Nervous System


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Nervous System

  1. 1. The Nervous System
  2. 2. A. Neurons: Basic Units of the Nervous System <ul><li>The basic unit of structure and function in the nervous system is the neuron (nerve cell). </li></ul><ul><li>Neurons conduct impulses throughout the nervous system. </li></ul><ul><li>Neuron consists of three parts: </li></ul><ul><ul><ul><li>cell body </li></ul></ul></ul><ul><ul><ul><li>dendrites: branchlike extensions of the neuron that receive impulses and carry them toward the cell body </li></ul></ul></ul><ul><ul><ul><li>axon: extension of the neuron that carries impulses away from the cell body and toward other neurons, muscles, or glands. </li></ul></ul></ul>
  3. 3. <ul><li>Example: </li></ul><ul><li>Neuron Structure </li></ul>
  4. 4. <ul><li>There are three types of neurons: </li></ul><ul><ul><ul><li>sensory neurons: carry impulses from the body to the spinal cord and brain </li></ul></ul></ul><ul><ul><ul><li>motor neurons: carry the response impulses away from the brain and spinal cord to a muscle or gland </li></ul></ul></ul><ul><ul><ul><li>interneurons: found within the brain and spinal cord, and process incoming impulses and pass response impulses on to motor neurons </li></ul></ul></ul>
  5. 5. <ul><li>Relaying an impulse </li></ul><ul><li>The nervous system sorts and interprets incoming information before directing a response. </li></ul><ul><li>Example: Shoulder Tap </li></ul><ul><li>Question: How does a shoulder tap get your attention? </li></ul><ul><li>Answer: </li></ul><ul><ul><ul><li>Receptors in the skin sense a tap or other stimulus. </li></ul></ul></ul><ul><ul><ul><li>Sensory neurons transmit the sensory impulse (touch message) to your spinal cord and then to your brain. </li></ul></ul></ul><ul><ul><ul><li>The message is interpreted by the brain. A response is sent to the motor neurons. </li></ul></ul></ul><ul><ul><ul><li>Motor neurons transmit the impulse (response message) to the neck muscles. </li></ul></ul></ul><ul><ul><ul><li>The neck muscles are activated, causing the head to turn. </li></ul></ul></ul>
  6. 6. <ul><li>Example: </li></ul><ul><li>Sensory neuron and motor neuron </li></ul>
  7. 7. <ul><li>A neuron at rest </li></ul><ul><li>A resting neuron is a neuron that is not transmitting an impulse (electrical message). </li></ul><ul><li>The neuron membrane contain four important transport systems: </li></ul><ul><ul><ul><li>Ion channel: allows ions in and out of the cell </li></ul></ul></ul><ul><ul><ul><li>Gated Na+ channel: allows sodium ions into the cell </li></ul></ul></ul><ul><ul><ul><li>Na+/K+ Pump: uses ATP to pump three sodium ions out of the cell for every two potassium ions it pumps in. </li></ul></ul></ul><ul><ul><ul><li>Gated K+ channel: allows potassium ions to move out of the cell </li></ul></ul></ul><ul><li>In a neuron at rest, the Na+/K+ pump and the presence of many negatively charged ions within the cell keeps the inside of the neuron cell more negatively charged than the outside. </li></ul><ul><li>These conditions cause the plasma membrane of the resting neuron cell to be polarized (inside of the cell is negative, outside of the cell is positive). </li></ul>
  8. 8. <ul><li>Example: Resting Neuron Cell </li></ul><ul><li>This polarization of a neuron cell allows it to transmit an impulse. </li></ul>
  9. 9. <ul><li>How an impulse is transmitted </li></ul><ul><li>The following steps summarizes how an impulse gets transmitted throughout the body: </li></ul><ul><ul><ul><li>When a stimulus excites a neuron, the gated Na+ channels in the membrane open up and sodium ions go inside into the cell. </li></ul></ul></ul><ul><ul><ul><li>The inside of the cell now becomes positively charged and the outside negatively charged. This change in charge is called depolarization. </li></ul></ul></ul><ul><ul><ul><li>This depolarization moves like a wave down the length of the axon. </li></ul></ul></ul><ul><ul><ul><li>As the impulse passes, gated sodium channels close, so that sodium ions to not enter inside the cell. The gated K+ channels open, letting potassium ions out of the cell. This action repolarizes the cell. </li></ul></ul></ul><ul><ul><ul><li>As gated potassium channels close, the Na+/K+ pump restores the ion distribution. </li></ul></ul></ul>
