The Nervous system
Do Now
• Put together the puzzle without
talking, making eye contact, or
using hand gestures.
• Did you find this difficult?
• What would make it easier?
• How does this relate to your
body?
Communication
• Nearly all multicellular
organisms have communication
systems.
• Specialized cells carry
messages from one cell to
another so that communication
among all body parts is smooth
and efficient.
Communicate to
maintain homeostasis
• There are two systems used for
communication in your body:
• The nervous system controls and
coordinates functions throughout
the body and responds to internal
and external stimuli with the use
of nerves
• The endocrine system performs a
similar function with the use of
hormones
Nervous Response
• Stimulus: any change that results in
a change in the organism.
• temperature, light, pressure,
sound, smell, etc.
• Response: any action resulting from
a stimulus.
• contraction of muscle cells
• secretion by a gland
• stimulation of another nerve fiber.
5
Neurons
• Messages carried by the nervous system
are electrical signals = impulses
• Nerve cells that transmit impulses =
neurons
• Sensory neurons: carry impulses from sense
organs to the spinal cord and brain
• Motor neurons: carry impulses from the
brain and spinal cord to muscles and glands
• Interneurons: connect sensory and motor
neurons and carry impulses between them
Parts of a Neuron
• Cell body = largest part containing
nucleus and cytoplasm (most
metabolic activity occur here)
• Dendrites = short, branched
extensions spreading out from the
cell body and they carry impulses
from the environment or other
neurons towards the cell body
• Axon = long fibers that carry
impulses away from the cell body
and ends at the axon terminal
A Neuron
Section 35-2
Nucleus
Axon terminals
Cell body
Myelin sheath
Nodes
Axon
Dendrites
Nerves
• Neurons bundle together to form nerves
• Some nerves may be only a few neurons,
and others may be hundreds or thousands
• The myelin sheath may insulate axons by
surrounding it
• There may be some gaps in the myelin
sheath called nodes
• Impulses jump from one node to the next,
increasing the speed impulses travel
Resting Nerve
• Nerve impulses are electrical
• The electric potential is created as
the result of a sodium - potassium
pump
• It uses ATP to pump sodium ions
(Na+) out and potassium ions (K+) in =
active transport
• This results in a negative charge
inside the cell membrane and positive
charge outside = resting potential
Nerve Impulse
• An impulse begins when a neuron is
stimulated by another neuron or by
the environment.
• An impulse causes positively
charged sodium ions to flow in
temporarily reversing the charge of
the cell membrane = action potential
• As the impulse passes, positively
charged potassium ions flow out and
the charges restore to the normal
resting potential
Figure 35-7 An Impulse
Section 35-2
Action Potential
At rest.
Action Potential
At the leading edge of the impulse, the
sodium gates open. The membrane becomes
more permeable to Na+ ions and an action
potential occurs.
As the action potential passes, potassium
gates open, allowing K+ ions to flow out.
Action Potential
The action potential continues to move along
the axon in the direction of the nerve impulse.
Synapse
• At the end of the neuron, the impulse reaches an
axon terminal where the impulse may be passed
along to another neuron or another cell
• The location where a neuron can transfer an
impulse to another cell = synapse
• The synapse is a small gap that separates the axon
terminal from the dendrites of the next neuron or
another cell
• The terminals contain tiny sacs or vesicles filled
with neurotransmitters = chemicals used by a
neuron to transmit an impulse across a synapse
• The neurotransmitters stimulate the next neuron
• The impulse will continue with the stimulation
exceeds the cell’s threshold
Figure 35-8 The Synapse
Section 35-2
Direction of Impulse
Dendrite of
adjacent neuron
Axon
Vesicle
Receptor
Axon
terminal
Synaptic cleft
Neurotransmitter
Reaction activity
• Reaction time = the amount of
time required for an impulse
travel from your sensory
neurons to your motor neurons
The Nervous System
• Neurons work together forming
the nervous system
• There are two major divisions of
the nervous system:
• Central nervous system (CNS)
• Peripheral nervous system (PNS)
Parts of the Nervous
system
• Central nervous system (CNS):
• Brain
• Spinal Cord
• Peripheral nervous system
(PNS):
• Sensory division
• Motor division
• Somatic nervous system
• Autonomic nervous system
Central Nervous System
• The CNS is the control center of
the body:
• Relays messages
• Processes information
• Analyzes information
Brain and Spinal cord
• Both are
• protected by bone
• wrapped in 3 layers of connective
tissue = meninges
• layers may have a space between
them filled with cerebrospinal fluid
which protects (shock absorber)
and exchanges nutrients and
waste
Brain
• About 100 billion neurons,
mainly interneurons
• Major parts of the brain:
•
•
•
•
•
Cerebrum
Cerebellum
Brain stem
Thalamus
Hypothalamus
Figure 35-9 The Brain
Section 35-3
Cerebrum
Thalamus
Pineal
gland
Hypothalamus
Cerebellum
Pituitary gland
Pons
Medulla oblongata
Spinal cord
Spinal Cord
• Links communication between the
brain and the rest of the body
• 31 pairs of spinal nerves branch
out from the spinal cord
connecting brain to body
• Reflexes = quick, automatic
responses to stimuli are
processed directly in the spinal
cord
Figure 35-11 The Spinal Cord
Section 35-3
Gray matter
Spinal nerve
Central canal
White matter
Meninges
Peripheral Nervous
System
PNS animation (Pain receptor) :
http://pennhealth.com/encyclopedia/em_Disp
layAnimation.aspx?gcid=000054&ptid=17
• Consists of nerves and associated
cells that are not part of the brain or
spinal cord
• Receives information from the
environment and relays commands
from the CNS to organs and glands
• Divided into two parts:
• Sensory division: transmits impulses
from sense organs to the CNS
• Motor division: transmits impulses from
the CNS to the muscles or glands
Somatic System
• Part of motor division that
regulates activities that are under
conscious control (movement of
skeletal muscles)
• Some reflexes too
What is a Reflex?
