Nervous Coordination And Muscles Flashcards
Describe the cell body
- includes usual cell organelles, nucleus, lots of rough endoplasmic reticulum
- associated with the production of proteins and neurotransmitters
Describe dendrons
Extensions if the cell body which subdivide into smaller branched fibres= dendrites ,that carry nerve impulses towards the cell body
Describe the axon
A single long fibre that carries nerve impulse away from the cell body
Describe schwann cells
Surround the axon
Protects axon
Provides electrical insulation
Also carries out phagocytosis
Plays a part in nerve regeneration
Wrap around axons many times= layers
Describe the myelin sheath
Forms a covering to the axon
Is made up of membranes of the schwann cells
Rich in the lipid myelin
Neurones with a myelin sheath= myelinated neurones
Describe the nodes of ranvier
Constrictions between adjacent schwann cells where there is no myelin sheath
Constrictions are 2-3um long
Occur every 1-3mm in humans
Describe sensory neurones
Transmit nerve impulses from a receptor to CNS or an intermediate neurone
Their cell body usually appears to be an extension of the axon
Describe intermediate neurones
Lots of dendrites both sides, in order to propagate an impulse between 2 neurones
Compare the endocrine and nervous system
Endocrine:
> uses hormones
> transmission is by neurones
> transmission is very rapid
> involves chemicals that travel to specific parts of the body
> response is localised
>response is rapid
> response is short lived
>effect usually temporary & reversible
Nervous system:
< wired and uses nerve impulses
< transmission is by the blood stream
< transmission is usually relatively low
< response is widespread
< response is long lasting
< response is slow
< effect may be permanent & irreversible
Give an example of the nervous system
Reflex action : eg.withdrawal of half from unpleasant stimulus
Give an example if the endocrine system
Control of blood glucose concentration
Describe the process of resting potential
- Three Na+ are actively pumped out of the axon and two K+ are actively pumped into the axon by the Na+/K+ pump
- As a result,there are more Na+ in the tissue fluid than the cytoplasm,and there are more K+ in the cytoplasm than in the tissue fluid- an electrochemical gradient is formed
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Describe the action potential
- At the resting potential,voltage gated Na+ channels are shut. Some of th voltage gated K+ channels are open, but most are closed
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Describe the passage of action potential in unmyelinated neurones
Eg: autonomic nervous system
1. The resting potential
At resting potential the concentration of sodium ions out of the axon membrane is very high. The concentration of potassium ions inside the axon is lower (but higher than the potassium outside the axon). The outside of the axon is positive in relation to the inside. The axon membrane is polarised
2. Initiation of the 1st action potential
- Stimulus if the next action potential
- Repolarisation of the axon
- Returning to resting potential
Describe the passage of an action potential in myelinated neurones
Structure: the axon is wrapped in a lipid rich layer fatty sheath = myelin
The myelin sheath is made from highly specialised cells= schwann cells
The myelin sheath acts as an electrical insulator which prevents the passage of ions into and out of the axon
Therefore no action potential can occur in the area of myelination and can only occur at the nodes of ranvier.
They effectively jump from node to node along the nerve fibre
This method of action potential propagation is saltatory conduction