Eyes, Ears & ….. Sensory and Motor Mechanisms

Sensory Receptors Mechanoreceptors: stimulated by physical stimuli (i.e. pressure, touch, stretch, motion, sound). Thermoreceptors: detect hot or cold, maintain body temperature Chemoreceptors: transmit information on solute concentration in a solution (taste, smell) Electromagnetic receptors: detect forms of electromagnetic energy (i.e. visible light, electricity, magnetism). Pain receptors: respond to excess heat, pressure, or chemicals released from damaged or inflamed tissues.

Regions of Mammalian Ear 1. Outer Ear: external pinna and auditory canal. Collects sounds and direct them to tympanic membrane (eardrum). 2. Middle Ear: vibrations are conducted through three small bones (malleus – hammer, incus – anvil, stapes – stirrup) and through oval window. Eustachian tube allows air pressure to be equalized between outer and middle ear. 3. Inner Ear: consists of fluid-containing channels lined by membrane situated in bone. Cochlea – involved in hearing Organ of Corti – snail shaped structure (here hair cell sound receptors are distorted from vibrations of sound waves) Semicircular canals – three fluid filled chambers located at right angles to each other, our sense of equilibrium and balance.

Fig. 50-8a Auditory canal Eustachian tube Pinna Tympanic membrane Oval window Round window Stapes Cochlea Incus Malleus Semicircular canals Auditory nerve to brain Skull bone Outer ear Middle ear Inner ear

Vision Compound eyes: several thousand light detectors each with own lens (insects and crustaceans) Single-lens eyes: vertebrates and some invertebrates Main parts of the vertebrate eye:  The sclera: white outer layer, including cornea (front and transparent)  The choroid: layer of pigmented cells inside sclera  The retina: innermost, contains photoreceptors – rods and cones Rods – light-sensitive but don’t distinguish colors Cones – distinguish colors but are not as sensitive to light  The iris: regulates the size of the pupil (hole at the center)  The lens: focuses light on the retina  The optic disk: a blind spot in the retina where the optic nerve attaches to the eye

Fig Optic nerve Fovea (center of visual field) Lens Vitreous humor Optic disk (blind spot) Central artery and vein of the retina Iris Retina ChoroidSclera Ciliary body Suspensory ligament Cornea Pupil Aqueous humor

Vertebrate Skeletal Muscle Contract/relax: antagonistic pairs w/skeleton Muscles: bundle of…. Muscle fibers: single cell w/ many nuclei consisting of…. Myofibrils: longitudinal bundles composed of…. Myofilaments:  Thin~ 2 strands of actin protein and a regulatory protein  Thick~ myosin protein Sarcomere: repeating unit of muscle tissue, composed of…. Z lines~ sarcomere border I band~ only actin protein A band~ actin & myosin protein overlap H zone~ central sarcomere; only myosin

Sliding-filament model Theory of muscle contraction Sarcomere length reduced Z line length becomes shorter Actin and myosin slide past each other (overlap increases)

Actin-myosin interaction 1- Myosin head hydrolyzes ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration” 2- Myosin head binds to actin; termed a “cross bridge” 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy configuration” 4- Binding of new ATP releases myosin head Creatine phosphate~ supplier of phosphate to ADP

Muscle contraction regulation, I Relaxation: tropomyosin blocks myosin binding sites on actin Contraction: calcium binds to toponin complex; tropomyosin changes shape, exposing myosin binding sites

Muscle contraction regulation, II Calcium (Ca+)~ concentration regulated by the…. Sarcoplasmic reticulum~ a specialized endoplasmic reticulum Stimulated by action potential in a motor neuron T (transverse) tubules~ travel channels in plasma membrane for action potential Ca+ then binds to troponin

Muscle contraction