Sensory Physiology-Audition And Vision

Question 1

What are the 4 steps in sound transduction?

Answer 1

1. Mechanical vibrations
2. Fluid waves
3. Chemical signals
4. Action potentially

Question 2

Explain signal transduction

Answer 2

1. First transduction: sound waves strike the tympanic membrane and become vibrations
2. The sound wave energy is transferred to the three bones of the middle ear which vibrate
3. Second transduction: the stapes is attached to the membrane of the oval window create fluid waves within the cochlea
4. Third transduction: the fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and release neurotransmitter

Question 3

What is excitation?

Answer 3

When the hair cells bend in one direction, the cell depolarizers, which increases action potential frequency in the associated sensory neuron

Question 4

What are the 3 divisions of the ear?

Answer 4

Inner, middle and external ear.

Question 5

What components define the nature of sound?

Answer 5

Frequency (Hz) humans hear 20 to 20,00p
-high and low pitch)

Intensity(dB) normal convo is about 60 dB
-loudness perceived

Question 6

Explain sound transduction

Answer 6

1. First transduction- sound waves strike the tympanic membrane and become vibrations
2. The sound wave energy is transferred to the three bones of the middle ear which vibrate
3. 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
4. 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)
5. Fourth transduction: neurotransmitter release onto sensory neurons creates action potentials that travel through the cochlear nerve to the brain
6. 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.

Question 7

What is required for fluid movement of the cochlea?

Answer 7

Oval window moves inwards, which requires the round window to move outward for fluid movement

Question 8

What 8s the function of the saccule?

Answer 8

Part 9f 5he cochlear which plays a role in balance

Question 9

What is the function of the organ of corti?

Answer 9

Part of the cochlea

Sensor for vibration and site of action potential generation

Question 10

What moves as a result of fluid wave vibration in the cochlea?

Answer 10

Tectorial and basal membrane which then causes the stereocilia to move

Question 11

Contrast hair cell and stereocilia at rest and excitation

Answer 11

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

Question 12

Explain the signal transduction releasing neurotransmitters

Answer 12

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

Question 13

Summarize the path to auditory cortex

Answer 13

• 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

Question 14

Explain the formation of an image by the eye

Answer 14

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

Question 15

How does the shape of a lens affect how light is refracted?

Answer 15

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

Question 16

What is the focal length?

Answer 16

The distance from the center of the lens to the focal point

Question 17

What is accommodation?

Answer 17

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

Question 18

What is hyperopia? How is it fixed?

Answer 18

Hyperopia, or farsightedness, occurs when the focal point falls behind the retina

Common in those with eye balls too short
Corrected with convex lens

Question 19

What is myopia? How is it corrected?

Answer 19

Myopia, or near-sightedness, occurs when the focal point falls in front of the retina

Myopia is corrected with a concave lens

Question 20

Explain the organization of the retina

Answer 20

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

Question 21

What are the types of the photoreceptors?

Answer 21

Cones- function under phototopic conditions

Rods- function under Scott pic conditions

Question 22

Summarize phototransduction

Answer 22

1. Light stimulates photo pigment in receptor which activates a G-protein
2. 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.
3. This causes a decrease in glutamate release, this then leads to reduction in inhibition of neurons, causing them to become excited.
4. Alters intracellular concentration of 2nd messenger
5. Ion channel closes
6. Change in membrane potential

In the absence of light, photoreceptors are de polarized, light hyperpolarizes photoreceptors, which makes them different from other photoreceptors

Question 23

Explain phototransduction in rods

Answer 23

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

1. Rhodopsin= retinal+opsonization (the photo pigment) absorbs light and G-protein (transducin) is activated
2. Effector enzyme activated
3. Reduces cGMP (the second messengers )
4. cGMP-gated Na+ channels close
5. Rod membranes Hyperpolarize in response to light and neurotransmitter release is decreased

Question 24

What pathway does retinofungal projection take?

Answer 24

Optic nerve

Optic chiasm (OX)

Optic tract

Question 25

Explain retinofungal projection

Answer 25

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

Question 26

Summarize the effect of retinofungal projection

Answer 26

Left side of brain gets information from right visual hemifield.

Right side of brain gets information from left visual hemifeld

Question 27

What happens when retinofungal projection gets lesions?

Answer 27

Optic nerve: monocular blindness

OX lesion: bitemporal hemianiopia

Optic tract lesion: homonymous (same) hemianopia