Neuron structure and functions by Dr. Pandian M, Dept of Physiology, DYPMCKOP this ppt for all MBBS, BDS, BPTH and other PRE & Para Medicos, Bio medicos

PHY3.1 �1. Describe the structure and functions of a neuron and neuroglia; ��2. Discuss Nerve Growth Factor & other growth factors/cytokines

1. NEURON Pandian M. Dept. of Physiology DYPMCKOP

2. PHY3.1 1. Describe the structure and functions of a neuron and neuroglia; 2. Discuss Nerve Growth Factor & other growth factors/cytokines

3. 3.1.1 Describe the different parts of neuron 3.1.2 Draw a neat and labeled diagram of neuron 3.1.3 Describe the functions of different parts of neuron 3.1.4 Classify the different types of neuron 3.1.5 Enlist different types of microglia 3.1.6 State the functions of different types of neuroglia 3.1.7 Name the factors promoting neuronal growth 3.1.8 Discuss the neurotrophins & other growth factors

4. NEURON Neuron, or the nerve cell, is the structural and functional Unit of the nervous system. Neuron is similar to any other cell in the body, having nucleus and all the organelles in cytoplasm. It is made up of countless neurons. The total Estimated neurons in the human brain is more than 10 12 . These connections that the body is made aware of changes in the environment , or of those inside the Body itself

5. Fig. 2-5, p. 32

6. Structure of the Neurons The membrane refers to the structure that separates the inside of the cell from the outside environment. The nucleus refers to the structure that contains the chromosomes. The mitochondria are the strucures that perform metabolic activities and provides energy that the cells requires. Ribosomes are the sites at which the cell synthesizes new protein molecules

7. Cell body The cell body of a neuron is also called the soma or perikaryon It may be round, stellate, pyramidal or fusiform in shape. Like any other cell mass of cytoplasm surrounded by a cell Membrane. The cell body contains a large nucleus with one or two nucleoli but there is no centrosome

8. Nissl granules/bodies These are basophilic granules, it present in the dendrites, absent from the axon hillock and the axon. Bodies - Composed of rough surfaced endoplasmic reticulum (ER). The presence of abundant granular ER is an indication of the high level of protein synthesis in neurons.

9. The proteins are needed for maintenance, repair, production of neurotransmitters and enzymes . These bodies disintegrate into Fine dust and which finally disappears ( chromatolysis ) on Fatigue, due to the effect of certain poisons and on sectioning of the axon.

10. NISSL GRANULES continue Nissle body disappears when When soma is anoxic Fatique Ischaemia Regeneration/degeneration state

11. Neurofibrillae :- These consist of microfilaments and microtubules. In certain degenerative disease like alzheimer’s disease, the neurofilament protein gets altered, Resulting in the formation of neurofibrillary tangles. Pigment granules are seen in some neurons . E.g - Neuromelanin is present in the neurons of substantia nigra . Aging neurons contain lipofuscin pigment.

12. Process of myelinogenesis

13. Cross sectional comparison of myelinated and unmyelinated nerve

14. CLASSIFICATION OF NEURON Neurons are classified by three different methods. A. Depending upon the number of poles B. Depending upon the function C. Depending upon the length of axon .

15. DEPENDING UPON THE NUMBER OF POLES Based on the number of poles from which the nerve Fibers arise, neurons are divided into three types: 1. Unipolar neurons 2. Bipolar neurons 3. Multipolar neurons.

16. 1. Unipolar neurons Unipolar neurons are the neurons that have only one Pole. From a single pole, both axon and dendrite arise.

17. 2. Bipolar neurons Neurons with two poles are known as bipolar neurons. Axon arises from one pole and dendrites arise from the other pole.

18. 3. Multipolar neurons Multipolar neurons are the neurons which have many poles. One of the poles gives rise to axon and all other poles give rise to dendrites.

19. II. Depending upon the function Depending upon the functions the neurons are of two Types—motor and sensory. 1. Motor neurons, also known as efferent nerve cells, Carry the motor impulses from the CNS to the peripheral Effector organs like muscles, glands and blood Vessels. These neurons have very long axon and short Dendrites.

20. AXOPLASMIC TRANSPORT

21. II. Depending upon the function 2. Sensory neurons , also known as afferent nerve cells, carry the sensory impulses from the periphery to the CNS. These neurons have short axon and long dendrites .

