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Nervous system

Nervous system. Nervous System: True or False?. Humans only use 10% of their brain or less. False!. The brain uses 20% of the energy we consume each day. True!. Mental abilities are separated into discrete left and right “halves”. False!

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Nervous system

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  1. Nervous system

  2. Nervous System: True or False?

  3. Humans only use 10% of their brain or less • False!

  4. The brain uses 20% of the energy we consume each day • True!

  5. Mental abilities are separated into discrete left and right “halves” • False! • Broad generalizations are often made in popular psychology about one side or the other having characteristic labels such as "logical" or "creative". These labels need to be treated carefully; although a lateral dominance is measurable, these characteristics are in fact existent in both sides,[1] and experimental evidence provides little support for correlating the structural differences between the sides with functional differences.[2]

  6. New neurons cannot be created • False!

  7. The brain makes up only 2% of our body weight • True!

  8. The brain does not change after growth that occurs during adolescence • False!

  9. A nerve is a type of cell • False!

  10. The brain uses the majority of the oxygen we breathe False!

  11. The longest cells in the human body are Neurons • True! The sciatic nerve can be over a meter long!

  12. The human brain is firm and grey • False! (well, sort of… it’s about as firm as tofu!)

  13. Functions of the Nervous System: Types of Nervous System Cells

  14. What is the nervous system? What are the functions of the nervous system? • A system of cells, tissue, and organs that regulate the body’s responses to external and internal stimuli. • Communication between organ systems. • Provides info about environmental conditions to all internal organs. • Translates environmental stimuli to messages understood by the cells • External stimuli: environmental factors that influence metabolic changes in a cell or physiological changes in tissues and organs. • Internal stimuli: cell secretions used to communicate info about a cell’s jobs and needs.

  15. Neurons & Neuroglia • Neural tube – developmental struct • Stem cells • Neurons & neuroglia • Neurons: • excitable cells • receive, interpret, and transmit external and internal stimuli. • Neuroglia: • maintain the excitability & health of neurons. • Don’t take part in communication. • Supportive.

  16. Types of Nervous System Cells: Neural Crest Cells • Derived from the neural tube • Bidirectional communication with neuroglia and neurons. • Play a role in the development of the nervous system.

  17. Anatomy of a neuron • Categorized by their cell anatomy and mode of communication

  18. Anatomy of a Neuron • Common features: • Axon: • Long process • Extends from cell body from the axon hillock • Transfers impulses to the terminus. • Usually one per neuron. • Some have branches (collaterals) that reach out to other neurons. • Job: initiate the electrical signal that will be transmitted from the axon to glands, muscles, other neurons.

  19. Anatomy of a neuron cont’d… Terminus: • Releases neurotransmitters—transmit info from one neuron to another. • Cells must possess neurotransmitter receptors if they are to respond to the stimulus

  20. Anatomy of a Neuron Terminus: Releases neurotransmitters Cell body (soma): contains nucleus & organelles, ER and Golgi bodies that produce specialized enzymes and secretions needed for nerve cell communication. • Dendrite: antennae. Receive stimuli from several sources • Axon: long process that comes off the body; transfers impulses to the terminus. Job: transmit electrical signal to glands, muscles, other neurons. Axon Hillock: where the axon originates

  21. Synapse • Neurons don’t directly touch the cells with which they communicate • Form a synapse: the junction where an impulse is transmitted from one neuron to another.

  22. Anatomy of a synapse 2. Pre-synaptic neuron: produces the neurotransmitter 4. Neurotransmitter: most pre-synaptic neurons produce 1 kind. Synaptic Cleft: the space between the terminus of one neuron and the dendrites of another. 5. Receptor: Post-synaptic neurons an have a variety of neurotransmitter receptors. 3. Post-synaptic neuron: receives the neurotransmitter

  23. Shapes of Neurons tell us about their functions

  24. Neuroglia and Stem Cells • Make up bulk of cells in the nervous system • Closely associated with neurons • High lipid content • White in appearance • Vulnerable to improper diet • Many types…

  25. Types of neuroglia • Astrocytes • Ependymal cells • Microglia • Oligodendrocytes Not pictured: • Radial glia • Satellite cells • Schwann cells

  26. astrocytes • A.k.a. macroglia • Largest class • Star-shaped, w/ many branches, or feet • Often associate w/ blood vessels • Control types of materials that pass from blood to neurons • Protects neurons from harmful agents • Creates blood-brain barrier • Mostly found in brain, spinal cord

