NVC Bio105 Lect09 Nervous I Sp16 Handouts/Lect09... · Sodium-potassium pump The sodium-potassium...

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Nervous System - Neurons

Biol 105 Chapter 7

Copyright © 2009 Pearson Education, Inc.

Outline

I.  Nervous system function II.  Central and peripheral nervous system III.  Nervous system cells IV.  Myelinated neurons V.  Nerve signal transmission VI.  Nerve Synapse


Nervous Tissues

§  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 §  Includes nervous tissue and sensory organs.

§  Nervous system functions to:

§ Sense the environment – it receives information from both outside and inside the body.

§ Process the information it receives.

§ Respond to information – send out orders.

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Two Parts of the Nervous System 1.  Central Nervous System (CNS)

§  Brain and Spinal Cord.

2.  Peripheral Nervous System (PNS) §  Nervous tissue outside brain and

spine. §  Sense organs.


Central Nervous System

Peripheral


Figure 8.1 The nervous system


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.

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Neuroglial Cells

§  Microglia – Immune system cells, engulf bacteria and cellular debris.

§  Astrocytes – Provide nutrients to neurons.

§  Oligodenrocytes and Schwann Cells – Form myelin sheaths.



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.

§  Axon – one projection that carries messages away from the cell body (can be very long).


Neurons Have Dendrites, a Cell Body, and an Axon

Figure 7.2

The cell body integrates input from other neurons.

Dendrites receive information from other neurons or from the environment.

The cell body controls the cell’s metabolic activities.

An axon conducts the nerve impulse away from the cell body.

Axon endings release chemicals called neurotransmitters that affect the activity of nearby neurons or an effector (muscle or gland).

Receiving portion of neuron

Sending portion of neuron

Cell body

Axon endings

Nucleus

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Copyright © 2009 Pearson Education, Inc. 12-12 Copyright © 2009 Pearson Education, Inc.

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.


Interneurons in the Central Nervous System

§  Interneurons are located between sensory and motor neurons within the CNS.

§  Interneurons integrate and interpret sensory signals.


Figure 8.1 The nervous system

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Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc.

Sensory Neurons

§  The afferent or sensory neuron cell bodies are located in dorsal root ganglion.


Motor Neurons

§  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.


The cell bodies of these neurons are located in the dorsal root ganglion

Motor

Senso

ry

50%50%1.  Motor 2.  Sensory

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The cell bodies of these neurons are located in the dorsal root ganglion

Motor

Senso

ry

50%50%1.  Motor 2.  Sensory


Neurons of the Nervous System

Figure 7.1

Interneuron

Sensory receptor for pain

Muscle (effector)

Motor neuron

Sensory neuron Cell

body

Impulse direction

12-5 Copyright © 2009 Pearson Education, Inc.

These neuroglial cells provide nutrients to neurons

Micr

oglia

Astr

ocytes

Olig

oden

rocy

tes

Schwan

n cells

25% 25%25%25%1.  Microglia 2.  Astrocytes 3.  Oligodenrocytes 4.  Schwann cells

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These neuroglial cells provide nutrients to neurons

Micr

oglia

Astr

ocytes

Olig

oden

rocy

tes

Schwan

n cells

25% 25%25%25%1.  Microglia 2.  Astrocytes 3.  Oligodenrocytes 4.  Schwann cells


These are projections of the neuron cell body that carry messages to the cell body

Axo

ns

Den

drite

s

50%50%1.  Axons 2.  Dendrites


These are projections of the neuron cell body that carry messages to the cell body

Axo

ns

Den

drite

s

50%50%1.  Axons 2.  Dendrites


Which of the following type of neuron would alert the brain that you had touched a hot object?

effer

ent n

euro

n

affer

ent n

euro

n

50%50%1.  efferent neuron 2.  afferent neuron

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Which of the following type of neuron would alert the brain that you had touched a hot object?

effer

ent n

euro

n

affer

ent n

euro

n

50%50%1.  efferent neuron 2.  afferent neuron


What type of neuron is the arrow pointing to?

Senso

ry M

otor

50%50%1.  Sensory 2.  Motor


What type of neuron is the arrow pointing to?

Senso

ry M

otor

50%50%1.  Sensory 2.  Motor


Myelinated Neurons

§  Neurons that have axons covered with neuroglial cells that contain the protein myelin are called myelinated neurons.

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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.

2.  Myelin sheaths from Schwann cells also help regenerate injured PNS neuron axons.


Two Types of Cells Myelinate neurons

§  Schwann cells and Oligodenrocytes are wrapped around neuronal axons.


Myelinated Neurons

§  Schwann cells are found in the PNS.

§  Oligodendrocytes are found in the CNS.

§  Nodes of Ranvier are spaces on the axon between the glial cells.


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Myelin Sheath

Figure 7.3b Copyright © 2009 Pearson Education, Inc.

Myelin Sheath

Figure 7.3c


Myelinated Neurons

Figure 7.3a

(a)

Cell body

Dendrites

Myelin sheath

Node of Ranvier

Nucleus

Schwann cell

In saltatory conduction, the nerve impulses jump from one node of Ranvier to the next.


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.

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Nerves

§  Nerves contain Neuron axons that are bundled together.

