification of sensory receptors
- free nerve ending
- nerve ending associated with accessory structure
- nerve ending associated with specialized receptor cells
free nerve ending
simplest!
- neurons with terminals that have no capsules and no specialized apparatus in their endings
- ex: pain receptors
nerve ending associated with accessory structures
e.g. pacinian corpuscle - mechanical touch
- myelinated nerve with the connective tissue wrapped around its nerve ending
nerve ending associated with specialized receptor cells
e.g. taste receptor
- specialized receptor cells that the nerve ending synapses
- bipolar afferent neurons synapse with taste receptors that pick up taste
physiological classification of receptors
- based on adaptation
1. slowly adapting
2. rapidly adapting
3. very rapidly adapting
receptive field
area in the periphery where application of an adequate stimulus will cause the receptor to respond
example receptive field
- DRG (somatosensory pain afferent)
- the central process goes into the spinal cord
- peripheral process innervates an area of the skin
- area innervated by this neuron has a receptor field in the periphery
sensory transduction
you apply a stimulus, the NS doesn’t understand bc energy forms have to be converted into APs
- converts a stimulus from that energy form into action potentials (spikes) that carry the information of the stimulus
ex: DRG
generator potentials
- intracellular recordings from the afferent nerve fiber
- in corpuscles
- insert probe
- apply a force
- stimulus is recorded into afferent fiber
- electrical depolarizations captures
receptor potentials (taste receptor)
- recorded in receptor cells
- taste substance contacts the taste receptor cells
- change in voltage
- release synaptic vesicles
- activate the afferent neuron
- AP
electrotonic (local) potentials properties
- passive
- decrement in space
- graded
- can summate
- can initiate action potential
(like IPSP and EPSP)
electrotonic (local) potentials types
- receptor potentials (in receptor cells)
- generator potentials (in neuron)
- synaptic potentials
- sub-threshold potentials
transduction process
- stimulus
- local change in permeability
- local depolarization (generator potential)
- conducted action potential
muscle spindles and their coding
- specialized muscle cells
- afferent sensory neurons wrap around these cells
- spindle is stretched so afferent neuron fires
- the more you stretch the more firing you get
muscle spindles
- cells in muscles
- receptor for muscle stretch
- striated endings
- proprioceptors
- inside the intrafusal muscle fibers
(rest of muscle fibers are extrafusal)
frequency coding
- if you suspend a weight on muscle then stretch it…
the more weight = more stretch = more spikes/minute - they tell us how the intensity of the stimulus is coded
muscle spindle recording`
record from spindle down the axon toward the body
frequency coding relationship when graphed
logarithmic
Weber-Fechner Law
- harder to discriminate stimulus intensity when sound is loud
- easier to discriminate when sound is lower
how is stimulus intesity coded?
- frequency of impulses
- recruitment of more afferents
sensory adaptiation
sensation produced by a constant stimulus declines with time
adaptation when graphed
stimulus applied for extended period of time:
- initially: high frequency
~adaptation~
- reduction of frequency and can even reach zero
do all receptors have adaptation? do they all adapt the same?
- no, pain receptors do not
- no, have different speeds
very rapidly adapting receptors
ex: Pacinian Corpuscle for vibration
- respond to changes in stimulation (burst of excitation)
Pacinian Corpuscle Adaptation
- apply a pressure stimulus to the
Pacinian Corpuscle - it gives you a spike
on the onset of the stimulus, just one
spike. - A vibrating stimulus
is needed for a decent response, a train
of impulses is generated, - then the
brain will know that the Pacinian
Corpuscle is being stimulated.
slowly-adapting receptors
respond only to the presence or absence of stimulus
