7 Muscle, ~8 Nerve

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  1. Muscle Tissue Consists of:
    • Muscle Cells (Myocytes, Myofibers - implies the cells are very long)
    • Stem (Satellite) Cells - for regeneration + renewal
    • Nerve Supply
    • somatic motor nerves for voluntary muscles
    • visceral motor nerves for involuntary muscles (can be sympathetic or parasympathetic)
    • sensory (protection + proprioception: so you know where in space your extremities are)
    • al muscle cells have excitable plasma membranes (means they’re capable of conveying APs, important in contraction)
    • connective tissues
    • blood vessels (large tissues so they have their own blood supply)
    • lymphatics
  2. What are the 2 types of non-muscle contractile tissue (cells that contract but that aren’t muscles)?
    1. Myoepithelial Cells: epithelial cells that contain contractile proteins; are abundant in glands & help them contract & release their product

    2. Myofibroblasts: fibroblasts differentiate into myofibroblasts (can contract) during wound healing to help close wounds
  3. What are the 4 classifications of muscle?
    • 1. Skeletal (Striated): voluntary muscles associated with skeletal movement (biceps, trapezius, deltoid - generally attached to bones)
    • 2. Visceral (Striated): voluntary visceral muscles (upper esophagus, pharynx, tongue - don’t attach to bones)
    • 3. Cardiac (Striated): under only autonomic (symp/parasymp) control (no voluntary control)
    • 4. Smooth (NON-Striated): under autonomic control; wide distribution (gut, bronchioles, BVs, ureter, gall bladder, etc. - any place where there’s a tube that constricts)
  4. Skeletal v. Visceral Striated Muscle
    • Skeletal: skeletal movement; cross & activate JOINTS
    • Visceral: DON'T connect bone to bone
    • in both, striations run perpendicular to cell line
  5. if a word starts with myo-, sarco-, or ends in -mysium:
    • it's referring to muscle
    • myofiber = myocyte = muscle cell
    • mysium means flesh
  6. Sarcolemma
    term used to describe a muscle cell’s plasma membrane & it’s external lamina (equivalent to the basal lamina)
  7. Sarcoplasm
    cytoplasm of a muscle cell
  8. Sarcoplasmic Reticulum
    • smooth ER of a muscle cell
    • important for calcium storage
  9. Skeletal Muscle
    • run the full length of the muscle
    • are unbranched, striated & multinucleated (needed because of how long they are)
    • controlled voluntarily
    • has a continuous external lamina; because of that there are no places where the plasma membranes of different cells meet ~ therefore there are no cell-cell gap junctions
    • UNLIKE cardiac/smooth muscle, the whole skeletal muscle cell is insulated from it's surroundings
  10. What are 2 skeletal muscles that AREN’T voluntary (atypical)?
    • Lower Pharynx & Diaphragm are made up of skeletal muscle but are involuntary
    • Diaphragm contracts on its own via the autonomic nervous system
  11. Skeletal Muscle Connective Tissue Investments
    • 1. EPImysium surrounds the entire muscle
    • 2. PERImysium surrounds each fascicle (group of cells)
    • 3. ENDOmysium surrounds an individual muscle fiber/cell
    • *ALL THESE CT ELEMENTS COME TOGETHER AT THE TENDON (which attach muscle to bone)*
  12. True Syncytium
    • a way to describe the multinucleated muscle fibers
    • a syncytium is a multinucleated cell that results from multiple cell fusions of uninuclear cells - this is what happens during muscle cell development
  13. Image Upload
    • because skeletal muscle is so jam-packed with contractile proteins, nuclei get PUSHED out to the periphery
    • spaces between the cells correspond to ENDOmesium (connective tissue)
    • can see muscle cell nuclei (& maybe fibroblast nuclei) near the endomesium because they’re pushed to the fiber periphery
    • cytoplasm of 1 muscle cell has “stippled” appearance because it’s packed with myofibrils
  14. Myofibrils
    • visually, are the dark & light regions that identify striated muscle as 'striated'
    • myofibrils themselves contain contractile proteins called myofilaments
    • myofilaments consist of repeating sarcomeres that are in sync with adjacent sarcomeres
  15. What separates indvidual myofibrils?
    the muscle fiber cytoplasm (sarcoplasm), which itself contains cell organelles (sarcoplasmic recticulum, mitochondria, lysosomes, etc.)
  16. Image Upload
    • sarcomere exists from the Z (dark) line in one thin actin filament to the Z line in the next
    • Z line: serves as an anchoring point for thin actin filaments (Z disk)
    • I band: thin actin filament bisected by the Z line; light staining
    • A band: thick myosin filaments; dark staining
    • M line: line in the middle of the A (thick myosin) band that anchors the myosin
    • H band: slightly lighter area just around the M line in the A (myosin) band where you only have only myosin (think) filaments, no actin (thin) filaments
    • the bubbly/dotty stuff between myofibril striation = cell organelles
  17. Muscle Contraction
    • when muscles contract the SARCOMERE shortens
    • occurs by a sliding filament mechanism
    • the Z-lines MOVE closer together
    • neither the I nor A bands shorten (Z within the I just moves)
    • H band (surrounding M line) disappears - is filled in with thin filaments that move toward the M line
    • Image Upload
    • I (actin thin) & H bands narrow; A (myosin thick) band width doesn’t change
  18. Tropomyosin
    • protein located on the surface of actin (thin, I filament)
    • in the absence of calcium, it - via the troponin complex - BLOCKS the active sites of actin
    • no calcium → actin can’t bind to myosin heads
    • when calcium is present, it changes tropomyosin's conformation → actin & myosin can now interact (+ ATP) & provide muscle contraction
    • control of muscle contraction has a lot to do with calcium
  19. How do motor neuron action potentials propagate through a bundle of muscle cells?
    • neuron meets muscle at motor endoplate, aka neuromuscular junction
    • action potential impulse can be transferred to surface of muscle cell, aka the sarcolemma
  20. How can this signal go deep into the muscle & interact with calcium stores?
    • *T tubule: indentation of plasma membrane that runs DEEP into the muscle (surrounds myofibrils)
    • cisterns of smooth ER also surround T tubules & they're filled with CALCIUM (structure is overall called a triad)
    • action potential → T tubule → sarcoplasmic reticulum → voltage gated calcium channels open → calcium floods sarcoplasm (relieving inhibition of myosin/actin interaction via Tropomyosin & the troponin complex)
  21. Dystrophin Complex
    • connects actin cytoskeleton (thin filaments) to cell's plasma membrane which is itself linked to the external lamina (CT) by another dystrophin-associated complex
    • it links cell contractile elements to the surrounding connective tissue to mobilize muscles connected to tendon
    • Image Upload
    • located around cell periphery (brown staining)
  22. Dystrophin Complex Deficiency (Muscular Dystrophy)
    • LOSE the ability to transfer mechanical force to move muscles (the cytoskeletal contractile elements are NOT connected to the external lamina CT)
    • hypercalcemia also results, leading to increased osmosis → mitochondrial rupture
    • Image Upload
  23. muscular control is dependent on:
    • motor & sensory components
    • 1. muscle fiber types
    • 2. motor unit density
    • 3. sensory fibers (propioception)
  24. What are the 2 different muscle fiber types?
    1. RED (slow twitch): many mitochondria & oxidative enzymes (AERobic); don't contract fast but CAN contract for long periods without fatiguing; eg. back muscles

