Sensory -Restrepo Flashcards
transduction
process of detection of a sensory input and transformation of information into a change in neuronal action potential
in sensory system, where does initial interaction with stimulus occur
sensory receptor cells
examples of sensory receptor cells
olfactory (odorants)
photoreceptors (sense light)
mechanoreceptors (detect touch/pressure)
2 main regions of interest in sensory receptor
1) receptive region (specialization associated with absorption of specific energy type)
2) synaptic region specialized to transmit info to next cell
how do sensory receptors differ from other neurons
receptove region especially sensitive to 1 of a variety of physical stimuli (heat, cold, mechanical deformation, light, chemicals)
receptor (generator) potential
stimulus-elicited change in membrane potential (depolarization or hyperpolarization)
short sensory receptor cells
receptor potential spreads via passive electronic transmission
which receptor types don’t need regenerative APs
short receptor cells
long receptors
(somatosensory receptor cell)
must employ regenerative APs to carry info from receptive end to synaptic release
receptor potential only affects limited portion of cell near receptive ending
(e.g. skin mechanoreceptors, cell bodies (soma) and long axons along spinal cord that synapse with 2nd order neurons in brainstem)
What happens after depolarization of sensory receptor cells
membrane depolarization in synaptic region–> opening of voltage sensitive Ca channels – vesicle fusion and release of NTs interact with lignad-gated (or G-protein-linked) receptors –> directly alter postsynaptic cells membrane potential
NT for most sensory receptor cells
glutamate
Membrane potentials arise from
differential conductance of membrane to certain ions
What alters opening of ion channels in sensory receptors
detection of adequate stimulus by receptor proteins
Results of opening of ion channels
depolarization in some neurons and hyperpolarization in others
Example of a cell depolarizing with stimulation
- muscle mechanoreceptors in sensory endings that dorsal root ganglion neurons extend into muscle spindle – mechanosensitive cation channels open in response to stretch
- due to increase in cation conductance in receptive membrane
- membrane potential moves toward 0 mV
- cation conductance increases/depolarization increases in a graded fashion with the intensity of the stimulus
Example of cell hyperpolarizing due to stimulus
- Rod photoreceptor
- have res;ting potentials between 0 and -70 mV (generally -30-40)
- some K channels open at rest in receptive area due to resting cation conductance open in the receptive area
- hyperpolarization response to stimulus when adequate stimulus causes some receptors of cation channels to close (K can’t get in so resting potential more negative– hyperpolarizes) –> decreased NT release
hyperpolarization of rod photoreceptors in response to light
receptor protein = rhodopsin
- when cis retinal (bound to rhodopsin) absorbs light–> retinal changes conformation to all trans-retinal –> conformation change in receptor protein from rhodopsin to metarhodopsin –> stimulates G protein transductin –> activates cGMP phosphodiesterase that causes breakdown of cGMP –>decrease of cGMP –> closure of cGMP-gated cation channels –> hyperpolarization and less NT release
Sensory systems convey info about attributes of a stimulus: what are these5 attributes
modality, intensity, quality, duration/ frequency, location
Sensory modalities
different forms of energy converted by nervous system into different sensations
Examples: vision, hearing, smell, taste, touch and thermoreception
information from sensory receptor cell to CNS is processed and used for what 3 main functions:
conscious sensation, control of movement, maintaining arousal
where is information routed to get through cerebral cortex
generally information becoming conscious goes through thalamus
T/F Separate pathways to CNS for different sensory systems
True
Subdivisions of thalamus
- each specialized in relaying and processing info for particular sensory modality
- visual –> Lateral genticulate nucleus to visual cortex in occipital lobe
- auditory through medial geniculate nucleus (MGN) to auditorycortex in temporal lobe
- olfactory system informaiton does NOT have to relay through thalamus to get to olfactory cortex
Receptor potential increases as _______ increases
intensity of stimulus
- due to fact that fraction of time transduction channel opens depends on stimulus intensity
- example – weak touch – open a small percent of time with weak tough and most of the time with strong touch
Are transduction channels voltage dependent
NO!! sensitive only to adequate stimulus
Transduction channels don’t open in response to depolarization
in Long receptor cells stimulus intensity is coded by what?
frequency of firing of APs
Types of peripheral nerve fibers
A alpha, Abeta, Adelta, C
A alpha fibers
1a - muscle spindle afferent, 1b= tendon organ afferent
- Diameter = 10-20 micrometers
- Speed: fASTEST
A beta fibers
(II)
- Mechanoreceptors of skin, secondary muscle spindle afferents
- Diameter 5-10 microm
- Speed: 2nd fastest
A delta
(III)
- Sharp pain, cold temperature
- Diameter: 2nd smallest
- Speed - second slowest
C fibers
(IV)
- Warm temperature, burning pain, itch, crude touch
- Diameter
- Speed: smallest/slowest and unmyelinated
