Nervous Coordination And Muscles

Question 1

Describe the cell body

Answer 1

• includes usual cell organelles, nucleus, lots of rough endoplasmic reticulum
• associated with the production of proteins and neurotransmitters

Question 2

Describe dendrons

Answer 2

Extensions if the cell body which subdivide into smaller branched fibres= dendrites ,that carry nerve impulses towards the cell body

Question 3

Describe the axon

Answer 3

A single long fibre that carries nerve impulse away from the cell body

Question 4

Describe schwann cells

Answer 4

Surround the axon
Protects axon
Provides electrical insulation
Also carries out phagocytosis
Plays a part in nerve regeneration
Wrap around axons many times= layers

Question 5

Describe the myelin sheath

Answer 5

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

Question 6

Describe the nodes of ranvier

Answer 6

Constrictions between adjacent schwann cells where there is no myelin sheath
Constrictions are 2-3um long
Occur every 1-3mm in humans

Question 7

Describe sensory neurones

Answer 7

Transmit nerve impulses from a receptor to CNS or an intermediate neurone
Their cell body usually appears to be an extension of the axon

Question 8

Describe intermediate neurones

Answer 8

Lots of dendrites both sides, in order to propagate an impulse between 2 neurones

Question 9

Compare the endocrine and nervous system

Answer 9

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

Question 10

Give an example of the nervous system

Answer 10

Reflex action : eg.withdrawal of half from unpleasant stimulus

Question 11

Give an example if the endocrine system

Answer 11

Control of blood glucose concentration

Question 12

Describe the process of resting potential

Answer 12

1. Three Na+ are actively pumped out of the axon and two K+ are actively pumped into the axon by the Na+/K+ pump
2. 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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Question 13

Describe the action potential

Answer 13

1. 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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Question 14

Describe the passage of action potential in unmyelinated neurones

Answer 14

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

3. Stimulus if the next action potential
4. Repolarisation of the axon
5. Returning to resting potential

Question 15

Describe the passage of an action potential in myelinated neurones

Answer 15

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

Question 16

What is the all or nothing principle

Answer 16

When a nerve is stimulated at the synapse –> some Na+ ion channels open –> Na+ ions diffuse in

Question 17

If below threshold what happens

Answer 17

No action potential

Question 18

If above threshold what happens

Answer 18

Rapid opening of Na+ ion channels –> action potential

Question 19

Speed of nerve impulse

Answer 19

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

Question 20

Describe the sequence of events which allows information to pass from one neurone to the next neurone across the cholinergic synapse

Answer 20

1. Impulses cause calcium ions channels to open and calcium ions diffuse into the synaptic knob
2. Vesicles move towards and fuse with the presynaptic neurone
3. Acetylcholine is released via exocytosis
4. Acetylcholine diffuses across the synaptic cleft
5. Acetylcholine binds with receptors on sodium ion channels in the post synaptic membrane
6. Sodium ion channels open and sodium ions diffuse into the post synaptic neurone
7. Depolarisation of postsynaptic neurone
8. If above threshold,an action potential is produced

Question 21

What is temporal summation

Answer 21

One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed threshold value

Question 22

What is spatial summation

Answer 22

Many different neurones connective trigger a new action potential by combining the neurotransmitter they released to exceed threshold value

Question 23

Why summation

Answer 23

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

Question 24

Describe the first way of inhibition (potassium ions)

Answer 24

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

Question 25

Descrive the second way of inhibition (chloride ions )

Answer 25

Presynaptic neurone releases a type of neurotransmitter that binds yo chloride ions protein channels on postsynaptic neurone

Question 26

Describe the skeletal muscle structure

Answer 26

Skeletal muscles act in antagonistic pairs against an incompressible Skelton
They are stimulated to contract by action potentials

Question 27

What is the myofibril structure

Answer 27

Myofibirils appear striped because of the way that actin and myosin protein filaments are arranged within them

Question 28

What is a sacromere

Answer 28

Actin and myosin filaments arranged