Neuroscience Vision and Auditory

Receptive Field

Receptive Field

Group of photoreceptors that send inputs to particular bipolar or retinal ganglion cells.

Order of the Retina

Photoreceptor -> Bipolar Cell -> Ganglion Cell

Center-Surround Receptive Field

Photoreceptors that are arranged with a central disk and concentric ring

How do Receptive Fields see Edges?

As the gaze pans over an edge the dark edge stimulates the photoreceptors causing it to depolarize the cell

What happens when a shadow passes across a photoreceptor?

The photoreceptor depolarizes releasing more neurotransmitters

Off Center On Surround

Light in the center inhibits the cell of interest while stimulation of the surround excites it

Turn on without light, off with light

Most active when light is on the edges only

On Center Off Surround

Light in the center excites the cell of interest while stimulation of the surround inhibits it

Turn on with light, off without light

Most active with light is in the center only

Glutamate A

Photoreceptor Depolarization

Glutamate B

Photoreceptor Hyperpolarization

Type M ganglion cells

• Large

• Color Insensitive

• Rapidly Adapting

• Movement of Stimuli

• Radiations 1 and 2

Type P ganglion cells

• Small

• Color Sensitive

• Slow Adapting

• Presence of Stimuli (Color)

• Radiations 3-6

M Ganglion vs P Ganglion Numbers

Type P outnumber type M 100:1

Nasal Fibers Radiation Layers

1, 4, and 6 (Contralateral Eye)

Temporal Fibers Radiation Layers

2, 3, and 5 (Ipsilateral Eye)

The Right LGN

Left visual field from left nasal and right temporal

The Left LGN

Right visual field from right nasal and the left temporal.

Manocellular Pathway

Type M Cells

Parvocellular Pathway

Type P Cells

Lateral-Inferior Loop

Meyers Loop

Through the Temporal Lobe to the inferior calcarine sulcus

Superior Portion of the Visual Field, Inferior Occipital Lobe and Retina

Medial-Superior Loop

Through the Parietal Lobe to the superior calcarine sulcus

Inferior Portion of the Visual Field, Superior Occipital Lobe and Retina

Calcarine Sulcus

This is where fibers end and flip everything up is down, left is right

Blob

Color

V1 Cells

A lined up arrangement of LGN Cells

Respond best to moving edges of light and shadow presented at a specific orientation and direction

Orientation Selectivity

Directional Selectivity

the preference of a neuron for a visual stimulus moving in a particular direction compared to all other possible directions

Ocular dominance columns

Cortical columns consisting of neurons that receive signals from the left eye only or the right eye only

Extrastriate cortex

Part of brain that contains the Dorsal and Ventral Streams

Dorsal Stream

-Where pathway

• Lateral Parietal

• Spacial Aspects of Vision and Movement

Ventral Stream

• What Pathway

• Inferior Temporal

• Color Processing, Object Recognition

Neurons in Layer 4

Specialized to detect contrast of borders.

Pupillary Light Reflex

• Should be Consensual

• If Direct Constricts and Left Dilates then Efferent issue with CN3

• If Direct stays dilated and Contralateral eye constricts then CN 2 Afferent Problem

Light Mechanism

1. Light is shined in Right eye

2. Light Splits At Optic Chiasm Going to Left and right Pretectal Nuclei

3. Pretectal Nuclei stimulates the Eddinger-Westphal Nucleus on both sides

4. The Left and Right Eddinger-Westphal Nuclei generate action potentials throught the right and left Occulomotor Nerves

5. The Signal goes through the Ciliary Ganglia to lens causing both pupils to constrict.

Efferent Pupillary Response

CN 3 Lesion or EW Lesion

Dilated Contralateral Eye

Afferent Pupillary Response

CN2 Lesion, or Retina

Dilated Direct Eye

Importance of Eye Movements

1. Fixation on a moving target

2. Fixation when head moves

3. Aquire and Fixate on new targets

4 Basic Eye Movements

1. Saccades

2. Smooth Pursuit Movements

3. Vergence

4. Vestibulo-ocular Movements

Saccades

Rapid voluntary movements of the eyes. No real perception.

Smooth Pursuit Movements

movements of the eye that, because they are not jerky, enable the viewer to maintain fixation on a moving object

Vergence

A type of eye movement in which the two eyes move in opposite directions; for example, both eyes turn toward the nose (convergence) or away from the nose (divergence).

Vestibulo-Ocular Movements

Stabilization of the eyes in relation to the head.

