Human Bio, CH 12, Sensory Mechanisms

Sensation

Being consciously aware of the stimulus. Ex: Hearing the sound of thunder

Perception

Understanding what the sensation means. Ex: The belief that a storm is approaching

Mechanoreceptors

Respond to forms of mechanical energy, such as waves of sound, changes in fluid pressure, physical tough or pressure, stretching, or forces generated by gravity & acceleration.

Thermoreceptors

Respond to heat or cold.

Pain receptors

Respond to tissue damage or excessive pressure or temperature.

Chemoreceptors

Respond to the presence of chemicals in the nearby area.

Photoreceptors

Respond to light

Receptor adaptation

The sensory neuron stops sending impulses even though the original stimulus is still present.

Somatic senses

Originate from receptors present at more than one location in the body. They include temperature, touch, vibration, pressure, pain, & awareness of body movements/positions.

Special senses

Originate from receptors that are restricted to particular areas of the body. They deliver highly specialized info about the external world. Include taste, smell, hearing, balance, & vision.

Encapsulated nerve endings

Enclosed in layers of connective tissue. Nearly all are mechanoreceptors.

Free nerve endings

Unencapsulated, the free endings of sensory nerves. Most respond to pain or temperature.

Pacinian corpuscles

Encapsulated nerve endings located in the dermis that respond to either deep pressure or high-frequency vibration.

Muscle spindle

Specialized structures for monitoring muscle length.

Referred pain

Slow pain from internal organs that is often perceived as originating from an area of the body completely removed from the actual source.

Taste buds

A cluster of about 25 taste cells & 25 supporting cells that separate the taste cells from each other.

Olfactory receptor cells

Odors are detected by these cells that are located in the upper part of the nasal passages.

Outer ear

Consists of the pinna, or visible portion of the ear, & the auditory canal.

Tympanic membrane

(Ear drum) Serves as a partition between the outer & middle ears.

Middle ear

Consists of an air-filled chamber within the temporal bone of the skull, bridged by 3 small bones: hammer, anvil, & stirrup.

Oval window

Must vibrate w/ sufficient force to produce pressure waves in the watery fluid of the inner ear.

Inner ear

Sorts sound by tone & converts them into impulses.

Cochlea

Sound is converted

Basilar membrane

The base of the cochlear duct if formed by this membrane & it supports a population of about 15,000 hair cells, the mechanoreceptor cells of the ear.

Organ of Corti

Together, the hair cells & the tectorial membrane are called this, the organ that converts pressure waves to action potentials.

Vestibular apparatus

A system of fluid-like canals & chambers in the inner ear. Consists of 3 semicircular canals for sensing rotational movement of the head, & the vestibule for sensing static (non-moving) position & linear acceleration & deceleration.

Otoliths

Hard crystals of bone-like material embedded in gel in the inner ear. Contribute to sensations of head position & movement.

Sclera

White, opaque outer layer of the eyeball.

Cornea

The transparent anterior portion of the eyeball.

Iris

A colored disk-shaped muscle that determines how much light enters the eye.

Pupil

Opening in the center of the iris through which light enters the eye.

Lens

A transparent, flexible, curved structure that focuses incoming light on the retina at the back of the eye.

Retina

Layers of tissue at the back & sides of the eye. Composed primarily of photoreceptor cells, neurons, & a few blood vessels.

Optic nerve

One of the two cranial nerves that transmit nerve impulses from the retina to the brain.

Macula

The central region of the retina, where photoreceptor density is the highest.

Optic disk/blind spot

The area of the retina where the axons of the optic nerve exit the eye. Has no photoreceptors, so it's presence creates a "blind spot" in each eye.

Fovea centralis

A small region at the center of the macula of the retina that is responsible for the highest visual acuity. Consists of densely packed cone cells.

Accommodation

The adjustment of lens curvature in the eye so we can focus on either near or far objects.

Myopia

A condition in which the eyeball is too long, causing distant visual objects to be focused in front of the retina, also called nearsightedness.

Hyperopia

Condition in which the eyeball is too short, causing nearby objects to be focused behind the retina, also called farsightedness.

Presbyopia

Eye condition in which an increase in stiffness of the lens results in an inability to focus on near objects. Typically begins after age 40.

Astigmatism

An eye condition in which unequal curvatures in different parts of the lens (or cornea) lead to blurred vision.

Rods

One of the two types of photo-sensitive cells in the retina.

Cones

One of the two types of photoreceptor cells in the retina of the eye. Provide for color vision. 3 types: red, green, blue.

Rhodopsin

The photopigment found in the rods of the eye.

Color blindness

General term for the inability to distinguish the full range of colors.

Nerve deafness

Deafness caused by damage to hair cells, sounds cannot be converted into impulses in sensory nerves.

Conduction deafness

Damage to the tympanic membrane or the bones of the middle ear, sound waves simply are not transferred to the inner ear at all.