Neural Physiology

1. Neural Physiology

2. Anatomical organization • One system • Two subdivisions • CNS • Peripheral

3. Anatomical organization • Central (CNS) • Brain • Spinal cord • Function • Integration of information • Generation of memory • Control of various systems • Mental activity

4. Anatomical organization • Peripheral • Sensory receptors • Detection of various sensations • Nerves • Conduits between sensory receptors and CNS • Ganglia • Cluster of nerve cells located outside of the spinal cord • Plexus • Network of neurons and axons located outside of the CNS

5. Anatomical organization • Nerves • Cranial • 12 pairs • Spinal • 31 pairs

6. Afferent and efferent nerves • Afferent/sensory • Transmission of signals from sensory receptors to the CNS • Entry route • Dorsal horn of the spinal cord • Efferent/motor • Transmission of information from the CNS to the organs • Motor neurons • Transmission routre • Ventral horn of the spinal cord

8. Autonomic nervous system (ANS) • Two divisions • Sympathetic • Parasympathetic • Enteric (not exactly a division of the ANS) • Regulation of the GI tract function • Plexuses

9. Neural tissue • Neural cell • Generation and reception of neural signal • Action potential • Glial cells • Support and protection

11. Types of neurons • Multipolar • Many dendrites • Single axon • Bipolar • Single dendrite • Single axon • Unipolar • No dendrite • Single axon

13. Glial cells within the CNS • Functions • Fluid secretion and composition maintenance • CSF by ependymal cells • Brain fluid by astrocytes • Formation of barrier • Blood-brain barrier by astrocytes • Response to inflammation • Reactive astrocytes • Microglia • Insulation of axon • Myelin sheath by origodendrocytes

14. Glial cells in the PNS • Schwann cells • Myelin sheath production • Satellite cells • Support and protection of the cell body

15. Myelination • Myelin sheath • Insulation of axon • Increased transmission speed • Saltatory conduction from one node of Ranvier to the next • Greater the thickness of sheath, faster the conduction

17. Nerve tissue organization • White matter • Bundles of myelinated axons • Neural tracts • Propagation of action potential from one area to the next • Neural cells and dendrites • Gray matter • Bundle of unmyelinated axons • Neural cells and dendrites • Integration and relaying of signals

18. Transmission of neural signal • Action potential • Exactly the same principle as the AP in the muscular system • Propagation • Across the entire length of the axon • One direction

19. Generation of action potential • Unmyelinated • Same as muscle • Myelinated • At node of Ranvier • Concentrated ion channels

20. Saltatory conduction

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22. Classification of nerve fiber • Basis • Functional specialization • Rapid transmission (motor neurons) = type A • Homeostasis/ANS = type B and type C (unmyelinated) • Diameter of axon • Myelination

23. Rate of action potential conduction • Myelination • Faster conduction • AP generated only at node of Ranvier • Effects of axon diameter • Larger the diameter, faster the conduction • Greater surface area for Na channels

24. Synapse • Junction between two cells • Communication • Nerve cells • Nerve cell and effector organs • Presynaptic • Send signals • Postsynaptic • Receive signals

25. Types • Electrical • Rare (retina) • Conduct signals via ion flow from one cell to the next • Connexon • Chemical • Common • Conduct signals via neurotransmitter

27. Steps of neural transmission • Arrival of action potential to the presynaptic terminal • Increased flow of Ca ions • Release of neurotransmitter • Increased intracellular Ca level • Binding of neurotransmitters to the Na channels a. Depolarization of postsynaptic membrane • Generation of local action potential • Propagation of action potential

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29. Neurotransmitters • Classes • Acetylchorine • Biogenic amines • Amino acids • Purines • Neuropeptides • Gases

30. Neurotransmitter action • Specific receptor for the specific neurotransmitter • Response • Stimulatory (AP generation) • Inhibitory (hyperpolarization) • Depends on types of receptors present on the cell

31. Regulation of neurotransmitter level • Rapid removal • Acetylchorinesterase • Removal of acetylchorine • Monoamine oxidase • Removal of norepinephrine

32. Neuromodulator • Influence generation of postsynaptic action potential • Presynaptic influence • Postsynaptic influence • Affects type of neurotransmitter being released

33. Excitatory vs. Inhibitory postsynaptic potential • Response of postsynaptic terminal to a neurotransmitter • Depolarization • Excitatory postsynaptic potential • Excitatory presynaptic neuron • Hyperpolarization • Inhibitory postsynaptic potential • Increased K or Cl permeability • Inhibitory presynaptic neuron

34. Presynaptic facilitation vs. inhibition • Anoaxonic synapses • Affects release of neurotransmitter • Facilitation • Increased release • Inhibition • Decreased release

36. Summation • Generation of action potential • One presynaptic AP is not enough • Summation • Temporal • Multiple AP from single presynaptic terminal • Facilitation for AP generation by the subsequent Aps • Spatial • AP from multiple axons

38. Generation of action potential • Excitatory vs. inhibitory stimulation • Depends on summation of stimulation by these fibers

39. Importance of synapses within the CNS • Integration of information • Sensory input must be strong enough to generate AP • If not, ignored • Large amount of information entering the CNS • Discarded

40. Neural pathway and circuit • Convergent • Activation/inhibition of neural activity by combining various information • Divergent • Simultaneous control of different system by a single neural input • Circulatory • Repeated stimulation/inhibition of the same pathway by a single neural input • Afterdischarge