Special Senses In the head Equilibrium u Static

Special Senses In the head

Equilibrium u Static equilibrium: body/head are still u Dynamic equilibrium: body/head move

Static Equilibrium u Organs of static equilibrium – Vestibule u Utricle u Saccule u Wall of vestibule lined with maculae which contain numerous hairs that serve as sensory receptors u Hair cells project into gelatinous material, as head moves, material moves the maculae…impulse along vestibulocochlear nerve

Dynamic Equilibrium u Organs of Dynamic equilibrium – Semicircular canals (3 planes) – Ampulla: swelling at end of canal that contains crista ampullaris—the sensory organs u Hair cells project up into gelatinous mass called capula u Rapid movement moves the hairs and an impulse is send to cerebellum u Mechanoreceptors in joints and neck and the visual cortex aid in equilibrium (detects body position)

Sight u Organs of sight: eyes u Accessory organs: – Eyelids—four layers—covers the eye u Skin u Muscle u Conjuctiva u Outer tunic – Lacrimal apparatus—lacrimal gland secretes tears, ducts which carry tears to nasal cavity – Extrinsic muscles—move the eyes

Eye u Three distinct layers u Outer tunic u Outer 1/6 that bulges forward is transparent cornea u Other 5/6—sclera (white part); in back there is optic nerve and blood vessels that attach

Eye u Middle tunic u Posterior 5/6—choroid coat, joined loosely with sclera; blood vessels here nourish tissues, also pigments produce melanin to absorb excess light and keep inside of eye dark u Ciliary body: contains muscles and ligaments that hold lens in place and change shape to focus light u Ability to change shape: accommodation

Middle tunic cont. u Iris: thin diaphragm (colored portion) that controls the size of the opening (called the pupil) to regulate how much light passes through u Aqueous humor: circulates through anterior cavity to nourish area

Eye u Inner tunic u Retina: contains the photorecptors; has many distinct layers of receptor cells u Fovea centralis: depression that produces the sharpest vision u Optic disk: where optic nerve joins retinal nerve fibers – Blind spot u Vitreous humor: transparent jellylike fluid that fills posterior cavity

Sight u Refraction: bending of light u Visual receptors: u Rods: more sensitive to light; produce vision in dim light (colorless) u Cones: less light sensitive, color vision, sharper images u Visual pigments u Optic nerves carry impulses