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CH11 > CH11 > Flashcards

CH11 Flashcards

1
Q

3 Functions of the Nervous System

A

**1. Sensory input **

2. Integration

  • *3. Motor output
    • *
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2
Q

• Information gathered by sensory receptors about internal and external changes

A
  1. Sensory input
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3
Q

• Interpretation of sensory input

A

Integration

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4
Q

• Activation of effector organs (muscles and glands) produces a response

A

Motor output

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5
Q

Divisions of the Nervous System

A

1 Central nervous system (CNS)
• Brain and spinal cord
• Integration and command center

2 Peripheral nervous system (PNS)
• Paired spinal and cranial nerves carry messages to and from the CNS

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6
Q

Peripheral Nervous System (PNS)
• Two functional divisions

A
  1. Sensory (afferent) division
    • Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints
    • Visceral afferent fibers—convey impulses from visceral organs
  2. Motor (efferent) division

• Transmits impulses from the CNS to effector organs

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7
Q

Motor Division of PNS

has what 2 types of nervous systems

A
  1. Somatic (voluntary) nervous system
    • Conscious control of skeletal muscles

  1. Autonomic (involuntary) nervous system (ANS)
    • Visceral motor nerve fibers
    • Regulates smooth muscle, cardiac muscle, and glands
    • Two functional subdivisions
    • Sympathetic
    • Parasympathetic
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8
Q

Histology of Nervous Tissue
• Two principal cell types

A
  1. Neurons—excitable cells that transmit electrical signals

  1. Neuroglia (glial cells)—supporting cells:
    • Astrocytes (CNS)
    • Microglia (CNS)
    • Ependymal cells (CNS)
    • Oligodendrocytes (CNS)
    • Satellite cells (PNS)
    • Schwann cells (PNS)

MOSSEA

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9
Q

This supporting cell has=
• Most abundant, versatile, and highly branched glial cells
• Cling to neurons, synaptic endings, and capillaries
• Support and brace neurons
• Help determine capillary permeability
• Guide migration of young neurons
• Control the chemical environment
• Participate in information processing in the brain

A

Astrocytes

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10
Q

* This Supporting cell has=*
• Small, ovoid cells with thorny processes
• Migrate toward injured neurons
• Phagocytize microorganisms and neuronal debris

A

Microglia

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11
Q

This Supporting Cell has=

  • Range in shape from squamous to columnar
  • May be ciliated
  • Line the central cavities of the brain and spinal column
  • Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
A

Ependymal Cells

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12
Q

_ This Supporting Cell has=_
• Branched cells
• Processes wrap CNS nerve fibers, forming insulating myelin sheaths

A

Oligodendrocytes

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13
Q

• Surround neuron cell bodies in the PNS

A

• Satellite cells

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14
Q
  • Surround peripheral nerve fibers and form myelin sheaths
  • Vital to regeneration of damaged peripheral nerve fibers
A

• Schwann cells (neurolemmocytes)

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15
Q

Neurons (Nerve Cells)
• Special characteristics:

A
  • Long-lived (→ 100 years or more)
  • Amitotic—with few exceptions
  • High metabolic rate—depends on continuous supply of oxygen and glucose
  • Plasma membrane functions in:
  • Electrical signaling
  • Cell-to-cell interactions during development
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16
Q

What is
• Biosynthetic center of a neuron
• Spherical nucleus with nucleolus
• Well-developed Golgi apparatus
• Rough ER called Nissl bodies (chromatophilic substance)
• Network of neurofibrils (neurofilaments)
• Axon hillock—cone-shaped area from which axon arises
• Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS

A

Cell Body (Perikaryon or Soma)

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17
Q

• Rough ER are called what

A

Nissl bodies (chromatophilic substance)

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18
Q

• Network of neurofibrils are also know as

A

(neurofilaments)

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19
Q

• Axon hillock are

A

cone-shaped area from which axon arises

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20
Q

• Clusters of cell bodies are called

A

* nuclei* in the CNS,

ganglia in the PNS

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21
Q

Processes
are

A

• Dendrites and axons

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22
Q

• Bundles of processes are called

A

• Tracts** in the **CNS
• Nerves in the PNS

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23
Q
  • Short, tapering, and diffusely branched
  • Receptive (input) region of a neuron
  • Convey electrical signals toward the cell body as graded potentials
A

Dendrites

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24
Q

The Axon

How many axon per cell arising from the axon hillock

A

one

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25
Q

The Axon

• Long axons are known as

A

(nerve fibers)

