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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