General principle of nervous system

1. General principle of nervous system • Nervous system • Multi-tasking unit in the body • Thinking • Regulation of actions

2. General design • Central nervous system neuron • Basic functional unit • 100 billion units • Signals received by synapses • Located in neural dentrites and cell bodies • Few hundreds to 200,000 synaptic connection

3. General design • Central nervous system neuron • Outgoing signals • Axon (branched) • Special feature • Signals move forward only • Signals travel in a specific direction for performing specific function

4. Sensory receptors • Initiation of nervous system activity • Sensory experience • Immediate reaction • Generation of memory

5. Somatic sensory system • Sensory information from the entire body surface and deep tissues • Information enters CNS via the peripheral nervous system

6. Somatic sensory system • Information conducted into multiple sensory areas • The spinal cord (all level) • The reticular substance of the lower brain • Thalamus • Celebellum • Cerebral cortex

7. Motor parts of nervous system • Motor functions of the nervous system • Skeletal muscle contraction • Smooth muscle contraction • Activity of endocrine and exocrine glands • Effectors • Anatomical structures whose functions are under neural control

9. Skeletal motor system • Autonomic motor system • Smooth muscles • Glands

10. Level of control • The spinal cord (all level) • The reticular substance of the lower brain • Thalamus • Celebellum • Cerebral cortex

11. Specific role for specific level of control • Lower level (lower brain and spinal cord) • Autonomic • Higher level • Thought process • Deliberate movement

12. Integrative function • Processing incoming information • Generation of appropriate mental and motor responses • Brain • Discards > 99% of all sensory information • Some relegated to subconscious • Channels information to proper integrative and motor region of the brain • Generation of appropriate responses

13. Role of synapses • Direct pathway of nerve impulses • Spreading of the signals throughout the nervous system • Very complex • Degree of difficulty in passing the impulses • Input from other areas in the nervous system • Facilitatory • Inhibitory • Selective blocking and passing of impulses • Selective amplification and channeling of the signals

14. Memory • Very small amount of input • Immediate responses • Larger portion • Stored for future motor activity and thought process • Majority in cerebral cortex but some in the lower brain

15. Role of synapses • Increased ability to pass the particular type of signal • Facilitation • Subsequent adaptation of brain to the particular signal • Repeated exposure and passing through the synapses • Generation of the signal within the brain and movement of the signal through synapses in the absence of input

16. Importance of memory • Reference point for the action • Comparison of new input with previously stored information • Generation of new memory or appropriate reaction

17. Major level of CNS function • Spinal cord • Lower brain/subcortical • Higher brain/cortical

18. Spinal cord • Neural circuits in the cord • Walking movements • Withdrawal reflex • Support reflex against gravity • Reflex regulating local blood vessel, digestive tract movement, or urinary excretion • Information from upper level of control • Commanding the cord center to perform specific function

19. Lower brain/subcortical • Primitive parts of the brain • Subconscious activities • Arterial pressure • Respiration • Equilibrium • Feeding reflex • Many emotional responses

20. Higher brain/cortical • Memory storehouse • Function in association with lower centers • Precise regulation of functions dictated by the lower center • Thought process • Use of information from lower centers to trigger activation of stored information

21. CNS synapses • Information • Action potential/nerve impulses • Each impulse • Blocked in its transmission from one neuron to the next • Changed from a single impulse to multiple impulses • Combined with other impulses to become more complex/intricate impulses

22. Types of synapses • Two types • Chemical • Electrical

23. Types of synapses • Electrical synapses • Conduct electricity from one cell to the next • Direct open fluid channels • Gap junctions • Very few in the CNS • Transmission of information • Either direction

24. Types of synapses • Chemical synapses • The majority of synapses used in signal transmission within the CNS • Neurotransmitters • One-way conduct • Chemical synapses • Signals transmission in only one direction • Neuron that secretes transmitter (presynaptic) • Neuron that receives transmitter (postsynaptic)

25. Importance of one-way conduction • Movement of signal toward specific goal • Focused transmission of signals from peripheral neurons toward the specific areas of the CNS

