THE BRAIN – AN ENCHANTED LOOM By, Dr. Shamanthakamani Narendran M.D.(Pead), Ph.D. (Yoga Science)
A well known brain scientist, Sir Charles Sherrington gave a rather fanciful description of the brain…..“…within that enchanted loom millions of flashing shuttles weave a dissolving pattern, always a meaningful one, though never the same…”
Through the ages artists, seers, and philosophers have spent considerable time and effort to try to understand the brain.
If we examine the brains of different species, it becomes obvious that one part remains the same, this is the ‘ core’ of the brain, which controls our basic needs (hungry, thirst, reproduction).
As we move from a fish to higher species (cat, monkey, Man) we find that an outer shell of brain tissue has ‘ mushroomed ’ around the core.
The outer shell is the thinking brain.
This makes all the difference – thus a shark catches its prey and eats it whenever it is hungry.
Man can wait for an appropriate time to gratify his wishes.
The nervous system can be considered as two division, based on the STRUCTURE & FUNCTION .
The parts of the nervous system which lie in the mid- or central line together make the central nervous system or CNS .
Those parts (nerve cells, nerves) which lie away from the centre make up the peripheral nervous system or PNS .
STRUCTURE OF THE BRAIN CNS Brain + Spinal cord PNS Nerves = Nerve cells
The division which controls the functions which are not under our will (beating of the heart, digestion of food) is called the anatomic nervous system or ANS .
The second division controls functions which are under our will (walking, moving our hands) and is called somatic nervous system .
FUNCTION OF THE BRAIN
A. Central nervous system B. Peripheral nervous system B1. Somatic nervous system B2. Autonomic nervous system 1. Cerebrum 2. Brainstem 3. Cerebellum 4. Spinal cord Somatic nervous system
Beginning with the structures which make up the core of the brain, the most important is the brain stem – ‘most vital part of the entire brain.’
An injury in the lower most parts (the pons and medulla) results in death, as the centres which control respiration, the heart functions and BP are situated here.
The brainstem also contains a complex network of brain cells and fibers which runs through its entire length. This network acts as an alarm system – all sensations are received here, and messages pass to the rest of the brain.
The BRAIN STEM CONNECTS the BRAIN to the SPINAL CORD.
Above the brainstem lies the cerebellum or little brain.
The cerebellum receives information about movement both from the higher centers (planners) and from the muscles (executers), so that changes can be made.
This is important to achieve balance.
Thus the cerebellum can be expected to be working very efficiently in a circus trapeze artiste, who ‘walks the tight rope’
The cerebellum also plays a role in speech and walking.
THE CEREBELLUM The CEREBELLUM is the SECOND LARGEST part of the Brain, and is located at the back of the Skull. It coordinates muscle movements.
In front of the brainstem and cerebellum lie the thalamus and hypothalamus.
The thalamus is very important centre, through which all sensory information passes.
Outgoing information to the muscles also passes through the thalamus. Considerable change can occur here.
The hypothalamus lies below the thalamus and though small has many important functions.
Maintaining the internal environment constant.
In spite of fluctuations in the EXTERNAL environment, the internal environment has to remain constant, if the enzymes and other chemicals have to function normally.
The hypothalamus is essential for us to feel HUNGRY and to STOP.
This is also true for thirst and drinking.
FEEDING / DRINKING
The hypothalamus sends messages to the concerned parts of the brain.
Behavior is regulated by the hypothalamus
The ductless glands (pituitary, thyroid, adrenals, pancreas, reproductive glands) and their secretions are regulated by the hypothalamus
CONTROL OVER THE ENDOCRINE SYSTEM
The involuntary functions, which go on without us being aware of them (eg. Digestion of food) are under the control of the autonomic nervous system.
It is situated in the brainstem, spinal cord, and in the periphery.
The ANS is in turn controlled by the hypothalamus.
CONTROL OVER THE AUTONOMIC NERVOUS SYSTEM
Parts of the hypothalamus are important for emotional responses, such as pleasure, pain, rage.
