NERVOUS SYSTEM Nervous System Overview Role: Maintain homeostasis 1. 2. 3. Sense changes (____ neurons) Integrate information (_______) Respond (______ neurons) Basic Anatomy 1. Mass = ____ lbs 3% total body mass Main Subdivisions 1. 2. Central Nervous System (CNS) Peripheral Nervous System (PNS) CELLS OF THE NERVOUS SYSTEM 2 Types of cells found in the N S: 1. NEURONS: nerve cells 2.NEUROGLIA (Glia): specialized connective tissue NEURONS Motor neurons Also called ________ neurons. Interneurons Also called _______neurons. Sensory neurons Also called _______neurons. STRUCTURE OF NEURON AXON: is surrounded by segmented wrapping called _______. - It is: Axon - long section, transmits impulses Dendrite - small extensions from the cell body; receive information Neurofibrils - fibers within the axon Interesting Facts about the Neuron Longevity – can live and function for a lifetime • •Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception •High metabolic rate – require abundant oxygen and glucose The nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be course and sometimes involve the whole body. Try surprising a baby! GLIA Glia or neuroglia: They are special types of supporting cells - Function: is to: * Large cells look like stars: astrocytes * Smaller cells are Microglia Example: Oligodendrocytes: helps hold fibers together, produce the fatty myelin sheath that envelops nerve fibers in the brain and spinal cord NERVES Nerve is a group of peripheral nerve fibers (axons) bundled together like the strands of a cable. Myelin is found on nerves and is white. Nerves are referred to as _____ matter of the PNS and also the CNS. Unmyelinated axons and dendrites are called ________. (because of their color) Brain = Gray over White Spinal Cord = White over Gray REFLEX ARC Nerve impulses are conducted from receptors to effectors over neuron pathways known as ___________ This results in a _______. (a contracted muscle or secretion from a gland) 2 types of reflex arcs: - two-neuron arcs: spinal cord and motor neuron - three-neuron arcs: sensory neurons, interneurons and motor neurons Animation http://www.youtube.com/watch?v=Y5nj3ZfeYDQ http://bcs.whfreeman.com/thelifewire/content/chp 46/46020.html RECEPTORS Impulse conduction normally starts in the_______. Found at the beginning of the dendrites of sensory neurons Location: MS (MULTIPLE Sclerosis) DAMAGE TO MYELIN Hard lesions replace the destroyed Myelin As the myelin is lost, nerve conduction is ______ Causing weakness, loss in coordination, visual impairment, speech disturbances No known cure, occurs most in women ages 2040. Synapse A microscopic space from the axon ending of one neuron to the dendrite of another neuron. The nerve impulse stops, chemicals are sent across the gap, the impulse continues alone the dendrites. Neurotransmitters Chemicals by which neurons communicate Some help us sleep, inhibit pain, make us energetic Examples Acetylcholine Norepinephrine and Dopamine- Serotonin- Endorphins- Neurotransmitters Excitatory - increase membrane permeability, increases chance for threshold to be achieved Inhibitory - decrease membrane permeability, decrease chance for threshold to be achieved The Action Potentialan All-or-None Electrical Signal Cell Membrane Potential At rest, the inside of a neuron's membrane has a negative charge. As the figure shows, a Na+ / K+ pump in the cell membrane pumps sodium out of the cell and potassium into it. However, more potassium ions leak out of the cell. As a result, the inside of the membrane builds up a net negative charge relative to the outside. Animations of Nerve Impulses http://highered.mcgrawhill.com/sites/0072495855/student_ view0/chapter14/animation __the_nerve_impulse.html Action Potential Overview Signals or impulses of communication Travel along axons Are “all-or-none” events Threshold must be reached Two phases 1. 2. Depolarization Repolarization Axon Diameter and Action Potentials Recall that axons are also called nerve fibers Larger fibers propagate impulses faster Larger fibers usually myelinated Smallest fibers are unmyelinated and therefore propagate impulses slower Resting Membrane Potential Recall that there is a separation of charges across the membrane of excitable cells. Extracellular fluid contains more sodium ions than are found inside a cell Cytosol contains more anions and negatively charged proteins Thus sodium ions cling to the outside cell surface Resting Membrane Potential Cell somewhat permeable to potassium Much less permeable to sodium Sodium quick to rush in when gates open following both electrical and concentration gradients Potassium not quick to rush out only has concentration gradient to drive flow Resting Membrane Potential • small build-up of anions in cytosol • equal build-up of cations in extracellular fluid Change in Membrane Potential Na+ channels open Fast Na+ influx Inside of cell becomes less negative If change is +15mV action potential occurs Ongoing Research Improve environment for spinal cord axons to bridge injury gap Find ways to stimulate dormant stem cells to replace lost, damaged, or diseased neurons Develop tissue cultured neurons that