  10. 10. <ul><li>Example: </li></ul><ul><li>Transmitting an impulse </li></ul>
  11. 12. <ul><li>An impulse can move down the complete length of an axon only when the threshold level is reached. </li></ul><ul><li>Threshold level: the level at which depolarization of the neuron occurs. </li></ul><ul><li>If the threshold level is not reached, the impulse quickly dies out </li></ul>
  12. 13. <ul><li>White matter and gray matter </li></ul><ul><li>Most axons are surrounded by white covering of cell call the myelin sheath. </li></ul><ul><li>The myelin sheath insulates the axon, preventing the movement of ions across its plasma membrane. </li></ul><ul><li>The ions move quickly down the axon until they reach a gap in the sheath, where the ions pass through the plasma of the nerve cell and depolarization occurs. </li></ul><ul><li>As a result, the impulse jumps from gap to gap, greatly increasing the speed at which the impulse travels. </li></ul>
  13. 14. <ul><li>The myelin sheath gives axons a white appearance. </li></ul><ul><li>In the brain and spinal cord, masses of myelinated axons make up what is called “white matter.” </li></ul><ul><li>The absence of myelin in axons accounts for the grayish color of “gray matter” in the brain. </li></ul>
  14. 15. <ul><li>Connections between neurons </li></ul><ul><li>Neurons lay end to end, meaning axons to dendrites and these parts do not touch. </li></ul><ul><li>A tiny space, called the synapse, lies between one neuron’s axon and another neuron’s dendrites. </li></ul><ul><li>Impulses must move across the synaptic space. </li></ul>
  15. 16. <ul><li>How do impulses move across the synaptic space? </li></ul><ul><ul><ul><li>As an impulse reaches the end of an axon, calcium channels open, allowing calcium to enter the end of the axon. </li></ul></ul></ul><ul><ul><ul><li>The calcium causes vesicles in the axon to fuse with the plasma membrane, releasing neurotransmitters into the synaptic space by exocytosis. </li></ul></ul></ul><ul><ul><ul><li>These neurotransmitters diffuse across the synapse to the dendrites of the next neuron and binds to receptors. </li></ul></ul></ul><ul><ul><ul><li>This causes ion channels to open which changes the polarity in the neuron, initiating a new impulse. </li></ul></ul></ul>
  16. 17. <ul><li>Example: Synapses </li></ul>
  17. 18. <ul><li>Enzymes in the synapse break down the neurotransmitters preventing continual firing of impulses. </li></ul><ul><li>The Secret Life of the Brain : Video </li></ul><ul><li>The Secret Life of the Brain : Video </li></ul>
  18. 19. B. The Central Nervous System <ul><li>The control center of the nervous system is the brain. </li></ul><ul><li>An impulse traveling through neurons in your body usually reaches your brain before being rerouted. </li></ul><ul><li>The central nervous system is made up of two parts: </li></ul><ul><ul><ul><li>Brain </li></ul></ul></ul><ul><ul><ul><li>Spinal cord </li></ul></ul></ul>
  19. 20. <ul><li>Central Nervous System </li></ul>
  20. 21. <ul><li>Two systems work together </li></ul><ul><li>The nervous system is made up two important systems working together: </li></ul><ul><ul><ul><li>Central Nervous System (CNS): brain and spinal cord </li></ul></ul></ul><ul><ul><ul><li>Peripheral Nervous System (PNS): all the nerves that carry messages to and from the CNS </li></ul></ul></ul><ul><li>The CNS and PNS work together to respond to stimuli from the external environment. </li></ul>
  21. 22. <ul><li>Anatomy of the brain </li></ul><ul><li>The brain is the control center of the entire nervous system. </li></ul><ul><li>The brain is divided into three main sections: </li></ul><ul><ul><ul><li>Cerebrum </li></ul></ul></ul><ul><ul><ul><li>Cerebellum </li></ul></ul></ul><ul><ul><ul><li>Brain stem </li></ul></ul></ul>
