My Science School

After a man and a woman have had sex, about 300 million sperm cells are present in the woman’s vagina. The sperms swim forward with the help of their tails with a common aim: to fertilize the egg cell. The egg cell ripens in the ovary of a woman only once a month. Certain hormones then trigger ‘ovulation’, in which the egg cell is released from the ovary in the fallopian tube. Fertilization occurs if the egg cell meets a sperm. Doctors assume that after ovulation, an egg cell can be fertilized for a maximum of 12-24 hours. A single sperm cell is enough to fertilize the egg cell. 

When a man and a woman have sex, the erect penis of the male is inserted into the vagina of the female. The sperm cells of the male are ejaculated into the vagina of the female. If an egg cell has been released in the ovary at that time, it may get fertilized by the sperm and the woman may become pregnant. The baby develops in the woman's uterus for about 40 weeks, till it is developed enough to be born. Usually, babies are born healthy, but sometimes they may be born with a disability.

We may not know exactly why we need to sleep, but we do know that our body needs sleep to rest and recover. If the sleep is inadequate, performance of the brain and the body goes down. One becomes irritable and cannot concentrate. After several days of inadequate sleep, one may start hallucinating. The duration of sleep needed depends on the person and the age. While most babies sleep for more than 12 hours a day, some old people need only 5-6 hours of sleep.

 

A stroke is a serious medical condition occurring as a result of an interruption in the supply of oxygen to the brain. The most frequent reason for a stroke is the blockage or bursting of a blood vessel in the brain. In both cases, the blood circulation and, hence, the supply of oxygen to the brain is interrupted. The result is damaged brain tissue. Stroke patients may lose all information that was stored in the damaged area and may have to relearn simple things like walking, swallowing, or writing. Sometimes, the brain can build new connections between the brain cells and repair the damage. 

It is the store of things learned and retained from our activity or experience. Our memory is a collection of knowledge, experiences, impressions, skills, habits, and many other things. It gives us the ability to learn and adapt from previous experiences as well as to build relationships. It has a lifelong storage capacity, and no computer of the world can match its performance. Short-term memory is the information that we are currently thinking of and it lasts for only a few seconds. Important things which we have experienced and would not like to forget are transferred from short-term memory into long-term memory.

Signal transmission through nerve cells is quite complicated. Like all the other cells, nerve cells also have a cell body with a nucleus. There are fine extended branches known as dendrites and a long ‘tail’ called the axon on the body of the nerve cells. Axons in the brain are smaller than 1 mm, whereas in the spinal cord they can be as long as 1 m. A chemical substance is released through an electrical impulse into the synapses present at the end of the axon. This chemical substance, known as the neurotransmitter, is transferred to the dendrite of another nerve cell and the signals are transmitted. 

The brain is made up of two halves. Different areas of the brain have different functions. All nerve cells in the brain, about 100 billion of them, are connected to one another and transmit information. This network of the nerve cells is expanded through learning and training. Our brain controls our actions, regulates our sleep, and allows us to feel sensations like pain and joy. If it is damaged, maybe due to a stroke, one has to relearn a lot of things like speaking, walking, or eating.