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Chapter 35
The Nervous System
Function: The nervous system controls and
coordinates the functions throughout the
body and responds to external and
internal Stimuli.
Name:
Class period:
Parts of the Brain
The Cerebrum
• The largest area of the brain
• Responsible for the voluntary or conscious
activities of the body
• The site of intelligence, learning and judgment
• Divided by a deep groove into the right and
left hemispheres
• Connected by the Corpus Callosum, band of
tissue
• Fold and grooves on surface- increase surface
area
• Made up of two layers
Cerebral Cortex
• Cerebral cortex-outer layer made up of gray
matter (densely packed nerve cell bodies)
• Processes information from the sense organs
and controls body movements
Inner Cerebrum
• Inner layer is made up of white matter
• Bundles of axons with myelin sheaths
• Myelin is a lipid layer that gives white matter
its color
• White matter connects the cerebral cortex
and the brain stem
The Cerebellum
• Second largest region of the brain
• Located at the back of the skull
• Coordinates and balances the actions of the
muscles so that the body can move gracefully
and efficiently
Cerebellum & Brain Stem
Brain Stem
• Connects the brain and the spinal cord
• 2 Regions– Pons and Medulla Oblongata
• Act as neural “switchboard” regulating the
flow of info between the brain and the rest of
the body
• Medulla Oblongata is responsible for body’s
important functions-blood pressure, heart
rate, breathing, swallowing- Involuntary
Actions
Thalamus
• Found between the brain stem and cerebrum
• Receives messages from all of the sensory
receptors throughout the body and relays that
information to the proper region of the
cerebrum for processing
Thalamus (red) &
Hypothalamus (bright orange/yellow)
Hypothalamus
• Sits just below the thalamus
(hypo- under)
• Control center for
recognition and analysis of
hunger, thirst, fatigue, anger
and body temperature
• Maintains homeostasis/
equilibrium in the body
• Coordination of the nervous
and endocrine systems
Spinal Cord
• Main communication link
between brain and rest of
body
• 31 pair of spinal nerves
branch out from spinal cord
connecting brain to all of the
diff. parts of body
• Certain kinds of information,
including some reflexes, are
processed directly in the
spinal cord
Cross Section of the Spinal Cord
The Spinal Cord
Section 35-3
Gray matter
Spinal nerve
Central canal
White matter
Meninges
Neurons/Nerve
Impulses/Synapses
Pg. 2
Neuron
Nucleus
Axon
terminals
Cell body
Myelin sheath
nodes
Axon
Dendrites
Neurons- specialized cells that carry messages by
transmitting electrical signals throughout the
nervous system
Types of neurons:
1. sensory- carry impulses from the sense
organs to the spinal cord and brain.
2. motor- carry impulses from the brain and
spinal cord to muscles and glands.
3. interneurons- connect sensory and motor
neurons and carry impulses between them.
sensory neurons-
motor neurons-
Interneuron
Structure of neurons:
1. cell body- largest part, contains the nucleus & most of the
cytoplasm; most metabolic activity of the cell takes place here
2. dendrites- short, branched extensions that spread out from
cell body; carries impulses from the environment/other
neurons toward the cell body.
3. axon- long fiber that carries impulses away from the cell body.
4. myelin sheath- insulating membrane around an axon. Gaps in
between sheaths are called nodes
5. Axon terminals- the branched part of the axon at the end
Neurons
• Neurons may have many dendrites but only
one axon
• Neurons are clustered into bundles called
nerves, a few to thousands bundled
• Myelin Sheath-insulating membrane with gaps
called nodes, area with no myelin
• Impulse jumps at nodes increasing the speed
of passage
Nerve Impulsean electrical impulse conducted along a nerve fiber.
1. resting potential- the neuron is not transmitting an impulse,
and the electrical charge across the cell membrane of a
neuron is in its resting state. The outside of the cell has a net
positive charge, and the inside of the cell has a net negative
charge.
2. action potential- the reversal of charges, from negative to
positive- called a nerve impulse; begins when a neuron is
stimulated by another neuron or by the environment-
impulse travels rapidly away from cell body and moves
toward axon terminals and into the synapse.
3. threshold- the minimum level of stimulus that is required to
activate a neuron -All or None- either there is an impulse or
there is not- strength of an impulse is always the same
The Synapse & Neurotransmitter
• Synapse: the location at
which a neuron can
transfer an impulse to
another cell
• Neurotransmitter:
chemicals used by a
neuron to transmit an
impulse across a
synapse to another cell
The Central Nervous System
(CNS)
• Main functions of the CNS: 1st conveys
messages between brain and spinal cord;
2nd processes info, problem solving
• 2 structures make-up the CNS:
1- brain
2- spinal cord
• The job for these 2 structures is to respond
to the environment
The Central Nervous System (CNS)
cont.
