Describe visual and auditory pathways.

Visual pathway:
The visual pathway is the route that visual information takes from the eyes to the brain. It begins with light entering the eye and being focused by the lens onto the retina at the back of the eye. The retina contains photoreceptor cells called rods and cones that convert light into electrical signals. These signals are then transmitted through the optic nerve to the brain, specifically to the thalamus and then to the visual cortex in the occipital lobe. Here, the brain processes and interprets the visual information, allowing us to see and perceive the world around us.

Auditory pathway:
The auditory pathway is the route that sound information takes from the ears to the brain. It begins with sound waves entering the ear and traveling through the ear canal to the eardrum. The eardrum vibrates in response to the sound waves, which are then transmitted through the middle ear bones to the cochlea in the inner ear. The cochlea contains hair cells that convert the vibrations into electrical signals, which are then transmitted through the auditory nerve to the brainstem and then to the auditory cortex in the temporal lobe. Here, the brain processes and interprets the sound information, allowing us to hear and perceive sounds.

## Visual Pathway

Retina:
- Photoreceptors (rods and cones): Convert light into electrical signals.
- Bipolar cells: Relay signals from photoreceptors to ganglion cells.
- Ganglion cells: Collect signals and send them via the optic nerve.

Optic Nerve:
- Carries signals from ganglion cells to the optic chiasm.

Optic Chiasm:
- Partial crossing of fibers from nasal retinas; fibers from temporal retinas remain uncrossed.

Optic Tracts:
- Carry signals from the optic chiasm to the lateral geniculate nucleus (LGN).

Lateral Geniculate Nucleus (LGN):
- Located in the thalamus; filters and relays visual information.

Optic Radiations:
- Carry signals from the LGN to the primary visual cortex in the occipital lobe.

Primary Visual Cortex (V1):
- Processes basic visual features such as shape, color, and movement.

## Auditory Pathway

Outer Ear:
- Pinna: Collects sound waves.
- External auditory canal: Directs sound waves to the tympanic membrane.

Middle Ear:
- Tympanic membrane: Vibrates in response to sound waves.
- Ossicles (malleus, incus, stapes): Amplify and transmit vibrations.
- Eustachian tube: Equalizes air pressure between the middle ear and the environment.

Inner Ear:
- Cochlea: A spiral-shaped structure containing the auditory receptors.
- Scala vestibuli: Contains perilymph, a fluid that is displaced by sound waves.
- Scala tympani: Also contains perilymph and is separated from the scala vestibuli by the basilar membrane.
- Scala media: Contains endolymph and separates the scala vestibuli and scala tympani.
- Organ of Corti: Located on the basilar membrane; contains hair cells that are the sensory receptors for hearing.

Auditory Nerve:
- Carries signals from the organ of Corti to the brainstem.

Cochlear Nucleus:
- Located in the brainstem; processes auditory information from the auditory nerve.

Superior Olivary Complex:
- Processes sound localization and binaural hearing.

Lateral Lemniscus:
- Carries signals from the cochlear nucleus and superior olivary complex to the inferior colliculus.

Inferior Colliculus:
- Integrates auditory information from both ears.

Medial Geniculate Nucleus (MGN):
- Located in the thalamus; filters and relays auditory information.

Auditory Radiations:
- Carry signals from the MGN to the primary auditory cortex in the temporal lobes.

Primary Auditory Cortex (A1):
- Processes basic auditory features such as pitch, loudness, and location.