1

10.1: Introduction

• Cell types in neural tissue:

• Neurons

• Neuroglial cells (also

known as neuroglia, glia,

and glial cells)

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Dendrites

Cell body

Axon

Nuclei of

neuroglia

© Ed Reschke

2

10.2: General Functions of

the Nervous System

• The three general functions of the nervous system:

• Receiving stimuli = sensory function

• Deciding about stimuli = integrative function

• Reacting to stimuli = motor function

3

Functions of Nervous System

• Sensory Function

• Sensory receptors gather information

• Information is carried to the CNS

• Integrative Function

• Sensory information used to create: • Sensations

• Memory

• Thoughts

• Decisions

• Motor Function

• Decisions are acted upon

• Impulses are carried to effectors

4

Divisions of the

Nervous System

• Central Nervous System (CNS)

• Brain

• Spinal cord

• Peripheral Nervous System (PNS)

• Cranial nerves

• Spinal nerves

5

Divisions of Peripheral

Nervous System

• Sensory Division

• Picks up sensory information and delivers it to the CNS

• Motor Division

• Carries information to muscles and glands

• Divisions of the Motor Division:

• Somatic – carries information to skeletal muscle

• Autonomic – carries information to smooth muscle,

cardiac muscle, and glands

6

Divisions Nervous System

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Sensory division Sensory receptors

Motor division

Skeletal muscle

Brain

(a) (b)

Spinal

cord Spinal

nerves

Cranial

nerves

Central Nervous System

(brain and spinal cord)

Peripheral Nervous System

(cranial and spinal nerves)

Smooth muscle

Cardiac muscle

Glands

Autonomic

Nervous

System

Somatic

Nervous

System

7

10.3: Description of Cells of

the Nervous System

• Neurons vary in size and shape

• They may differ in length and size of their axons and dendrites

• Neurons share certain features:

• Dendrites

• A cell body

• An axon

8

Neuron Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Cell body

Neurofibrils

Nucleus Nucleolus

Dendrites

Impulse

Nodes of Ranvier

Myelin (cut)

Axon

Axon

Chromatophilic

substance

(Nissl bodies)

Axonal

hillock

Portion of a

collateral

Schwann

cell

Nucleus of

Schwann cell

Synaptic knob of

axon terminal

9

Myelination of Axons

• White Matter

• Contains myelinated

axons

• Considered fiber tracts

• Gray Matter

• Contains unmyelinated

structures

• Cell bodies, dendrites

Dendrite

Node of Ranvier

Myelinated region of axon

Axon

(a)

Unmyelinated

region of axon

Neuron

cell body

Neuron

nucleus

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(c)

Enveloping

Schwann cell Schwann

cell nucleus

Unmyelinated

axon

Longitudinal

groove

10

Types of Neuroglial Cells

in the PNS

1) Schwann Cells

• Produce myelin found on peripheral myelinated neurons

• Speed up neurotransmission

2) Satellite Cells

• Support clusters of neuron cell bodies (ganglia)

11

Types of Neuroglial Cells

in the CNS

2) Astrocytes

• CNS

• Scar tissue

• Mop up excess ions, etc.

• Induce synapse formation

• Connect neurons to blood vessels

• Part of Blood Brain Barrier

3) Oligodendrocytes

• CNS

• Myelinating cell

4) Ependyma or ependymal

• CNS

• Ciliated

• Line central canal of spinal

cord

• Line ventricles of brain

•Produce CSF

1) Microglia

• CNS

• Phagocytic cell

12

Types of Neuroglial Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Microglial cell

Axon

Oligodendrocyte

Astrocyte

Capillary

Neuron

Myelin

sheath (cut)

Node of

Ranvier

Ependymal

cell

Fluid-filled cavity

of the brain or

spinal cord

13

10.4: Classification of Neurons

and Neuroglia

• Neurons vary in function

• They can be sensory, motor, or integrative neurons

• Neurons vary in size and shape, and in the number of axons

and dendrites that they may have

• Due to structural differences, neurons can be classified into

three (3) major groups:

• Bipolar neurons

• Unipolar neurons

• Multipolar neurons

14

Classification of Neurons:

Structural Differences

• Bipolar neurons • dendrite, axon, cb in middle

• Eyes, ears, nose

• Unipolar neurons

• Two ax process

• Ganglia of PNS

• Sensory

• Multipolar neurons

• 99% of neurons

• Many processes

• Most neurons of

CNS

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Dendrites

Axon Axon

Axon Direction

of impulse

(a) Multipolar

Central

process

Peripheral

process

(c) Unipolar (b) Bipolar

15

Classification of Neurons:

Functional Differences

• Sensory Neurons

• Afferent

• Carry impulse to CNS

• Most are unipolar

• Some are bipolar

• Interneurons

• Link neurons

• Aka association neurons

or internuncial neurons

• Multipolar

• Located in CNS

• Motor Neurons

• Multipolar

• Carry impulses away from CNS

• Carry impulses to effectors

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Central nervous system Peripheral nervous system

Cell body

Interneurons

Dendrites

Axon

Axon

Sensory (afferent) neuron

Motor (efferent) neuron

Cell body

Axon

(central process)

Axon

(peripheral process)

Sensory

receptor

Effector

(muscle or gland)

Axon

terminal

16

Regeneration of A Nerve Axon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Axon Site of injury Schwann cells

(a)

(b)

(c)

(d)

(e)

Changes

over time

Motor neuron

cell body

Former connection

reestablished

Schwann cells

proliferate

Schwann cells

degenerate

Proximal end of injured axon

regenerates into tube of sheath cells

Distal portion of

axon degenerates

Skeletal

muscle fiber

17

10.5: The Synapse

• Nerve impulses pass

from neuron to neuron at

synapses, moving from a

pre-synaptic neuron to a

post-synaptic neuron.

