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Divisions of the
Nervous System
Unit 8: Human Body Systems
Chapter 35-3
Divisions of the Nervous
System
• 2 major divisions:
Nervous
System
Central
Nervous
System
Peripheral
Nervous System
Brain
Spinal Cord
Nerve cells
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A. The Central Nervous
System (CNS)
• Control center of the
body
• Relays messages,
processes & analyzes
information
• Made of two parts:
– Brain
– Spinal cord
• 1. The Brain
– Impulses flow to and from the brain
– 100 billion neurons, mainly
interneurons
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• 2. Spinal Cord
– Main communication
link between brain
and the rest of the
body
– Processes
information such as
reflexes
1. Protection of the CNS
• Brain and spinal cord are protected by:
• a) Bone – skull and vertebrae
• b) Meninges – layers of connective
tissue that surround the organs
• c) Cerebrospinal fluid – fluid found in
between meninges and organ
– Acts as a shock absorber
– Continually circulates around the brain
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• DISEASE: Meningitis
– Inflammation of the meninges
– Can be caused by an viral ,
bacterial or microorganism
infection
– Causes headaches, neck
stiffness, confusion, sensitivity
to light and sound
– Can be life threatening
• DISEASE: Hydrocephalus
(“water on the brain”)
– Accumulation of CSF in the brain
– Exerts pressure on the brain
causing brain damage
2. Regions of the Brain
• Regions of the Brain
– Cerebral hemispheres (Left & Right)
– Diencephalon
– Brain stem
– Cerebellum
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a. Cerebral Hemispheres
(Cerebrum)
• Left and right
hemispheres
– Left brain – logic,
language, math
– Right brain – creativity
• Connected by the
corpus callosum
(communication link
between right and
left)
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• The surface is
made of ridges
(gyri) and
grooves (sulci)
Fissures (deep grooves)
divide the cerebrum
into four lobes
1. Occipital Lobe: visual
integration
2. Parietal: spatial
knowledge, math
3. Temporal: memories,
auditory, language
4. Frontal: emotion, future
planning, judgment,
muscle movements,
language
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• Limbic System –
involved in emotion,
motivation, arousal,
memory, and learning
– Amygdala – fear
– Hippocampus –
memory formation
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b. Diencephalon
•
•
•
Relay and control center
Sits on top of brain stem
Two main parts:
– 1) Thalamus – relay
between sensory
areas and cerebrum
– 2) Hypothalumus –
regulates involuntary
responses & hormone secretions of the
pituitary gland
c. Brain Stem
• Attaches brain to spinal
cord
• Parts of the brain stem
– Midbrain – vision,
hearing, motor control
– Pons – breathing, sleep
– Medulla oblongata involuntary activities
(breathing, heart rate,
blood pressure)
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d. Cerebellum
• “Little brain” inferior
to and posterior to
cerebral cortex
• Coordination,
posture, motor
learning
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3. Spinal Cord
• Cylinder of nervous
tissue that begins at
base of brain
• Protected by the
vertebral column and
meninges
• Spinal nerves extend
from the cord
through each
vertebrae
• Main communication
link between brain
and the body
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4. Traumatic Brain Injuries & Diseases
• Concussion
– Slight or mild brain injury
– Bleeding & tearing of nerve fibers happened
– Recovery likely with some memory loss
• Contusion
– A more severe TBI
– Nervous tissue destruction occurs
– Nervous tissue does not regenerate
• Cerebral edema
– Swelling from the inflammatory response
– May compress and kill brain tissue
• Cerebrovascular Accident (CVA)
– Commonly called a stroke
– The result of a blocked or ruptured
blood vessel supplying a region of
the brain
– Brain tissue supplied with oxygen
from that blood source dies
– Loss of some functions or death may
result
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Alzheimer’s Disease
• Progressive degenerative brain
disease
• Mostly seen in the elderly, but may
begin in middle age
• Structural changes in the brain include
abnormal protein deposits and twisted
fibers within neurons
• Victims experience memory loss,
irritability, confusion and ultimately,
hallucinations and death
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Peripheral Nervous System (PNS)
Sensory Division
Motor Division
Somatic NS
Autonomic NS
Sympathetic
Parasympathetic
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B. Peripheral Nervous System
(PNS)
• Peripheral Nervous System is
made up of all the nerves and
ganglia (nerve cell bodies) that
carry messages between the body
and the CNS
• Receives info from the
environment
• Transmits commands from CNS to
organs and glands
• Contains mostly motor and
sensory neurons
Divisions of the PNS
• Sensory division • Motor division
– transmits
– transmits
impulses from
impulses from
the central
sense organs to
the central
nervous system
nervous system
to the muscles
or glands
– Divided into 2
divisions
• Somatic
• Autonomic
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Motor Division
• Somatic N.S.
• Autonomic N.S.
• Regulates activities
that are under
conscious control
• Example: movement of
muscles (wiggle toe)
• Involved in reflexes
(quick, automatic
response to stimulus)
• Regulates activities
that are automatic or
involuntary
• Example: heart rate
• Consists of only motor
nerves
• Divided into two
divisions
– Sympathetic division
– Parasympathetic
division
Autonomic N.S. Division
• Sympathetic
• Parasympathetic
• “Fight
“Fight--oror-Flight”
• Takes over to increase
activities
• Remember as the “E”
“E”
division = exercise,
excitement,
emergency, and
embarrassment
• “Rest and Digest
• Conserves energy
• Maintains daily
necessary body
functions
• Remember as the “D”
division = digestion,
defecation, and
diuresis (urination)
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Peripheral Nervous System
& Reflexes
• The peripheral nervous system
is also involved in reflexes.
• A reflex is a quick and
unconscious response to a
stimulus
• The brain is not involved with
reflexes.
• The impulse travels up sensory
neurons,
neurons, to the spinal cord
(interneuron),
(interneuron), then immediately
travels down motor neurons for a
response.
• The pathway the impulse travels is
called the reflex arc
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Reflex Arc
• Receptor (sense organ) sensory neuron spinal cord motor neuron effector (muscle)
Internal Communication
• Internal communication is critical
to maintain homeostasis.
homeostasis.
• Sensory neurons are constantly
sending information to the brain
about the internal environment.
• The brain responds by sending
signals through the motor neurons
to maintain homeostasis.
homeostasis.
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The Nervous System
CNS
Brain
Spinal
Cord
PNS
Somatic NS
Voluntary
Movement
Autonomic NS
Involuntary
Movement
Sympathetic
Parasympathetic
NS
NS
fight or flight
rest & digest
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Reflex Pathway
• Sensory input >
– Sensory Neuron >
• Spine (Interneuron) >
–Motor neuron
»> Involuntary Reflex
(response)
Conscious Response
Pathway
• Sensory Input >
– Sensory Neuron >
• Brain (Interneurons) >
–Motor Neuron >
»Voluntary Movement
(Response)
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