Coordination and Response in Humans, practice questions

C, Hormonal coordination uses chemical hormones carried in the blood, giving a slower but longer-lasting and more widespread response.

B, A sensory neurone carries impulses from a receptor towards the central nervous system; the motor neurone carries them away to an effector.

B, The impulse triggers the release of a neurotransmitter that diffuses across the gap and starts a new impulse in the next neurone.

B, The impulse passes from the receptor through the sensory neurone, relay neurone and motor neurone to the effector.

B, The spinal cord acts as the processing centre, so the impulse does not need to travel to the conscious brain before the effector acts.

B, The cerebellum controls balance and coordination; the cerebrum controls conscious thought and the medulla oblongata controls involuntary actions.

C, Insulin, produced by the pancreas, lowers blood glucose concentration by making cells take up glucose and the liver store it as glycogen.

B, Insulin lowers blood glucose concentration while glucagon raises it, so their effects oppose each other.

B, When insulin is lacking or cells respond poorly to it, glucose is not taken up from the blood efficiently, so the concentration rises.

B, The hypothalamus monitors the body and controls the pituitary gland, so a nervous signal can trigger a hormonal response.

• Order: receptor, sensory neurone, relay neurone, motor neurone, effector.
• The reflex is processed in the spinal cord, so the motor impulse reaches the muscle quickly.
• The impulse to the brain, where pain is felt, takes longer than the reflex pathway.
• Therefore the hand moves away before the person is aware of the pain.
• The reflex protects the body by removing it from the harmful stimulus rapidly.
• This reduces the injury that the sharp object would otherwise cause.

• The pancreas releases the hormone insulin.
• Insulin makes body cells take up more glucose from the blood.
• Insulin also makes the liver store glucose as glycogen, so the concentration falls back to normal.
• During fasting the blood glucose concentration falls below normal.
• The pancreas releases glucagon, which makes the liver break down glycogen and release glucose.
• This raises the blood glucose concentration back towards normal by negative feedback.

• Stroke: the blood supply to part of the brain is interrupted, so neurones are starved of oxygen and die.
• The functions controlled by that region, such as movement or speech, are impaired.
• Diabetes mellitus: too little insulin is produced or cells respond poorly to it, so glucose is not taken up and blood glucose concentration rises.
• Both disorders are a failure of one specific part of a normal system.
• Knowing the healthy pathway shows exactly which part has stopped working.
• The disorder can then be described as the loss of that specific normal function.

The nervous system is made up of the central nervous system, the brain and spinal cord, where most information is processed and decisions are made, and the peripheral nervous system, the network of nerves that carries electrical impulses between the central nervous system and every receptor and effector in the body.

Sensory neurones carry impulses from a receptor towards the central nervous system, motor neurones carry impulses away from the central nervous system to an effector such as a muscle or gland, and relay neurones inside the brain or spinal cord connect the two, allowing impulses to be processed or redirected.

A synapse is a tiny gap between the end of one neurone and the start of the next. When an impulse arrives, it triggers the release of a chemical neurotransmitter that diffuses across the gap and binds to receptors on the next neurone, generating a new impulse and ensuring signals travel in one direction only.

A reflex arc is a fast, automatic, involuntary pathway that does not require conscious thought: a stimulus is detected by a receptor, carried by a sensory neurone to a relay neurone in the spinal cord, passed to a motor neurone, and finally reaches an effector, which responds within a fraction of a second.

A voluntary action, such as picking up a pen, is consciously decided and controlled by the brain, involves the cerebrum, and can be started, changed or stopped at will. An involuntary action, such as a reflex or the beating of the heart, happens automatically without conscious control and usually protects the body or maintains an internal process.

The endocrine system is a collection of glands that release hormones directly into the bloodstream rather than through a duct. Each hormone travels throughout the body but only affects target cells that carry the matching receptor, producing effects that develop more slowly than a nerve impulse but often last for a much longer time.

Four glands and their hormones are frequently examined: the pituitary gland releases growth hormone controlling body growth, the thyroid gland releases thyroxine controlling metabolic rate, the pancreas releases insulin and glucagon controlling blood glucose level, and the adrenal glands release adrenaline that prepares the body for a stressful or dangerous situation.

Hormone levels are usually regulated by negative feedback: when a condition such as blood glucose level rises or falls away from normal, a gland releases a hormone that pushes it back towards normal, and once normal is restored the gland reduces hormone release again. This feedback loop is central to how the endocrine system maintains a stable internal environment.

Damage to the nervous system disrupts coordination: a stroke occurs when blood supply to part of the brain is interrupted, killing the neurones in that region and impairing the function they controlled, while Parkinson's disease develops when neurones that produce a chemical needed for smooth movement gradually die, causing tremors and slow, stiff movement.

Diabetes mellitus develops when the body produces too little insulin or when body cells stop responding normally to the insulin that is present, so glucose is not taken up from the blood into cells efficiently and blood glucose level rises above the normal range, which can damage blood vessels and organs over time.