Chapter 12 Flashcards

1
Q

Everything done in NS involves (3) fundamental steps

A

1) sensory function detects internal & external stimuii
2) interpretation is made (analysis)
3) motor response occurs (reaction)

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2
Q

Divisions of the Nervous System (2)

A

CNS → brain & spinal cord

PNS → all nervous tissue outside CNS (includes nerves, ganglia, enteric plexuses & sensory receptors)

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3
Q

Most signals that __ muscles to ___ and __ to ___ originate in CNS

A

stimulate muscles to contract and glands to secrete originate in CNS

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4
Q

PNS is further divided into (3) ?

A

1) somatic sensory system (SNS)
2) autonomic nervous system (ANS)
3) enteric nervous system (ENS)

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5
Q
**SNS** 
consists of (3)?
A

1) somatic sensory (afferent) neurons
2) Somatic motor (efferent) neurons
3) Interneurons

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6
Q

SNS

1) somatic sensory (afferent) neurons

A

convey info from sensory receptors in head, body wall & limbs toward CNS

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7
Q

SNS

2) Somatic motor (efferent) neurons

A

conduct impulses from CNS to skeletal muscle under voluntary control in periphery

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8
Q

SNS

3) Interneurons

A

any neurons that conduct impulses between afferent and efferent neurons within the CNS

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9
Q

PNS → 2) ANS

consists of? (2)

A

1) Sensory Neurons
2) Motor Neurons

  • sympathetic division
    • parasympathetic division
      *
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10
Q

ANS → sensory neurons

A

convey info from :

autonomic sensory receptors mostly in visceral organs (stomach/lungs) → CNS

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11
Q

ANS → motor neurons

A

under involuntary control

conduct nerve impulses from CNS → smooth muscle, cardiac muscle & glands

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12
Q

ANS → motor neurons

  • (2) branches
A

Sympathetic division

Parasympathetic division

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13
Q

Neurons

  1. gather info where?
  2. process info where?
  3. transmit info where?
A

1) gather info at dendrites
2) process info in dendritic tree & cell body
3) transmit info down axon to axon terminals

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14
Q

Synapse

A

site of communication between two neurons OR between a neuron & another effector cell

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15
Q

Synaptic Cleft

A

gap between pre & postsynaptic cells

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16
Q

Synaptic end bulbs & other varicosities on axon terminals of presynaptic neurons contain many?

A

tiny membrane-enclosed sacs (synaptic vesicles) that store packets of neurotransmitter chemicals.

many neurons even contain 2 or 3 types of neurotransmitters, each with different effects on postsynaptic cell

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17
Q

Like muscle fibers, neurons are electrically excitable

  • communicate with each other using (2) types of electrical signals
A

1) Graded Potential
2) Action Potential

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18
Q

1) Graded Potential

A

used for short-distance communication only

only in dendrites & cell bodies

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19
Q

2) Action Potential

A

allow long-distance communication within body

at axon hillock

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20
Q

Producing electrical signals in neurons depends on ?

A

existance of resting membrane potential (RMP)

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21
Q

How is a cell’s RMP created?

A

created using ion gradients & variety of ion channels that open/close in response to specific stimuli

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22
Q

Prevalence of Ion Channels in Body

A

present in plasma membrane of all body cells but especially prominant part of NS

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23
Q

Steps of touching a pen → to CNS

A

touch → GP in sensory receptor of skin → triggers axon to form AP → along axon into CNS

→ causes release of neurotransmitters at synapse with interneuron → stimulates interneuron to form GP in dendrites & cell body (process repeats as interneurons in higher parts of brain [thalamus/cerebral cortex] are activated)

perception occurs when interneurons in cerebral cortex are activated

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24
Q

Steps of using a pen →

A

stimulus in brain → GP in dendrites/cell body of upper motor neuron → causes AP in axon → neurotransmitter release →GP in lower motor neuron → AP → neurotransmitter release at NMJ → stimulate muscle fibers → AP → contraction

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25
Q

When Ion channels are open, this allows..?

A

specific ions to move across plasma membrane down their electrochemical gradient

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26
Q

Electrochemical Gradient

A

concentration (chemical) difference plus an electrical difference

Chemical (concentration) part → ions move from areas of [high] to [low]

Electrical aspect → cations move toward negatively-charged area & anions move towards positively-charged area

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27
Q

Active channels open in response to?

