Overview of Sensory System Flashcards
How is the receptor (generator) potential related to the opening or closing of ion channels?
The detection of adequate stimulus by receptor proteins directly or indirectly alters the opening of ion channels. These may be depolarizing or hyperpolarizing.
How do depolarizing receptor (generator) potentials function?
Generally, they depolarize via an increase in nonspecific cation conductance in the receptive area membrane. The cation conductance increases in a graded fashion with the intensity of the stimulus.
How do hyper polarizing receptor (generator) potentials function?
Cells that hyperpolarize have some K+ channels, but also a substantial resting cation conductance open in the receptive area. The hyper polarizing response arises when adequate stimulus causes some of the open cation channels to close.
How does light hyper polarize rod cells/photoreceptors?
Photoreceptors have high cGMP and cGMP-gated cation channels maintain Em ~40. Rhodopsin is bound to disk membranes and 1-cis-retinal. Photons hit 1-cis-retinal -> 1-trans-retinal -> triggers conformational change in Rhodopsin -> metarhodopsin. Metarhodopsin activates G-Protein “Transducin” -> activates cGMP phosphodiesterase -> breaks down cGMP. Lower cGMP -> closing of cation channels. No AP is fired, signal is conducted by electronic transmission.
How does stretch depolarize mechanoreceptors?
Mechanoreceptors in the muscle spindle have stretch sensitive, non-specific ion channels connected to each other by cytoskeletal strands. Stretching of the muscle spindle membrane opens the channels and causes depolarization. This triggers an AP in the mechanoreceptor.
What does the concept of “Labeled Lines” illustrate?
Conscious awareness of sensory information is determined by specific neuronal connections proceeding from the sensory organ or receptor through the thalamus to the cerebral cortex.
What are the three main functions that sensory information is used to direct, and how is it routed to these functions?
Conscious sensation, control of movement, and maintaining arousal. Conscious sensation results from information being routed through the thalamus to the cortex. Other functions are controlled via other pathways.
How is visual information routed?
Visual information is relayed through the Lateral Geniculate Nucleus (LGN) of the thalamus to the visual cortex in the occipital lobe.
How is auditory information routed?
Auditory information is relayed through the Medial Geniculate Nucleus (MGN) of the thalamus to the auditory cortex in the temporal lobe.
How is stimulus intensity encoded by sensory receptors?
As a general rule, the receptor potential increases in magnitude as the intensity of the stimulus increases. Cell Em de/hyper-polarizes accordingly.
How does the receptor potential increase with increased signal intensity?
Transduction channels open in an all or none fashion, so the intensity of the signal affects the length of time that the transduction channels are open. This maintains a proportional relationship between stimulus and response.
Are transduction channels voltage-dependent?
No. Transduction channels only open in response to adequate stimulus. If they were also voltage sensitive, they could not be able to encode intensity information as the depolarization of the cell would interrupt.
How do long sensory receptor cells encode stimulus intensity?
Long sensory receptor cells encode stimulus intensity as an increase in frequency of action potentials.
What are the four most common classes of neurons, which are myelinated, and what information do they typically carry?
Aa - Myelinated, Proprioception/muscle spindle info; Ab - Myelinated, Touch/mechanoreceptors of skin; Ad - Poorly myelinated, Sharp pain/cold temperature; C - Unmyelinated, warm temp/dull pain/burning/itch.
What are the average diameters and transmission speed of the four most common classes of neurons?
Aa - Diameter: 10-20 um, Speed: 60-120 m/s; Ab - 5-10 um, 30-60 m/sec; Ad - 1-5 um, 4-30 m/sec; C - 0.2-1.5 um, 0.4-2 m/sec.
