neuroglia the supporting cells of cns .pptx

Neuroglia the supporting cells of cns

1. Glial cells - Introduction It is believed that German biologist Rudolf Virchow was the first to discover glial cells in 1856. (While looking for connective tissue in the brain, he identified substance connected to the neurons.) Neuroglial in Greek, means nerve glue. It was understood that glial cells only functioned as glue for the neurons. (having a passive role)

2. Glial cells, also called as neuroglia , are cell which are non-neuronal and are located within the  CNS & PNS They provides physical and metabolic support to neurons , including neuronal insulation and communication, and nutrient and waste transport. Glial cells - Introduction

3. Definition - Neuroglia or glia is the supporting cell of the nervous system. Neuroglial cells are non-excitable and do not transmit nerve impulse (action potential). So, these cells are also called non-neural cells or glial cells. When compared to the number of neurons, the number of glial cells is 10 to 15 times greater. Glial cells -

4. Neuroglial cells are distributed in CNS as well as PNS. Accordingly the neuroglial cells are classified into two types: A. Central neuroglial cells B. Peripheral neuroglial cells. Glial cells - Classification

5. Glial cells - Classification

6. Central Glial cells

7. Neuroglial cells in CNS are of three types: 1. Astrocytes 2. Microglia 3. Oligodendrocytes . 4. Ependymal cells 5. Radial glia Central Glial cells - Classification

8. 1. Astrocytes Astrocytes are star-shaped neuroglial cells present in all the parts of the brain. Two types of astrocytes are found in human brain: i . Fibrous astrocytes ii. Protoplasmic astrocytes .

9. 1. Fibrous Astrocytes Location - Fibrous astrocytes occupy mainly the white matter. Few fibrous astrocytes are seen in gray matter also. The processes of these cells cover the nerve cells and synapses.

10. 2. Protoplasmic Astrocytes Location - Protoplasmic astrocytes are present mainly in gray matter. The processes of neuroglia run between nerve cell bodies.

11. Astrocytes - Function Function - Formation of blood-brain barrier by sending processes to the blood vessels of brain, particularly the capillaries, They are responsible for formation of tight junction with capillary membrane. Tight junction in turn forms the blood-brain barrier.

12. Astrocytes - Function Function - Supporting network in brain and spinal cord. Maintain the chemical environment of ECF around CNS neurons Provide calcium and potassium. Regulate or control neurotransmitter level in synapses Regulate recycling of neurotransmitter during synaptic transmission.

13. Astrocytes - Function Function - Regulation or control of Neurotransmitter level. These cells have an ability to sense the levels of neurotransmitter in synapses. Because of this, astrocytes are important for modifying synapses and moreover how neurons communicate.

14. Astrocytes - Function Function - Regulation or control of Neurotransmitter level. This type of glial cell is also responsible for cleaning up what is left behind after synaptic transmission. Once a message has been received and transmitted to the next neuron, the astrocytes will recycle any of the left-over neurotransmitters.

15. Astrocytes - Function Similarly, once a neuron died, the astrocytes will clean this up as well as any excess potassium ions there may be in the environment. With the help of astrocytes, this filtering of substances is essential for maintaining a healthy brain. Also, astrocytes store glucose from the blood and utilise this to fuel the neurons, thus astrocytes are important for regulating metabolism as well as homeostasis

16. Oligodendrocytes ( oligodendroglia) Oligodendrocytes have only few processes, which are short. They produce myelin sheath around the nerve fibers in CNS.

17. Oligodendrocytes - Function Functions - i. Provide myelination around the nerve fibers in CNS where Schwann cells are absent ii. Provide support to the CNS neurons by forming a semi-stiff connective tissue between the neurons.

18. Oligodendrocytes - Function Functions - i. Provide myelination around the nerve fibers in CNS where Schwann cells are absent ii. Provide support to the CNS neurons by forming a semi-stiff connective tissue between the neurons.

19. Microglia Microglial are small cells with an oval shaped cell body and many small branches projecting out of it to enable them to move about.

20. Microgli a (Immune Cells) - Function The main function of these cells is to respond to any injuries or diseases in the CNS. When injury and disease are detected, the microglial are alerted and respond by moving to the injury site in order to either clear away any dead cells or to remove any harmful toxins or pathogens that may be present.

21. Microglia - Function Microglia also play a role in the development of the brain as well as Synaptic Pruning. Typically, far more synapses are created than are needed, when only the strongest and most important ones need to survive. Microglia directly contribute to removing synapses that are deemed as unnecessary, a process known as synaptic pruning.

22. Ependymal Cells Ependymal cells are located in the CNS that are column shaped and typically line up together to form a membrane. This membrane is called the ependyma , which is a thin membrane lining the spinal cord and ventricles of the brain.

23. Ependymal Cells - Function These cells have tiny hairlike structures on them called cilia, which face the open space of the cavities they line. Cilia move in a coordinated pattern to encourage the directional flow of cerebrospinal fluid.

