Reflex Arcs

Biology half-term homework

What is a reflex arc?
A reflex arc is the neural pathway that causes a reflex action. In animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur. Reflex action is a rapid automatic and involuntary response to a stimulus which is not under the control of the brain.
If we unknowingly touch a hot object, we immediately move our hand away from it. So moving our hand away on touching a hot iron is an example of reflex action as shown below.
Senses hot object
Response pulls hand away


What is a synapse?
A chemical synapse is a small gap, or commonly referred to as a connection, between two cells that allows for the first cell to communicate with the second cell through a chemical signal. These chemical signals are called neurotransmitters, and once they are released by the presynaptic cell, they act on the first and second cell through specialized protein molecules called neurotransmitter receptors.

What is a serotonin And what is its effect?
Serotonin is a hormone that is found naturally in the human brain; it is also found in some animals, including human beings. It is also found in a variety of plant sources, including vegetables, fruits, and mushrooms. Categorized as a neurotransmitter, it is important in transmitting nerve impulses. It is also described as a vasoconstrictor, which is a substance that can cause narrowing of the blood vessels. The amino acid tryptophan is credited with producing serotonin in the body.
If the brain has a lack of serotonin what can happen?
Low serotonin levels cause intense refined carbohydrate cravings that are very difficult to ignore.  In particular, these food cravings trigger impulse eating that is difficult to control with willpower alone.   Exercising willpower and determination becomes difficult because your emotions make you feel "What’s the use, even if I lose weight I’ll only gain...