Download 36.1: The Nervous System

The Nervous System
• 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
The Nervous System
• 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
• Neuron ≡ Basic Unit 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
• 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 sheath 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 and/or slowing of signal impulse
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
Types of Neurons
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 (active transport);slower
How an impulse is transmitted
• 2.Impulse: stimulus excites
neuron
– Na+ channels open
– Na+ goes inside,
therefore inside becomes
more +
– Depolarization occurs = a
nerve impulse
– Impulse moves in one
direction
– Depolarization works with
concentration gradient
Synapse: a connection
• Junction between nerve cells
• Connection between neurons &
effector cells
synapse
2003-2004
Synapse: a connection
– 1st cell releases chemical
(neurotransmitter) to trigger next cell
– where drugs affect nervous system
synapse
2003-2004
The Nervous Systems
cerebrum
cerebellum
spinal cord
• Central nervous system (CNS)
– brain & spinal cord
• Peripheral nervous system
(PNS)
– nerves from senses
– nerves to muscles/glands
– Both systems work together
cervical
nerves
thoracic
nerves
lumbar
nerves
femoral
nerve
sciatic
nerve
tibial
nerve
2003-2004
Anatomy of the brain
• Cerebrum:
– Conscious activities
– Intelligence
– Memory
– Language
– Voluntary activity
• Cerebellum:
̶ Coordinates motor
activity & balance
Anatomy of the brain
• Midbrain:
̶ reptilian brain (instincts,
emotions)
• Hindbrain/Brain stem:
̶ Medulla Oblongata:
involuntary activities
such as breathing &
heart rate
The Nervous System
Nervous
System
Central Nervous
System (CNS)
Peripheral
Nervous
System
(PNS)
Somatic
Nervous
System (voluntary)
Autonomic
Nervous
System
Relays information to and
from skin and skeletal
muscles.
(involuntary)
Relays information to
internal organs.
Sympathetic Nervous
System
Controls organs in times of stress.
Parasympathetic Nervous
System
Controls organs when body is at rest