Transcript Chapter 8 - Cloudfront.net

Chapter 23
The Nervous System
Outline of the Nervous System
The nervous system is divided into two
major parts:
1. The central nervous system
2. The peripheral nervous system
Central Nervous System
• Consists of the brain and spinal cord
• The brain is the principal organ of the
nervous system
• The brain weighs only about three pounds
• The brain communicates to the body
through the spinal cord.
Central Nervous System
• The spinal cord has nerves attached to it
• There are 31 pairs of spinal nerves and
serve to transmit to and from the body all
information
• There are 12 pairs of cranial nerves which
branch from the brain stem to send signals
to the eyes, ears, mouth, face, and scalp.
Central Nervous System
• The spinal cord and brain are covered by
a triple protection layer of tissues called
meninges
• The outer layer is the dura mater
• The middle layer is the arachnoid
• The inner layer is the pia mater
Central Nervous System
• Cerebrospinal fluid circulates through the
fibers of the arachnoid to cushion the
brain.
Central Nervous System
The brain and spinal cord is made of two
types of cells:
1. Glial cells – support/protect nerve tissue
2. Neurons – actual nerve cells
Neurons
• The cell body of each
neuron contains a
nucleus and
cytoplasm.
• Extending from the
cell body are
dendrites and axons
Neurons
• Dendrites receive
nerve impulses
• Axons send nerve
impulses
Neurons
• Gray matter – found
within the brain
• Gray matter consists
largely of cell bodies
• White matter of the
brain is composed of
axons and glial cells.
• White matter is white
because is has myelin
(a fatty covering)
Neurons
• Nerve cell bodies are found only in the
brain, the spinal cord, or in a ganglion
• A ganglion is a mass of cell bodies
• Ganglion in a large mass are called a
plexus
• You have a plexus in the back of the neck
and shoulder
Neurons
• A group of nerve cells in the brain or spinal
cord is a nerve center.
• The nerve center in the medulla oblongata
of the brain stem controls your breathing.
Neurons
There are three types of neurons:
1. Sensory neurons –transmit info from the
senses (and pain as well)
2. Motor neurons – relay info to body from the
central nervous system
3. Interneurons – relay signals between neurons
or groups of neurons – responsible for
processing info in the brain
Peripheral Nervous System
•
•
•
•
Consists of nerves
The twelve nerves branching from brain
The thirty-one pairs of spinal nerves
Most nerves contain both sensory and
motor nerves
Sensory Nerve Fibers
• Sensory nerve fibers carry messages of
light, taste, sound, touch, and pain from
other parts of the body to the spinal cord
and brain for analysis.
• Motor nerve fibers carry messages of
action from the brain and spinal cord to the
muscles and organs.
Nerves and How They Work
• Nerve cells – unlike other cells of the
body, neurons do not reproduce.
• When a nerve cell dies it is not replaced
Nerves and How They Work
• The axons that extend from the nerve cell
bodies in peripheral nerves are
surrounded by special glial cells called
Schwann cells which produce layers of
myelin sheath.
• The myelin sheath has gaps called “nodes
of Ranvier”
Transmitting a nerve Impulse
The Brain
The brain has three parts:
1. The cerebrum – upper brain – coordinates
thought, memory, and learned behaviors
2. The cerebellum – lower part of the brain –
controls balance and coordinates voluntary
muscle activity
3. The brain stem – connects spinal cord –
controls the involuntary muscles and activities
of autonomic nervous system.
Cerebrum
The cerebrum is the largest part of your
brain and is the physical organ that helps
you in the areas of
Consciousness
Memory
Voluntary Action
Thinking
Intelligence
Cerebrum
The cerebrum consists of two halves:
The right hemisphere
The left hemisphere
They are spilt by a longitudinal fissure (a deep groove)…
The left side of the hemisphere is connected to the right
side of the body…
The right side of the hemisphere is connected to the left
side of the body…
Cerebrum
• The two sides of the cerebrum are not
equal or identical…they perform different
functions…
• The left seems to specialize in details,
known procedures and logic…
• The right seems to specialize in “the big
picture”…creativity, intuitive approach to
problems…
Cerebrum
The two hemispheres
communicate with
each other through a
mass of nerve fibers
called the corpus
callosum, located in
the base of the
cerebrum.
Cerebrum
The cerebrum consists
of two layers:
1. Grey matter
2. White matter
Cerebrum
The brains grey matter
is located in the
cerebral cortex…the
outer layer of the
cerebrum.
Cerebrum
Cerebral lobes: the convolutions of each of
the cerebral hemispheres are divided by
shallow grooves into various regions, or
lobes…
They are:
1. the frontal lobe
2. the parietal lobes
3. the temporal lobes
4. the occipital lobes
Cerebrum
1. Frontal Lobes:
Associated with
personality, judgment,
and self control
Rear portion
called motor area – it
controls the voluntary
movement of skeletal
muscle.
Cerebrum
2. Parietal Lobes:
Behind frontal
lobe – analyses
sensations (touch and
pain)
Cerebrum
3. Occipital Lobes
Vision is
interpreted here
Located in back of
brain
Cerebrum
4. Temporal Lobes
Associated with
senses of hearing,
taste, and touch
Cerebellum
• Second largest part of the brain
• Lies behind the brain stem and below
occipital lobe
• It is divided into a left and right
hemisphere
• Like the cerebrum it is organized into grey
and white matter
Cerebellum
• The function of the
cerebellum is to
coordinate skeletal
muscle activity.
Cerebellum
• The cerebellum is trained to operate your
muscles habitually.
• Most complex muscle coordination is
handled by the cerebellum.
• Damage to the cerebellum means even
the simplest tasks are difficult.
Brain Stem
• Located between the cerebellum and the
spinal cord.
• The brain stem has three parts:
The medulla oblongata
The pons
The midbrain
Brain Stem
Medulla Oblongata
The lowest part of
the brain stem.
Monitors and
regulates breathing,
heartbeat, blood
pressure, and other
bodily functions.
Brain Stem
The Pons
Links cerebrum
and cerebellum
Assists in
breathing regulation
Coordinates some
eye movement and
facial expressions
Brain Stem
The Midbrain
Adjust the eye
pupils in response to
light…
Operate lens
muscles to focus
eyes…
Brain Stem
The reticular formation
Serves as the
master switch of the
cerebrum
It brings you to
consciousness