6.5 Neurones and synapses Flashcards
What do neurons transmit?
Electrical impulses
What are the two systems of the body that are used for internal communication?
Endocrine system and the nervous system
What does the endocrine system do?
Consists of glands that release hormones
What does the nervous system consist of?
Consists of nerve cells called neurons
How do neurons help with internal communication?
By transmitting nerve impulses
What is a nerve impulse?
An electrical signal
What do neurons look like?
- cell body with cytoplasm and nucleus
- narror outgrowths called nerve fibres along which nerve impulses travel
Along what do nerve impulses travel?
Narrow outgrowths called nerve fibres
* Dendrites and axons
What are two types of nerve fibres?
Dendrites and axons
What is the difference between axon and dendrites?
Dendrites: short branched nerve fibres (those used to transmit impulses between neurons in one part of the brain or spinal cord)
Axons: very elongated nerve fibres (those that transmit impulses from the tips of the toes or the fingers to the spinal cord.
What is the basic structure of a nerve fibre?
- the fibre is cylindrical in shape
- plasma membrane encosing a narrow region of cytoplasm
- diameter in most cases is about 1 micrometer
What are some nerve fibres coated with?
Some nerve fibres are coated along most of their length by a material called myelin
What does myelin consist of?
Many layers of phospholipid bilayers
How are myelin deposited?
Schwann cells deposit the myelin by growing round and round the nerve fibre.
* each time they grow around the nerve fibre a double layer of phospholipid bilayer is deposited
* there may be 20 or more layers when the schwann cell stops growing
What is the gap between the myelin?
Node of Ranvier
What can nerve impulses do in myelinated nerve fibres?
Saltatory conduction
* They can jump from one node of Ranvier to the next
What is saltatory conduction?
When nerve impulses jump from one node of Ranvier to the next
How is saltatory conduction beneficial?
It is much quicker than continuous transmission along a nerve fibre so myelinated nerve fibres transmit nerve impulses much more rapidly than unmyelinated enrve fibres
How is saltatory conduction beneficial?
It is much quicker than continuous transmission along a nerve fibre so myelinated nerve fibres transmit nerve impulses much more rapidly than unmyelinated enrve fibres
What is the resting membrane potentional of a neuron?
-70mV
When a neuron is not transmitting a singal because of the potential difference or voltage across its membrane
What causes the potential difference or voltage across a membrane of a neuron?
This potential is due to an imbalance of positive and negative charges across the membrane
What do sodium-potassium pumps do?
They transfer sodium (Na+) and potassium (K+) ions across the membrane.
Na+ ions are pumped out
K+ ions are pumped in
How is a concentration gradient for both ions created by the sodium-potassium pumps?
For every 3 Na+ ions are pumped out, only 2 K+ ions are pumped in
Why is the concentration gradient across the membrane steeper for Na+ than K+?
The membrane is about 50x more permeable to K+ ions than Na+ ions, so K+ ions leak back acorss the membrane faster than Na+ ions