can be used for transplantation purposes. Drugs that Affect Synapses and Neurotransmitters Strychnine poisoning can be fatal to humans and animals and can occur by inhalation, swallowing or absorption through eyes or mouth Strychnine is a neurotoxin which acts as an antagonist of acetylcholine receptors. It primarily affects the motor nerves in the spinal cord which control muscle contraction. An impulse is triggered at one end of a nerve by the binding of neurotransmitters to the receptors. Strychnine use by athletes? Drugs that Affect Synapses and Neurotransmitters •Cocaine, morphine, alcohol, ether and chloroform •Ecstasy LSD (hallucinogen) Dangers of Ecstasy (MDMA) The neurotransmitter serotonin is vital in regulating many of our basic functions. Serotonin is, among other things, the feel good neurotransmitter and helps to regulate body temp. Our brain cells are constantly trying to bring some amount of serotonin back into the cells and out of the synapse using serotonin reuptake transporters. Ecstasy essentially takes these upkeep transporters and reverses their roles. This causes a massive flood of serotonin from the brain cells into the synapse. The most common cause of Ecstasy-related death is overheating (hyperthermia). MDMA interferes with the body's ability to regulate its own body temperature and to see other warning signs allowing the body to overheat without discomfort especially when dancing for hours in hot clubs. LSD; lysergic acid diethylamide Actions/Effects: LSD alters the action of the neurotransmitters serotonin, norepinephrine, and dopamine, triggering extreme changes in brain function. Physical effects include increased body temperature, heart rate, and blood pressure. Psychological effects include perceptual and thought distortions, hallucinations, delusions, and rapid mood swings. Cocaine blocks reuptake of dopamine Central Nervous System Integrates and correlates incoming sensory information Source of thoughts, emotions, memories Most motor signals originate in CNS CNS (CENTRAL NERVOUS SYSTEM) Spinal Cord and Brain 4 Divisions of the brain: Brainstem Cerebellum Diencephalon Cerebrum . BRAINSTEM * Medulla Oblongata: largest part of the brainstem. - extension of the _________ - Location: lies below the _______ - Functions: reflex center -It controls: DIENCEPHALON Hypothalamus: - Structure: - Function: Acts as the major center for controlling the _____. (function of internal organs) - Controls _____________ - Centers for controlling: DIENCEPHALON THALAMUS: - Structure: dumbbell shaped mass of gray matter in each cerebral hemisphere - Function: - Produces emotions of pleasantness and unpleasantness associated with sensation CEREBELLUM Second largest part of the brain Structure: - composed of _____in outer layer and _______in the inner layer • Function: CEREBRUM Largest part of the brain Structure: Structures: Series of ridges and grooves -Ridges are called convolutions or ____ -Grooves are called _____ (deepest sulci are called fissures) -Divided into two halves- ________ -Hemispheres connected by the _________ CEREBRUM HEMISPHERES: Divided into lobes Lobes are named after bones that lie over them. CEREBRUM Function: mental process of all types Sensations Consciousness Thinking Memory Willed Movements Cerebrum Specific areas have specific functions Temporal lobe’s auditory areas interpret incoming nervous signals as specific sounds Visual area of the occipital lobe helps you understand and identify images If a specific part of the brain is damaged, for example the Primary Taste Area, you would not be able to taste things. __________CEREBRUM SPINAL CORD Structure: Outer part composed of white matter - Interior part composed of gray matter Function: center of all spinal cord reflexes - sensory tracts conduct impulses ___ the brain. - motor tracts conducts impulses ____ the brain Cutting the Cord Completely severing the spinal cord produces a loss of sensation for all areas below the cut, called anesthesia. It also produces a loss of the ability to make voluntary movements, called paralysis. Peripheral Nervous System (PNS) Cranial and Spinal Nerves Function: Cranial Nerves: - 12 pairs of cranial nerves - Functions vary SPINAL NERVES Structure: contain dendrites of sensory neurons and axons of motor neurons Function: conduct impulses necessary for sensations and voluntary movements Autonomic Nervous System (ANS) Structure: Consists of motor neurons that conduct impulses from spinal cord or brainstem to: 1. Cardiac Muscle tissue 2. Smooth muscle tissue 3. Glandular epithelial tissue Function: 2 Divisions of ANS 1. Sympathetic nervous system: -Structure: -Function: 2 Divisions of ANS 2. Parasympathetic Nervous System: Structure: Function: Autonomic Neurotransmitters Each division of the ANS signals its effectors with a different neurotransmitter. This is how an organ can tell which division is stimulating it. Ex. The heart responds to acetylcholine from the parasympathetic division by slowing down. If norepinephrine, from the sympathetic division, is present, the heart speeds up. ANS as a Whole Regulates the body’s autonomic functions in ways that maintain HOMEOSTASIS