Retinal and Visual System: Photoreceptors, Pathways, and Processing

What are the two types of photoreceptor cells in the retina?

Rods and Cones

What is the primary function of rods in vision?

Rods are responsible for night vision and detecting brightness.

Where are cones primarily concentrated in the eye?

Cones are concentrated in the fovea, the center of the retina.

What is the role of inner hair cells in hearing?

Inner hair cells are the actual sensors that send sound information to the brain.

How do outer hair cells contribute to hearing?

Outer hair cells amplify quiet sounds by physically moving.

What are olfactory receptor cells responsible for?

Olfactory receptor cells detect smell and are unique because they are actual neurons.

What is the function of taste cells?

Taste cells release neurotransmitters to communicate with neurons, allowing for taste perception.

What happens during absorption of light?

The object soaks up the light energy, preventing it from bouncing back to the eyes.

What is reflection in the context of light?

Reflection occurs when light bounces off an object and travels to the eyes.

What is transmission of light?

Transmission is when light passes through an object, like glass or water.

Why does a green leaf appear green?

It reflects green wavelengths of light while absorbing red and blue wavelengths.

What is additive color mixing?

Additive color mixing occurs when different colored lights are combined, adding wavelengths together.

What is subtractive color mixing?

Subtractive color mixing occurs when pigments absorb certain wavelengths, as in mixing paints.

What is the function of the cornea in the eye?

The cornea is the clear front surface that does most of the focusing of light.

What role does the lens play in vision?

The lens fine-tunes the focus of light by changing shape.

What is the purpose of the pupil?

The pupil is the opening that lets light into the eye.

What is the function of the iris?

The iris controls the size of the pupil.

What is the macula?

The macula is the region around the fovea, important for central vision.

What is the optic nerve's role?

The optic nerve carries visual information from the retina to the brain.

What is transduction in the context of vision?

Transduction is the process of converting light into electrical signals in photoreceptors.

What happens to retinal when light hits it?

Retinal changes shape from bent (11-cis-retinal) to straight (all-trans-retinal).

How do rods and cones differ in distribution?

Rods are found everywhere except the fovea, while cones are heavily concentrated in the fovea.

Why do pirates wear eye patches?

To keep one eye dark-adapted for better visibility in dark areas below deck.

What are the three types of cones in the eye?

S-cones (blue light), M-cones (green light), L-cones (red/yellow light).

What is the journey of visual information from the eye to the brain?

Light → Cornea and lens → Retina → Bipolar cells → Ganglion cells → Optic nerve → Optic chiasm → LGN → Primary Visual Cortex.

What creates the blind spot in the eye?

The blind spot is created where the optic nerve exits the eye, lacking photoreceptors.

What happens to axons from the nasal half of each retina?

They cross to the opposite side of the brain.

What is the Lateral Geniculate Nucleus (LGN)?

A relay station in the thalamus with six layers, where layers 1-2 are magnocellular and layers 3-6 are parvocellular.

What does the term 'Uppy-Downy' refer to in visual processing?

It describes how the image on the retina is upside down and backwards due to lens flipping.

What does 'Crissy-Crossy' describe in the visual pathways?

It refers to how visual information from the left visual field goes to the right hemisphere and vice versa.

What are the horizontal layers of the retina?

1. Photoreceptor layer, 2. Outer nuclear layer, 3. Outer plexiform layer, 4. Inner nuclear layer, 5. Inner plexiform layer, 6. Ganglion cell layer, 7. Nerve fiber layer.

What is convergence in the context of visual processing?

It refers to multiple cells connecting to one cell downstream, affecting sensitivity and acuity.

How does convergence affect the rod system?

Many rods converge onto one ganglion cell, leading to high sensitivity but low acuity.

How does convergence affect the cone system?

Little convergence occurs, often one cone to one ganglion cell, resulting in high acuity but low sensitivity.

What are parvocellular (P) cells responsible for?

