The Nervous System LECTURE PACKET 9 READING: CHAPTER 7
COPYRIGHT 2008 PEARSON EDUCATION
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Outline Nervous system function Central and peripheral nervous
system Nervous system cells Myelinated neurons Nerve signal
transmission Nerve synapse COPYRIGHT 2008 PEARSON EDUCATION
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The Nervous System It integrates and coordinates all the bodys
varied activities. It divides into two: 1. Central Nervous System
(CNS) - Brain and Spinal Cord 2. Peripheral Nervous System (PNS) -
Nervous tissue outside the brain and spinal cord COPYRIGHT 2008
PEARSON EDUCATION
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The Nervous System COPYRIGHT 2008 PEARSON EDUCATION
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Nervous Tissues There are two types of nervous tissues: 1.
Neurons (nerve cells) are excitable cells that generate and
transmit messages. 2. Neuroglial cells (also called glial cells)
support and protect neurons. COPYRIGHT 2008 PEARSON EDUCATION
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Nerve Cells Nerve cells function to conduct messages throughout
the body. When nerve cells are stimulated, an electrical signal
quickly travels through the never cell to the nerve ending,
triggering events. COPYRIGHT 2008 PEARSON EDUCATION
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Neuroglial Cells Microglia are immune system cells. They engulf
bacteria and cellular debris. Astrocytes provide nutrients to
neurons. Oligodendrocytes and Schwann cells form myelin sheaths.
COPYRIGHT 2008 PEARSON EDUCATION
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Neuron Cell body contains the nucleus (main body of the cell).
Dendrites are projections from the cell body that carry messages to
the cell body. An axon is one large projection that carry messages
away from the cell body. COPYRIGHT 2008 PEARSON EDUCATION
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Neuron COPYRIGHT 2008 PEARSON EDUCATION
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Neuron COPYRIGHT 2008 PEARSON EDUCATION
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Neuron COPYRIGHT 2008 PEARSON EDUCATION
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Neuron COPYRIGHT 2008 PEARSON EDUCATION
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Neuron Sensory (or afferent) neurons conduct information toward
the brain and spinal cord. - Generally extend from sensory
receptors (information gatherers) Motor (or efferent) neurons
conduct information away from the brain and spinal cord to an
effectoreither a muscle, which will contract, or a gland, which
will secrete its product. Interneurons are located between sensory
and motor neurons. COPYRIGHT 2008 PEARSON EDUCATION
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Neuron COPYRIGHT 2008 PEARSON EDUCATION
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Neuron The afferent, or sensory, neuron cell bodies are located
in the dorsal root ganglion. The efferent, or motor, neuron cell
bodies are located in the gray matter of the spinal cord. Their
axons leave the CNS and go to the skeletal muscles. COPYRIGHT 2008
PEARSON EDUCATION
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Reflex Arc COPYRIGHT 2008 PEARSON EDUCATION
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Cell bodies of these neurons are in the dorsal root ganglia
1.Motor 2.Sensory COPYRIGHT 2008 PEARSON EDUCATION
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These neuroglial cells provide nutrients to neurons 1.Microglia
2.Astrocytes 3.Oligodendrocytes 4.Schwann Cells COPYRIGHT 2008
PEARSON EDUCATION
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Which of the following type of neuron would alert the brain
that you had touched a hot object? 1.Afferent Neuron 2.Efferent
Neuron COPYRIGHT 2008 PEARSON EDUCATION
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Reflex Arc COPYRIGHT 2008 PEARSON EDUCATION
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Myelinated Neurons Neurons that have axons covered with glial
cells that contain the protein myelin are called myelinated
neurons. Myelinated neurons are able to carry messages faster than
non- myelinated neurons. COPYRIGHT 2008 PEARSON EDUCATION
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Functions of Myelinated Neurons 1.Myelin sheaths increase the
rate of conduction of a nerve impulse. 2.Myelin sheaths from
Schwann cells also help regenerate injured PNS neuron axons.
COPYRIGHT 2008 PEARSON EDUCATION
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Myelinated Neurons 1.Outside of the brain and spinal cord,
glial cells known as Schwann cells form neurons myelin sheaths.
2.In the CNS, oligodendrocytes form the myelin sheaths. - Nodes of
Ranvier are located in the spaces on the axon between adjacent
glial cells. COPYRIGHT 2008 PEARSON EDUCATION
Saltatory Conduction COPYRIGHT 2008 PEARSON EDUCATION With the
myelin sheath in place, a nerve impulse can jump from one node of
Ranvier to the next in a type of transmission known as saltatory
conduction.
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Multiple Sclerosis (MS) COPYRIGHT 2008 PEARSON EDUCATION It is
caused by the destruction of the myelin sheath that surrounds axons
found in the CNS. It can result in paralysis and loss of sensation,
including loss of vision.
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Nerve COPYRIGHT 2008 PEARSON EDUCATION Nerve is a bundle of
neurons axons, blood vessels, and connective tissue.
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Nerve COPYRIGHT 2008 PEARSON EDUCATION Nerve is a bundle of
neurons axons, blood vessels, and connective tissue.
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Membrane Potential COPYRIGHT 2008 PEARSON EDUCATION The
difference in charge between the inside and outside of the neuron
is the membrane potential.
