UNIT B: Human Body Systems
Chapter 8: Human Organization
Chapter 9: Digestive System
Chapter 10: Circulatory System and
Lymphatic System
Chapter 11: Respiratory System
Chapter 12: Nervous System:
Section 12.1
Chapter 13: Urinary System
Chapter 14: Reproductive System
UNIT B Chapter 12: Nervous System
Chapter 12: Nervous System
In this chapter, you will learn about the
structure and function of the nervous
system.
How might a researcher study the
effects of frequent head trauma?
Sport-Related Head Trauma and Brain
Function. Neurosurgeon Dr. Robert Cantu has
studied the brains of many deceased athletes,
including hockey and football players. He has
found that these players often suffered from
chronic traumatic encephalopathy (CTE), a
degenerative brain disease caused by repeated
blunt impact to the head.
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How might one determine which part
of the brain has been affected by
repeated blunt impacts?
Given the available information about
CTE, what steps do you feel should be
taken to prevent its occurrence (if any)?
UNIT B Chapter 12: Nervous System
12.1 Nervous Tissue
The nervous system coordinates and regulates the
functioning of the body’s other systems.
The nervous system consists of two major systems that
work together:
• Central nervous system (CNS): brain and spinal cord
• Peripheral nervous system (PNS): nerves that carry
sensory messages to the CNS and motor commands
from the CNS to the muscles and glands
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Section 12.1
UNIT B Chapter 12: Nervous System
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Figure 12.1 Organization of the nervous system. The sensory
neurons of the peripheral nervous system take nerve impulses from
sensory receptors to the central nervous system (CNS), and motor
neurons take nerve impulses from the CNS to muscles and glands.
Section 12.1
UNIT B Chapter 12: Nervous System
Section 12.1
The nervous system contains two types of cells:
• Neurons: cells that transmit nerve impulses between
parts of the nervous system
• Neuroglia: support and nourish neurons, maintain
homeostasis, form myelin that surrounds neurons, and
aid in signal transmission
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UNIT B Chapter 12: Nervous System
Section 12.1
Types of Neurons and Neuron Structure
There are three classes of neurons:
• Sensory neurons: take messages
to the CNS; have sensory receptors
that detect changes in the
environment
• Interneurons: receive input from
sensory neurons and other
interneurons in the CNS
• Motor neurons: take messages
away from the CNS to an effector
(an organ, muscle fibre, or gland);
o Effectors carry out responses to
environmental changes
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Figure 12.2 Types
of neurons.
UNIT B Chapter 12: Nervous System
Section 12.1
Neurons vary in appearance, but
most of them have three parts:
• Cell body: contains the nucleus
and other organelles
• Dendrites: extensions leading
toward the cell body that
receive signals from other
neurons and send them to the
cell body
• Axon: conducts nerve impulses
away from the cell body toward
other neurons or effectors
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Figure 12.2 Types
of neurons.
UNIT B Chapter 12: Nervous System
Section 12.1
Myelin Sheath
Some axons are covered by a
protective myelin sheath.
• In the PNS, a myelin sheath is
formed by Schwann cells, a type
of neuroglia that contains myelin
in the plasma membranes
• Schwann cells wrap around an
axon and lay down many layers
of plasma membrane
• Each Schwann cell myelinates
only part of an axon, leaving gaps
called nodes of Ranvier
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Figure 12.3 Myelin sheath. a. In the
PNS, a myelin sheath forms when
Schwann cells wrap themselves around
an axon. b. Electron micrograph of a
cross section of an axon surrounded by
a myelin sheath.
UNIT B Chapter 12: Nervous System
Section 12.1
Myelin in the PNS
• The myelin sheath plays an important role in nerve
generation in the PNS
• If an axon is severed, the myelin sheath remains and
serves as a passageway for new fibre growth
Myelin in the CNS
• In the CNS, myelin is produced by oligodendrocytes, a
type of neuroglia
• Nerve regeneration does not occur to any significant
degree in the CNS
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UNIT B Chapter 12: Nervous System
Section 12.1
Nervous tissue in the CNS
The CNS is composed of two types of nervous tissue:
• Grey matter
o Contains neurons with short, nonmyelinated axons
o Found in the surface layer of the brain and the central part
of the spinal cord
• White matter
o Contains myelinated axons that run together in bundles
called tracts
o Found deep within the grey matter of the brain and
surrounds the grey matter in the spinal cord
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UNIT B Chapter 12: Nervous System
Check Your Progress
1. Identify the three classes of neurons, and describe their
relationship to each other.
2. Describe the three parts of a neuron.
3. Distinguish the cell types that form the myelin in the PNS
versus the CNS.
4. Review the structure of grey matter and white matter, and
describe where each is found in the CNS and the PNS.
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Section 12.1
UNIT B Chapter 12: Nervous System
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Section 12.1
UNIT B Chapter 12: Nervous System
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Section 12.1