Sensory Physiology-Audition And Vision Flashcards
What are the 4 steps in sound transduction?
- Mechanical vibrations
- Fluid waves
- Chemical signals
- Action potentially
Explain signal transduction
- First transduction: sound waves strike the tympanic membrane and become vibrations
- The sound wave energy is transferred to the three bones of the middle ear which vibrate
- Second transduction: the stapes is attached to the membrane of the oval window create fluid waves within the cochlea
- Third transduction: the fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and release neurotransmitter
What is excitation?
When the hair cells bend in one direction, the cell depolarizers, which increases action potential frequency in the associated sensory neuron
What are the 3 divisions of the ear?
Inner, middle and external ear.
What components define the nature of sound?
Frequency (Hz) humans hear 20 to 20,00p
-high and low pitch)
Intensity(dB) normal convo is about 60 dB
-loudness perceived
Explain sound transduction
- First transduction- sound waves strike the tympanic membrane and become vibrations
- The sound wave energy is transferred to the three bones of the middle ear which vibrate
- Second transduction: the stapes is attached to the membrane of the oval window. Vibrations of the oval window create fluid waves within the cochlea. This leads to deflection of stereocilia of hair cells of cochlea then release of neurotransmitters then creates an AP
- Third transduction: the fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and release a neurotransmitter (we just mentioned this)
- Fourth transduction: neurotransmitter release onto sensory neurons creates action potentials that travel through the cochlear nerve to the brain
- Energy from the waves transfers across the cochlear duct into the tympanic duct and is dissipated back into the middle ear at the round window
4.
What is required for fluid movement of the cochlea?
Oval window moves inwards, which requires the round window to move outward for fluid movement
What 8s the function of the saccule?
Part 9f 5he cochlear which plays a role in balance
What is the function of the organ of corti?
Part of the cochlea
Sensor for vibration and site of action potential generation
What moves as a result of fluid wave vibration in the cochlea?
Tectorial and basal membrane which then causes the stereocilia to move
Contrast hair cell and stereocilia at rest and excitation
a) at rest: About 10% of the ion channels are open and a tonic signal is sent by the sensory neuron
b) excitation: when the hair cells bend in one direction, the cell depolarizes, which increases action potential frequency in the associated sensory neurons
Explain the signal transduction releasing neurotransmitters
Displacement of the cilia in one direction increases the tension on the tip link and increases the influx of potassium. The entry of potassium causes depolarization and in turn, the entry of calcium through VGCC’s. The entry of calcium causes the release of neurotransmitter
Summarize the path to auditory cortex
- Cochlea transforms sound waves into neural signals
- Primary sensory neurons transmit this information to brain:
- The cochlear nerve becomes part of the vestibular nerve to then form the vestibular cochlear nerve(nerve 8)CN VIII which travels to the medulla
- Ascending tracts from the medulla then synapse at nuclei in midbrain and thalamus before progressing to auditory cortex
Explain the formation of an image by the eye
Step 1: light enters the eye through the pupil then converges in the retina
Change in size of pupil changes how much light enters; constricts in bright light (dilates in dark)
Change in shape of lens shows better focusing the light
Step 2: As parallel light rays pass into a medium where they are slowed, they will bend (refract) . Parallel light rays entering the eye are refracted by the cornea
How does the shape of a lens affect how light is refracted?
Concave( both sides inward) cause light rays to spread
Convex- cause light rays to come together
In the eye, light rays should converge on the retina for an image to be properly focused
What is the focal length?
The distance from the center of the lens to the focal point
What is accommodation?
The lens performs changing the shape of the lens via contraction to ciliary muscles which relax zolua fibers.
Th8s causes the lens to become more round/thicken
What is hyperopia? How is it fixed?
Hyperopia, or farsightedness, occurs when the focal point falls behind the retina
Common in those with eye balls too short
Corrected with convex lens
What is myopia? How is it corrected?
Myopia, or near-sightedness, occurs when the focal point falls in front of the retina
Myopia is corrected with a concave lens
Explain the organization of the retina
Retina has a laminar organization, with the layers seemingly inside out
-Exception: In the fovea, the photoreceptors receive light directly because the fovea is a pit and so the interviewing neurons are pushed off the to the side. This is region of most acute vision
Exception: optic disc which is where the optic nerve and blood vessels leave the eye and thus, has no photoreceptors -the blind spot
What are the types of the photoreceptors?
Cones- function under phototopic conditions
Rods- function under Scott pic conditions
Summarize phototransduction
- Light stimulates photo pigment in receptor which activates a G-protein
- This stimulates effector enzyme(rhodopsin, which is a pigment in rods) activated rhodopsin decreases cyclic GMP which also causes a decreases cyclic GMP gated ion channels and they close, causing Hyperpolarization.
- This causes a decrease in glutamate release, this then leads to reduction in inhibition of neurons, causing them to become excited.
- Alters intracellular concentration of 2nd messenger
- Ion channel closes
- Change in membrane potential
In the absence of light, photoreceptors are de polarized, light hyperpolarizes photoreceptors, which makes them different from other photoreceptors
Explain phototransduction in rods
Membrane potential in complete darkness about -30 mV, dark current
In darkness, rhodopsin is high and ion channels are open
cGMP (2nd messenger) levels are high; ion channels are open, tonic release of neurotransmitter
- Rhodopsin= retinal+opsonization (the photo pigment) absorbs light and G-protein (transducin) is activated
- Effector enzyme activated
- Reduces cGMP (the second messengers )
- cGMP-gated Na+ channels close
- Rod membranes Hyperpolarize in response to light and neurotransmitter release is decreased
What pathway does retinofungal projection take?
Optic nerve
Optic chiasm (OX)
Optic tract
Explain retinofungal projection
Visual field: the part of the world seen by an individual with both eyes open and looking straight ahead
Each visual field (one for left eye, one for right eye) is divided into nasal and temporal halves (hemifields) and each half is divided into quadrants
Binocular part of visual field: the central portion seen by both eyes, where left and right visual fields overlap
Monocular zones: region only seen by the corresponding eye
Summarize the effect of retinofungal projection
Left side of brain gets information from right visual hemifield.
Right side of brain gets information from left visual hemifeld
What happens when retinofungal projection gets lesions?
Optic nerve: monocular blindness
OX lesion: bitemporal hemianiopia
Optic tract lesion: homonymous (same) hemianopia
