5.3.2: Structure and function of neurons Flashcards
what are impulses transmitted along?
Impulses are transmitted along neurones as an action potential.
What is the action potential carried as?
A rapid depolarisation of the membrane caused by an influx of sodium ions.
What are the three types of neurones?
- Motor neurones
- Sensory neurones
- Relay neurones
What is the role of a motor neurone?
To carry the action potential from the central nervous system to an effector such as a muscle or a gland.
What is the role of a sensory neurone?
To carry the action potential from a sensory receptor to the central nervous system.
What is the role of a relay neurone?
To connect sensory and motor neurones.
Why do neurones have many gated ion channels on their plasma membranes?
They control the entry and exit of sodium, potassium and calcium ions.
Why do neurones have many gated ion channels on their plasma membranes?
They control the entry and exit of sodium, potassium and calcium ions.
What do neurones have to maintain across their plasma membranes?
A potential difference.
What does the cell body in a neurone contain?
nucleus, many mitochondria and ribosomes.
Why do neurones have dendrites?
To connect to other neurones and carry impulses towards the cell body.
Where do axons carry impulses?
Away from the cell body.
What are neurones surrounded by?
Neurones are surrounded by a fatty layer that insulates the cell from electrical activity in other nerve cells nearby.
What is the fatty layer composed of?
Schwann cells closely associated with the neurone.
Describe the positioning of a motor neurone.
Motor neurones have their cell body in the CNS and have a long axon that carries the action potential out to the effector.
Describe the positioning of a sensory neurone.
Sensory neurones have a long dendron carrying the action potential from a sensory receptor to the cell body, which is positioned just outside the CNS.
Then they have a short axon carrying the action potential into the CNS.
Describe the positioning of a relay neurone.
Relay neurones connect the sensory and motor neurones.
They have many short dendrites and a short axon.
The number of dendrites and the number of divisions of the axon is variable.
What proportion of peripheral neurones in a vertebrate are myelinated neurones?
One third
What is a myelinated neurone?
Neurones that are insulated by an individual myelin sheath.
Most sensory and motor neurones are associated with many Schwann cells. What do these cells make up?
They are tightly wrapped round the neurone so that the sheath actually consists of several layers of membrane and thin cytoplasm from the Schwann cells.
What occurs at intervals around 1 to 3 mm along the neurone?
Gaps in the myelin sheath called nodes of Ranvier.
Why can movement of ions across the membrane only occur at the nodes of Ranvier and why is this useful?
Because the myelin sheath is wrapped tightly around the neurone which prevents the movement of neurones across the neurone membranes.
This means that the impulse or action potential jumps from one node to the next node . This makes conduction more rapid.
Describe how non-myelinated neurones are also associated with Schwann cells.
Several neurones are enshrouded in one loosely wrapped Schwann cell.
How does the structure of non-myelinated neurones affect how the action potential moves along the neurone?
The action potential moves along the neurone in a wave rather than jumping from node to node.
