Flashcards in Lecture 5: Sensory Systems Deck (90)
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sensation
process where physical or chemical stimuli from external environment or from body itself are transformed into neural signals (action potentials)
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Perception
brain processes neural signals to understand the stimuli
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Difference between sensation and perception
sensation is detecting a stimulus while perception is understanding the stimulus
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Three major steps of sensation
1. stimuli are captured by specialized cells (sensory receptor cells)
2. Captured signals are transformed into neural signals
3. neural signals are passed to the CNS
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What's different about sensory receptor cells for touch (aka somatosensation)?
Nerve endings serve as sensory receptors
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What does stimulation of sensory receptors by physical or chemical stimuli cause?
Selective ion channels open which results in changes to the membrane potential. If the integrated effect of local potentials is large enough, APs are triggered (temporal and spatial summation applies)
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How are sensory cells connected to the brain?
sensory nerves project to spinal cord or brainstem then synapse with spinal dorsal horn neurons which convey signals to primary sensory cortex via thalamus
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What do the dorsal horns of the spinal cord contain?
Cell bodies of sensory neurons
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What do the ventral horns of the spinal cord contain?
Cell bodies of motor neurons
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Primary sensory cortex
receive inputs mainly from thalamic relay nuclei (except olfactory cortex)
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Secondary sensory cortex
receive inputs mainly from primary cortex within the same sensory system
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association cortex
receive inputs from multiple sensory systems usually from the secondary sensory cortex .
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Transduction
captured signals are transformed into neural signals (generation of APs)
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Sound stimuli
Vibration of air molecules. Properties include: amplitude, frequency, and complexity.
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What contributes to complexity of a sound
sound waves of different amplitude and frequency
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What is the tympanic membrane and what is it attached to?
Tympanic membrane is the eardrum. It's attached to a series of bones called ossicles.
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Structures of the ossicles
malleus, incus, stapes
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Function of the ossicles
To amplify the vibrations by 20x
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Oval window
membrane covered opening to the cochlea
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What does vibration of the oval window do?
Moves the fluid in the cochlea
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How is sound converted into neural signals?
waves of air are converted to waves of fluid which is converted into AP spikes within cochlea when hair cells bend
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Why are the ossicles needed to amplify sound waves?
Soundwaves travel faster in fluid than in air but it takes much more energy to start the vibrations
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How many chambers in the cochlea
three, fluid filled chambers
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Membranes in the cochlea
Tectorial and basilar membranes
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What are the auditory sensory receptor cells and where are they found?
Hair cells. Found embedded in the basilar membrane.
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Describe a hair cell
Hair cells themselves have hair-like structures called stereocilia. The tops of the stereo cilia are attached to the tectorial membrane while cell bodies are embedded in basilar membrane.
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How do hair cells pick up sound stimuli?
Fluid vibration dislocates the tectorial and basilar membranes causing stereocilia to bend.
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What does the bending of the stereocilia do?
Opens mechanosensory ion channels called TRPA1 (transient receptor potential A1 channel) and K+ and Ca2+ ions enter depolarizing the hair cell.
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Does the hair cell itself fire action potentials?
No! The influx of K+ and Ca2+ triggers opening of voltage gated calcium channels. Calcium ions enter and trigger release of NTs which excite auditory nerves contacting the hair cell bottom. The nerves fire pattern of APs encoding stimulus.
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