Transcript AP-Chapter-9-Part-1 - McLaren

ESSENTIALS OF A&P
FOR EMERGENCY CARE
CHAPTER
9
The Nervous System:
Part One: The
Information Super
Highway
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Multimedia Asset Directory
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Multiple Sclerosis Animation
Neurosynapses Video
Muscle Contraction Animation
Epidural Placement Video
Spinal Cord Anatomy Animation
Brachial Plexus Animation
Lumbrosacral Plexus Animation
Cervical Spine Injuries Video
Reflex Arc Animation
Carpal Tunnel Syndrome Video
Electroneurodiagnosticians Video
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Introduction
• The nervous system is complex and
important to the body’s control system.
• The nervous system monitors conditions
and takes corrective action, when
necessary, to keep everything running
smoothly.
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Introduction
• The control systems of your body are the
nervous and endocrine systems which
receive help from your special senses.
• Like any control system, they have a large,
complex job that is sometimes difficult to
understand. Thus, the systems
themselves are perhaps the most complex
and vital systems.
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Learning Objectives
• List and describe the components and
basic operation of the nervous system.
• Contrast the central and peripheral
nervous systems.
• Define the parts and functions of the
nervous tissue.
• Discuss the anatomy and physiology of
the spinal cord.
• List and describe various disorders of the
nerves and spinal cord.
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Pronunciation Guide
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arachnoid mater (ah RAK noyd MAY ter)
astrocytes (ASS troh SITES)
axon (AK sahn)
cerebrospinal fluid (SER eh broh SPY nal)
chemical synapse (SIN naps)
commissures (KAHM ih shoorz)
corticobulbar tract (KOR ti coe BUL bar)
corticospinal tract (KOR ti coe SPY nal)
dendrites (DEN drights)
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dorsal root ganglion (GANG lee on)
dura mater (DOO rah MAY ter)
ependymal cells (eh PEN deh mall)
epidural space (EPP ih DOO rall)
ganglia (GANG lee ah)
glial cells (GLEE all)
gyri (JIE rie)
meninges (men IN jeez)
microglia (my KROG lee ah)
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myelin (MY eh lin)
neuroglia (glial cells) (noo ROG lee ah)
nodes of Ranvier (ron vee AYE)
oligodendrocytes (AH li go DEN droe sites)
pia mater (PEE ah MAY ter)
plexus (PLECK sus)
Schwann cells (SHWAN)
somatic nervous system (so MAT ick)
spinocerebellar tract (SPY no ser eh BELL ar)
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spinothalamic tract (SPY no thol AH mic)
subarachnoid space (SUB ah RACK noyd)
subdural space (sub DOO ral)
sulcus (SULL cus)
vesicles (VESS ih kulz)
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Parts and Basic Operations
• The brain and spinal cord is the central
nervous system (CNS) which controls the
total nervous system.
• Everything outside the brain and spinal
cord is part of the peripheral nervous
system (PNS).
• The input side of the nervous system is
the sensory system.
• The output side of the nervous system is
the motor system.
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Parts and Basic Operations
• The somatic nervous system controls skeletal
muscle and mostly voluntary movements.
• The autonomic nervous system controls
smooth muscle and cardiac muscle, along
with several glands.
• The autonomic system is divided into the
parasympathetic system that deals with
normal body functioning while the
sympathetic nervous system controls the
“fight or flight” response system.
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Figure 9-1 Organization of the nervous system.
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Real Life Example
• You park your car and get out to visit a friend.
As you step on the walk a large dog bounds
down the steps barking and snarling at you.
• Your sensory system gathers information
including; a large unfriendly dog, you are far
from the protection of your car, and no one is
around to help.
• The information goes into your spinal cord
and brain and you process the information to
make decisions. You are in danger;
something must be done!
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Real Life Example
• Your CNS sends directions to your organs
to gear up for action via the autonomic
nervous system.