  22. 23. <ul><li>The cerebrum </li></ul><ul><ul><li>Divided into two halves, called hemispheres, that are connected by bundles of nerves. </li></ul></ul><ul><ul><li>Controls conscious activities, intelligence, memory, language, skeletal muscle movements, and senses. </li></ul></ul><ul><ul><li>The cerebral cortex, is the outer surface of the cerebrum, is made up of gray matter. </li></ul></ul><ul><ul><li>The cerebral cortex has folds and grooves that increase its total surface area, and allows complex thought processes to occur. </li></ul></ul>
  23. 24. <ul><li>Cerebrum </li></ul>
  24. 25. <ul><li>The cerebellum </li></ul><ul><ul><li>Located at the back of the brain </li></ul></ul><ul><ul><li>Controls your balance, posture, and coordination </li></ul></ul><ul><ul><li>Injury causes your movements to become jerky. </li></ul></ul>
  25. 26. <ul><li>The brain stem </li></ul><ul><ul><li>Brain stem is divided into three parts: </li></ul></ul><ul><ul><ul><li>Medulla oblongata: part of the brain that controls involuntary activities </li></ul></ul></ul><ul><ul><ul><li>Pons: pathway connecting various parts of the brain with each other </li></ul></ul></ul><ul><ul><ul><li>Midbrain: pathway connecting various parts of the brain with each other </li></ul></ul></ul>
  26. 27. C. The Peripheral Nervous System <ul><li>The peripheral nervous system (PNS) carries impulses between the body and the central nervous system. </li></ul><ul><li>The PNS is divided into two parts: </li></ul><ul><ul><li>Somatic nervous system </li></ul></ul><ul><ul><li>Autonomic nervous system </li></ul></ul>
  27. 28. <ul><li>Peripheral Nervous System </li></ul>
  28. 29. <ul><li>Somatic Nervous System </li></ul><ul><ul><li>Portion of the nervous system composed of cranial nerves, spinal nerves, and all of their branches </li></ul></ul><ul><ul><li>Contains 12 pairs of cranial nerves from the brain, 31 pairs of spinal nerves from the spinal cord, and all of the their branches. </li></ul></ul><ul><ul><li>These nerves are bundles of neuron axons bound together by connective tissue, and the cell bodies are found along the spinal column. </li></ul></ul><ul><ul><li>Voluntary pathway that relays information between the CNS and skeletal muscles. </li></ul></ul>
  29. 30. <ul><li>Reflexes in the somatic system </li></ul><ul><ul><li>Sometimes a stimulus results in an automatic, unconscious response within the somatic nervous system. </li></ul></ul><ul><ul><li>Reflex: an automatic response to a stimulus </li></ul></ul><ul><li>Example: Hand jerks when you touch something hot </li></ul><ul><ul><li>A reflex impulse travels to the spinal column or brain stem where it causes an impulse to be sent directly back to a muscle. (message is not interpreted) </li></ul></ul><ul><ul><li>The brain becomes aware of the reflex only after it occurs. </li></ul></ul>
  30. 31. <ul><li>Somatic Nervous System: Reflex </li></ul>
  31. 32. <ul><li>The autonomic nervous system </li></ul><ul><ul><ul><li>Portion of the peripheral nervous system that carries impulses from the CNS to internal organs. </li></ul></ul></ul><ul><ul><ul><li>The impulses produce responses that are involuntary. (unconscious control) </li></ul></ul></ul><ul><ul><ul><li>The autonomic nervous system is divided into two parts: </li></ul></ul></ul><ul><ul><ul><ul><li>Sympathetic nervous system: controls many internal functions during times of stress. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Parasympathetic nervous system: controls many of the body’s internal functions when it is at rest. </li></ul></ul></ul></ul>
  32. 33. <ul><li>Autonomic Nervous System </li></ul>
  33. 34. <ul><ul><li>Sympathetic nervous system releases hormones such as epinephrine and norepinephrine, that results in the fight – or – flight response. </li></ul></ul><ul><ul><li>Both the sympathetic and parasympathetic systems send signals to the same internal organs. </li></ul></ul><ul><ul><li>The resulting activity of the organ depends on the intensities of the opposing signals. </li></ul></ul>
  34. 35. <ul><li>Parasympathetic Nervous System and Sympathetic Nervous System </li></ul>
  35. 36. <ul><li>Outline of the Nervous System </li></ul>
