GENERAL CONCEPTS OF NERVOUS SYSTEM
Learning Objectives
At the end of lecture, student will be able to:
•
Define nervous system.
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Define components of nervous system.
•
Explain parts of nervous system.
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Narrate CNS, PNS, and ANS.
LECTURE OUTLINE
The Nervous System
A network of billions of nerve cells linked together in a highly organized fashion
to form the rapid control center of the body.
Organization of the Nervous System
•
2 Big Initial Divisions:
– Central Nervous System:
• The brain + the spinal cord.
– The center of integration and control.
– Peripheral Nervous System:
•
•
The nervous system outside of the brain and spinal cord.
Consists of:
– 31 Spinal nerves.
» Carry info to and from the spinal cord.
–
12 Cranial nerves.
» Carry info to and from the brain.
General Organization Of The Nervous System
Two Anatomical Divisions :
–
Central nervous system (CNS):
•
•
–
Brain.
Spinal cord.
Peripheral nervous system (PNS):
•
•
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All the neural tissue outside CNS.
Afferent division (sensory input).
Efferent division (motor output).
–
–
Somatic nervous system.
Autonomic nervous system.
MAJOR FUNCTIONS
The Nervous system has three major functions:
– Sensory – monitors internal & external environment through presence of
receptors.
– Integration – interpretation of sensory information (information
processing); complex (higher order) functions.
– Motor – response to information processed through stimulation of effectors
– Muscle contraction.
– Glandular secretion.
Basic Functions of the Nervous System
•
Sensation:
Monitors changes/events occurring in and outside the body. Such
changes are known as stimuli and the cells that monitor them are
receptors.
•
Integration:
The parallel processing and interpretation of sensory information to
determine the appropriate response.
•
Reaction:
Motor output.
– The activation of muscles or glands (typically via the release of
neurotransmitters (NTs)).
Peripheral Nervous System
• 31 spinal nerves :
– We’ve already discussed their structure.
• 12 cranial nerves:
– How do they differ from spinal nerves?
– We need to learn their:
• Names.
• Locations.
• Functions.
Peripheral Nervous System
• Now that we’ve looked at spinal and cranial nerves, we can examine the
divisions of the PNS.
• The PNS is broken down into a sensory and a motor division.
• We’ll concentrate on the motor division which contains the somatic nervous
system and the autonomic nervous system.
Functional Classification of the Peripheral Nervous
System:
 Sensory (afferent) division:

Nerve fibers that carry information to the central nervous system.
 Motor (efferent) division:

Nerve fibers that carry impulses away from the central nervous
system.
Two subdivisions:


Somatic nervous system = voluntary.
Autonomic nervous system = involuntary.
Nervous Tissue: Support Cells (Neuroglia or Glia):
 Astrocytes:




Abundant, star-shaped cells.
Brace neurons.
Form barrier between capillaries and neurons.
Control the chemical environment of the brain (CNS).
 Microglia (CNS):


Spider-like phagocytes
Dispose of debris.
 Ependymal cells (CNS)


Line cavities of the brain and spinal cord.
Circulate cerebrospinal fluid.
 Oligodendrocytes(CNS):

Produce myelin sheath around nerve fibers in the central nervous
system.
Neuroglia vs. Neurons
•
•
•
•
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Neuroglia divide.
Neurons do not.
Most brain tumors are “gliomas.”
Most brain tumors involve the neuroglia cells, not the neurons.
Consider the role of cell division in cancer!
Support Cells of the PNS:
 Satellite cells:

Protect neuron cell bodies.

Form myelin sheath in the peripheral nervous system.
 Schwann cells:
Nervous Tissue: Neurons:
 Neurons = nerve cells:


Cells specialized to transmit messages.
Major regions of neurons.
 Cell body – nucleus and metabolic center of the cell.
 Processes – fibers that extend from the cell body (dendrites
and axons).
Neuron Anatomy:
 Cell body:


Nucleus.
Large nucleolus.
 Extensions outside the cell body:


Dendrites – conduct impulses toward the cell body.
Axons – conduct impulses away from the cell body (only 1!).
Axons and Nerve Impulses:



Axons end in axonal terminals.
Axonal terminals contain vesicles with neurotransmitters.
Axonal terminals are separated from the next neuron by a gap
 Synaptic cleft – gap between adjacent neurons.
 Synapse – junction between nerves.
Neuron Cell Body Location:


Most are found in the central nervous system:
 Gray matter – cell bodies and unmylenated fibers.
 Nuclei – clusters of cell bodies within the white matter of the central
nervous system.
Ganglia – collections of cell bodies outside the central nervous system.
Structural Classification of Neurons:
 Multipolar neurons – many extensions from the cell body.

