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Sunday, February 7, 2010


Potentials in Nerve Fibers: The structure of the neuron has a cell body and two types of fibers, the dendrites and the axon. It has a membrane and a sheath around its fibers called the myelin sheath. The nerve fibers are excited by stimuli and conduct excitation throughout their lengths. The mechanism of excitation is inextricable tied up with various electrical potentials and currents in the fiber. The potentials found in the nerve, and it deals with how they lead one another, and how they take part in excitation and conduction of nerve fibers.
The Resting Potential of a Nerve fiber: Diagram of a polarized membrane and measurement of resting potential. +’ve ions are on the out side and –‘ve ions on the inside of the membrane of the nerve cell. These makes a resting potential across the membrane, which can measured by hooking up a voltameter with one electrode at the cut end of a nerve fiber and the other on the outside of the fiber.
Electrical Stimulation: Based on polarization, it in turn, the chain of events that gives nerves their enhanced properties of irritability and conduction. These events can be studied by applying electrical stimuli to the membrane of the nerve fiber and then recording the electrical changes that occur. IT can do with the help of one pair of electrodes put on a nerve – one electrode inside and the other outside of fiber. When electrical stimuli are applied through 2 electrodes on the outside of the fiber, each electrode has different sign. One is +’ve and the other is –‘ve, just as are the two electrodes of a battery. The electrode that carries the –‘ve sign is called the cathode, the one with +’ve sign is called anode. The voltage or potential difference between the cathode and anode is the strength of the stimulus.

Neurons send messages electrochemically. This means that chemicals cause an electrical signal. Chemicals in the body are "electrically-charged" -- when they have an electrical charge, they are called ions. The important ions in the nervous system are sodium and potassium (both have 1 positive charge, +), calcium (has 2 positive charges, ++) and chloride (has a negative charge, -). There are also some negatively charged protein molecules. It is also important to remember that nerve cells are surrounded by a membrane that allows some ions to pass through and blocks the passage of other ions. This type of membrane is called semi-permeable.

Resting Membrane Potential
When a neuron is not sending a signal, it is "at rest." When a neuron is at rest, the inside of the neuron is negative relative to the outside. Although the concentrations of the different ions attempt to balance out on both sides of the membrane, they cannot because the cell membrane allows only some ions to pass through channels (ion channels). At rest, potassium ions (K+) can cross through the membrane easily. Also at rest, chloride ions (Cl-)and sodium ions (Na+) have a more difficult time crossing. The negatively charged protein molecules (A-) inside the neuron cannot cross the membrane. In addition to these selective ion channels, there is a pump that uses energy to move three sodium ions out of the neuron for every two potassium ions it puts in. Finally, when all these forces balance out, and the difference in the voltage between the inside and outside of the neuron is measured, you have the resting potential. The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside. At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.

Action Potential
The current flows arising from the electrotonic potential brings to the action of the nerve itself. The electrotonic currents disturb the equilibrium itself. The electrotonic currents disturb the equilibrium of the membrane and set off a set of events in the nerve fiber that is called the action potential.
The spike Potential: The most explosive and couspicuous event set off in the membrane is the spike potential, it is also called as nerve impulse. What happens is this: the out flowing electrotonic currents at the cathode, when they get sufficiently strong, bring about a collapse of the polarization of the membrane. And also it has something to do with changing resistance or chemical forces maintaining polarization. As a result, the small electrotonic potential leaps very suddenly into a relatively large –‘ve potential, the spike potential.
Properties of the Spike Potential: Threshold stimulus and potential
Action potentials occur only when the membrane in stimulated (depolarized) enough so that sodium channels open completely. The minimum stimulus needed to active an action potential is called the threshold stimulus. The threshold stimulus causes the membrane potential to become less negative. If the membrane potential reaches the threshold potential, the voltage regulated sodium channels all open. Sodium ions rapidly diffuse inward, and depolarization occurs.
All-or-None Law: Action potentials occur maximally or not all, in other words, there in no such things as partial or weak action potential. Either the threshold potential is reached an action potential occurs, or it isn’t reached and no action potential occurs.

