Cellular Neurobiology

1. Cellular Neurobiology Albert Cheung-Hoi YU 于常海 北京大學神經科學研究所 Neuroscience Research Institute Peking University Department of Neurobiology Peking University Health Science Center achy@bjmu.edu.cn

2. One of the Cajal’s many drawings of Brain circuity The letters label the different elements Cajal identified in an area of the human cerebral cortex that controls voluntary movement.

3. Cellular Components • Neurons: Excitable cells –“wiring”“Signal Senders” • Neuroglia: Support, Nurturing, Insulation

4. Nerve Cells Neuroglia Neurons

5. Structure of Neurons • Cell body (soma; perikaryon) • Axon : only one (branches are collaterals; terminals are end feet) • Dendrites : much shorter; one or more than one; branch extensively into dendritic trees (Axonal end feet) Axon Hillock

6. The Axon and Axon Collaterals

7. Neurons Structure & Function • Cell Body (Soma):Life Support • Protein Synthesis • Single Nucleus, RER (Nissl Bodies) • Axon: Longest process transmits messages away from cell body • Dendrites: Multiple processes off cell body – receive messages

8. What are inside of a neuron?   Neurons are similar to other cells in the body in some ways such as: 1. Neurons are surrounded by a membrane. 2. Neurons have a nucleus that contains genes. 3. Neurons contain : • Nucleus • Nucleolus • Microfilaments/Neurotubules • Endoplasmic Reticulum (ER) Mitochondria Golgi Apparatus • Nissl Bodies • Others

9. Axon and Dendrites • Dendrites : • dendrite tree • Axon : • axon hillock (axon origination) • axonal transport system • initial segment (first myelin sheath) • action potential generation • myelin sheath

10. Axons Dendrites Take information away from the cell body Take information to the cell body Smooth surface Rough surface (dendritic spines) Generally only 1 axon per cell Usually many dendrites per cell No ribosome Have ribosomes Can have myelin No myelin insulation Branch further from the cell body Branch near the cell body Differences between Axons and Dendrites

11. Neuron Classification by Shape • Multipolar: “multi-” many processes • Majority: Single axon, many dendrites (motor neuron and interneuron) • Bipolar: “bi-” 2 processes • Found in some sensory organs (retina, taste, smell, inner ear neuron) • Unipolar (pseudo-unipolar): “uni -” 1 process (with branches) • Sensory afferent neurons (dorsal root ganglia)

12. Classification of Neurons by Morphology

13. Classification of Neurons by Axon Length • Golgi type I Neurons • Long axons (longest from the cortex to the tip of spinal cord, 50-70 cm) • Golgi type II Neurons • Short axons (shortest axons terminate only a few micron from cell body, interneurons) • Amacrine Neurons • An unusual cell type, lack axons

14. Functional Classification of Neuron • Sensory neuron • from receptor to CNS; receive stimuli and transmit afferent impulses to CNS • Interneurons • communicating between neurons; form circuits in the CNS • Motor neuron • from CNS to effector cells; deliver efferent impulses out through the PNS to the effectors to carry out the actions directed by the CNS

15. Important FeaturesofNeurons • EXCITABLE Membrane: Able to regulate the movement of ions (charges) across and along membrane SIGNAL TRANSDUCTION • DO NOT Replicate: Damaged cells cannot be replaced!

16. Action Potential

17. Four Functional Regions of Model Neurons

18. Classification of Synapses • Impulse transmission : • electrical • chemical • Morphology : • axodendritic • axonsomatic • axoaxonic • dendrodendritic

19. Vesicles release Neurotransmitters 4 synapse

20. Synapse Structures • Chemical synapse : • presynaptic knob (presynaptic component) • synaptic vesicles • synaptic cleft • postsynaptic membrane (postsynaptic component) • Electrical synapse : • gap junctions

22. Types of synapse Dis-tance Cytoplasmic continuity Ultrastruct-ural component Agent of trans-mission Synaptic delay Direction of trans-mission Electrical 3.5 nm Yes Gap-junction channel Ion current Virtually absent Usually bidirectional Chemical 20-40 nm No Presynaptic vesicle and active zone; postsynaptic receptors Chemical transmitters Significant: at least 0.3 ms; usually 1-5 ms or longer Uni-directional Distinguishing Properties of Electrical and Chemical Synapses

23. At a chemical synapse, neurons transmit information across a cleft.

24. List of Some Neurotransmitters • Small Molecule Neurotransmitter Substances Acetylcholine (ACh); Dopamine (DA); Norepinephrine (NE); Serotonin (5-HT); Histamine • Amino Acids Gamma-aminobutyric acid (GABA); Glycine; Glutamate; Aspartate • Neuroactive Peptides - partial list!! Bradykinin; beta-endorphin; calcitonin; cholecystokinin; enkephalin; dynorphin; insulin; gastrin; substance P; glucagon; secretin; vasopressin; oxytocin, etc.

25. Axonal Transport Systems • Axonal transport : • intracellular communication • Bidirectional mechanism : • anterograde transport • retrograde transport • Classified by transport rates : • slow transport system (0.2 to 1 mm/day) • fast transport system (200 to 400 mm/day)

26. Hitching a Ride on “Retrorail”

27. Nucleus Membranes of organelles involved in synaptic transmission are returned to the cell body for reuse or degradation Cytoskeleton (Anterograde transport))

29. Component Rate (mm/day) Structure and composition Fast transport Anterograde 200-400 Small vesiculotubular structures, neurotransmitters; membrane proteins and lipids Mitochondria 50-100 Mitochondria Retrograde 200-300 Lysosomal vesicles and enzymes Slow transport SCb 2-8 Microfilaments, metabolic enzymes, clathrin complex SCa 0.2-1 Neurofilaments and microtubules Major Rate Components of Axonal Transport

30. Neurons differ from Other Cells 1. Neurons have specialized projections called dendrites and axons. Dendrites take information to the cell body and axons take information away from the cell body 2. Neurons communicate with each other through an electrochemical process 3. Neurons contain some specialized structures (like synapses) and chemicals (like neurotransmitters) 4. Nissl Bodies 5. DO NOT Replicate: Damaged cells cannot be replaced!