24. Radial glial Cells Radial glia is believed to be a type of stem cell These cells are able to make neurons as well as other types of glial such as astrocytes and oligodendrocytes.

25. Glial cells - Classification

26. Peripheral Glial cells

27. Neuroglial cells in PNS are of two types: 1. Schwann cells 2. Satellite cells. Peripheral Glial cells

28. Schwann cells Schwann cells are the major glial cells in PNS. They work in a similar fashion to oligodendrocytes as they also produce myelin sheath for the axons of neurons, however, they are located in the PNS.

29. i. Myelination in PNS The plasma membrane of these Schwann cells spirals around the axons of neurons to form the fatty insulation that is required for faster transmission of electrical signals. Also, each Schwann cell form a single  myelin sheath  around an axon, whereas oligodendrocytes form myelin sheaths for multiple surrounding axons. Schwann cells - Function

30. Schwann cells - Function ii. Nerve regeneration. In addition to insulating axons, Schwann cells give response to axon damage within the PNS as they can help in regenerating these damaged axons.

31. Schwann cells - Function iii. Remove cellular debris by phagocytosis. When any type of injury occurs, the Schwann cells are sent to the injury site to remove the dead cells. The Schwann cells also have the capability to occupy the original space of the neurons and regenerate the fibers in such a way that they are able to return to their original target sites.

32. Satellite cells Satellite cells are the glial cells present on the exterior surface of PNS neurons.

33. Satellite cells - Function Provide physical support to the PNS neurons Help in regulation of chemical environment of ECF around the PNS neurons. provide nutrient support and protection to neurons in PNS. These cells also absorb harmful toxins so that they do not damage the neurons, as well as detecting and responding to injury and disease in the same way that microglia do.

34. Reflex Activity

35. when hand is placed on a hot object, it is withdrawn immediately. When a bright light is thrown into the eyes, eyelids are closed and pupil is constricted to prevent the damage of retina by entrance of excessive light into the eyes. Introduction

36. Reflex activity is the response to a peripheral nervous stimulation that occurs without our consciousness. It is a type of protective mechanism and it protects the body from irreparable damages. DEFINITION

37. R eflex A rc Reflex arc is the anatomical nervous pathway for a reflex action. A simple reflex arc includes five components . 1. Receptor 2. Afferent Nerv e 3. Center 4. Efferent nerve 5. Effector organ.

38. 1. Receptor Receptor is the end organ, which receives the stimulus. When receptor is stimulated, impulses are generated in afferent nerve. 2. Afferent Nerve Afferent or sensory nerve transmits sensory impulses from the receptor to center. R eflex A rc

39. 3. Center Center receives the sensory impulses via afferent nerve fibers and in turn, it generates appropriate motor impulses. Center is located in the brain or spinal cord. 4. Efferent Nerve Efferent or motor nerve transmits motor impulses from the center to the effector organ. R eflex A rc

40. 5. Effector Organ Effector organ is the structure such as muscle or gland where the activity occurs in response to stimulus. Afferent and efferent nerve fibers may be connected directly to the center . In some places, one or more neurons are interposed between these nerve fibers and the center . Such neurons are called connector neurons or internuncial neurons or interneurons. R eflex A rc

41. C lassification O f R eflexes 1. I nborn or acquired 2. A natomical classification 3. P hysiological classification 4. Nu mber of synapse 5. V isceral or S omatic 6. C linical basis .

42. 1. D epending upon whether I nborn or A cquired R eflexes

43. 1. I nborn R eflexes(Natural or Unconditional) W hich are present since the time of birth, hence the name inborn reflexes. No t require d any previous learning, training or conditioning. e.g. is the secretion of saliva when a drop of honey is kept in the mouth of a newborn baby for the first time.

44. These reflexes are not inborn but, acquired after birth (developed after conditioning or training) Such reflexes need previous learning, training or conditioning. Example is the secretion of saliva by sight, smell, thought or hearing of a known edible substance. 2 . Acquired R eflexes ( Conditional)

45. 2. D epending upon situation of center (Anatomical classification)

46. i. Cerebellar Reflexes - center in cerebellum. ii. Cortical Reflexes - center in cerebral cortex. iii. Midbrain Reflexes - center in midbrain. iv. Bulbar or Medullary Reflexes - center in medulla oblongata. v. Spinal Reflexes - center in the spinal cord . 2. D epending upon situation of center

47. i. Cerebellar Reflexes - the reflexes which have their center in cerebellum. ii. Cortical Reflexes - the reflexes that have their center in cerebral cortex. 2. D epending upon situation of center

48. iii. Midbrain Reflexes - the reflexes which have their center in midbrain. iv. Bulbar or Medullary Reflexes - are the reflexes which have their center in medulla oblongata. v. Spinal Reflexes - Reflexes having their center in the spinal cord are called spinal reflexes 2. D epending upon situation of center

