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Flashcards in Chapter 11 Deck (109)
1

The Nervous System

Controlling and communication system of body
Cells communicate via electrical and chemical signals
-Rapid
-Specific
-Usually cause almost immediate responses

2

Functions of Nervous System

Sensory Input
-Information
Integration
-Processing
Motor Output
-Activation

3

Divisions of Nervous System

Central Nervous System (CNS)
Peripheral Nervous System (PNS)

4

Central Nervous System (CNS)

Contents
-Brain
-Spinal Cord
Location
-Dorsal Body Cavity
Function
-Integration and control center
--Interprets sensory input and dictates motor output

5

Peripheral Nervous System (PNS)

Contents
-Spinal nerves to and from spinal cord
-Cranial nerves to and from brain
Location
-Outside brain and spinal cord

6

2 Functional Divisions Peripheral Nervous System (PNS)

Sensory (afferent) division
Motor (efferent) division

7

Sensory (Afferent) Division of PNS

-Somatic sensory fibers- convey impulses from skin, skeletal muscles, and joints to CNS
-Visceral sensory fibers- convey impulses from visceral organs to CNS

8

Motor (Efferent) Division of PNS

Transmits impulses from CNS to effector organs
-Muscles and Glands

9

2 Divisions of Motor (Efferent) Division

Somatic Nervous System
Autonomic Nervous System

10

Motor Division of PNS: Somatic Nervous System of PNS

Somatic motor nerve fibers
-Conducts impulses from CNS to skeletal muscle
-Voluntary nervous system
--Conscious control of skeletal muscles

11

Motor Division of PNS: Autonomic Nervous System

Visceral motor nerve fibers
Smooth muscle, cardiac muscle, and glands
Involuntary nervous systems
Two functional Subdivisions
-Sympathetic
-Parasympathetic

12

Histology of Nervous Tissue

Higher cellular: little extracellular space
-tightly packed
Two principle cell types
-Neuroglia- Small cell that wraps delicate neurons
-Neurons (nerve cells)- Nerve cells, functional unit

13

Histology of Nervous Tissue: Neuroglia

Astrocytes (CNS)
Microglial Cells (CNS)
Satellite Cells (PNS)
Schwann Cells (PNS)

14

Astrocytes

Most abundant, versatile, and highly branched glial cells
Cling to neurons, synaptic endings, and capillaries

15

Astrocytes Function

-Support and brace neurons
-Play role in exchanges
-Guide migration of young neurons
-Control chemical environment around neurons
-Respond to nerve impulses and neurotransmitters
-Influence neuronal functioning

16

Microglial Cells

-Small, ovoid cells with thorny processes that touch and monitor neurons
-Migrates toward injured neurons
-Can transform to phagocytize microorganisms and neuronal debris

17

Satellite Cells

Surround neuron cell bodies in PNS
Function to similar to astrocytes

18

Schwann Cells

Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers
Regeneration

19

Neurons

Definition
-Structural unit of nervous system
Function
-Conduct impulses
Extreme longevity
-100 years or more
Amitotic- with few exceptions
High metabolic rate
All have cell body and one or more processes

20

Neuron Cell Body (Soma)

Center of neuron
-Synthesizes proteins, membranes, and other chemicals
Spherical nucleus with nucleolus
Most neuron cell bodies in CNS
-Nuclei- clusters of neuron cell bodies in CNS
Ganglia- lie along nerves in PNS
-Most common in Spinal Cord

21

Neuron Processes

Armlike processes extend from body
Tracts
-Bundles of neuron processes in CNS
Nerves
-Bundles of neuron processes in PNS
Two types of Processes
-Dendrites
-Axons

22

Dendrites

In motor neurons
-Hundreds of short, tapering, diffusely branched processes
Receptive (input) region of neuron
-Convey incoming messages toward cell body as graded potentials (short distance signals)

