Year 12 ATAR Human Biology
Unit 1 – The Nervous System
Week 1 2015/16 - Solutions
Chapter 3 – Nerve Cells & Nerve Impulses
Review Questions:
1.
Difference Between the CNS and PNS
The Central nervous system (CNS) comprises the brain and spinal cord whilst the peripheral
nervous system (PNS) is the part of the nervous system that connects the CNS to the receptors.
2.
a.
Difference between myelinated and unmyelinated fibre.
Myelinated fibres are covered with a myelin sheath where unmyelinated do not.
b.
How is the myelin sheath formed?
Sheaths are formed by Schwann cells wrapping around the axon of the fibre.
3.
Functional Neuron Types
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4.
Structural Neuron Types
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5.
Unipolar have one extension from the cell body, an axon.
Bipolar have two extensions from the cell body, an axon and a dendrite.
Multipolar have many dendrite extending from the cell body with one axon.
Difference between neuron, nerve and nerve fibre
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6.
Sensory (or receptor) neurons which are found in the sense organs or the skin
Motor (or effector) neurons are found heading towards organs and effectors of the body
Interneurons (or connector)
a.
A neuron is a nerve cell.
A nerve fibre is any long extension of cytoplasm of a nerve cell body, although the term
usually refers to an axon.
A nerve is a bundle of nerve fibres held together by connective tissue.
What is Electrical Potential?
Electrical potential is when positive and negative charges are separated and they have the
have the potential to create voltage.
b.
Potential of membrane when unstimulated.
-70 mV (The resting membrane potential)
7.
8.
How is potential of nerve cell membrane maintained?
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By actively moving ions across the membrane via the sodium/potassium pump.
By the membrane not being equally permeable to all ions and there are a large number of
negatively charged ions trapped inside the membrane.
a.
What is an action potential?
When sodium ions move into the nerve cell and being transmitted along the cell membrane
as a nerve impulse.
b.
What is an all-or-none response?
When a stimulus is strong enough to overcome the threshold and starts a nerve impulse
running independently. If the threshold is not reached, then the impulse is not transmitted.
9.
What is a Refractory Period?
The refractory period is the brief time after an action potential when the nerve cannot be
restimulated.
10.
a.
How is a nerve impulse transmitted along a nerve fibre?
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Stimulus is applied to the membrane
The voltage gated channels open with sodium ions rushing in, changing the polarity.
The Na+ ions diffuse down the axon changing the polarity causing Na+ ions to move in and
K+ to move out.
A Na+/K+ pump moves the Na+ out and the K+ in to restore the resting membrane potential.
(This is quite simplified.)
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11.
a.
What is a synapse?
A gap between two neurons.
b.
How is a nerve impulse transmitted?
By a neurotransmitter which is secreted across the synaptic cleft.
c.
Why are nerve impulse transmitted only in one direction?
An impulse can pass along an axon in either direction, but can only cross a synapse
in one direction because the synaptic vesicles are only found in the synaptic knobs
and end plates.
12.
Difference between synapse and neuromuscular junction
A synapse is the junction between a dendrite and an axon terminal while a neuromuscular junction
is the gap between branches of a motor nerve cell and a muscle fibre, also called a motor end
plate.
Apply Your Knowledge
1.
How do nerve cells differ from regular body cells?
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Unlike other body cells, neurons stop reproducing shortly after birth. Because of this, some
parts of the brain have more neurons at birth than later in life because neurons die but are
not replaced. While neurons do not reproduce, research has shown that new connections
between neurons form throughout life.
 Neurons have a membrane that is designed to sends information to other cells. The axon
and dendrites are specialized structures designed to transmit and receive information. The
connections between cells are known as a synapse. Neurons release chemicals known as
neurotransmitters into these synapses to communicate with other neurons.
2. Why is a nerve impulse described as an electrochemical charge?
It is described as such as the action potential is electrical in nature made by chemicals.
3. Effect of hyperkalaemia on resting membrane potential.
Increased K+ results in depolarization of the membrane potentials and then opens up some sodium
voltage-gated channels. This means that an action potential is not generated by itself. A higher
amount depolarizes the membrane resulting in a refractory period, meaning the nerve cannot be
stimulated.
4. Action Potential is another name for a nerve impulse. True?
Yes. End of story
5. Distinguishing different intensities of the same stimulus.
Some sensory neurons require a higher intensity to fire so you can distinguish different intensities of
the same stimulus.
6. Speed of nerve impulses.
Quicker in a myelinated fibres when compared to unmyelinated as the impulse jumps from Node of
Ranvier to Node of Ranvier instead of travelling along the entire fibre.