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26
Q

The Axon

• Occasional branches are known as

A

(axon collaterals)

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27
Q

The Axon

• Knoblike axon terminals are known as

A

(synaptic knobs or boutons)

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28
Q

The Axon

• Secretory region of neuron do what

A

• Release neurotransmitters to excite or inhibit other cells

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29
Q

Axons Functions are

A
  • Conducting region of a neuron
  • Generates and transmits nerve impulses (action potentials) away from the cell body
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30
Q

Axons: Function
• Molecules and organelles are moved along axons by motor molecules in two directions:

A

_ • Anterograde_—toward axonal terminal
• Examples: mitochondria, membrane components, enzymes

• Retrograde—toward the cell body
• Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins

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31
Q

• Segmented protein-lipoid sheath around most long or large-diameter axons are what

A

Myelin Sheath

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32
Q

Myelin Sheaths
functions is to:

A
  • Protect and electrically insulate the axon
  • Increase speed of nerve impulse transmission
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33
Q

• Schwann cells wraps many times around

A

• Schwann cells wraps many times around _the axon
_

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34
Q

• Myelin sheath are

A

•
• Myelin sheath—_concentric layers of Schwann cell membrane
_

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35
Q

peripheral bulge of Schwann cell cytoplasm
are known as

A

• Neurilemma

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36
Q
  • Myelin sheath gaps between adjacent Schwann cells
  • Sites where axon collaterals can emerge
A

• Nodes of Ranvier

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37
Q

• Thin nerve fibers that are unmyelinated
& One Schwann cell may incompletely enclose 15 or more ____________?

A

Unmyelinated Axons

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38
Q
  • Formed by processes of oligodendrocytes, not the whole cells
  • Nodes of Ranvier are present
  • No neurilemma
  • Thinnest fibers are unmyelinated
A

Myelin Sheaths in the CNS

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39
Q

• Dense collections of myelinated fibers

A

• White matter

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40
Q

• Mostly neuron cell bodies and unmyelinated fibers

A

• Gray matter

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41
Q

Structural Classification of Neurons
• Three types:

A
  1. Multipolar—
  2. Bipolar—
  3. Unipolar (pseudounipolar)—
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42
Q

1 axon and several dendrites
• Most abundant
• Motor neurons and interneurons

A
  1. Multipolar—
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43
Q

1 axon and 1 dendrite
• Rare, e.g., retinal neurons

A

Bipolar—

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44
Q

—single, short process that has two branches:
• Peripheral process—more distal branch, often associated with a sensory receptor
• Central process—branch entering the CNS

A

Unipolar (pseudounipolar)—

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45
Q

Functional Classification of Neurons
• Three types:

A
  1. Sensory (afferent)
  2. Motor (efferent)
  3. Interneurons (association neurons)
46
Q

• Transmit impulses from sensory receptors toward the CNS

A
  1. Sensory (afferent)
47
Q

• Carry impulses from the CNS to effectors

A
  1. Motor (efferent)
48
Q

• Shuttle signals through CNS pathways; most are entirely within the CNS

A

Interneurons (association neurons)

49
Q
  • Respond to adequate stimulus by generating an action potential (nerve impulse)
  • Impulse is always the same regardless of stimulus
  • Neurons are highly irritable
A

Neuron Function

50
Q

• Energy is required to separate opposite charges across a membrane

  • Energy is liberated when the charges move toward one another
  • If opposite charges are separated, the system has potential energy

• Opposite charges attract each other

A

Principles of Electricity

51
Q

measure of potential energy generated by separated charge

A

• Voltage (V)

52
Q

voltage measured between two points

A

• Potential difference:

53
Q

the flow of electrical charge (ions) between two points

A

• Current (I):

54
Q

hindrance to charge flow (provided by the plasma membrane)

A

• Resistance (R):

55
Q

substance with high electrical resistance

A

• Insulator:

56
Q

substance with low electrical resistance

A

• Conductor:

57
Q

• serve as membrane ion channels

A

•_ Proteins_

58
Q

• Two main types of ion channels

A
  1. Leakage (nongated) channels—always open
  2. Gated channels (three types):
    • Chemically gated (ligand-gated) channels—open with binding of a specific neurotransmitter
  • Voltage-gated channels—open and close in response to changes in membrane potential
  • Mechanically gated channels—open and close in response to physical deformation of receptors
59
Q

Gated Channels
• When gated channels are open:

A
  • Ions diffuse quickly across the membrane along their electrochemical gradients
  • Along chemical concentration gradients from higher concentration to lower concentration
  • Along electrical gradients toward opposite electrical charge
  • Ion flow creates an electrical current and voltage changes across the membrane
60
Q
  • Potential difference across the membrane of a resting cell
  • Approximately –70 mV in neurons (cytoplasmic side of membrane is negatively charged relative to outside)
A

Resting Membrane Potential (Vr)

61
Q

Resting Membrane Potential (Vr)

• Generated by:

A
  • Differences in ionic makeup of ICF and ECF
  • Differential permeability of the plasma membrane
62
Q

• Differences in ionic makeup in a

Resting Membrane Potential** **

A

• ICF has lower concentration of Na+ and Cl– than ECF

• ICF has higher concentration of K+ and negatively charged proteins (A–) than ECF

63
Q

• Differential permeability of membrane

in a

Resting Membrane Potential

A

• Impermeable to A–

• Slightly permeable to Na+ (through leakage channels)

• 75 times more permeable to K+ (more leakage channels)

• Freely permeable to Cl–

64
Q

• Negative interior of the cell is due to what?

A
    • much greater diffusion of K+ out of the cell than Na+ diffusion into the cell
    • *
65
Q

**• Sodium-potassium pump stabilizes the **

A

resting membrane potential by maintaining the concentration gradients for Na+ and K+

66
Q
  • *• Membrane potential changes when:
    • *
A

• Concentrations of ions across the membrane change

  • *• Permeability of membrane to ions changes
    • *
67
Q

**• Changes in membrane potential are **

A

** signals used to receive, integrate and send information**

68
Q

Membrane Potentials That Act as Signals
• Two types of signals

A

• Graded potentials
Incoming short-distance signals

• Action potentials
Long-distance signals of axons

69
Q

Changes in Membrane Potential thats

  • A reduction in membrane potential (toward zero)
  • Inside of the membrane becomes less negative than the resting potential
  • Increases the probability of producing a nerve impulse
A

• Depolarization

70
Q

Changes in Membrane Potential that has

  • An increase in membrane potential (away from zero)
  • Inside of the membrane becomes more negative than the resting potential
  • Reduces the probability of producing a nerve impulse
A

• Hyperpolarization

71
Q

** • Occur when a stimulus causes gated ion channels to open
• E.g., receptor potentials, generator potentials, postsynaptic potentials
• Magnitude varies directly (graded) with stimulus strength
• Decrease in magnitude with distance as ions flow and diffuse through leakage channels
• Short-distance signals**

• Short-lived, localized changes in membrane potential

• Depolarizations or hyperpolarizations

  • *• Graded potential spreads as local currents change the membrane potential of adjacent regions
    • *
A
  • *Graded Potentials
    • *
72
Q
  • Brief reversal of membrane potential with a total amplitude of ~100 mV
  • Occurs in muscle cells and axons of neurons
  • Does not decrease in magnitude over distance
  • Principal means of long-distance neural communication
A

Action Potential (AP)

73
Q

Generation of an Action Potential

  • Only leakage channels for Na+ and K+ are open
  • All gated Na+ and K+ channels are closed
A

• Resting state

74
Q

• Properties of gated channels

  • *• Each Na+ channel has two voltage-sensitive gates
    • *
A

• Activation gates
Closed at rest; open with depolarization

• Inactivation gates
Open at rest; block channel once it is open

Opens slowly with depolarization

75
Q

• Some K+ channels remain open, allowing excessive K+ efflux

• This causes after-hyperpolarization of the membrane (undershoot)

A

• Hyperpolarization

76
Q
  • Membrane is depolarized by 15 to 20 mV
  • Na+ permeability increases
  • Na influx exceeds K+ efflux
  • The positive feedback cycle begins
A

• At threshold:

77
Q

weak local depolarization that does not reach threshold

A

• Subthreshold stimulus—

78
Q

strong enough to push the membrane potential toward and beyond threshold

A

• Threshold stimulus—

79
Q

action potentials either happen completely, or not at all

A

• AP is an all-or-none phenomenon

80
Q

Coding for Stimulus Intensity

  • All action potentials are alike and are independent of stimulus intensity
  • How does the CNS tell the difference between a weak stimulus and a strong one?
A

• Strong stimuli can generate action potentials more often than weaker stimuli

• The CNS determines stimulus intensity by the frequency of impulses

81
Q

**
• Larger diameter fibers have less resistance to local current flow and have faster impulse conduction
**

A
  • *• Effect of axon diameter
    • *
82
Q
  • *• Continuous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons
    • *
A