Bipolar neurons – one axon and one dendrite.

Unipolar neurons – have a short single process leaving the cell body.
Somatic vs. Autonomic:
• Voluntary.
• Involuntary.
• Skeletal muscle.
• Smooth, cardiac muscle; glands.
• Single efferent neuron.
• Multiple efferent neurons.
• Axon terminals release acetylcholine. • Axon terminals release acetylcholine or
• Always excitatory.
norepinephrine.
• Controlled by the cerebrum.
• Can be excitatory or inhibitory.
• Controlled by the homeostatic centers in
the brain – pons, hypothalamus, medulla
oblongata.
Autonomic Nervous System
• 2 divisions:
– Sympathetic
• “Fight or flight”.
• “E” division.
– Exercise, excitement, emergency, and embarrassment.
– Parasympathetic
• “Rest and digest”.
• “D” division.
– Digestion, defecation, and diuresis.
Characteristics of the ANS
•
•
•
•
A part of the PNS.
Actions are involuntary (not under conscious control).
Regulated by centers in the hypothalamus and brain stem regions of the CNS.
The motor part is subdivided into the sympathetic division and the
parasympathetic division .
Components of the ANS
• Autonomic sensory receptors—located mainly in visceral organs.
• Autonomic sensory neurons—send information to the CNS from the
receptors.
• Autonomic integrating centers—in the CNS (hypothalamus and brain
stem).
• Autonomic motor neurons—send information from the CNS to
effectors; regulate visceral activities.
• Autonomic effectors—cardiac muscle, smooth muscle, and glands.
• The motor neuron part of the ANS consists of 2 motor neurons.
• The first motor neuron (preganglionic neuron) has its cell body in the CNS;
its axon (myelinated) extends from the CNS to an autonomic ganglion.
• The second motor neuron (postganglionic neuron) has its cell body in an
autonomic ganglion; its axon (unmyelinated) extends from the ganglion to an
effector.
INTRODUCTION:
1) 2 divisions which are antagonistic:
a) Sympathetic (thoracolumbar) –
T1-L2 fight or flight response.
B) Parasympathetic (craniosacral) –
Return body to normal (iii, vii, ix, x), s2-s4.
Structure:
a)Introduction - Nerve cell bodies both in and out of CNS. Those outside the
CNS are located in “knots” called ganglia.
b)Sympathetic :
1) Chain.
2) Collateral.
3) Pathways.
c)Parasympathetic:
1) Terminal.
2) Pathways.
 Sympathetic Division:
a)Introduction - The “fight or flight” division
b)Transmitters :
1) preganglionic = acetylcholine.
2) postganglionic = norepinephrine.
Adrenal medulla = 1 epinephrine (2 norepinephrine).
c)Receptors:
1) alpha - stimulated by epinephrine and norepinephrine.
2) beta - stimulated by epinephrine.
3) alpha, beta 1 depolarize.
4) beta 2 hyperpolarizes.
d)Adrenal medulla - acts like a postganglionic neuron, but releases epinephrine
as a hormone.
e) Adrenergic division
 Paraympathetic Division:
a)Introduction - Return to normal
b) Transmitters:
1) preganglionic = acetylcholine
2) postganglionic = acetylcholine
•
cholinergic division
c)Receptors:
1) nicotinic 1 - postganglionic neurons (nicotinic 2 - muscle).
2) muscarinic – organs.
6) Functions :
ORGAN
iris
ciliary muscles of eye
salivary glands
bronchi
sweat glands
blood vessels
adrenal gland
intestinal tract
intestinal glands
heart
liver
bladder
blood glucose
mental activity
basal metabolism
piloerector muscles
SYMPATHETIC
dilates
relaxes (far vision)
inhibits
dilates
stimulates
mostly constricts
stimulates
inhibits
inhibits
stimulates
releases glucose
inhibits
increase
increased
increased
stimulated
PARASYMPATHETIC
constricts
contracts (near vision)
stimulates
constricts
no action
no action
no action
stimulates
stimulates
inhibits
no action
stimulates
no action
no action
no action
no action