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Nervous System and Sense Organs = Ch 49 Neuron Structure • Also known as a nerve cell • Made of cell body, dendrites and axon • Dendrite – receives action potentials (many), extend from cell body • Axon (one) transmits action potential away from cell body Neuron Structure Neuron Structure • Electrical signals transmitted away from cell body = action potential • Axon covered in lipid layer = myelin sheath – Insulates neuron so it speeds up rate of transmission Nerve Impulse • Based on membrane potential (difference in electrical charge) across cell membrane • Membrane potential changes w/ + or – ions (Na and K) Resting Potential • Charge across membrane that exists when the neuron is not conducting action potential • Neg. charged proteins greater in cell • K+ ion conc. Is greater inside cell • Na+ ions greater outside cell • K+ readily diffuse out of cell leaving the cell negatively charged (-70 mV) Action Potential • Happens when cell is stimulated • Starts at point where cell body joins axon • Na+ rush in & Na+ channels open • Cell becomes more positive than outside • Outside becomes more neg. than before • Reverses “polarity” of the cell/environment Action Potential • Moves like a wave down length of axon – away from cell body • Afterward channels open, Na+ and K+ go back to “resting” state • Cannot “fire” again until resting state is reached • Requires a lot of ATP Neurotransmitters • A synapse is the area where neurons communicate…junction is called synaptic cleft • Released at end of axon across synaptic cleft (space between axon of one and dendrite of another) • Go toward receptors on another neuron causing opening of Na+ channels • If enough channels open the action potential starts and will continue to fire, if not, then the nervous signal is stopped (is inhibited) Neurotransmitters Organization – Gray matter = cell bodies – White matter = axons 1. Central Nervous System: brain + spinal cord 2. Peripheral Nervous System: not brain or spinal cord – Afferent neurons – from nerves in sense organs toward CNS – Efferent neurons – away from CNS to organs & glands – Interneurons btwn motor & sensory neurons Brain Structure Cerebrum • Largest Portion • Folded outer layer = cerebral cortex – Gray matter • 2 hemispheres for motor & sensory activities • Voluntary activity • Cerebral cortex used for: -higher mental functions, general movement, organ function, perception and behavioral reactions -split into the 4 lobes Cerebellum • Back of skull • Coordinates muscle action • Movement, balance, posture • Receives sensory impulses from muscles, tendons, joints, eyes, ears etc. Spinal Cord • Column of nerve tissue • Spinal nerves originate here • Sensory (afferent) neurons carry signals from receptors to spinal cord through dorsal roots • Motor (efferent) neurons carry signals from spinal cord to muscles and glands through ventral roots Protection • Skull and vertebrae • Protective layers (meninges) • Cerebrospinal fluid Peripheral Nervous System • Divided into sensory & motor divisions • Important For reflexes • Sensory division: gets info from internal and external environments • Motor Division- reaction to sensory info – Somatic nervous system – Autonomic Nervous System Somatic Nervous System • Control movement of skeletal muscles using neurotransmitter (acetylcholine) • Also can be automatic = maintain balance • Controls reflexes (involuntary & often protective movements) – Patellar reflex: ex. Of spinal reflex bypasses brain = super fast Autonomic Nervous System • Nerves that control internal conditions – respiration, heartbeat, blood vessels etc. • Divided into – parasympathetic- used during normal conditions – sympathetic division – used in physical or emotional stress “fight or flight” response Physiological Effects of the Autonomic Nervous System Perception of Stimuli • Types of Receptors – respond to….. – Mechano – movement, pressure – Photo – light – Chemo – chemicals – Thermo – temp. – Pain – tissue damage Types of Sensory Receptors Perception of Stimuli • Sensory receptors in higher conc. in sense organs than other body parts • Turn stimulus into electrical signals that are sent to brain Hearing & Balance • Ear – detects sound & – maintains balance • Sound vibrations directed into ear by “outer ear” • Balance: fluid filled semicircular canals and small hairs using mechanoreceptors – Bending of hairs releases neurotransmitters Hearing & Balance • Vision Eyes detect light & transmit signals to brain • Retina receives the image & transmits through optic nerve to brain • rods & cones (photoreceptors) in retina convert light to electrical signals brain can interpret – Rods respond dim light – Cones respond bright light & distinguish color Structure of the Eye • Taste – Chemicals from food enter taste bud (chemoreceptor) • Smell – Olfactory receptors in epithelium of nasal passage (chemoreceptor) Read info about Drugs, but it Is not on the test! Endocrine System = Ch 50 Types of Glands • Exocrine – Secrete non hormonal chemicals into ducts – Ex: sweat, digestive, salivary, mucous glands • Endocrine – Ductless, secrete hormones into bloodstream or fluid around cells Functions of Hormones – Regulate growth, development, behavior & reproduction • Types of Hormones Hormones: chemicals secreted by cells to influence the activity of other cells • Amino Acid Based or are Steroid/Thyroid Hormones…review in text for RG Amino Acid-Based Hormones Steroid & Thyroid Hormones – Lipids – can pass through target cell memb – Bind directly to receptor site in cytoplasm or nucleus Other Types of Hormones • Both act “locally” • Prostaglandins – Produced by many cells rather than endocrine glands – Smooth muscles that line air passages, blood vessels, intestines – Accumulate in injured areas • Neuropeptides – Secreted by nervous system – Ex: endorphins Hypothalamus & Pituitary Gland • Hypothalamus + pituitary gland = primary regulators of endocrine system • Control release of many other hormones • Hypothalamus releases hormones that stimulate or inhibit release of hormones from pituitary gland= temp control • Pituitary = Growth Hormone Upper Brain Stem • Links cerebrum w/ spinal cord • Hypothalamus – hunger, fatigue, anger, body temp. homeostasis – hormone control • Thalamus: relays sensory info to cerebral cortex Hormones Secreted by Pituitary Gland Thyroid Gland • Near lower part of larynx • Metabolism • Heart rate, blood pressure, temp., metabolic rates Thyroid Gland • Hyperthyroidism: overproduction of thyroid hormones, overactivity, high blood press., body temp • Hypothyroidism: lethargy, weight gain, low heart rate – Caused by iodine deficiency = goiter Adrenal Glands • Above each kidney – Epinephrine & norepinephrine: nervous system reaction “fight or flight” – Cause liver to produce glucose increased heart rate, pupils dilate, bronchial tubes enlarge Gonads • • • • Ovaries/Testes Produce steroid sex hormones Estrogen/progesterone from ovaries Testosterone Pancreas • Both exocrine & endocrine cells • Endocrine – Islets of Langerhans – Insulin: absorption of glucose in cells (lowers blood sugar) – Glucagon: liver releases glucose (increases blood sugar) • Type I diabetes, immune cells attack islet cells & require insulin injections • Type II diabetes: occurs after age 40, obesity, poor diet/exercise Other Endocrine Glands • Thymus – Beneath sternum, between lungs, formation of T-cells • Pineal – Near base of brain, melatonin sleep patterns • Parathyroid – In back of thyroid, increase concentration of calcium ions in blood for bone growth & muscle activity • Digestive organs – Stomach Gastrin – Small intestine secretin Homeostasis – Stable internal environment – Antagonistic hormones: opposite effect • Glucagon/insulin – Negative Feedback: initial hormone stimulates other hormones that inhibit release of initial hormone – has stabilizing effect – Positive Feedback: initial hormone stimulates other hormones that stimulate further release of initial hormone Negative Feedback Mechanisms