Chapter 2: Neurophysiology Flashcards by mike smith

When a neuron is adequately stimulated an electrical impulse is conducted along theaxon. This electrical phenomenon is called:

the action potential (nerve impulse)

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Basic Principles of Electricity: The human body is electrically neutral; therefore, it has the same number of ________ and _______ charges.

positive (+)

negative (-)

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Basic Principles of Electricity. Except:

a. There are areas in the human body where one charge dominates. The result is that some areas of the body are more (+) or more (-) than other areas.
b. We know that opposites attract. In order to keep these opposite charges separated, positive (+) and negative (-) charges must be used.
c. However, when opposite charges come together, energy is liberated that can be used to work.

Correct: We know that opposites attract. In order to keep these opposite charges separated, energy must be used

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____________ - When opposite (+)/(-) electrical charges are separated and no circuit is formed.

Potential Energy

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The measure of potential energy is called ________ and it is measured in _______ or _________.

voltage

volts(v)

millivolts (mV)

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Voltage is always measured between two points and is called ___________ between these two points.

potential difference

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___________ - Flow of electrical charge from one point to another. It can be used to stimulate function.

Current

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___________ - This hindrance to the flow of electrical current which is provided by intervening substances through which the current must pass.

Resistance

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Substances with high electrical resistance are called _________.

Insulators

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Substances with low resistance are called __________. .

Conductors

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True or False

The greater the voltage, the greater the current. The greater the resistance, the smaller the current:

True

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Plasma membranes have ion channels composed of protein. Some of these channels are always open (called ___________ ). Others are active (called ___________ ). Gated channels have a “ gate” that can open or close.

passive channels

gated channels

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____________ - gated channels open/close when the proper neurotransmitter gives the message.

Chemically

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_________ - gated channels open/close in response to changes in the voltage.

Voltage

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The potential difference between two points is measured by using two electrodes connected to a voltmeter. If one electrode is inserted into a neuron and the other rests on the outside surface. This is called:

The Resting Membrane Potential (RMP)

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The voltage measurement across the membrane is approximately _______ .

-70 mV

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___________ indicates the inside of the plasma membrane is negatively charged with respect to the outside.

The (-) sign

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The resting membrane potential is -70 mV and the membrane is said to be _________ .

polarized

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True or False:

Range of resting membrane potential (RMP) varies between neurons (-40 mV to - 90 mV). This RMP is generated by differences in the ionic composition of the intracellular and extracellular fluids.

True

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Neurons use changes in the membrane potential as communication signals for receiving, integrating and ____________ .

sending information

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Changes in membrane potential can be produced by:

a. Anything that changes membrane permeability.
b. Anything that alters ion concentration on the two sides of the membrane.

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There are two types of signals that are produced by a change in membrane potential:

a. Graded potentials - signals over short distances
b. Action potentials - long distance signals

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___________ - The inside of the plasma membrane becomes less (-) than the resting potential.

Depolarization

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_________ - Occurs when the membrane potential becomes more (-) than resting potential.

Hyperpolarization

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\_\_\_\_\_\_\_\_\_\_\_\_ increases the probability of producing nerve impulses, whereas, ___________ decreases the probability.

Depolarization hyperpolarization

\_\_\_\_\_\_\_\_\_\_\_\_\_ - These are short-lived local changes in membrane potential that can be either depolarization or hyperpolarization. These changes cause local flows of current that decrease with distance travelled.

Graded Potentials

What triggers Graded Potentials?

Graded potentials are triggered by some changes in the neuron's environment, that cause gated ion channels to open.

Types of graded potentials:

Receptor potential Postsynaptic potential

\_\_\_\_\_\_\_\_\_\_ - The stimulus is a neurotransmitter released by another neuron.

Postsynaptic potential

\_\_\_\_\_\_\_\_\_\_ - The receptor of a sensory neuron is excited by some form of energy like heat, light or other

Receptor potential

What happens during a Graded Potential?

A small area of the plasma membrane has been depolarized by a stimulus. Inside the cell (+) ions usually K+ migrate toward the more (-) areas away from the active area and (-) ions move towards more (+) ions; therefore, the inside of the cell becomes less negative and the outside become less positive.

This is the principle way that neurons communicate with each other. They do not decrease in strength with distances travelled like graded potentials.

Action potential

Action potential is a brief reversal of membrane potential with a total amplitude (change in voltage) of about \_\_\_\_\_\_\_\_\_\_\_\_.

100 mV (from -70 mV to +30 mV)

\_\_\_\_\_\_\_\_\_\_\_ - Is called a transmitted action potential.

Nerve impulse

The process of action potential generation, encompasses overlapping changes in membrane permeability, due to the opening and closing of active ion gates, all induced by depolarization of the axonal membrane.

Generation of an Action Potential

Phases of Generation of a Nerve Impulse:

1. Resting State: Active channels Closed 2a. Depolarizing Phase: Increase in sodium permeability and reversal of the membrane potential. 2b. Depolarizing Phase: Decrease in Sodium Permeability. 3. Repolarization Phase: Increase in Potassium Permeability. 4. Undershoot: Potassium Permeability continues

Increase Na+ permeability due to increased channel openings leads to greater depolarization which, in turn, leads to increased Na+ permeability and so on (positive feedback loop).

