Lecture 1 (Action Potentials)

Question 1

What are classified as excitable tissues?

Answer 1

Nerve, muscle and secretory tissues

Question 2

Define Excitation

Answer 2

Rapid response ability to cell’s excitation which is revealed by physical, physical-chemical processes and complex of functional changes

Question 3

Define Action Potential

Answer 3

Potential difference produced by ions distribution in excited site of the cell membrane

Question 4

What can excitation stimulus be?

Answer 4

• Mechanical influence
• Thermo signal
• Chemical signal
• Electric impulse (rarely)

Question 5

What does excitation stimulus in excitable tissues determine?

Answer 5

Active change of resting potential and generation of action potential

Question 6

What happens to the resting potential at excitation?

Answer 6

Resting potential is harshly changed (-70mv to +30mv) and in one sec returns to the initial value

Question 7

Describe the Stimulus-Response Model

Answer 7

1) A receptor converts a stimulus into a nerve impulse which is transmitted by a SENSORY NEURON to the CNS
2) RELAY NEURONS within CNS transmit signal to CONTROL CENTRE where information is processed
3) Motor neurons will transmit an impulse from CNS to an EFFECTOR ORGAN

Question 8

What is a Reflex?

Answer 8

A rapid and involuntary response to a stimulus

Question 9

What are the three main types of neurons in the nervous system?

Answer 9

• SENSORY NEURONS = conduct nerve impulses from receptors to CNS
• RELAY NEURONS = conduct nerve impulses within CNS
• MOTOR NEURONS = conduct nerve impulses from CNS to effectors

Question 10

What is the difference between depolarisation and repolarisation?

Answer 10

DEPOLARISATION is the change in membrane polarity when the neuron is firing and REPOLARISATION is the restoration of the resting potential

Question 11

The action potential moves along the axon in one direction because of the ____________ __________

Answer 11

Refractory period

Question 12

Describe the relationship between diameter of neuron and the speed of action potential

Answer 12

The larger the DIAMETER of the UNMYELINATED NEURON the less the resistance to current flow and the faster the PROPAGATION of the action potential

Question 13

What is the name of the gap in the myelin sheath covering?

Answer 13

Node of Ranvier

Question 14

What can be found in the nodes of Ranvier?

Answer 14

A concentration of voltage-gated sodium and potassium channels

Question 15

Describe what happens during Saltatory Conduction

Answer 15

When an action potential occurs at one node, the same intracellular and extracellular currents are created except the myelin dramatically reduces the current across the membrane so that the current that flows to the next node is strong enough to generate an action potential

Question 16

Myelin sheaths are formed by which cells?

Answer 16

Schwann cells

Question 17

Are Schwann cell membranes ion-impermeable?

Answer 17

YES

Question 19

Why do the intermodal regions not become excited?

Answer 19

• Depolarisation has to be “shared” by many membranes that are stacked in series
• There are few if any Na+ channels in the intermodal regions

Question 21

What factors result in faster conduction?

Answer 21

• The impulse jumps from node to node and does not have to wait for each intermodal section of the membrane to become excited
• During node excitation, it quickly depolarises the ADJACENT intermodal region and reaches much farther downstream

Question 22

What is the speed of a nerve impulse from head to toes in humans?

Answer 22

0.02 seconds

Question 23

The junction between two neurons is called a ________________

Answer 23

synapse

Question 24

What happens when an action potential reaches the axon terminal?

Answer 24

1) VOLTAGE-GATED CALCIUM CHANNELS are triggered open, Ca2+ ions diffuse into the cell and promote the fusion of vesicles (neurotransmitters) with the PLASMA MEMBRANE
2) NEUROTRANSMITTERS are released from the axon terminal by EXOCYTOSIS and cross the SYNAPTIC CLEFT and bind to appropriate neurotransmitters on the POST-SYNAPTIC MEMBRANE
[EXCITATORY NEUROTRANSMITTERS open ligand-gated SODIUM CHANNELS & INHIBITORY NEUROTRANSMITTERS open ligand-gated POTASSIUM/CHLORINE channels]
3) Combination of chemical messengers received determines if THRESHOLD is reached for ACTION POTENTIAL
4) Neurotransmitter molecules released into synapse are either RECYCLED (re-uptake pumps) or DEGRADED (enzymes)