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Dendrites

Impulse

Impulse

Impulse

Synaptic

cleft

Axon of

presynaptic

neuron

Cell body of

postsynaptic

neuron

Axon hillock of

Postsynaptic neuron

Axon of

presynaptic

neuron

18

Synaptic Transmission

• Neurotransmitters are

released when impulse

reaches synaptic knob

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Mitochondrion

Synaptic knob

(a)

Synaptic cleft

Neurotransmitter

Axon

Ca+2

Presynaptic neuron

Direction of

nerve impulse

Synaptic

vesicles

Cell body or dendrite

of postsynaptic neuron

Synaptic

vesicle

Vesicle releasing

neurotransmitter

Axon

membrane

Polarized

membrane

Depolarized

membrane

Ca+2 Ca+2

19

Animation: Chemical Synapse

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20

10.6: Cell Membrane Potential

• A cell membrane is usually electrically charged, or

polarized, so that the inside of the membrane is negatively

charged with respect to the outside of the membrane (which is

then positively charged).

• This is as a result of unequal distribution of ions on the

inside and the outside of the membrane.

21

Distribution of Ions

• Potassium (K+) ions are the major intracellular positive ions (cations).

• Sodium (Na+) ions are the major extracellular positive ions (cations).

• This distribution is largely created by the Sodium/Potassium Pump

(Na+/K+ pump).

• This pump actively transports 3 sodium ions out of the cell and 2

potassium ions into the cell.

22

Resting Potential

• Resting Membrane Potential

(RMP):

• 70 mV difference from

inside to outside of cell

• It is a polarized

membrane

• Inside of cell is negative

relative to the outside of

the cell

• RMP = -70 mV

• Due to distribution of

ions inside vs. outside

• Na+/K+ pump restores

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Axon Cell body

Low Na+

Axon terminal Low K+

High K+

High Na+

(a)

+

+ – –

+

+ – –

+

+

– + –

– + – +

–

+ –

+ –

+ – +

–

+ –

+ –

+ –

+ –

+ –

–70 mV

(b)

+

+ – –

+

+ – –

+

+

– + –

– + – +

–

+ –

+ –

+ –

+ –

+ –

+ –

+ –

–70 mV

Low Na+

Low K+ High K+

High Na+

Na+

K+

(c)

Pump

Impermeant

anions

23

Local Potential Changes

• Caused by various stimuli: • Temperature changes

• Light

• Pressure

• Environmental changes affect the membrane

potential by opening a gated ion channel

• Channels are 1) chemically gated, 2) voltage gated,

or 3) mechanically gated

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Gate-like mechanism Protein

(b) Channel open (a) Channel closed

Cell

membrane

Fatty acid

tail

Phosphate

head

24

Local Potential Changes

• If membrane potential becomes more negative, it has hyperpolarized

• If membrane potential becomes less negative, it has depolarized

• Graded (or proportional) to intensity of stimulation reaching

threshold potential

• Reaching threshold potential results in a nerve impulse, starting an

action potential

25

Local Potential Changes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

–62 mV

Na+

Na+

Neurotransmitter

(a)

–55 mV

Na+

Na+

Na+ Na+

Na+

Trigger zone (axon hillock)

(b)

Chemically-gated

Na+ channel

Presynaptic

neuron

Voltage-gated

Na+ channel

26

Action Potentials

• At rest, the membrane is

polarized (RMP = -70)

• Sodium channels open

and membrane

depolarizes (toward 0)

• Potassium leaves

cytoplasm and

membrane repolarizes

(+30)

• Threshold stimulus

reached (-55)

• Brief period of

hyperpolarization (-90)

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(a)

Region of depolarization (b)

Region of repolarization (c)

–70

–0

–70

–0

–70

–0 K+

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

K+ K+ K+ K+ K+ K+ K+

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

K+ K+ K+ K+ K+ K+ K+ K+

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

K+ K+ K+ K+ K+

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

K+ K+ K+ K+ K+

K+

K+

K+ K+

K+ K+

Na+ Na+ Na+

Na+ Na+ Na+

Threshold

stimulus

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

K+ K+ K+ K+ K+

K+ K+ K+ K+ K+

Na+ Na+ Na+

Na+ Na+ Na+

K+

K+

K+ K+ K+

K+ K+ K+

Na+ channels open

K+ channels closed

K+ channels open

Na+ channels closed

27

Action Potentials

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Milliseconds

1 0

0

+20

+40

2 3 4 5 6 7 8

Me

mb

ran

e p

ote

nti

al (m

illi

vo

lts

)

