Prof.aza 1 The Brain (Handout) prof. aza. 2 Brains exist because the distribution of resources necessary for survival and the hazards that threaten survival

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The Brain (Handout)The Brain (Handout)

prof. azaprof. aza

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Brains exist because the distribution of Brains exist because the distribution of resources necessary for survival and the resources necessary for survival and the hazards that threaten survival vary in space hazards that threaten survival vary in space and time. There would be little need for a and time. There would be little need for a nervous system in an immobile organism or nervous system in an immobile organism or an organism that lived in regular and an organism that lived in regular and predictable environment. predictable environment.

Brains are informed by the senses about the Brains are informed by the senses about the presence of resources and hazards; they presence of resources and hazards; they evaluate and store this input and generate evaluate and store this input and generate adaptive responses executed by the muscles.adaptive responses executed by the muscles.

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Figure 03a E. coli's Response to Chemical Figure 03a E. coli's Response to Chemical Gradient Gradient

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Some of the most basic features of Some of the most basic features of brains can be found in bacteria brains can be found in bacteria because even the simplest motile because even the simplest motile organisms must solve the problem of organisms must solve the problem of locating resources and avoiding locating resources and avoiding toxins.toxins.

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They sense their environment through a They sense their environment through a large number of receptors, which are large number of receptors, which are protein molecules embedded in the cell protein molecules embedded in the cell wall. The action taken in response to the wall. The action taken in response to the inputs usually depends on the gradient of inputs usually depends on the gradient of the chemicals (see Figure 03a). the chemicals (see Figure 03a).

Thus memory is required to compare the Thus memory is required to compare the inputs from different locations. The inputs from different locations. The strength of the signal is modulated by strength of the signal is modulated by immediate past experience. immediate past experience.

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This in turn regulates the strength of This in turn regulates the strength of the signal sent by chemical the signal sent by chemical messengers from the receptor to the messengers from the receptor to the flagellar motors. Thus even at the flagellar motors. Thus even at the unicellular level, the bacteria have unicellular level, the bacteria have already possessed the ability to already possessed the ability to integrate numerous analog inputs integrate numerous analog inputs and generate a binary (digital) and generate a binary (digital) output of stop or go. output of stop or go.

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In multicellar organism, cells specialized for In multicellar organism, cells specialized for receptor function are located on the surface. Other receptor function are located on the surface. Other cells specialized for the transmission and analysis cells specialized for the transmission and analysis of information are located in the protected interior of information are located in the protected interior and are linked to effector cells, usually muscles, and are linked to effector cells, usually muscles, which produce adaptive responses.which produce adaptive responses.

As do unicellular organisms, neurons integrate the As do unicellular organisms, neurons integrate the diverse array of incoming information from the diverse array of incoming information from the receptors, which in neurons may result in the firing receptors, which in neurons may result in the firing of an action potential (when the summation is of an action potential (when the summation is above a threshold level) rather than swimming above a threshold level) rather than swimming toward a nutrient source as in the unicellular toward a nutrient source as in the unicellular organisms organisms

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Once the threshold for generating an action Once the threshold for generating an action potential is reached, the signal is always potential is reached, the signal is always the same, both in amplitude and shape (a the same, both in amplitude and shape (a nerve consists of many neurons, it does not nerve consists of many neurons, it does not obey the all-or-none law). obey the all-or-none law).

Action potentials and voltage-gated sodium Action potentials and voltage-gated sodium channels are present in jellyfish, which are channels are present in jellyfish, which are the simplest organisms to possess nervous the simplest organisms to possess nervous systems. The development of this basic systems. The development of this basic neuronal mechanism set the stage for the neuronal mechanism set the stage for the proliferation of animal life that occurred proliferation of animal life that occurred during the Cambrian period. Among these during the Cambrian period. Among these Cambrian animals were the early chordates, Cambrian animals were the early chordates, which possessed very simple brains. which possessed very simple brains.

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Some of these early fish developed a unique way to Some of these early fish developed a unique way to insulate their axons by wrapping them with a fatty insulate their axons by wrapping them with a fatty material called myelin, which greatly facilitated material called myelin, which greatly facilitated axonal transmission and evolution of larger brains. axonal transmission and evolution of larger brains. Some of their descendants, which also were small Some of their descendants, which also were small predators, crawled up on the muddy shores and predators, crawled up on the muddy shores and eventually took up permanent residence on dry land.eventually took up permanent residence on dry land.