They process fine detail and color, have small receptive fields, and respond continuously to sustained stimuli.

What are magnocellular (M) cells responsible for?

They process motion and large-scale patterns, have large receptive fields, and respond to changes and movement.

How are the layers of the LGN organized in terms of eye input?

Layers 1, 4, and 6 receive input from the contralateral eye; layers 2, 3, and 5 receive input from the ipsilateral eye.

What is a receptive field?

The specific area of space that affects the firing of a particular neuron when stimulated.

What is the function of the pretectum in visual processing?

It controls the pupillary light reflex, causing both pupils to constrict when light shines in one eye.

What is the role of the superior colliculus?

It controls eye movements and visual orientation, including saccades and smooth pursuit.

What does the hypothalamus regulate in relation to visual processing?

It regulates circadian rhythms based on light levels detected by special ganglion cells.

What is blindsight?

A phenomenon where individuals with damage to V1 cannot consciously see but can still respond to visual stimuli.

What is center-surround antagonism?

A receptive field organization where the center and surround have opposite effects on cell firing.

What is the response of an ON-center, OFF-surround cell to light?

It fires more with light in the center and less with light in the surround.

How do ganglion cells and LGN cells respond to uniform light?

They produce a weak response because the center and surround cancel each other out.

What is the significance of edge detection in visual processing?

Cells respond best to edges and contrasts, which are crucial for seeing the boundaries of objects.

What do V1 neurons respond to compared to ganglion cells?

V1 neurons respond to more complex features than ganglion cells.

What is the response of ON-center cells to a small spot of light?

Strong firing

What happens to the firing of ON-center cells when only a ring of light is present in the surround?

Suppressed firing

What is the response of V1 neurons to oriented edges or bars?

They fire strongly only when a line at a specific angle appears in their receptive field.

What does a tuning curve represent for a V1 neuron?

It shows how much a neuron responds to different values of a stimulus feature, like orientation.

What are ocular dominance columns in V1?

Alternating stripes of neurons that prefer input from the left eye versus the right eye.

What is the function of the dorsal pathway in visual processing?

It processes spatial location and motion, answering 'Where is it?' and 'How do I interact with it?'

What is the role of the ventral pathway in visual processing?

It processes object identity, answering 'What is that object?'

What is sound defined as?

A longitudinal pressure wave that travels through a medium like air or water.

How is amplitude related to loudness?

Amplitude is the size of the pressure wave, while loudness is how we perceive that amplitude.

What does frequency measure in sound?

The number of waves that pass per second, measured in Hertz (Hz).

What is the perceptual quality of sound associated with frequency?

Pitch, which is how we perceive frequency as high or low.

What is the function of the pinna in the outer ear?

It funnels sound waves into the ear canal and helps localize sounds.

What is the role of the tympanic membrane (eardrum)?

It vibrates when sound waves hit it, acting as the boundary between the outer and middle ear.

What are the three tiny bones in the middle ear called?

Malleus (hammer), Incus (anvil), and Stapes (stirrup).

What is the cochlea's function in the inner ear?

It converts sound vibrations into neural signals.

What is the role of inner hair cells in the cochlea?

They are the true sensory receptors that send 95% of auditory information to the brain.

What does the basilar membrane do in the cochlea?

It vibrates at different locations depending on sound frequency, crucial for hearing different pitches.

What is the difference between inner and outer hair cells?

Inner hair cells send auditory information to the brain, while outer hair cells amplify sound.

What happens during the transduction process in auditory hair cells?

Sound waves cause the tympanic membrane to vibrate, leading to a series of amplifications and pressure waves in the cochlea.

What is the significance of the organ of Corti?

It contains hair cells, which are the actual sound receptors in the cochlea.

What is the relationship between sound complexity and timbre?

Complexity refers to the shape of the sound wave, while timbre is the quality or color of the sound.

What is the role of the tectorial membrane?

