Survey of Anatomy and Physiology Chap 9 Part Two

The Nervous System: The Body's Control Center

9

Part TwoPart Two

Specialized cells in Central Nervous System Central Nervous System

called neuroglia, or glial cells, perform specialized functions. Four types:

Neuroglia-Glial CellsNeuroglia-Glial Cells

Specialized cells in nervous system called

neuroglia, or glial cells, perform specialized functions

Nerve Tissue-Nerve Tissue-Glial CellsGlial Cells

Metabolic and Metabolic and structural supportstructural support




Attack Microbes Attack Microbes and remove and remove

debrisdebris




Cover and line Cover and line cavities of cavities of

nervous systemnervous system




Makes lipid Makes lipid insulation insulation

called myelin called myelin

Specialized cells in Peripheral Nervous System Peripheral Nervous System

called neuroglia, or glial cells, perform specialized functions. Two types:

Neuroglia-Glial CellsNeuroglia-Glial Cells




Makes myelin Makes myelin for PNSfor PNS




Support Support cellscells

Figure 9-2Glial cells and their functions.

Each part of neuron has

specific function Body/SomaBody/Soma: cell metabolism DendritesDendrites: receive

information from the environment

AxonAxon: generates and sends signals to other cells

Nerve Tissue-The Nerve Tissue-The NeuronNeuron

Figure 9-3A neuron connecting to a

skeletal muscle.

Each part of neuron has specific function:

Axon terminalAxon terminal: where signal leaves cellSynapseSynapse: where axon terminal and receiving cell combine

Neurons

Neurons are classified by how they look (structure)or what they do (function)

Neurons are classified by how they look (structure)or what they do (function)

Neurons can use their ability to generate generate

electricityelectricity to send, receive, and interpret signals

How Neurons WorkHow Neurons Work

Neurons are called excitableexcitable

cells; this simply means that if cell is stimulated it can carry

small electrical chargesmall electrical charge. Each time charged particles flow

across a cell membrane, there is tiny charge generatedtiny charge generated


All three muscle All three muscle types are

excitable cells, as are many gland cells

Cells are like miniature miniature batteriesbatteries, able to generate tiny currents simply by changing permeability of their membranes


Series of permeability permeability

changes changes within the cell and the

resultant changes in the charge across the cell membrane

The Action PotentialThe Action Potential

The Action PotentialThe Action Potential

• Polarized• Depolarized• Repolarization• Hyperpolarization• Refractory

Changes in the Cell

A cell that is not not

stimulatedstimulated or excited is called a resting cellresting cell; it is said to be polarizedpolarized

It has a difference in charge across its membrane, being more more negative inside negative inside than on the outside cell

Resting Cell-PolarizedResting Cell-Polarized

When cell is

stimulated, sodium sodium gatesgates in the cell membrane spring openopen, allowing sodium to travel across membrane

Sodium bits are positively chargedpositively charged, so cell becomes more positive as they enter

Stimulated Cell-Stimulated Cell-DepolarizedDepolarized

Sodium gates close after a few minutes and

potassium gates openpotassium gates open; potassium leaves cell, taking its positive charge with it

RepolarizationRepolarization

If cell becomes more

negative than resting it is called hyperpolarizedhyperpolarized

Action potential (AP) is cell moving through depolarization, depolarization, repolarizationrepolarization, and hyperpolarizationhyperpolarization

HyperpolarizationHyperpolarization

Cell cannot accept another stimulus until it

returns to its resting state, and this time period when it cannot accept another stimulus cannot accept another stimulus is called refractoryrefractory period

Refractory PeriodRefractory Period

Figure 9-4The action potential-

page 209.

Speed of

impulse conduction is

determined by amount of amount of myelin myelin and diameter of diameter of

axonaxon

Myelin Increases Myelin Increases ConductionConduction

Myelin is lipid lipid

insulation insulation or sheath formed by oligodendrocytesoligodendrocytes in CNS and…

Schwann celSchwann cells in PNS

Myelin Increases Myelin Increases ConductionConduction

Myelin is essential for speedy flow of AP's down axons; in unmyelinated axon, AP can only flow down axon by depolarizing each and every millimeter of axon (relatively slow process); in myelinated axons there are nodes located periodically, and only nodes must depolarize, allowing impulse to travel quickly as it skips from node to node

Myelinated axon vs. Myelinated axon vs. UnmyelinatedUnmyelinated

Myelin is essential for speedy flow of

Action potential down the axon

Un-myelinated axon has to depolarizeeach and every each and every

millimeter millimeter of axon

.5 meters/second.5 meters/second100 meters/second100 meters/second

Figure 9-5Wider axons conduct faster

Diameter of axon Diameter of axon also affects also affects speed of action potential

flow; wider the diameter of axon, faster the flow of

ions

Figure 9-5Impulse conduction via

myelinated axon.

