Ch 11: Nervous System & Nervous Tissue

1. Ch 11: Nervous System & Nervous Tissue Section 1 – Functions & Divisions of the Nervous System (pp. 386-387)

2. The Nervous System This is your brain…

3. The Nervous System And this is your brain – IN ANATOMY!! Or better yet…

4. The Nervous System Functions of the Nervous System 1) Sensory input - information about internal/external changes gathered by sensory receptors 2) Integration - interpretation of sensory input 3) Motor output - activation of effector organs (muscles, glands, etc.) - production of response

5. The Nervous System Divisions of the Nervous System 1) Central nervous system (CNS) - brain & spinal cord - integration & command center

6. The Nervous System Divisions of the Nervous System 2) Peripheral nervous system (PNS) - spinal & cranial nerves - carry messages to & from CNS Functional divisions of PNS: a) Sensory (afferent) division - carry information to the CNS from effector organs b) Motor (efferent) division - carry information away from CNS to effector organs

7. The Nervous System Divisions of the Nervous System 2) Peripheral nervous system (PNS) - spinal & cranial nerves - carry messages to & from CNS Motordivisions of PNS: a) Somatic (voluntary) nervous system - provides conscious control of skeletal muscles b) Autonomic (involuntary) nervous system - regulates smooth muscle, cardiac muscle,& glands - divided into sympathetic & parasympathetic systems

8. Ch 11: Nervous System & Nervous Tissue Section 2 – Histology of Nervous Tissue (pp. 388-395)

9. Neurons Neurons (aka “Nerve Cells”) - Fundamental units of the nervous system - Cells that are capable of carrying electrical signals Special characteristics: 1) long-lived (capable of living 100 years or more) 2) amitotic…cannot divide (with a few exceptions) 3) high metabolic rate (require continuous O2 & sugar supply) 4) plasma membrane designed for electrical signaling

10. Neurons Typical neurons have 4 distinct regions: 1) Dendrites - Receive & respond to signals from other neurons - Use special receptors to respond to neurotransmitters - Deliver electricalsignal to cell body 2) Cell body (aka “perikaryon” or “soma”) - Neuron’s integration center - Combines all incoming electrical signals - If incoming signals are positive enough, cell body allows signal to continue to axon

11. Neurons Typical neurons have 4 distinct regions: 3) Axon - Long, thin fiber…makes neurons longest cells in body - Carries electricalsignal away from cell body - Allows signals to be carried largedistances - Multiple axons are bundled together to form “nerves” 4) Synaptic terminals - Endings of the axons - Contain neurotransmitters (NTMs) - Release NTMs to other neurons, glands, or muscles

12. Other Cells of Nervous System Neuroglia - Literally means “nerve glue” - Cells that support the function of the nervous system - Are not capable of carrying electrical impulses Examples found only in Central Nervous System: 1) Astrocytes - Abundant, star-shaped cells that brace neurons - Control chemical environment of brain - Form barrier between capillaries & neurons

13. Other Cells of Nervous System Astrocyte

14. Other Cells of Nervous System 2) Microglia - Spider-like phagocytes that dispose of debris 3) Ependymal cells - Line cavities of the brain & spinal cord - Circulate cerebrospinalfluid

15. Other Cells of Nervous System 4) Oligodendrocytes - Produce myelin sheath around nervefibers in central nervous system *Myelin sheath - Acts like insulation - Prevents shortcircuits

16. Other Cells of Nervous System

17. Other Cells of Nervous System Examples of Neuroglia in the Peripheral Nervous System: 1) Satellite cells - protect neuron cellbodies in PNS 2) Schwann cells - form myelin sheath around axons in PNS - vital to regeneration of damaged peripheral nerves

18. Other Cells of Nervous System More on Myelin Sheath of PNS: - formed in a “Jelly roll”-like fashion - insulates the axons - enhances & increases speed of the electrical signal Nodes of Ranvier - Gaps in the myelin sheath formed by spaces between Schwann cells

19. Structural Classification of Neurons Multipolar Neurons - Characterized by manyextensions from cell body - All of the motor neurons

20. Structural Classification of Neurons Bipolar Neurons - Consist of only one dendrite & one axon - Found only in nose (smell) & eyes (vision)

21. Structural Classification of Neurons Unipolar Neurons - Consist of a single, shortextension leaving the cell body - All sensory neurons

22. Ch 11: Nervous System & Nervous Tissue Section 3 – Neuron Function & Action Potentials(pp. 399-404)

23. Information Processing Information Processing Requires 4 Basic Operations: • Determine the type of stimulus - Distinguished by variouswiringpatterns in the brain • Determine the intensity of the stimulus - Either by the number of times a single neuron “fires” or the total number of neurons “firing” at once • Integrate information from many different sources • Initiate & direct a response

24. Neuron Function Basic Neuron Function: - Neurons are highly irritable (responsive to stimuli) - Send signals over long distances by generating “action potentials” Action Potential - “nerve impulse” - a brief change in the electrical charges found on either side of the nerve cell membrane - travels from the cell body to the end of the axon - always the same strength regardless of stimulus

25. Neuron Function More on Action Potential: - created by the movement of positively charged sodium & potassium ions across the cell membrane of the axon - as charged particles move, they create electrical impulses - considered “all-or-none phenomenon”…either happen completely or not at all Threshold stimulus - minimum stimulus required to create an action potential

