1 / 62

Nervous Tissue

Nervous Tissue. Ch. 12. Overview of the Nervous System. Objectives List the structures and basic functions of the nervous system. Describe the organization of the nervous system. Structures. Nervous system Smallest and most complex system Billions of neurons Includes: Brain

halona
Télécharger la présentation

Nervous Tissue

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Nervous Tissue Ch. 12

  2. Overview of the Nervous System • Objectives • List the structures and basic functions of the nervous system. • Describe the organization of the nervous system.

  3. Structures • Nervous system • Smallest and most complex system • Billions of neurons • Includes: • Brain • Cranial nerves • Nerves – bundle of axons • Spinal cord – connects to brain • Spinal nerves

  4. Functions • Sensory – detect internal and external stimuli • Sensory neurons carry information to brain • Integrative – analyzes and stores information; makes appropriate responses • Perception – conscious awareness of sensory stimuli • Interneurons – participate in integration

  5. Function • Motor – causes movement or gland secretion in response to stimuli • Motor neurons – carry information to muscle or gland (effectors)

  6. Nervous System CNS – Central NS PNS – Peripheral NS Contains brain and spinal cord (axial) Processes sensory info Source of thoughts, emotions, memories • All tissue outside the CNS (appendicular) • Includes cranial nerves, branches, spinal nerves, sensory receptors • Divided further • SNS – somatic NS (body) • ANS – autonomic NS (self) • ENS – enteric NS (intestines)

  7. Nervous System

  8. Peripheral NS Branches • Somatic NS – voluntary • Consists of: • Sensory neurons in head, body, limbs, vision, hearing, taste, and smell that send messages to CNS • Motor neurons that conduct messages from CNS to skeletal musclesonly • Autonomic NS – involuntary • Consists of: • Sensory neurons in organs that send messages to CNS • Motor neurons that conduct messages from CNS to smooth muscle, cardiac muscle, and glands

  9. ANS Branches Sympathetic division Parasympathetic division Supports exercise or emergency actions “fight or flight” Ex: increases heart rate “rest and digest” Ex: decreases heart rate Usually work in opposing actions

  10. ENS “brain of the gut” Controls all activities associated with digestion and the gastrointestinal (GI) tract Involuntary

  11. Overall Organization

  12. Organization

  13. Review What are the components of the CNS and PNS? What kinds of problems would result from damage of sensory neurons, interneurons, and motor neurons? What are the components and functions of the SNS, ANS, and ENS? Which subdivisions of the PNS control voluntary actions? Involuntary actions?

  14. Histology of Nervous Tissue • Objectives • Contrast the histological characteristics and the functions of neurons. • Contrast the functions of neuroglia.

  15. Neurons vs. Neuroglia Neurons Neuroglia Provide unique functions Sensing, thinking, remembering, controlling muscle activity, regulating glandular secretions Support, nourish, and protect the neurons Maintain homeostasis in the interstitial fluid that bathes them

  16. Neurons • Vocabulary: • Neuron – nerve cell • Electrical excitability • the ability to respond to a stimulus and convert it into an action potential • Stimulus • any change in the environment that is strong enough to initiate an action potential • Action potential – nerve impulse • An electrical signal that propogates (travels) along the surface of the membrane of a neuron • Can travel up to 280 mph

  17. Parts of a Neuron • Three parts • Cell body • Main part of the cell • Includes organelles, nucleus, and cytoplasm • Dendrites • Receiving parts of the neuron • Short, tapered, and highly branched • Axon • Transmitting parts of the neuron • Long, thin, cylindrical

  18. Parts of a Neuron

  19. Parts of a Neuron Synapse – site of communication between 2 neurons or a neuron and an effector cell Synaptic end bulb – swollen end of an axon where synaptic vesicles hold neurotransmitters

  20. Neural Diversity • Multipolar neurons • Several dendrites, one axon • Found in brain and spinal cord • Bipolar neurons • One main dendrite, one axon • Eye, ear, olfactory of brain • Unipolar neurons • Axon and dendrite fuse at beginning and then branch • Occurs as an embryo

  21. Neural Diversity

  22. Others Purkinje cells – cerebellum Pyramidal cells – cerebral cortex of brain

  23. Neuroglia Actively participate in nervous tissue functioning Do not generate action potentials Can multiply and divide – neurons cannot

  24. Types of Neuroglia • CNS • Astrocytes – create blood-brain barrier, strength • Oligodendrocytes – create myelin sheath around CNS axons • Microglia – remove cellular debris during neural development • Ependymal cells – assist with circulation of cerebrospinal fluid • PNS • Schwann cells – create myelin sheath around PNS axons • Satellite cells – support, regulate exchange of materials

  25. Types of Neuroglia

  26. Types of Neuroglia

  27. Myelination Myelin sheath – multilayered lipid and protein covering around some axons Provides insulation Increases speed of nerve impulse If a cell has myelin we say that it is myelinated Gaps in the myelin sheath are called nodes of Ranvier

  28. Review Describe the parts of a neuron and the functions of each. Give examples of the structural diversity of neurons. Give examples of the different types of neuroglia. Where are each found? What do they do? What is myelin?

