honors nervous system mini-unit

7/21/2019 Honors Nervous System Mini-unit

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Chapter 28:

The Nervous System


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Cells in a multicellular organism must communicate!

Animal rely on 2 systems for regulation & communication

Endocrine System

Chemical

messengers

(hormones) carry

signal to target

cells

Slow, long-lasting

response

Like sending a runner

with a message

Nervous System

Electrical signal carries

message to target cells

Fast, short-lasting response

Like using a telephone


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3 functions of the nervous system:

1. Receiving signals from the

environment (inside or

outside the organism) and

sending them to the CNS(Sensory Input)

2. Processing signals from

many sources and

deciding on a response

(Integration)

3. Signaling effector cells to

create a response (Motor

Output)

Structural division


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Sensory receptorsgenerate a signal

in response to changes (stimuli) in

the internal or external environment.

Effectorcells (usually muscles or

glands) carry out the bodys response

to a stimulus.

Cells in the CNS integratethe many

incoming signals and associate them

with a response.

Functional division

Afferent - carry signal

toward CNS

Efferent - carry signal

away from CNS


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A neuron is the basic structural &

functional unit of the nervous system.

Signals always flow from:

dendrite cell body axon

How does the structure of

a neuron fit its function?

1

2

3


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A Simple Nerve Circuit the Reflex Arc.

A reflexis an autonomic response.

Copyright2002 Pearson Education, Inc., publishing as Benjamin Cummings


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How does a neuron transmit a signal? Think dominoes!

START THE SIGNA !N"C! #"$N 1ST#"%IN"

&R"&AGATE THE SIGNA'AING %"(ES #"$N INE

I!E A $A(E

RESET )E'"RE NE*T SIGNA SET #"%IN"ES +& AGAIN


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To understand this transmission, we must first understand a neuron

that is not transmitting a signal (resting neuron).

There is an imbalancebetween cations and anions

inside and outside the cell.

The ions never reach

equilibrium because the

Na/K pumptransports them

against their concentration

gradients and because the

electrical charges also affect

their movement.

Separation of charge =

Potential Energy =

Resting Potential


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A membrane with a potential difference

between the 2 sides is said to be polarized.

An unstimulated cell usually has a resting potentialof -70mV

The resting potential

is maintained by the

movement of ions

(K+and Na+) through

ungated ion

channels. These are

membrane proteins

forming tunnels that

are always open.


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The membrane also contains channels that can be open or closed

depending on conditions around them. These are called gated ion

channels. When gated channels open, it upsets the electro-

chemical balance of the cell and changes membrane potential.

Voltage-gated channelsopen

and close in response to changes

in charges.

Chemically-gated channels

open and close in response to a

chemical.

,,

--


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Such small changes in the membrane potential are called graded potentials.

hyperpolarization depolarization

Membrane potential

more negative

Membrane potential

less negative

Gated K+

channels

open

K+

diffusesout of cell

More

negative

membrane

potential

Gated Na+

channels

open

Na+

diffuses

into cell

Less

negative

membrane

potential


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If a depolarization reaches the

threshold potential, all of the

voltage gated Na+

channels open!

ACTION POTENTIAL

Positive Feedback

All-or-none

response


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The action potential moves down the

axon like a wave as Na+ions diffuse

to neighboring regions, opening theirvoltage-gated Na+channels

Remember the

dominoes!

Why does the action potential

only move in one direction?


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In myelinated neurons only unmyelinated

regions of the axon depolarize.

FASTER

TRANSMISSION


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What happens when the action potential

reaches the axon terminal?


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Functional Organization of the PNS

honors nervous system mini-unit

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