neuronal communication Flashcards
What are neurones?
Specialised nerve cells which make up the nervous system and transmit electrical impulses rapidly around the body to respond to stimuli.
What is the function of the soma/cell body?
The soma contains the nuceli of the nerve cell which is surrounded by cytoplasm and contains lots of ER and mitocondria for neurotransmitter production.
What are dendrons?
Dendrons are extensions which derive from the cell body and branch into smaller branches called dendrites for transmitting impulses towards cell body.
What are axons?
Axons are cables which transmit impulses away from the cell body to be received by other neurones.
What is the myelin sheath?
Acts as an insulating layer which covers the axon.
What are the nodes of ranvier?
Gaps between Schwann cells that result in the faster transmission of electrical impulses. They have no myelin sheath.
What is the purpose of a sensory neuron? What is its structure?
A neurone which transmits impulses from the sensory receptors to a relay , motor neurone or to the CNS.
They have a nuclei in the middle of the axon and have one dendron + one axon.
What is the purpose of a relay neurone? What is its structure?
Transmits impulses between neurones.
Has its cell body in the centre of the cell and has a short axon but many dendrons and dendrites.
What is the purpose of a motor neurone? What is its structure?
A motor neurone will transmit impulses from a relay to an effector such as a muscle or gland to elicit a response.
Has the structure of a typical neurone with one long axon and many short dendrites.
What is a myelinated neurone?
Neurones with axons covered with mylein sheaths made up of many layers of plasma membrane provided by the wrapping of Schwann cells. It acts as an insulating layer to conduct electrical impulses at a faster speed.
What is the function of the noes of Ranvier?
Allow electrical impulses to jump from one node to the next to allow faster transmission.
What is a sensory receptor?
Found in sensory organs, they detect changes in the environment and convert the stimuli into a nerve impulse to be passed to the CNS.
What is a transducer and why is a sensory receptor a transducer?
A transducer will convert a stimuli into a nerve impulse. The sensory receptor converts the environmental stimuli into a nerve impulse.
What is the pacinan corpuscle and how does it moderate?
A type of sensory receptor found in the skin and soles of your feet which detect mechanical pressure.
Moderates via stretched mediated sodium channels which can change shape to change its permeability to NA+ ions.
How does the pacinan corpuscle convert the pressure stimuli into a nerve impulse?
1] At resting potential, neurone membrane is too narrow to allow NA+ to pass.
2] When pressure is applied, pacinan corpuscle stretches causing it to be more permeable to NA+.
3] NA+ influx changes potential causing it to become polarised and trigger an action potential to the CNS.
How does nervous transmission occur?
An impulse sent across a neurone will temporarily alter the potential difference across the axon membrane switching it between resting potential and action potential.
What is resting potential?
Resting potential is when the neurone is not transmitting an impulse .
The outside of the membrane is more + charged than the inside and is polarised. Potential difference is -70 mV.
Established by movement of NA+ and K+ ions.
How is resting potential maintained?
+Sodium-potassium pump will actively transport NA+ out and pump K+ in but more NA+ will be pumped out than K+ in, 3:2 ratio.
+NA+ cannot diffuse back in as most gated NA+ ion channels are closed.
K+ channels remain open so they can diffuse back out into axon.
What is an action potential?
An action potential is triggered when a stimuli is detected causing the energy to temporarily reverse charges.
Membrane is depolarised and potential difference inside the membrane will become +40 mV.
Action potential causes the membrane to be more permeable to ions.
Describe the process which an action potential is triggered and returns back to resting state.
1] The membrane is at resting potential at -70mV, some K+ ion channels are closed but Na+ voltage gated ion channels are closed.
2] Stimuli energy causes Na+ voltage gated ion channels to open so the membrane is more permeable. Na+ ions will diffuse in.
3] The influx of Na+ ions will cause more Na+ ion channels to open via positive feedback.
4] Potential difference reaches 40mV , action potential is triggered.
5] Na+ ion gated channels will close whereas K+ ion voltage gates will open, Na+ ions can no longer enter the membrane by diffusion.
6] Re-polarisation occurs where K+ ions diffuse out the membrane down the electrochemical gradient to make the outside more negative.
7] Leads to hyper polarisation as it will be more negative than resting potential. K+ voltage ion gates will close and it will reestablish to -70mV via the sodium-potassium pump.
What is the propagation of action potentials ?
When an initial stimuli triggers , it causes the first region of the membrane to be depolarised which acts as a stimuli for the next region to be depolarised. This will occur across the membrane like a mexican wave.
What is the refractory period and what do they ensure?
A short period of time where the axon cannot be excited again where Na+ ion voltage-gated channels remain closed to prevent the propagation of the action potential backwards and forwards.
Ensures that action potentials are unidirectional and do not overlap.
What is saltatory conduction? Why is it faster than a continuous wave of depolarisation?
The way an electrical impulse will jump from one node of Ranvier to the next allowing faster conduction.
Depolarisation can only occur at the nodes of Ranvier as they have no mylein sheath.
This is faster than a wave of depolarisation because each time channels open and close it takes time, therefore reducing the places it occurs will increase action potential transmission.
Why is saltatory conduction more energy efficient?
Re-polarisation requires ATP using the sodium-potassium pump, so reducing the amount of re-polarisation required then less ATP will be used.
