Final answer:
Activation of extrajunctional receptors typically leads to enhanced synaptic transmission through effects such as depolarization and increased ion concentration, which in turn can result in heightened sensitivity and excitability of cells.
Step-by-step explanation:
The activation of extrajunctional receptors can lead to several physiological effects, as these receptors are often present in greater numbers in certain abnormal or modified situations, such as muscle denervation or in the presence of certain drugs. Typically, the activation of receptors by a neurotransmitter like acetylcholine can result in the opening of ligand-gated ion channels, leading to depolarization of the postsynaptic membrane and an excitatory postsynaptic potential (EPSP). Specifically, for extrajunctional receptors, this can mean enhanced sensitivity and excitability of the muscle fiber or neuron in areas outside of the normal synaptic junction. However, the exact effect of activating these receptors may vary depending on their location and the type of neurotransmitter involved. While the options a) Inhibition of neurotransmitter release, c) Suppression of receptor sensitivity, and d) Blockade of postsynaptic receptors are possible effects of certain drugs or neurotransmitters, they are not typically the result of activating extrajunctional receptors. Therefore, the most relevant effects related to the specific information provided would be b) Enhanced synaptic transmission due to depolarization and an increase in ion concentration, particularly K+.