The Nervous System Flashcards
What is a receptor?
Something that detects stimulus
What is an effector?
Cells that bring about a response to a stimulus, to produce an effect. These include muscle cells and cells found in glands.
How do receptors communicate with effectors?
Nervous and hormonal system.
What does a sensory neurone do?
Transmit electrical impulses from receptors to the central nervous system.
What does a motor neurone do?
Transmit electrical impulses from the central nervous system to effectors.
What do relay neurones do?
Transmit electrical impulses between sensory neurones and motor neurones.
Summarise the nervous system.
Electrical impulses carried by neurones.
Fast response.
Localised effect.
Short-lived effect.
What is the resting potential?
The inside of the axon is negatively charged relative to the outside. The voltage across the membrane is known as the potential difference. The resting potential is generated by ion pumps and channels.
How is the resting potential generated?
Na-K pumps use active transport to move 3 sodium ions out of the neurone for every 2 potassium ions moved in. (ATP required).
Potassium ion channels allow facilitated diffusion of K ions out of the neurone, down their concentration gradient.
Even though positive ions are moving in and out of the axon, more positive ions move out that in.
What happens during an action potential?
- Stimulus. Excites the membrane causing sodium channels out. Membrane more permeable to sodium so diffuse down gradient into neurone. Inside less negative.
- Depolarisation. Threshold reached, more Na channels open so more Na ions diffuse into neurone.
- Re-polarisation. At around +30mV the Na channels close and K channels open. K ions diffuse out down the concentration gradient. Potential starts to go back to normal.
- Hyper-polarisation. K channels are slow to close so theres an overshoot where too many K ions diffuse out. Potential difference becomes more negative than resting potential.
- Resting potential. Ion channels reset. The Na-K pump returns the membrane to resting potential.
What is the refractory period and what does it do?
A period of recovery where the membrane can’t be excited again. This gives a time delay between action potentials and allows them to act as seperate impulses in one direction.
What is a wave of depolarisation?
When an action potential occurs, some of the Na ions diffuse sideways causing Na channels in the next region to open and Na ions diffuse into that part. This causes a wave of depolarisation to travel down the neurone.
What is the all or nothing principle?
Once the threshold is reached, the action potential is always the same. Bigger generator potential will not cause bigger action potential but will cause them to fire more frequently.
What affects the speed of conduction? How?
- Myelination - myelin sheath is an electrical insulator. Depolarisation only occurs at the nodes of rangier so the impulse jumps node to node (saltatory conduction).
- Axon diameter - bigger diameters allows impulse to travel faster as there’s less resistance.
- Temperature - speed of conduction increases as temp increases.
What is a chemical mediator?
A chemical messenger that acts locally by cells releasing chemicals that bind to specific receptors on target cells to cause a response.
