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The Nervous System
By Eko Widodo
The nervous system is one of the 2 control systems
in our body. The nervous system is designed for fast
action.
It coordinates fast or rapid activities, such as muscle
movement.
Signaling is by electrical impulses, these are rapid,
specific and produce an almost immediate
response.
Functions of the Nervous
System
• Sensory input – gathering information
– To monitor changes occurring inside and outside the
body
– Changes = stimuli
• Integration
– To process and interpret sensory input and decide if
action is needed
• Motor output
– A response to integrated stimuli
– The response activates muscles or glands
Structural Classification of the Nervous System
• Central nervous system (CNS)
– Brain
– Spinal cord
• Peripheral nervous system (PNS)
–
–
–
–
Nerve outside the brain and spinal cord
Spinal nerves carry impulses to and from the spinal cord
Cranial nerves carry impulses to and from the brain
PNS links all parts of the body by carrying impulses from the
sensory receptors to the CNS and from the CNS to the
appropriate muscle or gland
• Sensory (afferent) division
– Nerve fibers that carry information to the
central nervous system
Figure 7.1
• Motor (efferent) division
– Nerve fibers that carry impulses away from
the central nervous system to muscles or
glands
Figure 7.1
• Motor (efferent) division
– Two subdivisions
• Somatic nervous system = voluntary
• Autonomic nervous system = involuntary
Figure 7.1
Organization of the Nervous System
Figure 7.2
Neuroglia - Support, insulate and protect
• Astrocytes
– Abundant, star-shaped cells
– Brace neurons
– Form barrier
between capillaries
and neurons
– Control the chemical
environment of
the brain
Figure 7.3a
• Microglia
– Spider-like phagocytes
– Dispose of debris
• Ependymal cells
– Line cavities of the
brain and spinal cord
– Circulate
cerebrospinal
fluid
Figure 7.3b–c
Nervous Tissue: Support Cells
• Oligodendrocytes
– Produce myelin sheath around nerve fibers in
the central nervous system
Figure 7.3d
Nervous Tissue: Support Cells
• Satellite cells
– Protect neuron cell bodies
• Schwann cells
– Form myelin sheath in the peripheral nervous
system
Figure 7.3e
Neurons have 2 major functions –
Irritability – ability to respond to a stimulus & convert it into
a nerve impulse
Conductivity – ability to transmit the impulse to other
neurons, muscles or glands
A nerve cell at rest is polarized, that is there is a charge
across the membrane.
Ion Concentration
Ion
K+
Na+
ClCa++
HCO3Mg++
proteins -
Cell mM ECF mM
139
4
12
145
4
116
<0.0002
1.8
12
29
0.8
138
1.5
9
The ion concentration results in a net negative charge on inside of
cell compared to ECF (extra cellular fluid)
++++
++++++
----------------- +++++++++++++
Starting a Nerve Impulse
Depolarization – a
stimulus depolarizes the
neuron’s membrane
A depolarorized membrane
allows sodium (Na+) to flow
inside the membrane
The exchange of ions initiates
an action potential in the
neuron
Figure 7.9a–c
Nerve Impulse Propagation
• The impulse
continues to move
Figure 7.9d–f
How Neurons Communicate at Synapses
Figure 7.10
• Drugs, sedatives and anesthetics can
disrupt the permeability of the plasma
membrane thereby blocking an AP.
• Cold and continuous pressure can hinder
impulse transmission as they interprept
the flow of blood (nutrients and oxygen) to
neurons.
• Multiple sclerosis – destruction of myelin
surrounding nerve, ends up short circuiting
The Reflex Arc
• Reflex – rapid, predictable, and involuntary
responses to stimuli
• Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
Figure 7.11a
Simple Reflex Arc
Figure 7.11b–c
Central Nervous System (CNS)
• CNS develops from the embryonic neural
tube
– The neural tube becomes the brain and spinal
cord
– The opening of the neural tube becomes the
ventricles
• Four chambers within the brain
• Filled with cerebrospinal fluid
Regions of the Brain
•
•
•
•
Cerebral hemispheres - cerebrum
Diencephalon
Brain stem
Cerebellum
Figure 7.12b
Cerebral Hemispheres
(Cerebrum)
• Paired (left and
right) superior
parts of the brain
• Include more
than half of the
brain mass
Figure 7.13a
Sensory and Motor Areas
of the Cerebral Cortex
Figure 7.14