  29. Electrical Signals in Neurons • Objectives • Describe the cellular properties that permit communication among neurons and effectors. • Compare the basic type of ion channels, and explain how they relate to action potentials and graded potentials. • Describe the factors that maintain a resting membrane potential.

  30. Mini-Physics Lesson Potential energy – energy stored in a system (the body) as a result of its position or chemical composition Kinetic energy – energy being used for motion or force

  31. Physics to Anatomy Neurons are excitable because of a voltage difference across the membrane - potential “Potential” will initiate an impulse that can travel through the nervous system Graded potentials – used for short-distance communication Action potentials – allow communication over short and long distance within the body

  32. Potential • Membrane potential – electrical voltage difference across the membrane • Resting membrane potential – membrane potential in an excitable cell • Like voltage stored in a battery • If + and – ends connect, electrons flow in a current • Current • Flow of charged particles • For the body – these are ions instead of elecrons

  33. Ion Channels Gradient – difference Electrochemical gradient – difference in charge and concentration Positive cations move toward negative areas, negative anions move toward positive areas Ion location can be controlled with gates that can open or close the pore

  34. Ion Channels Leakage channels Voltage-gated channels Ligand-gated channels Mechanically gated channels

  35. Ion Channels • Leakage channels • Randomly open and close • most cells leak more potassium (K+) than sodium (Na+) • voltage-gated channels • Opens in response to a change in voltage (membrane potential) • Generate and conduct action potentials

  36. Ion Channels • Ligand-gated channels • Opens and closes in response to chemical stimulus (nts, hormones, other ions – ligand molecule) • Ex: Ach opens channels that allow Na+ and Ca2+ to go in and K+ to go out • Work in 2 ways • ligand molecule can open or close the channel itself by binding • Ligand molecule activates another chemical messenger to open the channel

  37. Ion Chanenls • Mechanically gated • Opens or closes in response to stimulation by: • Vibration: sound waves • Pressure: touch • Tissue stretching • The channel is physically disrupted and opens

  38. Ion Channels

  39. Resting Membrane Potential • Exists due to negative ions in cytosol (ICF) and equal positive ions in ECF • The greater the difference in charge, the larger the potential • Example: • 5 Na+ on outside, 4 Cl- on inside – small potential • 25 Na+ on outside, 4 Cl- on insdie – great potential

  40. RMP • Most cells have potential between -40 to -90 mV; typical is -70mV • Minus sign means the cell is negative – not negative potential! • Any cell with potential is polarized • The potential varies between +5 to -100 mV

  41. How does the potential get there? • ECF • Rich in Na+ and Cl- • ICF • Rich in K+ • Also has P-, amino acids,

  42. RMP • Ion interaction • There are many K+ leakage channels, so K+ diffuse out • + ions exit, inside becomes more negative • - ions can’t leave because they are bound to molecules • - charges attract the K+ back in toward the cell • Few Na+ ions leak inward • This would destroy the membrane potential, so there are pumps that take care of this

  43. Na+/K+ pump • To keep the RMP • Pump out Na+ as it leaks in • Pump in K+ as it leaks out • 3 Na+ for each 2 K+ - this still maintains a negative charge in the cell

  44. RMP - Draw

  45. Review Define resting membrane potential. Describe each type of ion channel. Describe the cellular processes that create the resting membrane potential.

  46. Potentials • Objectives • Describe what causes a graded potential. • Understand the process for creating an action potential. • Explain depolarization and repolarization, including the relationship between them.

  47. Graded Potentials • When a stimulus causes a channel to open or close in an excitable cell • Causes more polarization (more - inside) • Causes less polarization (less – inside) • Hyperpolarized (much more – inside) • Depolarized (much less – inside) • Graded signals – vary in size • Spread out along plasma membrane and die out • Only used for short distance communication

  48. Generation of Action Potentials • Action potential (AP) or impulse – sequence of rapidly occurring events that take place in two phases • Depolarizing phase – negative membrane potential becomes • Less negative • Reaches 0 • positive • Repolarizing phase – membrane potential is • Restored to the resting state of -70 mV

  49. Action Potential

  50. Depol. vs. Repol. • Na+ channels open • Na+ rushes into cell • All or none principle • when depolarization reaches the threshold, the AP occurs • AP is always the same size • Like dominos – no matter how hard you push the first domino they will all fall or they won’t – same goes for the AP K+ channels open K+ flows out of cell

More Related