Depolarization of a local patch of membrane

Depolarization of the membrane reaches critical levels called the ________ (usually between -55 to -50 mV).

threshold

Which statement regarding Depolarizing Phase: Decrease in Sodium Permeability is TRUE? 1. The rising phase of the action potential is short. As the membrane potential passes 0 mV and becomes more (+) the (+) intracellular charge resists further Na+ entry. 2. Na+ channels begin to close after a few seconds of depolarization and soon the net influx of Na+ declines and then stops. 3. Now the action potential spike stops rising and reverses direction

1,2,and 3

In Repolarization Phase: As Na+ entry declines, voltage regulated K+ gates open and K+ rushes out of the cell. Cell interior becomes less (+). Membrane potential moves back towards the resting level. This is called __________ .

repolarization

K+ gates are sluggish and are slow to respond to the depolarization signal; therefore, the period of increased K+ permeability lasts longer than necessary, to restore polarity. As a result there is a period called the _________ .

undershoot

The generated action potential must be propagated (sent) to serve, as the neurons signalling device.

Propagation of an Action Potential

True about Propagation of an Action Potential, Except: 1. Once initiated, action potential is a self-propagating process that continues along the axon at a constant velocity. 2. Following depolarization, each segment of axonal membrane undergoes repolarization which restores the resting membrane potential in that area. 3. The propagation process just described, occurs on myelinated axons. 4. Following depolarization, each segment of axonal membrane undergoes repolarization which restores the resting membrane potential in that area.

Except: 3

Propagation that occurs in myelinated axons is called \_\_\_\_\_\_\_\_\_\_\_\_\_.

Saltatory Conduction

Not all local depolarization events produce action potentials. Depolarization must reach ‘threshold values’ if an axon is to „fire‟. Threshold is usually reached when the membrane has been depolarized by 15 to 20 mV from the resting value. This are called:

Threshold and the All or None Response

What determines Threshold?

Coding for Stimulus Intensity Absolute and Relative Refractory Periods Conduction Velocities of Axons

\_\_\_\_\_\_\_\_\_\_\_\_ - The threshold is the membrane potential at which the outward current carried by K+ is exactly equal to the inward current created by Na+.

Possibility

True or False: Regarding POSSIBILITY. 1. If an extra Na+ ion enters the cell, there is further depolarization opening more Na+ channels and allowing more Na+ ions to enter; but if an extra K+ ion leaves, the membrane potential is driven away from the threshold. Na+ channels close and K+ continues to diffuse out and resting value is restored.

True

\_\_\_\_\_\_\_\_\_\_\_ cause nerve impulses to be generated more often in a given time interval, compared with weak stimuli; therefore, __________ is coded by the number of impulses generated per second, instead of increases in the strength of the action potential.

Strong stimuli stimulus intensity

The ______________ occurs when a patch of neuron membrane is generating an action potential and its Na+ gates are open. The neuron is incapable of responding to another stimulus. This ensures each action potential is separated.

Absolute Refractory Period

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ is the interval following the absolute refractory period when Na+ gates are closed and K+ gates are open and repolarization is occurring.

The Relative Refractory period

A ___________ is unable to trigger an action potential during the relative refractory period but a very strong stimulus can reopen Na+ gates and allow another impulse to be generated; therefore, a ___________ can cause more frequent generation of action potentials.

threshold stimulus strong stimulus

The rate of impulse propagation depends on:

1. Influence of axon diameter 2. Influence of a myelin sheath

Fibres that transmit impulses most rapidly are found in __________ where speed is necessary, as in __________ where impulses travel __________ per second or more. Slower conducting axons usually serve internal organs like the gut.

neural pathways postural reflexes 100 meters

The larger the axon‟s diameter, the faster it conducts impulses.

Influence of axon diameter

Current can pass through the membrane of a myelinated axon, only at the Nodes of Ranvier where there is no myelinated sheath. Essentially all the voltage-regulated Na+ channels are concentrated at the nodes.

Influence of a myelin sheath

Classification of Nerve Fibres based on their diameter, degree of myelination and speed of conduction:

Group A Fibres - Lots of myelin Group B Fibres Group C Fibres

They are lightly myelinated fibres of intermediate diameter and transmit impulses at the rate of 3 to 15 m/s.

Group B Fibres

They are the smallest in diameter and unmyelinated, so they are incapable of saltatory conduction. Nerve conduction is about 1 m/s or less.

Group C Fibres

\_\_\_\_\_\_\_\_\_\_ are mostly somatic sensory and motor fibres serving the skin, skeletal muscles and joints. They have the largest diameter and thick myelin sheaths.They conduct impulses at speeds ranging from 15 to 150 m/s.

Group A Fibres

Examples of Nerve fibres that are belong to Group B and Group C Fibres.

ANS motor fibres visceral sensory fibres smaller somatic sensory fibres