General physiology cns 2013


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General physiology cns 2013

  1. 1. GENERAL PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM • Excitation in CNS • The reflex principle of CNS activity • General physiology of receptors
  2. 2. Both somatic and autonomic nervous systems have two divisions: • Sensory division (for collecting information) • Motor division (for executing the action) 2 The nervous system can be divided into two main parts: • Somatic (skeletal muscles) • Autonomic (visceral organs and vessels)
  3. 3. The main function of the nervous system is integration of the activity of all systems, organs and tissues It provide: 1. Regulation of movement 2. Maintenance of homeostasis 3. Individual adaptation of the organism to the external environment 4. Intelligence and mental activity 3
  4. 4. Organs and tissues effect of CNS 1. Functional (stimulation or inhibition) 2. Trophic (affect the metabolism of innervate organs for normal growth and development) 3. Vasomotor (vasoconstriction and vasodilatation) 4
  5. 5.  The principal and specific manifestation of the activity of the central nervous system is THE REFLEX  A REFLEX - is a regular reaction of the organism to a change in it’s external or internal environment, effected through the CNS in response to the stimulation of receptors 5
  6. 6. Reflex arcs include: 1. Receptor 2. Afferent neuron 3. Interneuron 4. Efferent neuron 5. Effector 2 1 3 4 5 6
  7. 7. • In a simple reflex arc there are two neurons and just one synapse. Such reflexes are therefore known as monosynaptic reflexes. – Other reflex arcs have one or more neurons interposed between the afferent and efferent neurons. These neurons are called interneurons • If there is one interneuron, the reflex arc will have two synaptic relays and the reflex is called a disynaptic reflex 7
  8. 8. Reflex rings include: 1. Receptor 2. Afferent neuron 3. Interneuron 4. Efferent neuron 5. Effector 6. Feedback 2 1 3 4 5 8 6
  9. 9. Classifications of receptors • By location: – Internal = interoceptors (visceroceptors, vestibuloceptors and proprioceptors) – External = exteroceptors (signal of the outside world ) 9 • By the physical nature of the stimuli: -phonoreceptors -photoreceptors -mechanoreceptors -thermoreceptors -chemoreceptors -baroreceptors
  10. 10. 10 • By sensitivity: – High-sensitive – Low-sensitive • By detection of the stimuli: – Mono-modal – Poly-modal • By adaptation: – Rapidly adapting( - fall with time) – Slowly adapting=non-adapting ( - const)
  11. 11. By mechanism of activation: 11
  12. 12. Functions of receptors • Detection (present or not?) • Object-quality discrimination (poor or strong?) • Sensory transduction (The process of transforming some property of the external or internal environment into nerve impulses) • Coding of stimulus intensity and duration – frequency of nerve impulses – pattern of nerve impulses 12
  13. 13. Adaptation and coding 13
  14. 14. Mechanism of excitation of the Primary receptor 1. stimulation of receptors' membrane 2. generation of receptors' potential - RP (a local response) 3. elecrotonic propagation of RP to an axon (the same cell) 4. generation of AP 5. AP propagate along afferent nerve 14
  15. 15. 15 Mechanism of excitation of the Secondary receptor. 1. Stimulation of receptors' membrane 2. Generation of receptors' potential - RP (a local response)
  16. 16. 3. Elecrotonic propagation of RP to presynaptic membrane (the same cell) 4. Release of chemical transmitter to synaptic cleft 5. Activation of postsynaptic membrane – generating potential (GP - a local response in another cell) 6. Elecrotonic propagation of GP to an axon 7. Generation of AP 8. AP propagate along afferent nerve 16
  17. 17. Structure of neuron 17
  18. 18. 1. Neuronal reception (receive information) 2. Integration of signals (excitation end inhibition) 3. Conduction 4. Regulation of effectors 5. Trophic 6. Neurosecretory 7. Memory 18 Functions of neuron
  19. 19. Classification of neurons By number of branches 19
