Transcript CH005a NERVOUS SYS - INTRO 10-22

The Nervous System:
Introduction
Transmission of signals for communication
and for coordination of body systems
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Nervous System Functions
Sensory input
 The nervous system has three overlapping functions
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Gathering of sensory input
Integration or interpretation of sensory input
Causation of a response or motor output
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Introduction
 Sensory input
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The nervous system has millions of sensory
receptors to monitor both internal and external
change
 Integration
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It processes and interprets the sensory input
and makes decisions about what should be
done at each moment
 Motor output
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Causes a response by activating effector organs
(muscles and glands)
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NERVOUS SYSTEM
CNS
Brain
PNS
Spinal Cord
Nerves
-Cranial nerves
- Spinal nerves
Ganglia
MOTOR
Efferent
- From CNS
Somatic-Motor
ANS
Parasympathetic
SENSORY
Afferent
- To CNS
Visceral
Somatic-Sensory
Sympathetic
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Nervous System
 Two types of cells in nervous system:
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Neurons – motor, sensory, association
Neuroglia – 6 types
 CNS (Central Nervous System):
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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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Neurons
 Functional unit of nervous system
 Have capacity to produce action
potentials
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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
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Functional classification is usually used to
describe how the neurons work within us
– see Table 8-1, p156
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Structural classification is based on the
number of processes that extend from the
cell body.
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1.
2.
3.
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Structural Classification of Neurons
 Based on number of processes found on cell body
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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 potential
eg. Acetylcholine
Inhibitory: prevents action potential
eg. GABA, Dopamine
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Neurotransmitters by function
 Excitatory – generally cause increase
excitability (depolarization)
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ACH = Acetylcholine
NE = Norepinephrine
EPI = Epinephrine
DA = Dopamine
 Inhibitory – generally cause decrease
excitability
(hyperpolarization)
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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:
Neurology
Rabies
Guillain-Barre
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