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Synapse • Junction between two neurons • Synaptic Knobs: Axon Terminal • Neurotransmitters – When the action potential reaches the axon terminal, the neurotransmitters are released from the vessicles. – Some are Excitatory: continue the impulse – Some are Inhibitory: stop the impulse Reflex Arc Reflexes • Knee-Jerk Reflex (Patellar Reflex) – Stimulates stretch receptors in the Quads – Send an impulse to the femoral nerve to contract the Quads • Withdrawal Reflex – Temperature or Pain Receptors are triggered – Sends an impulse to CNS (spinal cord) – Causes flexors to contract Types of Senses Types of Sensory Receptors • Chemoreceptors: chemicals become attached to receptors on their membranes. Smell and taste • Pain Receptors (Nociceptors): extreme chemical or thermal stimuli. Free nerve endings Types of Sensory Receptors • Thermoreceptors: respond to changes in temperature. Heat and cold receptors • Mechanoreceptors: compression, bending, stretching of cells. Touch, pressure, proprioception, hearing, and balance • Photoreceptors: respond to light: vision Referred Pain • Crossed wires in the cerebral cortex because the pathways are close together. • Sends signals to the skin instead of back to the organ where it originated. • Most sensations happen in the skin so the brain plays the odds and sends it to the skin. Touch, Pressure, and Vibration • Free Nerve Endings: – Simplest, most common sensory receptor – Scattered through most of body – Extreme touch, pressure or vibration • Meissner’s Corpuscles – Used to determined texture of objects. Fine descrimination. • Pacinian Corpuscles – Deep cutaneous pressure; vibration Temperature Sensation • Free Nerve Endings – Throughout body – Detect extreme temperatures as pain • Heat and Cold Receptors – 10 to 15 times more cold receptors Pain Sensation • Free Nerve Endings: – Stimulated by tissue damage (swelling) • Pain nerve fibers: – Acute: sharp pain, myelinated fibers, pain stops when stimulus is removed (superficial) – Chronic: aching pain, unmyelinated fibers, pain continues when stimulus is removed (deep) Pain Sensation • Visceral Pain and Referred Pain – Visceral pain: fewer receptors so it is more of a dull ache – Referred Pain: impulse travels to cutaneous tissue instead of visceral tissue • Regulation of Pain Impulses – Prevent nerve cells from releasing more pain signals – Endorphins and enkephalins - opiates Muscle Spindles Stretch Reflex • When muscle is stretched, the motor neurons are stimulated and cause stretched muscles to contract and shorten back to its resting length. • Stretch too far – pulls muscle back • Protective – to keep muscle from tearing Golgi Tendon Organs Golgi Tendon Organs • Too much strain (weight) on the muscle causes muscle to contract too hard • Muscle relaxes so you drop the weight • Protective reflex to keep muscle from tearing Olfactory Receptor Sense of Smell (Olfaction) • Neurons from the CNS directly contact the outside environment • Chemoreceptor – distinguish between chemical changes • Structure: Unipolar neurons • Function: Detect chemical changes in the air Sense of Taste (Gustation) • Taste bud structure: – On tongue and pharynx – 40-60 layers of epithelium shaped like an onion • Function: – Detects chemical changes in aqueous solution Taste Nerve Pathway • Cranial Nerves – VII (Facial) – Anterior 2/3 of tongue – IX (Glossopharyngeal) – Posterior 1/3 of tongue and part of roof of mouth – X (Vagus baby) - throat • Quick Adaptation – Palate needs to be reset Sense of Hearing External Ear • Ear (auricle) • External Auditory Meatus – ear canal • Tympanic Membrane (ear drum) – Vibrates in response to sound and is semitransparent • Function: – Collect sound waves to be sent to the middle ear Middle Ear • Structure: –Auditory Ossicles • Malleus – connects to eardrum • Incus – connects malleus to stapes • Stapes – connects to inner ear More Middle Ear • 2 small muscles Shock absorbers – pulls bones back so they won’t vibrate so hard if there is a loud noise • Tensor tympani – connects to malleus and wall of middle ear • Stapedius m. – connects stapes to wall of middle ear – Tympanic Reflex – protect receptors from loud sounds • When muscles contract they pull the malleus and stapes away from the ear drum and inner ear • 40 millisecond lag time Even More Middle Ear • Eustachian tube – Connects middle ear to pharynx (back of throat) – Allows drainage of fluid and pressure changes (equalization) – Bacteria can gain access to middle ear • Function of Middle Ear: – Transmit vibrations from ear drum to inner ear Inner Ear • Cochlea – Shell shaped – Houses hearing receptors • Osseous Labyrinth – Hollow area inside of shell • Membranous Labyrinth – Like a pool liner inside osseous labyrinth • Round and Oval Windows – Holes in the bone that the vibrations pass through – Stapes connects to the oval window More Inner Ear • Organ of Corti – Hearing receptor – Stimulated by vibrations in the watery/gelatinous fluid (tectorial membrane) in the cochlea • Function of the Inner Ear – Carries impulses to brain via the vestibulocochlear nerve VIII Sense of Equilibrium • Static Equilibrium – Movement in a straight line – Impulses picked up by the Vestibule and carried to brain via Cranial Nerve VIII – Macula are the receptors – Function: balance More Equilibrium • Dynamic Equilibrium – Movement in many directions or a spin – Impulses picked up by the semicircular canals – Crista Ampularis is the receptors – Function: to detect rotational changes in the body Sense of Sight • Function of the Eye: – Allow light through so the impulse can be sent to the brain Sense of Sight • Accessory Organs – Eyelids: keep junk out – Medial and Lateral Canthus – Eyelashes Lacrimal Apparatus: glands and ducts • Produce tears • Lubricates the eye Extrinsic Eye Muscles 6 skeletal muscles that move the eye • Controlled by Cranial Nerves III, IV and VI External Anterior Structures • Cornea • Conjunctiva Structure of the Eye • Three Tunics – Sclera - White – Choroid - dark – Retina - photoreceptors Retina • Fovea Centralis – area of best vision • Optic Disc • Optic Nerve Anterior Structures • Lens and Ciliary Muscles – Contract and pull lens to flatten it out • Iris - Colored part – Controls the size of the pupil Chambers of the Eye • Anterior Cavity – Aqueous Fluid • Posterior Cavity – Vitreous Fluid Pathway of Light Through the Eye • Refraction • Accommodation Visual Fields and Pathways to the Brain • Optic Chiasma • Optic Tracts • Optic Radiation Eye Reflexes • Convergence • Photopupillary Reflex Accommodation Pupillary Reflex