Transcript 35-2 The Nervous System

35-2 The Nervous System
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35-2 The Nervous System
35-2 The Nervous System
What are the functions of the nervous
system?
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35-2 The Nervous System
35-2 The Nervous System
The nervous system controls and
coordinates functions throughout the body
and responds to internal and external
stimuli.
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35-2 The Nervous System
Neurons
Neurons
The messages carried by the nervous system are
electrical signals called impulses.
The cells that transmit these impulses are called
neurons.
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35-2 The Nervous System
Neurons
Neurons are classified according to the direction in
which an impulse travels.
• Sensory neurons carry impulses from the
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.
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35-2 The Nervous System
Neurons
Structures of a Neuron
Nucleus
Dendrites
Axon
terminals
Cell body
Myelin sheath
Axon
Nodes
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35-2 The Nervous System
Neurons
The largest part of a typical neuron is the cell body.
It contains the nucleus and much of the cytoplasm.
Cell body
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35-2 The Nervous System
Neurons
Dendrites extend from the cell body and carry
impulses from the environment toward the cell body.
Dendrites
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35-2 The Nervous System
Neurons
The axon is the long fiber that carries impulses away
from the cell body.
Axon
terminals
Axon
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35-2 The Nervous System
Neurons
The axon ends in axon terminals.
Axon
terminals
Axon
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35-2 The Nervous System
Neurons
The axon is sometimes surrounded by an insulating
membrane called the myelin sheath.
There are gaps in the myelin sheath, called nodes,
where the membrane is exposed.
Impulses jump from one node to the next.
Myelin sheath
Nodes
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35-2 The Nervous System
The Nerve Impulse
The Resting Neuron (aka Resting Potental)
When resting, the outside of the neuron has a net
positive charge.
The inside of the neuron has a net negative
charge.
Also, the inside of the cell has more potassium
(K+) ions and few sodium (Na+) ions. Because…
The sodium-potassium pump in the nerve cell
membrane pumps potassium (K+) ions into the cell
and (Na+) ions out of the cell by active transport.
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35-2 The Nervous System
The Nerve Impulse
Sodium-Potassium Pump
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35-2 The Nervous System
The Nerve Impulse
How is a nerve impulse transmitted?
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35-2 The Nervous System
The Nerve Impulse
The Moving Impulse
An impulse begins when a neuron is
stimulated by another neuron or by the
environment.
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35-2 The Nervous System
The Nerve Impulse
During activity, the resting stage is reversed and an
impulse moves along the axon. This is called an
action potential.
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35-2 The Nervous System
The Nerve Impulse
During an action potential, the potassium pumps
open, allowing K+ ions to flow out of the neuron.
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35-2 The Nervous System
The Nerve Impulse
The impulse continues to move along the axon untill
it reaches the axon terminal.
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35-2 The Nervous System
The Nerve Impulse
Threshold
A stimulus MUST be strong enough to cause a
neuron to send an impulse.
The minimum level of a stimulus is called the
threshold.
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35-2 The Nervous System
The Nerve Impulse
Just Read (Do Not Write)
A stimulus that is stronger than the threshold
produces an impulse.
A stimulus that is weaker than the threshold
produces no impulse.
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35-2 The Nervous System
The Synapse
The Synapse
At the end of the neuron, the impulse reaches an
axon terminal. Usually the neuron makes contact
with another cell at this site.
The neuron may pass the impulse along to the
second cell.
The spot where an impulse is transferred to
another cell is called a synapse.
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35-2 The Nervous System
The Synapse
A Synapse
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35-2 The Nervous System
Neurotransmitters
are chemicals used by
a neuron to transmit
an impulse across a
synapse to another
cell.
The Synapse
Vesicle
Neurotransmitter
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35-2 The Nervous System
Neurotransmitters
attach to membrane
receptors on the
next cell.
The Synapse
Receptor
A new impulse
begins on the next
neuron cell.
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35-2 The Nervous System
The Synapse
Moments after binding to receptors,
neurotransmitters are released from the cell surface.
The neurotransmitters may then be broken down by
enzymes, or taken up and recycled by the axon
terminal.
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35-2 The Nervous System
35-3 Divisions of the Nervous
System
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35-2 The Nervous System
The Nervous System
The human nervous system has two major divisions:
•
central nervous system (CNS)
•
peripheral nervous system (PNS)
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35-2 The Nervous System
The Central Nervous System
The Central Nervous System
The CNS relays messages, processes information,
and analyzes information.
The CNS consists of the brain and the spinal cord.
The brain and spinal cord are wrapped in three layers
of connective tissue known as meninges.
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35-2 The Nervous System
The Central Nervous System
Between the meninges and the CNS tissue is a
space filled with cerebrospinal fluid.
Cerebrospinal fluid acts as a shock absorber that
protects the central nervous system.
