SOMATIC AND ENDOCRINE

Sensation

The conscious or subconscious awareness of changes in the external or internal environment.

Perception

The conscious awareness and interpretation of sensations and is primarily a function of the cerebral cortex.

General Senses

Include somatic sensations (tactile, thermal, pain and proprioceptive) and visceral sensations. They are scattered throughout the body and are relatively simple structures.

Special Senses

Include smell, taste, vision, hearing and equilibrium. They are concentrated in specific locations in the head, are anatomically distinct structures, and form complex neural pathways.

Free nerve endings

Bare dendrites; receptors for pain, thermal, tickle, itch, and some touch sensations.

Encapsulated nerve endings

Receptors for other somatic and visceral sensations, such as pressure, vibration, and some touch sensations.

Separate cells that synapses

Hair cells for hearing and equilibrium in the inner ear, gustatory receptor cells in taste buds, and photoreceptors in the retina of the eye for vision.

Exteroceptors

Located at or near body surface; sensitive to stimuli originating outside the body.

Interoceptors

Located in blood vessels, visceral organs and nervous system; provide information about the internal environment.

Proprioceptors

Located in muscles, tendons, joints and inner ear; provide information about body position, muscle length and tension, position and motion of joints, and equilibrium.

Mechanoreceptors

 Detect mechanical stimuli.

Thermoreceptors

Detects changes in temperature.

Nociceptors

Respond to painful stimuli from physical or chemical damage to tissues.

Photoreceptors

Detect light in the retina.

Chemoreceptors

Detect chemicals in mouth, nose and body fluids.

Osmoreceptors

Sense osmotic pressure of body fluids.

Meissner corpuscles (corpuscles of touch)

Capsule surrounds mass of dendrites in dermal papillae of hairless skin; sensations of touch, pressure, and slow vibrations; rapid adaptation rate.

Hair root plexuses

Free nerve endings wrapped around hair follicles in skin; touch sensation; rapid adaptation rate.

Merkel (tactile) discs (Type I cutaneous mechanoreceptors)

Saucer-shaped free nerve endings make contact with Merkel cells in epidermis; touch and pressure; slow adaptation rate.

Ruffini corpuscles (Type II cutaneous mechanoreceptors)

Elongated capsule surrounds dendrites deep in dermis and in ligaments and tendons; stretching of skin; slow adaptation rate.

Pacinian (lamellated) corpuscles

Oval, layered capsule surrounds dendrites; present in dermis and subcutaneous layer, submucosal tissues, joints, periosteum, and some viscera; pressure and fast vibrations; rapid adaptation rate.

Itch and tickle receptors

Free nerve endings in skin and mucous membranes; itching and tickling; both slow and rapid adaptation rate.

Warm receptors and cold receptors

Free nerve endings in skin and mucous membranes of mouth, vagina, and anus; warmth or cold; initially rapid, then slow adaptation rate.

Nociceptors

Free nerve endings in every tissue of the body except the brain; pain sensation; slow adaptation rate.

Muscle spindles

Sensory nerve endings wrap around central area of encapsulated intrafusal muscle fibers within most skeletal muscles; muscle length; slow adaptation rate.

Tendon organs

Capsule encloses collagen fibers and sensory nerve endings at junction of tendon and muscle; muscle tension; slow adaptation rate.

Joint kinesthetic receptors

Pacinian corpuscles, Ruffini corpuscles, tendon organs, and free nerve endings; joint position and movement; rapid adaptation rate.

Olfactory receptors

The first-order neurons of the olfactory pathway

Olfactory hairs

Cilia that project from the dendrites; respond to inhaled chemicals.

Odorants

Chemicals that have an odor and can therefore stimulate the olfactory hairs.

Supporting cells

Columnar epithelial cells of the mucous membrane lining the nose; provide physical support, nourishment, and electrical insulation and help detoxify chemicals.

Basal cells

Undergo cell division.

Bowman's gland

roduce mucus that is carried to the surface of the epithelium by ducts

Sensory Adaptation

Ability to become less sensitive to unchanging stimulus; receptors fatigue and stop responding to chemicals over time.

Taste bud

Where receptors for taste sensations are found (10,000 taste buds located at the tongue, soft palate, pharynx, and epiglottis). Consists of supporting cells, gustatory receptor cells, and basal cells.

Taste pore

Opening in the taste bud

Tastants

Chemicals that stimulate gustatory receptor cells

Papillae

Elevations of the tongue where taste buds are found; provide a rough texture.

Vallate (circumvallate) Papillae

Form an inverted V-shaped row at the back of the tongue.

Fungiform Papillae

Mushroom-shaped elevations scattered over the entire surface of the tongue containing about five taste buds each.

Foliate Papillae

Located in small trenches on the lateral margins of the tongue (most taste buds degenerate in early childhood).

5 Primary Tastes and Taste Thresholds

Sweet: Sucrose

Salty: Sodium chloride

Sour: Hydrochloric acid

Bitter: Quinine

Umami (meaty/savory): L-monosodium glutamate (MSG)

Three layers of tissue in the walls of the eye

The outer fibrous layer: sclera and cornea

The middle vascular layer or uveal tract: choroid, ciliary body, and iris

The inner nervous tissue layer: the retina

Sclera

White of the eye; forms outermost layer; maintains shape and gives attachment to extrinsic muscles.

Cornea

Clear transparent epithelial membrane; light rays pass through to reach the retina.

Choroid

Rich in blood vessels; absorbs light after it stimulates sensory receptors in the retina.

Ciliary Body

Acts like a sphincter; controls size and thickness of the lens.

Iris

Visible colored ring at the front of the eye.

Pupil

Center aperture; parasympathetic stimulation constricts it, sympathetic stimulation dilates it.

Lens

Highly elastic circular biconvex body; bends (refracts) light rays.

Retina

Innermost lining of the eye; delicate structure adapted for light stimulation.

Chambers of the Eye

• Anterior chamber: In front of lens; filled with aqueous humor which nourishes and bathes anterior eye.

• Posterior chamber: Behind lens; contains vitreous humor which maintains the shape of the eyeball and holds the retina in place.

Three Principle Regions of the Ear

1. External ear: Uses air to collect and channel sound waves. Includes auricle (pinna), external auditory canal, and tympanic membrane.

2. Middle ear: Uses a bony system to amplify sound vibrations. Includes ear ossicles (malleus, incus, stapes), eustachian tube (connects to throat to equalize pressure), and oval window.

3. Internal ear: Generates potentials to transmit sound and balance information to the brain. Includes semicircular canals (detect balance), vestibule (equilibrium), and cochlea (contains Organ of Corti, the organ of hearing).

Homeostatic Imbalances of Senses

Eyes

• Cataracts: Opaque structures in lens prevent light from passing through; vision fuzzy.

• Glaucoma: Increase in intraocular pressure due to buildup of aqueous humor in anterior chamber.

• Conjunctivitis: Pink eye; highly contagious bacterial infection.

• Astigmatism: Cornea or lens has abnormal shape; blurred images.

• Myopia: Nearsightedness.

• Hyperopia: Farsightedness.

Homeostatic Imbalances of Senses

Ears

• Deafness: Hearing loss.

• Ménière's Disease: Disturbance in equilibrium characterized by vertigo and tinnitus.

• Otitis: Inflammation of the ear (Otitis externa = swimmer's ear; Otitis media = middle ear infection; Otitis interna = labyrinthitis/inner ear infection).