Neural signalling - nerve impulses Flashcards
What do neurones transmit information in?
Impulses
Impulses travel extremely quickly along the neurone from one end to the other
What is an impulse?
An impulse is a momentary reversal in the electrical potential difference across the neurone cell surface membrane.
It is NOT an electrical current that flows along neurones.
What is the electrical potential difference across a membrane also known as?
Membrane potential
It can also be described as voltage or the difference in charge across a membrane
What is the resting potential of a neurone typically measured at?
-70 millivolts (mV)
This indicates that the inside of the resting axon is more negatively charged than the outside
What contributes to establishing and maintaining resting potential?
Two main processes:
* Active transport of sodium ions and potassium ions
* Difference in rates of diffusion of sodium ions and potassium ions
What type of proteins are involved in the active transport of sodium and potassium ions?
Sodium-potassium pumps
These pumps use ATP to transport sodium ions out and potassium ions into the axon
What is the unequal rate at which sodium and potassium ions are pumped?
3 sodium ions out for every 2 potassium ions in
This creates a concentration gradient across the membrane
How does the permeability of the neurone membrane differ for sodium and potassium ions?
Less permeable to sodium ions than potassium ions
This allows potassium ions to diffuse out faster than sodium ions can diffuse back in
What happens to the neurone membrane once resting potential is reached?
It is said to be polarised
This means the inside of the neurone is negatively charged compared to the outside
What is required to initiate a nerve impulse in a neurone?
Depolarisation of the neurone membrane
Depolarisation reverses the electrical potential difference across the membrane
What is the typical change in electrical potential during depolarisation?
From around -70 mV to around +40 mV
This occurs when an action potential is generated
What ions are involved in the movement during an action potential?
Sodium ions and potassium ions
Their rapid movement across the membrane leads to the generation of an action potential
What triggers the generation of an action potential?
When a neurone is stimulated by an environmental stimulus
This is detected by a receptor cell
What is the effect of myelination on nerve impulse speed?
Myelinated neurones conduct electrical impulses much more quickly than unmyelinated fibres
This is due to the insulation provided by the myelin sheath, which allows faster saltatory conduction.
How does the diameter of a neuron affect impulse conduction speed?
An axon with a wider diameter conducts an electrical impulse more quickly than a narrow axon
This is because a wider axon offers less resistance to the action potential.
What is saltatory conduction?
The process where electrical impulses jump from one node of Ranvier to the next
This process greatly speeds up the rate of transmission of impulses along myelinated neurones.
What are Schwann cells?
Specialised cells that wrap around the axon to form the myelin sheath
They are responsible for the insulation of axons in the peripheral nervous system.
What is the role of the myelin sheath?
Acts as an electrical insulator; impulses cannot pass through it
The lipid content of the myelin sheath provides high electrical resistance.
What are nodes of Ranvier?
Small, uninsulated sections in the gaps between individual Schwann cells
They are crucial for the process of saltatory conduction.
What is the typical diameter range for a human neurone?
Between 4 and 100 µm
This is significantly smaller than the giant axons of squids, which can be up to 1 mm wide.
True or False: A wider axon always conducts impulses faster than a myelinated axon.
False
Despite being wider, the speed of transmission is much faster in myelinated axons.
What does correlation refer to?
An association or relationship between variables
Correlation does not imply causation.
How can the correlation between diameter of a neurone and speed of impulse conduction be analyzed?
Using scatter graphs and different statistical tests
This helps in understanding the strength of the correlation.
Fill in the blank: The myelin sheath is built up in layers as the _______ grow around the axon.
Schwann cells
