Overview of Sensory Systems & Receptors Flashcards
Sensory receptor cells definiton
- detect stimulus (e.g. light) +
- transmit info to second order neuron through synaptic transmission
- e.g. photoreceptros of visual system
- e.g. olfactory receptor cells
Transduction definition
- process of detection of sensory input +
- transformation of info ==> neuronal signal (change in neuronal action potential)
Receptor potential definition
- stimulus interacts w/receptor proteins @ receptive region of sensory receptor neuron ==>
- direct or indirect change in membrane potential
- = depolarization OR hyperpolarization
- stimulus-elicited change = “receptor potential”
Short vs. Long Sensory receptors
- short: receptor potential diffuses to synaptic end passively ==> alter of NT release
- e.g. photoreceptor cells, auditory hair cells
- long: regenerative APs to carry signal (b/c receptor potential only impact local area)
- e.g. skin mechanoreceptors
NT for most sensory receptor cells
glutamate
Example/Mechanism of deploarzing receptor channel
- e.g. muscle mechanoreceptors
- depolarizing receptors = increase nonspecific cation conductance
- sensory endings have mechanosensitive cation channels that open in response to stretch ==> depolarization of membrane in a graded fasion with intensity of stimulus
Example/Mechanism of hyperpolarizing receptors
- hyperpolarizing receptors =
- resting potentials ~ -30-40 mV due to resting cation conductance
- response to stimulus ==> closing of cation channels
- e.g. rod photoreceptor
- light ==> 1-cis-retinal ==> (induced conformational change) ==> 1-trans-retinal
- trans-retinal ==> rhodopsin to metarhodopsin ==> transducin (g-protein) stimulation
- ==> cGMP phosphodiesterase activation ==> cGMP to guanosine ==> closing of cGMP-gated cation channels ==> hyperpolarizing of photoreceptor cell
- ==> passive diffusion ==> decreased NT release
Sensory modalities definition/examples
- Different forms of energy are converted by the nervous system into different
sensations or sensory modalities - Examples of sensory modalities are: vision, hearing, smell, taste, touch and thermoreception
Labeled lines concept
- Conscious appreciation of sensory modality is determined by specific neuronal connections from sensory organs through thalamus to cerebral cortex
Main functions of sensory information
- conscious sensation
- control of movement
- maintaining arousal
Coding of stimulus modality by CNS
- each sensory system is part of an anatomically unique pathway
- = separate chain of neuons for each sensory system
- CNS codes stimulus modality by which nerve cells are active
Trasduction of stimulus intensity
- Intensity = magnitude of the generator potential increases as the intensity of the stimulus is
increased - stimulus intensity determines fraction of time that the transduction channels stay open (or closed)
- long sensory receptor cells code stimulus intensity as increase in AP firing frequency
C peripheral nerve fibers =
- small, unmyelinated axons
- 1 microm diameter
- 0.4 - 2m/sec
- contained w/in mixed peripheral nerves (e.g. sciatic w/sensory + motor)
A peripheral nerve fibers =
- found in mixed peripheral nerves
- alpha
- most rapid conducting
- beta
- gamma
- muscle efferents
- delta
Nerve diameter impact on conduction speed
- increased diameter ==> increased conduction speed
A(alpha) fibers: numerical designation, nerve fibers, diameter/conduction speed
- Ia = muscle spindle afferents
- Ib = tendon organ afferent
- very wide + very fast conduction
A(beta) fibers: numerical designation, nerve fibers, diameter/conduction speed
- II
- mechanoreceptors of skin
- secondary muscle spindle afferents
- medium diameter + medium conduction speed(<>
A(delta) fibers: numerical designation, nerve fibers, diameter/conduction speed
- III
- sharp pain
- cold temperature
- small diamter + slower conduction
C fibers: numerical designation, nerve fibers, diameter/conduction speed
- IV
- warm temperature
- burning pain
- itch
- crude touch
- very small + unmyelinated + slowest conduction