  36. 37. D. Sensing Chemicals <ul><li>How are you able to smell and taste? </li></ul><ul><li>Answer: Chemical molecules of a substance stimulate receptors in your nose and mouth. </li></ul><ul><li>How does your sense of smell get activated? </li></ul><ul><ul><li>The receptors for smell are hair like nerve endings located in the upper portion of your nose. </li></ul></ul><ul><ul><li>Chemicals acting on these nerve endings initiate impulses in the olfactory nerve, which is connected to your brain. </li></ul></ul><ul><ul><li>In the brain, this signal is interpreted as a particular odor. </li></ul></ul>
  37. 38. <ul><li>Olfactory System </li></ul>
  38. 39. <ul><li>The senses of taste and smell are closely linked. </li></ul><ul><li>Example: Stuffed nose </li></ul><ul><li>You can smell a little, if anything, and since your sense of taste depends on your sense of smell, your sense of taste is dulled. </li></ul><ul><li>How does your sense of taste get activated? </li></ul><ul><ul><li>Chemicals dissolved in saliva contact sensory receptors on your tongue called taste buds. </li></ul></ul><ul><ul><ul><li>Taste buds: sensory receptors located on the tongue that result in taste perception. </li></ul></ul></ul><ul><ul><ul><li>There are four different tastes: </li></ul></ul></ul><ul><ul><ul><ul><li>Sour </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Salty </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Bitter </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sweet </li></ul></ul></ul></ul><ul><ul><li>Taste bud cells are depolarized, signals from your taste buds are sent to the cerebrum. </li></ul></ul><ul><ul><li>At the cerebrum, the signal is interpreted and you notice a particular taste. </li></ul></ul>
  39. 40. <ul><li>A young adult has approximately 10,000 taste buds. </li></ul><ul><li>As a person ages, his or her sense of smell becomes less sharp and taste buds may decrease in number or become less sensitive, so it may decrease one’s sense of taste. </li></ul>
  40. 41. E. Sensing Light <ul><li>How are you able to see? </li></ul><ul><li>Your sense of sight depends on receptors in your eyes that respond to light energy. </li></ul><ul><li>The retina, found at the back of the eye, is a thin layer of tissue made up of light receptors and sensory neurons. </li></ul><ul><li>Light enters the eye through the pupil and is focused by the lens onto the back of the eye, where it strikes the retina. </li></ul>
  41. 42. <ul><li>The retina contains two types of light receptors cells: </li></ul><ul><ul><ul><li>Rods: receptor cells adapted for vision in dim light; help detect shape and movement; black and white picture </li></ul></ul></ul><ul><ul><ul><li>Cones: receptor cells adapted for sharp vision in bright light; help detect color </li></ul></ul></ul><ul><li>These light receptors convert light signals into nerve impulses and relay them to the brain. </li></ul><ul><li>At the back of the eye, retinal tissue comes together to form the optic nerve, which leads to the brain, where images are interpreted. </li></ul>
  42. 43. <ul><li>Visual System </li></ul>
  43. 44. F. Sensing Mechanical Stimulation <ul><li>Hearing and touch depend on receptors that respond to mechanical stimulation. </li></ul><ul><li>Your sense of hearing </li></ul><ul><li>Sound waves enter your outer ear and travel down to the end of the ear canal, where they strike a membrane called the eardrum and cause it to vibrate. </li></ul><ul><li>Sound waves: waves created by air vibrations </li></ul><ul><li>The vibrations then pass to three small bones in the middle ear: </li></ul><ul><ul><ul><li>Malleus </li></ul></ul></ul><ul><ul><ul><li>Incus </li></ul></ul></ul><ul><ul><ul><li>stapes </li></ul></ul></ul>
  44. 45. <ul><li>Parts of the Middle Ear </li></ul>
  45. 46. <ul><li>As the stapes vibrates, it causes the membrane of the oval window, a structure between the middle and inner ear, to move back and forth. </li></ul><ul><li>The movement from the oval window causes fluid in the cochlea to move. </li></ul><ul><li>Cochlea: snail-shaped structure in the inner ear containing fluid and hairs; produces electrical impulses that the brain interprets as sound. </li></ul><ul><li>The fluid in the cochlea moves like a wave against the hair cells causing them to bend. </li></ul><ul><li>The movement of the hairs produces electrical impulses, which travel along the auditory nerve to the sides of the cerebrum, where they are interpreted as sound. </li></ul><ul><li>Hearing loss can occur if the auditory nerve or the hair cells in the cochlea are damaged. </li></ul>
