Tiêu đề 10. Neural Control and Co-ordination Theory.pdf ✅

1 EH EduHulk Download Free Study Material from EduHulk.com  Introduction : Nervous System  Nervous Tissue  Mechansim of impulse conduction  Synapse and transmission of impulse across the synapse  Nervous System  Central Nervous System (CNS)  Peripheral Nervous System (PNS) Contents... Table of Contents Introduction : Nervous System • Nervous system is ectodermal in origin. • The neural organisation is very simple in lower invertebrates. For example, in Hydra it is composed of a network of neurons. • The neural system is better organised in insects, where a brain is present along with a number of ganglia and neural tissues. The vertebrates have a more developed neural system. • The structural and functional unit of nervous system is neuron or nerve cell. Human body contain 30 billion neurons. • In our body the neural system and the endocrine system jointly regulates, coordinate and integrate all the activities of the organs so that they function in a synchronised fashion. • Coordination is the process through which two or more organs interact and complement the functions of one another. Neural - Hormonal regulation & coordination during physical exercises: • The energy demand is increased for maintaining an increased muscular activity. • The supply of oxygen is also increased therefore rate of respiration is increased. • Heart beat and increased blood flow via blood vessels. Neural - Hormonal regulation & coordination during physical rest : • The energy demand is decreased. • The activities of nerves, lungs, heart and kidney gradually return to their normal conditions. • Nervous System act as high speed service or no delay service. • It establish the homeostasis in internal environment of body. • It include components of three categories: Sensory organs (receptors), Communication system and Effectors Speech Taste Somatosensory cortex Motor cortex Speech Frontal association area Smell Hearing Auditory association area Somatosensory association area Reading Visual association area Vision Frontal Lobe (consciousness) Parietal Lobe (movement and stimulus perception) Occipital Lobe (vision) Temporal Lobe (speech recognition) Midbrain Pons Medulla Brain stem (basic, vital functions eg. breathing) Cerebellum (movement co-ordination) Brain (cerebrum) Spinal chord Autonomic (subconscious, control system) Somatic (voluntary, muscle movement) Lymphocytes Monocytes Macrophages Bone marrow Blood vessels Thymus Lungs Liver Intestines Parasympathetic (rest and digest) Sympathetic (fight or flight)     Central Nervous System     Peripheral Nervous System
2 EH EduHulk Download Free Study Material from EduHulk.com Nervous Tissue   Neuron : • The neural system of all animals is composed of highly specialised cells called neurons which can detect, receive and transmit different kinds of stimuli. • It is largest cell of the body and each neuron has two parts- 1. Cell body 2. Cell processes/Neurites : Dendrone and Axon 1. Cell body (Soma or Cyton or Perikaryon): • It has a round and large nucleus. Its cytoplasm contains all typical cell organelles (mitochondria, golgi complex, E.R., ribosomes etc.) except centriole. • Cytoplasm also contain two special organelles like Nissl's granules and neurofibrills. • Nissl's granules are also called Tigroid bodies which are made up of RER (ER + ribosome) and they synthesise protein. • Neurofibrills are small fibres which help in intra cytoplasmic impulse conduction. • Neuron lacks centriole (Present in Neuroblast cells ) so they can not divide after embryonic development. These cells remain in interphase (G0 ) throughout life. • They have some power of regeneration. • The cyton are generally found in Grey Matter of brain. The cyton of cerebellum are flask shaped which are called Purkinje cells. The nerve cell of female has bar body in its nucleus. Nuclei: Clusters or collections of cytons in CNS. Tract : Group of axon in CNS. Ganglia: Clusters or collections of cytons in PNS. Nerves : Group of axon in PNS. 2. Cell Processes : Dendrites: • These are small, numerous and conical shaped (Thick at base and thin at apex). They contain all cell organelles along with Neurofibrils and Nissl's granules. • They have membrane called receptor which recieves stimulus either from external or internal environment or from another neuron, so they are also called Afferent processes.
