Download nervous system

Memmler’s
The Human Body in Health and Disease
11th edition
Chapter 9
The Nervous System: The
Spinal Cord and Spinal Nerves
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Role of the Nervous System
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
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Structural Divisions
•Central nervous system (CNS)
– Brain
– Spinal cord
•Peripheral nervous system (PNS)
– Cranial nerves
– Spinal nerves
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Anatomic
divisions of
the nervous
system.
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Functional Divisions
Somatic nervous system
•Controlled voluntarily
•Effectors are skeletal muscles
•No further subdivisions
Autonomic (or visceral) nervous system (ANS)
•Controlled involuntarily
•Effectors are smooth muscle, cardiac muscle, and glands
•Subdivided into
–
Sympathetic nervous system
–
Parasympathetic nervous system
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Neurons and Their Functions
Neurons
•Functional cells of nervous system
•Highly specialized
•Unique structure
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Diagram of a motor
neuron. The break in
the axon denotes
length. The arrows
show the direction of
the nerve impulse.
ZOOMING IN
• Is the neuron shown
here a sensory or a motor
neuron?
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Structure of a Neuron
Cell body
•Nucleus
•Other organelles
Cell fibers
•Dendrites
•Axons
– Some are protected by myelin sheath
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Formation of a
myelin sheath.
(A)Schwann cells
wrap around the
axon, creating a
myelin coating.
(B) The outermost
layer of the Schwann
cell forms the
neurilemma.
Spaces between the
cells are the nodes
(of Ranvier).
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Types of Neurons
•Sensory neurons (afferent neurons)
– Conduct impulses to spinal cord, brain
•Motor neurons (efferent neurons)
– Conduct impulses to muscles, glands
•Interneurons (central or association neurons)
– Conduct information within CNS
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Nerves and Tracts
•Nerve: fiber bundle within PNS
•Tract: fiber bundle within CNS
•Organized into fascicles
•Connective tissue layers
– Endoneurium
– Perineurium
– Epineurium
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Neuroglia
Neuroglia (glial cells)
•Protect and nourish nervous tissue
•Support nervous tissue
•Aid in cell repair
•Remove pathogens and impurities
•Regulation composition of fluids around and between cells
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The Nervous System at Work
Electrical impulses sent along neuron fibers and
transmitted between cells at junctions
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The Nerve Impulse
•Plasma membrane carries electrical charge (potential)
•Plasma membrane is polarized (negative charge)
•Membrane potential reverses, generates electrical charge
(action potential)
– Resting state
– Depolarization
– Repolarization
• Sodium/potassium (Na+/K+) pump
•Myelin sheath speeds conduction
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The Synapse
Junction point for transmitting nerve impulse
•Axon (presynaptic cell)
•Dendrite (postsynaptic cell)
•Synaptic cleft
•Neurotransmitters
– Epinephrine (adrenaline)
– Norepinephrine (noradrenaline)
– Acetylcholine
•Receptors
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Neurotransmitters and Psychoactive Drugs
•Psychoactive drugs affect neurotransmitter activity in the
brain
•Used to treat depression, anxiety, obsessive-compulsive
disorder (OCD)
•Selective serotonin reuptake inhibitors (Example: Prozac)
– Block serotonin uptake
•Others block norepinephrine, dopamine.
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A synapse.
(A)The end-bulb of the
presynaptic
(transmitting) axon
has vesicles containing
neurotransmitter,
which is released into
the synaptic cleft to
the membrane of the
postsynaptic
(receiving) cell.
(B) Close-up of a
synapse showing
receptors for
neurotransmitter in
the postsynaptic cell
membrane.
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The Spinal Cord
•Links PNS and brain
•Helps coordinate impulses within CNS
•Contained in and protected by vertebrae
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Spinal cord and
spinal nerves. Nerve
plexuses
(networks) are
shown.
(A) Lateral view.
(B) Posterior view.
ZOOMING IN
• Is the spinal cord
the same length as
the spinal column?
How does the number
of cervical vertebrae
compare with the
number of cervical
spinal nerves?
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Structure of the Spinal Cord
•Unmyelinated tissue (gray matter)
– Dorsal horn
– Ventral horn
– Gray commissure
– Central canal
•Myelinated axons (white matter)
– Posterior median sulcus
– Anterior median fissure
– Ascending and descending tracts
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The spinal cord.
(A) Cross-section of the
spinal cord showing the
organization of the gray and
white matter. The roots of
the spinal nerves are also
shown.
(B) Microscopic view of the
spinal cord in cross-section
(x5).
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The Reflex Arc
•Receptor detects stimulus
•Sensory neuron transmits impulses to CNS
•CNS coordinates impulses and organizes response
•Motor neuron carries impulses away from CNS
•Effector carries out response
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Typical reflex arc. Numbers
show the sequence of
impulses through the spinal
cord (solid arrows).
Contraction of the biceps
brachii results in flexion of
the arm at the elbow.
ZOOMING IN
• Is this a somatic or an
autonomic reflex arc? What type
of neuron is located between
the sensory and motor neuron
in the CNS?
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Reflex Activities
•Simple reflex
– Rapid
– Uncomplicated
– Automatic
•Spinal reflex
– Stretch reflex
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Medical Procedures Involving the
Spinal Cord
•Lumbar puncture (spinal tap)
– Cerebrospinal fluid (CSF) removed for testing
•Drug administration
– Anesthetic (an epidural)
– Pain medication
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Diseases and Other Disorders of the
Spinal Cord
•Multiple sclerosis (MS)
•Amyotrophic lateral sclerosis
•Poliomyelitis
•Tumors
•Injuries
–
Monoplegia
–
Diplegia
–
Paraplegia
–
Hemiplegia
–
Tetraplegia
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The Spinal Nerves
•31 pairs
•Each nerve attached to spinal cord by two roots
– Dorsal root
• Dorsal root ganglion
– Ventral root
•Nerves near end of cord travel together in the cord until
each exits from its respective intervertebral foramen
•Mixed nerves
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Branches of the Spinal Nerves
•Cervical plexus
– Phrenic nerve
•Brachial plexus
– Radial nerve
•Lumbosacral plexus
– Sciatic nerve
•Dermatomes
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Dermatomes. A
dermatome is a
region of the skin
supplied by a single
spinal nerve.
ZOOMING IN
• Which spinal nerves
carry impulses from
the skin of the toes?
From the anterior hand
and fingers?
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Disorders of the Spinal Nerves
•Peripheral neuritis
•Sciatica
•Herpes zoster
•Guillain-Barré syndrome
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The Autonomic Nervous
System (ANS)
Regulates the action of glands, smooth muscles of hollow
organs and vessels, and heart muscle
•Preganglionic neuron connects spinal cord to ganglion
•Postganglionic neuron connects ganglion to effector
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Divisions of the Autonomic Nervous
System
•Sympathetic nervous system
•Parasympathetic nervous system
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Sympathetic nervous system
•Thoracolumbar area
•Collateral ganglia
– Celiac ganglion
– Superior mesenteric ganglion
– Inferior mesenteric ganglion
•Adrenergic system
•Activated in the four E’s: excitement, emergency,
embarassment, exercise
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Parasympathetic nervous system
•Arise in craniosacral areas
•Terminal ganglia
•Cholinergic system
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Autonomic nervous
system. The
diagram shows
only one side of
the body for each
division.
ZOOMING IN
• Which division of
the autonomic
nervous system has
ganglia closer to the
effector organ?
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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
PNS
•Adrenergic receptors
– Found on receptor cells of sympathetic nervous system
– Bind norepinephrine, epinephrine
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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
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