Download Nervous System - Napa Valley College

8/13/2009
Outline
Nervous System - Neurons
Biol 105
Lecture 9
Chapter 7
I.
II.
III.
IV.
V.
VI.
Nervous system function
Central and peripheral nervous system
Nervous system cells
Myelinated neurons
Nerve signal transmission
Nerve Synapse
Copyright © 2009 Pearson Education, Inc.
Nervous Tissues
Nervous System
 Includes nerve tissue and sense organs
 Nervous tissue functions to conduct
messages throughout the body.
 When nerve cells are stimulated, an electrical
signal quickly travels through the nerve cell to
the nerve ending, triggering events
 Nervous system functions to:
 Senses environment – receives
information from both outside and inside
the body
 Processes the information it receives
 Respond to information – sends out
orders
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Two Parts of the Nervous System
Central Nervous System
1. Central Nervous System (CNS)
 Brain and Spinal Cord
Peripheral
2. Peripheral Nervous System (PNS)
 Nervous tissue outside brain and
spine
 Sense organs
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
1
8/13/2009
Nervous System Cells
 Two types of nervous tissue cells
 Neurons – the cells that are responsible for
transmitting messages
 Neuroglial cells – cells that support the
neurons
Copyright © 2009 Pearson Education, Inc.
Neuroglial cells
 Microglia – immune system cells, engulf
bacteria and cellular debris
 Astrocytes – provide nutrients to neurons
 Oligodenrocytes and Schwann cells – form
myelin sheaths
Copyright © 2009 Pearson Education, Inc.
Figure 4.6
Parts of a Neuron
 Cell body – contains the nucleus, main body
of cell
 Dendrites – projections from the cell body
that carry messages to the cell body
 Axons – one large projection that carry
messages away from the cell body
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Neuron
Neurons Have Dendrites, a Cell Body, and an
Axon
Dendrites receive
information from
other neurons or
from the environment.
The cell body controls
the cell’s metabolic
activities.
Axon endings release
chemicals called
neurotransmitters that
affect the activity of
nearby neurons or an
effector (muscle or gland).
Nucleus
Cell
body
The cell body
integrates input
from other neurons.
Receiving portion of
neuron
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
An axon conducts the
nerve impulse away
from the cell body.
Axon
endings
Sending portion of neuron
Figure 7.2
2
8/13/2009
Neurons of the Peripheral Nervous System
 Neurons in the PNS are either carrying
messages to or from the CNS
 Afferent = Sensory neurons = Neurons carrying
messages to the CNS
 Efferent = Motor neurons = Neurons carrying
messages from the CNS
Copyright © 2009 Pearson Education, Inc.
12-12
Copyright © 2009 Pearson Education, Inc.
Interneurons in the Central Nervous System
 Located between sensory and motor
neurons within the CNS
 Interneurons integrate and interpret
sensory signals
Copyright © 2009 Pearson Education, Inc.
Sensory Neurons
Copyright © 2009 Pearson Education, Inc.
Motor Neurons
 The efferent or motor neuron cell bodies are
located in the gray matter of the spinal cord.
 The afferent or sensory neuron cell bodies
are located in dorsal root ganglion.
Copyright © 2009 Pearson Education, Inc.
 Their axons leave the CNS and go to the
skeletal muscles
Copyright © 2009 Pearson Education, Inc.
3
8/13/2009
Neurons of the Nervous System
Muscle
(effector)
Sensory
receptor
for pain
Impulse direction
Sensory
neuron
Cell
body
Motor
neuron
Interneuron
Copyright © 2009 Pearson Education, Inc.
12-5
Figure 7.1
Myelinated neurons
 Neurons that have axons covered with
neuroglial cells that contain the protein myelin
are called myelinated neurons
 Myelinated neurons are able to carry messages
faster than non-myelinated neurons
Copyright © 2009 Pearson Education, Inc.
Functions of Myelin Sheaths
1. The main benefit of myelin sheaths is that
myelinated neurons are able to carry
messages faster than non-myelinated neurons
Two Types of Cells that Myelinate neurons
 Schwann cells and Oligodenrocytes are
wrapped around neuronal axons
2. Myelin sheaths from Schwann cells also help
regenerate injured PNS neuron axons
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
4
8/13/2009
Myelinated Neurons
Myelinated neurons
Nucleus
 Schwann cells are found in the PNS
 Oligodendrocytes are found in the CNS
Dendrites
Cell
body
In saltatory conduction, the
nerve impulses jump from one
node of Ranvier to the next.
 Nodes of Ranvier are spaces on the axon
between the glial cells
Node of
Ranvier
Schwann cell
Myelin sheath
(a)
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Myelin Sheath
Copyright © 2009 Pearson Education, Inc.