  20. 20. 1. By form 2. By function (sensory, motor, vegetative, neu rosecrethory) 3. By location in NS 4. By location in reflex arc (afferent, inter-, efferent) 6. By effect (excitatory, inhibitory) 7. By form of activity (background and silent) 20
  21. 21. Functions of Glial cells 1. Ion buffer(astrocite) 2. Intake neurotransmitters 3. Isolation (olygodenrocyte, Sc hwanny-cells) 4. Protective (microglia) 5. Basic 6. Trophic 7. Transport 8. Regeneration of CNS and ontogenesis 21
  22. 22. Classification of synapses 1. By location (axo- somatyc, axo- dendrityc, axo-axonic) 2. By effect (excitatory and inhibitory) 3. By basis of process (electrical, chemical and electro-chemical) 4. By transmitter 22
  23. 23. Groups of neurotransmitters (by chemical building) 1. Esters (acetylcholine) 2. Monoamines (norepinephrine, dopamine, serotonin) 3. Amino acids (GABA (γ-Aminobutyric acid), glutamate) 4. Purines (adenosine, ATP) 5. Peptides (enkephalins, substance P, VIP) 6. Inorganic gases (NO) 23
  24. 24. Electrical (a) and chemical (b) synapses 24a b
  25. 25. Excitatory postsynaptic potentials (EPSP) 25
  26. 26. Inhibitory postsynaptic potential (IPSP) 26
  27. 27. Inhibition in CNS – it's active process, witch result is easing of excitation or its termination. Functions of inhibition: -Coordination -Protection Inhibition is always consequence of excitation.
  28. 28. Inhibition in CNS Inhibition following excitation Pessimal Presynaptic •Reciprocal •Recurrent •Lateral •Direct Primary Secondary Postsynaptic
  29. 29. Primary Inhibitions Presynaptic Postsynaptic Direct IPSP EPSP
  30. 30. Recurrent Lateral Reciprocal Primary Inhibitions
  31. 31. Secondary Inhibitions • Inhibition following excitation • Pessimal (νst > νmax)
  32. 32. Secondary Inhibitions •The activity of a nerve cell can be inhibited without the participation of special inhibitory structures. •Pessimal inhibition develops in the excitatory synapses as a result of strong depolarization of the postsynaptic membrane under the influence of nerve impulses arriving too frequently. •Inhibition following excitation - a discrete type of inhibition is that developing in a nerve cell after termination of excitation and which appears when excitation is followed by strong after- hyperpolarization of the cell membrane.
  33. 33. 34 Neural center is group of neurons acting together in the performance of a definite reflex or in regulation of a particular function.
  34. 34. • The nervous center in the broad sense of the word - groups of neurons, laying on the different floors CNS and incorporated not morphologically, but it is functionally for regulation of any strictly certain function. • The nervous center in the narrow sense of the word - group of neurons that are incorporated for performance of one function or a reflex and are located in the certain site of a brain.
  35. 35. Properties of the nervous centers are caused by structure and function of the synapses 1. One-way conduction. 2. Delayed conduction. (0,3-0,8 ms) • -Secretion of the mediator • -Diffusion of the mediator • -Generation of postsynaptic potential
  36. 36. 3. Summation of excitation. а). Special summation - the summing of the synaptic inputs from different neurons upon the dendrites and cell body of one neuron. 37
  37. 37. b). Temporal summation - occurs when one presynaptic neuron can increase its effect on one postsynaptic neuron by firing repeated. 38
  38. 38. 4. Transformation of rhythm – it’s change of action potentials frequency after their passage through synapse or neural center. Biological sense of transformation is: 1) amplification of the important signal for an organism; 2) reduction of a insignificant signal for an organism; 3) the coordinated activity of two different neurons in a reflex arch.
  39. 39. 5. Reflex after-action - continuation of reflex after termination of afferent stimulation. 1. After-depolarization of neurons 2. Reverberatory circuit 3. Long-term postsynaptic potential
  40. 40. 6. Long term potenciation (posttetanic potencyation) - amplification of reflex reaction after rhythmic and often irritation of the nervous center. The reason - accumulation in presynapse calcium ions.