Nerve impulse Nerve impulse jumpsjumps from the

bare areas between myelin

sheath called the Nodes of Ranvier Nodes of Ranvier which is FASTER

Watch Video “How Synapses Work”

https://www.youtube.com/watch?v=ZuclwAOJFh8

How Synapses WorkHow Synapses Work

When AP* arrives at axon terminal, terminal terminal depolarizes and calcium depolarizes and calcium gates open;gates open; calcium ions

flows into cell; when calcium flows in, it triggers change in

terminal


*Action potential

There are tiny sacs in terminal called vesiclesvesicles

that release their contents from cell when calcium flows in


VesiclesVesicles

Vesicles are filled

with molecules called

neurotransmittersneurotransmitters that send signal

from neuron across synapse to next

cell in line


Once released the

neurotransmitter binds to

receptors on postsynaptic

membrane. Each neurotransmitter has a specific

receptor


The specific neurotransmitter

determines whether the impulse continues

which is calledEXCITATION allowing

Sodium (Na+) channels to open and membrane is depolarized and

impulse continues


Sodium channels

The specific neurotransmitter

determines whether the impulse is

blocked which is called

INHIBITION allowing Potassium (K+) channels to open and the impulse

STOPS


Potassium channels

The receptor then

releases the neurotransmitter

after which it is reabsorbed by the synaptic knobs and

recycled or destroyed by

enzymes.


Enzymes

Use of neurotransmitters is called chemical chemical

synapsesynapse because chemicals carry informationchemicals carry information from one cell to another

Chemical SynapseChemical Synapse

Figure 9-6

. Step 1: The impulse travels down the axon.

Step 2: Vesicles are stimulated to release neurotransmitter

(exocytosis).

Step 3: The neurotransmitter travels across the synapse and

binds with the receptor site of post synaptic cell.

Step 4: The impulse continues down the dendrite.

Chemical SynapseChemical Synapse

NeurotransmittersNeurotransmitters

Acetylcholine Generally excitatory, but sometimes excitatory

Norepinephrine May be excitatory or inhibitory depending on receptor

Epinephrine May be excitatory or inhibitory depending on receptors

Serotonin Generally inhibitory

Endorphins Generally inhibitory

Clean up at the Clean up at the Synapse Synapse

After neurotransmittersneurotransmitters

create a nerve impulse at the

synapse, enzymes

“reuptake” or reuptake” or clean upclean up the

chemicals and use them again

Selective serotonin

reuptake inhibitors (SSRIs) are medications that medications that preventprevent cleanup cleanup of neurotransmitter serotonin from synapses, thus increasing effects of serotonin on receiving cell

AntidepressantsAntidepressants

Electrical vs Chemical Electrical vs Chemical SynapseSynapse

• Cells do not need chemicals to transmit information from one cell to another

• Can transfer info because of special connection called GAP JUNCTION

• Cells do not need chemicals to transmit information from one cell to another

• Can transfer info because of special connection called GAP JUNCTION

Gap junction

Electrical SynapseElectrical Synapse

Electrical synapses with gap junction are found in

the intercalated

discs of cardiac

muscle cells

Electrical synapses with gap junction are found in

the intercalated

discs of cardiac

muscle cells

Electrical vs Chemical Electrical vs Chemical SynapseSynapse

In Class In Class

WORKSHEETWORKSHEET

Complete the worksheet using ONLY YOUR NOTES-

NO TEXTBOOK or LAP TOPS, TABLETS

You will not need to complete the Chapter 9

worksheets for credit but use simply for STUDY GUIDE

for your test

EXAM-Chapters 6 & 7EXAM-Chapters 6 & 7

Your exam is Tuesday Oct 29 at 9:30 a.m. It will have questions from:•Power Point Presentations on Chapter 6 & 7•Essay on functions of skeletal system•Explain osteoporosis and cells of bone formation•Step by step of Muscle contraction•Diagram on specific joint•Extra credit: MUSCLE TONE page 149 in your textbook

Survey of Anatomy and Physiology Chap 9 Part Two

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