Final answer:
The threshold potential of a cell is determined by the cumulative effect of graded potentials that depolarize the cell membrane to a critical level, influenced by synaptic activity and ion permeability.
Step-by-step explanation:
The threshold potential of a cell is the critical level to which the membrane potential must be depolarized in order to initiate an action potential. The resting membrane potential of a typical neuron is about -70 mV, and the threshold potential is generally about 15 mV more positive. A stimulus causes graded potentials, which are temporary changes in the membrane potential. These can be either depolarizations or hyperpolarizations.
Graded potentials that cumulatively reach the threshold potential trigger an action potential. Factors influencing the threshold potential include the interaction between different types of graded potentials, the activity at synapses, and the permeability of the cell membrane to ions, particularly sodium (Na+) and potassium (K+).