Lecture 3 - Transmission within neurons

Question 1

Transmission within neurons

Answer 1

• How cells communicate within themselves
• Cells are specialised to their function (including neurons)

Question 2

Diffusion

Answer 2

Movement of particles from areas of high concentration to low concentration

Question 3

Electrical charge

Answer 3

Positive, negative, cations, anions, opposites attract

Question 4

Sensory neurons

Answer 4

Info from the body

Question 5

Interneurons

Answer 5

Link sensory and motor neurons

Question 6

Motor neurons

Answer 6

Info to the body (control contraction of muscles important for movement)

Question 7

Neurons

Answer 7

• One of two types of cells that make up nervous system
• Do all the information processing and information transmitting
• Many different types of neurons – differ in shape and size
• 86 billion neurons (Azevedo et al., 2009)
• Neurons, astrocytes, oligodendrocytes

Question 8

Structure of a neuron

Answer 8

• Multipolar neuron = most common in brain (lots of extensions)
• Soma (cell body) – contains nucleus
• Dendrites (dendron = ‘tree’) – receive messages
• Axon – carries info (action potential) from soma to terminal buttons
• Myelin sheath – wraps around axon
• Terminal buttons – at the end of the axon branches
• Structure aids function (information transmitting)
• Lots of branches to make connections with other neurons

Question 9

Glia

Answer 9

Supporting cells
Number about equivalent to number of neurons

Question 10

Astrocytes

Answer 10

Provides structural support to neurons and holds them in place, provide nutrients, surround synapse to help limit dispersion of neurotransmitters

Question 11

Oligodendrocytes

Answer 11

Produce myelin sheath that insulates axons, one cell can produce about 50 sections of myelin sheath. Schwann cells do same in PNS

Question 12

Microglia

Answer 12

Smallest of supporting cells, clear away dead/dying neurons and act as brain’s immune system, attacking foreign tissue and repairing damaged cells

Question 13

Nodes of Ranvier

Answer 13

Naked axon

Question 14

Cells

Answer 14

Provide support, waste services, supply of nutrients and chemicals

Question 15

What happens before neuron transmits to another neuron?

Answer 15

• An electrical process – ions move across a membrane
• All cells have an electrical charge
• They are more negative on the inside than the outside
• This results in a resting potential (a store of energy)
• Neurons can reverse their electrical charge

Question 16

Membrane

Answer 16

• Covers all cells
• Two layers of phospholipid molecules (head of molecules are phosphate and tail is a fatty acid)
• Heads are hydrophilic (attracted to water) and tails are hydrophobic (move away from water)

Question 17

Ion channel

Answer 17

Spans the membrane

Question 18

Ions

Answer 18

Charged molecules

Question 19

Cations

Answer 19

Positively charged ions

Question 20

Anions

Answer 20

Negatively charged ions

Question 21

Intercellular fluid

Answer 21

contains potassium ions (K+) and anions (A-)

Question 22

Extracellular fluid

Answer 22

contains sodium (Na+) and chloride (Cl-) ions

Question 23

The membrane potential

Answer 23

• The membrane potential is the difference in electrical potential inside and outside the cell
• Balanced by: diffusion and electrostatic pressure (attraction of particles depending on what charge they are – same repel and different attract)

Question 24

Organic anions A-

Answer 24

(concentrated inside the cell) cannot cross the membrane (why cell is negative on the inside)

Question 25

Potassium ions K+

Answer 25

(more concentrated inside the cell than outside) - Diffusion (wants to move out) - Electrostatic = attracted to inside (-ve) - Overall = forces balance so K+ doesn’t move

Question 26

Chloride ions (Cl-)

Answer 26

(more concentrated outside the cell than inside) - Diffusion (wants to move in) - Electrostatic = repelled from inside (-ve) - Overall = forces balance so Cl- doesn’t move

Question 27

Sodium ions Na+

Answer 27

(more concentrated outside the cell) - Diffusion (wants to move in) - Electrostatic = attracted to inside (-ve) - Overall = both force Na+ into the inside of the cell - Na+ kept under control by sodium-potassium pumps - 3x Na+ pumped out, 2x K+ pumped in

Question 28

Resting potential

Answer 28

- Inside = negative - Outside = positive - The resting potential of a neuron is -70mV - Maintaining the resting potential is important so the neuron can respond rapidly to a stimulus - An action potential is a reversal in the potential and is how information is sent through an axon (from one end to the other)

Question 29

Action potential

Answer 29

- The action potential is a rapid change in the membrane potential (polarisation) - It is an ‘all or none’ process (fires or does not fire) and it stays the same size throughout transmission down the axon

Question 30

Depolarization

Answer 30

Decrease from normal resting potential (brings membrane closer to 0)

Question 31

Hyperpolarization

Answer 31

Increase relative to resting potential (more negative)

Question 32

Process of the action potential

Answer 32

- (1) Threshold of excitation needed. Sodium channels open and are voltage dependent (only open at a certain point of membrane potential). Sodium enters cell (diffusion + electrostatic, cell begins to depolarise) - (2) Potassium channels (voltage dependent but open later) start to let out K+ - (3) Sodium channels close and become refractory (cannot open again, preventing sodium enter the neuron). Peak of action potential reached - (4) Potassium leaves cell through K+ channels (diffusion and electrostatic), causing repolarisation - (5) Potassium channel shut and sodium channel reset - (6) Membrane is hyperpolarised (due to K+ outside membrane). These diffuse away and the Na+K+ pump moves Na+ out the cell and K+ into the cell

Question 33

Propagation

Answer 33

- The action potential is transmitted down an axon via propagation - The action potential is regenerated at points along the axon due to the entry sodium ions at the neighbouring point (a bit like a chain of dominoes falling)

Question 34

Saltatory conduction

Answer 34

- Action potential regenerated along the axon at nodes of Ranvier - Benefits: fast conduction, more energy efficient (pumps only needed at nodes)