3.6.2.1 Nerve Impulses Flashcards
What is essential to survive?
Being able to sense changes in the environement or stimulus and respond to these changes
What is a sense organ?
An organ which has specialised cells that can detect stimulus called receptor cells
What is the 2nd stage of stimulus?
Coordination / processing / thinking
What are the steps between the stimulus and response?
Receptor: sensory cells
Co-ordinator: brain or spinal cord, CNS
Effector: muscle or gland
What is the purpose of the endocrine system?
It releases hormones in the blood (e.g. insulin)
What is the purpose of the exocrine system?
It releases enzymes into specific areas (e.g. saliva)
Does the endocrine or exocrine system have a greater effect on the body?
Endocrine (hormones)
What does the relay neurone look like?
See card
How do you draw a sensory neurone?
See card
How do you draw a motor neurone?
See card
What are resting potentials created by?
Created by the active transport of Na+ and K+
What can a nerve impulse be described as?
A wave of electrical activity
What happens to the sodium potassium pump in the axon at rest?
3Na+ ions are pumped out
2K+ ions are pumped in
This makes the neurone polarised at rest
This is known as an electrochemical gradient
What is the resting potential helped by?
Faster K+ diffusion caused by carrier proteins
How do K+ ions leak out of the axon during rest?
Down their concentration gradient via a carrier protein
Na+ ions do not do this as the membrane is impermeable to Na+
What creates an electrochemical gradient?
There are more sodium ions in the tissue fluid than in the axon, thus creating a gradient
What causes an action potential to be generated?
When a stimulus above a certain intensity (threshold) arrives at a receptor or nerve ending
When an action potential is first generated, what happens to the membrane potential?
There is a rapid switch in membrane potential from -65mV to +40mV
What is the process of the refractory period?
A stimulus reaches the threshold
The stimulus causes a local depolarisation of the membrane by Na+ channels opening
The change in membrane potential closes the Na+ channels and opens the K+ channels (voltage-gated)
The diffusion of K+ causes polarisation of the membrane including hyperpolarisation (caused by K+ channels closing more slowly
The resting potential is restored by active transport
What is a saltatory conduction?
Where Schwann cells form insulation
Where does the ion movement occur along the axon?
In the nodes of ranvier because there is no insulation to prevent ion movement
Where does action potential occur?
On adjacent nodes of ranvier
This makes it more rapid because the action potential makes jumps along the axon instead of travelling along it
What are the factors affecting the speed of an action potential?
Myeling sheath: is an insulator so forces the action potential to jump which increases the speed
Diameter of the axon: a greater diameter increases the speed of conductance due to less leakage of ions
Temperature: increases the rate of diffusion of ions so speeds up the nerve impulse
What is the all or nothing principle?
Any stimulus below the threshold value produces no stimulus
All action potentials are roughly the same size so either there is or isn’t an impulse
