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Anatomy & Physiology > Chapter 12: Neural Tissues Physiology > Flashcards

Chapter 12: Neural Tissues Physiology Flashcards

1
Q

General Neural Activity

A

Resting potential (stimulus produces) –> graded potential (may produce) –> action potential (triggers) synaptic activity –> information processing

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2
Q

Plasma Membrane

A

Polarized membrane; polarized at rest; -70 mV;
Outside = Net Positive
Inside = Net Negative

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3
Q

Functional Properties of Neurons

A

Polarized membranes
Intracellular: Low Na+; High K+
Extracellular: High Na+; Low K+

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4
Q

Resting Membrane Potential

A

The amount of energy it takes to keep the two charges separated.
Most neurons: -70mV

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5
Q

Membrane Channel Parts

A
  1. Passive (leak) channels = Always Open
  2. Active (gated) channels = channels that open and close in response to stimuli
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6
Q

Types of Gated Channels

A
  1. Voltage Gated Ion Channels
    - On Axons
  2. Chemically Gated Ion Channels
    - On Dendrites & Cell Body
  3. Mechanically Gated Ion Channels
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7
Q

Types of Change in Membrane Potential

A
  1. Depolarization
  2. Hyperpolarization
  3. Repolarization
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8
Q

Depolarization

A

Inside (Intracellular) becomes more positive
- Open Na+ channels

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9
Q

Hyperpolarization

A

Inside (Intracellular) becomes more negative
Open K+ channels

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10
Q

Repolarization

A

Return to resting membrane potential

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11
Q

Graded Potential

A

Could be either:
1. depolarization
2. hyperpolarization
- Function is to stimulate or inhibit an action potential
- Occur in dendrites or cell bodies
- Weaken as they travel

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12
Q

Action Potential

A

A self-propagated change in the membrane potential
Threshold = -60mV (What is required to change)

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13
Q

Action Potential Step 1

A
  1. Region of excitable membrane (axon) depolarizes to threshold
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14
Q

Action Potential Step 2

A
  1. Activation gates of voltage gated sodium channels open
    Na+ rushes into cell
    (Depolarization)
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15
Q

Action Potential Step 3

A
  1. Inactivation gates of voltage gated Na+ channels close
    at peak potential +30mV
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16
Q

Action Potential Step 4

A
  1. Voltage gated K+ channels to open; K+ rushes out; Repolarization
    reestablishment of
    resting membrane potential
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17
Q

Characteristics of Action Potentials

A
  1. on axon; moves in one direction, away from cell body
    Action potentials= nervous impulses
  2. Always depolarization
  3. Involves voltage gated ion channels
  4. Self-propagates – stay the same strength as it travels down the axon (affects adjacent voltage gated ion channels)
  5. Action potentials follow the all-or-none principle
  6. All stimuli that exceed threshold will produce identical action potentials.
  7. Refractory period lasts from time action potential begins until normal resting potential returns
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18
Q

Generation & propagation of Action potential

A
  1. Action potential is generated when threshold is reached
    - Change in voltage is strong enough to open voltage gated ion (Na+) channels
    - Graded potential towards axon hillock towards open voltage gated channels
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19
Q

Continuous Propagation in Unmyelinated Fibers

A
  • Spread of action potential across entire membrane in series of small steps
  • Open voltage gated channels in adjacent membrane patches
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20
Q

Continuous Propagation in Myelinated Fibers

A
  • Only exposed at Nodes of Ranvier
  • Saltatory conduction / propagation (to leap)
  • Action potential spreads from node to node, skipping down the membrane
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21
Q

Axon Classification

A
  • Different axons conduct at different speeds (velocity)
  • Myelinated (faster) and unmyelinated (slower) fibers
  • Larger diameter axons conduct at faster speeds
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22
Q

Type A Fiber

A

Myelinated, fat & fast (muscle movement and sensory for position)

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23
Q

Synapse

A

Site of intercellular communication junction between two neurons;
- neuromuscular junction
- neuroglandular junction
Allows for continuation of impulse

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24
Q

Type B Fiber

A

Myelinated but smaller (general sensations)

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25
Q

Type C fibers

A

Unmyelinated, small (smooth muscle)

26
Q

Presynaptic Neuron

A
  • Before synapse
  • Axon terminal
27
Q

Postsynaptic Neuron

A
  • After synapse
    1. dendrite
    2. cell body
    3. axon
28
Q

Types of Synapses

A
  1. Electrical
  2. Chemical
29
Q

Electrical Synapse

A
  • Rare
  • Pre- and postsynaptic cells are connected by gap junctions
  • Ions flow from one cell to another
30
Q

Chemical Synapse

A
  • Common
  • Cells don’t touch (synaptic cleft)
  • Electrical (nervous impulse)  chemical  electrical
  • Results in a graded potential (Postsynaptic potential)
  • May or may not generate an action potential
31
Q

