Neuronal Communication Flashcards
What is a sensory neuron’s function?
Transmit nervous impulses from receptors to the CNS.
What is a motor neuron’s function?
Transmit nerve impulses from the CNS to effectors.
What is a relay neuron’s function?
Transmit nervous impulses between sensory neurons and motor neurons.
What does it mean for a cell to be at resting potential?
When a nervous system receptor is in resting state there’s a difference in charge between the inside and outside of the cell. This is generated by ion pumps and channels. This means there’s a voltage across the membrane.
What happens to a cell at resting potential when a stimulus is detected?
The cell membrane is excited and becomes more permeable, allowing more sodium ion channels to open to move Na+ ions into the cell- altering the potential difference. The change in potential difference due to a stimulus is called the generator potential.
What happens when a bigger stimulus excites the membrane?
It will excite more, causing a bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is produced. If the generator potential is big enough it’ll trigger an action potential (nervous impulse) along a neuron. An action potential is only triggered if the generator potential reaches a certain level called the threshold level.
What happens if the stimulus is too weak?
The generator potential won’t reach the threshold, so there’s no action potential.
What are the function of dendrites and dendrons?
Carry nerve impulses towards the cell body.
What do axons do?
Carry nervous impulses away from the cell body.
How do sensory and motor neuron’s structure differ?
> Sensory have short dendrites with one long dendron to carry nervous impulses from receptor cells to the cell body but motor have many short dendrites that carry nerve impulses from the CNS to the cell body.
Sensory have one short axon that carries impulses from the cell body to the CNS whereas, motor have one long axon that carries nervous impulses from the cell body to effector cells.
What is the structure of a relay neuron?
Have many short dendrites that carry nerve impulses from sensory neurons to the cell body, and many short axons that carry nerve impulses from the cell body to motor neurons.
What is potential difference across the membrane when a neuron is in a resting state?
The outside of the membrane is positively charged compared to the inside. This is because there are more positive ions outside the cell than inside.
What is does mean that the membrane is polarised?
There’s a difference in charge, the voltage across the membrane when it’s at rest is called the resting potential - it’s about -70mV.
How is the resting potential is maintained?
The resting potential is created and maintained by sodium-potassium pumps and potassium ion channels in a neuron’s membrane, the sodium-potassium pump moves 3 Na+ out of the neuron for every 2 K+ moved in
What does it mean that there is an electrochemical gradient across the membrane?
The sodium-potassium pump moves moves sodium ions out but the membrane isn’t permeable to Na+, so they can’t diffuse back in creating a sodium ion electrochemical gradient because there are more positive sodium ions outside the cell than inside. It also moves K+ into the neuron but the membrane is permeable to them so they diffuse back out by faciliated diffusion through K+ channels.
What does it mean that the membrane becomes more permeable to sodium when it is excited?
More sodium ions diffuse into the neuron down the sodium ion electrochemical gradient, making the inside of the neuron less negative.
What happens at the depolarisation stage of nerve cells being stimulated?
If the potential difference reaches the threshold, voltage- gated sodium ion channels open. More Na+ diffuse into the neuron, this is positive feedback.
How does the action potential cause a wave of depolarisation?
1) When an action potential happens, some of the sodium ions that enter the neuron diffuse sideways.
2) This causes sodium ion channels in the next region of the neuron to open and sodium ions diffuse into that part.
3) This causes a wave of depolarisation to travel along the neuron.
4) The wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an action potential.
What happens in the repolarisation stage of an action potential?
At a potential difference of around +30mV the sodium ion channels close and voltage-gated potassium ion channels open. The membrane is more permeable to potassium so K+ diffuse out of the neuron down the K+ conc. gradient. This starts to get the membrane back to its resting potential. This is negative feedback.
What is hyperpolarisation?
K+ channels are slow to close so there’s a slight ‘overshoot’ where too many K+ diffuse out of the neuron. The potential difference becomes more negative than the resting potential.
What is the refractory period?
The neuron cell membrane after an action potential can’t be excited again straight away. This is because the ion channels are recovering and can’t be made to open (Na+ channels are closed during repolarisation and K+ channels are closed during hyperpolarisation).
What does a bigger impulse affect?
Once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is but it will cause more frequent impulses.
Explain the ‘all-or-nothing’ theory?
Once the threshold is reached, an action potential will always fire with the same change in voltage but if the threshold isn’t reached, an action potential won’t fire.
What does neurons being myelinated mean?
They have a myelin sheath, which is an electrical insulator. In the peripheral nervous system the myselin sheath is made of Schwann cells.
