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
What is the all or nothing principle
When a nerve is stimulated at the synapse –> some Na+ ion channels open –> Na+ ions diffuse in
If below threshold what happens
No action potential
If above threshold what happens
Rapid opening of Na+ ion channels –> action potential
Speed of nerve impulse
Once an action potential has been initiated at the start of the axon, the subsequent action potentials do not decrease in size. However the speed of propagation can vary and this depends on three properties of the axon
Describe the sequence of events which allows information to pass from one neurone to the next neurone across the cholinergic synapse
- Impulses cause calcium ions channels to open and calcium ions diffuse into the synaptic knob
- Vesicles move towards and fuse with the presynaptic neurone
- Acetylcholine is released via exocytosis
- Acetylcholine diffuses across the synaptic cleft
- Acetylcholine binds with receptors on sodium ion channels in the post synaptic membrane
- Sodium ion channels open and sodium ions diffuse into the post synaptic neurone
- Depolarisation of postsynaptic neurone
- If above threshold,an action potential is produced
What is temporal summation
One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed threshold value
What is spatial summation
Many different neurones connective trigger a new action potential by combining the neurotransmitter they released to exceed threshold value
Why summation
Avoids the nervous system being overloaded
Synapses acts as barriers
Effect of a stimulus can be magnified
Eg: rod cells –> bipolar neurone-> ganglion cell-> synaptic nerve
Describe the first way of inhibition (potassium ions)
Presynaptic neurone releases a type of neurotransmitter that causes opening of potassium protein channels on post synaptic neurone.
Opening of potassium channels –> diffusion of potassium ion out postsynaptic cell body
- greater potential difference across the membrane
-sodium ions diffusing in are not enough for post synaptic membrane to reach threshold
Outward diffusion of potassium ions ‘cancels out’ inward diffusion of sodium ions
Descrive the second way of inhibition (chloride ions )
Presynaptic neurone releases a type of neurotransmitter that binds yo chloride ions protein channels on postsynaptic neurone
Describe the skeletal muscle structure
Skeletal muscles act in antagonistic pairs against an incompressible Skelton
They are stimulated to contract by action potentials
What is the myofibril structure
Myofibirils appear striped because of the way that actin and myosin protein filaments are arranged within them
What is a sacromere
Actin and myosin filaments arranged