26. Synapses anatomy • Components of anterior motor neuron • Soma • Main body • Axon • Dendrites • Projections of soma • Presynaptic terminals • Cover surface of dendrites • End of nerve fibrils

27. Neurons in the brain • Different from anterior motor neuron • Size of the cell • Dendrite length, number, and size • Length and size of axon • Number of presynaptic terminals

28. Presynaptic terminal • Excitatory/inhibitory • Structures • Synaptic cleft • Transmitter vesicles • Neurotransmitters • Mitochondria • ATP production • Receptor proteins

29. Role of Ca ion • Presynaptic membrane • Large concentrations of voltage-gated Ca channels • Arrival of action potential • Large influx of Ca ions via opening of Ca channels • Release of neurotransmitters • Unclear mechanism

31. Receptor proteins • Surface of the postsynaptic neuron membrane • Binding site (extracellular) • Ionophore component (intracellular) • Ion channel • Secondary messenger activator

32. Ion channels • Cation channels • Activated by excitatory neurotransmitters • Prevents influx of anions (Cl) • Negatively charged canal • Anion channels • Activated by inhibitory neurotransmitters • Prevent influx of cations • Smaller diameter

33. Secondary messenger system • Prolonged excitation/inhibition • Changes in long-term response characteristics of the neuron • G-protein coupled receptors • Most common • Opening of the ion channels • Activation of cAMP/cGMP • Activation of intracellular enzymes • Activation of gene transcription

34. Excitation vs. inhibition • Additional dimension to nervous function • Excitation • Opening of Na channels • Increased membrane potential • Depressed conduction • K channels and/or Cl channels • Decreased diffusion of cations/anions • Increased positive charge • Various changes in the intracellular metabolism

35. Excitation vs. inhibition • Inhibition • Opening of Cl channels • Increased K conductance out of the neuron • Inhibition of cellular metabolism

36. Neurotransmitters • Two classes • Small-molecule, rapidly acting transmitters • Cause most acute responses • Acetylcholine, norepinephrine, dopamine, glycine, GABA, glutamine, serotonin, nitric oxide • Neuropeptides • Slow acting molecules • Larger in size • Prolonged action that results in long-term changes of neurons

37. Electrical events • Resting potential • Around -65 mV • Important for positive and negative control • Sensitive to changes • Charges evenly distributed throughout soma • Highly conductive intracellular fluid • Large diameter

38. Excitation • Transmitters • Increased Na permeabiity • Large influx of Na ions • Increased membrane potential • Excitatory post synaptic potential (EPSP) • -65 mV to -45 mV • Generation of action potential • Excitation requires simultaneous discharge of many terminals (Summation)

39. Inhibition • Inhibitory transmitters • Opening of chloride channels • Influx of Cl ions into the inside • Opening of K channels • Removal of K from inside • Hyperpolarization (-70 mV) • Inhibitory postsynaptic potential (IPSP)

40. Inhibition • Presynaptic inhibition • Release of inhibitory neurotransmitters • Opening of anion channels on the terminal fibril • Inhibition of synaptic transmission

41. Summation • Spatial summation • Generation of ESPS • Cannot be done by a single presynaptic terminal (0.5 to 1 mV ESPS) • Simultaneous stimulation of many terminals • Summation of ESPS to reach threshold of firing • Spatial Summation

42. Summation • Temporal summation • Release of transmitters • Opening of postsynaptic channels for a very short period • A second opening of the channels • Increased ESPS • Addition of successive rapid discharge • Summation of successive ESPS

43. Facilitation of neurons • Summated postsynaptic potential • Not enough for threshold • Neurons become facilitated • Membrane potential reaches near the threshold but not enough for firing • Quicker response to the stimuli

44. Role of dendrites • Signal reception • Summation of signals from many separate presynaptic nerve fibers • Excitation triggered by the signals from dendrites • Electronic conduction • No action potential conduction because of low voltage-gated Na channels and high threshold

45. Decremental conduction • Location of presynaptic terminals • Closer to the soma, greater the negative membrane potential becomes • Loss of ESPS from dendrites before reaching the soma • Permeable to K and Cl • Further the excitatory synapses are, greater the amount of decrease in ESPS