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Nervous System Chapter 49 1. The nervous system is the main system to communicate and coordinate body activities by sending electrical impulses. Nervous system forms a communication network in whole body. 2. Central nervous system CNS consists of Brain and Spinal Cord. The human brain contains about 100 billion neurons, organized into circuits more complex than the most powerful supercomputers. 3. Peripheral nervous system PNS consists of cranial nerves arising from brain and spinal nerves connected to spinal cord. These nerves bring information into or out of Central nervous System. PNS has also Somatic NS to pass instructions to skeletal muscles and ANS to pass instructions to visceral organs like heart, intestine etc. ANS has 2 divisions Sympathetic and Parasympathetic. Sympathetic division increases heart rate, breathing rate, blood pressure and is FIGHT or FLIGHT response. Parasympathetic is antagonistic to sympathetic and induces rest by lowering heart rate, breathing rate, blood pressure. It increases digestive activity by increasing secretions and bowl movements. It acts by REST and DIGEST response. 4. Specialized nerve cells are called Neurons. Supporting cells are Glial cells. 5. Glial cells nourish and anchor neurons. Some are phagocytes and others build myelin sheath around axons. 6. Sensory neurons bring information from sensory receptors like eyes to CNS. 7. Motor neurons take information from CNS to effectors like muscles or glands. 8. Association neurons receive information from sensory neurons and integrate it, interpret the meaning and pass instructions to motor neurons to act. 9. A neuron has a cell body. Many smaller branched appendages are called Dendrites. Dendrites bring in information (nerve impulse) to the cell body. A single longer appendage is called Axon. It takes information away from cell body. It branches at the end into terminal knobs. A terminal knob secretes a chemical called Neurotransmitter in the gap to the next neuron or muscle membrane. Most common neurotransmitter secreted is Acetylcholine. 10. Resting Potential: is when a nerve fiber has more positive ions outside and more negative ions inside (-70mV). It is not conducting any electrical impulse. 11. Action Potential (depolarization): is the sudden change on stimulation. Na+ ions move in. Now nerve fiber has more + ions inside (+30mV). Action potential or nerve impulse travels from cell body side to terminal knob side of axon. When the impulse reaches a part it becomes + inside and the part just behind it, returns to resting potential, Repolarization, due to outward movement of K+ ions. Comparison of Nervous System in animal phyla 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. Porifera does not have nerve cells. Cnidaria have nerve cells making a nerve net. There is no CNS. Cephalization, differentiation of head at anterior end, started in bilateral animals. Platyhelminthes have brain at anterior end and 2 lateral nerve cords joined by nerves. A nerve is only a bundle of nerve fibers. A ganglion is a cluster of neurons in PNS. A nerve cord has ganglia joined by bundles of nerve fibers. Annelida has CNS, a nerve ring with ganglia surrounding alimentary canal, at anterior end and a solid ventral nerve cord. Each segment has one ganglion in the nerve cord. Arthropoda also like annelids have a nerve ring surrounding alimentary canal. It is connected 2 solid ventral nerve cords with fused ganglia in each segment. Echinoderms have a nerve ring in the central disc around alimentary canal. A radial nerve enters each arm. Vertebrates have well defined CNS and PNS. Brain: has external Gray matter formed of neurons with unmyelinated axons. White matter lies deeper to gray matter in brain and has bundles of myelinated nerve fibers. Medulla and spinal cord have gray matter internal and white matter internal. Brain has 3 main parts. Fore Brain has cerebrum and diencephalon. Cerebrum is the largest part of brain. It is divided into 2 cerebral hemispheres. Each hemisphere has 4 lobes. It has cerebral cortex, gray matter of the folded surface. Cerebral cortex has special primary area for different functions. It is the seat of sensory input and motor output, language intelligence, imagination, calculations or processing. Most of the times we use word brain to mean cerebrum. Diencephalon has thalamus, lateral thick walls. Thalamus is the relay switch and direct information to different centers in cerebral cortex. Hypothalamus is the floor. Pituitary gland is attached to it. Hypothalamus controls hunger, thirst, sex drive, ANS and homeostasis like body temperature and water/salt balance. Cerebellum is the 2nd largest part of brain and is responsible for maintaining body posture and balance of body. 26. Brain Stem The remaining part of brain is the Brain Stem. It has Pons and Medulla parts which have the cardiac and breathing centers to regulate heart beat and rate of breathing. Spinal Cord 27. The spinal cord conveys information to and from the brain and generates basic patterns of locomotion 28. The spinal cord also produces reflexes independently of the brain 29. A reflex is the body’s automatic response to a stimulus. For example, a doctor uses a mallet to trigger a knee-jerk reflex 30. Arousal and Sleep 31. The brainstem and cerebrum control arousal and sleep 32. The core of the brainstem has a diffuse network of neurons called the reticular formation 33. These neurons control the timing of sleep periods characterized by rapid eye movements (REMs) and by vivid dreams. 34. Sleep is essential and may play a role in the consolidation of learning and memory 35. Emotions: Limbic System 36. Generation and experience of emotions involve many brain structures, including the amygdala, hippocampus, and parts of the thalamus 37. These structures are grouped as the limbic system 38. Alzheimer’s disease is a mental deterioration characterized by confusion and memory loss 39. Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain Sensory System: 40. Human body has 5 main sensory organs which collect information about environment. Some receptors also collect internal information like hunger, joint movement etc. 41. Skin: It gives us information about Touch, Pressure, Heat, Cold and Pain. Most receptors in skin are present inside dermis just below epidermis. 42. Nose: It has special sensory cells which collect information about smells of vapors. 43. Tongue: It has groups of sensory cells called taste-buds. Taste-buds detect 4 main types of taste salt, sweet, sour and bitter. 44. Eyes: Eyes collect visual information. Front of the eye is transparent to allow light to enter inside eye. It has to pass through a diaphragm called Iris, the colored part of eye. Iris has an opening at center called Pupil. If we get out in bright sunlight pupil quickly gets small to reduce the light entering eye. If we enter a dark room the pupil gets bigger to increase the light entering the eye. Eyes focus on far and near objects by changing the thickness of lens in the eye. The image is focused on Retina, the photo-sensitive layer. Retina has cone cells – give us colored vision in bright light and Rod Cells – give us black and white vision in dim light. 45. Ears: are the sensory organs for hearing and equilibrium. The external ear collects sound waves. After passing a duct sound wave hit Tympanum. 46. Middle ear: Tympanum passes vibrations to auditory ossicles, small bones in middle ear. These small bones pass vibrations to cochlea in inner ear. 47. Inner ear has 2 main parts cochlea and vestibule. 48. Cochlea a coiled duct has sensory cells that send impulses to brain. Brain interprets the meaning of sounds. 49. Vestibule is upper part of internal ear detects changes in body position and sends impulses to Cerebellum of brain. Cerebellum with the help of ears maintains balance = equilibrium of the body at rest or during motion. 50. Fishes have no auditory ossicles and ear does not hear sounds. Amphibians and reptiles have one auditory ossicle in middle ear. Mammals have 3 auditory ossicles in middle ear.