• A reflex is an involuntary behavior. Reflexes are
usually coordinated in the spinal cord not the brain.
• They are present from birth
• They are automatic
• They are meant to protect the body
• Examples:
• blinking (keeps your eyes hydrated)
• pulling your hand away when you touch
something hot.
• changing pupil size as you move from dark to
light.
Receptors & Effectors
• Receptor: a specialized
nervous tissue that is sensitive
to a specific stimulus.
•
•
•
•
nerve cells in skin
eyes
ears
taste buds
• Effectors: the part/s of the body
that respond
• muscles or glands
Reflex Arc
• The pathway that an impulse
travels:
•
•
•
•
•
•
•
1.
2.
3.
4.
5.
6.
7.
from the sensory receptor
up the sensory neuron
over the synapse
to the spinal cord (interneuron)
over another synapse
back down the motor neuron
to the effector
Reflex arc animations:
1. http://www.sumanasinc.com/webcontent/animations/content/reflexarcs.html
2. http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0016-swf_reflex_arc.swf
Autonomic System
• Part of the motor division that
regulates activities that are
automatic or involuntary (heart beat
and smooth muscle in digestive
system and blood vessels)
• Two parts that have opposite effects
on the organs they control:
• Sympathetic (“gas pedal”)
• Parasympathetic (“brake”)
Concept Map
Section 35-3
The Nervous
System
is divided into
Central nervous
system
Peripheral
nervous system
Motor
nerves
which consists of
that make up
Somatic nervous
system
Autonomic
nervous system
which is divided into
Sympathetic
nervous system
Parasympathetic
nervous system
Sensory
nerves
Sensory Receptors
• Neurons that react directly to stimuli
from the environment and send
impulses to other neuron and CNS
•
•
•
•
•
•
Light
Sound
Motion
Chemicals
Pressure
Changes in temperature
Sense organs
• Sensory receptors are
concentrated in the sense
organs:
•
•
•
•
•
Eyes
Ears
Nose
Mouth
Skin
Types of Sensory
receptors
• Sensory receptors within each organ
enable it to respond to particular
stimuli. The five general categories
of sensory receptors are:
•
•
•
•
•
Pain receptors
Thermoreceptors
Mechanoreceptors
Chemoreceptors
Photoreceptors
The 5 Senses
•
•
•
•
•
See
Hear
Smell
Taste
Touch
See (Vision)
• Photoreceptors = sense light
Hearing and Balance
• Sound = vibration in
air detected by
mechanoreceptors
• Balance = As head
moves, fluid shifts and
hair cells bend and
send impulses to the
CNS to determine
body motion and
position
Smell
• Smell = ability to detect chemicals
detected by chemoreceptors in nasal
passageway and send impulses to
CNS through sensory nerves
Taste
• How food tastes is
strongly influenced by
smell
• Taste = ability to sense
chemicals by
chemoreceptors in taste
buds mostly on tongue
(sweet, sour, salty and
bitter – sensitivity is
different on different
parts of tongue)
Touch
• Skin = largest
sense organ
containing pain
receptors,
thermoreceptors,
and
mechanoreceptors
Senses activity
• Different parts of skin have
different sensitivity because
there’s a different numbers of
receptors at different locations
Problems
• Drugs = substance that changes the
structure or function of the body
• Drugs can interfere with the action of
neurotransmitters at the synapse, which
can disrupt the functioning of the nervous
system
Stimulants
• Increase the actions regulated
by the nervous system by
increasing the release of
neurotransmitters at synapses
(increase heart rate, blood
pressure, and breathing rate)
•
•
•
•
Amphetamines
Cocaine
Nicotine
Caffeine
Depressants
• Decrease the actions regulated
by the nervous system (lowering
heart rate, breathing rate, blood
pressure, relaxing muscles, and
relieving tension)
• Alcohol
• Tranquilizers
Alcohol
• One of the most dangerous and abused
depressant drug that slows down
functioning rate of CNS
• Fetal alcohol syndrome (FAS) = a group of
birth defects caused by the effects of
alcohol on the fetus (heart defects,
malformed faces, delayed growth, and poor
motor development
• Alcoholism = disease of people who have
become addicted to alcohol
• Causes damage to liver where alcohol is
broken down
Addictions
• Some drugs that act on neurons of the
pleasure centers of the brain can produce
an addiction = an uncontrollable craving
for more of the drug or dependence on a
drug
• Cocaine – causes sudden release of the
neurotransmitter dopamine
• Opiates – mimic natural endorphins to overcome
pain
• Marijuana – produces temporary feeling of
euphoria and disorientation
• Drug abuse = using any drug in a way that
most doctors couldn’t approve
Commonly Abused Drugs
Section 35-5
Drug Type
Medical Use
Examples
Effects on the body
Stimulants
Used to increase alertness,
relieve fatigue
Amphetamines
Increase heart and respiratory rates;
elevate blood pressure; dilate pupils;
decrease appetite
Depressants
Used to relieve anxiety,
irritability, tension
Barbiturates
Tranquilizers
Slow down the actions of the central
nervous system; small amounts cause
calmness and relaxation; larger
amounts cause slurred speech and
impaired judgement
Opiates
Used to relieve pain
Morphine
Codeine
Act as a depressant; cause
drowsiness, restlessness, nausea