The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential. The action potential is an explosion of electrical activity that is created by a depolarizing current. This means that some event (a stimulus) causes the resting potential to move toward 0 mV. When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an action potential of a fixed sized will always fire...for any given neuron, the size of the action potential is always the same. There are no big or small action potentials in one nerve cell - all action potentials are the same size. Therefore, the neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle.

Action potentials are caused by an exchange of ions across the neuron membrane. A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized. It takes longer for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the depolarization. Also at about this time, sodium channels start to close. This causes the action potential to go back toward -70 mV (a repolarization). The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.


Neuroanatomy: During development, the telencyphelon give rise the striatum (caudate nucleus and putamen), the hippocampus and the neocortex, its cavity becomes the lateral ventricles (first and second ventricles). The diencephalons give rise to the subthalamus, thalamus and epithalamus, its cavity to the third ventricle. The mecencephalon give rise to the tectum, pretectum, cerebral peduncle and its cavity develops into the mesencephalic duct or cerebral aqueduct. Finally, the robencephalon give rise to the pones, the cerebellum and the medulla oblongata, its cavity becomes the forth ventricle.

Central nervous system



Telencephalon:- Rhinencephalon, Amygdala, Hippocampus, Neocortex, Basal ganglia, Lateral ventricles

Diencephalon:- Epithalamus, Thalamus, Hypothalamus, Subthalamus, Pituitary gland, Pineal gland, Third ventricle

Brain stem

Mesencephalon:- Tectum, Cerebral peduncle, Pretectum, Mesencephalic duct


Metencephalon:- Pons, Cerebellum

Myelencephalon:- Medulla oblongata

Spinal cord

The Myelencephalon: It is the part of medulla and joins the spinal cord to the higher centers of the brain. It contains autonomic nuclei concerned with breathing, heartbeat, and blood pressure. The medulla is also called the vital centre of the brain.
The Metencephalon: It consists of cerebellum, the pons, and parts of 4th ventricle and it going upward from medulla, the 2nd divisions of brain. The main functions of these areas are, to smoothening and coordinating of impulses leading to muscular movements and motor co-ordination.
Mesencephalon: It is a part of midbrain and also connecting to the forebrain and hind brain. The main part of it is called as tectum (which means “roof”) and the floor. The floor is a passageway between higher and lover system of nervous system. The sensory tract run upward and motor tracts will be on down ward and also it act as a motor reflex centers. The tectum has sensory duties and it divided into 2 pairs of sensory centers – four in all. Each one is called a colliculus and one pair centre called superior colliculi, and it lie a little above and ahead (anterior) of the other pair. These areas are mainly concentrating as visual centers. The other pair of colliculi is called the inferior colliculi and it lie a little behind and below the level of the superior colliculi and its function lies on hearing centers.
Diencephalon:- It has number of parts: the thalamus, optic tracts, and retinae of the eye, the pituitary body, the mammmillary bodies, the hypothalamus and 3rd ventricle.
Telencephalon:- It consists of the olfactory bulb, tracts, cerebral hemispheres, the lateral ventricles and the basal ganglia.

