Nerve cells and nerve impulses

Question 1

What is the nervous system?

Answer 1

The communication network and control centre of the body. Maintains a constant environment inside the body

Question 2

What are neurons?

Answer 2

the basic structural and functional units of the nervous system

Question 3

What is the myelin sheath

Answer 3

a layer of fatty material (in the CNS), cover the Schwann cells

Question 4

Node of ranvier

Answer 4

gaps in the myelin sheath

Question 5

Axon

Answer 5

carried nerve impulses away from the cell body

Question 6

What are the functional types of neurons?

Answer 6

Afferent
Efferent
Interneurons

Question 7

Afferent (sensory neurons)

Answer 7

carry messages from receptors in the sense organs, or in the skin, to the central nervous system

Question 8

Efferent (motor neurons)

Answer 8

carry messages from the central nervous system to the muscles and glands (the effectors)

Question 9

Inter-neurons (association or connector neurons)

Answer 9

• located in the central nervous system

- They are the link between the sensory and motor neurons

Question 10

What are the structural types of neurons?

Answer 10

Multi-polar
Bipolar
Unipolar

Question 11

Multipolar neurons

Answer 11

• Have one axon and multiple dendrites extending from the cell body
• The most common type
• Includes most of the interneurons in the brain and spinal cord and also the motor neurons

Question 12

Bipolar neurons

Answer 12

• Have one axon and one dendrite

- Occur in the eye, ear and nose, where they take impulses from the receptor cells to other neurons

Question 13

Unipolar neurons

Answer 13

• Have just one extension, an axon
• The cell body is to one side of the neuron
• Most sensory neurons

Question 14

What is a neuron

Answer 14

A nerve cell

Question 15

What is a nerve fibre

Answer 15

Any long extension of cytoplasm of a nerve cell body, although the term usually refers to an axon

Question 16

What is a nerve

Answer 16

A bundle of nerve fibres held together by connective tissue

Question 17

What is a synapse?

Answer 17

• The junction between the branches of adjacent neurons

- Usually occur between the axon of one neuron and a dendrite or cell body of another neuron

Question 18

What is a nerve impulse?

Answer 18

• An electrochemical change that travels along a nerve fibre

- Is due to the changes in the concentration of ions inside and outside the cell membrane

Question 19

Nerve impulses in un-myelinated fibres

Answer 19

Travel steady along the fibre

Question 20

Nerve impulses in myelinated fibres

Answer 20

Impulse jumps from one node of Ranvier to the next. Known as salutatory conduction and allows the impulse to travel a lot faster

Question 21

What is salutatory

Answer 21

when the impulse jumps form one node of Ranvier to the next

Question 22

What does extracellular fluid contain?

Answer 22

A high concentration of sodium ions

Question 23

What does intracellular fluid contain?

Answer 23

A high concentration of potassium ions

Question 24

Why does the inside have a relatively negative charge?

Answer 24

Because there are less potassium ions than sodium ions

Question 25

What is the membrane potential?

Answer 25

The potential difference in sodium and potassium ions

Question 26

What is the resting membrane potential?

Answer 26

• The membrane potential of an unstimulated nerve cell
• Can be measured and is about -70mV
• This means that the potential of the inside is 70mV less than the outside
• The neuron is said to be polarised

Question 27

What is the sub-threshold level?

Answer 27

the strength of an impulse needed for the cell membrane to become permeable to sodium ions (opening of the voltage gated sodium channels). Is usually about 15mV

Question 28

What causes depolarisation

Answer 28

The opening of the sodium gates causing the Na+ to move into the cell

Question 29

What causes the neuron to be repolarised?

Answer 29

Tthe closing of the sodium channels and the opening of the potassium channels

Question 30

What is the role of the sodium potassium pump?

Answer 30

To return the membrane to its original state

Question 31

What is the refractory period?

Answer 31

The brief time after the action potential where that part of the nerve fibre cannot be stimulated

Question 32

What happens with nerve impulses across the synapse?

Answer 32

• When the action potential reaches the axon terminals, there is an influx of Ca2+
• This causes neurotransmitters to be released and diffuse across the synapse, attaching to receptors of the next neuron, thus stimulating the next action potential

Question 33

Nerve impulses at the neuromuscular junction

Answer 33

1. The action potential reaches the axon terminal
2. This opens the calcium gates in the axon terminal membrane
3. Extracellular Ca2+ move into the axon terminal
4. This causes the neurotransmitter to be released (acetylcholine) into the synapse
5. The neurotransmitter attaches to receptors on the muscle membrane
6. This part of the muscle membrane is called the motor end plate
7. The attachment of the neurotransmitter causes the opening of sodium gates
8. Extracellular sodium ions move into the muscle fibre
9. The sodium depolarises the muscle cell
10. Depolarisation of the muscle cell causes the release of Ca2+ from the sarcoplasmic reticulum
11. This calcium causes the actin and myosin myofilaments to slide over each other
12. This makes the sarcomere shorter. The muscle is now contracted
13. Acetylcholinesterase is an enzyme that breaks down acetylcholine
14. The broken down acetylcholine is reabsorbed by the axon terminal and is recycled