5.1.3 - Neuronal communication Flashcards
Describe the structure of a motor neurone.
They have their cell body in the CNS and have a long axon that carries the action potential out to the effector.
Describe the structure of a sensory neurone.
Have a long dendron carrying the action potential from a sensory receptor to the cell body (positioned just outside CNS).
They then have a short axon carrying the action potential into the CNS.
Describe the structure of a relay neurone.
Connect the sensory and motor neurones together. Have many short dendrites and a short axon.
The no. of dendrites and the no. of divisions if the axon is variable.
Relay neurones are an essential part of the nervous system = conduct impulses in coordinated pathways.
What percentage of peripheral neurones in vertebrates are myelinated (insulated by a myelin sheath)?
1/3
Describe what a myelin sheath consists of.
Schwann cells make up a fatty sheath.
- the Schwann cells are wrapped tightly around the neurone
- sheath consists of several layers of membrane & thin cytoplasm of the Schwann cell.
What are the gaps in the myelin sheath called and how often do they occur along the neurone?
How big are the gaps?
At 1-3mm along neurone = gaps in myelin sheath called NODES OF RANVIER.
- each node is v short: (about 2-3μm long)
Why can the movement of ions across the membranes only occur at the nodes of Ranvier?
Because the myelin sheath is tightly wrapped around the neurone it prevents the movement of ions across neurone membranes.
How do the gaps along the myelin sheath affect the way that the neurone travels?
The impulse, or action potential, jumps from one node to the next.
- this makes conduction much more RAPID.
Describe non-myelinated neurones.
Non-myelinated neurones are associates with Schwann cells, BUT several neurones may be enshrouded in one loosely wrapped Schwann cell.
How does the action potential travel in non-myelinated neurones?
The action potential moves along the neurone in a wave rather than jumping from node to node.
Why are the advantages of myelination?
- myelinated neurones can transmit an action potential much more quickly.
Typical speed of transmission in MN is 100-120m/s compared to 2-20m/s in NMN.
Why is it important that myelinated neurones have a high speed of transmission?
MN carry action potentials over long distances.
- increased speed of transmission means action potential reaches end of neurone much more quickly.
> enables a more rapid response to a stimulus.
Why is it not that important for the NMN to have an increased speed of transmission?
NMN = usually shorter & carry action potentials over a SHORT distance.
- often used in coordinating body functions e.g. breathing, & action of digestive system.
∴ increased speed of transmission not required.
