2. HOW DOES THE NERVOUS SYSTEM COORDINATES AND
REGULATE FEEDBACK MECHANISMS TO MAINTAIN
HOMEOSTASIS?
• Our nervous system helps us receive information about what is
happening inside and around us and directs us to respond
appropriately to a given situation.
• This concrete example below shows that the body has the ability to
control and coordinate the activities of all its parts. This
characteristics is due to the presence of two organ systems, the
nervous and endocrine systems. The nervous system enables the
body to gather information from the outside environment and
respond quickly. The endocrine system on the other hand, although
slow in terms of response, produces longer-lasting effects due to the
hormones. These systems interact to coordinate the body’s activities.
3.
4. FUNCTIONS OF THE NERVOUS SYSTEM
• The nervous system controls and interprets all the activities that happen
within the body. It enables us to move, think, laugh, feel pain, or enjoy the
taste of food. It makes the body respond quickly to changes in the
environment by accomplishing four basic functions.
5. NEURON:
THE MESSAGE-CARRYING UNIT OF
THE NERVOUS SYSTEM
• The nervous system is constantly alive with activity. It buzzes with messages that
run to and from all parts of the body.
• Every second, hundreds of these messages are carried by strings of special cells
called neurons or nerve cells.
• Neurons are the basic functional units of structure and function of the nervous
system. They carry information through the nervous system in the form of nerve
impulses.
• Neurons are unique because, unlike most other cells in the body, they do not
reproduce. Once damaged, neurons cannot be replaced. This is not a cause for
concern, however, because the neurons we are born with are more than enough for
a lifetime.
6. PARTS OF A NEURON
• The cell body contains the nucleus (a large dark
structure), which controls all the activities of the cell.
Think of the cell body as switchboard of the
messages-carrying neuron.
• Running into this switchboard are one or more tiny,
branching, threadlike structures called dendrites,
which receive and carry information toward the cell
body.
• A long, tail-like fiber that extends from the cell body,
called axon, carries messages away from the cell
body.
• The myelin sheath covers the axon, which speeds up
the travel of the nerve impulses. Each neuron has
only one axon, but it can have many dendrites.
• The axon splits into many featherlike fibers, called
axon terminals (ends), at the far ends. Axon terminals
pass on messages to the dendrites of other neurons.
7. TYPES OF NEURONS
• Sensory Neurons are also called afferent neurons because their function is to
receive initial stimuli from the sense organs, where most receptors are
located. The sensory neuron’s goal is to transmit the nerve impulses to the
spinal cord and ultimately, to the brain so an action can be taken.
• Interneurons are called connector neurons or association neurons. They read
impulses received from sensory neurons. When an interneuron receives an
impulse from a sensory neuron, the interneuron determines what response
should be generated. If a response is required, the interneuron passes the
impulse on to the motor neurons.
• Motor neurons are also called efferent neurons, transmit impulses from the
brain and spinal cord to the effector cells, which may be those of muscles,
organs or glands. When motor neurons receive a signal from the interneuron,
they stimulate the effector cells to generate the reaction for the stimulus.
8. NERVE IMPULSES
• A nerve impulse is a wave of chemical and
electrical change that is conducted along the
membrane of a neuron. It travels from sensory
neuron to interneuron to motor neuron.
• When a nerve impulse travels along a neuron or
from one neuron to another, it does so in the
form of electrical and chemical signals. The
nerve impulse enters the neuron through the
dendrites and travels along the length of the
axon.
• The way in which a nerve impulse travels from
one neuron to another is a bit complex. Neurons
do not touch each other, neither do they touch
effector organs. Instead, there is a tiny gap
called a synapse between two adjacent neurons,
and also between neurons and effectors.
9. NERVE IMPULSES
• A nerve impulse is “ferried” across the
synapse by a chemical signal. This
happens when an impulse reaches the end
of the axon, sending information across
the synapse in the form of chemical
messengers called neurotransmitters,
which are stored in small sacs.
• When a nerve impulse reaches the axon
terminal, the sacs fuse with the axon’s
membrane and releases its
neurotransmitter molecules into the
synapse.
• The molecules then diffuse across the
synapse and bind to receptors on the next
neuron or effector cell.
11. DIVISIONS OF THE NERVOUS
SYSTEM
The nervous system is
divided into two main parts:
the central nervous
system and the peripheral
nervous system.
The two divisions of the
nervous system working
together as a team that
monitors, coordinates, and
controls the activities of the
entire body.
13. CENTRAL NERVOUS SYSTEM
The central nervous system is the
command center for the entire
body; it processes information and
sends instructions to other parts of
the body.
All the information gathered by
sensory receptors is delivered to
the central nervous system in the
form of nerve impulses.
The CNS processes the
information and responds by
sending nerve impulses to the
14. CENTRAL NERVOUS SYSTEM
Interpreting the information that pours in
from all parts of the body and issuing
the appropriate commands to these
very same parts are the responsibility of
the two parts of the central nervous
system: the brain and the spinal cord.
