Unit 3: Chapter 3 - Nerve Cells and Nerve Impulses

Question 1

Central Nervous System

Answer 1

Consists of the brain and spinal cord. It is the control centre for the whole nervous system.

Question 2

Peripheral Nervous System

Answer 2

The nerves that connect the CNS with the receptors muscles and glands.

Question 3

Neurons

Answer 3

Nerve cells. The basic structural and functional unit of the whole nervous system. They can very in shape and size but all consist of a cell body and two extensions from the body; the dendrites and the axon.

Question 4

Interneurons

Answer 4

Have many branches that are able to send or receive messages to or from adjacent neurons

Question 5

Cell body

Answer 5

The central part of a neuron containing the nucleus and other basic cell organelles

Question 6

Dendrites

Answer 6

Short extensions of the cytoplasm of the cell body. They are highly branched and carry messages (nerve impulses) into the cell body.

Question 7

Axon

Answer 7

Often a single, long extension of the cytoplasm. Usually carries nerve impulses away from the cell body

Question 8

Nerve impulses

Answer 8

A signal transmitted along a nerve fibre. It consists of a wave of electrical depolarization that reverses the potential difference across the nerve cell membranes.

Question 9

Myelin sheath

Answer 9

A layer of fatty material that may cover the axon of a neuron. If it covers the axon these neurons are referred to as myelinated.

Question 10

Nerve fibre

Answer 10

Any long extension of cytoplasm of a nerve cell body.

Question 11

Myelinated fibres

Answer 11

Any nerve fibre thats axon is covered in myelin sheath

Question 12

Grey matter

Answer 12

Areas of the brain that that consist of nerve cell bodies and unmyelinated fibres.

Question 13

White matter

Answer 13

Areas of the brain that consist of myelinated fibres (the lipid myelin that covers these fibres is white)

Question 14

Schwann Cells

Answer 14

Outside the brain and spinal cord, the myelin sheath is formed by these special cells.

Question 15

Nodes of Ranvier

Answer 15

The intervals (gaps) along the axon in the myelin sheath

Question 16

Sensory (receptor) neuron

Answer 16

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

Question 17

Motor (effector) neuron

Answer 17

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

Question 18

Multipolar neurons

Answer 18

These neurons have one axon and multiple dendrites extending from the cell body. Most common neuron found in the NS. Includes most of the interneurons in the brain and the spinal cord and also the motor neurons that carry messages to the skeletal muscles.

Question 19

Bipolar neurons

Answer 19

Have one axon and one dendrite, both axon and dendrite may have branches at their ends. Bipolar neurons occurs in the eye, ear and nose, where they take impulses from the receptor cells to other neurons.

Question 20

Unipolar neurons

Answer 20

Just have one extension, the axon. The cell body is to one side of the axon. Most sensory neurons that carry messages to the spinal cord are of this type.

Question 21

Synapse

Answer 21

The junction between dendrites and axon terminal of adjacent neurons (a small gap).

Question 22

Neuromuscular junction

Answer 22

A similar junction where an axon meets a skeletal cell

Question 23

Nerve impulse

Answer 23

The message that travels along the neuron

Question 24

Potential

Answer 24

When a group of oppositely charged particles are separated and have the potential to come together and released energy. Measured in volts or millivolts.

Question 25

Membrane potential

Answer 25

A difference of electrical charge between the inside and the outside of a neuron

Question 26

Resting membrane potential

Answer 26

Membrane potential of unstimulated nerve cell. Usually -70mV.
Inside of the membrane is 70mV less than outside (0)
This is due mainly to differences in K+ (30 times greater inside cell) and Na+ (10 times greater outside cell) ions.

Question 27

Sodium Potassium Pump

Answer 27

Active transport using energy of 3 Na+ OUT of cell and 2 K+ INTO cell.

Question 28

Depolarisation

Answer 28

When Na+ surge into cell at a greater rate of K+ moving out.

Question 29

All or none response

Answer 29

There must be enough current to pass the threshold (-55mV) to cause a stimulus. If there isn’t enough energy, nothing happens.

Question 30

Repolarisation

Answer 30

The restoration in membrane potential that returns it to a negative value just after the depolarization phase of an action potential has changed the membrane potential to a positive value.

Question 31

Action potential

Answer 31

Cells taking action. Rapid polarisation and depolarisation. A short-term change in the electrical potential on the surface of a cell (e.g. a nerve cell or muscle cell) in response to stimulation, and then leads to the transmission of an electrical impulse (nerve impulse) that travels across the cell membrane.

Question 32

Refractory period

Answer 32

Briefly after an action potential that part of the nerve fibre can’t be stimulated again (short period)

Question 33

Polarised

Answer 33

The act or process of producing a positive electrical charge and a negative electrical charge such that between a nerve cell internal electrical charge, which is negative, and the surrounding environment of a nerve cell, which is positive.

Question 34

Saltatory conduction

Answer 34

Nerve impulses jumping from one Node of Ranvier to another

Question 35

Postsynaptic

Answer 35

The receiving end of a discharge across a synapse

Question 36

Presynaptic neuron

Answer 36

A neuron from the axon terminal of which an electrical impulse is transmitted across a synaptic cleft to the cell body or one or more dendrites of a postsynaptic neuron by the release of a chemical neurotransmitter.

Question 37

Stimulus intensity

Answer 37

The size of a nerve impulse is always the same, regardless of the size of stimulus, and does not become weaker.

Question 38

How can we distinguish intensity?

Answer 38

1. Depolarisation of more nerve fibres with strong stimuli

2. More impulses in a given time than a weak stimulus

Question 39

Synapse transmission

Answer 39

At the synapse, there is no membrane. Another method of transmission must be involved.
Neurotransmitters

Question 40

Neurotransmitters

Answer 40

(Special chemicals that nerve impulses are converted into at the synapse) are released from the ends of the axon from vesicles.

Question 41

Synaptic vesicle

Answer 41

A small secretory vesicle that contains a neurotransmitter, is found inside an axon near the presynaptic membrane, and releases its contents into the synaptic cleft after fusing with the membrane.

Question 42

Synaptic cleft

Answer 42

The space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter. — called also synaptic gap

Question 43

Depressant

Answer 43

A drug tending to, slow lower or depress functioning of the nervous system (nerve impulses.) (alcohol)

Question 44

Stimulant

Answer 44

A drug that tends to speed up or raises levels of nerve impulses, nervous activity (Cocain)