A meter recorded the changes in potential difference at a specific point across
ID: 179671 • Letter: A
Question
A meter recorded the changes in potential difference at a specific point across the membrane of a squid axon during passage of an action potential (see diagram). Describe in words what happens in the recorded part of the axon membrane at each of the points labeled 1 to 5. What will happen to the observed recordings of the action potential as it is measured at each point as it continues along the remainder of the axon toward the synapse? Does it require any direct or indirect energy input to generate an action potential? If so, when and where is the energy used? What happens in time and space (along the axon) once an action potential begins? What factors ultimately limit the ability of the system to respond (that is, to continue to generate impulses)?Explanation / Answer
A)point 1 Stimulus
point 2 depolarization
point 3 Peak action potential
point 4 refractory period
point 5 Resting state.
The diagram shows phases as the action potential passes a point on a cell membrane. The membrane potential starts out -70 mV at the time zero. A stimulus is applied at time= 1ms, which raises the membrane potential above -55mV.(Threshold potential). After the stimulus is applied, the membrane potential rapidly rises to a peak potential of +40mV at time +ms(Depolarization). Just as quickly, the potential the drops and overshoots at -90 mV at time=3 ms(Repolarization) and finally the resting potential of -70 mV is reestablished at time= 5ms (Resting state).
B)Synaptic potential comes in two forms: excitatory and inhibitory. Excitatory post- synaptic potential (EPSPS) depolarize the membrane and move it closer to the threshold for an action potential. Inhibitory postsynaptic potential (IPSPs) hyperpolarize the membrane and move it farther away from the threshold. In order to depolarize a neuron enough to cause an action potential, there must be enough EPSPs to both counterbalance the IPSPs and also depolarize the membrane from its resting membrane potential to its threshold.
C)Action potential does not propagate passively, but actively, by means of voltage sensitive ion channels in the axon. This process requires energy from the neuron, which must maintain the activity of the ion pumps that rebalance the charge on either side of the membrane after an action potential has passed
D)action potentials play a central role in cell-to-cell communication by providing for the propagation of signals along the neuron's axon towards the axon ends which can then connect with other neurons at synapses, or to motor cells or glands. The diagram explained above repeats.
E)factors that limit the ability of the system to respond
1. Myelin sheath - This covers some of the nodes and acts as an electrical insulator where the action potential travels from one node of ranvier to the next by saltatory conduction.
2. Diameter of the axon - the larger the diameter of an axon increases the rate and speed of conductance as there is less leakage of ions.
3. Temperature - The higher the temperature the faster the conductance. This is because enzymes work faster at a high temperature which control the sodium-potassium pump needed to create action potentials.