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Structure and Function of
the Neurologic System
Chapter 14
1
Overview of the Nervous System
Central nervous system (CNS)
Brain and spinal cord
Peripheral nervous system (PNS)
Cranial nerves
Spinal nerves
Pathways
Afferent (ascending)
Efferent (descending)
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Overview of the Nervous System
Peripheral nervous system (PNS)
Somatic nervous system
Motor and sensory pathways regulating voluntary
motor control of skeletal muscle
Autonomic nervous system
Motor and sensory pathways regulating the body’s
internal environment through involuntary control of
organ systems
Sympathetic
Parasympathetic
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Cells of the Nervous System
Neuron
Variable size and structure throughout the
nervous system
Cellular constituents
Microtubules, neurofibrils, Nissl substances, and
ribosomes
Some neurons like olfactory neurons continue to
divide
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Neuron
Three components
Cell body (soma)
Located mainly in the CNS
Densely packed cell bodies in the CNS are nuclei
Densely packed cell bodies in the PNS are ganglia
Dendrites
Receptive portion of the neuron
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Neuron
Axons
Carry nerve impulses away from the cell body
Axon Hillock
Cone-shaped, Nissl-free area, where the axon leaves
the cell body
Initial segment of the axon
Area of the axon having the lowest threshold for
stimulation, so the action potentials begin at this point
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Neuron
Axons
Myelin
Endoneurium
Segmented layer of lipid material
Insulating substance
Formed and maintained by the Schwann cell
Delicate layer of connective tissue around each axon
Neurilemma
Thin membrane between the myelin sheath and the
endoneurium
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Neuron
Axons
Nodes of Ranvier
Saltatory conduction
The flow of ions between segments of myelin rather than along
the entire length of the axon
Divergence
Regular interruptions of the myelin sheath
Ability of branching axons to influence many neurons
Convergence
Branches of numerous neurons converging on one or a few
neurons
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Structural Classification of
Neurons
Based on the number of processes extending
from the cell body
Unipolar
Pseudounipolar
Bipolar
Multipolar
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Functional Classification of
Neurons
Sensory
Associational
Transmit impulses from sensory receptors to the
CNS
Transmit impulses from neuron to neuron
Motor
Transmit impulses from the CNS to an effector
organ
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Neuroglia
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Neuroglia
“Nerve glue”
Support the neurons of the CNS
Astrocytes
Oligodendroglia (oligodendrocytes)
Microglia
Ependymal cells
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Neuroglia
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Nerve Injury and Regeneration
Wallerian degeneration
Occurs distal to the cut
Swelling appears
Neurofilaments hypertrophy
Myelin sheath shrinks and disintegrates
Axon portion degenerates and disappears
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Nerve Injury and Regeneration
Proximal to the cut
Swelling and dispersal of the Nissl substance
Cell increases in metabolic activity, protein synthesis, and
mitochondrial activity
New terminal sprouts project from the proximal segment
Process limited to myelinated axons
Generally only in the PNS
Depends on location, type of injury, the inflammatory
response, and scar tissue formation
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Neuroglia
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Nerve Impulse
Neurons generate and conduct electrical and
chemical impulses by selectively changing the
electrical portion of their plasma membranes
and influencing other nearby neurons by the
release of neurotransmitters
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Synapses
Region between adjacent neurons is called a synapse
Impulses are transmitted across the synapse by
chemical and electrical conduction
Presynaptic neurons and postsynaptic neurons
Connections between pre- and postsynaptic neurons
Axoaxonic
Axosomatic
Axodendritic
Dendrodentritic
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Synapses
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Synapses
Neurotransmitters
>30 substances
Excitatory (excitatory postsynaptic potential)
Inhibitory (inhibitory postsynaptic potential)
Synaptic boutons
Synaptic cleft
Summation
Temporal summation
Spatial summation
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Central Nervous System
Forebrain
Midbrain
Cerebral hemispheres
Corpora quadrigemina, tegmentum, and cerebral
peduncles
Hindbrain
Cerebellum, pons, and medulla
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Central Nervous System
Reticular formation
Network of connected nuclei that regulate viral
reflexes, such as cardiovascular and respiratory
function
Together with the cerebral cortex is referred to as
the reticular activating system
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Central Nervous System
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Central Nervous System
Forebrain
Telencephalon
Cerebrum
Gyri, sulci, and fissures
Gray matter and white matter
Cerebral nuclei (basal ganglia)
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Forebrain
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Forebrain
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Central Nervous System
Diencephalon
Epithalamus
Thalamus
Hypothalamus
Subthalamus
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Central Nervous System
Midbrain
Corpora quadrigemina (tectum)
Tegmentum
Superior and inferior colliculi
Red nucleus and substantia nigra
Basis pedunculi
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Central Nervous System
Hindbrain (metencephalon)
Cerebellum
Pons
Myelencephalon
Medulla oblongata
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Central Nervous System