23

Axon: Structure

One axon per cell
-In some axon short or absent
-In other most of length of cell
-Some 1 meter long
Long axons called nerve fibers
Branches profusely at end (terminus)
Distal endings call axon terminals

24

Axon: Functional Characteristics

Conducting region of neuron
Generates nerve impulses
Transmits the Axon Terminal
-Secretory region
-Neurotransmitters released into extracellular space
Carries on many conversations with different neurons at same time
Lacks rough ER and Golgi Apparatus
-Relies on cell body to renew proteins and membrane
-Efficient transport mechanisms
-Quickly decay if cut or damaged

25

Transport Along the Axon

Molecules and organelles are moved along axons
-Anterograde
-Retrograde

26

Anterograde

Away from cell body
Examples
-Mitochondria
-Cytoskeleton elements
-Membrane components
-Enzymes

27

Retrograde

Toward body cell
Examples
-Organelles to be degraded
-Signal molecules
-Viruses
- Bacterial toxins

28

Myelin Sheath

Composed of myelin
-Whitish, protein-lipoid substance
Segmented sheath around most long or large-diameter axons
-Myelinated Fibers
Nonnyelinated fibers conduct impulses more slowly

29

2 Functions of Myelin

Protects and electrically insulates axon
Increases speed of nerve impulses transmission

30

Myelin in PNS

Formed by Schwann Cells
-Jelly roll
-One cell forms one segment of myelin sheath
Myelin Sheath
-Concentric layers of Schwann Cells around axon

31

Myelination in PNS

Myelin Sheath gaps
-Gaps between adjacent Schwann cells
-Sites where axon collaterals can emerge
Myelin sheath gaps between adjacent Schwann Cells
-Sites where axon collaterals can emerge
Nonmyelinated fibers

32

Myelination in CNS

Can wrap up to 60 axons at once
Myelin Sheath gap is present
No outer collar of perinuclear cytoplasm
Thinnest fibers are unmyelinated
White Matter
-Regions of brain and spinal cord with dense collections of myelinated fibers
-Usually fiber tracts
Gray Matter
-Mostly neuron cell bodies and nonmyelinated fibers

33

Structural Classification of Neurons

Multipolar- 3 or more processes
-1 axon, other dendrites
-Most common: major neuron in CNS

34

Functional Classification of Neurons

Grouped by direction in which nerve impulse travels relative to CNS
3 Types
-Sensory (Afferent)
-Motor (Efferent)
-Interneurons

35

Functional Classifications of Neurons: Sensory

-Transmit impulses from sensory receptors toward CNS
-Cell bodies in ganglia in PNS

36

Functional Classifications of Neurons: Motor

-Carry impulses from CNS to effectors
-Most cell bodies in CNS

37

Functional Classifications of Neurons: Interneurons

-Lie between motor and sensory neurons
-Shuttle signals through CNS pathways
-99% of body's neurons
-Most confined in CNS

38

Membrane Potential

-Excitability
-Respond to adequate stimulus by generating an action potential
--Action Potential- Nerve Impulse
-Impulse is the same as each neuron

39

Voltage

A measure of potential energy generated by separated charge
-Volts (V) or Milivolts (mV)
-Called Potential Difference
-Greater charge difference between points = higher voltage

40

Current

Flow of electrical charge (ions) between two points

41

Resistance

Hindrance to charge flow
-Insulator
-Conductor

42

Ohm's Law

The relationship of voltage, current, resistance
Current= voltage/resistance
-Current is directly proportional to voltage
-Current inversely related to resistance
-No net current flow between points with same potential

43

Role of Membrane Ion Channels

Large proteins: Ion channels
Two main types of ion channels
-Leakage (nongated) Channels
-Gated Channels

44

Gated Channels 3 Types

Chemically Gated Channels
-Neurotransmitter
Voltage-Gated Channels
-Potentials
Mechanically Gated Channels
-Physical

45

Gated Channels

When open
-Ions diffuse quickly across membrane along electrochemical gradients
--Chemical Gradients
--Electric Gradients