49. 3. D epending upon functional significance (Physiological classification)

50. i. Protective Reflexes or Flexor Reflexes ii. Antigravity Reflexes or Extensor Reflexes 3. D epending upon functional significance

51. These reflexes protect the body from nociceptic (harmful) stimuli. These reflexes are also called withdrawal reflexes or flexor reflexes. Protective reflexes involve flexion at different joints hence the name flexor reflexes. i. Protective Reflexes or Flexor Reflexes

52. These reflexes protect the body against gravitational force. These reflexes are also called the extensor reflexes because, the extensor muscles contract during these reflexes resulting in extension at joints. i. Antigravity Reflexes or extensor Reflexes

53. 4. D epending upon number of synapses

54. i. Monosynaptic Reflexes ii. Polysynaptic Reflexes 4. D epending upon number of synapses

55. Reflexes having only one synapse in the reflex arc are called monosynaptic reflexes. Stretch reflex is the best example for monosynaptic reflex and it is elicited due to the stimulation of muscle spindle. i. Monosynaptic Reflexes

56. Reflexes having more than one synapse in the reflex arc are called polysynaptic reflexes. Flexor reflexes (withdrawal reflexes) are the polysynaptic reflexes. ii. Polysynaptic Reflexes

57. 5. D epending upon whether Somatic or Visceral reflexes

58. i. Somatic Reflexes ii. Visceral or Autonomic Reflexes 5. D epending upon whether Somatic or Visceral reflexes

59. Somatic reflexes are the reflexes, for which the reflex arc is formed by somatic nerve fibers. These reflexes involve the participation of skeletal muscles. And there may be flexion or extension at different joints during these reflexes. i. Somatic Reflexes

60. Visceral or autonomic reflexes are the reflexes, for which at least a part of reflex arc is formed by autonomic nerve fibers. These reflexes involve participation of smooth muscle or cardiac muscle. Visceral reflexes include pupillary reflexes, gastrointestinal reflexes, cardiovascular reflexes, respiratory reflexes, etc. Some reflexes like swallowing, coughing or vomiting are considered as visceral reflexes. ii. Visceral Reflexes

61. 6. D epending upon clinical basis

62. Depending upon the clinical basis, reflexes are classified into four types: i. Superficial reflexes ii. Deep reflexes iii. Visceral reflexes iv. Pathological reflexes. 6. D epending upon clinical basis

63. Superficial reflexes are the reflexes, which are elicited from the surface of the body. Superficial reflexes are of two types: a) Mucus membrane reflexes. b) Skin reflexes. i. Superficial reflexes

64. a) MUCOUS MEMBRANE REFLEXES Mucous membrane reflexes arise from the mucus membrane. b) CUTANEOUS REFLEXES OR SKIN REFLEXES Cutaneous reflexes are elicited from skin by the stimulation of cutaneous receptors. i. Superficial reflexes

65. DEEP REFLEXES Deep reflexes are elicited from deeper structures beneath the skin like tendon. These reflexes are otherwise known as tendon reflexes. ii. Deep reflexes

66. Visceral reflexes are the reflexes arising from pupil and visceral organs. Following are few examples of visceral reflexes: 1. Pupillary reflexes 2. Swallowing reflex iii. Visceral reflexes

67. Pathological reflexes are the reflexes that are elicited only in pathological conditions. Few pathological reflexes are: 1. Babinski sign 2. Clonus 3. Pendular movements. iv. Pathological reflexes

68. It is named after the discoverer Joseph Babinski. In normal plantar reflex, a gentle scratch over the outer edge of the sole of foot causes plantar flexion and adduction of all toes. But in Babinski sign, there is dorsiflexion of great toe and fanning of other toes. When Babinski reflex is present - Babinski positive sign. When it is negative - Babinski negative sign. Conditions when Babinski sign is present - Upper motor neuron lesion. Physiological conditions - infancy (because of non-myelination of pyramidal tracts.) Babinski sign (Abnormal plantar reflex)

69. It is named after the discoverer Joseph Babinski. In normal plantar reflex, a gentle scratch over the outer edge of the sole of foot causes plantar flexion and adduction of all toes. But in Babinski sign, there is dorsiflexion of great toe and fanning of other toes. When Babinski reflex is present - Babinski positive sign. When it is negative - Babinski negative sign. Conditions when Babinski sign is present - U pper motor neuron lesion. Babinski sign (Abnormal plantar reflex)

70. Clonus – Clonus is a series of rapid and repeated involuntary jerky movements, which occur while eliciting a deep reflex.

71. Pendular movements are the slow oscillatory movements (instead of brisk movements) that are developed while eliciting a tendon jerk. Very commonly seen in patients affected by cerebellar lesion, while eliciting the knee jerk or patellar tendon reflex.