sensory receptors Flashcards
- Understand that mutations in genes that encode for proteins involved in phototransduction often lead to retinitis pigmentosa (Box B of Chapter 10 in Purves).
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Describe morphological features of sensory receptor
1) a receptive region, which may display a
morphological specialization associated with the absorption of a specific kind of physical energy; 2)Near the receptive region there is a region identifiable morphologically by being rich in mitochondria, presumably associated with the need for replacement of energy consumed in the transduction process. 3) soma. 4) axon. 5) a synaptic region, specialized to transmit information to the next cell in line. 1) a receptive region, which may display a
morphological specialization associated with the absorption of a specific kind of physical energy; 2)Near the receptive region there is a region identifiable morphologically by being rich in mitochondria, presumably associated with the need for replacement of energy consumed in the transduction process. 3) soma. 4) axon. 5) a synaptic region, specialized to transmit information to the next cell in line.
What is a transduction channel
A channel that detects some sort of sensory input and transforms that info into a change in neuronal polarization. NOT voltage gated channels
receptor potential
The interaction of a stimulus(light, heat, cold) with receptor proteins localized to the receptive region of sensory receptors elicits directly or indirectly a change in the membrane potential of the sensory receptor cell.
Examples of short sensory receptor cells
Rod photoreceptor cells and auditory hair cells
cell structure of short receptor cells vs long receptor cells
Short: does not have an axon. Long: has an axon
Describe receptor potential in short sensory receptor cells
The receptor potential spreads to the synaptic end of the cell by passive electrotonic transmission. Thus the receptor potential of a short cell very effectively alters the rate of transmitter release from that cell and so
regenerative action potentials are not necessary.The receptor potential spreads to the synaptic end of the cell by passive electrotonic transmission. Thus the receptor potential of a short cell very effectively alters the rate of transmitter release from that cell and so
regenerative action potentials are not necessary.
Examples of long sensory receptors
somatosensory receptor cell, skin mechanoreceptors
Describe receptor potential in long sensory receptor cells
must employ regenerative action potentials to carry
information from the receptive ending (e.g. in skin or muscle) to the synaptic release site (e.g., in the spinal cord or brain stem) because the receptor potential itself only affects a limited portion of the cell near the receptive ending.must employ regenerative action potentials to carry
information from the receptive ending (e.g. in skin or muscle) to the synaptic release site (e.g., in the spinal cord or brain stem) because the receptor potential itself only affects a limited portion of the cell near the receptive ending.
Neurotransmitter for most sensory receptor cells
glutamate
Describe depolarizing receptor potentials
Stimulus causes increase in nonspecific cation conductance in the receptive area membrane. This conductance increase causes the membrane potential to move toward 0 mV.The cation conductance increase, and hence the depolarization, increases in a graded fashion with the intensity of the stimulus.
example of depolarizing sensory receptors
Muscle mechanoreceptors: dorsal root ganglion neurons extend sensory endings into muscle spindles. These sensory endings have mechanosensitive cation channels that open in response to stretch, depolarizing the cell
Describe hyperpolarizing receptor potentials
Sensory receptors have resting potentials btw 0mV and -70mV. Stimulus causes cation channels in receptive area to close, hyperpolarizing the cell.
example of hyperpolarizing sensory receptors
rod photoreceptor - 1. light stimulation of 1-cis-retinal bound to rhodopsin receptor in optic disc causes change of conformation to 1-trans-retinal which further changes rhodopsin to metarhodopsin which activates G protein transducin. 2. cGMP phosphodiesterase (PDE) is activated. 3. PDE hydrolyzes cGMP reducing its concentration. 4. cGMP gated- cation channels close. 5. hyperpolarization and the synaptic end does not release neurotransmitter anymore
Unique feature of photoreceptors
The photoreceptor does not fire action potentials. Rather, the hyperpolarization is transmitted to the synaptic end by electrotonic transmission
examples of hyperpolarizing and depolarization sensory receptors
Some receptors, such as hair cells of the auditory system, respond to stimulation with an oscillatory change in generator potential alternating between depolarization and hyperpolarization
Five attributes of a stimulus
modality (ie, vision, hearing, smell, taste) ,intensity (stimulus strength) , quality (ie. Color of light, vibration, etc), duration or frequency (how many times per second the stimulus takes place ie. Pitch) and location
Where does sensory information that becomes concious realy
through thalamus to the cerebral cortex
Which nuclei relay visual info, auditory info, and olfactory info
Visual: relayed through the lateral geniculate nucleus (LGN) of the thalamus to visual cortex in the occipital lobe. Auditory: relayed through the medial geniculate
nucleus (MGN) to auditory cortex in the temporal lobe. Olfactory: is an exception as the information does not have to relay through thalamus to reach olfactory cortex.
How does receptor potential change as intensity of stimulus changes
The magnitude of the generator potential increases as the intensity of the stimulus is increased, because the fraction of the time that transduction channels spend in an open state depends on stimulus intensity
Are transduction channels voltage sensitive
No, they are only sensitive to the adequate stimulus
How do long sensory receptor cells respond to increased stimulus intensity
As stimulus intensity increases, these cells increase in action potential firing frequency.
How are peripheral nerves classified in terms of conduction velocity and size?
Aa: Muscle spindle afferents (Ia) and tendon organ afferents (Ib), 10-20um diameter, 60-120m/sec speed. Ab: mechanoreceptors of skin, secondary muscle spindle afferents (II), 5-10um diameter, 30-60m/sec. Ad: Sharp pain, cold temp (III), 1-5um diameter, 4-30 m/sec speed. C: warm temp, burning pain, itch, crude touch (IV), 0.2-1.5um diameter (unmyelinated), 0.4-2m/sec
What is the relationship between size/myelination and conduction velocity?
larger/myelinated: fastest. Smaller/unmyelinated: slowest
list the cells/nerves involved in transmission of light, sound and taste
light: photons > photoreceptors > CN2. Sound: change in pressure > hair cells > CN8. Taste: Chemical in air > olfaction > olfactor sensory neurons > CN1 OR chemical in saliva > taste cells > CN7,9,10
Which somatosensory system detects touch and proprioception
posterior colum-medial lemniscus tract
Which somatosensory system detects pain and temp
anterolateral tract
