(a) Adrenaline hormone in the adrenal gland is secreted in scary situations in human beings. Adrenaline hormone is also called as an emergency hormone. It is produced in the medulla in the adrenal glands as well as some of the central nervous system's neurons. Within a couple of minutes during a stressful situation, it is quickly released into the blood, sending impulses to organs to create a specific response. After the stress has subsided, adrenaline's effect can last for up to an hour.
The impact of adrenaline release in our body are as follows:
1. Adrenaline triggers the body's fightor-flight response. This reaction causes air passages to dilate to provide the muscles with the oxygen they need to either fight danger or flee.
2. It also triggers the blood vessels to contract to re-direct blood towards major muscle groups, including the heart and lungs.
3. The body's ability to feel pain also decreases as a result of adrenaline.
4. Blood vessels dilate (enlarge) in our muscles.
5. Blood vessels constrict in our digestive tract to slow digestion.
6. Kidneys make more renin (to increase blood pressure).
7. Glucose production increases, for energy.
OR
(b) (i) A: Sensory neuron or Nerve
B: Relay neuron or Interneuron
C: Effector
(ii) The functions of A and C are as follows:
A: The sensory neuron conducts the nerve impulses towards the Central Nervous System (CNS). The CNS is comprised of the brain and the spinal cord.
C: The effector organ shows response by contracting or secreting a product.
(c) Reflex arcs have been evolved in animals because the thinking process of the brain is not fast enough. Many animals have very little or none of the complex neuron network needed for thinking. So, it is quite likely that reflex arcs have evolved as efficient way of functioning in the absence of true thought processes. However, even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.