46

The Resting Membrane Potential

Potential difference across membrane of resting cell
-Approximately -70mV in neurons
-Cytoplasmic side of membrane negatively charged relative to outside
-polarized
Generated by
-Differences in ionic makeup of ICF and ECF

47

ECF

Outside Neuron
Higher concentration of Na+
Balanced chiefly by chloride ions (Cl-)

48

ICF

Inside Neuron
Higher concentration of K+
Balanced by negatively charged proteins

49

K+

Plays most important role in membrane potential

50

Differences in Plasma Membrane Permeability

Impermeability
Slightly permeable to Na+
-through leakage channels
25 times more permeable to K+ than sodium
-more leakage channels
-potassium diffuses out of cell down concentration gradient
Very permeable to Cl-

51

Resting Membrane Potential

More potassium diffuses out than sodium diffuses in
-Cell more negative inside
-Establishes resting membrane potential
Sodium-Potassium pump stabilizes resting membrane potential
-Maintains concentration gradients for Na+ and K+
-3 Na+ pumped out of cell; 2 K+ pumped in

52

Membrane Potential Changes: Used as Communication Signals

Membrance potential changes when
-Concentration of ions across membrane change
-Membrane permeability to ions change
Changes produce 2 types signal
-Graded Potentials
-Action Potentials

53

Graded Potentials

Incoming signals operating over short distances
Short-lived, localized changes in membrane potential
-Magnitude varies with stimulus strength
-Stronger stimulus- more voltage changes; farther current flows
Either depolarization or hyperpolarization
Current flows but dissipates quickly and decays
-Graded potentials are signals only over short distances

54

Action Potentials

Long-distance signals of axons
Principle way neurons send signals
Means of long-distance neural communication
Occur only in muscle cells and axons of neurons
Do not decay over distance as graded potentials do

55

Properties of Gated Channels: K

Each K+ channel has one voltage-sensitive gate
Closed at rest
Opens slowly with depolarization

56

Generation of an Action Potential: Resting State

All gated Na+ and K+ channels are closed
Only leakage channels for Na+ and K+ are open
-This maintains the resting membrane potential

57

Generation of an Action Potential: Depolarizing Phase

Depolarizing local currents open voltage-gated Na+ channels
-Na+ rushes into cell
Na+ influx causes more depolarization which opens more Na+ channels
Positive feedback causes opening of all Na+ channels- a reversal of membrane polarity to +30mV
-Spike of action potential

58

Generation of an Action Potential: Repolarizing Phase

Na+ channel gates close
Membrane permeability to Na+ declines to resting state
-Action Potential spike stops rising
Slow voltage-gated K+ channels open
-K+ exits the cell and internal negativity is restored

59

Role of Sodium-Potassium Pump (Na+/K+)

Repolarization resets electrical conditions
After repolarization Na+/K+ pumps (thousands of them in an axon) restore ionic conditions

60

Threshold

Not all depolarization events produce action potentials
For axon to "fire", depolarization must reach threshold
-That voltage at which the action potential is triggered
At Threshold:
-Na+ permeability increases
-Na+ influx exceeds K+ efflux
-The positive feedback cycle begins

61

The All-or-None Phenomenon

An action potential either happens completely, or it does not happen at all

62

Coding for Stimulus Intensity

-All action potentials are alike and are independent of stimulus intensity
-Strong stimuli cause action potentials to occur more frequently
-Higher frequency means stronger stimulus

63

Absolute refractory Period

When voltage-gated Na+ channels open neurons cannot respond to another stimulus
-Time from opening of Na+ channels until resetting of the channels
-Ensures that each action potential is an all-or-none event
-Enforces one-way transmission of nerve impulses

64

Relative Refractory Period

Follows absolute refractory period
-Most Na+ channels have returned to their resting state
-Some K+ channels are still open
-Repolarization is occurring
Threshold for action potential generation is elevated
-Inside of membrane more negative than resting state
Only exceptionally strong stimulus could stimulate an action potential

