P.H.Y.S.I.O.

The Ear Hearing is the detection of sound waves and sound is the result of vibration, or waves, travelling through a medium. Auditory stimuli travel farther and more quickly than chemical ones, but not as fast as light. Auditory receptors provide better directional information than chemoreceptors. The  cochlea  is a bony structure containing part of the cochlear duct. The vestibular canal lies above this duct, while the tympanic canal lies below it. All three chambers are filled with fluid. Pressure waves travel down the tympanic canal to the  round window , which transmits pressure back to the middle ear. The  organ or court  transduces sound in the cochlea: The  basilar membrane  is the bottom of the cochlear duct, where hairs are attached Hair cells are found with their associated neurons The  tectorial membrane  is an overhanging, gelatinous membrane where hair cells hit. The  stereocilia  of hair cells be...

The Eye There are 5 special senses: Olfaction (smell) Gustation (taste) Vision Equilibrium Hearing Important structures of the eye Sclera: the white portion of the eye composed of tough connective tissue Cornea: the transparent portion through which light enters Iris: the coloured portion of the eye which contracts to decrease pupil size (parasympathetic response) and dilates to increase pupil size (sympathetic response) Lens: transparent structure that completes the focusing of light onto the retina. There are cells on the interior of the lens with no nuclei nor organelles, and are filled with  crystalline which provide clarity and focusing power to the lens. NOTE: a cataract is damage to the crystallins, where the transparency of the lens is lost. Fovea: site of receptors for cones Retina: inner layer of fibrous tissue surrounding the eye. The retina is comprised of three cell layers: rods and cones, bipolar cells and ganglion cells. Gangli...

Mechanism of Hormone Action Water Soluble Hormones Water soluble hormones cannot cross the plasma membrane and therefore have to use second messengers, e.g. cyclic AMP. Water soluble hormone binds to membrane receptor, e.g. adenylate cyclase via G protein AC catalyses the synthesis of cAMP cAMP changes metabolism by activating enzymes and phosphorylating membrane proteins (opening channels). cAMP is deactivated by PDE (phosphodiesterase) Lipid Soluble Hormones Lipid soluble hormones (steroid hormones) can diffuse across the plasma membrane and bind to and activate receptors in the cytoplasm or nucleus. The activated receptor-hormone complex alters gene expression and directs the synthesis of new proteins. This alters cellular metabolism. Thyroid Hormones Thyroid hormones are transported across the cell membrane and bind to receptors at the mitochondria and nucleus. They form the hormone-receptor complex, which binds to DNA, much like steroid hormones. Genes are a...

What Are Hormones? Hormones have several general functions: Help regulate: Chemical composition and volume of internal fluids Metabolism and energy balance Contraction of smooth and cardiac muscle fibres Glandular secretions Some immune system activities Control growth and development Regulate operation of reproductive systems Help establish circadian rhythms Mobilise body's defence against stressors Hormones are able to change the physical or biological properties of a target cell by: Altering membrane permeability Activating or inactivating key enzymes Changing genetic activity Hormones differ from the nervous system in that, they: Offer indirect communication Are slow acting and produce a slow response Respond only to chemical stimuli Are capable of secreting (although the nervous system is capable of this, too) Are delivered to target cells by the blood Have an effect on cells far from the site of release Can target virtually all cells in ...

Hormones of the Endocrine System Pineal Gland The pineal gland secretes melatonin. Sets diurnal rhythm (circadian rhythm) Contributes to Seasonal Affective Disorder Inhibits reproductive functions until puberty Antioxidant: protects CNS neurons from free radical injury Anterior Pituitary Gland The anterior pituitary gland secretes: Growth Hormone Stimulates cellular growth Regulates metabolism Increases protein synthesis, protein catabolism and uptake of amino acids Thyroid Stimulating Hormone Controls secretions and activities of thyroid gland Follicle Stimulating Hormone In males: stimulates sperm maturation In females: stimulates follicle development and oestrogen secretion Lutenizing Hormone In males: stimulates leydig cells to synthesise androgens In females: stimulates ovulation and oestrogen and progesterone secretion Prolactin Stimulates mammary gland development Initiates and maintains milk production by mammary glands...