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35-2 The Nervous System
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35-2 The Nervous System
What are the functions of the nervous system?
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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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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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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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Neurons
Structures of a Neuron
Axon terminals
Myelin sheath
Cell body
Nodes Axon
Dendrites
Nucleus
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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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Neurons
Dendrites extend from the cell body and carry impulses from the environment toward the cell body.
Dendrites
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Neurons
The axon is the long fiber that carries impulses away from the cell body.
Axon terminals
Axon
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Neurons
The axon ends in axon terminals.
Axon terminals
Axon
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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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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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The Nerve Impulse
Sodium-Potassium Pump
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The Nerve Impulse
How is a nerve impulse transmitted?
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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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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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The Nerve Impulse
During an action potential, the potassium pumps open, allowing K+ ions to flow out of the neuron.
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The Nerve Impulse
The impulse continues to move along the axon untill it reaches the axon terminal.
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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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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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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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The Synapse
A Synapse
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The Synapse
Neurotransmitters are chemicals used by a neuron to transmit an impulse across a synapse to another cell.
Vesicle
Neurotransmitter
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The Synapse
Neurotransmitters attach to membrane receptors on the next cell.
A new impulse begins on the next neuron cell.
Receptor
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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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35-3 Divisions of the Nervous System
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The Nervous System
The human nervous system has two major divisions:
• central nervous system (CNS)
• peripheral nervous system (PNS)
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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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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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The Brain
Parts of The Human Brain
Thalamus Thalamus
Pineal glandPineal gland
CerebellumCerebellum
Spinal cordSpinal cord
Hypothalamus Hypothalamus
Pituitary glandPituitary gland
CerebrumCerebrum
Brain stemBrain stemPonsPons
Medulla Medulla oblongataoblongata
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The Brain
The Brain
The brain is the place to which impulses flow and from which impulses originate.
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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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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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The Brain
Lobes of the Cerebrum
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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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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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The Brain
Cerebellum Cerebellum
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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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The Brain
PonsPons
Medulla oblongataMedulla oblongata
Brain stemBrain stem
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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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The Brain
Thalamus Thalamus
Hypothalamus Hypothalamus
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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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The Brain
The hypothalamus controls recognition and analysis of hunger, thirst, fatigue, anger, and body temperature.
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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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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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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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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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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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The Peripheral Nervous System
Reflex Arc
Sensory Sensory receptorsreceptors
Effector (responding Effector (responding muscle)muscle)
Interneuron Interneuron Spinal cordSpinal cord
Sensory neuronSensory neuron
Motor Motor neuronneuron
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35-2
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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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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.