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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
•
•
•
•
•
•
cerebrum
diencephalon
brain stem
cerebellum
meninges
blood-brain barrier
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Cerebrum
• cerebral cortex
– gyrus
– sulcus
– fissure
• lobes
–
–
–
–
frontal
parietal
occipital
temporal
• primary motor cortex
• primary somatic sensory cortex
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Cerebrum
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Diencephalon
• thalamus
• hypothalamus
• epithalamus
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Brain Stem
• midbrain
• pons
• medulla oblongata
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The Brain
• cerebellum
• blood-brain barrier
• meninges
– dura mater
– arachnoid mater
– pia mater
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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
Functional Anatomy of the Peripheral
Nervous System
•
•
•
•
nerve structure
cranial nerves
spinal nerves and nerve plexuses
autonomic nervous system
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Nerve Structure
• endoneurium
– covers axons
• perineurium
– bundles fascicles
• epineurium
– wraps nerves
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Cranial Nerves
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Spinal Nerves and Nerve Plexuses
•
•
•
•
•
•
31 pairs
dorsal root
ventral root
dorsal ramus
ventral ramus
plexuses
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Autonomic Nervous System
• preganglionic and postganglionic neurons
• sympathetic nerves
– fight-or-flight action
• parasympathetic nerves
– resting or digesting action
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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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Cerebral Palsy
• damage to brain
– before birth
– during birth
– during infancy
• motor function impairment
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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
multiple sclerosis
epilepsy
Parkinson’s disease
dementia and Alzheimer’s disease
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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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