Peripheral Response Mechanism

Peripheral Response Mechanism
It consists of receptors, sensory nerves carrying messages inward from the receptors, a central nervous system made up of brain and spinal cord enclosed in the body cases of the head and spinal column, motor nerves carrying impulses outward from the CNS, and finally various effectors of the body such as muscles and glands. In this chapter we will study the receptors, the effectors, and the peripheral nerves going into and out of the nervous system.
The functions of Cells: It was the discovery of Robert Hooke (1665) that a very lowly organism, cork, is made up of cells. Today we have come to recognize that the Cell Doctrine (1838) applied to all animals and plants. The cell is the fundamental unit of living organisms. The three important parts of cell are membrane, the cytoplasm and the nucleus. These three parts are inter-related.
Properties of the Membrane:- The membrane is the boundary of the cell. It will keep something in, and out of, cell. Because it is porous, because it will allow many things to pass through. The “things” in this case are chemical molecules or charged ions making up the positive or negative parts of molecules. The properties of the membrane maintain the equilibrium of pressures and of ions on the 2 side of it. Some ions and molecules press from the out side inward and some from inside outward. Some pass in and some pass out. From this general property of equilibrium derive some other important properties of the membrane – Polarization is one of them.
Under cell chemistry, some substances, called electrolytes, dissociate when they are dissolved in water, and many substance in the body are electrolytes. The molecules burst into two parts, one carrying a positive charge and other a negative charge. Each part is called an ion. The more positive ion collect on one side of the membrane, while an excess of negative ions collects on the other side. There may be equilibrium of ions – the number of ions on the two sides may be equal – but one side may be more positive or more negative than the other. This state of affairs is called polarization of the membrane.
Polarization derives two other important properties of cell – i.e., cells of the nervous system. These are irritability and conductivity i.e., properties which are always interlinked in cell functions. –When a membrane is in equilibrium and when it is polarized, any loss of ions or change in the charges of ions on the one side of the membrane breakdown or disturbs the equilibrium – Any such disturbances, however, will cause a counter-reaction, because the membrane to maintain a equilibrium. Ions may move through the membrane or otherwise rearrange themselves on the membrane because of thrown into disequilibrium. This property of the membrane is called irritability.
Sometimes the counter-reactions is not confirmed to the part of the membrane that has been disturbed. Ions and molecules more about in neighboring regions of he membrane to help restore the equilibrium in the irritated part. As a result the disturbance runs along the whole membrane from one point to the next. Thus, conduction occurs – a very important property of certain cells in the body.
Properties of Cytoplasm:- Cytoplasm is main mass of the cell. It makes up the general area of the cell within the membrane and outside the nucleus. They are in two types: 1. Secreation 2. Contractility
1. Secreation:- The various chemical substances in the cytoplasm may so react with each other that they make new substances, these may remain in the cell to help with important unction in the life of the cell, or they may pass out through the membrane and to circulated to other cells for their use. The substances that are manufactured in the cytoplasm and pass out of the membrane to help out constructively with the life process are called secreations. – many substances made as waste products of the cell’s chemistry, which also pass out of the membrane because the cell no longer “wants” them – these are excreations.
2. Contractility:- When molecules change in shape or size or move about in a mass in such a way that the shape of the membrane and the cell is changed, it is called as contraction or contractility.
Properties of Nucleus:- It is main body of the cytoplasm of the cell. It is the centre most part of the cell. The most important single property of the nucleus is reproduction. Nucleuses are strands of complex chemical materials known as chromosomes. Chromosomes are made up with genes, which are to govern the reproduction of the organism. Eg:- In sexual reproduction, two different cells must come together and their chromosomes interact with each other before the reproduction starts.

The Response Mechanism
These are receptors, the nerve cells, and the effectors.
The Receptors:- A responds to all sorts of stumuli. There are four classes of receptors, they are 1. thermal receptors, 2. mechanical receptors, 3. chemical receptors, and 4. photic receptors.
Neurons:- The nerve cell or neuron is the second of three links in the receptor-adjuster-effector mechanism. The neuron has 3 parts: the dendrites, the cell, and the axon. The cell body is sometimes called the soma and sometimes the perikaryon. The nerve cell are the 2 kinds of fibres, the dendrites and the axon. These both have their separate features.
Types of Neurons:- 1. Motor neuron of the spinal cord 2. Neuron of the motor area of the brain. 3. Short connecting neuron called Golgi type II 4. a bushy cell found in net works of neurons.
The effectors:- There are 2 main classes of effectors – the muscles and the glands. Muscles:- These are divided into different types: There are 3 main kinds of muscles:- 1. Smooth muscle cell 2. Straiated muscles 3. Cardiac muscle. Glands:- It receive effector neurons from the nervous system and their function is to secreate chemical substances that are important to the life of the organism. Gland – Internal environment and whereas Muscle for external environment. The 2 major classes of glands are – the duct and the ductless. The duct glands empty their secreations into the cavity of the body. Eg:- duct glands of the digestive tract, whereas the ductless glands put their secreations directly into the blood.
Periphreal and CNS
The NS is divided into 2 main parts: CNS +PNS. The CNS consists of brain and spinal cord, which lie within the bony cases of the skull and spine. The parts of the NS outside the skull and spine make up the PNS. The PNS consists largely of nerve fibers or axons, which 1. carry nerve impulses from the sensory receptors of the body inward to the CNS and 2. carry nerve impulses for the movements of muscles and the excitation of certain glands outward from the CNS. The PNS has 2 divisions: Somatic NS and autonomic NS. The somatic NS motor fibers active the striped muscles of the body, such as that move the arms and legs, while sensory fibers come from major receptor organ of the body- the eye, the ears, touch receptors and so on. And ANS motor fibers activate the smooth muscles such, as stomach secreations from glands – salivary glands and regulate activity in the type of muscles found in heart. Sensory fibers in the ANS carry information from the internal bodily organs that is perceived as pain, warmth, cold, or pressure. The autonomic system has 2 divisions: sympathetic and parasympathetic system.
The CNS: CNS consists of brain and spinal cord. It can be subdivided and named in various ways. The brain in further divided into 5 main parts: the telencephalon, the diencephalons, the mesencephalon, the metencephalon and the myelencephalon.