• Effects of myelination

83
Q
  • Myelin sheaths insulate and prevent leakage of charge
  • Saltatory conduction in myelinated axons is about 30 times faster
  • Voltage-gated Na+ channels are located at the nodes
  • APs appear to jump rapidly from node to node
A

• Effect of myelination

84
Q

• Nerve fibers are classified according to:

A

**
• Diameter
• Degree of myelination
• Speed of conduction**

85
Q

• Large diameter, myelinated somatic sensory and motor fibers

A

• Group A Nerve fibers

86
Q

• Intermediate diameter, lightly myelinated ANS fibers

A

• Group B Nerve fibers

87
Q

Smallest diameter, unmyelinated ANS fibers

A

• Group C Nerve fibers

88
Q
  • A junction that mediates information transfer from one neuron:
  • To another neuron, or
  • To an effector cell
A
  • *The Synapse
    • *
89
Q

conducts impulses toward the synapse

A

• Presynaptic neuron—

90
Q

transmits impulses away from the synapse

A

• Postsynaptic neuron—

91
Q

Types of Synapses
—between the axon of one neuron and the dendrite of another

A

**• Axodendritic **

92
Q

Types of Synapses
• between the axon of one neuron and the soma of another

A

• Axosomatic

93
Q

Types of Synapses

• Less common types:

A
  • Axoaxonic (axon to axon)
  • Dendrodendritic (dendrite to dendrite)
  • Dendrosomatic (dendrite to soma)
94
Q
  • Less common than chemical synapses
  • Neurons are electrically coupled (joined by gap junctions)
  • Communication is very rapid, and may be unidirectional or bidirectional
A

Electrical Synapses

95
Q

Electrical Synapses

• Are important in:

A

• Embryonic nervous tissue

• Some brain regions

96
Q

• Specialized for the release and reception of neurotransmitters

A

Chemical Synapses

97
Q

Chemical Synapses

• Typically composed of two parts

A

• Axon terminal of the presynaptic neuron, which contains synaptic vesicles

• Receptor region on the postsynaptic neuron

98
Q
  • Fluid-filled space separating the presynaptic and postsynaptic neurons
  • Prevents nerve impulses from directly passing from one neuron to the next
A

Synaptic Cleft

99
Q

Synaptic Cleft

• Transmission across the synaptic cleft:

A

• Is a chemical event (as opposed to an electrical one)

• Involves release, diffusion, and binding of neurotransmitters

• Ensures unidirectional communication between neurons

100
Q

• What happens Within a few milliseconds, the neurotransmitter effect is terminated
•

A
  • Degradation by enzymes
  • Reuptake by astrocytes or axon terminal
  • Diffusion away from the synaptic cleft
101
Q

Postsynaptic Potentials
• Graded potentials
• Strength determined by:

A

• Amount of neurotransmitter released

  • *• Time the neurotransmitter is in the area
    • *
102
Q

• Types of postsynaptic potentials

A

1. EPSP—excitatory postsynaptic potentials

2. IPSP—inhibitory postsynaptic potentials

103
Q

• One or more presynaptic neurons transmit impulses in rapid-fire order

A

• Temporal summation

104
Q

• Postsynaptic neuron is stimulated by a large number of terminals at the same time

A

• Spatial summation

105
Q
  • Released at neuromuscular junctions and some ANS neurons
  • Synthesized by enzyme choline acetyltransferase
  • Degraded by the enzyme acetylcholinesterase (AChE)
A
  • *• Acetylcholine (Ach)
    • *
106
Q

Chemical Classes of Neurotransmitters
• Peptides (neuropeptides) include:

A

• Substance P
Mediator of pain signals

• Endorphins
Act as natural opiates; reduce pain perception

• Gut-brain peptides
Somatostatin and cholecystokinin

107
Q
  • Act in both the CNS and PNS
  • Produce fast or slow responses
  • Induce Ca2+ influx in astrocytes
  • Provoke pain sensation
A
  • *• Purines such as ATP:
    • *
108
Q
  • Synthesized on demand
  • Activates the intracellular receptor guanylyl cyclase to cyclic GMP
  • Involved in learning and memory
A

• Nitric oxide (NO)

109
Q

is a regulator of cGMP in the brain

A

**• Carbon monoxide (CO) **

110
Q
  • Lipid soluble; synthesized on demand from membrane lipids
  • Bind with G protein–coupled receptors in the brain
  • Involved in learning and memory
A

• Endocannabinoids

CH11 (1 decks)

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