The Nervous System. Nervous System Functions 1. gather sensory input 2. integration- process and interpret sensory input 3. cause motor output

Transcription

1 The Nervous System Nervous System Functions 1. gather sensory input 2. integration- process and interpret sensory input 3. cause motor output

2 The Nervous System 2 Parts of the Nervous System 1. central nervous system (CNS)- brain, spinal cord 2. peripheral nervous system (PNS)- all other parts a. sensory or afferent division- transmits information gathered from somatic afferent fibers and visceral afferent fibers b. motor or efferent division- transmits information from the CNS to effector organs, muscles and glands somatic or voluntary nervous system- somatic motor nerve fibers controls skeletal muscle autonomic nervous system- controls smooth muscle, cardiac muscle and glands (involuntary)» 2 parts: sympathetic and parasympathetic Central Nervous System

3 The Nervous System Central Nervous System

4 The Autonomic Nervous System Part of the peripheral nervous system Main nervous system to control the function of the major organs Composed of sensory & motor neurons Sensory originate at the organ Motor return to the organ Involuntary Two branches to carry information from the brain Sympathetic & Parasympathetic Dual innervation of the major organs

5 The Sympathetic Generally Division The sympathetic division speeds up all organs except the digestive and urinary systems (it slows these down). FIGHT OR FLIGHT

6 The Parasympathetic Generally Division The parasympathetic division slows down all organs except the digestive and urinary systems (it speeds these up). REST AND DIGEST

7 Autonomic Nervous System

8 The Nervous System 2 main cell types in the nervous system: neurons and supporting cells (neuroglia, glial cells) Neurons conduct messages throughout the body extreme longevity amitotic high metabolic rate

9 Supporting Cells of CNS 4 types in the CNS 1. astrocytes "star cells" support and brace neurons secrete NGF (nerve growth factor) anchor them to blood capillaries; nourishment clean up the chemical environment part of the blood brain barrier 2. microglia help maintain the health of neurons phagocytic macrophages 3. ependymal cells line the central cavities of the brain and spinal cord help to create & circulate cerebrospinal fluid 4. oligodendrocytes produce myelin sheaths most common of all neuroglial cells

10 Supporting Cells of CNS

11 Supporting Cells of PNS 2 types in the PNS 1. satellite cells surround neuron cell bodies clean up chemical environment 2. schwann cells form myelin sheaths around large nerve fibers in PNS vital to nerve fiber regeneration

12 3 Functional Neuron Groups 1. sensory or afferent- transmit messages from sensory receptors to the CNS; majority are unipolar; located in PNS 2. motor or efferent- carry impulses away from the CNS; located in PNS 3. interneurons or association- lie between motor and sensory neurons; they shuttle signals through the CNS; located in CNS

13 3 Functional Neuron Groups

14 A Neuron

15 Neuron Structural Classification 4 major structural neuron groups 1. multipolar- 3 or more processes 2. bipolar- 2 processes: axon and dendrite; found in sense organs 3. unipolar- single short process T-like division; sensory neurons 4. anaxonic- many dendrites, no axons

16 Neuron Structural Classification

17 Neuron Vocabulary & Structure nuclei- clusters of cell bodies in the CNS ganglia- clusters of cell bodies in the PNS tracts- bundles of neuron processes in the CNS nerves- bundles of neuron processes in the PNS white matter- myelinated fibers gray matter- nerve cell bodies and unmyelinated fibers

18 Electricity Principles voltage- measure of potential energy generated by separated charge; unit = volt current- flow of electrical charge resistance- hindrance to flow of charge electrochemical gradient- differences in concentration of ions across a membrane chemically gated and voltage gated channels maintain the electrochemical gradient membrane potential a difference in charge across the membrane of a cell

19 The Resting Membrane Potential varies from -40mV to -90 mv the resting voltage of the membrane is about -70 mv cell cytosol contains less Na+ and more K+ than the extracellular fluid Cl- balances the Na+ outside and anionic proteins balance the K+ inside the cell membrane

20 The Na/K Pump the Na+/K+ pump maintains the concentrations (3 Na+ out/2 K+ in) changes in membrane potential acts as communication- 2 types: graded (short distances) & action potentials (long distances)

21 The Resting Membrane Potential Depolarization- reduction in membrane potential; the inside of the membrane becomes less negative than the resting potential Hyperpolarization- membrane potential increases becoming more negative than the resting potential

