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Chapter 33
Nervous
System
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Sect 33.2 –
Organization of the
Nervous
System
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33.2 Organization of the NS
Objectives
•Describe the major divisions of the
nervous system.
•Compare and contrast the somatic
nervous system with the autonomic
nervous system.
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33.2 Organization of the NS
Main Idea
•The central nervous system
and the peripheral nervous
system are the two major
divisions of the nervous
system.
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33.2 Organization of the NS
Central Nervous System
•Nervous system consists of two major
divisions
◦ the central nervous system (CNS)
◦ the peripheral nervous system (PNS)
•CNS
◦ has two major structures
 brain
 spinal cord
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33.2 Organization of the NS
Central Nervous System
•CNS
◦ composed most of interneurons
◦ function
 to coordinate all of the body’s activities
◦ the CNS
 relays messages
 processes information
 analyzes responses
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33.2 Organization of the NS
Central Nervous System
•Typical pathway
◦ sensory neuron pass info to the spinal
cord
 interneurons in the cord might
□ respond
via a reflex arc
□ relay the info to the brain
◦ in the brain
 info processed in at least 2 ways
□ brain tissue sends message to motor
neurons
~ via the cord
~ body reacts accordingly
□ info
may be stored for later use
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33.2 Organization of the NS
Central Nervous System
•Brain
◦ weighs an average of 1.4 kg (3 lbs)
◦ composed of about 100 x 109 neurons
◦ has two major functions
 overseeing the daily operations of the body
 interpreting all of the info it receives
◦ composed of 3 major parts
 cerebrum
 brain stem
 cerebellum
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33.2 Organization of the NS
Central Nervous System
•Brain
Cerebellum
Cerebrum
Brain Stem
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33.2 Organization of the NS
Central Nervous System
•Cerebrum
◦ largest and most prominent area of the
human brain
◦ functions of the brain include
 thought processes (learning)
 memory
 language
 speech
 voluntary body movements
 sensory perception
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33.2 Organization of the NS
Central Nervous System
•Cerebrum
◦ deep groove
 running front to
back
 divides the
cerebrum into L
& R hemispheres
◦ hemispheres
 connected by a
band of tissue
□ called the
corpus
callosum
Corpus Callosum
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33.2 Organization of the NS
Central Nervous System
•Cerebral
hemispheres
◦ each cerebral
hemisphere deals
with the opposite
side of the body
 the left hemisphere
□ controls
the right
side of the body
 the right hemisphere
□ controls
the left
side of the body
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33.2 Organization of the NS
Central Nervous System
•The Cerebellum
◦ second largest region of the brain
◦ located at the back of the brain
◦ it controls
 balance
 posture
 coordination
◦ it controls skeletal muscle movements
 so that they are
□ coordinated
□ smooth
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33.2 Organization of the NS
Central Nervous System
•The Cerebellum
Cerebellum
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33.2 Organization of the NS
Central Nervous System
•The Brain Stem
◦ connects the brain and spinal cord
◦ it has two regions:
 the medulla oblongata
 the pons
◦ the medulla oblongata helps control
 breathing rate
 heart rate
 blood pressure
◦ The pons
 aids in breathing
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33.2 Organization of the NS
Central Nervous System
•The Brain Stem
Medulla Oblongata
Brain stem
Pons
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33.2 Organization of the NS
Central Nervous System
•The Hypothalamus
◦ located atop the brain stem
◦ is essential for homeostasis
◦ it regulates
 body temperature
 thirst
 appetite
 water balance
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33.2 Organization of the NS
Central Nervous System
•The Hypothalamus
Hypothalamus
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33.2 Organization of the NS
Central Nervous System
•Spinal Cord
◦ main communications link between
 the brain
 the rest of the body
◦ continuous with the medulla oblongata
◦ some info is processed in the cord
 example: most reflexes
◦ protected by the vertebrae
◦ gives off 31 pairs of spinal nerves
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33.2 Organization of the NS
Central Nervous System
•Spinal Cord
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33.2 Organization of the NS
Peripheral Nervous System
•PNS
◦ contains all the neurons that are not
part of the CNS
 this includes
□ all
the nerves
□ their associated cells
◦ nerve
 = a bundle of axons
 may contain
□ only sensory neurons
□ only motor neurons
□ a mixture of both
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33.2 Organization of the NS
Peripheral Nervous System
•PNS includes
◦ cranial nerves
◦ spinal nerves
•Cranial nerves
◦ 12 nerves
 come off
the brain
□ go directly to areas they serve
◦ mixture of nerves
 sensory
 motor
 mixed
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33.2 Organization of the NS
Peripheral Nervous System
•Spinal nerves
◦ 31 pairs of nerves
 come off the
brain
□ pass down the
spinal cord
□ then to their
respective area
◦ mostly mixed
nerves
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33.2 Organization of the NS
Peripheral Nervous System
•PNS
◦ has two major divisions
 somatic nervous system (SNS)
 autonomic nervous system (ANS)
•Somatic NS nerves relay info
◦ from external sensory receptors to the
CNS
◦ from the central nervous system to
skeletal muscles
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33.2 Organization of the NS
Peripheral Nervous System
•SNS
◦ includes
 all voluntary muscle movements
 reflexes
◦ reflex
 = a quick, automatic response to a
stimulus
 most go only to the spinal cord
□ not to the brain
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33.2 Organization of the NS
Peripheral Nervous System
•ANS
◦ regulates involuntary activities
◦ activities under subconscious control
◦ carries impulses
 from the CNS
 to the
□ heart
□ other internal organs
◦ has two branches
 sympathetic nervous system
 parasympathetic nervous system
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33.2 Organization of the NS
Peripheral Nervous System
•Sympathetic NS
◦ is most active in times of
 emergency
 stress
◦ causes increases in certain functions
 heart rate
 breathing rate
◦ produces the “fight or flight” response
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33.2 Organization of the NS
Peripheral Nervous System
•Parasympathetic NS
◦ is most active in times of relaxation
◦ counterbalances the effects of the SNS
 restores the body to a resting state
•Interaction between
◦ sympathetic NS
◦ parasympathetic NS
◦ helps the body maintain homeostasis
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33.2 Organization of the NS
Question
•The part of the brain that is
responsible for coordination and
balance is the
a. cerebellum.
b. cerebrum.
c. brain stem.
d. thalamus.
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33.2 Organization of the NS
Question
•Reflex arcs are actions that are a part
of the peripheral nervous system's
a. sensory division.
b. somatic system.
c. autonomic system.
d. motor division.
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33.2 Organization of the NS
Question
•Which of the following is NOT
under the control of the autonomic
nervous system?
a. heartbeat
b. digestion
c. walking
d. sweating
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33.2 Organization of the NS
Q U E S T I O N S ??
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