HBHD13e Ch9

Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter 9
The Nervous System:
The Spinal Cord and Spinal Nerves

Copyright © 2015 Wolters Kluwer • All Rights Reserved
Overview

Key Terms
acetylcholine motor presynaptic
action potential nerve receptor
afferent nerve impulse reflex
autonomic nervous system neuritis repolarization
axon neuroglia saltatory conduction
dendrite neuron sensory
depolarization neurotransmitter somatic nervous system
effector norepinephrine sympathetic nervous system
efferent parasympathetic nervous system synapse
ganglion plexus tract
interneuron postsynaptic

Overview of the Nervous System
Learning Objective
1.Outline the organization of the
nervous system according to
structure and function.

Neurons and Their Functions
Learning Objectives
2.Describe the structure of a neuron.
3.Explain the construction and
function of the myelin sheath.
4.Describe how neuron fibers are built
into a nerve.

Neuroglia
Learning Objective
5.List four types of neuroglia in the
central nervous system, and cite the
functions of each.

The Nervous System at Work
Learning Objectives
6.Diagram and describe the steps in
an action potential.
7.Explain the role of
neurotransmitters in impulse
transmission at a synapse.

The Spinal Cord
Learning Objective
8.Describe the distribution of gray
and white matter in the spinal cord.

The Spinal Nerves
Learning Objective
9.Describe and name the spinal
nerves and three of their main
plexuses.

Reflexes
Learning Objectives
10.List the components of a reflex
arc.
11.Define a simple reflex, and give
several examples of reflexes.

Learning Objectives
12.Compare the locations and
functions of the sympathetic and
parasympathetic nervous systems.
13.Explain the role of cellular
receptors in the action of
neurotransmitters in the autonomic
nervous system.
The Autonomic Nervous System

Learning Objective
14.Describe eight disorders of the
spinal cord and spinal nerves.
Clinical Aspects of the Spinal Cord and
Spinal Nerves

Case Study
Learning Objective
15.Using the case
study, describe the
effects of
demyelination on
motor and sensory
function.

Word Anatomy
Learning Objective
16.Show how word parts are used to build words related to
the nervous system.

Overview of the Nervous System
Role of the Nervous System
•Coordinates all body systems.
•Detects and responds to stimuli.
•Brain and spinal cord act as switching centers.
•Nerves carry messages to and from centers.

Overview of the Nervous System (cont.)
Structural Divisions
•Central nervous system (CNS)
– Brain
– Spinal cord
•Peripheral nervous system (PNS)
– Cranial nerves
– Spinal nerves

Figure 9-1 Anatomic divisions of the nervous system, posterior
view.
What structures make up the central nervous system?
The peripheral nervous system?

Functional Divisions of the PNS

✓
Checkpoints
9-1 What are the two divisions of the nervous system
based on structure?
9-2 What division of the PNS is voluntary and controls
skeletal muscles? What division is involuntary and controls
smooth muscle, cardiac muscle, and glands?

?
Pop Quiz
9.1 Which division of the nervous system
exclusively controls skeletal muscles?
A)Peripheral nervous system
B)Central nervous system
C)Somatic nervous system
D)Autonomic nervous system

?
Pop Quiz Answer
9.1 Which division of the nervous system
exclusively controls skeletal muscles?
A)Peripheral nervous system
B)Central nervous system
C)Somatic nervous system
D)Autonomic nervous system

Neurons and Their Functions
Learning Objectives
2.Describe the structure of a neuron.
3.Explain the construction and function of
the myelin sheath.
4.Describe how neuron fibers are built
into a nerve.

Neurons and Their Functions (cont.)
Structure of a Neuron
•Neurons are the functional cells of the nervous system.
•They are highly specialized with a unique structure
related to their function.
– Cell body
• Contains the nucleus and other organelles
– Cell fibers
• Dendrites carry impulses to cell body.
• Axons carry impulses away from cell body.

Figure 9-2 Diagram of a motor neuron.
How do you know the neuron shown here is a motor
neuron? Is it part of the somatic or visceral nervous
system? Explain.

Figure 9-3 Microscopic view of a neuron.

