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The Nervous system

Learn about the nervous system and how communication occurs through neurons. Explore the different parts of a neuron and understand how impulses travel through synapses. Discover the functions of the central nervous system and peripheral nervous system, including the brain and spinal cord. Explore reflexes and the pathway of impulse transmission.

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The Nervous system

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  1. The Nervous system

  2. Communication Nearly all multicellular organisms have communication systems. Specialized cells carry messages from one cell to another so that communication among all body parts is smooth and efficient.

  3. Communicate to maintain homeostasis • There are two systems used for communication in your body: • The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli with the use of nerves • The endocrine system performs a similar function with the use of hormones

  4. Nervous Response Stimulus: any change that results in a change in the organism. temperature, light, pressure, sound, smell, etc. Response: any action resulting from a stimulus. contraction of muscle cells secretion by a gland stimulation of another nerve fiber. 4

  5. Neurons • Messages carried by the nervous system are electrical signals = impulses • Nerve cells that transmit impulses = neurons • Sensory neurons: carry impulses from sense organs to the spinal cord and brain • Motor neurons: carry impulses from the brain and spinal cord to muscles and glands • Interneurons: connect sensory and motor neurons and carry impulses between them

  6. Parts of a Neuron Cell body = largest part containing nucleus and cytoplasm (most metabolic activity occur here) Dendrites = short, branched extensions spreading out from the cell body and they carry impulses from the environment or other neurons towards the cell body Axon = long fibers that carry impulses away from the cell body and ends at the axon terminal

  7. Nucleus Axon terminals Cell body Myelin sheath Axon Nodes Dendrites A Neuron Section 35-2

  8. Nerves • Neurons bundle together to form nerves • Some nerves may be only a few neurons, and others may be hundreds or thousands • The myelin sheath may insulate axons by surrounding it • There may be some gaps in the myelin sheath called nodes • Impulses jump from one node to the next, increasing the speed impulses travel

  9. Synapse At the end of the neuron, the impulse reaches an axon terminal where the impulse may be passed along to another neuron or another cell The location where a neuron can transfer an impulse to another cell = synapse The synapse is a small gap that separates the axon terminal from the dendrites of the next neuron or another cell The terminals contain tiny sacs or vesicles filled with neurotransmitters = chemicals used by a neuron to transmit an impulse across a synapse The neurotransmitters stimulate the next neuron The impulse will continue with the stimulation exceeds the cell’s threshold

  10. Figure 35-8 The Synapse Section 35-2 Direction of Impulse Dendrite of adjacent neuron Axon Receptor Vesicle Axon terminal Synaptic cleft Neurotransmitter

  11. The Nervous System • Neurons work together forming the nervous system • There are two major divisions of the nervous system: • Central nervous system (CNS) • Peripheral nervous system (PNS)

  12. Parts of the Nervous system • Central nervous system (CNS): • Brain • Spinal Cord • Peripheral nervous system (PNS): • Sensory division • Motor division • Somatic nervous system • Autonomic nervous system

  13. Central Nervous System • The CNS is the control center of the body: • Relays messages • Processes information • Analyzes information

  14. Brain and Spinal cord • Both are • protected by bone • wrapped in 3 layers of connective tissue = meninges • layers may have a space between them filled with cerebrospinal fluid which protects (shock absorber) and exchanges nutrients and waste

  15. Brain • About 100 billion neurons, mainly interneurons • Major parts of the brain: • Cerebrum • Cerebellum • Brain stem • Thalamus • Hypothalamus • http://www.teachersdomain.org/resource/hs11.sci.life.stru.brainact/

  16. Cerebrum Thalamus Pineal gland Hypothalamus Cerebellum Pituitary gland Pons Medulla oblongata Spinal cord Figure 35-9 The Brain Section 35-3

  17. Spinal Cord Links communication between the brain and the rest of the body 31 pairs of spinal nerves branch out from the spinal cord connecting brain to body Reflexes = quick, automatic responses to stimuli are processed directly in the spinal cord

  18. Gray matter Central canal Spinal nerve White matter Meninges Figure 35-11 The Spinal Cord Section 35-3

  19. Reaction activity • Reaction time = the amount of time required for an impulse travel from your sensory neurons to your motor neurons

