Neuron Structures
8.1 Know the structure and function of sensory, relay and motor neurones including the role of Schwann
cells and myelination.
Neurons
• All neurons have a cell body with a nucleus, cytoplasm and other typical organelles.
• The cell body has extensions that connect to other neurons:
o Dendrites and dendrons carry nerve impulses towards the cell body.
o Axons carry nerve impulses away from the cell body.
• A neuron is a single cell.
• A nerve is a tissue – a group of neurons and blood vessels surrounded by a protective covering.
Sensory Neurons
• One long dendron carries nerve
impulses from receptor cells ! cell
body.
• Cell body in middle of neuron.
• One short axon carries nerve impulses
from cell body ! CNS
Motor Neurons
• Many short dendrites carry nerve impulses
from CNS ! cell body.
• One long axon carries nerve impulses
from cell body to effector cells.
Relay Neurons
• Many short dendrites carry nerve impulses
from sensory neurons to cell body.
• An axon carries nerve impulses from the
cell body to motor neurons.
5
, Resting Potential
Membrane Potential
• Membrane Potential: Voltage across a cell’s plasma membrane.
• The inside of a cell is negative relative to the outside.
• Resting Potential: Membrane potential of an non-stimulated neuron.
• The resting potential is maintained by ion pumps and channels in the plasma membrane.
• Action Potential: The series of changes in the membrane potential of a neuron caused by an
electrical impulse.
• These changes occur as charged ions move into and out of the neuron across the plasma membrane.
Establishing and Maintaining Resting Potential
The Na+/K+ pump, located within the plasma membrane of a neuron, establishes a concentration gradient for
Na+ and K+.
1. 3 Na+ ions in the cytoplasm bind to the Na+/K+ pump.
2. ATP is hydrolysed into ADP + Pi.
3. Pi binds to the Na+/K+ pump, causing the 1st conformational change.
4. The 3 Na+ ions are released into the extracellular fluid.
5. 2 K+ ions in the extracellular fluid bind to the Na+/K+ pump.
6. Pi is released from the pump, causing the 2nd conformational change.
7. The 2 K+ ions are released into the cytoplasm.
K+ channels and Na+ channels are also present within the cell membrane:
• K+ channels allow for the passive diffusion of K+ ions out of the cell, down their conc. gradient.
• The membrane is much less permeable to Na+ due to the presence of fewer Na+ channels.
• Hence the passive diffusion of Na+ makes negligible contribution to the resting potential.
• There is an overall electrochemical equilibrium for K+ which polarises the membrane to a resting
potential of -70mV.
6
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller JunaidAli025. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £2.99. You're not tied to anything after your purchase.