• 3 protective mechanisms:
– the skull and vertebrae
– The structures are wrapped in meninges
(connective tissue) & it consists of 3 layers
(protection)
– Cerebral spinal fluid (CSF):1st bathes brain and
spinal cord -2nd shock absorber that protects
CNS -3RD allows for exchange of nutrients and
waste products between blood and nervous
tissue
Peripheral Nervous System
• Function: receives info. from the environment
and relays commands from the CNS to organs
and glands
• It lies OUTSIDE the CNS
• Includes all nerves and associated cells that are
not part of the brain and spinal cord
• divided into sensory & motor divisions
– Motor: transmits impulses from the CNS to muscles or
glands
• Motor can be further divided into:
– Somatic Nervous System
– Autonomic Nervous System
– Sensory: transmits impulses from sense organs to the
CNS
• (own notes on sensory receptors pg. 906)
Motor divisionSomatic Nervous System (SNS)
Pg. 5
Somatic Nervous System (SNS)
• regulates activities that are under conscious control
• Movement of skeletal muscles
• Some somatic nerves involved with reflexes & can
act with or without conscious control
Pg. 5
How a reflex works (reflex arc)
• Stimulus:
1. step on tack
2. stimulates sensory receptors/sensory neurons
in foot
3. impulse travels via sensory neuron to spinal
cord
4. spinal cord neurons (interneurons) activate
motor neurons
5. impulse travels via motor neuron to muscle
6. muscles in foot contract, pulling foot away
(effector muscle= muscle that is moving)
**All of this takes only a fraction of a second
Pg. 5
Motor divisionAutonomic Nervous System (ANS)
Pg. 6
Autonomic Nervous System (ANS)
•
•
•
Regulates activities that are
automatic/involuntary
Nerves of ANS control functions not under
conscious control
Controls other body systems
–
Pg. 6
ex: when you run, the ANS:
1. increase heart rate and blood flow to skeletal
muscles
2. stimulates sweat glands and adrenal gland
3. decrease contractions of smooth muscle in digestive
system
Autonomic Nervous System (ANS) cont
•
Divided into 2 sections:
1. Sympathetic-increase heart rate (think “gas
pedal”)
2. Parasympathetic-decrease heart rate (think
“brakes”)
•
•
Pg. 6
Opposite effect on organs- help body
maintain homeostasis
*most organs controlled by both
III.
The Senses
A. Sensory receptors- are neurons that react to stimuli in
the environment. These receptors send impulses to
the central nervous system.
1. 5 types of sensory receptors:
a. pain receptors- respond to pain.
b. thermoreceptors- respond to temperature.
c. mechanoreceptors- respond to pressure.
d. chemoreceptors- respond to chemicals.
e. photoreceptors- respond to light.
Figure 35-14 The Eye
Section 35-4
Vitreous humor
Muscle
Lens
Fovea
Aqueous humor
Cornea
Pupil
Optic nerve
Iris
Blood vessels
Ligaments
Retina
Choroid
Sclera
Figure 35-15 The Ear
Section 35-4
Anvil Stirrup
Hammer
Oval
window
Semicircular canals
Cochlear nerve
Cochlea
Bone
Auditory canal
Tympanum
Round window
Eustachian tube
The Senses of Smell and Taste
Section 35-4
Olfactory
(smell) bulb
Taste
sensory
area
Olfactory
nerve
Thalamus
Cerebral cortex
Smell
receptor
Nasal cavity
Smell
sensory area
Taste bud
Taste
pore
Taste
receptor
Sensory
nerve fibers
Drugs & the Nervous System:
•
A drug is any substance, other than food,
that changes the structure of function of the
body
3 ways that drugs affect the body:
1. Kill bacteria and useful in treating diseases
2. Some affect a particular system
•
•
Digestive
Circulatory
3. MOST POWERFUL are the ones that cause
changes in the NS, especially to the brain and
the synaptic gaps (between the neurons)
The following are drugs that affect
synaptic gaps or neurotransmitters:
Stimulants (such as amphetamines, cocaine, nicotine &
caffeine)
– Medical uses are to increase alertness & relieve fatigue
– They increase actions regulated by the nervous system
– They increase heart rate, respiratory rate, blood
pressure, breathing rate, dilates pupils and decreases
appetite.
– They increase the release of neurotransmitters at some
synapses in the brain.
Depressants: (such as Barbiturates & tranquilizers)
• Medical uses are to relieve anxiety, irritability &
tension
• They decrease the rate of functions regulated by
the brain & slows actions of CNS
• They decrease heart rate, blood pressure &
breathing rate
• Small amounts cause calmness & relaxation; Large
amounts cause slurred speech & impaired judgment
• NOTE: if used with alcohol, can depress CNS so
much that breathing STOPS!!!
Cocaine:
• Causes a sudden release in the neurotransmitter dopamine
(usually released normally when a basic need- such as
hunger or thirst- is fulfilled). This produces intense feeling
of pleasure & satisfaction. HOWEVER, since so much is
released so quickly, dopamine amounts are depleted and
when the drug wears off, intense sadness and depression
occurs, causing psychological dependency. (Crack is an even
more potent form of cocaine causing even more intense
symptoms and quicker dependency)
• Also a powerful stimulant that increases heart rate & blood
pressure which can lead to heart damage or heart attack
Opiates: (such as Morphine, codeine & oxycotin)
• Medical uses are to relieve pain
• These mimic natural chemicals in the brain known
as endorphins, which help to relieve pain
• These act as depressants causing drowsiness,
restlessness & nausea
• Drug produces strong feelings of pleasure and
security, but the body quickly adjusts and needs
higher levels each time to achieve same feelings:
EXTREMELY ADDICTIVE!
• A user who tries to stop taking these will suffer
uncontrollable pain, sadness & sickness because the
body can not produce enough natural endorphins.
Marijuana
• Tetrahydrocannabinol (THC) active ingredient
• Most widely abused illegal drug!