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6
The Nervous
System
Lesson 6.1: Overview of the Nervous System
Lesson 6.2: Transmission of Nerve Impulses
Lesson 6.3: Functional Anatomy of the Central
Nervous System
Lesson 6.4: Functional Anatomy of the Peripheral
Nervous System
Lesson 6.5: Injuries and Disorders of the
Nervous System
Chapter 6: The Nervous System
Lesson 6.1
Overview of the
Nervous System
• The function of the nervous system is to
coordinate all body systems! This is
accomplished by the transmission of signals
(electrochemical) from body parts to the brain and
back to the body parts..
• The nervous system is composed of:
• Neurons
• Neuroglial cells (also known as neuroglia, glia, and glial
cells)
• Blood vessels
• Connective tissue
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Two Major Divisions
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Organization of the Nervous System
• two major divisions
– central nervous system (CNS) – consists of the brain
and spinal cord
– peripheral nervous system (PNS) – consists of cranial
nerves and spinal nerves
• sensory receptors
• afferent (sensory) nerves – transmit nerve impulses from
the sensory receptors in the skin, muscles, and joints to
the CNS
• efferent (motor) nerves – transmit nerve impulses from the
CNS to the muscles and glands
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The Efferent Nerves
• somatic nervous system
– voluntary – carries information to skeletal muscle
• autonomic nervous system
– involuntary – carries information to smooth muscle,
cardiac muscle, and glands
– sympathetic
– parasympathetic
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brain
spinal
cord
cranial
nerves
Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves)
Sensory division
spinal
nerves
Sensory
receptors
Motor division
Somatic
Nervous
System
Autonomic
Nervous
System
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Skeletal
muscle
Smooth muscle
Cardiac muscle
Glands
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Nervous Tissues
• neuroglia
– also known as glial cells
– support the neurons
– protect the neurons
• neurons
– transmit nerve impulses
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Neuroglia
• central nervous system
–
–
–
–
astrocytes
microglia
ependymal
oligodendrocytes
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Neuroglia - CNS
• Astrocytes – most numerous - positioned between
neurons and capillaries – protect neurons from
harmful substances in the blood
• Microglia – absorb and dispose of dead cells and
bacteria
• Ependymal – form a protective covering around
the spinal cord and central cavities within the brain
• Oligodendrocytes – produce myelin (fatty
insulating material that surrounds nerve fibers)
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Neuroglia - PNS
• peripheral nervous system
– Schwann cells – form fatty myelin sheaths around nerve
fibers
• insulation from myelin sheath speeds up
neurotransmission
• a bundle of myelinated nerve fibers (axons) = “white
matter”
• a bundle of unmyelinated nerve fibers (cell
bodies/dendrites) = “gray matter”
• nodes of Ranvier – uninsulated gaps between sections of
myelin where the axon is exposed
– satellite cells – provide cushioning
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Neuroglia - PNS
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Parts of a Neuron
• cell body (soma) - central portion of neuron - contains
usual organelles
• neuron processes (two types) - extensions from cell
body
• Dendrites – many per neuron; short & branched; receptive
portion of neuron; carries impulse toward cell body
• Axon - one per neuron; long, thin process; carries impulses
away from cell body; terminations of axon branch = axon
terminals
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Parts of a Neuron
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Neuron Types by Function
• sensory neurons
– send impulses toward CNS
• motor neurons
– send impulses away from CNS
• interneurons
– transport impulses between neurons
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Structural Types of Neurons
• Due to structural differences, neurons can be classified into three (3)
major groups:
•
Bipolar neurons – two extensions; one fused dendrite leads
toward cell body and one axon leads away from cell body
ex. Specialized parts of eyes, nose, & ears (sensory)
•
Unipolar neurons – one process from cell body; forms central
& peripheral process; only distal ends are dendrites
ex. Some sensory neurons in the PNS
•
Multipolar neurons – many extensions; many dendrites lead
toward cell body and one axon leads away from cell body
ex. All motor neurons and interneurons
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Neuron Structures
• bipolar
• unipolar
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• multipolar
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Review and Assessment
Match these words with 1–4 below: sympathetic
nervous system, myelin, synapse, axon.