Challenged by the severe temperature changes in Challenged by the severe temperature changes in the terrestrial environment, some experimented the terrestrial environment, some experimented with becoming warm-blooded, and the most with becoming warm-blooded, and the most successful became the ancestors of birds and successful became the ancestors of birds and mammals. Changes in the brain and parental care mammals. Changes in the brain and parental care were a crucial part of the set of mechanisms that were a crucial part of the set of mechanisms that enabled these animals to maintain a constant body enabled these animals to maintain a constant body temperature. temperature.

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Animals with large brains are rare -- there are Animals with large brains are rare -- there are tremendous costs associated with large brains tremendous costs associated with large brains (the active human brain consumes about 20 (the active human brain consumes about 20 watts). The brain must compete with other organs watts). The brain must compete with other organs in the body for the limited amount of energy in the body for the limited amount of energy available, which is a powerful constraint on the available, which is a powerful constraint on the evolution of large brains. Large brains also evolution of large brains. Large brains also require a long time to mature, which greatly require a long time to mature, which greatly reduces the rate at which their possessors can reduces the rate at which their possessors can reproduce. Because large-brained infants are reproduce. Because large-brained infants are slow to develop and are dependent on their slow to develop and are dependent on their parents for such a long time, parents for such a long time, the parents must the parents must invest a great deal of effort in raising their invest a great deal of effort in raising their infants.infants.


Figure 03b Maternal Care Figure 03b Maternal Care


Young reptiles function as miniature versions Young reptiles function as miniature versions of adults, but baby mammals and birds are of adults, but baby mammals and birds are dependent because of their poor capacity to dependent because of their poor capacity to thermo-regulate, the consequence of their thermo-regulate, the consequence of their need to devote most their energy to growth. need to devote most their energy to growth. Most mammals solve the problem with Most mammals solve the problem with maternal care (Figure 03b), shelter, warmth, maternal care (Figure 03b), shelter, warmth, and milk. and milk.

In most birds, both parents cooperate to In most birds, both parents cooperate to provide food and shelter to their young. The provide food and shelter to their young. The expanded forebrain and parental care provide expanded forebrain and parental care provide mechanisms for the extra-genetic mechanisms for the extra-genetic transmission of information from one transmission of information from one generation to the next. generation to the next.


This transmission results from the close This transmission results from the close contact with parents during infancy, which contact with parents during infancy, which provides the young with opportunity to provides the young with opportunity to observe and learn from their behavior; the observe and learn from their behavior; the expanded forebrain provides an enhanced expanded forebrain provides an enhanced capacity to store these memories. The capacity to store these memories. The expanded forebrain and the observation of expanded forebrain and the observation of parents are probably necessary for the parents are probably necessary for the establishment of successful care giving establishment of successful care giving behavior itself, as the young mature into behavior itself, as the young mature into adults that will in their turn have to serve adults that will in their turn have to serve dependent young. During the period of dependent young. During the period of infant dependency, baby mammals and infant dependency, baby mammals and birds play, birds play,


During the period of infant dependency, During the period of infant dependency, baby mammals and birds play behavior baby mammals and birds play behavior that may be essential for the that may be essential for the development of the forebrain. The baby's development of the forebrain. The baby's playful interaction with its environment playful interaction with its environment may serve to provide the initial training may serve to provide the initial training of the forebrain networks that ultimately of the forebrain networks that ultimately will enable the animal to localize, will enable the animal to localize, identify, and capture resources in its identify, and capture resources in its environment.environment.



The human brain can be divided into The human brain can be divided into three parts: three parts: the hindbrainthe hindbrain, which has , which has been inherited from the reptiles; the been inherited from the reptiles; the limbic system, which was first limbic system, which was first emerged in mammals; and emerged in mammals; and the the forebrainforebrain, which has its full , which has its full development in human. Different development in human. Different views of the human brain are shown in views of the human brain are shown in Figure 03c and 04d. Tables 01 lists the Figure 03c and 04d. Tables 01 lists the functions of the different parts of the functions of the different parts of the human brain. The brain is separated human brain. The brain is separated into two hemispheres. into two hemispheres.


Apart from a single little organ -- the Apart from a single little organ -- the pineal gland in the centre base of the pineal gland in the centre base of the brain -- every brain module is brain -- every brain module is duplicated in each hemisphere. The left duplicated in each hemisphere. The left brain is calculating, communicative and brain is calculating, communicative and capable of conceiving and executing capable of conceiving and executing complicated plans -- the reductionistic complicated plans -- the reductionistic brain; while the right one is considered brain; while the right one is considered as gentle, emotional and more at one as gentle, emotional and more at one with the natural world -- the holistic with the natural world -- the holistic brain. brain.