65

Conduction Velocity

Rate of action potential propagation depends on
-Axon diameter (Large vs. Small)
-Degree of Myelination (Contains vs. nonmyelin)

66

Conduction Velocity: Effects of Myelination

Insulate and prevent leakage of charge
Saltatory conduction (possible only in myelinaed axons) is about 30 times faster
-Voltage-gated Na+ channels are located at myelin sheath gaps
-Action potential generated only at gaps
-Electrical signal appears to jump rapidly from gap to gap

67

Nerve Fiber Classification

-Diameter
-Degree of myelination
-Speed of conduction

68

Multiple Sclerosis (MS)

Autoimmune disease affecting primarily young adults
Myelin sheaths in CNS destroyed
-Immune system attacks myelin
-Impulse conduction slows and eventually ceases
-Demyelinated axons increase Na+ channels
Symptoms
-Visual disturbances
-Weakness
-Loss of muscular control
-Speech disturbance
-Urinary Incontinence
Treatment
-Drugs that modify immune system's activity improve lives

69

Synapse

Nervous system works because information flows from neuron to neuron
Neurons functionally connected by synapses
-Junctions that mediate information transfer
--one neuron to another neuron
--one neuron to an effector cell

70

Presynaptic Neuron

-Neuron conducting impulses toward synapse
-Sends information

71

Postsynaptic Neuron

Neuron, Muscles cell, or Gland cell
-Neuron transmitting electrical signal away from synapse
-Receives the information
Most function as both

72

Chemical Synapses

Most Common
Specialized for release and reception of chemical neurotransmitters
Two Parts
Electrical impulse changed to chemical across synapse, then back into electrical

73

Two Parts of Neurotransmitter

Axon terminal of presynaptic neuron
-Contains synaptic vesicles filled with neurotransmitter
Neurotransmitter receptor region on postsynaptic neuron's membrane
-Usually on dendrite or cell body

74

Synaptic Cleft

30-50 nm wide
Prevents nerve impulses from directly passing from one neuron to next

75

Transmission Across Synaptic Cleft

-Chemical event
-Depends on release, diffusion, and receptor binding of neurotransmitter
-Ensures unidirectional communication between neurons

76

Information Transfer Across Chemical Synapses
(Watch Video)

Action Potential arrives at axon terminal of presynaptic neuron
Causes voltage-gated Ca2+ channels to open
-Ca2+ floods into cell
Fusion of synaptic vesicles with axon membrane
Exocytosis of neurotransmitter into synaptic cleft occurs
-Higher impulse frequency- more released
Neurotransmitter diffuses across synapse
Binds to receptors on postsynaptic neuron
-Often chemically gated ion channels
Ion channels are opened
Causes an excitatory or inhibitory event
Neurotransmitter effects terminated

77

Termination of Neurotransmitter Effects

Within a few milliseconds neurotransmitter effect terminated in one of three ways
-Re-uptake
-Degradation
-Diffusion

78

Termination of Neurotransmitter Effects: Re-uptake

By astrocytes or axon terminal

79

Termination of Neurotransmitter Effects: Degradation

By enzymes

80

Termination of Neurotransmitter Effects: Diffusion

Away from synaptic cleft

81

Synaptic Delay

Time needed for neurotransmitter to be released, diffuse across synapse, and bind to receptors
-0.3-5.0 milliseconds

82

Postsynaptic Potentials

Neurotransmitter receptors cause graded potentials that vary in strength with
-Amount of neurotransmitter released
-Time neurotransmitter stays in area

83

Types if Postsynaptic Potentials

EPSP
IPSP
Not Action Potentials

84

EPSP

Excitatory Postsynaptic Potentials

85

IPSP

Inhibitory Postsynaptic Potentials

86

Excitatory Synapses and EPSPs

Neurotransmitter binding opens chemically gated channels
-Allows simultaneous flow of Na+ and K+ in opposite directions
Na+ influx greater than K+ efflux - net depolarization called EPSP not AP
EPSP help trigger AP if EPSP is of threshold strength
-Can trigger opening of voltage gated channels, and cause AP to be generated

