Chapter 3 A- Nerve Cells & Nerve Impulses

Question 1

What is a neuron?

Answer 1

A nerve cell, basic structural and functional units of the nervous system

Question 2

What do all neurons consist of?

Answer 2

• cell body

- two extensions: axon and dendrites

Question 3

Neuron: cell body

Answer 3

• contains nucleus, organelles and cytoplasm

Question 4

Neuron: dendrites

Answer 4

• fairly short extensions of the cytoplasm
• highly branched
• carry nerve impulses into the cell body

Question 5

Neuron: axon

Answer 5

• single, long extension of the cytoplasm
• length varies greatly, can be very long
• most covered with layer of fatty material called the myelin sheath

Question 6

What is a nerve fibre?

Answer 6

Term used for any long extension of a neuron, usually refers to an axon

Question 7

Neuron: myelinated fibre

Answer 7

• axon with myelin sheath

Question 8

Neuron: unmyelinated fibre

Answer 8

• axon with no myelin sheath

Question 9

What does grey matter consist of?

Answer 9

Cells with unmyelinated fibres

Question 10

What does white matter consist of?

Answer 10

Cells with myelinated fibres

Question 11

Neuron: Schwann cells

Answer 11

• wrap around myelin sheath

- forms myelin sheath

Question 12

Neuron: nodes of Ranvier

Answer 12

• gaps in the myelin sheath

Question 13

Neuron: neurilemma

Answer 13

• outermost coil of the Schwann cell

- helps repair injured fibres

Question 14

What are the functions of the myelin sheath?

Answer 14

• acts as an insulator
• protects axons from damage
• speeds up movement of nerve impulses along axon

Question 15

What are the three functional types of neurons?

Answer 15

1. sensory (receptor) neurons
2. Motor (effector) neurons
3. Inter neurons

Question 16

What is the function of sensory neurons?

Answer 16

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

Question 17

What is the function of motor neurons?

Answer 17

• carry messages from the central nervous system to muscles and glands - the effectors

Question 18

What is the function of interneurons?

Answer 18

• located in the central nervous system and are the link between sensory and motor neurons

Question 19

What are the structural types of neurons?

Answer 19

1. Multipolar neurons
2. Bipolar neurons
3. Unipolar neurons

Question 20

Structure of multipolar neurons:

Answer 20

• have one axon and multiple dendrites extending from the cell body

Question 21

Where are multipolar neurons found?

Answer 21

• most of the interneurons in the CNS

- motor neurons

Question 22

Structure of bipolar neurons:

Answer 22

• one axon and one dendrite

- both axon and dendrite may have many branches

Question 23

Where are bipolar neurons found?

Answer 23

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

Question 24

Structure of unipolar neurons:

Answer 24

• have just one extension: an axon

- the cell body is to the side of the axon

Question 25

Where are unipolar neurons found?

Answer 25

- sensory neurons that carry impulses to the spinal chord

Question 26

What is a synapse?

Answer 26

The junction between the branches of adjacent neurons

Question 27

What is a neuronmuscular junction?

Answer 27

The synapse that exists where an axon meets a skeletal muscle cell

Question 28

What is the all-or-none response?

Answer 28

A stimulus is either strong enough to trigger an impulse, or it is not. The magnitude of an impulse is always the same.

Question 29

How are we able to distinguish stimuli of different intensities?

Answer 29

- a strong stimulus causes depolarisation of more nerve fibres than a weak stimulus - a strong stimulus produces more nerve impulses in a given time than a weak stimulus

Question 30

What ions are found in high concentration inside the membrane?

Answer 30

- K+ | - variety of negative ions that come from organic substances made by the cell

Question 31

What ions are found in high concentration outside the membrane?

Answer 31

- Na | - Cl

Question 32

The cell membrane is highly permeable to __________

Answer 32

- K | - Cl

Question 33

The cell membrane is slightly permeable to __________

Answer 33

- Na

Question 34

How does the cell membrane maintain the potential difference?

Answer 34

- actively moves ions across the membrane (sodium-potassium pump) - there are a large number of negatively charges ions trapped inside the cell

Question 35

Where are unipolar neurons found?

Answer 35

Sensory neurons

Question 36

Where are bipolar neurons found?

Answer 36

Sensory neurons in the eye, ear and nose

Question 37

Where are multipolar neurons found?

Answer 37

Connector neurons, motor neurons

Question 38

Which way does the nerve impulse travel?

Answer 38

Axon to dendrites