Download The Nervous System

The Nervous System
Fundamentals of the Nervous System
and Nervous Tissue
Function of the Nervous System
(1) Sensory Input: Monitors changes
(stimuli) occurring inside and outside
the body via sensory receptors
(2) Integration: Processes and
interprets the sensory input and decides
what to do at each moment
(3) Motor Function: Causes a
response by activating effector organs
(muscles or glands)
Homeostasis:
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The nervous system is responsible to
sense changes in the body (receptor),
analyses the change (control centre),
and cause a response (effector)
The nervous system has ultimate
control over homeostasis
Divisions of the Nervous System
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CNS: brain and spinal
cord
PNS: outside the CNS;
nerves that extend from
the brain and spinal cord;
spinal nerves carry
impulses to and from the
spinal cord and cranial
nerves carry impulses to
and from the brain
Peripheral Nervous System
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Sensory/Afferent Division: convey
impulses to the CNS from sensory
receptors; (1) Somatic Afferent
Fibers: from skin, skeletal muscles,
and joints (2) Visceral Afferent Fibers:
from visceral organs (ventral body
cavity)
Motor/Efferent Division: transmits
impulses from the CNS to effector
organs, muscles, and glands (2 parts)
Peripheral Nervous System
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Motor/Efferent Division:
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Somatic Nervous System: aka
voluntary NS because we consciously
control our skeletal muscles; motor
impulses from the CNS to skeletal muscles
Autonomic Nervous System: aka
involuntary NS; visceral motor nerve
fibers that regulate the activity of smooth
muscles, cardiac muscles, and glands; 2
divisions
Peripheral Nervous System
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Motor/Efferent Division:
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Autonomic Nervous System:
(1) Sympathetic Nervous System: “Fight
or Flight”
(2) Parasympathetic Nervous System:
“Rest and Digest”
Autonomic Nervous System
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5 types of Adrenergic receptors
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Alpha one – causes???
Alpha two - TBA
B1 –heart – causes ??? (three things)
B2 –lungs – causes ???
Dopaminergic – renal causes patient to
pee!
Receptors

NOREPI
ACH
EPI
= muscarinic or
nicotinic

If receptor responds to
norephinephrine or epinephrine
= adrenergic
Five types!
muscarinic
nicotinic
If receptor responds to
acethylcholine is
cholinergic and two types
adrenergic
Sympathetic
Preganglionic
Acetylcholine
Nicotinic receptor
Postganglionic
Norepinephrine
Adrenergic receptor
Parasympathetic
Preganglionic
Acetylcholine
Nicotinic receptor
Postganglionic
Acetylcholine
Muscarinic receptor
Nervous Tissue

2 principle types of cells

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(1) Neurons: the excitable nerve cells
that transmit electrical signals
Basic structural & functional unit of NS
(2) Neuroglia: supporting cells that
surround and wrap the more delicate
neurons
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
Like connective tissue
Together they form the structures of
both the CNS and PNS
Neurons
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Cell body
Nerve fibers:
Dendrites receive info into cell body
Axons conduct info away from cell body
Axonal terminals at ends contain
neurotransmitter to permit
communication between neurons
May be myelinated or unmyelinated
Neurons
Gray & White Matter in the CNS
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Gray Matter:
contains mostly
nerve cell bodies
and unmyelinated
fibers
White Matter:
contains dense
collections of
myelinated fibers
and are primarily
fiber tracts
Reflexes
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Rapid, predictable, automatic
responses to stimuli, in which a
particular stimulus always causes the
same motor response; unlearned,
unpremeditated, and involuntary,
considered to be built into our neural
anatomy
Occur over neural pathways called
reflex arcs that have 5 elements:
(1) receptor (2) sensory neuron (3)
CNS integration center (4) motor
neuron (5) effector
Reflex Arc
Resting Membrane Potential
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The potential difference between the
inside (cytoplasmic side) of a neuron’s
membrane and the outside; the value
varies from –40 mV to –90 mV
(millivolts); membrane is polarized
The resting membrane potential is
generated by differences in the ionic
makeup of the intracellular and
extracellular fluids; primarily sodium
(outside) and potassium (inside)
Graded Potentials

Short-lived, local changes in membrane
potential that can be either depolarizations
(i.e. less negative inside) or
hyperpolarizations (i.e. more negative
inside); called “graded” because their
magnitude varies directly with the
strength of the stimulus; the stronger the
stimulus, the more the voltage changes and
the farther the current flows; triggered by
some change in the neuron’s environment
(heat, light, etc)
Action Potentials
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Only cells with excitable membranes
(neurons and muscle cells) can
generate action potentials, which are
the way neurons communicate
In neurons, a transmitted action
potential is also called a nerve impulse
Action Potentials
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They are generated by changes in
membrane permeability to Na+ and
K+ which cause depolarization
(inside the membrane becomes
more positive) followed by
repolarization (return to negativity
on the inside of membrane)
Action Potentials
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Threshold: when the membrane has
been depolarized by 15 to 20 mV from
the resting value, an action potential
will occur (same size every time)
All or None Phenomenon: the
action potential either happens
completely or it doesn’t happen at all
Conduction Velocities of Axons
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(1) Influence of axon diameter: the
larger the axon’s diameter, the faster
it conducts impulses
(2) Influence of a myelin sheath: if
present, the myelin sheath
dramatically increases the speed of
transmission because myelin acts as
an insulator to prevent leakage of
charge from the axon; the electrical
signal jumps from node of Ranvier to
node of Ranvier (1mm) along the axon
Synapse
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The functional junction between two
neurons or between a neuron and an
effector
In order to propagate nerve impulses
from neuron to neuron, they have to
meet; the junctions are the synapses; the
gap between them is the synaptic cleft
Neurotransmitters are released into the
cleft to facilitate (or inhibit) transmission
Happenings at the NMJ…..
http://www.blackwellpublishing.com/matthews/nmj.html
Depolarization
Neurotransmitter Removal
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The neurotransmitter must be
removed from the synaptic cleft once
its job is done
This occurs via diffusion, break down
via enzymes or transport via special
membrane proteins
Some drugs act on this area (E.g SSRI
and MAOIs)