Special Project in Biology

2. NERVOUS SYSTEM
 Nervous system is the chief
controlling and coordinating
system of the body. It controls
and regulates all activities of the
body, whether voluntary or
involuntary, and adjusts the
individual (organism) to the given
surroundings.

3.  The basic working unit of the nervous
system is a cell called a neuron. The
human brain contains about 100 billion
neurons. A neuron consists of a cell
body containing the nucleus, and special
extensions called axons (pronounced
AK-sonz) and dendrites (pronounced
DEN-drahytz).
 Nerves are cylindrical bundles of fibers
that start at the brain and central cord
and branch out to every other part of the
body.

4. WHAT ARE THE PARTS OF
THE NERVOUS SYSTEM?
The nervous system consists of two main
parts:
 Central nervous system
 Peripheral nervous system

5. CENTRAL NERVOUS
SYSTEM
 The central nervous system
is made up of the brain and
spinal cord.
 The brain sends messages
through the spinal cord and
nerves of the peripheral
nervous system to control
the movement of the
muscles and the function of
internal organs.

6. BRAIN
 The brain is the center of our thoughts,
the interpreter of our external
environment, and the origin of control
over body movement. Like a central
computer, it interprets information from
our eyes (sight), ears (sound), nose
(smell), tongue (taste), and skin (touch),
as well as from internal organs such as
the stomach.

7. PARTS OF THE BRAIN
 The cerebrum is the largest
part of the brain and is
composed of right and left
hemispheres. It performs
higher functions like
interpreting touch, vision and
hearing, as well as speech,
reasoning, emotions,
learning, and fine control of
movement.
 The cerebellum is located
under the cerebrum. Its
function is to coordinate
muscle movements,
maintain posture, and
balance.
 The brainstem acts as a
relay center connecting the
cerebrum and cerebellum to
the spinal cord. It performs
many automatic functions.

8. SPINAL CORD
 The spinal cord is the highway for
communication between the body and
the brain. When the spinal cord is
injured, the exchange of information
between the brain and other parts of the
body is disrupted.

9. PERIPHERAL NERVOUS
SYSTEM
 The peripheral nervous
system is made up of
sensory neurons, ganglia
(clusters of neurons) and
nerves that connect to
one another and to the
central nervous system.

10. The peripheral nervous system is divided into the
somatic and the autonomic nervous system.
SOMATIC NERVOUS SYSTEM
 The somatic nervous system is under
voluntary control, and transmits signals from
the brain to end organs such as muscles. The
sensory nervous system is part of the somatic
nervous system and transmits signals from
senses such as taste and touch (including
fine touch and gross touch) to the spinal cord
and brain. The autonomic nervous system is
a 'self-regulating' system which influences the
function of organs outside of voluntary
control, such as the heart rate, or the
functions of the digestive system.

11. AUTONOMIC NERVOUS SYSTEM
 The autonomic nervous system controls
involuntary responses to regulate
physiological functions. The brain and spinal
cord from the central nervous system are
connected with organs that have smooth
muscle, such as the heart, bladder, and
other cardiac, exocrine, and endocrine
related organs, by ganglion neurons. The
most notable physiological effects from
autonomic activity are pupil constriction and
dilation, and salivation of saliva. The
autonomic nervous system is always
activated, but is either in the sympathetic or
parasympathetic state.

12. SYMPATHETIC NERVOUS SYSTEM
 The sympathetic system is activated during a “fight or flight”
situation in which great mental stress or physical danger is
encountered. Neurotransmitters such as nor epinephrine,
and epinephrine are released, which increases heart rate and
blood flow in certain areas like muscle, while simultaneously
decreasing activities of non-critical functions for survival, like
digestion. The systems are independent to each other, which
allows activation of certain parts of the body, while others
remain rested.
PARASYMPATHETIC NERVOUS SYSTEM
 Primarily using the neurotransmitter acetylcholine (ACh) as a
mediator, the parasympathetic system allows the body to
function in a “rest and digest” state. Consequently, when the
parasympathetic system dominates the body, there are
increases in salivation and activities in digestion, while heart
rate and other sympathetic response decrease. Unlike the
sympathetic system, humans have some voluntary controls
in the parasympathetic system. The most prominent
examples of this control are urination and defecation.

13. PARASYMPATHETI
C
Body at rest
SYMPATHETIC
Emergency situations
Eyes Constricts pupils Dilates pupils
Heart Beat more slowly Beats faster and stronger
Lungs Constricts airways Relaxes airways, which
lets you breathe more
deeply
Digestion Stimulates digestion Inhibits digestion
Muscles Reduces blood flow to
skeletal muscles
Increases blood flow to
skeletal muscles