Certain groups of nerve cells in the hypothalamus receive information from the eyes and hence regulate the body’s rhythms according to the light – dark cycle.
BIOLOGICAL CLOCK SLEEP – MEMORY – Two other functions of the hypothalamus
Is a wrinkled cap, which is the highest centre.
It is responsible for complex functions such as reasoning, creativity, anticipation.
Man is distinguished from other primates (monkeys) by a highly evolved cortex.
There are two cerebral hemispheres, which communicate with one another through a thick bundle of nerve fibers.
The two hemispheres are fairly symmetric, but they have different function.
Also sensations from the left side of the body pass to the right side of the brain.
TWO BRAINS IN ONE
Insight Reasoning Art awareness Scientific skills Imagination Written language Three dimensional awareness Number skills Music awareness Spoken language Left hand control Right hand control RIGHT HEMISPHERE LEFT HEMISPHERE
There are specific areas for each sensation.
HIGHER FUNCTIONS SUCH AS REASONING, DISCRIMINATION, MEMORY Each Hemisphere of the Cerebrum is divided into Four regions called LOBES . These LOBES are named for the SKULL BONES that cover them, FRONTAL, PARIETAL, TEMPORAL, and OCCIPITAL LOBES .
This is the part of brain which lies behind the forehead.
It has been described as the ‘character cortex’.
This description was partly based on a very unfortunate accident.
A road digger, called Phineas Gage was working with a drill, when a horrible accident took place.
The drill went backwards with a great deal of force and went through his forehead and into his brain.
He recovered physically, but his behavior was radically altered – for the worse .
He would use foul language, be unconcerned about his appearance or conduct.
This stray accident was further substantiated by the work of two scientists in the mid – 1930s.
They reported a dramatic experiment which was in the hospital laboratory.
This animal had suddenly developed spells of violence and was considered dangerous.
It had to be ‘put to sleep’ – at this stage of medical history the function of the frontal lobes was not known.
Hence these scientists decided to try removing the frontal lobe in the monkey before sacrificing it.
The experiment had startling consequences.
The aggressive chimpanzee suddenly became very quiet and tractable.
The dramatic change reported by these scientists impressed a Portuguese psychiatric, Egas Moniz.
He decided to try the same treatment on psychiatric patients who were violent and uncontrollable.
His results appeared to be equally favorable and dramatic.
Unmanageable patients could now be handled very easily.
Dr. Moniz was awarded a Nobel Prize for his work.
However, soon it became apparent that all was not well with these patients.
They had lost their individuality, spontaneity, and creativity.
They were like ‘shells of their former selves’
Of course, after this, frontal lobectomy was no longer considered to be a good solution for unmanageable patients.
Nowadays, it is performed very rarely and in a much restricted form.
The part of the cortex lies to the side, in the area corresponding to the temple.
The function of this prat of the brain was discovered in a very interesting way.
A noted neurosurgeon (Penfield) took advantage of the fact that brain tissue feels no pain and carried out brain surgery under local anesthesia.
Thus the patients were conscious throughout and not feeling pain.
Penfield stimulated parts of the temporal cortex with electric currents.
The effects were startling – the patients were able to recall memories which were forgotten long ago – one of them could clearly recall a conversation between two of his cousins when they were children.
Is concerned with putting together information.
This can be understood with an example. Imagine that you are sitting with your eyes closed and someone puts something in your hand. If the object is round, made of metal and fairly flat, then you combine this information with the memory of coins you have seen earlier and you are able to say that the object is a coin.
Thus you put together information from your hand (sensation) and from your memory. This putting together is done by the parietal cortex .
BRAIN GROWTH IN FETUS
The spinal cord is the downward continuation of the brainstem.
It is about 45 cm long and is protected by the back bone. There are four main parts of the backbone.
The uppermost part, which corresponds to the neck is called the cervical part.
Corresponding roughly to the chest is the thoracic portion.
Lower down, approximately in the abdominal region is the lumbar part.
The fourth part corresponds to the pelvic region and is called the sacral portion.