The The cerebral cortexcerebral cortex is covered in a thin is covered in a thin skin of deeply wrinkled grey tissue called skin of deeply wrinkled grey tissue called the grey matter (densely packed neurons the grey matter (densely packed neurons for information processing). Each infold on for information processing). Each infold on the surface is known as a sulcus, and each the surface is known as a sulcus, and each bulge is know as a gyrus. While the white bulge is know as a gyrus. While the white tissue inside are axons -- tentacles which tissue inside are axons -- tentacles which reach out to other cells (to relay reach out to other cells (to relay information). information).

The cortex can be broken down into many The cortex can be broken down into many functional regions, each containing functional regions, each containing thousands of cortical columns (oriented thousands of cortical columns (oriented perpendicular to the cortical surface). perpendicular to the cortical surface).


Columns are typically about half a Columns are typically about half a millimeter in diameter and contain millimeter in diameter and contain about one hundred thousand neurons. about one hundred thousand neurons. They are the units of cognition (the They are the units of cognition (the mental process of acquiring knowledge mental process of acquiring knowledge by the use of reasoning, intuition or by the use of reasoning, intuition or perception). Table 02 below lists the perception). Table 02 below lists the location and functions of the major location and functions of the major components in the human brain. components in the human brain.


The third, or parietal, eye is a light-sensitive spot thought to sense changing light conditions. Opsin proteins sensitive to blue and green light has been identified in the cell

Figure 03e Brain Waves


It is well known that the brain is an It is well known that the brain is an electrochemical organ; a fully functioning electrochemical organ; a fully functioning brain can generate as much as 20 watts of brain can generate as much as 20 watts of electrical power. Even though this electrical electrical power. Even though this electrical power is very limited, it does occur in very power is very limited, it does occur in very specific ways that are characteristic of the specific ways that are characteristic of the human brain. Electrical activity emanating human brain. Electrical activity emanating from the brain can be displayed in the form from the brain can be displayed in the form of brainwaves. There are four categories of of brainwaves. There are four categories of these brainwaves, ranging from the most these brainwaves, ranging from the most active to the least active. Figure 03e is active to the least active. Figure 03e is produced by an produced by an EEGEEG (ElectroEncephaloGraph) chart(ElectroEncephaloGraph) chart


Figure 03e is produced by an Figure 03e is produced by an EEGEEG (ElectroEncephaloGraph) chart recorder to (ElectroEncephaloGraph) chart recorder to show the different kind of brainwave according show the different kind of brainwave according to the different state of the brain. These are all to the different state of the brain. These are all oscillating electrical voltages in the brain, but oscillating electrical voltages in the brain, but they are very tiny voltages, just a few they are very tiny voltages, just a few millionths of a volt. Electrodes are placed on millionths of a volt. Electrodes are placed on the outer surface of the head to detect the outer surface of the head to detect electrical changes in the extracellular fluid of electrical changes in the extracellular fluid of the brain in response to changes in potential the brain in response to changes in potential among large groups of neurons. The resulting among large groups of neurons. The resulting signals from the electrodes are amplified and signals from the electrodes are amplified and recorded.recorded.


One division of the autonomic nervous One division of the autonomic nervous system, called the sympathetic nervous system, called the sympathetic nervous system, dominates in times of stress. It system, dominates in times of stress. It controls the "fight or flight" reaction, controls the "fight or flight" reaction, increasing blood pressure, heart rate, increasing blood pressure, heart rate, breathing rate, and blood flow to the breathing rate, and blood flow to the muscles. Another division, called the muscles. Another division, called the parasympathetic nervous system, has the parasympathetic nervous system, has the opposite effect. It conserves energy by opposite effect. It conserves energy by slowing the heartbeat and breathing rate, slowing the heartbeat and breathing rate, and by promoting digestion and and by promoting digestion and elimination (of waste). elimination (of waste).

Autonomic Nervous SystemAutonomic Nervous System


Most glands, smooth muscles, and cardiac Most glands, smooth muscles, and cardiac muscles constantly get inputs from both the muscles constantly get inputs from both the sympathetic and parasympathetic systems. sympathetic and parasympathetic systems. The CNS controls the activity by varying the The CNS controls the activity by varying the ratio of the signals. Depending on which ratio of the signals. Depending on which motor neurons are selected by the CNS, the motor neurons are selected by the CNS, the net effect of the arriving signals will either net effect of the arriving signals will either stimulate or inhibit the organ. Figure 07 stimulate or inhibit the organ. Figure 07 shows the various organs and actions, shows the various organs and actions, which are related to the two different which are related to the two different divisions. divisions.


