Structural Organization of Nervous System

Transcription

1 Nervous System

2 Structural Organization of Nervous System

3 Myelinated Neuron

4 Myelin White, fatty material which covers nerve fibers(axons) Protects and insulates fiber Increases the rate of transmission of nerve impulses

5 Myelination of axons outside the CNS Schwann cells specialized supporting cells; wrap themselves around axon Coil of wrapped membrane = myelin sheath Sheath formed by many cells; has gaps(indentations) between cells Nodes of Ranvier

6 Schwann cell-myelin sheath

7 Myelinated neuron

8 Impulse Conduction Fibers with myelin sheaths conduct impulses much faster than unmyelinated fibers. Nerve impulse jumps from node to node along fiber this occurs because no current can flow across axon where there is a fatty myelin sheath. Saltatory Conduction

9 Saltatory conduction in myelinated axons ews/actionp.html s/

10 Multiple Sclerosis Degeneration of myelin sheath Disrupt nerve transmission

11 Physiology of Nerve Impulses Resting Inactive State 1. Neuron is polarized = fewer positive ions on inner face of cell membrane than on outer face in tissue fluid 2. Major + ions inside cell = K+ Major + ions outside cell = Na+ 3. As long as inside more negative than outside neuron is inactive

12 Generation of impulse Stimulus may be heat, light, pressure, sound or chemical Result permeability properties of plasma membrane change for very brief period 1. Gates of Na+ channels open 2. Na+ rushes into cell 3. DEPOLARIZATION occurs = change in polarity across membrane

13 Nerve Impulse chapter14/animation the_nerve_impulse. html

14 Propagation of Impulse IF stimulus strong enough and Na+ influx great enough, local depolarization activates transmission of long distance impulse (action potential, nerve impulse) All or none response (propagated over entire axon or does not happen at all)

15 Repolarization Almost immediately, membrane becomes impermeable to Na+ and permeable to K+ ions. K+ flows out restoring the membrane to polarized or resting potential Finally, initial concentrations of Na+ and K+ restored by Na, K pump (pumps Na+ out and brings K+ in).

16 Conduction of Impulse from one neuron to another Generally, transmission of information from one neuron to another is chemical via neurotransmitter molecules Neurotransmitters are chemicals released from an axon terminal, that diffuse across synaptic cleft and stimulate depolarization of the next neuron

17 chapter14/animation transmission_acros s_a_synapse.html

18 Conduction of Nerve Impulse from one neuron to another Electrochemical event -transmission down neuron is electrical -transmission from neuron to neuron is chemical

19 Reflexes

20 CNS Functions of major areas Cerebrum Consciousness, voluntary movement, interpretation of sensation, speech, memory, logical and emotional response

21 Brain Anatomy

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23 Diencephalon Thalamus, Hypothalamus, Epithalamus 1. Thalamus relay station for sensory impulses 2. Hypothalamus autonomic nervous system control center Regulate temperature, water balance, metabolism Center for drives and emotions Regulates pituitary gland

24 Brain Stem Midbrain, pons and medulla oblongata Ascending and descending nerve tracts Control centers for heart rate, blood pressure, breathing, swallowing, vomiting, reflex centers for vision and hearing, wake/sleep cycles

25 Cerebellum Precise timing for skeletal muscle activity and controls balance and equilibrium

26 Protection of CNS Meninges Dura mater outermost, leathery layer Arachnoid mater weblike, attaches innermost and outermost Pia mater innermost layer, clings to curface of brain Meningitis inflammation of meninges

27 Cerebrospinal Fluid (CFS) Formed from blood by choroid plexes in roof of ventricles Similar to blood plasma Function: Cushioning, protection

28 Blood Brain Barrier Neurons separated from blood borne substances by blood brain barrier Capillaries in brain are relatively impermeable Of water soluble substances, allow only water, glucose and essential amino acids to pass through (many toxins, wastes and drugs cannot enter) Permeable to gases and fat soluble substances (therefore, alcohol, nicotine and anesthetics can affect brain)

29 Autonomic Nervous System Parasympathetic NS Origin: Cranial nerves and Sacral nerves Sympathetic NS Origin: Thoracic and Lumbar nerves

30 Autonomic Nervous System Together, the sympathetic and parasympathetic systems regulate autonomic body systems (including heart, smooth muscle in visceral organs, and glands) to maintain homeostasis.

31 Generally, Parasympathetic regulates systems at rest Sympathetic regulates systems under stress (e.g. excitement, fear, exercise)

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33 Harmful Effects on Brain Development Nervous system is formed during the first month of embryonic development Any maternal infection early in pregnancy may impair nervous system development e.g. rubella(measles) Other factors: lack of oxygen (may occur due to smoking), radiation, drugs like alcohol, opiates, cocaine)