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Spring 2022 Sensory-Neural Systems, Biology Mid-term Exam Solution: The University of California, Irvine

Most biology students struggle with exams on Sensory-neural systems. If you are sailing in the same boat, you will be happy to know our biology test takers specialize in writing assessments that require knowledge of sensory-neural systems. To prove to you that we are equal to the task, we have shared a sample sensory-neural system exam question and answer. The test was submitted by a student from the University of California, Irvine, and impeccably solved by one of our top-rated experts. You too can contact us at any time if you need help with an exam on sensory-neural systems.

EEG results are often used by neuro-surgeons to understand changes in brain activity and diagnose brain conditions. Describe the Berger effect and how the advanced form of Berger’s equipment (EEG) is used to map brain electrodes.

With the arrival of sleep different wave patterns appear, and an EEG the advanced form of Berger's equipment - can inform when someone is asleep, dreaming, unconscious, anaesthetized or waking up. This synchronization of waves is of course a problem. Brain cells might be expected to discharge at random, but instead, there is unison. Are there pacemakers in the brain regimenting the discharges? Of what use is the rhythm? And why are different wave patterns associated with an epileptic fit? The complexity of the rhythms involved, so cleverly detected by the assiduous Dr Berger, are still just as complex, and the job of deciphering patterns in terms of varying stimuli is being handed over to computers. Therefore, although the human brain is far more cunning and compact than any computer, and although computers were devised by human brains, it may be computers which can inform the brain what makes it tick so cyclically, and why. It was a United States Air Force scientist who was the first to teach himself to alter his alpha rhythms, switching them on and off at will. He could speak his mind, as it were, without moving a muscle.

Concussion Picture the scene. (Practically every film director has already done so.) The victim walks into the room and glances about him. The villain, whose earlier glancing had supplied him with a vase, poker or paper-weight then knocks out the victim with one cruel blow. The victim slumps stays unconscious a while, then comes round, shakes his head, takes in the situation and rushes out of the room. It is all easy. It is bogus.

The cause of unconsciousness is genuine enough; it is the instant recovery that is improbable and misleading. A concussion is most likely to be caused if the head is rapidly accelerated: a threshold speed of twenty-eight feet per second is sometimes quoted. The speed of the blow is therefore important, whatever the size of the blunt instrument. It so happens that a rabbit punch on the neck and a straight left to the jaw are both good at producing acceleration, but a short neck with thick muscles is more able to resist efforts to accelerate its head. Any subsequent unconsciousness may be so fleeting that the victim is scarcely aware of it; it may last less than thirty seconds, as with most boxing knock-outs; or it may last for days and weeks, as in many car accidents.

Generally speaking, the unpleasantness of the return to consciousness and the extent of amnesia surrounding the event is proportional to the degree of unconsciousness. Nausea, headache, unsteadiness and amnesia are probable if the concussion has been at all prolonged. The instant recovery and awareness of the screen victim are both highly improbable and give the impression that such a mishap is annoying but trivial. Dr Macdonald Critchley, a specialist in the effects of brain mistreatment, has said no unconsciousness can ever be regarded as trivial, that blood clots could form and enlarge as a result of the injury, that evidence exists of an association between tumours and severe concussion, and that blows not even causing knock-outs can cause damage to brain cells.

Boxers still die regularly. So do participants in virtually all other sports; but, unlike most other sports, the aim of boxing is calculated violence. In 1965 when 'Sonny' Banks died of a blood clot on the brain, aged twenty-four, three days after he had been knocked out by Leotis Martin, he was the sixty-fourth American boxer to die in five years of ring injuries. Dr Milton Helpern, then New York City's chief medical examiner, performed autopsies on dead boxers. Medical World News quoted him after he had conducted studies on four knocked-out victims: 'When burr holes were made in the heads of the unconscious boxers, brain tissue oozed out like toothpaste from a tube.' The four men had survived unconscious from fifty-five hours to nine days after their knock-outs. Two of them had hit their heads on the mat when they fell: two had just slumped to the ground.

A report from Finland published in the Lancet in November 1982 gave results of a survey concerning fourteen boxers who had been Finnish, Scandinavian or European champions. It concluded that 'modern medical control of boxing cannot prevent chronic brain injuries but may create a dangerous illusion of safety. The only way to prevent brain injuries is to disqualify blows to the head. In the same year the American Medical Association recommended that doctors should have the right to interrupt a bout in order to examine a boxer and, if need be, stop the fight. Currently, doctors have this power only in Michigan.

Memory 'If we remembered everything we should be as ill as if we remembered nothing', said William James, and for a long time that just about summed up mankind's ability at comprehending mankind's memory, or indeed the memory of any creature. R. W. Gerard lamented in 1949 that the current understanding of the mind 'would remain as valid and useful if, for all we knew, the cranium was stuffed with cotton wadding'. B. D. Burns, reviewing the whole subject of memory theory eight years later, concluded that no hypothesis had proved a wild.

'It may well be that we are at last on the way to solving...how memories are stored in the brain', said Lord Adrian in 1965. Perhaps the future did look brighter than, for no one is so optimistic now. The chemistry of memory has advanced, in that much more is known than previously, but the progress has been in the nature of hillside walks; the accomplishment of each knoll merely gives a better, and more realistic, view of the miles and miles that lie ahead. Finding the chemical basis is only half (or less) of the story. Memory has three ingredients: there are the three R's of registration, retention and recall. Everyone registers more than he can retain and retains more than he can recall. If RNA is the chemical that, by having its molecular pattern altered during registration, is the card index basis of memory this fact does not explain how the card index is either maintained (retention) or used (recall). What is the system that does either or both?

