1. Cell Biology of the Nervous System D. Allen, Ph.D.

2. Types of Cells in the Nervous System Glial –Supporting cells Neurons Neural Stem Cells

3. Relatively new discovery Both developing and adult brains Precursors to both neurons and glial cells Role in mature brains unclear –Hippocampus – neurons that have divided

4. Glial cells – Supporting cells Macroglia –Astrocytes – CNS –Oligodendrocytes – CNS –Schwann Cells – PNS Microglia –Microglia - CNS

5. CNS - Macroglia

6. Astrocytes Star-shaped Functions –Cell signaling –Scavengers –Blood-brain barrier –Development –Support for neurons

7. Other functions of astrocytes Clean up cellular debris Component of blood brain barrier (restrict substances that enter the brain from the blood) Astrocytes produce trophic substances that help keep neurons alive and promote neuron process outgrowth Radial glia – form a framework for migration of neurons during development

8. Myelin-producing cells Schwann cells – PNS Oligodendrocytes – CNS Functions of myelin –Insulate axons and soma of neurons –Speed up rate of transmission of action potentials Schwann cells also can be phagocytic

10. Schwann cells Promote regeneration in the peripheral nervous system Surround unmyelinated axons, but do not form a myelin sheath (p 25)

11. Microglia Phagocytic cells Macrophages that migrate into brain Normally at rest in brain Become activated after injury, infection or disease

12. Ingest and destroy bacteria Destroy injured or aging neurons Associated with some diseases –Alzheimer’s disease –AIDS

13. Neurons

14. Dendrites Soma (cell body) Axon Presynaptic terminal (bouton)

15. Soma Contains nucleus Site of protein synthesis Receives information from other neurons

16. Dendrites Project from soma –Branchlike extensions Specialized for receiving information One or many dendrites

17. Axon Specialized for the transmission of information Single axon Arises from axon hillock Action potentials occur only at the axon Axon can branch at their distal end (axon collaterals)

18. Presynaptic terminal At ends of axon branches Specialized for transmission of information to other cells at the synapse Usually use neurotransmitters to transmit the information

19. Axoplasmic transport The distance from the soma (site of protein synthesis) to the presynaptic terminal can be 1-2 meters. This is too long for diffusion to be effective. Axoplasmic transport is the mechanism for the relatively rapid transport of organelles and molecules to and from the presynaptic terminal

20. Axoplasmic transport Anterograde transport Retrograde transport Slow axoplasmic transport (1 mm/day)

21. Types of Neurons Bipolar –Dendrite root –Axon Pseudounipolar –Specialized bipolar neurons –Both processes are axons Multipolar –Multiple dendrite –Single axon

22. Functions of neurons Bipolar –Transmitting information from one neuron to another –Many sensory neurons

23. Multipolar –Receive and integrate large amounts of information –Spinal motor neurons 8000 synapses on dendrites 2000 synapses on soma –Purkinje cells in cerebellum 150,000 synapses on dendrites

24. Interactions between Neurons Two main overall patterns –Divergence –Convergence

25. Convergence and Divergence

26. Divergence A single axon has several branches that terminate on many different cells Single sensory neuron - proprioception –Interneurons that mediate reflexes –Cerebral cortex for consciousness of sensation –Cerebellum – unconscious proprioception

27. Convergence Multiple inputs from different neurons terminate on a single neuron Neurons may: –Respond to 2 or more stimuli Texture and temperature –Respond to complex stimuli Lines at a specific angle

28. Convergence in visual system Rods and cones – points of light Retina – On center / Off surround Visual cortex – bars of light

29. Most neurons require excitatory input from more than one neuron in order to fire an action potential –Summation Spinal motor neurons – 10,000 synapses

30. Diseases of Myelination With demyelination, there is a slowing or even blocking of action potentials Peripheral demyelination –Metabolic abnormalities –Viruses –Toxic chemicals –Immune system Central demyelination

31. Demyelination 2 diseases Guillan-Barre –Peripheral demyelination –Schwann cells Multiple Sclerosis –Central demyelination –Oligodendrocytes

32. Guillain-Barre Acute inflammation and demyelination Patient Hx –Mild infection –Symptoms begin 2-3 weeks later –Thought to be autoimmune attack on myelin in peripheral nervous system

33. G-B – Signs and Symptoms Decreased sensation Motor paralysis Cranial nerves often affected –Difficulty chewing, swallowing, speaking, facial expressions Weakness in respiratory muscles Altered sensation/pain Autonomic dysfunction

34. G-B Prognosis Symptoms worsen over 2-3 weeks, then plateau Patient then usually gradually gets better (weeks to years) If demyelination is severe, there may be scarring and a permanent loss of axons ~3% mortality – cardiac or respiratory problems

35. Multiple Sclerosis Central nervous system demyelination Incidence –High in this region (ND 2 nd highest state) –2-3X in women –Highest in whites, Scandinavian descent –Living in northern climates before age of 15 –Highest prevalence in young adults Increases up to age 35, then gradually declines

36. MS Autoimmune disease Will see patches of demyelination, called plaques, due to the degeneration of oligodendrocytes Variable course of the disease –Periods of exacerbation and remission In chronic MS, the myelin sheath is replaced by glial scarring

37. MS – Initial S & S Sensory symptoms usually first complaint –Paresthesia – abnormal non-painful sensations –Dysesthesia – abnormal painful sensations –In one extremity or head and face Visual blurring Diplopia – double vision