A

stimulus (they are “gated”)

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28
Q

(3) types of active, gated channels

A

1) ligand-gated
2) voltage-gated
3) mechanically-gated

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29
Q

Ligand-gated Channels

A

respond to a neurotransmitter or hormone and are mainly concentrated at synapse

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30
Q

Voltage-gated Channels

A

respond to changes in transmembrane electrical potential & mainly located along neuronal axon

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31
Q

Mechanically-gated Channels

A

respond to mechanical deformation (applying pressure to receptor due to vibration, touch, stretch)

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32
Q

Leakage channels

A

gated but NOT active

  • open & close randomly
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33
Q

RMP exists because of?

A

small buildup of negative ions in cytosol inside membrane & positive ions in ECF on surface

→ occurs very close to membrane, cytosol elsewhere is electrically neutral

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34
Q

Why is RMP slightly negative?

A

leakage channels favor gradient where more K+ leaks out than Na+ leaks in

(more K+ channels than Na+ channels)

  • also large negatively charged proteins that always remain in cytosol
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35
Q

What would eventually destroy RMP if left unchecked?

A

small inward leakage of Na+

36
Q

What offsets inward Na+ leak & outward K+ leak?

A

NA+/K+ ATPases (sodium-potassium pump)

  • pumps out Na+ as fast as it leaks in
37
Q

Polarized cell

A

A cell that exhibits an RMP

38
Q

Cell is “primed”

A

Cell in polarized state (exhibiting an RMP) → ready to produce an AP

39
Q

To produce an AP, what needs to happen first?

A

Graded potential must first be produced in order to depolarize cell to threshold

40
Q
  • A graded potential occurs whenever …?
A

ion flow in mechanically/ligand-gated channels produce current that is localized

    • it spreads to adjacent regions for short distance & then dies out within few millimeters of its point of origin.*
41
Q

(2) types of Graded Potentials

A

1) Depolarizing graded potential
2) Hyperpolarizing graded potential

42
Q

1) Depolarizing graded potential

A

From RMP, stimulus that causes cell to be less negatively charged than ECF

43
Q

2) Hyperpolarizing graded potential

A

stimulus that causes cell to be more negatively charged

44
Q

Graded potentials have dif names depending on (2)

A

type of stimulus

where they occur

45
Q

Graded Potentials occur mainly in? (2)

A

dendrites & cell body

do NOT travel down axon

46
Q

(2) main phases of AP

A

1) depolarizing
2) repolarizing

47
Q

AP steps

A

GP → depolarization of neuron from -70mV to threshold (-55mV)

→ Na+ channels open → Na+ inflow → inside becomes more positive

repolarization Na+ channels inactivating, K+ channels **open → ** K+ outflow

after-hyperpolarizing phase → K+ channels still open, membrane potential becomes even more negative (-90mV)

As K+ channels close, MP returns to resting level (-70mV)

48
Q

Absolute refractory period

A

period of time during which cell can’t generate another AP, no matter how strong stimulus is

coincides with period of Na+ channel activation & inactivation (inactivated Na+ channels must 1st return to resting state.)

This places an upper limit of 10–1000 nerve impulses/second, depending on neuron

49
Q

Relative refractory period

A

period of time during which 2nd AP can be initiated, but only by larger-than-normal stimulus

  • coincides with when voltage-gated K+ channels are still open after inactivated Na+ channels have returned to resting state.
50
Q

Do graded potentials exhibit refractory periods?

A

NO

In contrast to action potentials, graded potentials do not exhibit refractory period

51
Q

Propagation of AP down length of axon begins at?

A

trigger zone near axon hillock by passive spread

52
Q

Propagation of AP down length of axon begins at trigger zone near axon hillock by passive spread, the current proceeds by (2)

A

1) continuous conduction
2) saltatory conduction

53
Q

1) continuous conduction

A

slower, in unmyelinated axons

54
Q

2) saltatory conduction

A

much faster process in myelinated axons

AP jumps from one node to next

55
Q

In addition to nodes of Ranvier that allow saltatory conduction, speed of an AP is also affected by? (3)

A

1) axon diameter
2) amount of myelination
3) temperature

56
Q

(2) factors that play role in determining perception of stimulus or extent of response

A

1) Frequency of AP
2) # of neurons recruited (activated)

57
Q

(3) Fiber Types of Neuronal Axons

A

1) A fibers
2) B fibers
3) C fibers

58
Q

1) A fibers

A

large, fast (12-130 m/sec) → (290 mph)

myelinated neurons

carry touch & pressure sensations

many motor neurons are this type

59
Q

2) B fibers

A

medium size & speed (15 m/sec) → 34 mph

comprise myelinated visceral sensory

60
Q

3) C fibers

A

smallest & slowest (2 m/sec)

comprise unmyelinated sensory & autonomic motor neurons

61
Q

Signal transmission at the synapse is ..

