Nervous system

Fast control requires signals to travel rapidly between a stimulus, the central nervous system, and an effector. The nervous system performs this function through electrical impulses carried by neurons, allowing quick responses such as withdrawing a hand. Thus option B is correct. The digestive, respiratory, and excretory systems perform important physiological functions, but they are not the main system for rapid coordination of responses.

Plants lack the nervous system and specialised neurons found in animals, but they still coordinate growth and responses. They do this through chemical messengers called plant hormones or phytohormones, including auxin, gibberellin, cytokinin, ethylene, and abscisic acid. Neurons, bones, and blood cells are animal structures, not the plant mechanism. Thus, option A is correct.

The nervous system is the main rapid control and coordination system in humans. Receptors detect changes, sensory neurons carry impulses to the central nervous system, and motor neurons transmit commands to muscles or glands. The digestive, excretory, and respiratory systems perform important life processes, but they are not the primary system for rapid coordination. Therefore, option A is correct.

The spinal cord is usually the main integration centre for a reflex action because it provides a short pathway that produces a rapid protective response. Sensory information enters the spinal cord, is processed through an interneuron, and a motor impulse travels to the effector. Therefore option B is correct. The brain can receive information and may later interpret it, but the heart, liver and lung are not the usual control centres of a reflex arc.

The central nervous system, or CNS, consists of the brain and spinal cord. It receives and processes information, coordinates responses and communicates with the rest of the body through peripheral nerves. Therefore option A is correct. The peripheral nervous system includes nerves outside the brain and spinal cord, while the endocrine and digestive systems use hormones or digestive organs and are not formed by these two structures.

Quick responses require signals to travel rapidly from a receptor to an effector. Nervous control uses electrical impulses along neurons and chemical transmission at synapses, so it acts much faster than endocrine control. Therefore option A is correct. Hormones travel through the blood and usually act more slowly, while digestion and respiration are physiological processes, not independent control systems for every rapid response.

The governing concept is stimulus detection by specialised sensory receptors. A thorn prick directly stimulates receptors in the skin, including receptors associated with touch and pain. These receptors generate nerve impulses that travel through sensory nerves toward the central nervous system. Therefore option A is correct. Bright light activates photoreceptors in the eye, sweet taste activates taste receptors in the tongue, and a bell activates auditory receptors in the ear.

The governing concept is the organisation of the nervous system. The central nervous system consists of the brain and spinal cord, while the peripheral nervous system includes nerves outside them. These nerves connect the central system with sensory receptors, muscles, glands, and other body parts, carrying signals in both directions. Therefore option A is correct. Hormone production, blood filtration, and digestion are functions of other organs or systems.

The stapes is the smallest bone in the human body. It is one of the three auditory ossicles in the middle ear and helps transmit sound vibrations from the incus towards the inner ear. The incus and malleus are also middle-ear bones, but both are larger than the stapes. Exam tip: Remember: stapes is the smallest bone, while the femur is the largest.

The brain and spinal cord together form the central nervous system, which receives information and controls and coordinates body responses and activities. The peripheral nervous system consists of nerves that connect the CNS to the rest of the body; it does not include the brain and spinal cord. Exam tip: Remember CNS as Brain + Spinal cord.

A neuron is the structural and functional basic unit of the nervous system. It receives and transmits messages as electrical signals, enabling control and coordination in the body. The digestive system is involved in breaking down food, so it is not the correct answer. Exam tip: Remember that a neuron is a nerve cell of the nervous system.