  41. 41. 7. Occlusion The phenomenon occlusion will be, that the quantity of excited neurons at simultaneous irritation afferent inputs of both nervous centers appears less, than the arithmetic sum of excited neurons at separate irritation of everyone afferent an input separately. The phenomenon occlusion results in decrease in force of expected total response. EPEP
  42. 42. 8. Simplification EPSP+ EPSP=AP EPSP EPSP The simultaneous irritation afferent inputs cause such response that appears more than the arithmetic sum of reactions at separate irritation afferent inputs. The phenomenon of the central simplification is characterized by opposite effect of occlusion.
  43. 43. 44 • The afferent impulses from peripheral; • Various humoral stimulants (hormones, C02, etc.); The are impulses continuously sent from nerve centers to the periphery maintain the tone of the skeletal muscles and of the smooth muscles of the intestine, and vascular tone. 9. Reflex tone - constant excitation of the nerve centers.
  44. 44. 45 • The fatigue of the nervous centers is connected to fatigue of interneuronal synapses. The reasons of fatigue is: • Sharp fall in the reserves of synthesized mediator in the nerve ending, • reduction in synapse of energy reserve (such as ATP), • diminished sensitivity of the postsynaptic membrane to the mediator (it is called habituation or desensitization or accommodation). 10. Fatigue of the nervous centers.
  45. 45. 46 • The cortical cells of the hemispheres are especially badly damaged by a cessation of blood supply; within as little as 5 or 6 minutes they undergo irreversible changes and die. •Nerve cells and synapses possess a selective sensitivity to certain poisons, which are therefore known as nerve poisons (strychnine, morphine, amphetamine, beptazol, narc otic drugs (ether, chloroform, barbiturates), alcohol, and many others). 11. High sensitivity surplus C02, lack 02 and poisons.
  46. 46. 47 Coordination is an association of all actions of organism in a single whole, association neurons in the uniform functional ensemble deciding specific target. Allocate the following principles of coordination: 1. divergence and convergences 2. feedback connection 3. irradiation excitation 4. Induction 5. reciprocal innervation 6. dominants 7. plasticity of the nervous centers 8. subordinations 9. common final way PRINCIPLES OF COORDINATION IN CNS
  47. 47. Relaying of signals thought neuronal pools. Divergence and Convergence
  48. 48. 1. Receptor; 2. Afferent neuron; 3. Interneuron; 4. Efferent neuron; 5. Effector. 6. Feedback 2 1 3 4 5 49 6 Feedback.
  49. 49. 50 Irradiation of excitation. • At strong and long irritation of the nervous center the pulses acting in CNS, raise not only the given reflex center, but also other centers. •Irradiation is suppressed inhibitory neurons. •They interfere to irradiation of excitation and provide hit of impulses in strictly certain nervous center.
  50. 50. 51 Principle of an induction. These are contrast changes of excitability of the nervous center. • If in the nervous center inhibition develops after excitation is a negative consecutive induction. • If excitation develops after inhibition cause a positive consecutive induction.
  51. 51. Reciprocal innervations. Examples: antagonistic mutual relations between motoneurons of muscles flexor and extensor, between ispiratory and expiratory neurons the respiratory center, and other.
  52. 52. 53 Principle of a dominant. • The dominant center refers to temporarily prevailing nervous center of hypererethism in CNS. • The dominant center subordinates to itself all work of a brain and inhibits other centers. It possesses a next of properties: 1. At this moment excitability and its liability neurons raises. 2. Intensity of its excitation amplifies even the weakest irritations because of high ability to sum EPSP. 3. It is very proof, it is difficult for inhibition. 4. It is capable to inhibiting other centers. 5. It is capable to draw to itself excitation of other nervous centers.
  53. 53. 54 Principle of plasticity of the nervous centers • At damage of the separate centers of a brain their function can pass to other structures of a brain. • Process of compensation of the lost functions is carried out at obligatory participation of a hemisphere.
  54. 54. 55 Principle of subordination (cephalisation) •In CNS hierarchical mutual relations take place: the underlaying department submits to instructions of an overlying department. •Evolution of nervous system has consisted in moving function of regulation from underlaying in again educated overlying departments of CNS. It is refers to cephalisation.
  55. 55. 56