  46. 47. <ul><li>Cochlea, Oval window, Stapes, Semicircular Canals </li></ul>
  47. 48. <ul><li>Your sense of balance </li></ul><ul><li>The inner ear also converts information about the position of your head into nerve impulses which travel to your brain, informing it about your body’s equilibrium. </li></ul><ul><li>Maintaining balance is the function of your semicircular canals. </li></ul><ul><li>Semicircular canal: structures in the inner ear containing fluid and hairs that help the body maintain balance. </li></ul><ul><li>Example: Tilting the head </li></ul><ul><li>Causes the fluid to move which bends the hair and produces impulses. Neurons from the semicircular canals carry the impulses to the brain, which sends an impulse to stimulate your neck muscles and readjust the position of the head. </li></ul>
  48. 49. <ul><li>Your sense of touch </li></ul><ul><li>Receptors in the dermis of the skin respond to changes in: </li></ul><ul><ul><ul><li>Temperature </li></ul></ul></ul><ul><ul><ul><li>Pressure </li></ul></ul></ul><ul><ul><ul><li>pain </li></ul></ul></ul><ul><li>Although some receptors are found all over your body, those responsible for responding to particular stimuli are usually concentrated within certain areas of your body. </li></ul>
  49. 50. <ul><li>Light pressure receptors </li></ul><ul><ul><li>Found in the following areas : </li></ul></ul><ul><ul><ul><li>dermis of the fingertips </li></ul></ul></ul><ul><ul><ul><li>Eyelids </li></ul></ul></ul><ul><ul><ul><li>Lips </li></ul></ul></ul><ul><ul><ul><li>tip of the tongue </li></ul></ul></ul><ul><ul><ul><li>palms </li></ul></ul></ul><ul><li>When these receptors are stimulated, you perceive sensations of light touch. </li></ul>
  50. 51. <ul><li>Heavy pressure receptors </li></ul><ul><ul><li>Found in the following areas: </li></ul></ul><ul><ul><ul><li>Joints </li></ul></ul></ul><ul><ul><ul><li>muscle tissue </li></ul></ul></ul><ul><ul><ul><li>certain organs </li></ul></ul></ul><ul><ul><ul><li>Palms </li></ul></ul></ul><ul><ul><ul><li>Fingers </li></ul></ul></ul><ul><ul><ul><li>soles of your feet </li></ul></ul></ul><ul><ul><li>When these receptors are stimulated, you perceive heavy pressure. </li></ul></ul>
  51. 52. <ul><li>Free nerve ending </li></ul><ul><ul><li>Extend into the lower layers of the epidermis. </li></ul></ul><ul><ul><li>Are receptors for the following sensations: </li></ul></ul><ul><ul><ul><li>Itch </li></ul></ul></ul><ul><ul><ul><li>Tickle </li></ul></ul></ul><ul><ul><ul><li>Hot </li></ul></ul></ul><ul><ul><ul><li>Cold </li></ul></ul></ul><ul><ul><ul><li>pain </li></ul></ul></ul><ul><ul><li>Heat receptors are found deep in the dermis. </li></ul></ul><ul><ul><li>Cold receptors are found closer to the surface of the skin. </li></ul></ul><ul><ul><li>Pain receptors can be found in all tissues of the body except those in the brain. </li></ul></ul>
  52. 53. <ul><li>Receptors on the skin </li></ul>
  53. 54. G. Nervous System Disorders <ul><li>Meningitis: -Viral or Bacterial infection in the brain </li></ul><ul><li>-Bacterial meningitis is the inflammation of the meninges (membranous coverings of the brain and spinal cord) </li></ul><ul><li>-Symptoms: fever, severe headache, stiff neck, sore throat, and vomiting, followed by respiratory illness </li></ul><ul><li>-Can cause permanent brain damage </li></ul>
  54. 55. <ul><li>Alzheimer’s Disease: </li></ul><ul><li>-Form of dementia that affects a person’s memory, ability to reason, make judgments and function in everyday situations </li></ul><ul><li>-brain cells degenerate, reducing the responsiveness of the remaining cells to many of the chemicals that transmit signals </li></ul>
  55. 56. <ul><li>Parkinson’s Disease: </li></ul><ul><li>-Degenerative disorder of the nervous system </li></ul><ul><li>-Patients with this disease may exhibit shaking, tremors, sluggish movents, or muscle rigidity </li></ul><ul><li>-Rigidity in muscles is one of the serious effects </li></ul><ul><li>-May become difficult to move around </li></ul>