3 EH EduHulk Download Free Study Material from EduHulk.com Dendrites Nissl's granules Cell body Nucleus Schwan cell Axon Myelin sheath Node of Ranvier Synaptic knob Axon terminal Structure of a neuron Dendrites Synapses Axon Axon hillock Membrane Nucleolus Nucleus Smooth Endoplasmatic Reticulum Nerve cell body Golgi apparatus Polyribosomes Rough Endoplasmatic Reticulum Mitochondrion Ribosomes Axon : • These are always one, long and of similar thickness. • The cytoplasm of axon is called Axoplasm and its covering is called Axolemma. • Axon has mitochondria and neurofibrills but lacks Nissl's granules. • Axon carry impulses away from cyton (towards other neuron or Effector organs). So axon is also called Efferent process/Nerve fibres. • The terminal branches of axon are called telodendria • Swollen axon terminals are known as synaptic knob/nerve ending which contain many mitochondria and synaptic vesicles. • Synaptic vesicles are filled with neurotransmitters. • Most common neurotransmitter is Acetyl choline synthesized by mitochondrial enzyme choline acetyl transferase. Neurotransmitters/Neurohormones Stimulatory Inhibitory Helps in impulse conduction Inhibits impulse conduction Examples : Acetyle choline, Examples : Glycine, GABA, Nor-epinephrine/Nor-adrenaline Dopamine, Serotonin
4 EH EduHulk Download Free Study Material from EduHulk.com • The axon along with Neurilemma (sheet of schwan cells) is Nucleus of Schwann cell Schwann cell Neurilemma Axon Myelin sheath called as Nerve fibre. • Axon is considered as functional process of neuron. • In long axon each Schwann cell secret phospholipids around axon called Myelin sheath (medullary sheath). • Myelin sheath is secreted by schwan cells in PNS and by oligodendrocytes in CNS. • The myelin sheath is discontinuous covering while neurilemma is a continuous covering. (found at nodes as well as at internodes) • Myelin sheath is absent at Nodes of Ranvier, thus nodes can permit ionic exchange across axolemma which is necessory for impulse conduction. • Myelin Sheath insulates heat of neuron and also prevents ionic exchange across axolemma and speed up impulse transmission. It helps in regeneration of neuron. Axon : Two types Medullated or Myelinated Non Medullated or un-myelinated • Myelin sheath or medullary sheath present • Myelin sheath or medullary sheath absent • Due to myelin sheath speed of impulse • Due to absence of myelin sheath speed of impulse transmission is 50 times fast. This type of impulse conduction is slow. This is ordinary wavy conduction. conduction is called Saltatory conduction • Due to presence of myelin sheath they appear • They appear Grey (Grey neuron) white (White Neuron) • Examples : Cranial and spinal nerves • Examples : Somatic and autonomic nervous system Types of Neuron : 1. On the basis of processes : (a) Apolar (Nonpolar) Neuron : • They have numerous processes (Neurites) but no physiological division. • Each process can bring impulse to cyton and takes away the impulse from cyton. • In animal kingdom the nerve is first evolved in coelentrates. Example : Coelentrates. (b) Unipolar Neurons : • It has only one axon and no dendrite. Example : Non chordate neuron, in early embryo of chordates (c) Bipolar Neurons : • One dendrone and one axon. Examples : Retina and Olfactory epithelium
5 EH EduHulk Download Free Study Material from EduHulk.com (d) Multipolar Neuron : • Numerous dendrite and one axon. Example : Most of the neurons of Vertebrates (e) Pseudounipolar Neuron • Its axon divides into two branches, one of them act as dendron while other act as axon. In this nerve impulse transmitts directly and do not enter in cyton. Example : Dorsal root ganglion of spinal cord. 2. On the basis of functions : Sensory/Afferent Neuron Motor/Efferent Neuron Internuncial Neuron/Inter neuron They connect sensory organ (receptor) They connect CNS to effector Small and most abundant. to CNS. organs. They are present only in CNS & Two types: Two types: connect two or more neurons. (i) Somatic sensory neuron: (i) Somatic motor neuron: Also called as Adjustor neuron Body wall Impulse    CNS. CNS Impulse    Body wall. (ii) Visceral sensory neuron: (ii) Visceral motor neuron: Visceral organs Impulse    CNS. CNS Impulse    Visceral organs. Functional Properties of Neurons : (a) Excitability and conductivity : • Neurons receive stimuli (excitability) and conduct it as an electrochemical wave or impulse (Conductivity). (b) All or none rule : • If threshold value or higher value stimulus is given to a neuron then impulse conducts with maximum speed i.e. All. (Magnitude of response is maximum) • When sub threshold value stimulus is given to a neuron then it will be not excited/no conduction of impulse takes place. i.e. None. • Threshold value : Minimum value of stimulus that can excite a neuron. (c) Summation : • If a series of subthresholds stimuli applied nerve fibre may succeeds in initiating an impulse. This additive effect is called as summation. (d) One way conduction : • Generally impulse is carried in one direction. • Dendron Cyton Axon Neuroglial cells : • These cells are more abundant than neurons but do not participate in impulse conduction. • They support or pack neurons (Supportive cells). These are as follows :