• Your heart rate, blood pressure, and
respiration rate increase. You begin to
sweat. More blood is delivered to your
skeletal muscles and heart in order to get
you fully ready to respond. This is all
involuntary, meaning you cannot
consciously control it.
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Real Life Example
• Your somatic nervous system readies your
skeletal muscles to get you out of there.
This is often called the “fight or flight”
response and will be discussed later in
further depth. If you can control your fear,
you back slowly away from the situation. If
you are scared witless, you run from the
yard as fast as possible. Either way, you
can hopefully escape the danger, with
your skin and pride intact.
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Neuroglia
• Specialized cells in the nervous system
called neuroglia, or glial cells, perform
specialized functions.
• In the CNS there are four types of glial cells
– Astrocytes – metabolic and structural support
cells
– Microglia – remove debris
– Ependymal cells – cover and line cavities of the
nervous system
– Oligodendrocytes – make a lipid insulation called
myelin
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Neuroglia
• In the PNS there are two types of glial
cells:
– Schwann cells – make myelin for the PNS
– Satellite cells – support cells
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Figure 9-2 Glial cells and their functions.
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Neurons
• All of the control functions of the nervous
system must be carried out by a group of
cells called neurons.
• Neurons have many branches and even
what appears to be a tail.
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Neurons
• Each part of a neuron has a specific
function
– Body – cell metabolism
– Dendrites – receive information from the
environment
– Axon – generates and sends signals to other
cells
– Axon terminal – where the signal leaves the
cell
– Synapse – where the axon terminal and
receiving cell meet
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Figure 9-3 A neuron connected to a skeletal muscle.
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Classification of Neurons
• Neurons can be classified by how they look
(structure)
– Unipolar – 1 process with a peripheral and central
projection
– Bipolar – 2 processes, 1 axon and 1 dendrite
– Multipolar – many processes
• Or what they do (function)
– Input neurons are known as sensory neurons.
– Output neurons are known as motor neurons.
– Neurons which carry information between neurons
are called interneurons (inter – between) or
association neurons.
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How Neurons Work
• Neurons are a kind of cell called an
excitable cell. This simply means that if the
cell is stimulated it can carry a small
electrical charge.
• Each time charged particles flow across a
cell membrane, there is a tiny charge
generated.
• All three muscle types are excitable cells,
as are many gland cells.
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How Neurons Work
• Cells are like miniature batteries, able to
generate tiny currents simply by changing
the permeability of their membranes.
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Action Potential
• A cell that is not stimulated or excited is
called a resting cell; it is said to be
polarized.
• It has a difference in charge across the
membrane, being more negative inside
than outside the cell.
• When the cell is stimulated:
– Gates (called sodium gates) in the cell
membrane spring open allowing sodium to
travel across the membrane.
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Action Potential
• When the cell is stimulated:
– These sodium bits are positively charged, so
the cell becomes more positive as they enter.
– A cell that is more positive is called
depolarized.
– The sodium gates close.
– Potassium gates open and potassium leaves
the cell, taking its positive charge with it. This
is called repolarization.
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Action Potential
• When the cell is stimulated:
– If the cell becomes more negative than resting
it is called hyperpolarized.
– Action potential (AP) is the cell moving
through depolarization, repolarization, and
hyperpolarization.
– The cell cannot accept another stimulus until
it returns to its resting state, and this time
period when it cannot accept another stimulus
is called the refractory period.
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Figure 9-4 Depolarization and repolarization.
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Local Potentials
• Neurons can use their ability to generate
electricity to send, receive, and interpret
signals.
• If you hit your thumb with a hammer,
dendrites in your thumb are stimulated by
the blow and sodium gates open, sodium
flows into the dendrites and they become
depolarized. The number of cells affected
depends on how hard you hit your thumb.
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Local Potentials
• In local potential the size of the stimulus
determines the excitement of the cell.
Many sensory cells work via local
potentials, which is how your CNS
determines the size of the environmental
change.