A

one-way transfer from presynaptic neuron to postsynaptic neuron

62
Q

When AP reaches end bulb of axon terminals…

A

voltage-gated Ca2+ channels open → Ca2+ flows inward from ECF → triggering release of neurotransmitter

→ crosses synaptic cleft & binds to ligand-gated receptors on post-s membrane

63
Q

Conversion of signal from pre to post-synaptic neuron

A

presynaptic neuron converts electrical signal (nerve impulse) into chemical signal (released neurotransmitter)

postsynaptic neuron recieves this chemical signal → generates electrical signal (postsynaptic potential)

64
Q

Synaptic Delay

A

time required for these processes at chemical synapse (conversion of electrical signal → chemical → electrical)

about 0.5 msec

65
Q

Neurotransmitter effects can be modified by in many ways (4)

A

1) synthesis → stimulated/blocked
2) release → blocked/enhanced
3) removal → stimulated/blocked
4) receptor site → blocked/activated

66
Q

Agonist

A

any chemical that enhances or stimulates the effects at a given receptor

67
Q

Antagonist

A

any chemical that blocks or diminishes the effects at a given receptor

68
Q

A neurotransmitter causes either an …(2)

A

excitatory or an inhibitory graded potential

69
Q

Excitatory postsynaptic potential (EPSP)

A
  • causes depolarization of postsynaptic cell, bringing it closer to threshold

    • Although single EPSP normally does not initiate a nerve impulse, postsynaptic cell does become more excitable.*
70
Q

Inhibitory postsynaptic potential (IPSP)

A
  • hyperpolarizes postsynaptic cell taking it farther from threshold.
71
Q

Spatial Summation

A

summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time

involves input from dif neurons stimulating post-s neuron in dif parts of membrane at same time

72
Q

Temporal Summation

A

summation of postsynaptic potentials in response to stimuli that occur at same locations in the membrane of a postsynaptic cell but at different times

73
Q

Whether or not postsynaptic cell reaching threshold depends on ?

A

net effect after summation of all postsynaptic potentials.

74
Q

If neurotransmitter could linger in synaptic cleft, it would influence ?

A

postsynaptic neuron/muscle fiber/gland cell indefinitely

Therefore, removal of neurotransmitter is essential for normal function

75
Q

Removal of neurotransmitters is accomplished by ? (3)

A

1) Diffusion
2) Enzymatic Degredation
3) Re-uptake by cells

76
Q

1) Diffusion

A

Some of the released neurotransmitter molecules diffuse away from synaptic cleft.

Once a neurotransmitter molecule is out of reach of its receptors, it can no longer exert an effect.

77
Q

2) Enzymatic Degredation

A

Certain neurotransmitters are inactivated through enzymatic degradation.

For example, the enzyme acetylcholinesterase breaks down acetylcholine in the synaptic cleft.

78
Q

3) Re-uptake by cells

A

Many neurotransmitters are actively transported back into neuron that released them (reuptake).

Others are transported into neighboring neuroglia (uptake).

  • The neurons that release norepinephrine, for example, rapidly take up norepinephrine & recycle it into new synaptic vesicles. *
  • →membrane proteins that accomplish such uptake are called neurotransmitter transporters.*
79
Q

Integration

A

process by post-synaptic neuron that combines all excitatory & inhibitory inputs & responds accordingly

→occurs over & over as interneurons are activated in higher parts of the brain (such as the thalamus & cerebral cortex).

80
Q

Neuronal Circuit

A

many neurons organized into complex networks

81
Q

Types of Circuits (4)

A

1) Diverging
2) Converging
3) Reverbrating
4) Parallel after-discharge

82
Q

1) Diverging

A

small # of neurons in brain stimulate much larger # of neurons in spinal cord.

83
Q

2) Converging

A

opposite of diverging circuit

large # of neurons stimulate smaller # of neurons in spinal cord

84
Q

3) Reverbrating
- used in?

A

impulses sengt back through circuit time & time again

used in breathing, coordinated muscular activies, waking up & short-term memory

85
Q

4) Parallel after-discharge

used in?

A

involve single presynaptic cell that stimulates group of neurons, which then synapse with common postsynaptic cell

– used in precise activities such as mathematical calculations

86
Q
A