WEEK 4: Nervous System - PHYSIOLOGY

Question 1

What is a membrane potential?

Answer 1

= Difference in electrical charge from the inside to the outside of a neuron. Measured in volts.

Question 2

What is a current?

Answer 2

= When ion channels in the membrane open and the ions move across membrane.

Question 3

The production of a nerve impulse depends on which two basic features of a plasma membrane?

Answer 3

a) The existence of a resting membrane potential (difference in electrical charge when at rest; inside is 70 millivolts more negative than outside at rest)

b) Presence of specific types of ion channels (ions move through channel to cause action potential or electrical current)

Question 4

What are the different types of ion channels?

Answer 4

• leak channels
• ligand-gated channels
• mechanically gated channels
• voltage-gated channels
• sodium-potassium pump (active)

Question 5

Ion channels; leak channels

Answer 5

• Randomly alternate from being open and close
• When its open, ions can move with the concentration gradient
• We have sodium and potassium leak channels.

Question 6

Leak channels; ligand-gated

Answer 6

• Opens in responds to binding of ligand or chemical stimulus.
• Can be neurotransmitter, hormone, ion binding to the channel.
• i.e., in plasma membrane of muscle and the Acyl

Question 7

Leak channels; mechanically gated

Answer 7

• open with mechanical stimulus i.e., vibrations like sound waves in ear, touch, or pressure on skin, stretching of muscle/organ (gastrointestinal).
• Distorts channel from resting position and it opens.

Question 8

Leak channels; voltage-gated

Answer 8

• Open in response to change in voltage or membrane potential.
• Sodium and potassium channels.

Question 9

Leak channels; sodium voltage gated

Answer 9

CLOSED = no sodium can move through, but when activated by an impulse they can.

OPEN = sodium ions can move down across concentration gradient.

INATIVATED = closed and incapable of opening. Important for conducting electrical impulse in one direction.

Question 10

Leak channel: sodium-potassium pump

Answer 10

• Moves it against the concentration gradient in an attempt to restore the resting membrane potential.

Question 11

List the steps of the Sodium-Potassium Pump

Answer 11

1) Three sodium ions bind to intracellular sites on the sodium-potassium pump

2) A phosphate group is transferred to the pump via the hydrolysis of ATP

3) The pump undergoes a conformational change, translocating sodium across the membrane.

4) The conformational change exposes two potassium binding sites on the extracellular surface of the pump.

5) The phosphate group is released which causes the pump to return to its original conformation.

6) This translocates the potassium across the membrane, completing the ion exchange

Question 12

What is an action potential?

Answer 12

= rapid depolarisation and repolarisation of the membrane potential.

Question 13

Stage of resting membrane potential?

Answer 13

= voltage-gated NA and K channels closed. Little movement of ions. The membrane potential is sitting at -70 mV.

Question 14

Stage of depolarisation?

Answer 14

= Voltage-gated NA channels open. Na moves into the cell. Graded potentials inch the membrane potential closer to the threshold.

Question 15

Stage of repolarisation?

Answer 15

= voltage-gated NA channel inactivated. Voltage-gated K channel opens. K moves out of the cell.

Question 16

Stage of hyperpolarisation?

Answer 16

= voltage-gated NA channel closed. Voltage-gated K channel open. K continues to exit the cell.

Question 17

What is the difference between an action and graded potential?

Answer 17

ACTION = rapid depolarisation and repolarisation of the membrane potential.

• What transmits information.

GRADED = slight deviation in membrane potential.

• Depolarising graded (changes bring it closer to threshold)
• Hyperpolarising (changes bring it further from threshold)
• A few can be summed together and these generally cause action potential

Question 18

What are refractory periods?

Answer 18

= time during which an organ or a cell is incapable of repeating a particular action

= in a neuron it is the period of time following an action potential, during which another action potential can’t be generated

TWO KINDS = absolute and relative refractory

Question 19

What is an absolute refractory period?

Answer 19

• Another action potential can’t occur no matter the stimulus.

= because the sodium channels are already open (can’t open further) or they’re inactivated. We need sodium coming in to trigger the action potential.

Question 20

What is a relative refractory period?

Answer 20

• An action potential can be generated, but only by a larger than normal stimulus.
• We have this so neurons aren’t continually stimulated.
• Important so that an action potential propagates in one direction only.

Question 21

What is propagation?

Answer 21

PROPAGATION: the way an action potential moves along an axon. Can only propagate in one direction.

• only moves in one direction due to the refractory period (it closes the channel for a certain amount of time)

TWO TYPES: continuous and saltatory

Question 22

What is continuous propagation?

Answer 22

• One part stimulated, membrane researches threshold, the voltage-gated sodium channels open, sodium moves into the neuron and the influx of sodium causes the membrane potential to change in the next segment of the axon.
• Occurs in unmyelinated axons and muscle.
• Is relatively slow as each part of the axon needs to be stimulated.

Question 23

What is saltatory propagation?

Answer 23

SALTAR = leaping

• Much faster as it can leap entire sections of axons.
• One part of axon stimulated, reaches threshold, opens sodium-gated channels and sodium moves or skips across the entire section until it reaches the nodes of Ranvier.

Question 24

What are synapses and what are the two types?

Answer 24

SYNAPSE = area of transmission of an action potential. Either between two neurons or a neuron and a gland or muscle.

TWO TYPES = electrical and chemical

Question 25

What are electrical synapses?

Answer 25

• Conducted directly through the plasma membrane of adjacent neurons through gap junctions.
• These gap junctions contain tubular connexon’s that connect the cytosol through cells directly.

Question 26

What are the advantages of electrical synapses?

Answer 26

1) Because the signal transmission is through the direct gaps, it can occur very quickly.

2) They can also coordinate the transmission of signals very precisely i.e., in the intestines.

Question 27

What are chemical synapses?

Answer 27

• No gap junctions or connexons
• Completely separated
• There is a synaptic cleft
• A signal moves from an electrical signal, to a chemical signal as it diffuses across the interstitial fluid and then back into an electrical signal

Question 28

Explain the processes at a chemical synapse

Answer 28

1. Action potential arrives at the axon terminal.
2. Voltage-gated CA channels open.
3. CA enters the cell.
4. CA signal to vesicles.
5. Vesicles move to the membrane.
6. It binds to the membrane and releases the neurotransmitter by exocytosis.
7. Neurotransmitters diffuse across the synaptic cleft and binds to the receptors.

Question 29

What is summation?

Answer 29

= the additive effect of several electrical impulses on a neuromuscular junction, the junction between a nerve cell and a muscle cell.

2 types:
- excitatory postsynaptic potentials
- inhibitory postsynaptic potentials