Special Senses

Sensation

The process initiated by stimulating sensory receptors.

Perception

The conscious awareness of stimuli.

General Senses

Senses that have receptors distributed over a large part of the body.

Somatic Senses

Provide sensory information about the body and the environment.

Visceral Senses

Provide information about various internal organs, primarily involving pain and pressure.

Special Senses

Senses that are more specialized in structure and localized to specific parts of the body.

Mechanoreceptors

Respond to mechanical stimuli.

Photoreceptors

Respond to light.

Thermoreceptors

Respond to temperature changes.

Nociceptors

Respond to stimuli that result in the sensation of pain.

Pressure

A general sense that provides information about the force applied to the body.

Pain

A general sense that provides information about tissue damage or potential damage.

Temperature

A general sense that provides information about hot or cold stimuli.

Vibration

A general sense that provides information about rapid oscillations.

Itch

A general sense that provides information about the need to scratch.

Proprioception

A general sense that provides information about body position and movement.

Free nerve endings

The simplest and most common types of sensory receptors.

Touch receptors

More complex receptors that are involved in detecting light touch and pressure.

Merkel disks

Small, superficial nerve endings involved in detecting light touch and superficial pressure.

Hair follicle receptors

Receptors associated with hairs.

Light touch receptors

Very sensitive receptors that are not very discriminative in locating the point of touch.

Meissner corpuscles

Receptors for fine, discriminative touch located just deep to the epidermis.

Ruffini corpuscles

Deeper tactile receptors that detect continuous pressure in the skin.

Pacinian corpuscles

The deepest receptors associated with tendons and joints, relaying information about deep pressure, vibration, and body position.

Pain

A group of unpleasant perceptual and emotional experiences.

Local anesthesia

The suppression of action potentials from pain receptors in local areas of the body through the injection of chemical anesthetics near a sensory receptor or nerve.

General anesthesia

A treatment where chemical anesthetics that affect the reticular activating system are administered to suppress pain sensations.

Referred pain

Pain that is perceived to originate in a region of the body that is not the source of the pain stimulus.

Olfaction

The sense of smell.

Odorants

Airborne molecules that enter the nasal cavity and trigger the sense of smell.

Olfactory neurons

Bipolar neurons within the olfactory epithelium that detect odorants.

Olfactory epithelium

The lining of the superior part of the nasal cavity where olfactory neurons are located.

Olfactory receptors

Receptor molecules on the membranes of specialized cilia that bind to odorants and initiate action potentials.

Neuronal pathways for olfaction

The pathways that carry action potentials from olfactory neurons to the areas of the cerebrum responsible for perception and interpretation of smell.

Olfactory nerves

The cranial nerves that carry action potentials from olfactory neurons to the olfactory bulb.

Olfactory bulb

The structure where olfactory neurons synapse with interneurons that relay action potentials to the brain.

Olfactory tracts

The tracts through which action potentials from olfactory neurons are relayed to the olfactory cortex.

Olfactory cortex

The area of the brain involved in the conscious perception of smell and the visceral and emotional reactions linked to odors.

Taste buds

The sensory structures that detect taste stimuli, oval structures located on the surface of certain papillae, also distributed throughout other areas of the mouth and pharynx.

Taste cells

Cells in the interior of taste buds that contain hairlike processes called taste hairs, which extend through a tiny opening in the surrounding stratified epithelium called a taste pore.

Five basic taste sensations

Sour, Salty, Bitter, Sweet, Umami (savory).

Olfactory sensations

Influence taste sensations and can be demonstrated by comparing the taste of some food before and after pinching your nose.

Neuronal pathways for taste

Taste sensations are carried to the brain by three cranial nerves - facial nerve (VII), glossopharyngeal nerve (IX), and vagus nerve (X).

Visual system

Includes eyes, accessory structures, and sensory neurons.

Accessory structures of the eye

Eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles.

Eyebrows

Protect the eyes by preventing perspiration from running down the forehead and into the eyes, and help shade the eyes from direct sunlight.

Eyelids

Protect the eyes from foreign objects and help keep the eyes lubricated by spreading tears over the surface.

Conjunctiva

A thin, transparent mucous membrane covering the inner surface of the eyelids and the anterior surface of the eye.

Lacrimal apparatus

Consists of the lacrimal gland, nasolacrimal duct, and associated structures, responsible for producing tears and draining excess tears.

Extrinsic eye muscles

Six skeletal muscles attached to the surface of each eyeball, responsible for the movement of the eyeball.

Anatomy of the eye

The eyeball is composed of three tissue layers called tunics - fibrous tunic, vascular tunic, and nervous tunic.

Fibrous tunic

The outer layer of the eyeball consisting of the sclera and cornea.

