Visual Pathway and Brain Function

Visual Pathway

• The visual pathway involves the crossing of signals at the optic chiasm, where the right side of the brain receives signals from both eyes for the left side of an object, and the left side of the brain receives signals from both eyes for the right side of an object.
• The visual cortex is located in the occipital lobe of the brain.

Structure of the Ear

• The ear is divided into three main regions: the external ear, middle ear, and internal ear.
• The ear contains receptors for sound waves and equilibrium (balance).
• The ear can convert sound vibrations into electrical signals 1000 times faster than photoreceptors can respond to light.

External Ear

• The external ear collects sound waves and passes them inward.
• The external ear is made up of the auricle, external acoustic meatus (or external auditory canal), and tympanic membrane (eardrum).

Middle Ear

• The middle ear is a small, air-filled cavity within the petrous part of the temporal bone.
• The middle ear contains the auditory ossicles (malleus, incus, and stapes) and is bounded by the tympanic membrane laterally and a wall of bone medially.
• The auditory ossicles form a chain interconnecting the tympanic membrane and the oval window.
• Two small skeletal muscles (stapedius and tensor tympani) control the movement of the ossicles and prevent damage from excessively loud noises.

Inner Ear

• The inner ear contains the vestibulocochlear organ, which is concerned with the reception of sound and the maintenance of balance.
• The inner ear is divided into two main divisions: the outer bony labyrinth and the inner membranous labyrinth.
• The bony labyrinth is a series of cavities in the petrous part of the temporal bone and is filled with fluid called the perilymph.

Eyeball Structure

• The eyeball is made up of many structures designed to support and protect the photoreceptor cells, as well as gather, focus, and process light into images.
• The eyeball is divided into three layers: fibrous, vascular, and retina.
• The fibrous layer consists of the cornea and sclera.
• The vascular layer consists of the choroid, ciliary body, and iris.
• The retina is the internal layer and consists of a pigmented layer and a neural layer.

Fibrous Tunic

• The fibrous tunic is the outer coat of the eyeball and consists of the anterior cornea and posterior sclera.
• The cornea is a transparent fibrous coat that covers the colored iris and helps focus light rays onto the retina.
• The sclera is a coat of dense connective tissue that covers the entire eyeball except the cornea and gives shape to the eyeball, makes it more rigid, and protects its inner parts.

Temporal Bone

• The temporal bone contains the middle and inner ear structures.
• The external acoustic meatus (or external auditory canal) is located on the lateral side of the temporal bone.
• The internal acoustic meatus is an opening in the petrous part of the temporal bone.

Receptors for Equilibrium and Hearing

• The receptors for equilibrium are located in the vestibulocochlear organ.
• The receptors for hearing are located in the cochlea.
• The auditory pathway to the brain involves the transmission of sound vibrations from the tympanic membrane to the auditory ossicles, and then to the oval window, which leads to the cochlea and finally to the brain.

Visual Pathway

• The visual pathway involves the crossing of signals at the optic chiasm, where the right side of the brain receives signals from both eyes for the left side of an object, and the left side of the brain receives signals from both eyes for the right side of an object.
• The visual cortex is located in the occipital lobe of the brain.

Structure of the Ear

• The ear is divided into three main regions: the external ear, middle ear, and internal ear.
• The ear contains receptors for sound waves and equilibrium (balance).
• The ear can convert sound vibrations into electrical signals 1000 times faster than photoreceptors can respond to light.

External Ear

• The external ear collects sound waves and passes them inward.
• The external ear is made up of the auricle, external acoustic meatus (or external auditory canal), and tympanic membrane (eardrum).

Middle Ear

• The middle ear is a small, air-filled cavity within the petrous part of the temporal bone.
• The middle ear contains the auditory ossicles (malleus, incus, and stapes) and is bounded by the tympanic membrane laterally and a wall of bone medially.
• The auditory ossicles form a chain interconnecting the tympanic membrane and the oval window.
• Two small skeletal muscles (stapedius and tensor tympani) control the movement of the ossicles and prevent damage from excessively loud noises.

