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NERVOUS SYSTEM

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Title: NERVOUS SYSTEM


1
NERVOUS SYSTEM
2
NERVOUS SYSTEM COMPONENTS
  • Brain
  • Cranial nerves
  • Spinal cord
  • Spinal nerves
  • Ganglia - cell bodies of neurons outside
  • brain spinal cord
  • enteric plexuses
  • Sensory receptors

3
NERVOUS SYSTEM ORGANIZATION
  • Central Nervous System - thought, emotion,
  • brain memory
  • spinal cord
  • Peripheral Nervous System (PNS)
  • Somatic (SNS) - voluntary
  • Autonomic (ANS) - involuntary

4
Subdivisions of the Nervous System
5
AUTONOMIC NERVOUS SYSTEM
  • Sensory
  • Motor
  • - sympathetic
  • - parasympathetic

6
Subdivisions of Nervous System
7
NERVOUS SYSTEM FUNCTIONS
  • Sensory
  • Integrative
  • Motor
  • Concerned with homeostatic regulation

8
NERVOUS TISSUE
  • Neurons - conduct impulses
  • Neuroglia - do not conduct
  • impulses

9
NEURON DIVERSITY
  • Sensory (afferent) neurons
  • Transmit information from receptors to the brain
    or spinal cord (CNS)
  • Interneurons (association neurons)
  • Located in the CNS
  • process, store retrieve information
  • Motor (efferent) neuron
  • send signals from the CNS to muscles gland
    cells (effectors)

10
INTERNEURONS(90 of neurons)
  • Located only in the CNS
  • Purkinje cells in cerebellum
  • Renshaw cells in spinal cord
  • Pyramid cells in brain

11
NEURON DIVERSITY
  • Multipolar has several dendrites
  • Bipolar has one main dendrite one axon
  • Unipolar - axon dendrite fuse into a single
    process
  • Anaxonic has several dendrites but no axon

12
Neuron Diversity
13
NEUROGLIA DIVERSITY
  • Astrocytes in CNS contribute to blood brain
    barrier regulate composition of brain tissue
    fluid
  • Oligodendrocytes - in CNS - produce myelin
  • Microglia (macrophages) - in CNS
  • Ependymal cells - in CNS - line cavities
    produce cerebrospinal fluid
  • Schwann cells - in PNS - produce myelin
  • Satellite cells - in PNS - uncertain function

14
Neuroglial Cells of CNS
15
DEFINITIONS
  • Dendrites - receiving or input portions of neuron
  • Cell body Soma Perikaryon
  • Nissl bodies - clusters of rough ER
  • Neurofibrils bundles of actin filaments
    (cytoskeleton)

16
DEFINITIONS
  • Axon - long, thin, cylindrical, impulse
    propagative portion of neuron
  • Myelin sheath - insulating layer around a nerve
    fiber
  • Synapse - junction between two neurons or between
    neuron and effector

17
PROPERTIES OF NEURONS
  • Electrically excitable
  • Communicate via electrical signals.
  • Generate action potentials for short long
    distance communication
  • Generate local (graded) potentials only for
    short distance communication
  • Limited regenerative ability

18
PROPERTIES OF NEURON MEMBRANES
  • Polarized - have resting potential (- 70 mV) -
    inside of a nerve cell membrane is negative
    charge relative to the outside
  • Specific ion channels - allow flow of ions
  • - Leakage channels (always open)
  • - Gated channels (open close)

19
RESTING MEMBRANE POTENTIAL
  • Due to unequal distribution of ions across
    membrane
  • Relative permeability of membrane to sodium
    potassium ions - (50 to 100 times greater to
    potassium than to sodium in a resting neuron)
  • Electrochemical gradient exists.

20
Ionic Basis of Resting Membrane Potential
  • Na concentrated in extracellular fluid (ECF)
  • K concentrated in intracellular fluid cell (ICF)

21
GATED ION CHANNELS
  • Voltage - open in response to change in membrane
    potential (voltage)
  • Ligand - open close in response to
  • specific chemical stimulation e.g.
    transmitters, hormones, ions
  • Mechanical - open close in response to
    mechanical stimulation e.g. vibration, pressure,
    stretching

22
LIGAND-GATED CHANNELS
  • Ligand molecules may bind directly with a channel
    protein cause channel opening or closure.
  • Ligand molecules e.g. hormones may act indirectly
    via a membrane G protein that activates a
    messenger in the cytosol to operate the channel
    gate.

23
ACTION POTENTIALS
  • All-or-none events - occur if depolarization
    reaches a certain threshold (about -55 mV)
  • Always have the same amplitude
  • Depolarizing phase Repolarizing phase
  • After-hyperpolarization
  • Refractory period - absolute relative - action
    potential cannot be generated

24
IMPULSE CONDUCTION
  • Continuous - in muscle fibers
  • unmyelinated axons
  • Saltatory - in myelinated axons
  • impulses jump quickly from one node of Ranvier
    to the next

25
Impulse Conduction in Unmyelinated Fibers
26
CONDUCTION ACROSS SYNAPSES
  • Electrical synapses - connexons (tubular
    proteins) allow ionic current to spread directly
    between adjacent cells through gap junctions
  • Chemical synapses - neurotransmitters allows
    impulse conduction between neurons

27
POSTSYNAPTIC POTENTIALS
  • Excitatory - (EPSP) - occurs if postsynaptic
    membrane becomes depolarized (less negative) -
    glutamate aspartate are excitatory
    neurotransmitters
  • Inhibitory - (IPSP) - occurs if postsynaptic
    membrane becomes hyperpolarized (more negative) -
    glycine ?-aminobutyric acid (GABA) are
    inhibitory neurotransmitters

28
EVENTS AFTER SYNAPTIC CONDUCTION
  • Diffusion of transmitter from synaptic cleft
  • Active uptake of transmitter substance by
    neurotransmitter transporters in neuron
  • Spatial temporal summation

29
Chemical Synapse Structure
  • Presynaptic neurons have synaptic vesicles with
    neurotransmitter and postsynaptic have receptors

30
NEUROTRANSMITTERS
  • Acetylcholine
  • Amino acid neurotransmitters
  • Monoamines
  • catecholamines (epinephrine, norepinephrine
    dopamine)
  • indolamines (serotonin histamine)
  • Neuropeptides

31
SUMMATION
  • Temporal summation - occurs when a single synapse
    receives many EPSPs in a short period of time
  • Spatial summation - occurs when a single synapse
    receives many EPSPs from many presynaptic cells
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