Transcript Biology of Humans 2/e

The Nervous
System
The Brain
Copyright © 2007 Pearson Prentice Hall, Inc.
Overview: The nervous system is composed of both the CNS & PNS
The Central Nervous System
• The brain and spinal
cord are protected by
the bones of the
vertebral column and
skull, three connective
tissue membranes that
form the meninges,
and cerebrospinal
fluid
• Inflammation of the
meninges is called
meningitis
The Brain
• The cerebrum consists of two hemispheres which receive
sensory information from and direct the movements of
the opposite side of the body
The corpus callosum
connects the two
cerebral hemispheres
• The sensory, motor, and association areas are in the cerebral cortex
• The primary somatosensory area receives sensory information
from the body while the primary motor area controls the skeletal
muscles
The Brain
• Association areas communicate with the
sensory and motor areas, and with other
parts of the brain
• The most complex of these areas is the
prefrontal cortex which enables us to
reason and think in the abstract
• The thalamus is the relay station of the brain for
all sensory information except smell. It also
directs motor activity, cortical arousal and
memory
• The hypothalamus
maintains homeostasis by
regulating blood pressure,
heart rate, breathing rate,
digestion and body
temperature
• The hypothalamus
coordinates the nervous and
endocrine systems through
its connection to the
pituitary gland
– It is a center for
emotions and serves as
the master biological
clock
• The cerebellum integrates information from
the motor cortex and sensory pathways to
produce movements
– It also stores memories of learned motor skills.
• The medulla oblongata contains reflex centers to regulate the rhythm
of breathing, force and rate of the heartbeat, and blood pressure
– It serves as the pathway for all sensory messages to the higher
brain centers and motor messages leaving the brain
• The limbic system, which includes several brain
structures, is largely responsible for emotions
•The reticular
activating system
(RAS) filters sensory
input and keeps the
cerebral cortex in an
alert state (Green
arrows)
The spinal cord
conducts messages
between the brain
and the body and
serves as a reflex
center
• Spinal nerves arise
from the cord and
exit through the
openings between the
stacked vertebrae of
the vertebral column
The Spinal
Cord
• A reflex action is an
automatic response
to a stimulus in a
pre-wired circuit
called a reflex arc
The Peripheral Nervous System
• The body has 31 pairs of spinal nerves
The Peripheral Nervous System
• The body has12 pairs of cranial nerves
The Peripheral Nervous System
• The peripheral nervous system includes
the sensory receptors, the peripheral nerves
and ganglia, and specialized motor endings
that stimulate the effectors
The Peripheral Nervous System
• The peripheral nervous system is divided
into the somatic nervous system, which
governs conscious sensations and voluntary
movements, and the autonomic nervous
system, which is concerned with our
unconscious, involuntary internal activities
The Peripheral Nervous System
• The autonomic nervous system can be
divided into the sympathetic and
parasympathetic nervous systems, two
branches with antagonistic actions
The Peripheral Nervous System
• The sympathetic nervous system gears up
the body for stressful or emergency
situations while the parasympathetic
nervous system adjusts body functioning so
that energy is conserved during nonstressful
times
Disorders of the Nervous System
Vary in Health Significance
• Headaches are usually caused by tension in
the neck or by dilation of the blood vessels
of the head
• Migraine headaches are caused by an
imbalance in the brain’s chemistry
Disorders of the Nervous System
• A stroke results when the brain is deprived
of blood and nerve cells die
• The extent and location of the damage
caused by a stroke depends on the affected
region of the brain
Disorders of the Nervous System
• A coma is caused by trauma to neurons in
regions of the brain responsible for
stimulating the cerebrum
• A comatose person is totally unresponsive
to all sensory input and cannot be awakened
Disorders of the Nervous System
• A spinal cord injury results in loss of
function below the site of injury