It hangs over the hair cells and causes them to bend when the basilar membrane moves.

What is the auditory canal's function?

It amplifies frequencies around 3,000 Hz, which is the range of human speech.

What is the significance of hypercolumns in V1?

They contain neurons responsive to all orientations and both eyes for a specific area of the visual field.

What occurs when the oval window is pushed?

Vibrations enter the fluid-filled cochlea, initiating the process of sound transduction.

What happens to the firing rate of a V1 neuron when a line at its preferred orientation appears?

The firing rate peaks at the neuron's preferred orientation.

What causes stereocilia to bend in hair cells?

Their tips are in contact with the stationary tectorial membrane above them.

What happens when stereocilia bend toward the tallest hair?

Mechanically-gated ion channels open, allowing potassium ions (K⁺) to rush into the hair cell.

What is the result of potassium ions entering the hair cell?

It depolarizes the hair cell.

What triggers neurotransmitter release in hair cells?

Calcium influx from voltage-gated calcium channels.

What neurotransmitter is released by hair cells?

Glutamate.

How does the direction of bending stereocilia affect hair cell activity?

Bending toward the tallest stereocilium opens channels (excitation), while bending away closes channels (inhibition).

What does tonotopic organization refer to?

A map where nearby locations respond to nearby frequencies, like keys on a piano.

Where is tonotopic organization found in the auditory system?

Cochlea, cochlear nuclei, inferior colliculus, medial geniculate nucleus, and primary auditory cortex.

What is place coding in the cochlea?

Encoding different frequencies based on where maximum vibration occurs along the basilar membrane.

How does the basilar membrane respond to high frequencies?

The base (near the oval window) is narrow and stiff, responding to high frequencies (up to 20,000 Hz).

How does the basilar membrane respond to low frequencies?

The apex (far end) is wide and floppy, responding to low frequencies (down to 20 Hz).

What is temporal coding in auditory processing?

Encoding sound frequency based on the timing of neural firing patterns, known as phase locking.

What is the limitation of temporal coding?

It works well only up to about 4,000-5,000 Hz because neurons can't fire fast enough for higher frequencies.

What unique function do outer hair cells perform?

They physically change length in response to electrical changes, amplifying sound vibrations.

What is the role of the motor protein prestin in outer hair cells?

It causes the cell to contract when depolarized and elongate when hyperpolarized, amplifying sound.

How much can outer hair cells amplify quiet sounds?

By up to 1,000 times (60 dB).

What distinguishes inner hair cells from outer hair cells?

Inner hair cells are flask-shaped and provide 95% of auditory information, while outer hair cells are cylindrical and provide only 5%.

What is the pathway sound information takes to reach the auditory cortex?

Cochlea → Spiral Ganglion → Auditory Nerve → Cochlear Nuclei → Superior Olivary Complex → Lateral Lemniscus → Inferior Colliculus → Medial Geniculate Nucleus → Auditory Radiations → Primary Auditory Cortex.

What is the significance of bilateral processing in the auditory system?

Information from each ear goes to both hemispheres, crucial for sound localization.

What cells are responsible for transduction in olfaction?

Olfactory receptor neurons (ORNs) in the olfactory epithelium.

How do taste receptor cells transduce taste signals?

They release neurotransmitters onto sensory neurons when taste molecules bind to their receptors.

What is the first processing center for olfactory information?

The olfactory bulb, located under the frontal lobe.

What happens to axons of olfactory receptor neurons?

They pass through tiny holes in the cribriform plate to reach the olfactory bulb.

What is the role of glomeruli in the olfactory bulb?

Each glomerulus receives input from all ORNs that express the same receptor type.

What is the primary function of the Primary Olfactory Cortex?

Conscious smell perception.

Which brain structure is responsible for emotional responses to smells?

Amygdala.

What role does the Entorhinal cortex play in olfaction?

It connects to the Hippocampus, which is involved in smell memories.