THE SPINAL CORD
There is a small, final part which is the ‘tailbone’ or coccyx . (in man this portion has no function)
This column of backbones or vertebrae offers protection to the spinal cord which lies within it.
The spinal cord can also be considered to have four parts (cervical, thoracic, lumbar, sacral).
The spinal cord is shorter than the vertebral column.
Hence, the four parts of the spinal cord and the surrounding vertebral column do not correspond exactly.
The spinal cord is concerned with transmitting sensations (pain, temperature) from the body to the brain pass to the body. This is called the sensory pathway. Also messages from the brain pass to the body. This is called the motor pathway.
The different parts of the spinal cord can also communicate with one another.
In some cases, where our responses are very quick and automatic, the spinal cord ‘decides’ on its own, what has to be done.
For example, if we touch a hot surface we move our hand away instantly, without thinking.
THE AUTONOMIC NERVOUS SYSTEM [ANS]
As already described earlier, this part of the nervous system controls those functions which go on even when we are not aware of them, such as the digestion of food.
The ANS has two divisions
The sympathetic nervous system
The Parasympathetic nervous system
These two divisions arise from different parts of the central nervous system and have different functions.
The parasympathetic division arise form the brainstem and the sacral portion of the spinal cord .
The sympathetic division arises from the thoracic and lumbar parts .
For both divisions, from these parts of the brainstem or spinal cord, nerve cells send messages through their axons to another group of nerve cells called a ganglion .
The nerve fiber (axon) from a ganglion neuron passes to the different structures (heart, stomach, etc.)
As described earlier, the transmitting nerve fiber, or axon releases chemicals at its ending.
These chemicals influence other cells.
These may be other nerve cells, muscle cells, or other organs (heart, stomach, etc.)
This chemical responsible for the many effects detailed below – of the parasympathetic division (such as slowing the heart, or digestion of food).
Another important difference –
Sympathetic nerve fires release NOR ADRENALIN .
This is a derivative of adrenalin.
In everyday language we often say that “we can feel the adrenalin coursing through our bloodstream”…. Meaning that we are aroused/stimulated.
The Autonomic Nervous System Structure Sympathetic Stimulation Parasympathetic Stimulation Iris (eye muscle) Pupil dilation Pupil constriction Salivary Glands Saliva production reduced Saliva production increased Oral/Nasal Mucosa Mucus production reduced Mucus production increased Heart Heart rate and force increased Heart rate and force decreased Lung Bronchial muscle relaxed Bronchial muscle contracted Stomach Peristalsis reduced Gastric juice secreted; motility increased Small Intestine Motility reduced Digestion increased Large Intestine Motility reduced Secretions and motility increased Liver Increased conversion of glycogen to glucose --- Kidney Decreased urine secretion Increased urine secretion Adrenal medulla Norepinephrine and epinephrine secreted --- Bladder Wall relaxed Sphincter closed Wall contracted Sphincter relaxed
The sympathetic nervous system brings about all the changes for the fight or flight response which occurs during stress.
The parasympathetic nervous system carries out functions needed for normal, everyday functioning – digestion of food, formation of urine.
Coming to the differences in effects, in a general sense
Within 5 to 10 seconds of total stoppage of blood supply to the brain, a person loses consciousness, within 2 minutes all the energy stores are used up and brain death occurs. BLOOD SUPPLY TO THE BRAIN AND THE CEREBROSPINAL FLUID
It is very interesting to note that through the brain makes up about 2% of the body weight – the blood flow/min is about 15% of the output from the heart. (the average adult brain weights about 1400 g).
Thus the brain has a blood supply of about 750-1000 mL/min .
This blood supply remains constant during various conditions, such as exercise, and sleep .
Probably the most important factor which can make the blood vessels to the brain dilate (become wider) is carbon-dioxide .
This gas is produced whenever cells are active.
Hence cells are active the carbon-dioxide which is produced increases the blood supply automatically.
The brain also has another fluid,
which is clear and transparent.
The CSF is formed from the blood.
It is present in spaces (ventricles) within the brain.
It also is present around the brain, between layers of tissue wrapped around the brain.