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Sunday, February 7, 2010

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.

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