Neuronal communication Flashcards
What is habituation?
An animal may learn to ignore a stimulus due to repeated exposure
What is sensitisation?
Over time, organisms may become more sensitive due to exposure , e.g. over sensitising to noise
What is a nerve?
An enclosed cable like bundle of nerve fibres / neurones / cells
What do Pacinian corpuscles respond to?
pressure changes in the skin
Describe resting potential of Pacinian corpuscle and how it is maintained
The inside of the axon has slightly negative electrical potential compared to the outside (-65mv). This is maintained by the sodium potassium pump, which pumps 3 Na+ out of axon and 2 K+ in. This creates a concentration gradient for Na+ to diffuse in and K+ out, but most sodium channels are closed so it cannot diffuse in. Some potassium channels are open so some potassium diffuses out resulting in inside being more negative than outside.
Describe what happens when pressure is applied to Pacinian corpuscle
Each Pacinian corpuscle surrounds a nerve ending on a sensory neurone. When stimulus applied, lamellae are compressed which stretches part of the neuronal membrane. This allows stretch mediated sodium ion channels to open so Na+ enters the axon, causing DEPOLARISATION of the membrane (this is a change in the electrical potential of membrane called generator potential). If generator potential is large enough, it will reach the threshold potential value so an ACTION POTENTIAL will be triggered causing neurone to fire. Kinetic energy (stimulus –> electrical impulse).
What is the all or nothing response?
A certain level of stimulus ( threshold value) will always trigger a response. If threshold value not met, no action potential triggered. Threshold value = minimum receptor potential needed to generate an action potential. This produces an action potential which always has the same magnitude
What is the structure of a sensory neurone?
- cell body outSide CNS
-short axon
-long dendron
-receive input from receptor
-nodes of Ranvier
What is the structure of a motor neurone?
-cell body in CNS
-long axon (no dendron)
-nodes of Ranvier
Describe a myelinated neurone
-myelin sheath made up of Schwann cells wrapped tightly around the neurone. There are gaps between adjacent Schwann cells called nodes of Ranvier. Myelin sheath prevents ion movement across neurone membranes, so impulse jumps from node to node called saltatory conduction which makes conduction more fast
Describe non myelinated neurones
They are enveloped by Schwann cells, but several neurones are enclosed loosely by one Schwann cell and no myelin sheath formed. This means ion movement is not prevented so action potential travels across neurone in a wave, much slower transmission
How does diameter of axon affect speed of conduction?
Greater diameter = faster conduction ( narrow axon means there is resistance to flow of ions)
How does temperature affect speed of conduction?
At higher temperature, ions have more kinetic energy so travel quicker along axon
What is the refractory period?
After an axon has transmitted an impulse, it cannot transmit another straight away as the resting distribution of K+/Na+ needs to be restored and membrane has to be repolarised. This is important as it means action potentials will only be propagated forwards to region which is not in refractory period, and it separates action potentials as it means by the time a second action potential is generated, the first has already passed further down
What are the roles of synapses?
-allows neurones to communicate
-ensures one way transmission between neurones
