Nervous System

Question 1

What is the CNS

Answer 1

The central nervous system (CNS) consists of the brain and spinal
cord. It is made up of billions of non-myelinated nerve cells and longer, myelinated axons (axons with myeline sheath) and dendrons that
carry nerve impulses. Nervous tissue is made of nerve cells called
neurons.

Question 2

What is Resting Potential

Answer 2

Resting potential is the term given to a neuron that is not transmitting an action potential and is at rest.

Question 3

What is Action Potential

Answer 3

Fast-twitch oxidative muscle fibres are similar in structure to slow-twitch muscle fibres. They contain many mitochondria, myoglobin and blood capillaries, but they can hydrolyse ATP much more quickly and, therefore contract quickly. They are relatively resistant to fatigue.

Question 4

Explain what happens at the synapse

Answer 4

 When the nerve impulse reaches the end of the neuron, it must
cross a gap called a synapse to get to the next neuron or the effector
cell.
 A nerve impulse crosses the synapse in the form of a chemical transmitter called a neurotransmitter.
 Neurotransmitters diffuse across the synapse and initiate an action
potential in the neuron on the other side. The presynaptic neuron
ends in a swelling called the synaptic bulb and it contains many mitochondria as ATP is needed.
 The neurotransmitters are stored in temporary vesicles in the synaptic bulb that can fuse with the surface to release the neurotransmitters into the synapse.
 They also contain voltage-gated calcium ion channels.

Question 5

What is Parkinson’s Disease

Answer 5

Parkinson’s disease is a genetic disease that affects the nervous system. Parkinson’s sufferers are not able to produce the naturally occurring chemical dopamine, a neurotransmitter that helps smooth and normal movements.
Without this, people show symptoms of:
 slow movement
 speech problems
 tremors when moving
 poor balance

Question 6

Exaplain the performance of the drug L-dopa

Answer 6

The drug, L-dopa, replaces the dopamine that is lost in people with Parkinson’s disease. Serotonin is another of the body’s naturally occurring neurotransmitters. It is normally active in the brain and can cause problems if it is not produced. Some forms of depression are caused by a reduced amount of serotonin in the brain.

Question 7

Explain what happens through Resting and Action Potential

Answer 7

1) Nerve impulses are ionic imbalances that travel from one end of a neuron to the other
because of a potential difference.
2) When a neuron is at rest, the inside of the cell is negatively charged relative to the out-
side.
3) Sodium-potassium channels pumping Na+ ions to the outside of the cell and K+ ions into
the cell. The resting potential is approximately -70mV.
4) When a stimulus is applied, an action potential occurs.
5) Sodium channels open, and the sodium ions flood into the cell. The positive sodium ions
cause the resting potential of the cell to decrease – this is called depolarization.
6) Once +40mV is reached, the Na+ channels close and the K+ channels open. K+ floods out of
the cell and the charge goes back down – this is called repolarisation.
7) This process of depolarisation and repolarisation continues, and the action potential
moves down the neuron.
8) To continue its journey through the nervous system, the signal needs to start an action
potential in the next neuron. The two neurons will not be in direct contact and the ac-
action potential cannot ‘jump’ across the synaptic cleft (gap).
9) As the action potential reaches the end of the first neuron, Ca2+ channels are opened, and
Ca2+ flows into the cell.
10) This induces vesicles containing neurotransmitters to fuse with the presynaptic membrane, and the neurotransmitters diffuse across the synaptic cleft.
11) The neurotransmitters move across the synapse and bind to complimentary receptors in
the postsynaptic membrane.
12) This triggers the opening of Na+ channels, which causes depolarisation of the membrane
and the start of a new action potential in the second neuron.
13) The neurotransmitters are then actively absorbed back into the original neuron or an
the enzyme is released to break them down, stopping them from generating continuous action potentials.