Topic 6 Flashcards
(32 cards)
What is a neurone?
Electrical signals that pass along nerve cells.
Neurones coordinate…
The activities of sensory receptors, decision-making centres in the central nervous system, and effectors such as muscles and glands.
Neurones have a long fibre known as an …
Axon.
The axon of some neurones is insulated by … with small uninsulated sections along its length called …
A fatty sheath.
Nodes of Ranvier.
The fatty sheath is made of…
Myelin.
What is myelin?
A substance made by specialised cells known as Schwann cells. Myelin is made when Schwann cells wrap themselves around the axon along its length.
The presence of Schwann cells means that…
The electrical impulse does not travel down the whole axon, but jumps from one node to the next.
The ‘jumping’ of the electrical impulse between nodes of Ranvier is called…
Saltatory conduction.
Saltatory conduction speeds up…
of the impulse and its transfer from one cell to another.
Neurone cell bodies contain many extensions called…
Dendrites.
Dendrites allow the cell bodies to…
Connect to many other neurones and receive impulses from them, forming a network for easy communication.
There are three main types of neurones which are…
Sensory, relay and motor.
Sensory neurones carry…
Impulses from receptors to the CNS (brain or spinal cord).
Relay (intermediate) neurones are found…
Entirely within the CNS and connect sensory and motor neurones.
Motor neurones carry…
Impulses from the CNS to effectors (muscles or glands).
Neurones transmit electrical impulses, which travel…
Quickly along the neurone cell surface membrane from one end of the neurone to the other.
In a resting axon (one that is not transmitting impulses), the inside of the axon always…
Always has a negative electrical potential compared to outside the axon - this is called the resting potential.
This potential difference when there are no impulses is usually about…
-70mV.
Two factors contribute to establishing and maintaining the resting potential…
- The active transport of sodium ions and potassium ions.
- Differential membrane permeability.
Explain the active transport of sodium ions and potassium ions. (4 marks).
- Carrier proteins called sodium-potassium pumps are present in the membranes of neurones.
- These pumps use ATP to actively transport 3 sodium ions out of the axon for every 2 potassium ions that they actively transport in.
- This means that there is a larger concentration of positive ions outside the axon than there are inside the axon.
- The movement of ions via the sodium-potassium pumps establishes an electrochemical gradient.
Explain differential membrane permeability.
- The cell-surface membrane of neurones has selective protein channels that allow sodium and potassium ions to move across the membrane by facilitated diffusion.
- The protein channels are less permeable to sodium ions than potassium ions.
-This means that potassium ions can diffuse back down their concentration gradient, out of the axon, at a faster rate than sodium ions.
Describe action potential (3 marks)
- Neurones transmit electrical impulses, which travel extremely quickly along the neurone cell surface membrane from one end of the neurone to the other.
- These impulses, known as action potentials, occur via very brief changes in the distribution of electrical charge across the cell surface membrane.
- Action potentials are caused by the rapid movement of sodium ions and potassium ions across the membrane of the axon.
Describe resting potential.
- In a resting axon (one that is not transmitting impulses), the inside of the axon always has a slightly negative electrical potential compared to outside the axon. This potential difference is usually about -70mV.This is called the resting potential.