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Spinal Cord
Lies within the vertebral canal and is
protected by the vertebral column
Connects the brain and the body
Conducts somatic and autonomic reflexes
Provides motor pattern control centers
Modulates sensory and motor function
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Spinal Cord
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Spinal Cord
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Spinal Cord
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Reflex Arc
Receptor
Afferent (sensory) neuron
Efferent neuron
Effector
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Reflex Arc
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Upper and Lower Motor Neurons
Upper motor neurons
Efferent pathways primarily relaying information
from the cerebrum to the brain stem or spinal
cord
Synapse with interneurons
Lower motor neurons
Neurons having direct influence on muscles
Cell bodies originate in the gray matter of the
spinal cord, but their axons extend into the PNS
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Neuromuscular Junction
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Motor Pathways
Lateral corticospinal
Corticobulbar
Basal ganglia
Vestibulospinal
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Sensory Pathways
Anterior spinothalamic
Lateral spinothalamic
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Protective Structures
Cranium
Eight bones
Frontal
Occipital
Temporal (2)
Parietal (2)
Sphenoid
Ethmoid
Galea aponeurotica
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Protective Structures
Meninges
Protective membranes surrounding the brain and
spinal cord
Dura mater
Arachnoid
Pia mater
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Meninges
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Protective Structures
Cerebrospinal fluid (CSF) and the ventricular
system
CSF is a clear, colorless fluid similar to blood
plasma and interstitial fluid
125 to 150 mL
Produced by the choroid plexuses in the lateral,
third, and fourth ventricles
Reabsorbed through the arachnoid villi
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Protective Structures
Vertebral column
33 vertebrae
7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4
fused coccygeal
Intervertebral disks
Nucleus pulposus
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Vertebral Column
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Vertebral Column
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Blood Supply to the Brain
800 to 1000 mL per minute
CO2 is the primary regulator for CNS blood
flow
Internal carotid and vertebral arteries
Arterial circle (circle of Willis)
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Blood Supply to the Brain
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Blood Supply to the Brain
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Blood Supply to the Brain
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Blood Supply to the Brain
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Blood Supply to the Spinal Cord
Vertebral arteries
Anterior spinal arteries
Posterior spinal arteries
Aorta
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Blood Supply to the Spinal Cord
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Peripheral Nervous System
31 pairs of spinal nerves
Names correlate with the vertebral level from
which they exit
Mixed nerves
Arise from the anterior and posterior horn cells of
the spinal cord
12 pairs of cranial nerves
Sensory, motor, and mixed
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Peripheral Nervous System
Fascicles
Rami
Plexuses
Bundles of myelinated axons in the PNS
Brachial plexus
Lumbar plexus
Sacral plexus
Dermatomes
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Peripheral Nervous System
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Autonomic Nervous System
Located in both the CNS and PNS
Coordinates and maintains a steady state among the
visceral (internal) organs
Neurons
Preganglionic (myelinated)
Postganglionic (unmyelinated)
Two divisions
Sympathetic
Parasympathetic
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Sympathetic Nervous System
Mobilizes energy stores in times of need
Receives innervation from cell bodies located
from the first thoracic through the second
lumbar
“Fight or flight response”
Thoracolumbar division
Sympathetic (paravertebral) ganglia
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Sympathetic Nervous System
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Parasympathetic Nervous System
Functions to conserve and restore energy
Receives innervation from cell bodies located
in the cranial nerve nuclei and sacral region of
the spinal cord
“Rest or repose response”
Craniosacral division
Preganglionic neurons travel to ganglia close
to the organs they innervate
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Parasympathetic Nervous System
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Neurotransmitters and
Neuroreceptors of the ANS
Sympathetic preganglionic fibers
Sympathetic postganglionic fibers
Acetylcholine and cholinergic receptors
Norepinephrine and adrenergic receptors
Parasympathetic pre- and postganglionic
fibers
Acetylcholine and cholinergic receptors
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Neurotransmitters and
Neuroreceptors of the ANS
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Aging and the Nervous System
Decrease in the number of neurons
Decreased brain weight and size
Senile plaques
Neurofibrillary tangles
Slowing of neurologic responses
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Tests of Nervous System Function
Skull and spine roentgenograms
Computed tomography
Magnetic resonance imaging
Magnetic resonance angiography
Positron emission tomography scan
Brain scan
Cerebral angiography
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Tests of Nervous System Function
Myelography
Echoencephalography (ultrasound)
Electroencephalography
Evoked potentials
Cerebrospinal fluid analysis
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