Coordination and Response: Answers

When someone touches a hot iron, they immediately pull their hand away. Explain the events which occur during this reflex response.

Receptors in the skin which detect heat (the stimulus) send an electrical impulse to the spinal cord via a sensory neuron. In the spinal cord, the impulse passes from the sensory neuron to a motor neuron through a relay neuron. The impulse travels along the motor neuron to the arm muscle (the effector) which contracts in order to pull the hand away from the iron.

What happens when an impulse reaches a synapse?

When an electrical impulse reaches the end of the neuron, vesicles containing neurotransmitters are released into the synapse. The neurotransmitters diffuse across the synapse (the gap between two neurons) and bind to receptors on the next neuron. When the neurotransmitters bind to the receptors, this generates an impulse in the next neuron.

What is meant by the term ‘homeostasis’?

Homeostasis is the maintenance of a constant internal environment. For example, optimum levels of glucose are maintained in the blood through homeostatic control.

Give some differences between nervous and hormonal control.

The nervous system is rapid and has short-lasting effects on the body. Information is sent through neurons as an electrical impulse and as neurotransmitters across synapses. The hormonal system is much slower and has longer-lasting effects. Hormones travel around the body in the bloodstream until they reach their target organs.

How does the hypothalamus maintain a constant body temperature?

The hypothalamus in the brain ensures that body temperature stays close to 37 degrees. When the temperature of our blood fluctuates, it sends impulses to the skin and blood vessels to adjust our temperature through vasoconstriction, vasodilation, sweating, shivering and stimulating hair follicles to stand on end.

Describe the functions of the following hormones: adrenaline, ADH, insulin and luteinising hormone (LH).

Adrenaline stimulates the ‘fight-or-flight’ response which prepares our bodies for action. It increases heart rate, increases breathing rate, increases blood flow to our muscles while reducing blood flow to the digestive system, causes pupils to dilate and converts glycogen to glucose so our cells can respire more.

ADH is released when the water content of our blood is low. It makes the collecting duct wall of the nephron tubule more permeable, so more water is reabsorbed from the kidney into the bloodstream.

Insulin is released when glucose levels are high (e.g. after a meal). It converts glucose into glycogen which is stored in the liver until it is needed.

Luteinising hormone (LH) causes an egg to be released from the ovaries in a process called ovulation.