Neurones Flashcards
What is a neurone?
A specialised cell transmitting nerve impulses; a nerve cell
What is the structure of a myelinated motor neurone?
Schwann cells are the cells that lay down the protective myelin sheath around the axon of medullated (myelinated) nerve fibres
What are the different types of neurone?
- Motor (or efferent) neurons; send information away from the central nervous system to muscles or glands
- Interneurones; send information between sensory neurones and motor neurones. Most interneurones are located in the central nervous system.
What is a resting potential?
The electric potential of a neurone or other excitable cell relative to its surroundings when not stimulated or involved in passage of an impulse.
How is resting potential established in a neurone?
Sodium-Potassium pumps move two potassium ions inside the cell as three sodium ions are pumped out to maintain the negatively-charged membrane inside the cell; this helps maintain the resting potential.
What is an action potential?
The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.
How does an action potential pass along an unmyelinated axon?
- Action potentials in unmyelinated neurones travel much slower than that or myelinated neurones.
- The speed of action potentials is also dependent on the diameter of the axon. Wider axons have lower resistance than narrow axons and signals can travel faster in large axons.
How does an action potential pass along a myelinated axon?
The myelin sheath insulated the axon and inhibits current leakage through the plasma membrane. This allows the current to travel the long distances between nodes without decaying below threshold level.
What factors affect the speed of conductance of an action potential?
- Impulses travel faster in myelinated neurones > Saltatory Conduction
- Schwann cells prevent diffusion of ions
- Temperature affects speed of conduction of impulses. Higher temp increases rate of diffusion of ions.
- Impulses faster in an axon with larger diameter.
What is the refractory period?
A period immediately following stimulation during which a nerve of muscle is unresponsive to further stimulation. This is when the voltage gated ion channels in the neurone membrane becomes unresponsive.
What is meant by the all-or-nothing principle?
That the strength by which a nerve or muscle fibre responds to a stimulus is independent of the strength of the stimulus. If that simulus exceeds the threshold potential, the nerve or muscle fibre will give a complete response; otherwise, there is no response.
What is a synpase?
A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter.
