Nervous Control Flashcards
What do dendrites do?
Carry nerve impulses towards the cell body
What do axons do?
Carry neber impulses away from the cell body
Describe the structure and function of sensory neurones
One long dendron carries nerve impulses from receptors to the cell body
One short axon carries nerve impulses from cell body to CNS
Describe the structure and function of relay neurones
Many short dendrites carry never impulses from sensory neurones to cell body
An axon carries nerve impulses from cell body to motor neuorne
Describe the structure and function of motor neurones
Many short dendrites carry nerve impulses from CNS to cell body
One long axon carries nerve impulses from cell body to effector cells
What does it mean that some neurones are myelinated?
They contain a myelin sheath which acts as an electrical insulator, made up of Schwann cells
What are the patches of bare membrane in between Schwann cells?
Nodes of Ranvier
What the term ‘receptors are specific’ mean?
They only detect one particular stimulus
What is a potential difference?
Voltage across a membrane that is generate by ion pumpe and ion channels
What controls pupil size?
The iris
What happens to pupil in dim light?
Radial muscles contract
Circular muscles relax
Pupil dilates
What happens to pupil in bright light?
Radial muscles relax
Circular muscles contract
Pupil constricts
What is the figure for resting potential
-70 mv
Describe the polarity when a neurone is at rest:
The outside of the membrane is positively charge
The inside of the membrane is negatively charged
How is the resting potential maintained?
Sodium potassium pumps AND potassium ion channels in the neurone membrane
Describe the sodium potassium pumps
Use active transport to pumo 3 sodium ions out of the neurone for every 2 potassium ions pumped in
Requires ATP
How is an electrochemical gradient built up?
- Sodium-potassium pumps move sodium ions out of neurone, membrane is not permeable to sodium so they can’t diffuse back into neurone = sodium ion electrochemical gradient
- Sodium-potassium pumps move potassium into cell but membrane is permable to potassium due to potassium ion channels (facilitated diffusion) so can diffuse back out of neurone
- outside of cell is positively charged compared to inside
Describe the sequence of events in an action potential:
- Stimulation causes membrane to become slightly depolarised due to small influx of socdium ions
- Threshold value of -55 mv reached
- Voltage gated sodium channels open, sodium ions diffuse into neurone down its electrochemical gradient = cell becomes depolarised
- membrane polarity peaks at 40mv
- potassium channels open slowly so potassiumnions diffuse out of the cell down an electrochemical gradient = repolarisation
- too much potassium leaves neurone causing hyperpolarisation
- generates a refractory period
How does a nerve impulse travel along the neurone?
- some sodium ions that enter the neurone diffuse sideways
- sodium ion channels open in the next region of the neurone and diffuse in, causing a wave of depolarisation
Why is the refractory period useful?
- Ensures action potentials only travel in one direction (hyperpolarisation of previous region means further from threshold value)
- Ensures a time delay between one action potentil and the next, eo they don’t overlap
How do local anaesthetics work?
- Bind to sodium ion channels in the membrane of neurones
- Stops sodium ions moving into the neurones so the membrane will not depolarise
Prevents action potentials being conducted and stops info about pain being sent to brain
In a myelinated neurone, where does depolarisation occur?
Only happens at the nodes of Ranvier
What is saltatory conduction?
Where a impulse jumps from node to node in a myelinated neurone, making it very fast
What is conduction velocity?
The speed at which an impulse moves along a neurone
