Action and graded potentials LO5-7

Question 1

In the body… (charge)

Answer 1

Exterior = postive
Interior = negative
This potential energy (voltage) separating these chargers is the membrane potential

Question 2

For neurons to generate an electrical signal, their plasma membrane must

Answer 2

exhibit a resting membrane potential of -70mV

Question 3

Chemically gated channel

Answer 3

open in response to a chemical stimulus eg: neurotransmitter
Located along the plasma membrane
of the dendrites & cell body

Question 4

Mechanically-gated Channels

Answer 4

Open in response to mechanical stimulation
e.g. touch, vibration and pressure
Located along the plasma membrane of
the dendrites

Question 5

Voltage gated channels

Answer 5

Open and close in response to voltage changes
(i.e. changes in membrane potential)
Located along the plasma membrane of
the axon and axon terminals

Question 6

Gated channels and membrane potential

Answer 6

1. stimulus
2. opens gated channels
3. Na+ or K+ ions flow across the plasma membrane
4. membrane potential changes
5. electrical signal generated

Question 7

Depolarisation

Answer 7

-55 to +30
Inside of the cell positive like the outside
Na channels open (ECF to ICF)

Question 8

Repolarisation

Answer 8

+30 to -70
Inside of the cell negative again, returns to normal
Na channels close
K channels open
(Na ICF - EFC)

Question 9

Hypolarisation

Answer 9

-70 to -90
making inside of the cell more negative than normal
K channels close (slowly)
(ICF - ECF)

Question 10

Graded potential

Answer 10

• Are small changes in the membrane potential
• Originate in the dendrites or cell body of a neuron, when
  a stimulus opens chemically-gated or mechanically-gated
  channels
• Are short distance signals
• distance travelled is proportional to stimulus strength
• stronger stimulus = bigger change in membrane potential
  = further signal will travel
  Small depolarisation or mall hypolerisation

Question 11

Action potential

Answer 11

• are long distance
• originate in the initial segment of an exon
• stimulate voltage-gated Na+ channels to open
• are self propagating
• Depolarisation, repolararisation, hyperpolarisation

Question 12

Synapse

Answer 12

1. AP arrives and depolerises axon terminal
2. voltage gated CA+ channels open
3. influx of CA2 triggers synaptic vesicles to release neurotransmitters into synaptic cleft
4. Neurtrotransmiters bind to chemically gated channels on the post synaptic neuron
5. chemically gates ion channels open (NA enter ICF, plasma membrane of postsyanpic neuron depolerises, GP is produced)
6. Excitatory postsynaptic potential depolarises initial segment of postsynaptic neuron to threshold (-55) (AP generated

Question 13

Termination of synaptic transmission

Answer 13

1. The neurotransmitter diffuses away
   from the synaptic cleft
2. The neurotransmitter is degraded by enzymes present in the synaptic cleft
3. The neurotransmitter re-enters the axon terminal and destroyed by enzymes or reused. This process is
   known as reuptake