-Detect heat or cold and help maintain body temperature

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1 Sensory Receptors -Transduce stimulus energy and transmit signals to the central nervous system -Reception occurs when a receptor detectd a stimulus -Perception occurs in the brain as this information is processed *Reflex has only reception* Mechanoreceptors -Are receptors stimulated by physical stimuli, such as pressure, touch, stretch, motion, or sound -Detect moving fluid or settling particles in the ear Thermo receptors -Detect heat or cold and help maintain body temperature Chemoreceptor -Transmit information about solute concentration in a solution. Taste and smell receptors are two types of these.

2 Electromagnetic Receptors -Detect various forms of electromagnetic energy such as visible light (photoreceptors) electricity and magnetism Pain Receptors -Respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissue Three Regions of the Mammalian Ear-Outer Ear -Is the external pinna and auditory canal -These collect sound and direct them to the tympanic membrane (eardrum), which separates the outer ear from the middle ear Three Regions of the Mammalian Ear- Middle Ear -Vibrations are conducted through three small bones (malleus, incus, and stapes) and though the oval window -The Eustachian tube allows air pressire to be equalized between the outer and middle ear

3 Three Regions of the Mammalian Ear- Inner Ear The Semicircular Canals -Then the vibrations are conducted to the inner ear, which consists of fluid-containing channels lined by hair receptors to detect stimuli -The cochlea is involved in hearing, it is a snailshaped structure containing fluid and hair receptors, which are distorted from the vibrations caused by sound waves -These hair cells are the actual receptors of sound- when they bend, they send a nerve impulse to the thalamus which stimulates the auditory cortex of the brain -Are three fluid-filled chambers located at right angles to each other. They are also filled with fluid and hair receptors -Our sense of equilibrium results when hair cells within them are distorted by being off balance and nerve impulses are then sent to the thalamus and to the cerebellum The Senses of Taste and Smell rely on similar sets of sensory receptors -Taste buds are modified epithelial cells situated on different parts of the tongue and mouth -When each type of receptor is stimulated, it sends nerve impulses to the thalamus and then to the gustatory cortex to perceive taste Single-lens eyes are found in vertebrates and some invertebrates: Structures of the Eye -The sclera of the eye is tough and white -The transparent cornea, allows light into the eye and acts as fixed lens -The choroid is a layer of pigmented cells inside the sclera -The retina is the innermost layer of the eyeball. It contains the photoreceptor cells (rods and cones) -Where it is pierced by the optic nerve, there are no photoreceptors, this is the blind spot -The rods are for vision in dim light, and the cones for color vision

4 Structures of the Eye Continued Nervous stimulation and the physical interaction of protein filaments are required for muscle function Sarcomere -The iris is the pigmented area at the front of the eyeball, it is a muscular structure that regulates the amount of light admitted though the pupil, which is the hole at its center -Aqueous humor fills the anterior cavity of the eye and the vitreous humor fills the posterior cavity of the eye -Rhodesian is the light-absorbing pigment that triggers a signal transduction pathway that ultimately leads to sight -When stimulated, it sends nerve impulses to the thalamus and then to the visual cortex of the brain -Skeletal muscle is attrached to bones and responsible for the movement of bones. It consists of long muscle fibers, each of which is a single muscle cell -Skeletal muscle is striated (striped in appearance) -Each muscle fiber is a bundle of myofibrils, which in turn are composed of two kinds of myofilaments: -The thin filaments are actin -The thick filaments are myosin -Is the basic contractile unit of the muscle -Z lines make up the border of sarcomeres, actin is attached here -During muscle contraction, the length of the sarcomere is reduced, actin filaments slide over the myosin -The sliding-filament model states that the thick and thin filaments slide past each other so that their degree of overlap increases Mechanism for Muscle Contraction -A motor neuron will cause a muscle fiber to contract when its depolarization causes the neurotransmitter acetycholine to be released into the synapse of the neuromuscular junction -As acetycholine binds to receptors on the muscle fiber depolarization of the muscle cell leads to 5 steps

5 Depolarization of a Muscle Fiber 1.An action potential spreads along T-tubules (transverse tubules0 to the sarcoplasmic reticulum 2.This depolarization causes the sarcoplasmic reticulum to release calcium ions 3.The calcium ions bind to troponin and cause it to move, exposing the myosin sites on actin 4.Actin and myosin now interact as myosin heads attach to the actin filaments, after being phosphorylated by ATP 5.The muscle contracts, with actin filaments sliding over myosin