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The Nervous System: Introduction
Transmission of signals for communication and for coordination of body systems
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Nervous System Functions
The nervous system has three overlapping functions Gathering of sensory input Integration or interpretation of sensory input Causation of a response or motor output
Sensory input
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Introduction Sensory input
The nervous system has millions of sensory receptors to monitor both internal and external change
Integration It processes and interprets the sensory input
and makes decisions about what should be done at each moment
Motor output Causes a response by activating effector organs
(muscles and glands)
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NERVOUS SYSTEM
CNS PNS
MOTOREfferent
- From CNS
SENSORYAfferent- To CNS
Nerves-Cranial nerves- Spinal nerves
Ganglia
Somatic-Motor ANS Visceral Somatic-Sensory
Brain Spinal Cord
Parasympathetic Sympathetic
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Nervous System Two types of cells in nervous system:
Neurons – motor, sensory, association Neuroglia – 6 types
CNS (Central Nervous System): Brain – cerebrum, diencephalon, brain stem,
cerebellum Spinal Cord – horns, columns; ascending and descending tracts
PNS (Peripheral Nervous System): Cranial nerves – 12 pairs Spinal nerves – 31 pairs
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NeuronsFunctional unit of nervous systemHave capacity to produce action
potentials electrical excitability/electrical impulses
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Neuron: Parts and Functions
of Ranvier
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Classification of Neurons
Neurons can be classified functionally or structurally Functional classification is usually used to
describe how the neurons work within us– see Table 8-1, p156
Structural classification is based on the number of processes that extend from the cell body.
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1.
3.2.
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Structural Classification of Neurons
Based on number of processes found on cell body multipolar = several dendrites & one axon
most common cell type bipolar neurons = one main dendrite & one axon
found in retina, inner ear & olfactory unipolar neurons = one process only(develops from a bipolar)
are always sensory neurons
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Blood-Brain Barrier The blood-brain barrier is selective and
incomplete, not an absolute barrier Nutrients, such as glucose, essential amino
acids, and some electrolytes, move passively by facilitated diffusion through the endothelial cell membranes
Bloodborne metabolic wastes, such as urea and creatinine as well as proteins, certain toxins, and most drugs, are prevented from entering brain tissue
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The Nervous System:Nerve Impulses
Action potentials = AP
Neuronal electrical activity
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Electrical Activity of Axons
Functional characteristics of neurons: Excitability/irritability:
Ability to respond to stimuli by producing electrical impulses.
Conductivity:Ability to transmit electrical impulses
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Ion Channels
Proteins within the membrane can open and close, thus allowing ions to travel in or out.
K+ channels allow outward flow
Na+, inward
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The Nervous System:
The Synapse
Neurotransmitters
TRANSMISSION across a Synapse
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Transmission of Nerve Impulses Between Neurons
Synapse: junction between neurons, muscles, glands
Signal is carried by neurotransmittors that diffuse across the synaptic cleft.
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Fig. 12.14
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Transmission of Nerve Impulses Between Neurons
Neurotransmitters can be:
Stimulatory: initiates action potentialeg. Acetylcholine
Inhibitory: prevents action potentialeg. GABA, Dopamine
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Neurotransmitters by function Excitatory – generally cause increase excitability
(depolarization) ACH = Acetylcholine NE = Norepinephrine EPI = Epinephrine DA = Dopamine
Inhibitory – generally cause decrease excitability (hyperpolarization)
GABA = Gamma-aminobutyric acid 5-HT = Serotonin Endorphins, enkephalins, dynorphins
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Nervous System and Aging:
Page 178
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Clinical Terms:
NeurologyRabiesGuillain-Barre