• The dendrites carry the depolarization to
the sensory neuron cell body, which takes
the information and generates an action
potential if the stimulus is big enough.
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Local Potentials
• One difference between action potentials
and local potentials is that action
potentials are “all-or-none,” meaning the
depolarization always finishes and is
always the same size, while local
potentials vary in size depending on the
stimulus.
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Impulse Conduction
• The speed of impulse conduction is
determined by the amount of myelin and
the diameter of the axon.
• Myelin is a lipid insulation or sheath
formed by the oligodendrocytes in the
CNS and Schwann cells in the PNS.
• Myelinated nerves look white while
unmyelinated nerves are gray.
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Impulse Conduction
• Myelin is essential for speedy flow of AP’s
down the axons. In an unmyelinated axon,
the AP can only flow down the axon by
depolarizing each and every centimeter of
the axon (a relatively slow process). In
myelinated axons there are nodes located
periodically, and only the nodes must
depolarize, allowing the impulse to travel
quickly as it skips from node to node.
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Figure 9-5 Impulse conduction via myelinated axon.
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Clinical Application:
Multiple Sclerosis
• Multiple sclerosis (MS) is a disorder of the
myelin in the CNS. Many areas of myelin
are destroyed. In these areas, impulse
conduction is slow or impossible.
Symptoms of MS differ depending on
where the myelin damage occurs.
Disturbances in balance, vision, speech,
or movement is possible. MS occurs more
in women, and patients are usually under
50.
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Impulse Conduction and
Diameter
• The diameter of the axon also affects the
speed of the AP flow. The wider the
diameter of the axon, the faster the flow of
ions.
• Myelination and larger diameters allow for
a huge difference in speed.
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Impulse Conduction and
Diameter
• Small unmyelinated axons have speeds as
low as 0.5 meters/second while largediameter myelinated axons may be as fast
as 100 meters/second. That’s 200 times
faster!!
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How Synapses Work
• When the AP arrives at the axon terminal,
the terminal depolarizes and calcium gates
open. Calcium flows into the cell. When
calcium flows in, it triggers a change in the
terminal.
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How Synapses Work
• There are tiny sacs in the terminal called
vesicles which release their contents from
the cell when calcium flows in. These
vesicles are filled with molecules, called
neurotransmitters, used to send the signal
from the neuron across the synapse to the
next cell in line.
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Neurotransmitters
• The neurotransmitters bind to the cell
receiving the signal, opening or closing
gates. Some excite the receiving cell and
some calm it down.
• The last step in the transfer of information
is to clean up, removing the
neurotransmitter from the synapse to
prevent it from binding to the receiving
cell.
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Neurotransmitters
• This type of synapse is called a chemical
synapse because neurotransmitters carry
the information from one cell to another.
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Figure 9-6 The Chemical Synapse. Step 1: The impulse travels down the axon. Step 2:
Vesicles are stimulated to release neurotransmitter (exocytosis). Step 3: The neurotransmitter
travels across the synapse and binds with the receptor site of post synaptic cell. Step 4: The
impulse continues down the dendrite.
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Chemical Synapses and
Medications
• Our understanding of chemical synapses
has lead to several breakthroughs for
treating mental illness.
• Many medications on the market today are
designed to modify synapses.
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Chemical Synapses and
Medications
• Selective serotonin reuptake inhibitors
(SSRIs) are good examples. These
medications prevent the clean up of the
neurotransmitter serotonin from synapses,
thus increasing the effects of serotonin on
the receiving cell.
• Many antidepressants and anti-anxiety
drugs are SSRIs.
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Table 9-1 Selected Common Neurotransmitters.
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Electrical Synapses
• Some cells do not need the chemicals to
transmit information from one cell to another.
• These synapses are electrical synapses,
transferring information freely because they
have special connections called gap
junctions.
• These kinds of connections can exist
between any types of excitable cells.
