Nerves and Hormones
Messages get around our body with the purpose of telling other parts
what to do. Of the two main methods that we'll look at, the first is
"the Nervous System".
This is a fast way of communicating as it is done with electrical signals conducted along nerves. They start with a stimulus and end with a response. For example, seeing a cup falling over-----grabbing the cup before it falls.
They follow a simple pattern:
Receptor -> Sensory Neuron -> CNS -> Motor Neuron -> Effector
The receptor is the part that detects, e.g. skin receptor. The sensory neuron transmits the signal to the CNS or Central Nervous System which sends another signal along the correct motor neuron to the effector. The effector is always a muscle or a gland so you either move or a gland secretes.
Sometimes, these responses are automatic and you cannot control them. We always think of being tapped on the knee by a doctor and your knee jerking as automatic but there are others. You cannot help pulling you hand away from a flame and you cannot stop your iris from expanding or contracting.
If you accidentally leaned your hand onto a hot surface, a signal would be generated from the receptor in your skin, it would travel along the sensory neuron into your spine. The signal would pass over the gap called a Synapse (causing a tiny delay as it relies on a chemical signal) into the relay neuron, back along the motor neuron and into the effector which would be a muscle in your arm that would contract and pull your hand away from the danger. Because this was calculated in your spine, your muscle started to move before your brain knew that you were burned, It is automatic and no conscious thought was involved. Look at the path below.
The second type of communication in the body is through a much slower means. This is by secreting hormones which are chemical messengers. These are slower and last longer. These chemicals are called hormones.
One of the most complicated examples of control by hormones, is the menstrual cycle. During a complete cycle, different events and processes are controlled as in this diagram. Thee main hormones are:
FSH or Follicle Stimulating Hormone which is secreted by the pituitary gland. This hormone makes the egg mature in the ovary, it also stimulates the ovary to produce Oestrogen. Oestrogen stimulates the uterus wall to thicken awaiting pregnancy and in turn inhibits the production of FSH. Luteinising Hormone (LH) is produced and it stimulates the ovary to release a mature egg.
These hormones are a key component in the contraceptive pill. By taking a pill that contains oestrogen at regular intervals they prevent the production of FSH meaning that no eggs mature.
The hormones are not just used to prevent pregnancy, they are used to help to treat infertility. Supplementing hormones can cause the maturing and releasing of an egg that may not have been happening naturally. Also, after IVF, when an artificially fertilised egg is placed back on the uterus lining (implanted), hormones can be given to ensure that the wall thickness is maintained to increase the chances of a successful pregnancy.