The Nervous System Part II
Objectives:
• Describe and recognize nervous
system structures in other organisms
• Understand and explain the
structures and functions of the
central nervous system.
• Identify the major structures within the
brain.
How do single celled organisms such
as the amoeba respond to stimuli?
• The image on the left
shows an amoeba
engulfing a bacteria by
phagocytosis.
• How is it that the
amoeba can detect,
chase, and engulf its
prey without any
nervous system
structures?
Response to stimuli in single celled
organisms is achieved by membrane
receptors.
• Single celled organisms such as protists and bacteria
can detect changes in their environment and respond
to stimuli using receptor proteins embedded in their
cell membranes.
• For example, an amoeba can follow a bacteria based
on the trail of metabolic wastes the bacteria is giving
off.
• These waste molecules bind to the amoeba’s
chemoreceptors allowing the amoeba to chase and
capture the bacteria. This is called chemotaxis
Evolution of a nervous system
Nerve Net in Hydra and Jellyfish
• The nervous system of
the hydra and jellyfish is
in the form of an irregular
network of neurons called
a nerve net.
• This nerve net allows the
muscles of the hydra to
move in a coordinated
manner.
The Nervous System of the Earthworm
is a Bit More Complex
• The earthworm has a central nervous
system and a peripheral nervous system.
• The central nervous system is made up of
a primitive brain connected to a pair of
nerve cords.
• The nerve cords connect to a ganglion in
each segment.
• A ganglion is a ―mini-brain‖ made up of
interneurons that switch, relay, and
coordinate nerve impulses.
Earthworm regulation
• The peripheral nervous
system of the
earthworm is made up
of nerves branching off
of the cns to all parts of
the worm’s body.
• The earthworm
contains sensory and
motor neurons.
• They have specialized
structures for detecting
light, chemicals,
vibration and heat.
Regulation in the grasshopper
• The nervous system of the grasshopper is
similar to that of the earthworm.
• The CNS is made up of a brain in the head
region, nerve cords that run the length of the
body, and ganglia.
• Peripheral nerves branch from the ganglia to all
other parts of the body.
• Sense organs of the grasshopper are more
highly developed than that of the earthworm.
Terms you will need to
define and know.
- Central Nervous System - Hypothalamus
- Peripheral Nervous System - Reflex
- Meninges - Gray matter
- Cerebrospinal Fluid - White matter
- Cerebrum - Ganglia
- Cerebral Cortex
- Cerebellum
-Brain Stem
- Thalamus
Two Divisions of the Human
Nervous System
• Neurons do not act alone. Instead they
are joined together to form a complex
network—the nervous system. The
nervous system is separated into two
major divisions.
1. The Central Nervous System (CNS)
2. The Peripheral Nervous System (PNS)
The Central Nervous System
• Consists of the brain
and the spinal cord.
• The skull protects the
brain and the
vertebrae protect the
spinal cord
• Both the brain and
spinal cord are
wrapped in three layers
of connective tissue
called meninges.
Meninges and Cerebrospinal Fluid
• There are three
layers of meninges
that surround and
protect the brain and
spinal cord.
• Between two of the
layers is a space
filled with
cerebrospinal fluid
which acts as a shock
absorber for the CNS.
Blood Brain Barrier
• Contains
extensive
capillaries
• Protects
brain: Limits
what can
contact the
brain and
what cannot.
• Contains
many glucose
transporters
Summary of CNS Protective Structures
• Skull and Vertebrae
• 3 Layers of Meninges
• Cerebrospinal Fluid
• Blood-Brain Barrier
The Brain
• The brain is the main processing area
of the Central Nervous System.
• The brain helps to relay messages,
process and analyze information.
• The brain consists of:
–Cerebrum
–Cerebellum
–Brain stem
The Brain
The Cerebrum
• The cerebrum is the largest and most
prominent region of the human brain.
• It is responsible for the voluntary, or
conscious activities of the body.
• It is the site of intelligence, learning, and
judgment.
• A deep groove divides the cerebrum into
right and left hemispheres.
• Corpus callosum is the band of tissues
that connects the two hemispheres
The Cerebrum
• Each half of the
cerebrum deals mainly
with the opposite side of
the body.
• The right hemisphere is
thought to be associated
with artistic ability and
creativity.
• The left hemisphere
may be associated with
mathematical ability,
logic, and analysis.
The Cerebrum
• Folds and groves
on the surface of
each hemisphere
greatly increase
the surface area of
the cerebrum.
• Each hemisphere
of the cerebrum is
divided into lobes.
The lobes are
named for the
bones of the skull
that cover them.
The Cerebrum – Cerebral Cortex
• The cerebrum consists of two surfaces.
The outer surface of the cerebrum is
called the cerebral cortex and consists
mostly of gray matter.
• Gray matter consists mainly of densely
packed neuron cell bodies.
• The cerebral cortex processes
information from the sense organs and
controls body movements
The Cerebrum
• The inner surface of the cerebrum
consists of white matter, which is
made up of bundles of axons with
myelin sheaths.
• The myelin sheaths give the white
matter its characteristic color.
White Matter and Gray Matter
The Cerebellum
• The second largest region of the brain is
the cerebellum, which is located in the
back of the skull.
• Although the commands to move muscles
come from the cerebral cortex, the
cerebellum coordinates and balances the
actions of the muscles so the body can
move gracefully and efficiently.
The Brain Stem
• The brain stem connects the brain and
the spinal cord.
• The brain stem consists of two regions,
the pons and the medulla oblongata.
• Each of these regions acts as a neural
―switchboard‖ regulating the flow of
information between the brain and the rest
of the body.
• Blood pressure, heart rate, breathing, and
swallowing are controlled by the brain
stem.
Thalamus and Hypothalamus
• Thalamus: receives
messages from the sense
organs and relays
information to the cerebrum
for processing.
• Hypothalamus: control
center for recognition and
Thalamus
analysis of hunger, thirst,
Hypothalamus fatigue, anger, and body
temperature.
Summary of Brain Structures
The Spinal Cord
• The spinal cord is the major nerve pathway to
and from the brain.
• It is protected by the vertebral column and the
meninges.
• 31 pairs of spinal nerves branch out from the
spinal cord, connecting the brain to the body.
• Certain kinds of information, such as reflexes,
are processed directly in the spinal cord.
• A reflex is a quick, automatic response to a
stimulus. It allows the body to respond to
danger immediately.
The Spinal Cord