• They are found in the intercalated discs
between cardiac muscle fibers.
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The Neuromuscular Junction
• The neuromuscular junction is a chemical
synapse creating a specialized synapse
between somatic (voluntary) motor
neurons and the skeletal muscles they
innervate.
• The surface of the muscles is studded with
sodium channels that are ligand gated.
These open or close when a molecule
binds to a receptor that is part of the
channel, like a key fitting into a lock.
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The Neuromuscular Junction
• In the case of skeletal muscles, the ligand
is the neurotransmitter acetylcholine,
which is released from the terminal of a
motor neuron and binds to the surface of
skeletal muscle, opening sodium channels
and causing the skeletal muscle to
depolarize. The muscle then contracts.
• Acetylcholinesterase is the enzyme
responsible for cleaning up the synapse.
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Spinal Cord and Spinal Nerves
• The spinal cord is a hollow tube running
inside the vertebral column, from the
foramen magnum to the second lumbar
vertebrae.
• The spinal cord is like a sophisticated
neural information superhighway.
• There are 31 segments, each with a pair
of spinal nerves, named for the
corresponding vertebrae.
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Spinal Cord and Spinal Nerves
• The spinal cord ends at L2 in a pointed
structure called the conus medullaris.
Hanging from the conus medullaris is the
cauda equina (horses tail), spinal nerves
which dangle loosely and float in a bath of
cerebral spinal fluid (CSF).
• The spinal cord has two widened areas,
the cervical and lumbar enlargements,
which contain the neurons for the upper
and lower limbs respectively.
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Figure 9-7 The spinal cord.
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Meninges
• The meninges are a protective covering of
both the brain and spinal cord.
• They help to set up layers that act as
cushioning and shock absorbers.
– dura mater
 outer layer is thick fibrous tissue
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Meninges
• They help to set up layers that act as
cushioning and shock absorbers.
– arachnoid mater
 middle layer is a wispy, delicate layer, resembling a
spider web, composed of collagen and elastic
fibers acting as a shock absorber and transporting
dissolved gases and nutrients as well as chemical
messengers and waste products
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Meninges
• They help to set up layers that act as
cushioning and shock absorbers.
– pia mater
 innermost layer, fused to the neural tissue,
containing blood vessels that serve the brain and
spinal cord
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Meningeal Spaces
• A series of spaces are associated with the
meninges.
– Between the dura mater and the vertebral
column is a space filled with fat and blood
vessels called the epidural space.
– Between the dura mater and the arachnoid
mater is the subdural space filled with a tiny
bit of fluid.
– Between the arachnoid mater and the pia
mater is the large subarachnoid space filled
with CSF that acts as a fluid cushion.
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Meningeal Spaces
• These three membranes and their fluidfilled spaces, together with the bones of
the skull and vertebral column, form a
strong protective system against CNS
injury.
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Figure 9-8 The meninges of the brain and spinal cord.
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Figure 9-8 (continued) The meninges of the brain and spinal cord.
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Clinical Application:
Epidural Anesthesia
• Often during labor, or in preparation for a
cesarean section, a woman will receive
“an epidural.” An epidural is an injection of
local anesthesia into the epidural space.
The anesthetic is usually delivered via a
catheter (small tube). Ideally, epidural
anesthesia allows a woman to continue to
participate actively in the birth without
severe labor pains.
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Clinical Application:
Epidural Anesthesia
• Epidural injections of steroids are
sometimes prescribed for patients with
chronic lower back injuries to relieve pain
and inflammation.
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Internal Anatomy of the
Spinal Cord
• The spinal cord is divided in half by an
anterior median fissure (deep groove) and
a posterior median sulcus (shallow
groove).
• The interior of the spinal cord is then
divided into a series of sections of white
matter columns and gray matter horns.