The Myelin Sheath
•Some axons insulated and protected by a fatty myelin
sheath.
•In the PNS, myelin sheath is formed by Schwann cells.
– Outermost membrane of Schwann cell forms
neurilemma.
•In the CNS, myelin sheath formed by oligodendrocytes.
•Myelinated axons make up white matter.
•Unmyelinated axons make up gray matter.

Figure 9-4 Formation of a myelin sheath.

Types of Neurons

Nerves and Tracts
•Nerve—fiber bundle within the PNS
•Tract—fiber bundle within the CNS
•Organized into fascicles
•Connective tissue layers
– Endoneurium
– Perineurium
– Epineurium

Figure 9-5 Structure of a nerve.
What is the deepest layer of connective tissue in a nerve?
What is the outermost layer?

✓
Checkpoints
9-3 What is the name of the neuron fiber that carries
impulses toward the cell body? What is the name of the
fiber that carries impulses away from the cell body?
9-4 What color describes myelinated fibers? What
color describes the nervous system’s unmyelinated tissue?
9-5 What name is given to nerves that convey
impulses toward the CNS? What name is given to nerves
that transport away from the CNS?
9-6 What is a nerve? What is a tract?

?
Pop Quiz
9.2 Which fibers conduct impulses away from the cell
body?
A) Dendrites
B) Axons
C) Cell bodies
D) Neurilemma

?
Pop Quiz Answer
9.2 Which fibers conduct impulses away from the cell
body?
A) Dendrites
B) Axons
C) Cell bodies
D) Neurilemma

Neuroglia (cont.)
Functions of Neuroglia
•Protect, support, and nourish nervous tissue
•Aid in cell repair
•Remove pathogens and impurities
•Regulate composition of fluid around cells
Examples of Neuroglia
•Schwann cells
•Astrocytes
•Oligodendrocytes
•Ependymal cells

Figure 9-6 Astrocytes, a type of neuroglia.
Neuroglia (cont.)

Neuroglia (cont.)
✓
Checkpoint
9-7 What is the name of the nervous system’s
nonconducting cells, which protect, nourish, and support
the neurons?

Neuroglia (cont.)
?
Pop Quiz
9.3 Which of the following is NOT an example of a
neuroglial cell?
A) Neuron
B) Astrocyte
C) Schwann cell
D) All of the options are neuroglia.

Neuroglia (cont.)
?
Pop Quiz Answer
9.3 Which of the following is NOT an example of a
neuroglial cell?
A) Neuron
B) Astrocyte
C) Schwann cell
D) All of the options are neuroglia.

The Nervous System at Work (cont.)
Overview
•The nervous system works by means of electric impulses
sent along fibers and transmitted from cell to cell at highly
specialized junctions called synapses.

The Nerve Impulse
•Resting state
– Plasma membrane is polarized
– Leak channels
– Sodium–potassium pump
•Action potential
– Depolarization
– Repolarization
•Role of myelin—saltatory conduction

Figure 9-7 The action potential.

Figure 9-8 A nerve impulse.
What happens to the charge
on the membrane at the
point of an action potential?

Figure 9-9 Saltatory conduction.

The Synapse
•Junction point for transmitting nerve impulse from
neuron to another cell
•Basic structure
– Axon (presynaptic cell)
• Releases neurotransmitter, a chemical signal
– Synaptic cleft
– Dendrite (postsynaptic cell)
• Binds neurotransmitter via receptors

Examples of Neurotransmitters
•Norepinephrine
•Serotonin
•Dopamine
•Acetylcholine

Figure 9-10 A synapse.

✓
Checkpoints
9-8 What are the two stages of an action potential,
and what happens during each?
9-9 What ions are involved in generating an action
potential?
9-10 How does the myelin sheath affect conduction
along an axon?
9-11 What is the junction between two neurons called?
9-12 As a group, what are all the chemicals that carry
information across the synaptic cleft called?