Multiple Sclerosis (MS)
 Caused by the destruction of the myelin
sheath that surrounds axons found in the
CNS
 Can result in paralysis and loss of
sensation, including loss of vision
Copyright © 2009 Pearson Education, Inc.
Figure 7.3a
Myelin Sheath
Figure 7.3b
Copyright © 2009 Pearson Education, Inc.
Figure 7.3c
Nerve
 Nerve contain Neuron axons are bundled
together
 These bundles contain
 Axons
 Blood vessels
 Connective tissue
Copyright © 2009 Pearson Education, Inc.
5
8/13/2009
Nerve
Connective tissue surrounding one nerve
Blood supply
Axons within a connective
tissue sheath
One axon
(d) The anatomy of a nerve
Figure 8.9d
Copyright © 2009 Pearson Education, Inc.
The Nerve Impulse Is an Electrochemical
Signal
 A nerve impulse, or action potential, involves
sodium ions (Na+) and potassium ions (K+)
that cross the cell membrane through the ion
channels

 Each ion channel is designed to allow only
certain ions to pass through
Action Potential
Cross section
Axon membrane
Neuron plasma
membrane
Extracellular
fluid
Cytoplasm
Continually open ion channels
“Gated” ion channels
Ion channels
Ion channels can be open continuously or opened and
closed by a m olecular gate
Copyright © 2009 Pearson Education, Inc.
Membrane Potential
 The difference in charge between the inside
and outside of the neuron is the membrane
potential
Sodium -potassium pump
Sodium-potassium pump
The sodium-potassium pump
uses cellular energy (ATP) to
pum p sodium ions out of the
cell and potassium ions into
the cell
Copyright © 2009 Pearson Education, Inc.
Figure 7.4
Resting Membrane Potential
 A neuron that is not conducting a message is
said to be “Resting”
 When a neuron is resting there is more
sodium (Na+) outside the neuron cell and
more potassium (K+) inside the cell
 The inside of the cell has a negative charge
compared to the outside the cell
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
6
8/13/2009
Resting Membrane Potential
Copyright © 2009 Pearson Education, Inc.
Sodium Potassium Pump
 To maintain this resting membrane potential
the neuron pumps Na+ out of the cell and K+
into the cell.
 The transport proteins take 3 Na+ ions out for
every 2 K+ ions into the cell = Na+/K+ pump
 This is Active Transport – requiring ATP
Copyright © 2009 Pearson Education, Inc.
Steps of an Action Potential
The Nerve Impulse
Copyright © 2009 Pearson Education, Inc.
Figure 7.5 (1 of 4)
Action Potential
 An electrochemical signal conducted along
an axon. It is a wave of depolarization
followed by repolarization
 Depolarization is caused by sodium ions
entering the axon
 Repolarization is caused by potassium
ions leaving axon
Copyright © 2009 Pearson Education, Inc.
Action Potential
1. The axon is depolarized when voltage gated
sodium ion channels open and Na+ comes
rushing in, causing the inside of the neuron to
become positively charged
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Figure 7.5 (2 of 4)
7
8/13/2009
Action Potential
Steps of an Action Potential
2. The axon is repolarized when voltage gated
potassium ion channels open up and allow K+
to go out of the axon

This returns the membrane potential to be
negative on the inside of the neuron

The action potential travels down the axon
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Action Potential
Figure 7.5 (3 of 4)
The Nerve Impulse
 After the action potential, the sodium
potassium pump restores the original
conditions by pumping sodium (Na+) out of
the cell and potassium (K+) back into the cell
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
The Nerve Impulse
Figure 7.5 (4 of 4)
Action Potentials
 It is an all or nothing response – if it is not
a great enough stimulation the channels
won’t open. The level of the action
potential is always the same.
 The direction is always one way down the
axon. The sodium channels are
inactivated for awhile after the action
potential passes = refractory period.
PLAY
Animation—The Nerve Impulse
Copyright © 2009 Pearson Education, Inc.
Figure 7.6
Copyright © 2009 Pearson Education, Inc.
8
8/13/2009
Nerve Synapse
Components of the Synapse
 How are messages passed from one nerve to
the next or from the nerve to a muscle?
 The junction between two neurons or
between a neuron and a muscle is called a
synapse
1. Presynaptic neuron is the transmitting
neuron
2. postsynaptic neuron is the receiving neuron
or the muscle
3. And the gap in between them = synaptic
cleft
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Synaptic Transmission
Presynaptic neuron
Dendrites
Axon
Nucleus
 Presynaptic neuron has synaptic
vesicles that contain neurotransmitters
Cell
body
Impulse
Impulse
Step 1: The impulse reaches
the axon ending of the
presynaptic membrane.