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Resting Membrane Potential COPYRIGHT 2008 PEARSON EDUCATION A
neuron that is not conducting a message is said to be resting. The
inside of the cell has a negative charge relative to the outside of
the cell.
Sodium Potassium Pump COPYRIGHT 2008 PEARSON EDUCATION To
maintain resting membrane potential, the neuron pumps Na + out of
the cell and K + into the cell. The transport protein (Na + -K +
ATPase, or sodium-potassium pump) takes out 3 Na + out for every 2
K + into the cell. This is active transport. It requires ATP.
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Nerve Impulse COPYRIGHT 2008 PEARSON EDUCATION A nerve impulse,
or action potential, involves sodium ions (Na + ) and potassium
ions (K + ) that cross the cell membrane through ion channels. Each
ion channel is designed to allow only certain ions to pass
through.
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Membrane Potential Changes COPYRIGHT 2008 PEARSON EDUCATION
Depolarization: Making the membrane more positive Repolarization:
Going back to resting membrane potential Hyperpolarization: Making
the membrane more negative
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Action Potential COPYRIGHT 2008 PEARSON EDUCATION
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Steps of an Action Potential COPYRIGHT 2008 PEARSON EDUCATION
1. The axon is depolarized when voltage-gated sodium ion channels
open and Na + comes rushing in, causing the inside of the neuron to
be more positive (depolarized).
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Steps of an Action Potential COPYRIGHT 2008 PEARSON
EDUCATION
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Steps of an Action Potential COPYRIGHT 2008 PEARSON EDUCATION
2. The axon is repolarized when voltage-gated potassium ion
channels open up and allow K + to go out of the axon.
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Steps of an Action Potential COPYRIGHT 2008 PEARSON
EDUCATION
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Steps of an Action Potential COPYRIGHT 2008 PEARSON EDUCATION
The sodium-potassium pump will restore the original conditions It
pumps sodium out of the cell and potassium into the cell.
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The Nerve Impulse COPYRIGHT 2008 PEARSON EDUCATION
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Action Potential Characteristics COPYRIGHT 2008 PEARSON
EDUCATION They are all or nothing responses. If it is not a great
enough stimulation, the voltage-gated channels wont open. The
magnitude and shape of an action potential is always the same. The
direction is always one way down the axon. The sodium channels are
inactivated for a while after the action potential passes
(refractory period).
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When a neuron is resting, sodium ions have a greater
concentration 1. Inside the neuron 2. Outside the neuron 3.
Concentration is the same both outside and inside COPYRIGHT 2008
PEARSON EDUCATION
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When a neuron is depolarizing, which ions come into the neuron
1.Calcium 2.Sodium 3.Potassium 4.Chloride COPYRIGHT 2008 PEARSON
EDUCATION
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When a neuron is depolarizing, the inside of the neuron cell
becomes 1.Positively charged 2.Negatively charged COPYRIGHT 2008
PEARSON EDUCATION
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Nerve Synapse COPYRIGHT 2008 PEARSON EDUCATION The junction
between two neurons of between a neuron and a muscle is called a
synapse. This is how message is passed from one point to another
point.
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Components of a Synapse COPYRIGHT 2008 PEARSON EDUCATION
1.Presynaptic neuron is the transmitting neuron. It contains
neurotransmitters, or the chemical messengers. 2.Postsynaptic
neuron is the receiving neuron or the muscle. 3.And the gap in
between them is called the synaptic cleft.
Nerve Synapse COPYRIGHT 2008 PEARSON EDUCATION The junction
between two neurons of between a neuron and a muscle is called a
synapse. This is how a message is passed from one point to another
point.
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Transmission Across Synaptic Cleft COPYRIGHT 2008 PEARSON
EDUCATION 1.The action potential gets to the end of the presynaptic
axon. 2.The action potential triggers calcium (Ca 2+ ) to enter the
presynaptic axon terminal. 3.Calcium triggers synaptic vesicles
located at the axon terminal to merge with the neural
membrane.
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Transmission Across Synaptic Cleft COPYRIGHT 2008 PEARSON
EDUCATION 4. The synaptic vesicles release the neurotransmitters
into the synaptic cleft. 5. These neurotransmitters travel across
the synaptic cleft to the postsynaptic neuron (or the muscle). 6.
Neurotransmitter binds to receptors on the postsynaptic neuron (or
muscle).
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Transmission Across Synaptic Cleft COPYRIGHT 2008 PEARSON
EDUCATION 7. These receptors are ligand-gated sodium ion channels,
which allow sodium (Na + ) to enter the postsynaptic neuron (or
muscle) and triggers an action potential in the postsynaptic neuron
(or muscle). 8. Once the neurotransmitters are released, they need
to be destroyed or contained quickly or they will continue to
stimulate the nerve.
Myasthenia Gravis COPYRIGHT 2008 PEARSON EDUCATION
Acetylcholine is a neurotransmitter that acts in both the PNS and
the CNS. It causes voluntary muscles to contract.
Acetylcholinesterase hydrolyzes the neurotransmitter acetylcholine.
Myasthenia gravis is an autoimmune disease that attacks the
acetylcholine receptors, resulting in reduced muscle strength.
