Option E.5 – The Human Brain
E.5.1 – Label, on a diagram of the brain, the medulla oblongata, cerebellum,
hypothalamus, pituitary gland and cerebral hemispheres
During the development of the embryo, the brain begins as the neural tube, which then becomes the three main structures of the forebrain, midbrain, and hindbrain. These structures continue to fold and thicken into the other parts of the brain.
In mammals, the brain develops cerebral hemispheres from the forebrain. The majority of the neurons in the human brain are found here. The brain is encased in the cranium for protection. Immediately around it
The brain is encased in the cranium for protection. Immediately around it are the meninges or membranes. For additional protection, the space in between the membranes and the brain is filled with fluid to cushion the movement of the brain.
E.5.2 – Outline the functions of each of the parts of the brain listed in E.5.1
The brain performs many functions, including receiving impulses from sensory receptors, integrating and correlating incoming information in association centres, sending impulses to effector organs, storing information and building up an accessible memory bank and initiating impulses from its self-contained activities.
Medulla Oblongata
This is located in the brainstem. It controls automatic functions, including breathing, blood pressure, swallowing, digestion, vomiting and heart rate. It also controls homeostasis in the body. In this area, the nerve fibres between the brain and spinal column cross over, which means that the left side of the body is controlled by the right side of the brain, and vice versa.
Cerebellum
This is located in the hindbrain. It coordinates unconscious functions including movement and balance. This is important for the integration of sensory perception, coordination, and motor control. It has neural connections to link with the cerebral motor cortex, which sends message to the muscles, and the spinocerebellar tract, which gives feedback on the position of the body in space. It has an essential role in coordinating and fine-tuning motor movements.
Hypothalamus
Located in the forebrain and forms a link between the nervous and endocrine systems. It regulates unconscious systems, such as the impulses to the cardiac muscle, glands, metabolism and smooth muscle. It sends messages to the pituitary gland to control the release of hormones. The hypothalamus also secretes some hormones into the pituitary gland.
This is also the control centre for maintaining homeostasis, including body temperature, blood glucose concentration, fatigue, thirst and blood pH. Feeding and eating reflexes, aggression, fight-or-flight response and reproductive behaviour (sexual desire) are also controlled in the hypothalamus.
Pituitary Gland
This is attached to the hypothalamus, and is the main hormone-producing gland. It regulates bodily functions and releases some hormones produced in the hypothalamus. It regulates homeostasis by releasing hormones to stimulate the endocrine glands. This gland is divided into two sections: the posterior lobe stores and releases hormones that are secreted from the hypothalamus, whilst the anterior lobe produces and secrete the hormones that regulate bodily functions.
Cerebral Hemispheres
These are located in the forebrain and make up most of the brain. This is a distinguishing feature between the human brain and other mammals, showing greater development. They are the integrating centre for the more complex functions of the brain, including learning, memory and emotion. These coordinate the body’s voluntary activities and some involuntary ones. They also form the integrating centre of memory, learning, emotions and other complex functions.
The brain is divided into the right and left cerebral hemispheres, linked by the corpus callosum. The two hemispheres are asymmetrical, although there is some variation between individuals. The hemispheres are folded with deep grooves to extend the surface. The surface is covered in the layer of grey matter called the cerebral cortex. It is made up of densely packed non-myelinated neurons which have a huge number of synaptic connections.
E.5.3 – Explain how animal experiments, lesions and FMRI (function magnetic resonance imaging) scanning can be used in the identification of the brain parts involved in specific functions
Animal Experiments
In these investigations, a part of the animal’s brain is removed or connections with the brain are severed. The animal remains alive so that the functions of the brain can be examined. The effect this has on the animal’s behaviour gives understanding of the role of that area or those connections.
However, these days, with the different attitudes towards ethics, along with the developments in technology, such experiments are less frequently conducted. This is to prevent the suffering or sacrifice of the animals.
Another example includes the testing of the response of animals to certain drugs and recording their behaviour.
