The diagram on the next page shows the sympathetic and parasympatic nervous systems and which part each affects.
The autonomic nervous system
Blue = parasympathetic
Red = sympathetic
The diagram on the next page shows the two divisions of the nervous system and some of the key nerves and their functions.
The brain and spinal cord are the CNS. These parts don’t just interpret incoming information and help coordinate the body’s activities as explained above but they also dictate responses based on past experiences, current conditions and reflexes. For example someone that may have burnt their hand in the past may be less likely to do what they did before which caused the burn. Here is a diagram showing the major divisions of the vertebrate nervous system.
The brain is a major part of the CNS, it is similar to a computer in that it does logical processing and has data storage (the memory), however a computer can be easily fixed where as a brain cannot. This is because nerve tissue is delicate and needs good physical protection and a good blood supply, if it gets damaged then repair is slow if ever at all. The brain is also home to complex development, emotion, creativity, learning and self-awareness. The brain has three major parts, the cerebrum, the cerebellum and the brain stem.
The cerebrum is the largest part of the human brain and is further divided into four parts, known as lobes, shown in the diagram below.
The frontal lobes are associated with emotions, personality such as social and sexual behavior, judgment, initiation, impulse control, memory, planning, reasoning, language, movement, motor function, spontaneity and problem solving. “There are important asymmetrical differences in the frontal lobes, The left frontal lobe is involved in controlling language related movement, whereas the right frontal lobe plays a role in non-verbal abilities” (neuroskills.com/brain-injury/frontal-lobes.php, 18/1/12). However this is not always strictly true and both lobes are involved in nearly all behavior with most people. The parietal lobes are divided into two parts; one involves perception and sensation while the other involves integration of sensory information, mainly visual information “The first function integrates sensory information to form a single perception (cognition) The second function constructs a spatial coordinate system to represent the world around us” (Kandel, Schwartz & Jessel, 1991). The occipital lobe is associated with visual processing and involved in visual perception, such as recognizing objects and colors and the temporal lobe deals with perception, memory, speech and recognition of auditory stimuli. The cerebrum is also split into two halves, the right and left hemispheres; generally the right hemisphere coordinates the left of the body and vice a versa. The two hemispheres are connected by the corpus callosum. The bulk of the cerebrum is the neocortex, a six layered structure only found in mammals. “It is thought that the neocortex is a recently evolved structure, and is associated with "higher" information processing by more fully evolved animals (such as humans, primates, dolphins, etc)” (serendip.brynmawr.edu/bb/kinser/Structure1.html, 18/01/12).
The cerebellum also has two hemispheres and is associated with regulating the body’s movement, balance and posture. Inside of it is the limbic system which contains the hypothalamus, hippocampus, amygldala and thalamus. The brain stem is underneath this limbic system and is made up of the midbrain, pons and medulla and is responsible for basic vital life functions such as, blood pressure, heartbeat and breathing
There can be dysfunctions of the nervous system, three of these are motor neuron disease, multiple sclerosis and Parkinson’s disease.
Motor neuron disease (MND) affects the motor neurons and there are different kinds of this neurological disorder, some can affect many things on an individual where as some kind’s effect mainly one pacific thing. Over all it leads to wasting of the muscles which can cause loss of mobility as well as difficulty with speech, breathing, and swallowing, however not everybody will have all of these symptoms. Some people with MND may have difficulty with speech if the neurons that control speech function work incorrectly or are damaged. They may slur their speech or stammer. This may mean that the individual may stop speaking all together because of embarrassment or the difficulty they have. Walking can also be effected “Sudden changes to the walking patterns as well as hops or other types of movement can occur when the Motor Neuron Disease is present” (motorneuronedisease.org, 18/01/12). Some people with motor neuron disease may find it difficult to breathe because signals that are usually sent to the lungs and surrounding tissues are stopped. This can cause people to pass out and in serious cases can cause death. It is not completely known what causes motor neuron disease, however there may be a link to genetics as it can be seen to run in families. Although it is known that damage to the nerve is caused, it is still unsure why this happens, although it is theorized from some evidence that free radical molecules are responsible, “Some evidence has shown that an excess of glutamate (a major nervous system chemical messenger) may be responsible for nerve damage. Glutamate plays an important role in the fast transmission of nerve signals.” (bbc.co.uk/health/physical_health/conditions/mnd1.shtml, 18/01/11) when there is too much of it is thought that it damages the brain and spinal cord because it is overactive.
