Sense organs are extensions of the central nervous system (CNS) that continuously monitor what is going on inside and outside the animal. At the heart of all sense organs are sensory receptors - various kinds of specially modified nerve endings. When triggered by an appropriate stimulus, a sensory receptor generates a nerve impulse that travels to the CNS and is interpreted as the appropriate sensation.
The sensory receptors of common domestic animals are sensitive to 4 general types of stimuli:
I. General terminology
II. General senses
A. Visceral sensationsB. Touch
C. Temperature
D. Proprioception
E. Pain
1. Nociceptors
2. Nociception
a. Transduction
b. Transmission
c. Modulation
d. Perception
3. Subjective consequences of severe/chronic pain
4. Objective consequences of severe/chronic pain
a. Behavioral
b. Autonomic
c. Neuroendocrine
d. Metabolic
e. Immune
f. Morphologic
III. Special senses
A. Taste1. Taste budsa. Locationsb. Gustatory cells
c. Taste pore
B. Smell
1. Olfactory epitheliuma. Olfactory cellsb. Mucous layer
C. Hearing
1. External eara. Pinnab. External auditory canal
c. Tympanic membrane
2. Middle ear
a. Functionb. Ossicles
i. Malleusii. Incus
iii. Stapes
c. Eustachian tube
i. Locationii. Function
3. Inner ear
a. Cochleai. Locationii. Structure
iii. Organ of Corti
(a). Hair cells(b). Tectorial membrane
D. Equilibrium
1. Vestibulea. Maculaeb. Otoliths
c. Functions
2. Semicircular canals
a. Cristab. Function
E. Vision
1. Major layers of eyeballa. Outer fibrous layeri. Corneaii. Sclera
iii. Limbus
b. Middle vascular layer
i. Choroid(a). Tapetumii. Ciliary body
iii. Iris
c. Inner nervous layer
i. Retina2. Major compartments of eyeball
a. Aqueous compartmenti. Aqueous humorii. Anterior chamber
iii. Posterior chamber
b. Vitreous compartment
i. Vitreous body3. Lens
a. Structureb. Function
c. Attachments
d. Accommodation
i. Distant visionii. Close vision
4. Iris
a. Structureb. Function
5. Retina
a. Functionb. Structure
i. Pigment layerii. Photoreceptors
(a) Rods(b) Cones
iii Neurons, synapses, & nerve fibers
iv. Optic disk
6. Formation of a visual image
7. Extra-ocular structures
a. Conjunctivai. Palpebral conjunctivaii. Bulbar conjunctiva
b. Eyelids
i. Medial canthusii. Lateral canthus
iii. Tarsal glands
iv. Third eyelid
c. Lacrimal apparatus
i. Lacrimal glandii. Lacrimal puncta
iii. Lacrimal sac
iv. Nasolacrimal duct
d. Eye muscles