Cerebrospinal fluid also permits exchange of
nutrients and waste products between blood and
nervous tissue.
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35-2 The Nervous System
The Brain
Parts of The Human Brain
Cerebrum
Thalamus
Pineal gland
Hypothalamus
Pituitary gland
Cerebellum
Pons
Brain stem
Medulla
oblongata
Spinal cord
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35-2 The Nervous System
The Brain
The Brain
The brain is the place to which impulses flow and
from which impulses originate.
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35-2 The Nervous System
The Brain
The Cerebrum
Is the largest region of the brain.
It controls the voluntary (conscious) activities.
Used for intelligence, learning, and judgment.
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35-2 The Nervous System
The Brain
A deep groove divides the cerebrum into
hemispheres, which are connected by a band of
tissue called the corpus callosum.
Each hemisphere is divided into regions called lobes.
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35-2 The Nervous System
The Brain
Lobes of the Cerebrum
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35-2 The Nervous System
The Brain
Each half of the cerebrum deals with the opposite
side of the body:
• The left half of the cerebrum controls the right
side of the body.
• The right half of the cerebrum controls the left
side of the body.
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35-2 The Nervous System
The Brain
The outer layer of the cerebrum is called the cerebral
cortex and consists of gray matter.
The inner layer of the cerebrum consists of white
matter, which is made up of bundles of axons with
myelin sheaths.
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35-2 The Nervous System
The Brain
Cerebellum
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35-2 The Nervous System
The Brain
The Cerebellum
Is second largest region of the brain.
It coordinates and balances the actions of the
muscles so that the body can move gracefully
and efficiently.
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35-2 The Nervous System
The Brain
Pons
Brain stem
Medulla oblongata
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35-2 The Nervous System
The Brain
The Brain Stem
The brain stem connects the brain and spinal
cord.
It has two regions: the pons and the medulla
oblongata. Each region regulates information
flow between the brain and the rest of the body.
Blood pressure, heart rate, breathing, and
swallowing are controlled in the brain stem.
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35-2 The Nervous System
The Brain
Thalamus
Hypothalamus
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35-2 The Nervous System
The Brain
The Thalamus and Hypothalamus
The thalamus receives messages from all
sensory receptors throughout the body and
relays the information to the proper region of the
cerebrum for further processing.
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35-2 The Nervous System
The Brain
The hypothalamus controls recognition and
analysis of hunger, thirst, fatigue, anger, and
body temperature.
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35-2 The Nervous System
The Spinal Cord
The Spinal Cord
The spinal cord links the brain and the rest of the
body.
Information, including some kinds of reflexes, are
processed directly in the spinal cord.
A reflex is a quick, automatic response to a
stimulus.
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35-2 The Nervous System
The Peripheral Nervous System
The Peripheral Nervous System
The PHS is all of the nerves and associated cells
that are not part of the brain and the spinal cord.
The PHS includes cranial nerves, spinal nerves,
and ganglia.
Ganglia are collections of nerve cell bodies.
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35-2 The Nervous System
The Peripheral Nervous System
Two divisions of the peripheral nervous system.
The sensory division transmits impulses from
sense organs to the central nervous system.
The motor division transmits impulses from
the central nervous system to the muscles or glands.
The motor division is divided into the somatic
nervous system and the autonomic nervous system.
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35-2 The Nervous System
The Peripheral Nervous System
The Somatic Nervous System
The SNS regulates conscious control activities
such as the movement of skeletal muscles.
Some somatic nerves are involved with reflexes.
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35-2 The Nervous System
The Peripheral Nervous System
A reflex arc includes a sensory receptor, sensory
neuron, motor neuron, and effector that are involved
in a quick response to a stimulus.
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35-2 The Nervous System
The Peripheral Nervous System
Sensory neuron
Reflex Arc
Motor
neuron
Interneuron
Spinal cord
Effector (responding
muscle)
Sensory
receptors
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35-2
Neurons that carry impulses from the brain and
spinal cord to the muscles are
a. interneurons.
b. sensory neurons.
c. resting neurons.
d. motor neurons.
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35-2
The part of the neuron that carries impulses
toward the cell body is the
a. axon.
b. myelin sheath.
c. dendrite.
d. nodes.
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35-2
The minimum level of a stimulus that is required
to activate a neuron is called its
a. action potential.
b. resting potential.
c. threshold.
d. synapse.
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35-2
Chemicals that are used by a neuron to transmit
impulses are called
a. neurotransmitters.
b. synapses.
c. axons.
d. inhibitors.
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35-2
An action potential begins when
a. sodium ions flow into the neuron.
b. potassium ions flow into the neuron.
c. sodium and potassium ions flow into the
neuron.
d. sodium and potassium ions flow out of the
neuron.
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