The brain is the main control center of
the central nervous system. It transmits
and receive messages through the
spinal cord.
The spinal cord provides the link
between the brain and the rest of the
body.
15. THE BRAIN
Being a very important and delicate
organ, the brain is well protected and
encased in a bone called skull.
The brain is bathed with a watery fluid
that cushions it against sudden impact,
such as when one bumps the head or
experience a nasty fall.
It appears gray because of the
presence of the cell bodies of
approximately 100 billion neurons.
Despite the presence of billions of
neurons, the mass of the brain is about
1.4 kilograms only.
16. THE BRAIN
The brain is divided
into three main parts:
the cerebrum,
cerebellum and
brain stem.
17. THE CEREBRUM
It makes up 85% of the human
brain.
The surface of the cerebrum is
called the cerebral cortex, which
is lined with the deep, wrinkled
grooves that increase the surface
area so that more thinking
activities can occur.
This is the area where learning,
intelligence and judgment occur.
Aside from the this enormous
19. THE CEREBELLUM
The cerebellum is the second
largest part of the brain and is
located behind the brain stem.
It coordinates the actions of the
muscles and maintains balance
so that the body can move
smoothly, steadily and
effectively.
Balance, equilibrium and
posture are made possible by
the cerebellum.
20. THE BRAIN STEM
The brain stem connects the
spinal cord to the rest of the
brain.
It coordinates many survival
functions of the body such as
breathing, heart rate, sleep and
wakefulness.
Three distinct regions make up
the brain stem: the midbrain, the
21. THE BRAIN STEM
The medulla oblongata controls
involuntary actions such as
heartbeat, breathing and blood
pressure.
The midbrain processes visual
and auditory reflexes.
The pons helps control
respiratory functions.
22. THE BRAIN STEM
The thalamus serves as a relay
station by directing incoming
messages from the spinal cord to
the appropriate parts of the brain.
The hypothalamus monitors
internal conditions such as water
content and temperature. It acts
as the link between the
endocrine and nervous systems.
23. THE SPINAL CORD
The spinal cord is a tube-like
organ of neurons and blood
vessels.
Located inside the backbone, or
spine, the spinal cord is about
1.8 cm wide, nearly the same
size as a garden hose.
Aside from the bones of the
spine, three membranes called
meninges, cushions of fluid,
protect the spinal cord.
24. THE SPINAL CORD
The spinal cord relays nerve
impulses to and from the brain.
Impulses from the peripheral
nervous system are conducted
to the spinal cord, which then
brings the message to the brain.
The brain, in turn, sends
impulses down the spinal cord to
the motor nerves of the
peripheral nervous system.
25. THE SPINAL CORD
The neurons, in a pathway
called the reflex arc, carry the
nerve impulses for an automatic
response.
A reflex that does not involve the
brain is called a spinal reflex,
which enables us to respond
quickly because we do not have
to think about it.
26. THE SPINAL CORD
The reflex arc when we remove our hand from
a hot object.
28. PERIPHERAL NERVOUS
SYSTEM
The Peripheral Nervous System is the
link between the central nervous system
(brain and spinal cord) to the rest of the
body.
It is made up of a network of bundled
ropelike structures called nerves, which
extend or branch out from the central
nervous system to the different organs
of the body.
The PNS gathers and delivers
29. PERIPHERAL NERVOUS
SYSTEM
The Peripheral Nervous System
consists of 43 pairs of nerves that arise
from the brain and spinal cord, leading
to organs throughout the body.
Many of the nerves in the PNS are
under the direct control of the conscious
mind.
The PNS is divided into two parts: the
Somatic Nervous System and the
Autonomic Nervous System.
30. SOMATIC NERVOUS SYSTEM
The part of the PNS that
stimulates skeletal muscles
under our conscious control is
called the somatic nervous
system.
Its main parts are the cranial
nerves and the spinal
nerves.
31. AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system
controls body activities that are
involuntary; that is, those that
happen automatically, without our
thinking about them.
It directs motor nerve fibers in
smooth muscles, cardiac muscles
and the glands.
Contractions of the heart muscle
and movement of smooth muscles
surrounding the small intestine are
activities under the control of
32. DIVISIONS OF THE AUTONOMIC NERVOUS
SYSTEM
The autonomic nervous system
can be further divided into two
groups that have opposite
effects on the organs they
control.
These two divisions- the
parasympathetic and the
sympathetic – maintain stability
in the body by working against
33. DIVISIONS OF THE AUTONOMIC NERVOUS
SYSTEM
The parasympathetic division is
most active under normal
conditions; it keeps the body
functioning even when the
person is not active.
It controls the “fight-or-flight”
response during a stressful
situation like the nervousness
we experience when speaking
34. DIVISIONS OF THE AUTONOMIC NERVOUS
SYSTEM
The sympathetic division
increases blood pressure, heart
rate, and breathing rate.
Such an increase may be
necessary if extra energy and
strength are needed to deal with
the stressful situation. But when
the situation is over, the
parasympathetic nerves bring
the blood pressure, breathing