Extraocular Movements

Controlled by 3 sets of muscles

Horizontal Movements of the Eyes

Lateral Rectus: CN 6 Looks Out Medial Rectus: CN 3 Looks In

Vertical Movements of the Eyes

Superior Rectus: CN 3 Looks Up Inferior Rectus: CN 3 Looks Down

Intorsion of the Eye

Superior Oblique: CN 4 Looks Down and In

Extorsion of the Eye

Inferior Oblique: CN 3 Up and In

Superior Rectus H Position

Out and Up Part of H

Inferior Rectus H Position

Out and Down Part of H

Lateral Rectus H Postion

Out Part of H

Medial Rectus H Position

In Part of H

Superior Oblique H Position

In and Down Part of H

Inferior Oblique H Position

In and Up Part of H

3 Characteristics of CN 3 Nerve Damage

1. Down and Out Gaze

2. Drooping Eyelid (Ptosis)

3. Pupillary Dilation

Ways Age Affects Sight

• Pupil Grows Smaller

• Yellowing of Lens (harder to see green and red)

• Night Vision becomes more difficult (More Rod loss than cone loss)

• Weakened Eye Muscles

• Decreased Contrast Sensitivity

Age-related macular degeneration (AMD)

• Breakdown of light sensitive cells in the macula

Dry AMD (90%), Wet (10%)

Wet is caused by leaking blood vessels behind the retina. Typically leads to Blindness

Glaucoma

#1 leading cause of blindness

Gradual Blinding from the sides in

Increased fluid pressure in the eye

Cataracts

Clouding of the eyes's lens

Glare and fading colors

Diabetic Retinopathy

Complication of diabetes

Blood Vessel Hemorrhage

No symptoms before major bleeding

Sound Wave

Half Compression of Air, and Half Decompression to make Wave

Frequency

Cycle per second, Translates to pitch

Amplitude

Intensity, translated to loudness

Max Amplitude

160 dB, Pain at 140 dB

Anything above 85 dB is considered Harmful

Track of Sound

1. Eardrum vibrates

2. Middle Ear Bones Vibrate

3. Oval Window Vibrates

4. Fluid in Cochlea Moves

5. Vibration of Basilar Membrane

6. Receptor Hair Cells Voltage becomes positive due to K+ influx

7. Increased Action potential in Auditory Nerve

8. Action Potential is Relayed to the Brain

9. Hearing Occurs

External Ear

pinna, external auditory canal, tympanic membrane

Pinna

the visible part of the ear

funnel

Auditory Canal

the area that sound waves pass through to reach the eardrum

Tympanic Membrane

The eardrum.

A structure that separates the outer ear from the middle ear and vibrates in response to sound waves.

Rinne Test

hearing test using a tuning fork; checks for differences in bone conduction and air conduction

Air should be louder than Bone Conduction

Middle Ear

malleus, incus, stapes

Eustachian Tube

A narrow tube between the middle ear and the throat that serves to equalize pressure on both sides of the eardrum

2 Muscles that Attach to the Ossicles

Tensor Tympani: Tension on the Tympanic Membrane, Attaches to the Malleus

Stapedius: Attaches and stabilizes the stapes

When these muscles are contracted sound conduction decreases

Acoustic Reflex

a reflex that protects the ear from intense sounds, via contraction of the stapedius and tensor tympani muscles

High frequency easier to hear in an environment with low frequency

Dampens sound of your voice or chewing

Inner Ear

contains cochlea, semicircular canals, and vestibular sacs

Cochlea

Amplifies sound and converts to neural signals

3 fluid chambers of the cochlea

scala vestibuli (Perilymph), scala media (Endolymph), scala tympani (Perilymph)

Organ of Corti

Center part of the cochlea, Contains Hair Cells Basilar/Tectorial membranes, and auditory nerve fibers

Helicotrema

apex of the cochlea, where the scala vestibuli and scala tympani meet

Thinner and more flexible than the base

Low Frequencies

Base (of the cochlea or basilar membrane)

High frequencies

Outer Hair Cells

Receptor Cells that show convergent connectivity, for loudness discrimination

Efferent

Inner Hair Cells

Convey almost all information about sound waves to the brain (using afferent fibers)

Stereocilia

small hairlike projections on the tops of inner and outer hair cells

Protrude into the Scala Media

Movements of the basilar membrane result in:

Shearing Force agains the Inner and Outer Hairs and the tectoral membrane, Sending Signals

Transduction

1. Basilar Membrane Moves Upward

2. Inner Hair Cells Move towards the Longest Stereocilia

3. K+ Channels Open

4. Depolarization occures

5. Action Potential in Spiral Ganglion that enter the auditory nerve

The Basilar Membrane is located

Between the Scala Media and Scala Tympani

Excitation of Retina Layers Steps

1. Photoreceptors depolarized with dark or hyperpolarize with light

2. Glutamate A is released with depolarization and Glutamate B is released with hyperpolarization

3. On Center Off Surround Bipolar Cells Turn on with Light , while Off Center On Surround Turn off with light

4. When a Bipolar Cell turns on, the ganglion cells is activated, sending a signal down the optic nerve.

Order from best to worst output of signals for On Center Off Surround

1. 3/4 Light

2. Full Light

3. No Light

4. 1/4 Light

Order from best to worst output of signals for Off Center On Surround

1. 3/4 Dark

2. Full Dark

3. No Dark

4. 1/4 Dark