Sensory Receptors Flashcards
Understand that the basis for the receptor (generator) potential is the opening or closing of different ion channels
The detection of the adequate stimulus by receptor proteins directly or indirectly alters the opening of ion channels.
What is a transduction channel, and how does it differ from voltage-dependent ion channels?
The sensory receptor differs from other neurons in that its receptive region is especially sensitive to one of a variety of physical stimuli such as light, heat, cold, mechanical deformation or to chemicals dissolved in solution. The interaction of the stimulus 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
Why are action potentials necessary to transmit
information in long sensory receptors?
Because the receptor potential itself only affects a limited portion of the cell near the receptive ending. Action potentials allow transmission of information for distances as long as 4 ft!
How do we perceive the modality of a stimulus?
Which modality a sensory organ responds to is determined by the selectivity of the sensory receptor cells. Conscious appreciation of sensory modality is determined by specific neuronal connections from sensory organs through thalamus to cerebral cortex. Thus, there is a separate chain of neurons (a separate labeled line) for each sensory system.
What is the route generally taken by sensory information that will reach sensory cortex to become conscious?
In general, information that becomes conscious is relayed through the thalamus to the cerebral cortex
Understand that, with the exception of the olfactory system, sensory systems send axonal input into the thalamus where they convey information, through synaptic input, into thalamic neurons. Thalamic neurons then convey information to sensory cortex.
The thalamus contains several subdivisions (nuclei) some of which are specialized in relaying and processing information for particular sensory modalities. Visual information is relayed through the lateral geniculate nucleus (LGN) of the thalamus to visual cortex in the occipital lobe, while auditory information is relayed through the medial geniculate nucleus (MGN) to auditory cortex in the temporal lobe. The olfactory system is an exception as the information does not have to relay through thalamus to reach olfactory cortex.
Explain how stimulus intensity is encoded by sensory receptors.
The reason the receptor potential changes as a function of stimulus intensity is because the fraction of the time that transduction channels spend in an open state depends on stimulus intensity. Transduction channels are not voltage-dependent; they are sensitive only to the adequate stimulus. Thus, unlike voltage-dependent sodium channels, transduction channels do not open in response to cell depolarization.
How is encoding of stimulus intensity different between short and long receptors?
In long sensory receptor cells, depolarization elicits an increase in the firing frequency of action potentials. As a result, stimulus intensity is coded by frequency of firing of action potentials in long receptor cells. In short sensory cells, intensity is determined by the amount of opened channels.
What is the relationship between size/myelination
and conduction velocity?
smaller diameter leads to slower velocity. A-alpha, A-beta, and A-delta are myelinated axons. A-alpha: Muscle spindle afferent and tendon organ afferent. A-beta: Mechanoreceptors of skin, secondary muscle spindle afferents. A-delta: Sharp pain, cool temperature, extreme hot temperature.
C fibers are unmyelinated and so have slower speed- sense warm temp, burning, pain, itch, crude touch
What are the different types of sensory receptors?
Special senses:
Visual- light- photons
Auditory- oscillatory changes in air pressure
Vestibular system- balance
Chemical senses- flavor- taste- water soluble chemicals
Chemical senses- olfaction- volatile chemicals in the air
Somatosensory system:
Anterolateral system- pain and temperature
Posteromedial (lemniscus)- touch (exteroception), proprioceptio
How does the photoreceptor rod work?
Light leads to hyper polarization. The cell starts at Vm of -40 and goes to -70 with stimulation through second messenger transduction. The cell starts with many open K channels and many open cGMP channels (non-selective cation). Rhodopsin is a 7 trasmembrane spanning domain, but with light stimulation, it becomes trans and will bind transducin, which becomes activated and then activates cGMP phosphodiesterase that converts cGMP to Guanosine. This Amplifies the signal and stops releasing neurotransmitters.
How do mechanoreceptors of the DRG touch neuron work?
With stretch, the tethered gates open and the cell depolarizes, creating an action potential that travels up the axon
