General and Special Senses, Endocrine System

Stimuli

Bodies constantly exposed to sensory information

Sensation

Conscious awareness of stimuli

Receptor

Structure converting sensory stimulus to nerve impulse; two classes: general senses and special senses

General senses

Temperature, pain, touch, stretch, pressure

Special senses

Gustation, olfaction, vision, equilibrium, audition

Sensory adaptation

Decreased response to a constant stimulus over time; tonic receptors (adapt slowly) and phasic receptors (adapt rapidly—sends a burst of signals)

External anatomy of eye

Palpebrae (eyelids), sclera (white, protective outer layer), cornea (transparent anterior portion of eye; refracts light), iris (pigmented structure that controls pupil diameter), pupil (opening in the iris)

Conjunctiva

Lines inner eyelid and anterior sclera; lubricates and protects eye; contains blood vessels supplying sclera

Lacrimal apparatus

Lacrimal gland (produces tears), lacrimal puncta (drains tears), nasolacrimal duct (carries tears into nasal cavity)

Eye lens

Biconvex; transparent structure inside eyeball; held in place by suspensory ligaments; goes through accommodation (changes shape)

Fibrous tunic

Superficial layer; avascular; consists of sclera (provides eye shape and protects delicate internal components) and cornea (acts as eye’s outermost lens and refracts light rays)

Near focus

Ciliary muscle contracts, releases pull on lens, lens get fatter, focusing on things that are near

Far focus

Ciliary muscle relaxes, pulls on lens, lens gets flatter, focusing on things that are farther

Vascular tunic

Middle layer; choroid (blood supply), ciliary body (adjusts lens shape), iris (controls pupil diameter)

Neural tunic

Innermost/deepest layer; retina (neural tunic of eye), pigmented layer (absorbs stray light), neural layer (contains photoreceptors that detect light); visual information travels to brain through CN II

Retinal landmarks

Optic disc (blind spot): where optic nerve exits, contains no photoreceptors; macula lutea: lateral to blind spot, center is fovea centralis

Anterior eye cavity

Between cornea and lens; contains aqueous humor that nourishes avascular structures and helps maintain intraocular pressure

Posterior eye cavity

Vitreous chamber; between lens and retina; contains vitreous humor that helps maintain eyeball shape

Hearing

Audition; detecting sound waves; converting them into nerve impulses

Equilibrium

Balance; detect position of head

External ear

Auricle (directs sound waves), external auditory canal (channels sound), tympanic membrane (vibrates to sound)

Middle ear

Between tympanic membrane and inner ear; contains auditory ossicles

Auditory ossicles

Malleus (hammer), incus (anvil), stapes (stirrup); amplify sound and transmit to oval window

Pharyngotympanic tube

Eustachian tube that connects middle ear with nasopharynx; equalizes pressure between external ear and middle ear

Inner ear bones

Contains vestibule, semicircular canals, and cochlea

Equilibrium of inner ear

Utricle (horizontal) and saccule (vertical) detect linear acceleration and head position relative to gravity; semicircular ducts detect rotational (angular) acceleration; all ducts responsible for interpreting equilibrium; transmit this info via vestibular branch of CN VIII

Hearing of inner ear

Cochlear duct (scala media); membranous portion of cochlea and contains the spiral organ (Organ of Corti); involved in hearing

Spiral organ (organ of corti)

Located in cochlear duct, rests on basilar membrane, contains hair cells with stereocilia

Mechanism of hearing

When sound waves enter via scala vestibuli, fluid vibrations cause the basilar membrane to move; movement of basilar membrane bends hair cell stereocilia; bending produces electrical signals in hair cells; auditory information travels to brain through cochlear branch of CN VIII; pressure waves continue through scala tympani; round window allows pressure displacement

Low frequencies

Travel farther distances

High frequencies

Travel shorter distances

Endocrine system

Ductless glands; hormones released into and travel through blood; target cells have receptors; potentially widespread effects; generally slower, longer-lasting responses

Nervous system

Electrical signals, fast, specific

Endocrine system major functions

Metabolism (rate of reactions in the body), growth and development, reproduction, homeostasis

Homeostasis

Stable internal conditions controlled by feedback loops

Components of a feedback loop

Sensor (detects changes), integrating center/controller (receives and integrates information), effector (responds to changes)

Negative feedback

Most common; antagonistic; response reverses change; increased change leads to increased response which leads to decreased change which leads to decreased response

Insulin in blood glucose regulation

Blood glucose increases → pancreatic beta cells release insulin → insulin promotes glucose uptake and storage → blood glucose decreases → insulin secretion decreases

Positive feedback

Amplifies initial change; less common than negative feedback; continues until the initiating stimulus is removed or a terminating event occurs; increased change leads to increased response which leads to amplified change which leads to amplified response

Milk letdown

Baby suckles at the nipple → nipple mechanoreceptors detect stimulation → hypothalamus signals posterior pituitary to release oxytocin → oxytocin causes milk ejection → continued suckling maintains oxytocin release; cycle continues while suckling persists

Hypothalamus

Control center of endocrine system; regulates pituitary

Anterior pituitary

Controlled by releasing/inhibiting hormones; produces its own hormones when hypothalamus tells it to

Posterior pituitary

Stores and releases hypothalamic hormones

Thyroid stimulating hormone

Anterior pituitary hormone; thyroid hormone release

Adrenocorticotropic hormone

Anterior pituitary hormone; adrenal cortex

Follicle stimulating hormone/ Luteinizing hormone

Anterior pituitary hormone; gonads (make sex cells)

Growth hormone

Anterior pituitary hormone; growth

Prolactin

Anterior pituitary hormone; milk production

Anti-diuretic hormone

Posterior pituitary hormone; kidneys, water retention

Oxytocin

Posterior pituitary hormone; milk ejection and uterine contractions

Thyroid hormone (TH)

Produces by thyroid; increases metabolic rate

Calcitonin

Produced by thyroid; lowers blood calcium

Parathyroid hormone (PTH)

Increases blood calcium

Adrenal glands

Adrenal medulla (signaling molecules for fast responses: produces epinephrine and norepinephrine); adrenal cortex (water retention and stress (slow) response: produces cortisol and aldosterone)

Cortisol

Stress response and metabolism

Aldosterone

Sodium retention and electrolyte balance

Pancreas

Produces insulin (decreases blood glucose) and glucagon (increases blood glucose)

Pineal gland

Produces melatonin and regulates circadian rhythm

Gonads

Testes produce androgens (especially testosterone); ovaries produce estrogen and progesterone