Chapter 7 Anatomy and Physiology of the Special Senses

Anterior Chamber

This is the space between the iris and the cornea. It connects to the posterior chamber through the pupil

Cornea

This clear tissue forms the anterior surface of the eyeball and focuses light (along with the lens) on the retina

Iris

Pigments in the iris give the eye its “color” and block excessive light from entering

Pupil

This is the opening connecting the anterior and posterior chambers. Light passes through this structure on its way to the lens and retina

Posterior Chamber

This is the space between the lens and the iris. It connects to the anterior chamber through the pupil

Lens

This structure is made of a gel-like protein and helps focus light on the retina

Ciliary Body

This structure contains smooth muscle cells that regulate the shape of the lens by pulling on the suspensory ligaments. Aqueous humor is also secreted by capillaries within this structure

Vitreous Humor (Body)

This “jelly ball” helps maintain the spherical shape of the eye. Accumulation of cellular debris due to inflammation, as well as partial liquefaction of this structure, contribute to the “floaters” some people see as they grow older.

Retina

This is the layer of cells that convert light energy to electric impulses (action potentials) which are then transmitted to the brain by the optic nerve

Choroid

This layer contains blood vessels that nourish the eye, and its dark color absorbs stray light

Sclera

This is the tough white outer covering of the eye

Optic Nerve

This sensory nerve carries electrical impulses (action potentials) from the eye to the brain

Blind Spot

This area of the retina does not contain any light-receptive cells that send impulses to the brain, because it is the location where the optic nerve exits the eye

Superior Rectus Muscle

This muscle rotates the eye upward

Superior and Inferior Oblique Muscles

Rotate the eyes clockwise or counter clockwise when the head tilts to either side. The result is that the eyes rotate counter to the direction of the tilt, and visual images remain more stable

Inferior Rectus Muscle

This muscle rotates the eye downward

Lateral Rectus Muscle

This muscle rotates the eye laterally

Medial Rectus Muscle

This muscle rotates the eye medially

Lacrimal Gland

This gland produces tears

Pinna/auricle

This is the outer portion of the ear that people like to pierce and use to display jewelry. It helps channel sound vibrations into the auditory canal.

External Acoustic Meatus

This is the outer tunnel that transmits sound vibrations to the tympanic membrane

Tympanic Membrane

This structure is often referred to as the “ear drum” Sound vibrations traveling through the external auditory canal strike this membrane and cause it to vibrate. Movement of the tympanic membrane is transmitted to the malleus, and then to other bones of the middle ear

Middle Ear

This is the area between the tympanic membrane and the cochlea

Malleus

This is the first of three middle ear bones that amplify vibrations of the tympanic membrane and transmit those vibrations to the membrane covering the oval window

Incus

This is the second of three middle ear bones that amplify vibrations of the tympanic membrane and transmit those vibrations to the membrane covering the oval window

Stapes

This is the third of three middle ear bones that amplify vibrations of the tympanic membrane and transmit those vibrations to the membrane covering the oval window

Oval Window

This is the membrane-covered opening to the scala vestibuli. The stapes attaches to the membrane of this structure.

Inner Ear

Contains the cochlea, vestibule, utricle, ampullae, and semicircular ducts.

Vestibule

This is the bony structure that houses the utricle and saccule. It is also the entry into the semicircular canals.

Semicircular Canals/Ducts

This fluid-filled system of chambers that form part of the inner ear and help convert movement of the head into electric impulses (action potentials) that are transmitted to the brain. These impulses create your sense of angular movement (spinning/turning) in all three axes (dimensions).

Cochlea

This snail shell-shaped structure contains the chambers and tissues that convert sounds (vibrations) to the electric impulses (action potentials) that are transmitted to the brain.

Cochlear Duct

This is the central chamber in the cochlea that contains the hearing apparatus

Scala Vestibuli

Sound vibrations enter this chamber via the oval window. This structure is continuous with the scala tympani.

Scala Tympani

Sound vibrations in the scala vestibuli may enter this chamber before they exit via the round window

Round Window

This membrane-covered opening transmits vibrations (pressure waves) from the scala tympani of the inner ear

Auditory (Eustachian) Tube

This tube helps keep the air pressure in the middle ear the same as the air pressure outside the body, thus allowing the tympanic membrane to move easily

Vestibulocochlear Nerve

This cranial nerve used to be called the “auditory nerve.” However, since it transmits sensory information from both the cochlea (sounds) and vestibule (equilibrium/balance), its name was changed to be more descriptive.