Figure 07 ANS Side ViewFigure 07 ANS Side View



Brain waves originate from the cerebral Brain waves originate from the cerebral cortex, but also reflect activities in other cortex, but also reflect activities in other parts of the brain that influence the cortex, parts of the brain that influence the cortex, such as the reticular formation. Because such as the reticular formation. Because the intensity of electrical changes is directly the intensity of electrical changes is directly related to the degree of neuronal activity, related to the degree of neuronal activity, brain waves vary markedly in amplitude brain waves vary markedly in amplitude and frequency between sleep and and frequency between sleep and wakefulness. Beta wave rhythms appear to wakefulness. Beta wave rhythms appear to be involved in higher mental activity, be involved in higher mental activity, including perception and consciousness. It including perception and consciousness. It seems to be associated with consciousness, seems to be associated with consciousness, e.g., it disappears with general anesthesia. e.g., it disappears with general anesthesia.


Other waves that can be detected are Other waves that can be detected are Alpha, Theta, and Delta. When the Alpha, Theta, and Delta. When the hemispheres or regions of the brain are hemispheres or regions of the brain are producing a wave synchronously, they producing a wave synchronously, they are said to be coherent. Alpha waves are said to be coherent. Alpha waves are generated in the Thalamus (the are generated in the Thalamus (the brain within the brain), while Theta brain within the brain), while Theta waves occur mainly in the parietal and waves occur mainly in the parietal and temporal regions of the cerebrum. temporal regions of the cerebrum.


The Alpha and Theta wavesThe Alpha and Theta waves

seem to be associated with creative, insightful seem to be associated with creative, insightful thought. When an artist or scientist has the "aha" thought. When an artist or scientist has the "aha" experience, there's a good chance he or she is in experience, there's a good chance he or she is in Alpha or Theta. These two kinds of brain waves are Alpha or Theta. These two kinds of brain waves are also associated with relaxation and, stronger also associated with relaxation and, stronger immune systems. Therefore, many people try to immune systems. Therefore, many people try to train themselves to enter such states through train themselves to enter such states through various biofeedbackvarious biofeedback77 techniques (with varying techniques (with varying degree of success). degree of success).

Delta Waves occur during sleep. They originate Delta Waves occur during sleep. They originate from the cerebral cortex when it is not being from the cerebral cortex when it is not being activated by the reticular formation. In slow-wave activated by the reticular formation. In slow-wave sleep, the entire brain oscillates in a gentle rhythm sleep, the entire brain oscillates in a gentle rhythm quite unlike the fragmented oscillations of normal quite unlike the fragmented oscillations of normal consciousness. consciousness.


Peripheral Peripheral Nervous Nervous SystemSystem

Figure 05 Cranial Nerves


Figure 05 Cranial Nerves


Figure 06

Spinal Nerves


The peripheral nervous systemThe peripheral nervous system

The peripheral nervous system is outside the CNS. The peripheral nervous system is outside the CNS. It consists of the various nerves that connect It consists of the various nerves that connect particular parts of the CNS with particular organs. particular parts of the CNS with particular organs. Humans have 12 pairs of cranial nerves and 31 Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial nerves (Figure 05) pairs of spinal nerves. Cranial nerves (Figure 05) are either sensory nerves, motor nerves, or mixed are either sensory nerves, motor nerves, or mixed nerves. All of them, except the vagus nerve, control nerves. All of them, except the vagus nerve, control the head, the face, the neck, and the shoulders. the head, the face, the neck, and the shoulders. The vagus nerve controls the internal organs. Table The vagus nerve controls the internal organs. Table 03 lists the functions of the various cranial nerves. 03 lists the functions of the various cranial nerves. All spinal nerves (Figure 06) are mixed nerves that All spinal nerves (Figure 06) are mixed nerves that take impulses to and from the spinal cord. Table 04 take impulses to and from the spinal cord. Table 04 describes the symptom of spinal cord injury (SCI) describes the symptom of spinal cord injury (SCI) with the particular spinal nerve(s).with the particular spinal nerve(s).