§  These bundles contain: § Axons § Blood vessels § Connective tissue


Nerve

Figure 8.9d

(d) The anatomy of a nerve

Blood supply

Axons within a connective tissue sheath

One axon

Connective tissue surrounding one nerve


An Ion is an atom that has gained or lost a

Neu

tron

Proton

Electro

n

33% 33%33%1.  Neutron 2.  Proton 3.  Electron

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An Ion is an atom that has gained or lost a

Neu

tron

Proton

Electro

n

33% 33%33%1.  Neutron 2.  Proton 3.  Electron


How can an ion pass through a membrane

Simple

diffusio

n

Facilit

ated d

iffusio

n

Active

transp

ort

Both 2 an

d 3

All of th

e above

20% 20% 20%20%20%

1.  Simple diffusion 2.  Facilitated diffusion 3.  Active transport 4.  Both 2 and 3 5.  All of the above


How can an ion pass through a membrane

Simple

diffusio

n

Facilit

ated d

iffusio

n

Active

transp

ort

Both 2 an

d 3

All of th

e above

20% 20% 20%20%20%

1.  Simple diffusion 2.  Facilitated diffusion 3.  Active transport 4.  Both 2 and 3 5.  All of the above


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 ion channels.

§  Each ion channel is designed to allow only certain ions to pass through.

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Action Potential

Figure 7.4

Extracellular fluid

Neuron plasma membrane

Cytoplasm

Sodium-potassium pump The sodium-potassium pump uses cellular energy (ATP) to pump sodium ions out of the cell and potassium ions into the cell

Continually open ion channels “Gated” ion channels Sodium-potassium pump Ion channels Ion channels can be open continuously or opened and closed by a molecular gate

Cross section

Axon membrane


§  The difference in charge between the inside and outside of the neuron is the membrane potential.

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.

Resting Membrane Potential


Resting Membrane Potential

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The Nerve Impulse

Figure 7.5 (1 of 4) 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.


NA/K ATPase


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.

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Steps of an 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.


Action Potential

Figure 7.5 (2 of 4)


Steps of an Action Potential

2.  The axon is repolarized when voltage gated potassium ion channels open and allow K+ to flow 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.


Action Potential

Figure 7.5 (3 of 4)

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Action Potential

§  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.


The Nerve Impulse

Figure 7.5 (4 of 4)


The Nerve Impulse

Figure 7.6 Copyright © 2009 Pearson Education, Inc.

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.

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When a neuron is resting, sodium ions have a greater concentration:

insid

e the n

euro

n cell

outside

the n

euro

n cell

conce

ntrati

on is

the .

..

33% 33%33%1.  inside the neuron cell 2.  outside the neuron cell 3.  concentration is the

same


When a neuron is resting, sodium ions have a greater concentration:

insid

e the n

euro

n cell

outside

the n

euro

n cell

conce

ntrati

on is

the .

..

33% 33%33%1.  inside the neuron cell 2.  outside the neuron cell 3.  concentration is the

same


When a neuron is depolarizing, which ions come into the neuron?

Calc

ium (C

a++)

Sodium (Na+

)

Potassiu

m (K+)

Chlorin

e (Cl-)

25% 25%25%25%1.  Calcium (Ca++) 2.  Sodium (Na+) 3.  Potassium (K+) 4.  Chlorine (Cl-)


When a neuron is depolarizing, which ions come into the neuron?

Calc

ium (C

a++)

Sodium (Na+

)

Potassiu

m (K+)

Chlorin

e (Cl-)

25% 25%25%25%1.  Calcium (Ca++) 2.  Sodium (Na+) 3.  Potassium (K+) 4.  Chlorine (Cl-)

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When a neuron is depolarizing, the inside of the neuron cell becomes

Positive

ly ch

arged

Neg

ative

ly ch

arge

d

50%50%1.  Positively charged 2.  Negatively charged


When a neuron is depolarizing, the inside of the neuron cell becomes

Positive

ly ch

arged

Neg

ative

ly ch

arge

d

50%50%1.  Positively charged 2.  Negatively charged


Nerve 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.


Components of the 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.

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Presynaptic neuron

§  Presynaptic neuron has synaptic vesicles that contain neurotransmitters.


Synaptic Transmission

Figure 7.8 (1 of 3)

Nucleus

Impulse

Synaptic knob

Axon Dendrites

Cell body

Synaptic cleft

Synaptic vesicle

Impulse

Membrane of postsynaptic neuron

Step 1: The impulse reaches the axon ending of the presynaptic membrane.

Step 2: Synaptic vesicles release neurotransmitter into the synaptic cleft.



Figure 7.8 (2 of 3)

Neurotransmitter

Receptor (of sodium ion channel) on postsynaptic membrane

Step 3: Neurotransmitter diffuses across synaptic cleft.

Synaptic vesicle



Figure 7.8 (3 of 3)

Step 5: Sodium ion channels open.

Step 4: Neurotransmitter molecules bind to receptors on the postsynaptic neuron.

Step 6: Sodium ions enter the postsynaptic neuron, causing depolarization and possible action potential.

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1.  The action potential gets to the end of the presynaptic axon.

2.  The action potential triggers Ca2+ to enter the presynaptic axon terminal.

3.  The Ca2+ triggers synaptic vesicles located at the axon terminal to merge with the neural membrane.

Transmission Across the Synaptic Cleft


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).




7.  These receptors may be 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).

8.  Once the neurotransmitters are released they need to be destroyed or contained quickly or they will continue to stimulate the nerve.


Neurotransmtters

§  Acetylcholine §  Acts in both the PNS and the CNS as a

neurotransmitter. §  Causes voluntary muscles to contract. §  Acetylcholinesterase.

§  Myasthenia gravis is an autoimmune disease that attacks the acetylcholine receptors, resulting in reduced muscle strength.

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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


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


§  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

Important Concepts

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§  How do ions pass through membranes

§  What is the function of the sodium potassium pump

§  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.

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.

§  Components of the synapse

§  Function of neurotransmitters, how do they work, where do they work, know the ions involved and their functions.

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

Important Concepts


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

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