Lesions
The brain can be damaged in a number of ways, including accidents, strokes, and tumors. Many investigations have been conducted on people who have suffered brain damage to establish the effect of it on behaviour and body functions. In addition, this allows us to identify the specific areas of the brain that control certain functions. Post-mortem investigation of stroke victims has also been beneficial for understanding the role of each area of the brain. One example is the study of people with epilepsy who had their corpus callosum cut.
One example is the study of people with epilepsy who had their corpus callosum cut. By experimenting with placing objects in their left and right visual fields, it was determined that the left hemisphere is primarily responsible for language.
FMRI
Magnetic resonance imaging of the brain can be conducting while the individual is performing certain functions to see which areas have the greatest neural activity at that point. It is a non-invasive technique, and provides information in high resolution. The scans can show activity in any part of the brain. The subject may be given a series of tasks to perform during the scan, and the results are recorded on a computer.
MRI involves measuring the emission of electromagnetic energy from hydrogen atoms using a strong magnet. By sending pulses of radio waves, the location of the hydrogen atoms can be determined. Functional magnetic resonance imaging is an extension of this: it allows us to identify activity in the different areas of the brain. It looks at the supply of red blood cells to these areas, since blood flow is increased in active areas.
E.5.4 – Explain sympathetic and parasympathetic control of the heart rate, movements of the iris and flow of blood to the gut
The peripheral nervous system is divided into a number of complex parts. Within it is the autonomic nervous system, which controls the unconscious activities and functions of the body. It is controlled by the medulla and hypothalamus, as well as some conscious regions of the brain. Motor neuron nerve fibres run from the brain and spinal cord to specific tissues, organs and glands. These attach to the smooth muscle, which surround the internal organs and glands.
The autonomic nervous system is divided into the sympathetic and parasympathetic nervous system. The two systems are antagonistic.
E.5.5 – Explain the pupil reflex
The iris muscles will contract or relax depending on the amount of light present to control how much light enters the eye. This protects the retina from damage. These muscles are controlled by the parasympathetic nervous system.
E.5.6 – Discuss the concept of brain death and use of the pupil reflex in testing for this
Brain death is when all functions of the brain are irreversibly ceased. The tests for brain death include:
- Absence of pupil reflex – pupils remain in mid position and do not react to changes
in light - o Bright light is shone on the eyes. The pupils will constrict if the patient is alive. If not, this indicates brain death. The patient may still be living, but have suffered serious, irreparable brain damage that will eventually lead to death. Doctors will know that preserving the patient will not allow for recovery.
- Eyes do not blink when touched
- Eyes do not rotate in their sockets when the head is moved
- No movement of extremities
- Eyes do not move when iced water is placed in the outer ear canal
- Gag reflex – No cough or gagging when a suction tube is placed well into the trachea
- Breathing does not commence when the patient is taken off the ventilator
E.5.7 – Outline how pain is perceived and how endorphins can act as painkillers
The receptors of the nervous system allow us to register and respond to stimuli. These receptors include our sense organs and nerve endings. For example, in our skin, there are a range of small receptors that detect different aspects of touch. Some respond to sensation such as vibrations and flutters, other respond to pressure, and others are specific to pain.
Pain helps us to respond to things that are damaging our bodies. These pain receptors are found everywhere in the body except for the brain, which
These pain receptors are found everywhere in the body except for the brain, which send messages to the cortex of the cerebral hemispheres. Pain comes in two forms:
- Fast pain – This occurs rapidly after the stimulus is received. The feeling of pain is acute and localised, and is not felt deep within the body.
- Slow pain – This occurs after a delay with gradually increasing intensity. It will often become chronic, burning or throbbing pain. It can be felt deep in the body and will seem to come from a large area.
Response
The body releases endorphins from the pituitary gland when we experience pain so that normal activity is not inhibited. These will block the release of the neurotransmitters that send pain signals. Endorphins travel through the blood to the brain. Exercising also increases levels of endorphins to give a sense of euphoria.
The same principle is applied to the use of other painkillers to keep the patient aware of the pain, whilst reducing its intensity so that normal functioning can continue.