Structure and Functions of the Human Brain

a) Draw a diagram to show the structure of the human brain.

b) Outline the function of the following regions of the human brain: medulla oblongata, cerebellum, hypothalamus, pituitary gland, cerebral hemisphere.

Medulla oblongata:

The medulla oblongata contains the neural centres of the autonomic nervous system and therefore controls automatic activities such as breathing, heart rate, blood pressure, swallowing digestion, production of saliva etc.

Cerebellum:

The cerebellum is responsible for unconscious functions such as movement and balance. It receives information from the balance organs in the ears and from receptors in muscles and tendons which indicate how stretched the muscles are. However, the cerebellum does not initiate movements but only controls them. Therefore, a damage of this part of the brain would result in uncoordinated movement.

Hypothalamus:

The hypothalamus basically is the link between the brain and the endocrine system. It produces the hormones which are later secreted by the posterior pituitary gland and stimulates the secretion of hormones from the anterior pituitary gland by nerve impulses.

Pituitary gland:

The pituitary gland is made up of two parts: the anterior pituitary gland and the posterior pituitary gland. The anterior pituitary gland consists of endocrine tissue and secretes hormones like FSH, LH, GH ect. These hormones produced in the anterior pituitary gland are released after a stimulus given from the hypothalamus in the form of neurosecretions and control and regulate many body functions. The posterior pituitary gland does not produce hormones but stores those produced in the hypothalamus. These hormones are ADH (antidiuretic hormone) which regulates the re-uptake of water into the kidneys and oxytocin which causes the uterine wall to contract. After being stimulated by nerve impulses from the hypothalamus the posterior pituitary gland releases these hormones into the bloodstream.

Cerebral hemisphere:

The cerebral hemisphere is the area in the brain which acts as the integrating centre for high complex functions like learning, emotions and memory and it also controls the body’s voluntary actions. The outer part of the cerebral hemisphere is called the cerebral cortex and is divided into four areas: the sensory area, the motor area, the auditory association area and the visual association area.

c) Explain how animal experiments, brain lesion and FMRI scanning can be used to examine the functioning of the brain.

The brain and the way in which it functions and processes thoughts have always been a great area of interest for scientist and yet they have long been a mystery.

In the earlier years of brain research tests have been done on animals, preferably primates as their brain has the most similarities with a human brain. For the experiments scientists had to remove parts of the skull to get access to the brain. The animals were then either given stimuli or they had small parts of the brain removed after which the scientists observed what effects these surgical processes had on the behaviour of the tested animal. However, in order to be able to observe the animals the experiments had to be carried out on living animals, called vivisection. During such procedures many animals suffered or even died. Obviously many scientists and animal right activists had ethical objections to the experiments so that they were performed more rarely.

In the 1890s scientists discovered a new method to observe brain functions: they observed brain lesions, damaged areas in the brain, to study the functioning of the brain. The french neurologist Jean-Martin Charcot had a patient who wasn’t able to speak except from the word “Tan”. He discovered that this man had a huge tumour which damaged the whole left side of this brain. From this information he set up the hypothesis that the left half of the brain contains the speech centrum. The case of Phineas Gage also sets up a similar hypothesis: He had accidentally passed a metal pin through his skull into the frontal lobes of his brain after which his personality and capacity for social interactions severely altered. Thus, scientists suggested that the frontal lobes are involved in actions which have to do with social behaviour and personality. Today, we know, confirmed by many other patients who suffered from brain lesions, that these suggestions were right and scientists were able to identify the function of big parts of the human brain. For example lost a man the desire to smoke after a stroke which damaged his “insula”, a region of the brain in which as we now know the craving-centre of the brain lies.

Although this method allows quite precise insight into the brain, there now is a much better method which can be done on healthy living humans: functional magnetic resonance imaging (fMRI). It is a scanning method which can detect how the flow of blood changes in the brain. When neuronal activity increases there also is an increased demand for oxygen so that there is an increased blood flow to the regions of increased neural activity; fMRI can measure these changes and record them on activation maps showing which parts of the brain are involved in a particular mental process.

First a high-resolution scan of the person or object to be observed is taken before the subject of the experiment is given a stimulus and a series of low-resolution scans are taken. On these scans changes in the blood flow in the brain can be seen and the areas can be linked to a specific function. For example, if people have to follow a moving object on a screen with a cursor, this requires the coordination of sight, eye movement and hand movement and thus the region which coordinates these receive increased blood flow which can be clearly seen on fMRI scans taken from people performing such an action as on the picture below.

The advantages of the fMRI scanning technique is that it can be done on healthy human individuals; scientists do not rely anymore on ill people having brain lesions and they do not have to sacrifice animals anymore, instead they can do repeated studies on humans and also animals without there being any ethical objections to it.