7.Excitability and excitation: general characteristics. Propagation of action potentials along the nerve fibers. Nerve fiber types. Flashcards

1
Q

What are the main biological properties of neurons

A

Excitability and conductivity

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2
Q

What is the significance of excitability and conductivity

A

transmission of information
afferent fibers transmit from peripheral organs to CNS
Efferent fibers transmit from CNS to periheral organs

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3
Q

How does propagation of action potentials occur

A

spread of local currents from active regions to inactive regions

ELECTROTONIC CONDUCTION

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4
Q

What is conduction velocity

A

The speed at which action potentials travel along nerve fiber

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5
Q

What are the cable properties that are major concepts in conduction velocity

A

Time constant and length constant

the higher the permeability, the lower the resistance, and vice versa.

Longitudinal resistance (Rl ): is the resistance that counteracts electric
current in the cytosol and ECF.

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6
Q

What are 2 factors that affect time constant

A

membrane resistance + membrane capacitance

Time constant is highest when both of these are high

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7
Q

How can you increase the conduction velocity of a nerve

A

Increasing nerve diamter- the larger the fiber, the lower the internal resistance

Myelination- myelin increases membrane resistance but decreases membrane capacitance. High resistance means it forces the action potential to take path of least resistance
At nodes of Ranvier, the resistance is low-saltatory conduction

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8
Q

What is rheobase

A

The lowest intensity of stimulus that can cause A.P after prolonged stimulation

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9
Q

What is chronaxie

A

Time requires for a stimulus that is 2x rheobase to induce a A.P

Rehobase is the minimum intensity of stimulus to induce AP

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10
Q

What is the Erlanger and Gasser classification of nerve fibres

A

A- alpha, beta, delta, gamma
B
C

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11
Q

Which is the fastest nerve fiber

A

A
largest diameter

skeletal muscle, receptors of muscle spindle etc

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12
Q

If the action potential is stimulated in the middle of the nerve fiber, how will the impulse travel

A

Action potential travels in both directions, centrally and peripherally

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13
Q

What is the threshold potential

A

-55mv

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14
Q

What determines the excitability of given excitable tissue

A

Difference between resting membrane potential (-70mV) and threshold potential (-55mV)

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15
Q

What is the law for all or nothing stating

A

Upon threshold or above threshold all APs have the same amplitude

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16
Q

What is the biological significance of refractory periods

A
  1. Limit the max frequency of effective stimuli
  2. determine direction of nerve propogation
17
Q

Can an AP generated in 1 nerve fibre be transmitted to neighbouring nerve fibers within a single nerve

A

NO IT CANT- law for isolated conduction

the resistance in the extracellular space is much lower than the transmembrane resistance of adjacent unexcited nerve fibers

18
Q

Differences between myelinated and unmyelinated AP conduction

A

unmyelinated - Na+ channels are evenly distributed along axonal membrane- slow conduction

Myelinated- myelin sheath increases transmembrane resistance. The nodes have the highest conc of Na+ channels with lowest resistance

19
Q

What is time constant

A

The time constant (τ) gives us an idea about ​​the time it takes for initially
applied voltage to drop to 37% of its original value.

It is usualy 2-15 ms

20
Q

How can physiological continuity of nerve be interrupted

A

Blocking voltage gated Na+ channels eg lidocaine

Cooling

Demyelination leading to decrease of length constant

Compression of nerve leading to resistance for local currents

21
Q

Mechanism of neuromuscular transmission

A
  • Depolarization of presynaptic terminal by AP
  • Voltage gated Ca2+ channels open and Ca2+ flows into presynaptic terminal
  • Ach extruded by exocytosis into synaptic cleft
  • Ach binds to receptors on postsynaptic membrane (motor end plate)
  • Na+/K+ channels open leading to depolarization and excitory postsynaptic potential
  • This EPSP causes generation of AP
    in the adjacent muscle tissue, were
    voltage-gated Na+ channels are
    again available.
  • Ach is then degraded to choline
    and acetate by acetylcholinesterase
    (AchE).