?
Pop Quiz
9.4 Potassium channels open early in the action
potential to cause membrane:
A) Depolarization
B) Potential
C) Repolarization
D) Degradation

?
Pop Quiz Answer
9.4 Potassium channels open early in the action
potential to cause membrane:
A) Depolarization
B) Potential
C) Repolarization
D) Degradation

The Spinal Cord (cont.)
Overview
•Links the PNS and brain
•Helps coordinate impulses within the CNS
•Contained in and protected by vertebrae

Structure of the Spinal Cord
•Inner gray matter (unmyelinated axons)
– Dorsal horn
– Ventral horn
– Gray commissure
– Central canal
•Outer white matter (myelinated axons)
– Posterior median sulcus
– Anterior median fissure
– Ascending and descending tracts

✓
Checkpoints
9-13 How are the gray and white matter arranged in the
spinal cord?
9-14 What is the purpose of the tracts in the spinal cord’s
white matter?

?
Pop Quiz
9.5 What fluid is found in the central canal of the spinal
cord?
A) Blood
B) Cerebrospinal fluid
C) Lymph
D) Saline

?
Pop Quiz Answer
9.5 What fluid is found in the central canal of the spinal
cord?
A) Blood
B) Cerebrospinal fluid
C) Lymph
D) Saline

The Spinal Nerves (cont.)
• 31 pairs
• Each nerve attached to the spinal cord by two roots.
– Dorsal root with dorsal root ganglion (sensory)
– Ventral root (motor)
• Nerves near end of cord travel together in the cord until
each exits from its respective intervertebral foramen.
• Mixed nerves contain both sensory and motor fibers.

Figure 9-11 Spinal cord and spinal nerves.
Is the spinal cord the same length as the spinal column?
How does the number of cervical vertebrae compare to the
number of cervical spinal nerves?

Branches of the Spinal Nerves
•Cervical plexus
– Phrenic nerve
•Brachial plexus
– Radial nerve
•Lumbosacral plexus
– Sciatic nerve
•Dermatomes

Figure 9-12 Dermatomes.
Which spinal nerves carry
impulses from the skin of
the toes? From the
anterior hand and
fingers?

✓
Checkpoints
9-15 How many pairs of spinal nerves are there?
9-16 What types of fibers are in a spinal nerve’s dorsal
root? What types are in its ventral root?
9-17 What is the term for a network of spinal nerves?

?
Pop Quiz
9.6 The phrenic nerve arises from the:
A) Brachial plexus
B) Lumbosacral plexus
C) Abdominal plexus
D)Cervical plexus

?
Pop Quiz Answer
9.6 The phrenic nerve arises from the:
A) Brachial plexus
B) Lumbosacral plexus
C) Abdominal plexus
D)Cervical plexus

Reflexes (cont.)
The Reflex Arc

Figure 9-13 Typical
reflex arc.
Is this a somatic or
an autonomic
reflex arc?
What type of neuron
is located between
the sensory and
motor neuron in the
CNS?
Reflexes (cont.)

Reflexes (cont.)
Reflex Activities
•Simple reflex
– Characteristics
• Rapid
• Uncomplicated
• Automatic
– Types
• Stretch reflex
• Withdrawal reflex

Reflexes (cont.)
✓
Checkpoint
9-18 What is the name for a pathway through the
nervous system from a stimulus to an effector?

Reflexes (cont.)
?
Pop Quiz
9.7 What is the correct order of impulse conduction
through a reflex arc?
A) Sensory neuron, receptor, effector, interneuron,
motor neuron
B) Receptor, sensory neuron, interneuron, motor
neuron, effector
C) Receptor, motor neuron, sensory neuron,
interneuron, effector
D) Effector, sensory neuron, motor neuron,
interneuron, receptor

Reflexes (cont.)
?
Pop Quiz Answer
9.7 What is the correct order of impulse conduction
through a reflex arc?
A) Sensory neuron, receptor, effector, interneuron,
motor neuron
B) Receptor, sensory neuron, interneuron, motor
neuron, effector
C) Receptor, motor neuron, sensory neuron,
interneuron, effector
D) Effector, sensory neuron, motor neuron,
interneuron, receptor

Spinal
Learning Objectives
12.Compare the locations and
functions of the sympathetic and
parasympathetic nervous systems.
13.Explain the role of cellular
receptors in the action of
neurotransmitters in the autonomic
nervous system.

The Autonomic Nervous System (cont.)
Function
•Regulates the action of glands, smooth muscles of hollow
organs and vessels, and heart muscle
Structure
•Preganglionic neuron connects the spinal cord to
ganglion.
•Postganglionic neuron connects ganglion to effector.