Synaptic Cleft

A

Space between two cell membranes of synapse

32
Q

Neurotransmitter

A
  • Chemicals released from the presynaptic neuron to stimulate postsynaptic neuron.
  • Found in synaptic vesicles in synaptic terminals
33
Q

Types of Neurotransmitters

A
  1. Excitatory
  2. Inhibitory
    Acetylcholine is both:
    - Stimulates skeletal muscle , some synapses in CNS
    Inhibits cardiac muscle
    - Depends on what channels the receptors are sitting on (Na+ or K+)
34
Q

Inhibitory Neurotransmitter

A
  • Hyperpolarizes the postsynaptic membrane
  • Harder to generate an action potential
35
Q

Excitatory Neurotransmitter

A
  • Depolarizes the postsynaptic membrane
  • More likely to generate and action potential
36
Q

Synapses involving Acetylcholine

A
  • Cholinergic synapses
  • All Cholinergic synapses release acetylcholine
  • Most widespread neurotransmitter
  • Neuromuscular junctions
  • Some synapses in CNS
  • Neuron to neuron synapses in PNS
37
Q

Cholinergic Synapse Event 1

A
  1. Action potential arrives at axon terminals depolarizing synaptic knob
38
Q

Cholinergic Synapse Event 2

A
  1. Depolarization opens voltage gated Ca++ channels
    - Ca++ rushes in
    - Ca++ causes the exocytosis of ACh (synaptic vesicle fuse with membrane)
39
Q

Cholinergic Synapse Event 3

A
  1. ACh diffuses across the synaptic cleft
    - binds to receptors on postsynaptic membrane
    - chemically gated Na+ channels open
    - Na+ rushes in and causes depolarization (graded potential)
40
Q

Cholinergic Synapse Event 4

A
  1. ACh is removed
    - Breakdown by acetylcholinesterase (an enzyme)
    - Reabsorb breakdown products to resynthesize ACh
    - Return to resting potential
41
Q

Synaptic Fatigue

A

Use up Ach faster than it can be produced weakens synapse

41
Q

Synaptic Delay

A
  • Events at a synapse take time
  • More control in complicated neural pathways involving thousands of synapses
  • Reflexes – simple neural pathways
  • Fastest=one synapse
  • Very quick responses
42
Q

Norepinephrine/Noradrenaline

A
  • Adrenergic synapses release (NE)
  • CNS & ANS (typically excitatory)
43
Q

Dopamine

A
  • Basal nuclei (part of brain) - CNS
  • Inhibitory neurotransmitter important in muscle control
44
Q

Serotonin

A
  • Happy neurotransmitter in CNS
  • Low levels = depression
45
Q

GABA

A

Gamma Aminobutyric Acid
- CNS – reduces anxiety
- Other neurotransmitters – difficult to study
- Amino acids, peptides, polypeptides, ATP and gases (NO, CO)

46
Q

Function of Neurotransmitters

A

Function through 3 mechanisms
1. Direct effect on membrane potential
2. Indirect effect by G proteins
3. Indirect effect by intracellular enzymes (Lipid soluble substance)

47
Q

Direct Action

A
  • Change in permeability of membrane
  • Move ions  change membrane potential
  • ACh
48
Q

Indirect Effect by Intracellular Enzymes Lipid soluble gases

A
  • Pass through membrane
  • Bind to enzymes
  • Alter permeability or cellular activity
49
Q

Indirect Effect by G Proteins

A
  • Neurotransmitter is the 1st messenger
  • Bind to receptor on cell membrane
  • Activates enzyme(G protein)
  • Results in a second messenger (cAMP) Second messenger causes change in membrane permeability or cellular activity
50
Q

Information Processing

A
  • Neural pathways can involve thousands of synapses
  • A typical interneuron synapses with 1000  10,000 other neurons
  • Simplest level of information processing occurs at the cellular level
  • Postsynaptic neurons are either stimulated or inhibited by postsynaptic potentials
  • Axon hillock integrates excitatory and inhibitory stimuli affecting cell body and dendrites.
51
Q

Post Synaptic Potentials

A
  • Graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter.
  • Can be either excitatory or inhibitory
52
Q

EPSP

A
  • EPSP (excitatory postsynaptic potential)
  • Depolarization
  • More likely to generate an action potential
53
Q

IPSP

A
  • IPSP (inhibitory postsynaptic potential)
  • Hyperpolarization
  • Harder to generate an action potential
54
Q

Summation

A

Combining EPSPs and IPSPs to generate or inhibit an action potential

55
Q

Temporal Summation

A

1 presynaptic neuron
- Fires in rapid succession
- Reach threshold

56
Q

Spatial Summation

A
  • Several presynaptic neurons
  • All fire at the same time
  • Reach threshold
57
Q

Facilitation

A
  • A membrane whose membrane potential shifts closer to threshold.
  • Larger facilitation, less stimuli needed for AP
  • Some drugs; ex. Nicotine
58
Q
A
59
Q
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60
Q
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Anatomy & Physiology (13 decks)

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