1. high alert
2. transmits impulses away from cell body
3. fatty insulating material
4. gap between neurons
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Chapter 6: The Nervous System
Lesson 6.2
Transmission of
Nerve Impulses
Transmission of Nerve Impulses
Transmission of nerve impulses is an
electrochemical process
 Creation of an action potential is electrical
 Neurotransmitters released at the synapse is chemical
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Transmission of Nerve Impulse
When a neuron is inactive or at rest:
 Potassium ions are inside the cell and sodium ions are
outside the cell membrane
 Inside of cell is more negatively charged than outside of
cell
 Difference in electrical charge inside and outside of cell
= cell membrane is polarized
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Transmission of Nerve Impulse
Activation of a neuron:
 Stimulus causes the sodium channels to open
 Sodium ions enter the neuron causing the inside of the
membrane to become more positive = cell membrane is
depolarized
 Depolarization occurs only at the nodes of Ranvier
 Opening of sodium channels is like a domino effect
creating more sodium channels to open along the
membrane = action potential (electrical impulse)
 All-or-none concept – electrical charge of the action
potential is always the same size and travels the full
length of the axon
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Action Potential
Direction of nerve impulse
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Transmission of Nerve Impulse
Discharge of the action potential
 Membrane becomes permeable to potassium ions
 Potassium ions diffuse out of the cell
 Membrane is restored to its polarized state with a more
negative charge inside the cell = repolarization
 Refractory period = time between the completion of the
action potential and repolarization
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Transmission of Nerve Impulse
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Impulse Transmission
Factors affecting speed of impulse transmission:
– Faster in myelinated axons vs nonmyelinated axons
where the myelin sheath acts as an insulator
• Saltatory conduction – action potentials jump over
myelinated regions of the axon
– Faster in nonmyelinated axons with larger diameters vs.
nonmyelinated axons with smaller diameters
– Faster in warmer temps because of an increase in ions
diffusion rates
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Impulse Transmission
Transmission at synapses
 When an action potential reaches an
axon terminal, calcium
gates open and calcium
ions flow into the terminal
 Influx of calcium causes the
neurotransmitter vesicles
to release the neurotransmitter
into the synapse
 Neurotransmitters connect
to a receptor site on a joining
neuron or muscle fiber
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• Introduction to Anatomy and Physiology Student
Site Video.html
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Neurotransmitters
2 types of neurotransmitters:
– Excitatory neurotransmitter – acetylcholine – activates
muscle fibers
– Inhibitory neurotransmitter – endorphins – inhibit nerve
cells from discharging more pain signals
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Reflexes
- simple, rapid, involuntary response to stimuli that
follows a reflex arc involving both the PNS and
CNS
2 types
 Somatic reflexes – involve the stimulation of skeletal
muscles – when touching a hot surface, nerve impulses
travel from a sensory nerve to an interneuron in the
spinal cord to a motor neuron, bypassing the brain
Reflex video.html
 Autonomic reflexes – send involuntary stimuli to the
cardiac muscles of the heart and the smooth muscles of
the organs – digestion, elimination, sweating
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Review and Assessment
Fill in the blanks with: reflexes, saltatory conduction,
neurotransmitter, or action potential.
1. A(n) _______________ is an all or none
response.
2. _______________ occurs only in myelinated
axons.
3. _______________ are rapid, involuntary
responses.
4. The axon terminal has tiny vesicles filled with
_______________.
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Chapter 6: The Nervous System
Lesson 6.3
Functional Anatomy of the
Central Nervous System
The Brain
4 Regions




Cerebrum
Diencephalon
Brain stem
Cerebellum
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Cerebrum
• cerebral cortex





Outer surface of cerebrum
Contains nonmyelinated gray matter
Gyrus – curved, raised area
Sulcus – grooves between gyri
Fissure – deep grooves
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Cerebrum
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Cerebrum
• lobes
– Frontal – memory, intelligence, behavior, emotions, motor function,
smell
– Parietal – pain, touch, hot/cold, speech
– Occipital – vision, speech
– Temporal – hearing, smell, memory, speech
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• primary motor cortex – anterior side of central sulcus
• primary somatic sensory cortex – posterior side of central
sulcus
• central sulcus – separates frontal lobes from parietal lobes
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Motor Cortex
Somatosensory cortex
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Diencephalon
• Thalamus – relays sensory impulses to the
sensory cortex
• Hypothalamus – autonomic center regulating
metabolism, heart rate, blood pressure, hunger,
thirst, energy level, and body temp
• Epithalamus – regulates hormones secreted by
the pineal gland
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Diencephalon
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Brain Stem
• Midbrain – relays sensory and motor impulses
• Pons – assists with regulation of breathing
• Medulla oblongata – regulates heart rate, blood
pressure, and breathing, and controls the reflexes
of coughing, sneezing, and vomiting
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Brain Stem
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Cerebellum
• Below the occipital lobe
• Coordinates body movement and balance
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Blood Brain Barrier
• Substances can pass less freely through
capillaries in the brain compared to capillaries in
other parts of the body
• Protects the brain against surges in hormones,
ions, and some nutrients
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Meninges
• Membranes covering brain and spinal cord
– dura mater (“hard mother”) – tough, outer doublelayered membrane
– arachnoid mater – middle layer - web-like tissue
 subarachnoid space – contains cerebrospinal
fluid which cushions the brain and spinal cord
– pia mater (“gentle mother”) – innermost membrane
of brain and spinal cord
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Meninges
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Spinal Cord
• Major pathway for relaying sensory impulses to the
brain and motor impulses from the brain
• Exterior is myelinated white matter
• Butterfly-shaped gray matter, composed of neuron
cell bodies and interneurons, are centrally located
• Dorsal, ventral, and lateral projections of gray
matter are called horns
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Spinal Cord
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Review and Assessment
True or False?