Visual, auditory, gustatory, olfactory, and tactile

The 5 senses (sight, hearing, taste, smell, and touch)

Sense

A system that consists of a sensory cell type that responds to a specific kind of physical energy, and corresponds to a region in the brain where the signals are integrated

Exteroceptors

Sensory receptors involved in sight, hearing, touch, taste, and smell that transmit information describing external stimuli

Interoceptors

Sensory receptors, such as chemoreceptors and baroreceptors that transmit information describing the internal condition of our bodies.

Proprioceptors

A special type of interoceptor that innervate muscles, ligaments, joints, and tendons (such as the patellar tendon) to advise your brain of your body’s movement and position.

Accommodation

The lens’ ability to change shape when necessary to focus light reflected from near or far objects

Myopia (Nearsightedness)

Occurs when the eyeball is too long, the focusing apparatus (cornea or lens) is too strong, or both. As a result, light from a distance is focused in front of the retina and blurring of the image results. These patients see well up close but will often need glasses or contacts for distant objects

Hyperopia (Farsightedness)

Occurs when the eyeball is too short, the focusing apparatus is too weak, or both. As a result, light is focused improperly behind the retina. Can see well far but not close.

Presbyopia

When we are young, the lens can accommodate, more strongly bend light rays onto the retina, and restore some distance vision. But eventually, these patients will usually need some correction. As we age, the lens of the eye loses elasticity and, therefore, the ability to accommodate for near vision. It can be corrected with convex reading glasses or bifocals.

Astigmatism

Occurs when the cornea is not perfectly round, but instead takes on an irregular football shape. This causes blurry vision, because light passing through certain areas of the cornea will be bent more than light from other areas. Therefore, there will be multiple focal points

Binocular vision

Humans have two eyes working together in concert. This affords many advantages, including a wider field of view and depth perception.

Depth Perception

The ability to locate objects in three-dimensional space accurately. A precise version of this requires that both of your eyes accurately focus on an object.

Ossicles

The middle ear bones. The tympanic membrane vibrates to transmit vibrations to these middle ear bones.

Conduction Deafness

Any problem with the external or middle ear structures involved in conducting sound vibrations results in this issue.

Sensorineural Deafness

Any problem with the structures inside the cochlea (inner ear) results in this issue

Hair Cells

Sensory receptors on the semicircular canals

Cupulas

Hair cells are attached to these dome-shaped, gelatinous structures.

Endolymph

Makes up the rest of the semicircular canals. When your head moves from side to side as in shaking your head “no,” the cupula becomes distorted as _____ flows past it, and the hair cells trapped inside bend, which communicates to the brain that the head is rotating in space.

Utricle and Saccule

The two vestibular sacs associated with the semicircular canals. Receptors in these sacs provide sensations of gravity and linear acceleration and a sense of equilibrium. Can communicate head tilt, or a rapid change in acceleration, like when sitting in a car and slamming on the brakes.

Otoliths

Tiny stones that sit on the surface of the utricle, which communicates horizontal movement, and saccule, which communicates vertical movement. It is the tumbling of these “stones from one side to the other over the _______ membrane that communicates head tilt and other equilibrium movements to the CNS

Motion Sickness

Common phenomenon resulting when visual input from the eye communicates to the brain that position is not changing, but the semicircular canals and vestibular sacs are communicating that there is motion. Commonly occurs when looking down to read in a car or sitting below deck in a boat.

General Senses

Composed of exteroceptors, interoceptors, and proprioceptors

Special Senses

Composed of sight, hearing, taste, smell

Adaptation

Refers to the process by which a sensory system becomes insensitive to a continuing source of stimulation

Nociceptors

Pain receptors. They do not adapt quickly. They are activated above 45 degrees C.

Mechanoreceptor

A type of exteroceptor that depolarizes and generates action potentials when it (or adjacent tissue) is deformed by pressure, stretch, or vibration

Tactile (Meissner’s) Corpuscle

One type of mechanoreceptor that senses gentle pressure on the skin.

Receptive Field

The area of skin that a tactile receptor can respond to. These can overlap or be spread out.

Thermoreception

The sense of heat and cold. Cold receptors are sensitive to temps lower than 37 degrees C, while warm receptors are sensitive from 37 degrees C to 45 degrees C.

Temperature Receptors

Found in the dermis of the skin & adapt between 20 degrees C and 40 degrees C. Outside of this range, these receptors do not adapt, thereby helping to prevent temperature-related injury to tissues.

Homostatic Thermoreceptors

Provide feedback on internal body temperature. They are located close to the hypothalamus in the brain and are responsible for setting the internal “thermostat” to a constant 37 degrees C in a healthy person.