Inner Ear

• The inner ear contains the vestibulocochlear organ, which is concerned with the reception of sound and the maintenance of balance.
• The inner ear is divided into two main divisions: the outer bony labyrinth and the inner membranous labyrinth.
• The bony labyrinth is a series of cavities in the petrous part of the temporal bone and is filled with fluid called the perilymph.

Eyeball Structure

• The eyeball is made up of many structures designed to support and protect the photoreceptor cells, as well as gather, focus, and process light into images.
• The eyeball is divided into three layers: fibrous, vascular, and retina.
• The fibrous layer consists of the cornea and sclera.
• The vascular layer consists of the choroid, ciliary body, and iris.
• The retina is the internal layer and consists of a pigmented layer and a neural layer.

Fibrous Tunic

• The fibrous tunic is the outer coat of the eyeball and consists of the anterior cornea and posterior sclera.
• The cornea is a transparent fibrous coat that covers the colored iris and helps focus light rays onto the retina.
• The sclera is a coat of dense connective tissue that covers the entire eyeball except the cornea and gives shape to the eyeball, makes it more rigid, and protects its inner parts.

Temporal Bone

• The temporal bone contains the middle and inner ear structures.
• The external acoustic meatus (or external auditory canal) is located on the lateral side of the temporal bone.
• The internal acoustic meatus is an opening in the petrous part of the temporal bone.

Receptors for Equilibrium and Hearing

• The receptors for equilibrium are located in the vestibulocochlear organ.
• The receptors for hearing are located in the cochlea.
• The auditory pathway to the brain involves the transmission of sound vibrations from the tympanic membrane to the auditory ossicles, and then to the oval window, which leads to the cochlea and finally to the brain.

Visual Pathway

• The right side of the brain receives signals from both eyes for interpretation of visual sensations from the left side of an object.
• The left side of the brain receives signals from both eyes for interpretation of visual sensations from the right side of an object.

Structure of the Ear

• The ear is divided into three main regions: external, middle, and internal ear.
• The ear contains receptors for sound waves and equilibrium (balance).

External Ear

• The external ear collects sound waves and passes them inward.

Eyeball Structure

• The eyeball is made up of many structures designed to support and protect the photoreceptor cells, as well as gather, focus, and process light into images.
• The adult eyeball measures approximately 2.5 cm in diameter and is divided into three layers: fibrous, vascular, and retina.

Layers of the Eyeball

• The fibrous layer (fibrous tunic) is the external layer that consists of two parts: cornea and sclera.
• The vascular layer (vascular tunic) is the middle layer that consists of three parts: choroid, ciliary body, and iris.
• The retina is the internal layer that consists of a pigmented layer and a neural layer.

Fibrous Tunic

• The fibrous tunic is the outer coat of the eyeball that consists of an anterior cornea and posterior sclera.
• The cornea is a transparent fibrous coat that covers the colored iris and helps focus light rays onto the retina.
• The sclera, the white of the eye, is a coat of dense connective tissue that covers the entire eyeball except the cornea and gives shape to the eyeball, makes it more rigid, and protects its inner parts.

Middle Ear

• The auditory tube (eustachian tube) connects the middle ear with the pharynx (throat) and allows air pressure to equalize on both sides of the tympanic membrane.
• The auditory ossicles are three tiny bones that extend across the middle ear cavity and are named for their shapes: malleus, incus, and stapes.
• The auditory ossicles form a chain interconnecting the tympanic membrane and the oval window.
• Two tiny skeletal muscles, stapedius and tensor tympani, control the amount of movement of the ossicles and prevent damage from excessively loud noises.

Inner Ear

• The inner ear contains the vestibulocochlear organ concerned with the reception of sound and the maintenance of balance.
• The inner ear is often referred to as the labyrinth and consists of two main divisions: the outer bony labyrinth and the inner membranous labyrinth.
• The bony labyrinth is a series of cavities in the petrous part of the temporal bone and is filled with fluid called the perilymph.