Action potential

Hyperpolarization

–40

–20

–60

–80

Resting

potential

Resting potential

reestablished

28

Action Potentials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a)

Direction of nerve impulse

+ +

+ +

+

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

+ + + + + + + +

+ + + + + + + + +

(b)

+ +

+ +

+ + + + + + + + +

+ + + + + + + + +

(c)

+ +

+ +

+ + + + + + + + +

+ + + + + + + + +

Region of

action potential

29

Animation: Action Potential

Propagation in Myelinated Neurons

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30

Animation: Action Potential

Propagation in Unmyelinated Neurons

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31

All-or-None Response

• If a neuron axon responds at all, it responds completely –

with an action potential (nerve impulse)

• A nerve impulse is conducted whenever a stimulus of

threshold intensity or above is applied to an axon

• All impulses carried on an axon are the same strength

32

Refractory Period

• Absolute Refractory Period • Time when threshold stimulus does not start another

action potential

• Relative Refractory Period • Time when stronger threshold stimulus can start another

action potential

33

Impulse Conduction

34

Animation: The Nerve Impulse

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35

10.3 Clinical Application

Factors Affecting Impulse Conduction

36

10.7: Synaptic Transmission

• This is where released neurotransmitters cross the

synaptic cleft and react with specific molecules called

receptors in the postsynaptic neuron membrane.

• Effects of neurotransmitters vary.

• Some neurotransmitters may open ion channels and

others may close ion channels.

37

Synaptic Potentials

• EPSP

• Excitatory postsynaptic potential

• Graded

• Depolarizes membrane of postsynaptic neuron

• Action potential of postsynaptic neuron becomes more likely

• IPSP

• Inhibitory postsynaptic potential

• Graded

• Hyperpolarizes membrane of postsynaptic neuron

• Action potential of postsynaptic neuron becomes less likely

38

Summation of

EPSPs and IPSPs

• EPSPs and IPSPs are added

together in a process called

summation

• More EPSPs lead to greater

probability of an action

potential

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Nucleus

Neuron

cell body

Presynaptic

knob

Presynaptic

axon

Neurotransmitters

39

40

Neurotransmitters

41

Neuropeptides

• Neurons in the brain or spinal cord synthesize neuropeptides.

• These neuropeptides act as neurotransmitters.

• Examples include:

• Enkephalins

• Beta endorphin

• Substance P

42

10.4 Clinical Application

Opiates in the Human Body

43

10.8: Impulse Processing

• Way the nervous system processes nerve impulses and acts

upon them

• Neuronal Pools

• Interneurons

• Work together to perform a common function

• May excite or inhibit

• Convergence

• Various sensory receptors

• Can allow for summation of impulses

• Divergence

• Branching axon

• Stimulation of many neurons ultimately

44

Neuronal Pools

• Groups of interneurons that make synaptic connections

with each other

• Interneurons work together to perform a common function

• Each pool receives input from other neurons

• Each pool generates output to other neurons

45

Convergence

• Neuron receives input from several

neurons

• Incoming impulses represent

information from different types of

sensory receptors

• Allows nervous system to collect,

process, and respond to information

• Makes it possible for a neuron to

sum impulses from different sources

1 2

3

(a)

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46

Divergence

• One neuron sends impulses

to several neurons

• Can amplify an impulse

• Impulse from a single neuron

in CNS may be amplified to

activate enough motor units

needed for muscle contraction

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(b)

4

5

6

47

Important Points in Chapter 10:

Outcomes to be Assessed

10.1: Introduction

Describe the general functions of the nervous system.

Identify the two types of cells that comprise nervous tissue.

Identify the two major groups of nervous system organs.

10.2: General Functions of the Nervous System

List the functions of sensory receptors.

Describe how the nervous system responds to stimuli.

10.3: Description of Cells of the Nervous System

Describe the three major parts of a neuron.

Define neurofibrils and chromatophilic substance.

48

Important Points in Chapter 10:

Outcomes to be Assessed

Describe the relationship among myelin, the neurilemma, and the

nodes of Ranvier.

Distinguish between the sources of white matter and gray matter.

10.4: Classification of Neurons and Neuroglia

Identify structural and functional differences among neurons.

Identify the types of neuroglia in the central nervous system and their

functions.

Describe the Schwann cells of the peripheral nervous system.

10.5: The Synapse

Define presynaptic and postsynaptic.

Explain how information passes from a presynaptic to a postsynaptic

neuron.

49

Important Points in Chapter 10:

Outcomes to be Assessed

10.6: Cell Membrane Potential

Explain how a cell membrane becomes polarized.

Define resting potential, local potential, and action potential.

Describe the events leading to the conduction of a nerve impulse.

Compare nerve impulse conduction in myelinated and unmyelinated

neurons.

10.7: Synaptic Transmission

Identify the changes in membrane potential associated with excitatory

and inhibitory neurotransmitters.

10.8: Impulse Processing

Describe the basic ways in which the nervous system processes

information.

50

Quiz 10

Complete Quiz 10 now!

Read Chapter 11.