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Internal Anatomy of the
Spinal Cord
• There are three types of horns: the dorsal
horn is involved in sensory functions, the
ventral horn involved in motor function,
and the lateral horn dealing with
autonomic functions. The horns are the
regions where the neuron’s cell bodies
reside.
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Internal Anatomy of the
Spinal Cord
• There are also dorsal, lateral, and ventral
columns, the white matter of the spinal
cord. These columns act as nerve tracts,
pathways, or axons, running up and down
the spinal cord to and from the brain.
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Internal Anatomy of the
Spinal Cord
• Ascending pathways carry information
from your sense of touch to the spinal cord
and then to your brain from all parts of the
skin, joints, and tendons.
– The dorsal column tract carries fine-touch and
vibration information to the cerebral cortex.
– The spinothalamic tract carries temperature,
pain, and crude touch information to the
cerebral cortex.
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Internal Anatomy of the
Spinal Cord
• Ascending pathways carry information
from your sense of touch to the spinal cord
and then to your brain from all parts of the
skin, joints, and tendons.
– The spinocerebellar tract carries information
about posture and position to the cerebellum.
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Internal Anatomy of the
Spinal Cord
• Descending pathways carry motor
information (orders for voluntary
movements) from the brain to the spinal
cord. The axons from all pathways
synapse on motor neurons in the ventral
horn.
– The corticospinal tract carries orders from the
brain to the motor neurons in the ventral horn
of the spinal cord.
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Internal Anatomy of the
Spinal Cord
• The axons from all pathways synapse on
motor neurons in the ventral horn.
– The corticobulbar tract carries orders from the
brain to motor neurons in the brain stem
(more details later).
– The reticulospinal and rubrospinal tracts
(along with several other tracts) carry
information from the brain to the brain stem
and ventral horn, which helps to coordinate
movements.
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Internal Anatomy of the
Spinal Cord
• The commissures, gray and white,
connect left and right halves of the cord so
the two sides of the CNS can
communicate. The central canal is a cavity
in the center of the spinal cord filled with
CSF.
• The spinal roots project from both sides of
the spinal cord in pairs, and fuse to form
spinal nerves.
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Internal Anatomy of the
Spinal Cord
• The dorsal root, with the embedded dorsal
root ganglion, a collection of sensory
neurons, carries sensory information while
the ventral root is motor.
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Figure 9-9 Internal anatomy of the spinal cord.
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Spinal Nerves
• Nerves are the connection between the
CNS and the world outside the CNS.
• Nerves are, therefore, part of the PNS.
• All nerves consist of bundles of axon,
blood vessels, and connective tissue.
• Nerves run between the CNS and organs
or tissues, carrying information into and
out of the CNS.
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Spinal Nerves
• The nerves connected to the spinal cord
are called spinal nerves, each named for
the spinal cord segment to which they are
attached.
• All spinal nerves are mixed nerves which
means they carry both sensory and motor
information.
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Spinal Nerves
• Spinal nerves from the thoracic spinal cord
project directly to the thoracic body wall
without branching, while all other spinal
nerves branch extensively, recombining
with nerves from other spinal cord
segments before projecting to peripheral
structures. These complex branching
patterns are called plexuses.
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Figure 9-10 Spinal cord plexuses.
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Figure 9-10 (continued) Spinal cord plexuses.
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Clinical Application:
A Matter of Centimeters
• Did you know that the difference between
being able to breathe on your own after a
spinal cord injury and being dependent on
a ventilator is literally a matter of
centimeters? One of the nerves that
projects from the cervical plexus is a nerve
called the phrenic nerve, a motor nerve for
your diaphragm, your main breathing
muscle.
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Clinical Application:
A Matter of Centimeters
• If the spinal cord is damaged below the
cervical plexus the phrenic nerve still
functions, while an injury between the
brain and the cervical plexus blocks the
path to the phrenic nerve paralyzing your
diaphragm.