Synaptic
knob
Step 2: Synaptic
vesicles release
neurotransmitter
into the synaptic
cleft.
Synaptic
cleft
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Synaptic Transmission
Membrane of
postsynaptic neuron
Figure 7.8 (1 of 3)
Synaptic Transmission
Step 4: Neurotransmitter
molecules bind to
receptors on the
postsynaptic neuron.
Neurotransmitter
Synaptic
vesicle
Step 3: Neurotransmitter
diffuses across synaptic cleft.
Step 5: Sodium
ion channels
open.
Step 6: Sodium
ions enter the
postsynaptic
neuron, causing
depolarization and
possible action
potential.
Receptor (of sodium ion
channel) on postsynaptic membrane
Copyright © 2009 Pearson Education, Inc.
Synaptic
vesicle
Figure 7.8 (2 of 3)
Copyright © 2009 Pearson Education, Inc.
Figure 7.8 (3 of 3)
9
8/13/2009
Transmission across synaptic cleft
Transmission across synaptic cleft
1. The action potential gets to the end of the
presynaptic axon
4. The synaptic vesicles release the
neurotransmitters into the synaptic cleft
2. The action potential triggers Ca2+ to enter
the presynaptic axon terminal
5. These neurotransmitters travel across the
synaptic cleft to the postsynaptic neuron
(or the muscle)
3. The Ca2+ triggers synaptic vesicles located
at the axon terminal to merge with the
neural membrane
6. Neurotransmitter binds to receptors on the
postsynaptic neuron (or muscle)
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Transmission across synaptic cleft
Neurotransmtters
7. These receptors are ligand gated sodium ion
channels which allow Na+ to enter the
postsynaptic neuron (or muscle) and triggers
an action potential in the postsynaptic neuron
(or muscle contraction)
 Acetylcholine
8. Once the neurotransmitters are released they
need to be destroyed or contained quickly or
they will continue to stimulate the nerve
 Myasthenia gravis is an autoimmune
disease that attacks the acetylcholine
receptors, resulting in reduced muscle
strength
Copyright © 2009 Pearson Education, Inc.
 Acts in both the PNS and the CNS as a
neurotransmitter
 Causes voluntary muscles to contract
 Acetylcholinesterase
Copyright © 2009 Pearson Education, Inc.
Important Concepts
 Read Chapter 8
 What are the functions of nervous system
 What are the two types of cells in nervous tissue
(neuroglial cells and neurons).
 What are the three types of neuroglial cells and
their functions
 What are the two main divisions of nervous
system (CNS, PNS) and where each is found
Copyright © 2009 Pearson Education, Inc.
10
8/13/2009
Important Concepts
 What are the parts and functions of a neuron
 What are the three types of neurons (sensory,
interneuron and motor neurons) and their
functions, and where are they located
 Where are the cell bodies are located for motor
and sensory nerve cells
Copyright © 2009 Pearson Education, Inc.
Important Concepts
 How do ions pass through membranes
 What is the function of the sodium potassium
pump
Important Concepts
 What are schwann cells and oligodendrocytes and
what are their function
 Where Schwann vs oligodendrocytes are found
 What is the cause and effects of multiple sclerosis
 What are the parts of a nerve
Copyright © 2009 Pearson Education, Inc.
Important Concepts
 What ions enter and the leave the neuron during
the depolarization and repolarization steps of
action potential, what is the relative charge of the
inside vs the outside of the neuron during these
events, what is the order of events.
 What are the steps of messages being conducted
through a neuron, starting with the resting stage
and ending with the next neuron or muscle being
stimulated.
 Components of the synapse
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Important Concepts
 What is acetylcholine, where is it found, what effect
does it have, how is acetylcholine removed from
the synaptic cleft
 What is the cause and effect of Myasthenia gravis
Copyright © 2009 Pearson Education, Inc.
 Function of neurotransmitters, how do they work,
where do they work, know the ions involved and
their functions.
Definitions
 Afferent neurons, efferent neurons, dendrites,
axons, sensory neurons, interneuron, motor
neurons, myelin, myelin sheath, myelinated
neurons, schwann cells, oligodendrocytes,
nodes of ranvier, nerve, ions, ion channels,
ligand gated ion channels, voltage gated ion
channels, action potential, repolarization,
depolarization, membrane potential, resting
potential, sodium potassium pump, refractory
period, synapse, synaptic cleft, synaptic
vesicles, neurotransmitters,
acetylcholinesterase, presynaptic neuron,
postsynaptic neuron, stimulate, inhibit
Copyright © 2009 Pearson Education, Inc.
11