Similarly, there is short-term memory-looking up a number, dialling it, and forgetting it - and there is long-term memory. Are these different or merely two aspects of the same phenomenon? It is relevant that memory difficulties of the aged have been demonstrated to be dominantly difficulties of recall: short-term retention is scarcely influenced by advancing years.

Nerves On old Olympus' topmost top a fat-eared German viewed a hop. So, runs one of the non-obscene jingles for remembering the brain's cranial nerves. Obviously, the central nervous system does not exist in isolation: it must be connected to every part of the body. In all, there are forty-three pairs of nerves joining the C.N.S. with everywhere else. Of this number twelve pairs go to and from the brain itself, and thirty-one pairs go to and from the spinal cord. The nerves may be either entirely sensory- passing information only inwards and towards the brain; or, more frequently, they may be a mixture of both incoming and outgoing fibers. Each of the forty-three has specific functions; hence the necessity for knowing which does what; hence the jingle which stands for the twelve names: olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, auditory (ear) glosso- pharyngeal, vagus, accessory and hypoglossal.

Once again everything makes much more immediate sense in the more primitive forms of animal life. The fishes, for example, have both cranial and spinal nerves (although only ten cranial nerves, and a varying number of spinal nerves) but everything is simpler. The brain and spinal cord lie in a straight line, the nerves branch off along the length of this central nervous system much like rungs along a ladder, and they tend to be associated with an organ lying nearby. The first one receives impulses from the nose, the second from the eye, and so forth down to the tail. The human being acquired this same system but only after it had evolved for the differing shapes of the amphibia, reptiles, mammals and primates. The result is that the No. 1 cranial nerve still receives impulses from the nose, No. 2 from the eye, and so on, but neither the nose nor eye nor brain nor any other organ is sited in the same manner as in the earliest fishes. Consequently, the regular rung-like simplicity has gone. Instead, the cranial nerves run much more awkward courses in their atavistic efforts to join the same organ to the same bit of brain even though both brain and organ have radically altered proportions, sizes, shapes and locations. The spinal nerves are also much more complex in the human being than in the fishes. The ladder-like regularity exists to a certain extent, but the human spinal cord does not even run the entire length of the human backbone. It starts where it joins the brain and then only continues downwards for 18 ins. (46 cms.). After the small of the back and for the last 10 ins. (25 cms.) of the spinal column, there is no spinal cord, only a horse's tail of fibers, tracts and occasional nervous complexes. Fibers leading from this spinal cord are always both sensory and motor. Even though the cord is quite long, and is connected to thirty-one pairs of spinal nerves as against twelve pairs of cranial nerves for the brain, and even though it is such an important trunk route for impulses, the spinal cord is far, far less bulky than the brain. It is about in. (13 mm.) wide and only weighs an ounce (28 gms.), a fiftieth of the brain's weight.

When a neuron dies it cannot be replaced. The nerve cells are so specialized that they have lost the ability to make new cells, and neurons are being lost all the time. Should an axon be cut sufficiently far away from its mother cell the peripheral part of the axon will slowly wither and die. The neuron itself will not necessarily die, although part of the axon on its side of the cut may perish. Sometimes the remaining axon will grow afresh from the region of the cut towards the peripheral area that it used to serve. Growth may be slow, but some higher animals have demonstrated an ability to grow new axons at about one-eighth of an inch (3-4 mm.) a day. This rate of about an inch (25 mm.) a week means that quite a time may elapse after the axon's severing before it arrives again at its destination and establishes a functional connection once more. Should the nerve be severed within the central nervous system of the brain and spinal cord the connection is broken for all time, but this does not always create such a severance as this seems to imply. Often the body can find a way around such a problem. Other pathways are made use of and developed with use.

The all-or-none transmission of a stimulus along a nerve fibre means a system even simpler than the Morse code. There are not even dots and dashes, just dots. The dots are all equal dots, none louder than the rest. Therefore, the only way to vary the intensity of such a stimulus is to alter the frequency, the number of dots per second. Even though a nerve amplifies a stimulus as it travels along the fiber the whole system is back to normal very rapidly, so much so that several hundred impulses can be impelled along a given fiber every second. Frequencies higher than 1,000 impulses per second have been experimentally measured in some mammal fibers, but human fibers usually conduct at frequencies lower than 100 per second.

The many thousands of millions of neurons within the nervous system of each human being give some idea of his or her potential and excellence when compared with the modest neurological equipment of an insect. The bee and the ant, apart from being objects of veneration for their wisdom and diligence, lead complex social lives and construct cunning homes for themselves. The bee has about 7,500 nerve cells, and the ant has even fewer. Mankind, not always wise or diligent, has two million times more neurons at his command than the bee, whether he uses them more skillfully or not. In the main they are not used, as so much of the brain can be removed without apparent effect, and as individuals (such as hydrocephalic) with but a minute portion of the normal brain bulk has even achieved university degrees. It would seem, as Alfred Russel Wallace phrased it, that 'an instrument has been developed in advance of the needs of its possessor".

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