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From the Streets:
Spinal Cord Injuries
• Spinal-cord injuries vary in severity:
– Cord concussion
– Cord contusion
– Cord compression
– Cord lacerations
– Complete transection
– Incomplete transection
– Cord hemorrhage
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From the Streets:
Spinal Cord Injuries
• Several syndromes can develop with
spinal-cord injury.
– Anterior-cord syndrome
– Central-cord syndrome
– Brown-Séquard syndrome
– Cauda equina syndrome
– Spinal shock
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Figure 9-12 Mechanisms associated with cervical spine, vertebral, and spinal cord injury.
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Reflexes
• Reflexes are the simplest form of motor
output you can make.
• Reflexes are generally protective,
involuntary, and usually get bigger as the
stimulus gets bigger.
• Some familiar reflexes are the patellar
reflex, which keeps you vertical, and your
startle reflex, which causes you to jump at
loud sounds.
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Reflexes
• The amazing thing about reflexes is that
they can often occur without your brain
being involved, involving only your spinal
cord.
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From the Streets:
Reflexes
• Reflex testing can be a useful examination
tool.
• Stretch reflexes evaluated by tapping on a
part of a muscle with a reflex hammer
• Table 9-2 illustrates how responses are
graded.
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Table 9-2 Mechanisms associated with cervical spine, vertebral, and spinal cord injury.
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From the Streets:
Reflexes
• Decreased reflex (hypoflexia) or absent
reflex (areflexia) may result from
temporary or permanent damage to:
– Skeletal muscles
– Dorsal or ventral nerve roots
– Spinal nerves
– The spinal cord
– The brain
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From the Streets:
Reflexes
• Increased reflex (hyperreflexia) usually
stems from diseases that affect higher
centers or descending tracts.
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From the Streets:
Reflexes
• Babinski reflex
– This reflex should be assessed in all critically
ill or critically injured patients
– Characterized when the big toe dorsiflexes
and the other toes fan out when the bottom of
the foot is stroked along the lateral aspect of
the sole.
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Figure 9-13 Abdominal reflex. Gently stroking the skin of the abdomen should cause
contraction of the underlying muscles and move the umbilicus toward the location of the
stimulation.
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Figure 9-13 Plantar reflex. Stroking the lateral aspect of the plantar surface of the foot
should cause plantar flexion of the toes. Dorsiflexion of the great toe and fanning of the other
toes following stimulation is considered a positive Babinski reflex, which suggests problems
with higher centers within the brain.
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Common Disorders
of the Nervous System: Part I
•
•
•
•
•
•
•
Peripheral neuropathy
Spinal trauma
Guillain-Barré syndrome
Myasthenia gravis
Botulism
Meningitis
Carpal tunnel syndrome
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Peripheral Neuropathy
• Peripheral neuropathy refers to a number
of disorders involving damage to
peripheral nerves.
• Symptoms vary depending on whether the
sensory, motor, or autonomic function is
affected.
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Peripheral Neuropathy
• Symptoms include muscle weakness,
decreased reflexes, numbness, tingling,
paralysis, pain, abnormal sweating,
digestive abnormalities, and difficulty
controlling BP.
• Non-genetic neuropathy can be grouped
as systemic disease, trauma, and infection
or autoimmune disorders.
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Spinal Trauma
• Even though the spinal cord is protected, it
can be damaged by trauma.
• The spinal cord can be partially or
completely severed, crushed, or bruised.
Bruises may resolve with time.
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Spinal Trauma
• Spinal cord injury usually results in
paralysis and sensory loss below the
injury.
– Cervical injury may result in quadriplegia, and
if the diaphragm is paralyzed the individual
can’t breathe on their own.
– Thoracic spinal cord damage and lower
causes paraplegia. Patients can move their
arms.
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Guillain-Barré Syndrome
• Guillain-Barré syndrome (GBS) is a rapid
onset paralysis caused by inflammation of
peripheral nerves.
• Patients develop weakness and ascending
paralysis.
