Pakistan MCQs

Sensory cells generally require a minimum stimulus intensity before producing a receptor potential strong enough to signal the nervous system.

Dendrites increase the receptive surface of a neuron. Multiple dendrites allow integration of inputs from several neurons or receptors.

Glucagon is secreted by pancreatic alpha cells and stimulates glycogen breakdown and glucose release, helping maintain blood glucose during fasting.

Invertebrates often use neurosecretory cells and endocrine-like messengers to regulate reproduction, growth, and behavior, even without vertebrate-type glands.

Hearing depends on mechanical vibrations that stimulate hair cells or related mechanoreceptors. These receptors convert sound waves into neural signals.

Sensory adaptation is reduced responsiveness during continuous stimulation. It allows animals to remain sensitive to new or changing stimuli.

Nodes of Ranvier are gaps in myelin where ion exchange occurs. Saltatory conduction between nodes increases impulse speed.

Endocrine glands release hormones into blood or body fluids. These chemical messengers reach target cells with specific receptors.

Nematodes use signaling pathways to regulate development, molting, reproduction, and stress responses. Chemical communication is not limited to vertebrates.

Olfactory receptors are chemoreceptors that detect airborne molecules. They help animals locate food, mates, predators, and environmental signals.

The inner ear contains balance organs that detect head movement and position. Damage can disrupt equilibrium and coordination.

Cephalopods have large brains and advanced sensory systems for invertebrates. Their behavior includes learning, camouflage, and complex movement control.