Chapter 17 Sensory Organs

Sensation

The process of sensing stimuli from the environment.

Perception

The conscious awareness of a sensation (how the brain interprets the stimuli).

Transducer

A device or cell (like a sensory receptor) that transforms energy from one form into another (e.g., light into electrical impulses).

Sensory Organ

A sensory receptor combined with associated tissues, usually associated with special senses.

General Senses

Distributed throughout the body (e.g., touch, temperature, pain, pressure, vibration, proprioception).

Special Senses

Localized and specialized (the 'big five': sight, smell, taste, hearing, and balance).

Free nerve endings

Primarily detect pain and temperature.

Encapsulated sensory receptors

Receptors enclosed in a capsule of epithelial or connective tissue.

Meissner's (tactile) corpuscle

Detects light touch and two-point discrimination.

Pacinian (lamellar) corpuscle

Detects deep pressure and vibration.

Associated sensory receptors

Wrapped around another organ (e.g., hair follicles).

Hair follicle receptor

Detects movement of hair.

Muscle spindle

Skeletal muscle receptor that maintains muscle tone and detects stretching for the stretch reflex.

Golgi tendon organ

Detects tension in tendons and initiates the reflex to relax the muscle.

Odors

Chemical stimuli detected by olfactory receptors.

Pheromones

Chemical signals released by an animal that affect the behavior or physiology of others of the same species.

Olfactory epithelium

Specialized sensory tissue in the nasal cavity that contains olfactory receptor cells.

Olfactory bulbs

Neural structures of the forebrain where olfactory nerves terminate.

Olfactory tracts

Neural pathways that carry signals from the bulbs to the brain.

Vomeronasal organ

An accessory olfactory organ (Jacobson's organ) used primarily to detect pheromones.

Taste bud

The sensory organ for taste, containing a cluster of receptor cells.

Taste pore

The small opening at the top of the taste bud through which chemicals enter.

Gustatory cell

The actual sensory neuron within the taste bud that detects chemicals.

Electromagnetic spectrum

The range of all types of EM radiation.

Photoreceptors

Cells (rods and cones) sensitive to light.

Layers of the Eye

Outer (fibrous), Middle (vascular), and Inner (sensory/retina).

Sclera

The 'white' of the eye; tough outer connective tissue.

Cornea

The transparent front part of the eye

Choroid

The vascular middle layer that provides blood to the retina.

Ciliary body

Contains muscles that control the shape of the lens.

Lens

The clear structure that refracts lights waves.

Iris

color part of the eye, controls contrection and dilation

Pupil

The opening in the center of the iris.

Retina

The innermost layer containing photoreceptors.

Rods/Cones

Rods detect light/dark and movement (low light); Cones detect color and sharp detail.

Fovea

The area of the retina with the highest concentration of cones (sharpest vision).

Aqueous humor

Clear fluid in the front of the eye.

Vitreous humor

Clear, jelly-like substance in the main chamber of the eye.

Signal path

Light → Cornea → Aqueous humor → Pupil → Lens → Vitreous humor → Retina.

Nerve path

Photoreceptors → Optic nerve (Cranial Nerve II) → Optic Chiasm → Visual Cortex.

Monocular vision

Eyes on the sides of the head; wide field of view but little depth perception.

Binocular vision

Fields of vision overlap.

Stereoscopic vision

The ability to perceive depth/3D due to binocular overlap.

Refraction

The bending of light as it passes through different media (cornea/lens).

Accommodation

The process of changing the lens shape to focus on objects at different distances.

Pineal/Parietal organ

'Third eye' structures in some lower vertebrates that detect light levels and regulate biological rhythms.

Mechanoreceptors

Receptors responsive to physical deformation (touch, pressure, sound).

Hair cell

The basic unit of mechanoreception, featuring stereocilia (hair-like projections).

Neuromast organ

A cluster of hair cells and associated cells.

Lateral line system

A system of neuromast organs in fish/amphibians that detects water currents and vibrations.

Vestibule

The central part of the inner ear used for static balance.

Semicircular canals

Three fluid-filled tubes that detect rotational/dynamic balance.

Otoliths (otoconia)

Small 'ear stones' or crystals that move with gravity to trigger hair cells for balance.

External Ear

Includes the pinna and external auditory meatus (canal).

Pinna (auricle)

the ear itself

external auditory meatus

The tube that sound waves go into

Middle Ear

Contains the tympanic membrane (eardrum) and the ossicles (malleus, incus, stapes)

tympanic membrane

eardrum

ossicles (malleus, incus, stapes)

small bones in ear

Eustachian tube

Equalizes pressure in the middle ear.

Inner Ear

Includes the vestibule, semicircular canals, cochlea, and organ of Corti

vestibule

structure that helps to detect balance

semicircular canals

important for balance

Cochlea

snail-shaped spiral

organ of Corti

sound organ in the cochlea

External ear function

Collects sounds waves

Middle ear function

amplifies sound waves

Inner ear function

where sound waves cause bending of stereocilia, which converts sound waves to nerve impulses

Conversion

Sound waves (air) → Mechanical vibration (eardrum/ossicles) → Fluid waves (cochlea) → Bending of stereocilia → Nerve impulses.

Electroreceptors

Receptors that detect weak electrical fields (common in sharks, some fish, and monotremes).

Ampullae of Lorenzini

Specialized electroreceptors in sharks that detect the electrical fields produced by the muscles of prey.