– Severe cases require a ventilator to support
breathing until paralysis resolves.
– The disorder is temporary and many patients
require rehabilitation after recovery.
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Guillain-Barré Syndrome
• The cause is unknown, but may be viral
infection or autoimmune.
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Myasthenia Gravis
• Myasthenia gravis is an autoimmune
disorder.
• The immune system attacks and destroys
acetylcholine receptors at the
neuromuscular junction.
• Motor neurons continue to release
acetylcholine but the receptor number is
reduced so motor neurons can’t
communicate with skeletal muscles.
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Myasthenia Gravis
• Eye muscles are usually the first affected.
Some patients experience difficulty
swallowing, chewing, or talking.
• The disease is progressive, but the course
of disease varies among patients.
• Treatment includes cholinesterase
inhibitors, corticosteroids,
immunosuppressant drugs, and plasma
exchange. A few patients spontaneously
recover.
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Botulism
• Botulism is a form of paralysis caused by
toxins produced by the bacterium
Clostridium botulinum.
• Botulism can be caused by ingesting the
toxin in food or from a wound infection.
• The bacteria grows most commonly in
improperly prepared canned food,
especially home-canned food.
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Botulism
• The toxin keeps neurotransmitters from
being released at the neuromuscular
junction, causing paralysis.
• Initial symptoms include visual
disturbances, slurred speech, dry mouth,
and muscle weakness. Paralysis will
spread to limbs and respiratory muscles.
• Botulism is treated with anti-toxin and
supportive care.
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Meningitis
• Meningitis is an infection, from either
viruses or bacteria, of the meninges.
• Bacterial meningitis is a potentially fatal
infection.
• The bacteria first infect the upper
respiratory tract and then travel to the
meninges.
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Meningitis
• At-risk patients include the elderly,
immunosuppressed, very young children,
and college students who live in dorms.
• Survivors of meningitis often have severe
neurological impairment, including
deafness and severe brain damage.
• Viral meningitis is a much milder version of
the disease and is caused by viruses that
enter the mouth before traveling to the
meninges.
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Carpal Tunnel Syndrome
• Carpal tunnel syndrome is an inflammation
and swelling of the tendon sheathe
surrounding the flexor tendon of the palm.
• This is a result of repetitive motion, such
as typing on a keyboard.
• As a result of the inflammation, the median
nerve is compressed producing tingling
sensations or numbness of the palm and
first three fingers.
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Snapshots from the Journey
• The nervous system is the body’s
computer. It has a sensory, integration,
and motor system. The input and output
nerves are in the PNS, and the brain and
spinal cord are the SNS.
• The tissue of the nervous system is made
up of two types of cells: neurons, which
send, receive, and process information,
and neuroglia, which support the neurons.
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Snapshots from the Journey
• Neurons are excitable cells. They do their
jobs by carrying tiny electrical currents
caused by changes in cell permeability to
certain ions. These tiny electrical currents
can be all-or-none responses (action
potentials), can change depending on the
size of the stimulus (local potentials), can
travel down axons (impulse conduction),
or can be used to transmit information
from one cell to another (synapses).
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Snapshots from the Journey
• Your CNS is surrounded by a threelayered membrane system: dura mater,
arachnoid mater, and pia mater,
collectively known as the meninges.
Cerebrospinal fluid is also contained in the
space between the arachnoid and pia
maters.
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Snapshots from the Journey
• The spinal cord has 31 segments, each
with a pair of spinal nerves. The spinal
nerves are a part of the peripheral nervous
system.
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Snapshots from the Journey
• The spinal nerves are made of a pair of
spinal roots. The ventral root is integral to
motor function, and the dorsal root is
integral to sensory function. Spinal nerves
are mixed; they carry both sensory and
motor information.
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Snapshots from the Journey
• A series of tracts run up and down the
spinal cord to and from the brain. The
tracts going toward the brain carry sensory
information to the brain. The tracts coming
from the brain toward the spinal cord carry
motor information from the brain.