Autonomic Nervous SystemAutonomic Nervous System

One division of the autonomic nervous One division of the autonomic nervous system, called the sympathetic nervous system, called the sympathetic nervous system, dominates in times of stress. It system, dominates in times of stress. It controls the "fight or flight" reaction, controls the "fight or flight" reaction, increasing blood pressure, heart rate, increasing blood pressure, heart rate, breathing rate, and blood flow to the breathing rate, and blood flow to the muscles. Another division, called the muscles. Another division, called the parasympathetic nervous system, has the parasympathetic nervous system, has the opposite effect. It conserves energy by opposite effect. It conserves energy by slowing the heartbeat and breathing rate, slowing the heartbeat and breathing rate, and by promoting digestion and elimination and by promoting digestion and elimination (of waste). (of waste).


Most glands, smooth muscles, and cardiac Most glands, smooth muscles, and cardiac muscles constantly get inputs from both the muscles constantly get inputs from both the sympathetic and parasympathetic systems. sympathetic and parasympathetic systems. The CNS controls the activity by varying the The CNS controls the activity by varying the ratio of the signals. Depending on which ratio of the signals. Depending on which motor neurons are selected by the CNS, the motor neurons are selected by the CNS, the net effect of the arriving signals will either net effect of the arriving signals will either stimulate or inhibit the organ. Figure 07 stimulate or inhibit the organ. Figure 07 shows the various organs and actions, shows the various organs and actions, which are related to the two different which are related to the two different divisions. divisions.


Figure 08 ANS Front View


Figure 07 ANS Side ViewFigure 07 ANS Side View


Motor fibers that govern involuntary responses, do Motor fibers that govern involuntary responses, do not lead directly to the organs they innervate. not lead directly to the organs they innervate. Instead, they make their trips in two stages. The Instead, they make their trips in two stages. The first set of fibers leads from the CNS to ganglia first set of fibers leads from the CNS to ganglia (which are collections of nerve cell bodies) that lie (which are collections of nerve cell bodies) that lie outside the CNS (the preganglionic fibers). At the outside the CNS (the preganglionic fibers). At the ganglia the fibers form synaptic junctions with the ganglia the fibers form synaptic junctions with the dendrites of as many as twenty different cell dendrites of as many as twenty different cell bodies. The axons of these cell bodies form a bodies. The axons of these cell bodies form a second set of fibers, the postganglionic fibers. It is second set of fibers, the postganglionic fibers. It is these postganglionic fibers that lead to the organs. these postganglionic fibers that lead to the organs. The chief ganglia involved in the autonomic The chief ganglia involved in the autonomic nervous system form two lines running down either nervous system form two lines running down either side of the spinal column. They are outside the side of the spinal column. They are outside the bony vertebrae. bony vertebrae.


These two lines of ganglia outside the column These two lines of ganglia outside the column resemble a pair of long beaded cords. At the lower resemble a pair of long beaded cords. At the lower end, the two cords join and finish in a single central end, the two cords join and finish in a single central stretch. These lines of ganglia are sometimes called stretch. These lines of ganglia are sometimes called the sympathetic trunks (used by the sympathetic the sympathetic trunks (used by the sympathetic nervous system). Not all ganglia are located in the nervous system). Not all ganglia are located in the sympathetic trunks. Some are not; and it is possible sympathetic trunks. Some are not; and it is possible for a preganglionic fiber to go right through, making for a preganglionic fiber to go right through, making no synaptic junction there at all, joining instead no synaptic junction there at all, joining instead with ganglia located in front of the vertebrae. For with ganglia located in front of the vertebrae. For the parasympathetic nervous system, some of the the parasympathetic nervous system, some of the ganglia separating the preganglionic fibers from the ganglia separating the preganglionic fibers from the postganglionic fibers are actually located within the postganglionic fibers are actually located within the organ the nerve is servicing. organ the nerve is servicing.


In that case, the preganglionic fiber runs In that case, the preganglionic fiber runs almost the full length of the total track, almost the full length of the total track, whereas the postganglionic fiber is at most whereas the postganglionic fiber is at most just a few millimeters long.just a few millimeters long.

The splanchnic nerves, which originate The splanchnic nerves, which originate from some of the thoracic nerves, have from some of the thoracic nerves, have their preganglionic fibers ending in a mass their preganglionic fibers ending in a mass of ganglia lying just behind the stomach. It of ganglia lying just behind the stomach. It represents the largest mass of nerve cells represents the largest mass of nerve cells that is not within the CNS and is sometimes that is not within the CNS and is sometimes called the "abdominal brain". It is a vital called the "abdominal brain". It is a vital spot to be protected during boxing. spot to be protected during boxing.


Documents

Prof.aza 1 The Brain (Handout) prof. aza. 2 Brains exist because the distribution of resources necessary for survival and the hazards that threaten survival