Physiology is the science of bodily functions; it has to do with process going on science of behaviour. Psychology is the science of behaviour, in psychology we try to see how human beings and members of the animal kingdom adjust to the word they live in. Physiological psychology is simply to put these subjects together and see how the physiological processes of the body are related to behavioural adjustments.
It has many divisions:
1. Physiology:- It contain the basic anatomy, physiology, and biochemistry. IT help us to study two main features of the body, the response mechanism and the internal environment. Response mechanism involves our various senses organs, our nerves, our nervous system, and the various muscles and glands that we use when we make responses. The internal environment, on the other hand, is the complex of substances – the food materials we take in, the secretions of our glands, the metabolic productions of our body’s functions – that move around the body in the blood and lymph and make up on essentially chemical environment for the nervous system and response mechanism in general.
2. Sensory Functions:- This group mainly focus on psychology of the senses, i.e., how well man and animals can discriminate various kinds of sensory stimuli and how they perceive what goes on about them. And also we are studying the sensory systems of the body, i.e., how the sense organs are built, what sensory nerves connect with them, where these nerves go in the brain, what centers they serve there, and how these centers are affected by different conditions of the internal environment. Then we will study the main features of sensory functions such as – four main attributes of sensations – intensity, quality, space and time. A light seems bright or dim, a sound loud or faint, or a pain mild or strong, it is an example of intensity. We experience of various stimuli also has quality, some lights are red and others green, we hear tones of high pitch and low pitch, all these are an example of quality. Visual objects, for example, have shape, size, distance, and locations – all spatial aspects (space). Even sound seem big or small, near or far away, all are example of space. Finally, we also sense the time in which stimuli occur – whether it is long or short intermittent or steady.
3. Motor Functions:- Under this section, we will study the motor functions i.e., of the ways in which we will make movements and responses to our world.
4. Motivation:- Under this concepts, we will study, sleep and activity, bodily needs, instinctive behaviour, and mating behaviour. Drives and basic motives, in fact begin in our internal environment. This environment can affect the organs of the body in various ways. It can excite such receptors as these in our stomach, hear, or blood vessels, and these in turn can stimulate us to do something or it can directly excite some of the muscle of the body. Finally it directly excites some of the centers of the brain so that these centers bring out motivational behaviour.
5. Learning and Memory:- In this group, will study the different sorts of learning and memory localized in the particular parts of the nervous system. People sometimes forget many memories and habits after some part of their brain is injured, but they can get back the habits they lost by a little more practices of the damage has not been too bad. It will help us to study how the brain and body work in our learning and memory.
6. Man and His Disorder:- It deals with the functions of the brain in man and complex problems of memory, sensory and motor functions. And also deals with problems of learning, intelligence and disorder of personality, learning, and intelligence about their physiological basis.