Chapter 2: Neurophysiology Flashcards
When a neuron is adequately stimulated an electrical impulse is conducted along theaxon. This electrical phenomenon is called:
the action potential (nerve impulse)
Basic Principles of Electricity: The human body is electrically neutral; therefore, it has the same number of ________ and _______ charges.
positive (+)
negative (-)
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.
b.
Correct: We know that opposites attract. In order to keep these opposite charges separated, energy must be used
____________ - When opposite (+)/(-) electrical charges are separated and no circuit is formed.
Potential Energy
The measure of potential energy is called ________ and it is measured in _______ or _________.
voltage
volts(v)
millivolts (mV)
Voltage is always measured between two points and is called ___________ between these two points.
potential difference
___________ - Flow of electrical charge from one point to another. It can be used to stimulate function.
Current
___________ - This hindrance to the flow of electrical current which is provided by intervening substances through which the current must pass.
Resistance
Substances with high electrical resistance are called _________.
Insulators
Substances with low resistance are called __________. .
Conductors
True or False
The greater the voltage, the greater the current. The greater the resistance, the smaller the current:
True
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
____________ - gated channels open/close when the proper neurotransmitter gives the message.
Chemically
_________ - gated channels open/close in response to changes in the voltage.
Voltage
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)
The voltage measurement across the membrane is approximately _______ .
-70 mV
___________ indicates the inside of the plasma membrane is negatively charged with respect to the outside.
The (-) sign
The resting membrane potential is -70 mV and the membrane is said to be _________ .
polarized
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
Neurons use changes in the membrane potential as communication signals for receiving, integrating and ____________ .
sending information
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.
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
___________ - The inside of the plasma membrane becomes less (-) than the resting potential.
Depolarization
_________ - Occurs when the membrane potential becomes more (-) than resting potential.
Hyperpolarization
____________ 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:
- 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. - Repolarization Phase: Increase in Potassium Permeability.
- 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?
- 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.
- Na+ channels begin to close after a few seconds of depolarization and soon the net influx of Na+ declines and then stops.
- 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:
- Once initiated, action potential is a self-propagating process that continues along the axon at a constant velocity.
- Following depolarization, each segment of axonal membrane undergoes repolarization which restores the resting membrane potential in that area.
- The propagation process just described, occurs on myelinated axons.
- 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.
- 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:
- Influence of axon diameter
- 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
