CBNS 106 Review

1. CBNS 106 Review Lecture 2

2. Brain Cells • Neurons (100 billion) • Process information • Sense environmental changes • Communicate changes to other neurons • Command body response • Glia (10 times more) • Insulate, support and nourish neurons

3. Staining • Nissl Stain • Facilitates study of cytoarchitecture • Golgi Stain • Shows soma and neurites (dendrites and axon)

9. Different classes of neurons

10. Afferent – INFO  CNS

12. ASTROCYTES!!!

13. CBNS 106 Lecture 3

16. - Astrocytes buffer excess potassium, cycle it from ecs to bbb

17. CBNS 106 Review Lecture 4 and 5

18. Action Potential Actual Ideal

21. “Resting” Cell During AP

23. Action Potential Conduction The entry of positive charge during the action potential causes the membrane just ahead to depolarize to threshold Orthodromic conduction – action potentials conduct only in one direction Antidromic conduction – backward propagation Typical conduction velocity ~ 10 m/sec Action potentials last ~ 2 msec

24. Factors Influencing Conduction Velocity Spread of action potential along membrane • Dependent upon axon structure Path of the positive charge • Inside of the axon (faster) • Across the axonal membrane (slower) * If the axon is narrow and there are many open membrane pores then most of the current will flow out across the membrane. * If the axon is wide and there are few open membrane pores, then most of the current will flow down inside the axon * The farther the current goes down the axon, the farther ahead the action potential will depolarize the membrane and thus the faster the action potential.

25. Factors Influencing Conduction Velocity Saltatory Conduction – The propagation of an action potential down a myelinated axon Axonal excitability • Axonal diameter (bigger = faster) • Number of voltage-gated channels Myelin: Facilitates current flow • Myelinating cells – Schwann cells in the PNS – Oligodendroglia in CNS

26. CBNS 106 Review Lecture 6

27. Synaptic Transmission • The process of information transfer at a synapse • Direction of Flow • One direction, Neuron-to-Target Cell • 1st Neuron called Presynaptic Neuron • Target Cell called Postsynaptic Neuron • Two Types of synapses • Chemical • Electrical

28. Synaptic Transmission • Electrical Synapses: - They allow the direct transfer of ionic current from one cell to another - Gap junction - Cells are said to be “electrically coupled” • Flow of ions from cytoplasm to cytoplasm - Very fast transmission • Postsynaptic potentials (PSPs) - Synaptic integration: Several PSPs occurring simultaneously to excite a neuron (i.e.causes AP)

29. Synaptic Transmission Types of Synapses - Axodendritic (a) - Axosomatic (b) - Axoaxonic (c) - Asymmetrical membrane differentiations (a) - Symmetrical membrane differentiations (b)

30. Synaptic Transmission • Chemical Synapses: – Neurotransmitter, the chemical is used to transfer information from one cell to another - Most synaptic transmission in the mature human nervous system is chemical.

31. Synaptic Transmission Principles of Chemical Synaptic Transmission • Basic Steps – Neurotransmitter synthesis – Load neurotransmitter into synaptic vesicles – Neurotransmitter Release • Vesicles fuse to presynaptic terminal • Neurotransmitter spills into synaptic cleft – Binds to postsynaptic receptors – Biochemical/Electrical response elicited in postsynaptic cell – Removal of neurotransmitter from synaptic cleft

32. Synaptic Transmission Neurotransmitter Release – Exocytosis: Process by which vesicles release their contents; 60 microsec Mechanisms • Process of exocytosis stimulated by release of intracellular calcium, [Ca2+]i • Proteins alter conformation - activated • Vesicle membrane incorporated into presynaptic membrane • Neurotransmitter released • Vesicle membrane recovered by endocytosis

33. Neurotransmitter Recovery and Degradation – Diffusion: Away from the synapse – Reuptake: Neurotransmitter re-enters presynaptic axon terminal – Enzymatic destruction inside terminal cytosol or synaptic cleft – Desensitization: e.g., AChE cleaves Ach to inactive state

34. Neurotransmitters • Amino acids: Small organic molecules • e.g., Glutamate (Glu), Glycine (Gly), gammaaminobutyric acid (GABA) • Amines: Small organic molecules • e.g., Dopamine (DA), Acetylcholine (Ach), Norepinephrine (NE), Serotonin (5-HT) • Peptides: Short amino acid chains (i.e. proteins) stored in and released from secretory granules • e.g., Dynorphin, Enkephalins

35. PSP Generation • EPSP = excitatory postsynaptic potential – Transient postsynaptic membrane depolarization by presynaptic release of neurotransmitter • IPSP = inhibitory postsynaptic potential – Transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of neurotransmitter

36. Synaptic Integration • Process by which multiple synaptic potentials combine within one postsynaptic neuron • Allows for neurons to perform sophisticated computations • Integration: PSPs added together • Spatial: PSPs generated simultaneously in different spaces • Temporal: PSPs generated at same synapse in rapid succession

37. Synaptic Integration • Synaptic vesicles: Elementary units of synaptic transmission • Quantum: An indivisible unit • Miniature postsynaptic potential (“mini”) • Quantal analysis: Used to determine number of vesicles that release during neurotransmission • Neuromuscular junction: About 200 synaptic vesicles, EPSP of 40mV or more - CNS synapse: Single vesicle, EPSP of few tenths of a millivolt

38. Synaptic Integration • IPSPs and Shunting Inhibition – Excitatory vs. inhibitory synapses: Bind different neurotransmitters, allow different ions to pass through channels – Membrane potential less negative than -65mV = hyperpolarizing IPSP • Shunting Inhibition: Inhibiting current flow from soma to axon hillock (a) Stimulation of the excitatory input causes inward postsynaptic current that spreads to the soma, where it can be recorded as an EPSP. (b) When the inhibitory and excitatory inputs are stimulated together, the depolarizing current leaks out before it reaches the soma.

39. Chemical Synaptic Transmission Principles Autoreceptors – Presynaptic receptors sensitive to neurotransmitter released by presynaptic terminal – Act as safety valve to reduce release when levels are high in synaptic cleft (autoregulation)