26. Neuron Function Conduction velocity: - the speed action potentials travel - vary widely…some faster than others - fastest occur at 100 meters/sec or more! Rate determined by… 1) Axon diameter - larger diameter = faster conduction velocities 2) Degree of myelination - more myelin = faster conduction velocities

27. Ch 11: Nervous System & Nervous Tissue Section 4 – The Synapse & Neurotransmitters (pp. 406-421)

28. The Synapse Synapses: - junctions that regulate information between two neurons - also found between neurons & effector cells/organs Presynaptic neuron - conduct impulses toward synapse Postsynaptic neuron - conduct impulses away from synapse

29. Types of Synapses Two most common types of synapses: 1) Axodendriticsynapse - between the axon of one neuron & the dendrite of another 2) Axosomaticsynapse - between the axon of one neuron & the cell body of another *These may be either “electrical” or “chemical” synapses… Animation: Synapses

30. Electrical Synapses Electrical Synapses: - not as common as chemical synapses - neurons are physically connected by gap junctions - electrical signal travels directly through the gap junction - very rapid; utilized in very fast events…reflexes

31. Chemical Synapses Chemical Synapses: - specialized for releasing & receiving neurotransmitters Typically composed of two parts: 1) Axonterminal - found on presynaptic neuron - contains synaptic vesicles w/ neurotransmitters 2) Receptor region - found on postsynaptic neuron - has special receptors that receiveneurotransmitters

32. Synaptic Cleft Synaptic Cleft: - fluid-filled space between pre- & post-synaptic neurons - prevents nerve impulses from directly passing from one neuron to the next

33. Synaptic Cleft Transmission of Electrical Impulse Between Neurons: - Electrical signal reaches end of axon - Neurotransmitters are released from synaptic terminals - Neurotransmitters diffuse through synaptic cleft - Neurotransmitters bind to receptor sites on adjacent dendrites Animation: Neurotransmitters

34. Synaptic Cleft Terminating effects of neurotransmitters: - occurs within a few milliseconds of NTM release - happens as a result of either the… 1) NTMs being brokendown by enzymes 2) NTMs being reabsorbed into the axon terminal 3) NTMs diffusing away from synaptic cleft

35. Neurotransmitters Types of neurotransmitters: - most neurons make 2 or more NTMs - the number of times per second that a neuron “fires” determines which NTM is actually released - over 50 different NTMs have been identified

36. Specific Neurotransmitters Neurotransmitters & Functions: 1) Acetylcholine - Activate skeletal muscles 2) Dopamine - Important in generalmovement 3) Epinephrine - Activates organs of sympathetic nervous system 4) Serotonin - Influences mood (“mellow”) & sleep 5) Endorphins - Influences mood (“feel good”), reduces pain 6) Nitricoxide- Important in forming memories

37. Ch 11: Nervous System & Nervous Tissue Section 5 – Neural Integration…Circuits (pp. 422-423)

38. Organization of Neurons Types of circuits: 1) Diverging circuits - one incoming nerve fiber stimulates multiple fibers - often acts as an “amplifying” circuit Ex = single neuron in brain can activate hundreds of motor neurons in spinal cord and ultimately thousands of skeletal muscle fibers

39. Organization of Neurons Types of circuits: 2) Converging circuits - multiple nerve fibers in different areas combine signals into one fiber - often have a “concentrating” effect; strong stimulation or strong inhibition Ex = seeing a baby smile, smelling baby powder, hearing baby laugh all combine to trigger “warm/fuzzy” feelings in parents

40. Organization of Neurons Types of circuits: 3) Reverberating (oscillating) circuits - chain of neurons arranged in a loop - results in signal that is sent through the circuit over & over in a rhythmic pattern Ex = sleep-wake cycles, breathing, arms swinging when walking

41. Organization of Neurons Processing information in the nervous system: 1) Serial processing - input travels along onepath to a specific destination - works in all-or-none manner producing specific response Ex = spinal reflexes

42. Neural Pathways Direct Behavior Reflex - Simplest behavior - Involuntary movement of body part in response to stimulus - Occur without involving the consciousportions of the brain - Signal sent to spinalcord & immediately back to source - Usually help keep you from beinghurt

43. Organization of Neurons Processing information in the nervous system: 2) Parallel processing - input travels along severalpathways - one stimulus promotes many responses - crucial for higher-level mental functioning Ex = a smell usually isn’t processed as just an odor; also usually triggers memories of experiences associated w/ the smell

44. Ch 11: Nervous System & Nervous Tissue Section 6 – Homeostatic Imbalances (pp. 422-423)

45. Homeostatic Imbalances Multiple Sclerosis (MS): - autoimmune disease; mainly affects young adults - myelin sheaths in the CNS become destroyed - sheaths turn into nonfunctional, hardened lesions - leads to short-circuiting of nerve impulses - eventually impulse conduction ceases Symptoms - visual/speech disturbances, weakness, loss of muscle control, & loss of bladder control

46. Homeostatic Imbalances Neuroblastoma: - malignant tumor that occurs in the peripheral nervous system of children Rabies: - viral infection of nervous system - transmitted through bites from infected animals - causes inflammation of brain, delirium, & death

47. Homeostatic Imbalances Shingles: - viral infection of the sensory neurons found in the skin - scaly, painful blisters; similar to chickenpox but w/ pain - seen mostly in adults over 50 years old