Sclera

The firm, white, outer connective tissue layer of the eyeball that helps maintain its shape and protects internal structures.

Cornea

The transparent anterior part of the eye that permits light to enter and refracts the entering light.

Vascular tunic

The middle layer of the eyeball consisting of the choroid, ciliary body, and iris.

Choroid

The posterior portion of the vascular tunic that contains a vascular network and pigment cells, appearing black to absorb light.

Ciliary body

Continuous with the anterior margin of the choroid, contains ciliary muscles that attach to the lens.

Lens

A flexible, biconvex, transparent disc that helps focus light onto the retina.

Iris

The colored part of the eye that regulates the diameter of the pupil, controlling the amount of light entering the eye.

Pupil

The opening in the center of the iris through which light passes.

Parasympathetic stimulation

Causes the circular smooth muscles of the iris to contract, constricting the pupil.

Sympathetic stimulation

Causes the radial smooth muscles of the iris to contract, dilating the pupil.

Nervous Tunic

The innermost tunic of the eye, consisting of the retina.

Retina

The posterior five-sixths of the eye that is composed of two layers - pigmented retina (outer) and sensory retina (inner).

Photoreceptor cells

Cells in the sensory retina that respond to light.

Rods

Photoreceptor cells that are more common than cones, function in dim light, and do not provide color vision.

Cones

Photoreceptor cells that require more light to be stimulated, provide color vision, and are sensitive to blue, green, or red.

Macula

A small spot near the center of the posterior retina, containing the fovea centralis.

Fovea centralis

The part of the retina where light is most focused when looking directly at an object, contains only cone cells, and has the greatest ability to discriminate fine images.

Optic disc

A white spot just medial to the macula, through which blood vessels enter the eye and axons from the retina meet to form the optic nerve.

Anterior chamber

One of the three chambers of the eye, located between the cornea and the lens, filled with aqueous humor.

Posterior chamber

One of the three chambers of the eye, located between the cornea and the lens, filled with aqueous humor.

Vitreous chamber

The largest chamber of the eye, located posterior to the lens, filled with vitreous humor.

Aqueous humor

A fluid that helps maintain pressure within the eye, refracts light, and provides nutrients to the inner surface of the eye.

Vitreous humor

A transparent, jellylike substance that helps maintain pressure within the eye and holds the lens and retina in place.

Glaucoma

A condition where the pressure in the eye increases due to blocked aqueous humor flow, potentially leading to blindness.

Light Refraction

The bending of light as it passes from air to a denser transparent substance.

Focal point

The point at which light rays converge after being refracted, located just anterior to the retina in the eye.

Accommodation

The process of changing the shape of the lens to adjust focus on objects closer than 20 feet from the eye.

Rhodopsin

A photosensitive pigment found in rod photoreceptors that interacts with light to produce action potentials in the retina.

Night blindness

A condition characterized by difficulty seeing in dim light, often caused by a deficiency in vitamin A or retinal detachment.

Cone cells

Photoreceptor cells in the retina that allow for the perception of colors, with different types of cones sensitive to blue, red, or green light.

Ganglion cells

Interneurons in the sensory retina that receive input from rod and cone cells and synapse with bipolar and horizontal cells before forming the optic nerve.

Visual field

The area from which each eye collects light.

Optic nerve

Conducts action potentials from the retina to the brain.

Optic chiasm

The point where the two optic nerves connect and signals from each eye are received by both sides of the brain.

Optic tracts

Pathway for ganglionic axons beyond the optic chiasm, most of which terminate in the thalamus.

Optic radiations

Fibers from the thalamus that project to the visual cortex in the occipital lobe, where vision is perceived.

Binocular vision

Depth perception that requires both eyes and occurs where the two visual fields overlap.

Diplopia

Double vision resulting from misalignment of the two eyes.

External ear

The part extending from the outside of the head to the tympanic membrane (eardrum).

Middle ear

An air-filled chamber medial to the tympanic membrane.

Inner ear

A set of fluid-filled chambers medial to the middle ear, involved in both hearing and balance.

Oval window

Opening that connects the middle ear with the inner ear.

Auditory ossicles

Three ear bones (malleus, incus, and stapes) that transmit vibrations from the tympanic membrane to the oval window.

Mastoid air cells

Air-filled spaces in the mastoid process of the temporal bone that connect to the middle ear.

Auditory tube (eustachian tube)

Opening that connects the middle ear to the pharynx and equalizes air pressure.

Tympanic membrane

The eardrum, which can be distorted by unequal pressure and dampen vibrations.

Bony labyrinth

Interconnecting tunnels and chambers within the temporal bone in the inner ear.

Membranous labyrinth

Smaller set of membranous tunnels and chambers within the bony labyrinth.