Divisions of the Autonomic Nervous
•Sympathetic nervous system
•Parasympathetic nervous system

Functions of the Autonomic Nervous System
•Sympathetic nervous system
– Fight-or-flight response
•Parasympathetic nervous system
– Returns body to normal
•Systems generally have opposite effects on organ

Sympathetic Nervous System Anatomy
•Preganglionic neurons in thoracolumbar area
•Ganglia:
– Sympathetic chain ganglia
– Collateral ganglia
•Postganglionic neurons are adrenergic (norepinephrine)

Parasympathetic Nervous System Anatomy
•Preganglionic neurons in craniosacral areas
•Terminal ganglia
•Postganglionic neurons are cholinergic (acetylcholine)

Figure 9-14
Autonomic nervous
system.
Which division of
the autonomic
nervous system
has ganglia closer
to the effector
organ?

The Role of Cellular Receptors
•“Docking sites” on postsynaptic cell membranes
•Two types:
– Cholinergic receptors
• Nicotinic (bind nicotine) on skeletal muscle cells
• Muscarinic (bind muscarine, a poison) on effector
cells of the PNS
– Adrenergic receptors
• Found on receptor cells of the sympathetic nervous
system
• Bind norepinephrine, epinephrine

✓
Checkpoints
9-19 How many neurons are there in each motor
pathway of the ANS?
9-20 Which division of the ANS stimulates a stress
response? Which division reverses the stress response?

?
Pop Quiz
9.8 Which of the following is NOT an action of the
sympathetic nervous system?
A) Increase in blood pressure
B) Stimulation of skeletal muscle
C) Stimulation of the adrenal gland
D)Dilation of the pupils

?
Pop Quiz Answer
9.8 Which of the following is NOT an action of the
sympathetic nervous system?
A) Increase in blood pressure
B) Stimulation of skeletal muscle
C) Stimulation of the adrenal gland
D)Dilation of the pupils

Spinal Nerves (cont.)
Medical Procedures Involving the Spinal Cord
•Lumbar puncture (spinal tap)
– Cerebrospinal fluid (CSF) removed for testing
•Drug administration
– Anesthetic (an epidural)
– Pain medication

Figure 9-15 Lumbar puncture and epidural anesthesia.
Clinical Aspects of the Spine and Spinal Nerves (cont.)

Diseases and Other Disorders of the Spinal Cord
•Diseases
– Multiple sclerosis (MS)
– Amyotrophic lateral sclerosis
– Poliomyelitis
•Tumors

Diseases and Other Disorders of the Spinal Cord
(cont.)
•Injuries
– Monoplegia
– Diplegia
– Paraplegia
– Hemiplegia
– Tetraplegia

Disorders of the Spinal Nerves
•Neuropathy
•Mononeuropathy
•Polyneuropathy
– Tumors
– Toxins
– Infections
• Herpes zoster
– Autoimmune disorders
• Guillain-Barré syndrome

Clinical Aspects of the Spine and Spinal Nerves (cont.)
Figure 9-16 Carpal tunnel syndrome.

✓
Checkpoints
9-21 What is removed in a lumbar puncture?
9-22 What is the meaning of the word root plegia?
9-23 What term is used for any disorder of the nerves?

?
Pop Quiz
9.9 Ms. L has been experiencing muscle weakness. Her
physician informs her that she has abnormal antibodies
attacking the myelin sheath around neurons in her
central nervous system. The most likely diagnosis is:
A) Poliomyelitis
B) Multiple sclerosis
C) Amyotrophic lateral sclerosis
D) Peripheral neuropathy

?
Pop Quiz Answer
9.9 Ms. L has been experiencing muscle weakness. Her
physician informs her that she has abnormal antibodies
attacking the myelin sheath around neurons in her
central nervous system. The most likely diagnosis is:
A) Poliomyelitis
B) Multiple sclerosis
C) Amyotrophic lateral sclerosis
D) Peripheral neuropathy

Case Study (cont.)
• Damage to white matter tracts in the brain and spinal
cord prevents the transmission of nerve impulse to and
from the CNS and PNS.
– Damage to sensory tracts leads to sensory deficits.
– Damage to motor tracts leads to motor deficits.

Word Anatomy (cont.)

HBHD13e Ch9

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