22. Functional Classes of Neurons I. Afferent neurons A. Transmit information into the CN system from receptors at their peripheral endings B. Cell body and the long peripheral process of the axon are in the PN system ; only the short central process of the axon enters the central nervous system C. Most have no dendrites (do not receive inputs from other Neurons)

23. II. Efferent neurons A. Transmit information out of the central nervous system to Effector cells, particularly muscles, glands, or other neurons B. Cell body, dendrites, and a small segment of the axon are in the central nervous system; most of the axon is in the Peripheral nervous system

24. III. Interneurons A. Function as integrators and signal changers B. Integrate groups of afferent and efferent neurons into Reflex circuits C. Lie entirely within the central nervous system D. Account for 99 percent of all neurons

25. METABOLISM AND HEAT PRODUCTION IN THE NERVE FIBRES Like other cells, the metabolic activities occur in the nerve fibres . The metabolism in nerve fibres occurs at a very low level. About 70% of the total Energy required is used to maintain polarization of the Membrane by the action of Na+–K+ ATPase pump . The Energy is supplied mainly by combustion of sugars and Phospholipids. During nerve activity, the ATP and Creat . P Breakdown, i.e. Undergo hydrolysis and supply energy for the propagation of the nerve impulse.

26. Heat production in the nerve fibres In a nerve fibre , heat is produced in three phases: 1. Resting heat is the amount of heat produced during the Inactive stage. 2. Initial heat is the amount of heat produced during AP (stage of activity). It is about 10% of the total heat produced, results from anaerobic metabolic activity due to breakdown of ATP and CP

27. 3. Delayed or recovery heat is produced during the recovery phase which follows the phase of activity. The energy is produced by aerobic metabolic activities and is about 30 times the initial heat. The energy produced during the recovery stage is used for resynthesis of ATP and CP and as such for restoring the normal Excitability of the nerve fibre .

28. III. Depending upon the length of axon Depending upon the length of axon, neurons are divided Into two types: 1. Golgi type I neurons 2. Golgi type II neurons .

29. 1. Golgi type I neurons Golgi type I neurons have long axons. Cell body of these Neurons is in different parts of central nervous system and their axons reach the remote peripheral organs. 2. Golgi type II neurons Neurons of this type have short axons. These neurons are present in cerebral cortex and spinal cord.

30. Functions of Neuron

31. ZONES OF THE NEURON From the functional point each neuron is divided into four Zones 1. Receptor zone (dendritic zone) 2. Site of origin of conducted impulse 3. Zone of all or none transmission 4. Zone of secretion of transmitter (nerve endings).

32. Receptor zone (dendritic zone) is the region, where local Potential changes are generated by integration of the Synaptic connections. 2. Site of origin of conducted impulse is the site, where Propagated AP are generated . In case of Spinal motor neuron , initial segment and in cutaneous Sensory neurons first node of ranvier is the site of origin of conducted impulses.

33. One-way propagation of an action potential. For simplicity, potentials are shown only on the upper membrane, local currents are shown only on the inside of the membrane, & repolarizing currents are not shown. Action potential is initiated in region 1, and local currents depolarize region 2.

34. Action potential in region 2 generates local currents; region 3 is depolarized toward threshold, but region 1 is refractory.

35. Action potential in region 3 generates local currents, but region 2 is refractory.

36. 3. Zone of all or none transmission in the neuron is the Axon. 4. Zone of secretion of transmitter (nerve endings). The Propagated impulses (action potential) to nerve endings Cause the release of neurotransmitter .

37. Functional organization of neurons

38. NEUROGLIA Neuroglia or the glial cells are the supporting cells present Within the brain and spinal cord.

39. Neuroglial cells Glia are the other major component of the nervous system and include the following: Astrocytes helps synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon. Microglia - remove waste material and other microorganisms that could prove harmful to the neuron.

40. TYPES OF GLIA Oligdendrocytes & schwann cells - build the myelin sheath that surrounds the axon of some neurons. Radial glia - guide the migration of neurons and the growth of their axons and dendrites during embryonic development.

41. Fig. 2-10, p. 35

42. Neurotrophins (NGF) Nerve growth factors Insulin like growth factors Platelet growth factor Fibroblast growth factor Brain derived growth factor Neurotrophins (NGF) 3,4, and 5 Glial cell derived neurotrophins

43. Contd …. First neurotrophins isolated Present in salivary gland ,plasma and other tissue Made up of 2 alpha, 2 beta and 2 gamma subunits Beta subunit similar to insulin Required for growth and maintains of neurons

44. How to remember the Cranial nerves ???? O ne O f O ur T rend T eacher A sked F or V ery G ood V an A t H ospital

45. Referred :- Text book of Medical Physiology Guyton, 12 th edition, Text book of Medical Physiology Indu khurana , Text book of Medical Physiology Vander’s Text book of Medical Physiology Sembulingam & LPR

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