22 Action Potentials (AP s) neurons & muscle cells generate AP s a brief reversal of membrane potential whole event lasts a few milliseconds do not decrease in strength over distance nerve impulse- neuron transmitted AP only axons can generate AP s

23 AP Generation Resting State: Voltage-gated channels closed Depolarizing Phase: increase in Na permeability & reversal of the membrane potential more positive voltage gated ion channels open * Threshold- depolarization of the membrane to a certain level causing self generating depolarization Repolarizing Phase: decrease in Na permeability & increase in K permeability more negative Na channels close; Na influx stops K gates open; repolarization- internal negativity is restored Undershoot: potassium permeability continues resulting in hyperpolarization excessive negative = higher membrane potential Na/K pump restores original ionic distributions

24 AP Generation

25 AP Generation all or none phenomenon- AP either happens completely or doesn t happen at all stimulus intensity is determined by the frequency of impulse transmission Refractory Period absolute refractory period- ensures that an AP will not fire too close to another cannot be stimulated = no membrane potential relative refractory period- period following absolute refractory period where the membrane is hyperpolarized from K efflux; the only AP that will fire is from an exceptionally strong stimulus start of repolarization

26 Graded or Local Potentials short lived changes in the membrane potential their magnitude varies with the stimulus (graded) decrease in strength over distance (decremental) local potentials are added up in the trigger zone of the axon hillock

27 Neural Integration ability of neurons to process information, store and recall it EPSP (Excitatory Post Synaptic Potential) occurs when the Trigger Zone adds up all electrical charges between pre and post synaptic neurons and is a positive number * This may cause an AP if threshold is exceeded * If threshold is not met, AP is aborted Temporal Summation- a single synapse generates EPSPs quickly; the previous EPSP has not faded before the next arrives Spatial Summation- several synapses give EPSPs on a single neuron

28 Neural Integration IPSP (Inhibitory Post Synaptic Potential) occurs when the Trigger Zone adds all electrical charges between pre and post synaptic neurons and is a negative number * This hyperpolarizes the cell!

29 Neural Integration If summation of Local Potentials at the Trigger Zone is... Positive (but less than 15mV) = EPSP is aborted Positive (and > 15 mv) = EPSP + impulse Negative = IPSP

30 A Neuron

31 AP Conduction Velocities larger axons conduct impulses faster myelin sheath influence continuous conduction- unmyelinated axons; slow conduction salatory conduction- myelinated axons, electrical signal jumps form node to node causing faster conduction

32 Synapses Synapse- a junction where information is transferred from neuron to neuron or neuron to effector cell presynaptic- neuron conducting the impulse postsynaptic- neuron that receives & conducts the impulse Electrical synapses less common, yet rapid the cells are connected by protein channels that allow current carrying ions to pass Chemical synapses use neurotransmitters to open & close ion channels in the membrane 2 types: excitatory- depolarize the membrane summate- add together» temporal- occurs when a neuron receives impulses in rapid fire order» spatial- occurs when 1 neuron is stimulated by many other neurons inhibitory- hyperpolarize the membrane

33 Neurotransmitter 1.Acetylcholine Types 2.Amino Acid glycine, glutatmate, aspartate & gamma aminobutyric acid (GABA) 3.Monoamines catecholamines (epinephrine, norepinephrine, dopamine), histamine & serotonin 4.Neuropeptides 2 to 40 amino acid chains

34 Neural Coding How does the nervous system translate information into a meaningful pattern of AP? Labeled Line Code nerve fibers are specific for the information they carry Threshold Differences each neuron has a different threshold for firing an action potential Recruitment additional neurons are stimulated as the stimulus increases Frequency of Firing the greater the stimulus the greater the rate of firing

35 Neural Pools & Circuits 1. Diverging Circuits 1 nerve fiber branches and synapses with several postsynaptic cells

36 Neural Pools & Circuits 2. Converging Circuits many nerves synapse on 1 neuron or neural pool

37 Neural Pools & Circuits 3. Reverberating Circuit neurons are stimulated in sequential order, but one neuron in the chain branches back to stimulate the first neuron

38 Neural Pools & Circuits 4. Parallel After-Discharge Circuit 1 neuron diverges to several chains which eventually lead back to one neuron