87

Inhibitory Synapses and IPSPs

Reduces postsynaptic neuron's ability to produce an action potential
-Makes membrane more permeable to K+ or Cl-
--If K+ channels open, it moves out of cell
--If Cl- channels open, it more into cell
Neurotransmitter hyperpolarizes cell
-Inner surface of membrane becomes more negative
-Action potential less likely to be generated

88

Synaptic Integration: Summation

A single EPSP cannot induce an action potential
EPSPs can summate to influence postsynaptic neuron
IPSPs can also summate
Most neurons receive both excitatory and inhibitory inputs from thousands of other neurons
-Only if EPSP's predominate and bring to threshold- Action Potential

89

Integration: Synaptic Potentiation

Repeated use of synapse increases ability of presynaptic cell to excite postsynaptic neuron
-Ca2+ concentration increases in presynaptic terminal and postsynaptic neuron

90

Neurotransmitters

Language of nervous system
50 or more neurotransmitters have been identified
Most neurons make two or more neurotransmitter
-Neurons can exert several influences
Released at different stimulation frequencies

91

Classification of Neurotransmitters: Function

Great diversity of functions
Classified by
-Effects- excitatory vs. inhibitory
-Actions- direct vs. indirect

92

Effects

Neurotransmitter effects can be excitatory (depolarizing) and/or inhibitory (hyperpolarizing)
Effect determined by receptor to which it binds

93

Direct Action

Neurotransmitter binds to and opens ion channels
Promotes rapid responses by altering membrane potential

94

Indirect Action

Neurotransmitter acts through intracellular second messenger
Broader, longer-lasting effects similar to hormones

95

Channel Linked Receptors

Mediate fast synaptic transmission

96

Channel-Linked (Ionotropic) Receptors: Mechanism of Action

Ligand-gated ion channels
Action is immediate and brief

97

Basic Concepts of Neural Integration

Neurons function in groups
There are billions of neurons in CNS
-Must be integration so the individual parts fuse to make a smoothly operating whole

98

Organization of Neurons: Neuronal Pools

Functional groups of neurons
-Integrate incoming information
-Forward processed information to other destinations

99

Circuits

Patterns of synaptic connections in neuronal pools

100

4 Types of Circuits (Look at Diagrams)

Diverging
Converging
Reverberating
Parallel after Discharge

101

Diverging Circuit (Look at Diagrams)

One input, many outputs
An amplifying circuit

102

Converging Circuit (Look at Diagrams)

Many inputs, one output
A concentrating citcuit

103

Reverberating Circuit (Look at Diagrams)

Signal travels through a chain of neurons, each feeding back to previous neurons
An oscillating circuit
Controls rhythmic activity

104

Parallel after Discharge Circuit (Look at Diagrams)

Signal Stimulates neurons arranged in parallel arrays that eventually converge on a single output cell
Impulses reach output cell at different times, causing a burst of impulses call an after-discharge

105

Patterns of Neural Processing: Serial Processing

Input travels along one pathway to specific destination
System works in all-or-none manner to produce specific, anticipated response

106

Spinal Reflexes

Rapid, automatic responses to stimuli
Particular stimulus always causes same response
Occur over pathways called reflex arcs: 5 parts
-Receptor
-Sensory Neuron
-CNS Integration Center
-Motor Neuron
-Effector

107

Patterns of Neural Processing: Parallel Processing

Input travels along several pathways
Different parts of circuitry deal simultaneously with the information
-One stimulus promotes numerous responses
Important for higher-level mental functioning

108

Developmental Aspects of Neurons

Nervous system originates from neural tube and neural crest formed from ectoderm
The neural tube becomes CNS

109

Cell Death

About 2/3 of neurons die before birth
-If do not form synapse with target
-Many cells also die due to apoptosis (programmed cell death) during development