  27. Ependymal cells • Primary secretory cells • Line cavities of brain, spinal column • Produce cerebrospinal fluid (CSF) • Bathes, nourishes, protects brain, spinal cord • Cilia help circulate CSF

  28. Microglia • Highly variable • Found throughout nervous system • Many carry out phagocytosis, removing infectious agents, repair damage • Others produce secretions that maintain neuron health, assist in healing • Malfunctions often produce disorders

  29. Oligodendrocytes • Large, w/ numerous branching processes • Wrap around axons of neurons • Form an insulating cover (myelin sheath) • Found only in brain, spinal cord • Speeds up nerve transmission

  30. Radial glia • Found in developing nervous system • Provide framework for growing interconnections • In adults, assist maintenance of brain and eyes • Communicate “needs” of these cells

  31. Satellite cells • Small, numerous • Cover surface of neurons outside brain, spinal cord • Help maintain chemical environment • May help w/ nerve cell repair

  32. Schwann cells • Form myelin sheath around axons of neurons outside of brain, spinal cord (in PNS) • Gaps between cells called nodes of Ranvier • Help speed transmission

  33. Functions of the Nervous System: Neuron physiology

  34. Review of Diffusion • Materials diffuse from high  low concentration • Membranes act as a barrier to diffusion… they can be “selective” about what can pass • In general, things that are large/charged need special “permission” to pass through the membrane • They need a channel/gate that gives them a pathway • Ions, like Sodium (Na+), Potassium (K+), and Chloride (Cl-) are normally not allowed through

  35. Opposites attract! • In general, the following are true about ions: • They will repel each other (likes repel) • They will be attracted to an opposite charge

  36. How do neurons communicate with one another? • Neurons are excitable! • They transmit a signal that was received by the dendrites/cell body down through the axon • Cytoplasm must be ready! • Neurons transmit information to other cells via an action potential

  37. Meet the proteins! Na+/K+ Pump K+ pore (leaks) Na+ gated channel K+ gated channel

  38. What has to happen to a neuron before it generates or propagates an action potential? • Must maintain an excitable condition called resting potential. • Chemically unstable condition • Sodium ion concentration higher outside cell than inside • Creates a diffusion potential; sodium “wants” to enter • Potassium ions higher inside cell than outside • A.k.a. a “salty banana” Sodium/potassium pump maintains this potential

  39. Resting phase = polarized! Na+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ Na+ Na+ - PROTEIN - K+ K+ - PROTEIN - K+ K+ K+ K+ K+ K+ Na+ Na+ K+ K+ - PROTEIN - - PROTEIN - - PROTEIN - - PROTEIN -

  40. First Look: Action potential animation • Animation

  41. What are the four stages of an action potential? • Debatable… some have 6 phases • Depolarization • Repolarization • Hyperpolarization • Recovery phase

  42. Phase 1: Depolarization • Cytoplasm’s charge starts at ~ -70 mV • Dendrites receive stimulus from a. another cell or b. the environment • Sodium channels open, allowing rapid influx • If enough channels open, cytoplasm’s charge reaches -55 mV = threshold • Required for an action potential to propagate, or travel, across the cell membrane

  43. All-or-nothing! • At threshold, more Na+ channels open • Charge of cytoplasm increases to +30 mV • Each depolarized segment of axon depolarizes the adjacent segment… like falling dominoes

  44. Side note… • Potassium gated ion channels are also stimulated to open during a depolarization! • They are slower to respond • They don’t fully open enough to allow K+ ions to flow out until the sodium gates have both opened AND closed!

  45. Phase 2: Repolarization • Sodium channels closed, and potassium channels finally open • K+ ions diffuse outward, causing the cell’s interior to become more negative (lost + ions) • Neuron is becoming repolarized.

  46. hyperpolarization • Repolarization is rapid! • Cell moves past resting potential (-70 mv) and overshoots, reaching -90 mV. • K+ gated ion channels are slow to close as well… • This is hyperpolarization…

  47. Hyperpolarization • K+ gates on K+ channel proteins are slow to close, allowing this hyperpolarization • Why does this occur? • Prevents neuron from becoming stimulated during repolarization period • Prevents action potential from travelling both forward AND backward… becomes a unidirectional signal. = REFRACTORY PERIOD

  48. Recovery phase • Sodium/Potassium pumps return cell to resting potential (Na+ outside, K+ inside) • Some cells send a second impulse before recovery is complete = tetany

  49. Another animation • Click here

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