1. The gyri divide the brain into 4 regions.
2. The hypothalamus regulates blood pressure.
3. The meninges has 3 layers.
4. The cerebellum coordinates balance.
5. The pons is also called the interbrain.
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Chapter 6: The Nervous System
Lesson 6.4
Functional Anatomy
of the Peripheral
Nervous System
Peripheral Nervous System - Nerve
Structure
• endoneurium
– covers axons
• perineurium
– bundles fascicles
• epineurium
– encases fascicles and
blood vessels
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Cranial Nerves
•
•
•
•
•
•
12 pairs
Olfactory nerve – smell
Optic nerve – sight
Oculomotor – eye movement
Vestibulocochlear – hearing, balance
Glossopharyngeal – throat muscle movements,
taste
• Vagus – autonomic control of heart, lungs,
digestion, taste, communication between brain and
organs
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Cranial Nerves
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Spinal Nerves and Nerve Plexuses
• 31 pairs
• dorsal root (posterior) and ventral root (anterior)
unite to form the left and right spinal nerves at
each spinal level
• dorsal ramus and ventral ramus split from the
spinal nerves – carry nerve impulses to the muscle
and skin of the trunk
• Plexuses – interconnections of nerves formed from
the ventral rami in the cervical and lumbar regions
of the spinal cord
– 4 plexuses – cervical, brachial, lumbar, and sacral
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Autonomic Nervous System
• Involuntary nervous system that activates the
heart, smooth muscles, and glands
• Ganglion – enlarged junction of nerve tissue
composed mainly of nerve cell bodies
• Preganglionic neurons – originate in the lateral
horn of the spinal cord and terminate in a ganglion
• Postganglionic neurons – originate in a ganglion
and terminate in a cardiac muscle, smooth muscle,
or gland
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Autonomic Nervous System
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Autonomic Nervous System
Sympathetic nervous system
 Fight-or-flight response
 Sympathetic nerves stimulate the adrenal gland to
release epinephrine (adrenaline) – increases heart and
breathing rates and sweating
Parasympathetic nervous system
 Controls automatic day-in and day-out functions of the
circulatory, respiratory, and digestive systems
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Review and Assessment
Match these words with 1–4 below: efferent,
ganglion, optic, perineurium.
1. wraps fascicles
2. motor
3. a cranial nerve
4. enlarged junction
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Chapter 6: The Nervous System
Lesson 6.5
Injuries and Disorders of
the Nervous System
Injuries to the Brain and Spinal Cord
• traumatic brain injury
• cerebral palsy
• spinal cord injury
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Traumatic Brain Injury
• violent impact to head
– mild
– moderate
– severe
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Spinal Cord Injuries
•
•
•
•
C1–C3: usually fatal
C1–C4: quadriplegia
C5–C7: paralysis of lower extremities
T1–L5: paraplegia
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Common Diseases and Disorders of the
CNS
• meningitis – inflammation of the meninges around the brain
or spinal cord – can be viral or bacterial
• multiple sclerosis – autoimmune disease in which the
body’s immune system destroys the myelin sheaths of
nerve cell axons
• epilepsy – abnormal electrical activity in the brain
• Parkinson’s disease – slow but progressive destruction of
the brain’s cells responsible for the production of the
neurotransmitter dopamine which plays a role in motor
functions
• dementia and Alzheimer’s disease – loss of function in 2 or
more areas of cognition including memory, thinking,
judgment, behavior, perception, and language
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Review and Assessment
Match these words with 1–4 below: quadriplegia,
multiple sclerosis, dementia, cerebral palsy.
1. inflammation destroys myelin sheath
2. loss of memory and thinking
3. loss of function below the neck
4. may begin before birth
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