Neural Control and Coordination

â€Å"NEURAL CONTROL AND CO-ORDINATION† Co-ordination – It is the process through which two or more organs interact and complement the functions of each other. Neuron – It is the functional and structural unit of nervous system. Therefore, the nervous system is also known as NEURAL SYSTEM. Neurons with longer projections are said to be the longest cells in our body. There are about 100 billion neurons and most of them exist in the brain. Some neurons have flask-shaped and are called Purkinje cells. They are found in the cerebellum of brain. Shortly after birth neurons do not develop.A neuron has two main parts viz. a) Cell body or Cyton or Soma – It may be up to 13. 5  µm in diameter and may be irregular, oval, rounded, etc. Neuroplasm and neurolemma are its cytoplasm and cell membrane. A cyton consists of cell organelles like other cells. Besides, it also has neurofibrils, neurotubules and Nissls granules or bodies. Neurofibrils take part in transmissio n of impulse Nissls granules or bodies are irregular masses of rough endoplasmic reticulum on which free ribosomes and polysomes are attached. Nissls granules probably synthesize protein for the cell. ) Cytoplasmic processes or neuritis – They are of two types. 1. Dendrites or dendrons – They contain neurofibrils, neutubules and Nissls granules. They conduct nerve impulse towards the cell body and are called afferent processes (receiving processes). They may be one to several. 2. Axon or Axis – It is a single long process of uniform thickness. The part of cyton from where the axon arises is called Axon hillock and is the most sensitive part of a neuron. An axon does not have Nissls granules, golgi complex, ribosome, etc. So cyton supplies protein to axon.Its cell membrane and cytoplasm are known as axolemma and axoplasm respectively. Axon ends in a group of branches called terminal arborizations (axon terminals or telodendria). They have synaptic knob to form sy napse where axon and dendrite of two successive neurons can meet. Motor end plate – The part of sarcolemma that lies beneath the axon terminals (nerve endings). Axon conducts nerve impulses away from the cell body hence called efferent processes. TYPES OF AXON There are two types such as myelinated (medullary) and non-myelinated (non-medullary) In myelinated neurons, the axon is surrounded by myelin sheaths.Myelin sheaths have regular interruptions called node of Ranvier. The space between two successive node of Ranvier is called internodes. Around the myelin sheaths, there is a delicate sheath made up of nucleated cells called Schwann cells. VARIOUS PARTS OF NEURAL SYSTEM It can be divided as Central Nervous System (CNS) and Peripheral nervous system (PNS). Central Nervous System; The CNS comprises brain and spinal cord. BRAIN: It is the anterior most part of the CNS. It lies inside the cranial cavity of the skull. It weighs from 1220 to 1400gms. It has membranes called meni nges (sing. eninx), they are 1) Piamater – It is thin and innermost membrane Sub arachnoid space lies between piamater and arachnoid membrane. Cerebro Spinal Fluid (CSF) is found in this space . It provides medium for exchange of food materials, wastes, respiratory gases, etc. 2) Arachnoid mater – It is thin and spider webby. It is the middle membrane. Subdural space lies between arachnoid mater and dura mater. 3) Duramater – It is the outermost fibrous membrane. **Fontanales – Membranous areas between the cranial bones of foetal skull. Structure of human brain: It has three parts viz. ) Forebrain or Prosencephalon – It includes olfactory lobe, cerebrum and diencephalon Olfactory lobe – It lies in the temporal lobe. * Function – It receives impulses from the nose. Cerebrum – It is the largest and most complicated part of the brain . Its outer portion is called the outer cortex and it forms the GREY MATTER. Beneath the grey matt er, there are millions of medullated (myelinated) nerve fibres. They form white matter. * Function -It creates ideas, touch, perception, reasoning, decision making. * Diencephalon – Hypothalamus is located here. Hypothalamus maintains homeostasis.It is also called therefore called THERMOREGULATORY CENTRE OR THERMOSTAT. It keeps body temperature at roughly 37 °C. 2) Mid-brain or Mesencephalon – It comprises cerebellum, pons varolii and medulla oblongata. Cerebellum – It is the second largest part of brain and it has purkinje cells. * Function – It controls rapid muscular activities like running, talking and typing. Pons varolii – It is located above the medulla oblongata. Pneumotaxic centre is present here. **Pneumotaxic centre limits inspiration. Medulla oblongata – It continues with spinal cord. * Function – It regulates heart rate, blood pressure, etc.