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Case Study
During the biggest game of his high school
football career, Bill, the best wide receiver in
the league, leaps high into the air in the end
zone to score the game-winning touchdown.
A player for the other team hits him hard,
knocking him into the goal post. Bill
crumples to the ground, unmoving. When
the EMT’s get to him, Bill is paralyzed on
both sides of his body and in respiratory
arrest.
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Case Study Questions
• Where is Bill’s injury most likely located?
• How can you tell?
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From the Streets
A 60-year-old female drives to your EMS
department because she is experiencing
“numbness and tingling” in her hands &
fingers. Your patient interview reveals that
the complaint has been going on for almost
three months and has become worse over
the last two weeks. She has a history of
diabetes.
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From the Streets Questions
• What division of the nervous system is
involved in her condition?
• What is the term that describes her feeling
of “numbness and tingling”?
• What is the most likely diagnosis?
• What is her prognosis?
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From the Streets Questions
• What division of the nervous system is
involved in her condition? The peripheral
nervous system
• What is the term that describes her feeling
of “numbness and tingling”? Paresthesia
• What is the most likely diagnosis?
Peripheral neuropathy
• What is her prognosis? Peripheral
neuropathy is a chronic & degenerative
disease process
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Review Questions
1. The input side of your nervous system is
known as:
a. Motor
b. Sensory
c. Association
d. All of the above
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Review Questions
2. Neurons with a central and peripheral
projection are known as:
a. Unipolar
b. Bipolar
c. Multipolar
d. Northpolar
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Review Questions
3. During depolarization ____ ions move
___ a neuron.
a.
b.
c.
d.
K+, out of
K+, into
Na+, out of
Na+, into
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Review Questions
4. The ventral root of the spinal cord is:
a. Sensory
b. Motor
c. Association
d. None of the above
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Review Questions
5. Spinal nerves carry what kind of
information?
a. Sensory
b. Motor
c. Mixed
d. Vertebral
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Review Questions
6. A spinal injury at T3 would cause:
a. Paralysis of all four limbs
b. Paralysis from the waist down
c. Paralysis in all four limbs and respiratory
arrest
d. Paralysis of the arms
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Review Questions
7. Sodium channel blockers, which prevent
sodium channels from working, would
block what part of the action potential?
a. Hyperpolarization
b. Depolarization
c. Repolarization
d. Afterpotential
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Review Questions
8. Multiple sclerosis is often associated with
a decrease in these neuroglia.
a. Astrocytes
b. Schwann cells
c. Oligodendrocytes
d. Microglia
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Review Questions
1. The speed of impulse conduction is
determined by _______ and ______.
2. ________ potentials are all or none.
3. The spinal cord has white matter
_______ and gray matter ______.
4. _______ fluid is contained in the ______
space between the arachnoid mater and
pia mater.
Essentials of A&P for Emergency Care
Bruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Copyright ©2011 by Pearson Education, Inc.
All rights reserved.
End of Chapter
Review Questions
5. A ______ is an involuntary, protective
movement that is generated without the
brain.
6. The virus polio causes loss of motor
function but not of sensory function,
because it infects neurons. These
neurons are located in the ___________
horn of the spinal cord.
Essentials of A&P for Emergency Care
Bruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Copyright ©2011 by Pearson Education, Inc.
All rights reserved.
End of Chapter
Review Questions
1. Explain the changes in a neuron during an
action potential.
2. List the steps in chemical synaptic
transmission.
3. List the layers of protection around the
CNS.
4. List the types of neuroglia and their
functions.
5. Explain the results of spinal cord injuries in
the following locations: C2, T3 and L2.
Essentials of A&P for Emergency Care
Bruce J. Colbert • Jeff Ankney • Karen T. Lee • Bryan E. Bledsoe
Copyright ©2011 by Pearson Education, Inc.
All rights reserved.