Multiple sclerosis is an auto-immune condition (where the immune system attacks the CNS) and usually occurs in young adults. MS affects the white matter in the brain and spinal cord. The fatty layer (myelin sheath) wraps around the nerve fibers and electrically insulates them, in MS the immune system destroys this in a way which the neurons axons can no longer conduct potential actions in a productive way. This can lead to physical and cognitive disability such as dysfunction of the bowl, bladder and/or cognitively, vision and/or walking difficulties, tremors, pain, fatigue and many other symptoms. There are many types of MS varying in the way or extent it affects the CNS. One of these is relapsing MS, this is where people can recover from MS completely or partially and may have discrete attacks, however the disease can still advance and neurological problems may still occur. Another type of MS is progressive MS, this is where the disease slowly progresses over time. Relapsing MS “affects 85% of all MS patients. 50% of these patients will eventually experience progressive MS with or without periods of recovery. There are other types of more aggressive, progressive MS which affects the other 15% of the MS patients.” (Cecil textbook of medicine, Volume 2, L Goldman, W.B. Saunders, 2000, Page 2147). The cause of MS is not yet known, although it is believed that there may be some links with genetics, infections or other environmental factors.
Parkinson’s disease (PD) is a progressive neurological disorder and effects movement, balance and muscle control because of an age-related deterioration of certain nerve systems; however young people can also be susceptible to the disease. “In PD, brain cells deteriorate (or degenerate) in an area of the brain called the substantia nigra. From the substantia nigra, specific nerve cell tracts connect to another part of the brain called the corpus striatum, where the neurotransmitter called dopamine is released.” (emedicinehealth.com/parkinson_disease/page2_em.htm, 18/1/12) the alterations in dopamine can lead to medical problems, however the mechanism for the brain cell loss is not known. In Parkinson’s disease the nerves that produce dopamine break down causing, stooping of posture, muscle rigidity, involuntary tremor, shuffling walk, slowness of movements, and perhaps an affected intelligence later on in the disease. Although it is not known why this happens it is thought to be because of a number of reasons, and it is thought that there can be some risk factors to Parkinson’s disease, such as contracting a viral infection in later life or having a head trauma. It is also thought that a number of things cause it to happen such as medication and drug’s, but it is not known why this is, it is thought that it may be because of the way the medication or drugs work that they interfere with the brain’s natural dopamine. “Due to feedback inhibition, L-dopa can eventually cause the symptoms of Parkinson's Disease that it initially relieves. Dopamine receptors can also eventually contribute to Parkinson's disease symptoms by decreasing the sensitivity of dopamine receptors.” (viartis.net/parkinsons.disease/causes.htm, 18/1/12) Genetic mutations of the Parkinson’s disease can also be inherited; this can make a person more prone to getting the disease rather than directly causing it.
References.
Human body, Ted Smart, Darling Kinderley Limited, London
, 16/01/12
neuroskills.com/brain-injury/frontal-lobes.php, 18/1/12
Kandel, Schwartz & Jessel, 1991
serendip.brynmawr.edu/bb/kinser/Structure1.html, 18/01/12
motorneuronedisease.org, 18/01/12\
Cecil textbook of medicine, Volume 2, L Goldman, W.B. Saunders, 2000, Page 2147
emedicinehealth.com/parkinson_disease/page2_em.htm, 18/1/12
viartis.net/parkinsons.disease/causes.htm, 18/1/12