  20. Receptors & Effectors Receptor: a specialized nervous tissue that is sensitive to a specific stimulus. nerve cells in skin eyes ears taste buds Effectors: the part/s of the body that respond muscles or glands

  21. Reflex Arc • The pathway that an impulse travels: • 1. from the sensory receptor • 2. up the sensory neuron • 3. over the synapse • 4. to the spinal cord (interneuron) • 5. over another synapse • 6. back down the motor neuron • 7. to the effector Reflex arc animations: 1. http://www.sumanasinc.com/webcontent/animations/content/reflexarcs.html 2. http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0016-swf_reflex_arc.swf

  22. Common Diseases and Disorders

  23. Common Diseases and Disorders (cont.)

  24. Common Diseases and Disorders (cont.)

  25. Common Diseases and Disorders (cont.)

  26. Sensory Receptors • Neurons that react directly to stimuli from the environment and send impulses to other neuron and CNS • Light • Sound • Motion • Chemicals • Pressure • Changes in temperature

  27. Sense organs • Sensory receptors are concentrated in the sense organs: • Eyes • Ears • Nose • Mouth • Skin

  28. Types of Sensory receptors • Sensory receptors within each organ enable it to respond to particular stimuli. The five general categories of sensory receptors are: • Pain receptors • Thermoreceptors • Mechanoreceptors • Chemoreceptors • Photoreceptors

  29. The 5 Senses See Hear Smell Taste Touch

  30. See (Vision) Photoreceptors = sense light

  31. Hearing and Balance • Sound = vibration in air detected by mechanoreceptors • Balance = As head moves, fluid shifts and hair cells bend and send impulses to the CNS to determine body motion and position

  32. Smell Smell = ability to detect chemicals detected by chemoreceptors in nasal passageway and send impulses to CNS through sensory nerves

  33. Taste How food tastes is strongly influenced by smell Taste = ability to sense chemicals by chemoreceptors in taste buds mostly on tongue (sweet, sour, salty and bitter – sensitivity is different on different parts of tongue)

  34. Touch Skin = largest sense organ containing pain receptors, thermoreceptors, and mechanoreceptors

  35. Senses activity • Different parts of skin have different sensitivity because there’s a different numbers of receptors at different locations

  36. Problems Drugs = substance that changes the structure or function of the body Drugs can interfere with the action of neurotransmitters at the synapse, which can disrupt the functioning of the nervous system

  37. Stimulants • Increase the actions regulated by the nervous system by increasing the release of neurotransmitters at synapses (increase heart rate, blood pressure, and breathing rate) • Amphetamines • Cocaine • Nicotine • Caffeine

  38. Depressants • Decrease the actions regulated by the nervous system (lowering heart rate, breathing rate, blood pressure, relaxing muscles, and relieving tension) • Alcohol • Tranquilizers

  39. Alcohol • One of the most dangerous and abused depressant drug that slows down functioning rate of CNS • Fetal alcohol syndrome (FAS) = a group of birth defects caused by the effects of alcohol on the fetus (heart defects, malformed faces, delayed growth, and poor motor development • Alcoholism = disease of people who have become addicted to alcohol • Causes damage to liver where alcohol is broken down

  40. Addictions • Some drugs that act on neurons of the pleasure centers of the brain can produce an addiction = an uncontrollable craving for more of the drug or dependence on a drug • Cocaine – causes sudden release of the neurotransmitter dopamine • Opiates – mimic natural endorphins to overcome pain • Marijuana – produces temporary feeling of euphoria and disorientation • Drug abuse = using any drug in a way that most doctors couldn’t approve

  41. Commonly Abused Drugs Section 35-5 Used to increase alertness, relieve fatigue Used to relieve anxiety, irritability, tension Used to relieve pain Stimulants Depressants Opiates Amphetamines Barbiturates Tranquilizers Morphine Codeine Increase heart and respiratory rates; elevate blood pressure; dilate pupils; decrease appetite Slow down the actions of the central nervous system; small amounts cause calmness and relaxation; larger amounts cause slurred speech and impaired judgement Act as a depressant; cause drowsiness, restlessness, nausea Drug Type Medical Use Examples Effects on the body

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