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 UNIT III
 HUMAN ANATOMY & PHYSIOLOGY - III
 (Musculo skeletal system, neural control and coordination)
  This unit covers the most important systems in human body like musculo-skeletal system and nervous system including brain, spinal cord, nerves and nerve impulse.
 
 Important Points for Students  in these topics.
 The Muscle:
 *    Skeletal muscle is syncytial as each muscle fibre is formed by the fusion of embryonic mononucle-ate myoblasts.
 *    Large number of parallel filame-nts, myofilaments or myofibrils are present in sarcoplasm.
 *    Alternate dark and light bands are present in each myofibril.
 *    Light band is 'I' band which contains actin and two regulatory proteins like troponin and tropo myosin.
 *    Dark band is 'A' band which contains Myosin protein.
 *    'I' band is bisected by 'Z' line or Krause's membrane or Dobie's line.
 *    Sarcomere is the portion of the myofibril between two succe ssive 'Z' lines. It is the functional unit of contraction.
 *    Students should learn the struct-ure of contractile proteins & triad system.
 *    Motor unit is the motor neuron and the set of muscle fibres inne-rvated by all the teloden drites.
 *    Motor end plate or neuro mus cular junction is the junction between a motor neuron and the sarcolemma.
 *    Sarcolemma invaginates into the sarcoplasm and forms transverse tubules (T-tubules) between A and I bands. Each T tubule is flanked on either side by several terminal cisternae of the sarcoplasmic reticulum.
 *    T tubule and the two terminal cisternae on both sides of it form the Triad system. Most of the stored Calcium of the sarcocyte is present in terminal cisternae.
 *    Red muscle fibres have more myoglobin. They have more mito-chondria which can utilise the large amount of oxygen. So these muscles are known as aerobic muscles.
 *    White muscle fibres have very less quantity of myoglobin and appear as pale or whitish. They have few mitochondria but more sarcoplasmic reticulum. They depend on anaerobic process for the release of energy.
 
 The Skeleton:
 *    206 bones present in the skeletal system of adult human being.
 *    Axial skeleton and appendicular skeleton are the two parts of the human skeletal system.
 *    Axial skeleton consists of 80 bon-es with the parts like skull, verte-bral column, sternum and ribs.
 *    Skull consists of 22 bones under 2 sets like cranial and facial.
 *    Sternum is breast bone with 3 parts like manubrium, middle part and inferior xiphoid process.
 *    12 pairs of ribs are present in human chest. Ribs are bicephalic as they have 2 articulation sur-faces on dorsal end which attach with vertebrae.
 *    First 7 pairs are true ribs (verte bro-sterna) as they attach dor- sally with thoracic vertebrae and ventrally with sternum.
 
 Appendicular skeleton:
 *    It consists of 126 bones..
 *    Each forelimb has 30 bones like humerus, radius and ulna, carpals - 8, metacarpals -5
     and phalanges - 14.
 *    Each hindlimb has 30 bones like femur, tibia and fibula, tarsals-7, metatarsals-5,digits-14,patella-1.
 *    Students should prepare about the disorders of muscular and skeletal systems like Myasthenia gravis, muscular dystrophy, tetany, arthritis, osteoporosis and gout.
 
 Human Nervous System:
 *    Brain is present in cranial cavity and lined by 3 cranial meninges like dura mater, arachnoid mater and piamater.
 *    Brain has 3 major parts like fore brain, midbrain and hindbrain
 *    Forebrain consists of olfactory bulb,cerebrum and dience phalon.
 *    Diencephalon consists of epitha- lamus, thalamus and hypo-thalamus.
 *    Hypothalamus is considered as thermostat of the body.
 *    Limbic system is formed by the inner parts of cerebrum and deep parts like amygdale, hippocam- pus etc.,
 *    Mid brain consists of 4 corpora quadrigemina (optic lobes)
 *    Hind brain comprises cerebell- um, pons Varolii and medulla oblongata.
 *    Spinal cord travels through neural canal of vertebral column. It sho-ws two enlargements like cervical and lumbar enlargements.
 *    Spinal cord tapers in to a conical portion known as conus medullari which ends at the level of the intervertebral disc between the 1st and 2nd lumbar vertebrae in the adult. The extension of conus medullaris as the non-nervous fibrous tissue to the coccyx is known as filum terminale.
 *    Central canal or spinal neurocoel is the cavity of spinal cord.
 *    Cranial nerves of brain and spinal nerves of spinal cord form peri-pheral nervous system.
 *    12 pairs of cranial nerves are pre-sent in the form of motor, sensory and mixed types.
 *    Parasympathetic division is considered as cranio-sacral outflow with terminal ganglia.
 *    Neurons can respond to external and internal stimuli and conduct nerve impulses.
 *    Axolemma of a neuron has 3 types of ion channels like leakage channels, ligand-gated channels and voltage gated channels.
 *    Range of Resting membrane pot-ential in neurons is -40 to - 90 mV.
 *    At resting phase, the axolemma is polarized. Later it becomes depolarised and repolarised and finally hyperpolarised before coming back into polarisation.
 *    The condition of various types of voltage gated channels during all these phases is most important for competitive exams.
 
  The Eye & Ear:
 *    Eye is present in eye orbit of skull. It has accessory structures like eye lids, eye lashes, eye brows, lacrimal apparatus and extrinsic muscles.
 *    Lacrimal fluid contains lysozyme as bactericidal enzyme.
 *    6 extrinsic or extra ocular eye muscles are superior, inferior, lateral medial rectus muscles and superior oblique and inferior oblique muscles. They help in the movement of eye by receiving innervations from the III, IV & VI cranial nerves.
 *    Wall of Eye ball has three layers like fibrous tunic, vascular tunic, nervous tunic (retina)
 *    The ear has three regions like external, middle and internal ear.
 *    Disorders of human neural system are Alzheimers disease, mening-itis, parkinsons disease and stroke or cerebro vascular accident.