Download 36.1: The Nervous System

19: The Nervous
System
Section Objectives:
Analyze how nerve impulses travel within the
nervous system.
Interpret the functions of the major parts of the
nervous system.
Compare voluntary responses and involuntary
responses.
The Nervous System
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Controls and coordinates the
body’s responses to changes
in the environment
HOW:
Stimulus: a change in the
external or internal environment
which initiates an impulse
Impulse~ an electro-chemical
charge generated along a
neuron
Receptors~ structures
specialized to detect certain
stimuli
Response~ a reaction to a
stimulus
Effectors~ what responds to a
stimulus such as muscles or
glands
Neurons: Basic Units of the
Nervous System
• Neurons conduct impulses throughout the nervous
system.
• A neuron is a long cell that consists of three regions:
a cell body, dendrites, and an axon.
Neurons: Basic Units of the
Nervous System
• Dendrites~ receive impulses and carry them toward
the cell body
• Axon~ carries impulses away from the cell body and
toward other neurons, muscles, or glands.
• Cell body~ contains the nucleus
Myelin
coating
signal
direction
 Axon coated with insulation
made of myelin cells

speeds signal
 signal hops from node to node

330 mph vs. 11 mph
myelin coating
Multiple Sclerosis
2003-2004
 immune system (T cells) attacks myelin coating
 loss of signal
Fun facts about neurons
• Most specialized cell in
animals
• Longest cell
– blue whale neuron
• 10-30 meters
– giraffe axon
• 5 meters
– human neuron
• 1-2 meters
Nervous system allows for
1 millisecond response time
2003-2004
Neurons: Basic Units of the
Nervous System
3 Types of neurons.
• 1. Sensory neurons: carry impulses from the
body to the spinal cord and brain (sense
receptors)
• 2. Motor neurons carry the response
impulses away from the brain and spinal cord
to a muscle or gland. (effectors)
• 3.Interneurons: connect sensory &motor
neurons within the brain and spinal cord
Types of neurons
sensory neuron
(from senses)
interneuron
(brain & spinal chord)
2003-2004
motor neuron
(to muscle)
How an impulse is
transmitted
• 1. Resting: no impulse, cell is polarized ( + on
outside & - on inside)
– Sodium/Potassium pump in axon using ATP maintains this
polarity
How an impulse is
transmitted
• 2.Impulse: stimulus
excites neuron
– Na+ gates open
– Na+ goes inside,
therefore inside
becomes more +
– Depolarization
occurs ~ a nerve
impulse
– Impulse moves in
one direction
Synapse ~ connection between
neurons & effector cells
Junction between nerve cells
– 1st cell releases chemical
(neurotransmitter) to trigger next cell
– where drugs affect nervous system
synapse
2003-2004
Nervous System
cerebrum
cerebellum
spinal cord
• Central nervous
system (CNS)
cervical
nerves
thoracic
nerves
– brain & spinal cord
lumbar
nerves
• Peripheral nervous
system (PNS)
femoral
nerve
– nerves from senses
– nerves to muscles
2 systems work together
sciatic
nerve
tibial
nerve
2003-2004
Anatomy of the brain
• Cerebrum:
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Conscious activities
Intelligence
Memory
Language
Voluntary activity
• Cerebellum:
-Coordinates motor activity
-balance
Medulla Oblongata:
involuntary activities such as
breathing,&heart rate
Nervous
System
Central Nervous
System (CNS)
Somatic Nervous
System (voluntary)
Relays information to and
from skin and skeletal
muscles.
Peripheral
Nervous
System
(PNS)
Autonomic
Nervous
System
(involuntary)
Relays information to
internal organs.
Sympathetic Nervous
System
Parasympathetic Nervous
Controls organs in times of stress.
Controls organs when body is at rest
System