    2. WHITE (fast twitch): bigger muscle cells, contract quickly; fewer mitochondria & oxidative enzymes (ANaerobic); quicker to fatigue; eg. quadraceps

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  25. Motor Unit Density (also important for muscle control)
    Coarse Control: a single neuron controls many muscle fibers (neuron can split ~1,000 times) → LESS control

    Fine Control: a single neuron exerts control on only a few muscle fibers (splits maybe 3-4 times) → MORE control
  26. Muscle Fiber Sensory Perception
    • provide proprioceptive information because they're made up of muscle cells AND nerves
    • eg. muscle spindle & golgi tendon organs
  27. Muscle Spindle
    • a combination of muscle fibers & afferent (sensory) nerves that provide proprioceptive information (the extent to which muscles are extended or relaxed) & mediate the stretch reflex
    • if a muscle stretches really quickly the muscle spindle can stimulate a contractile reflex to shorten the muscle (what you do when you test reflexes)
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  28. Golgi Tendon Organ
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    • located in the TENDON & provide sensory information about how much a muscle is being stretched
    • involved in both proprioception AND inhibition reflex - protects muscle from OVER-stretching
  29. Inhibition Reflex
    reflex activated by golgi tendon organ that causes a overstretched muscle about to tear from the tendon to relax
  30. Cardiac Muscle
    • involuntary striated muscle only found in the heart controlled autonomically
    • sympathetic speeds up heart beat
    • parasympathetic slows heart down
    • consists of relatively short cells connected by end-to-end junctions
    • has a DISCONTINUOUS external lamina - there are gap junctions between cells
    • cells are BInucleate
    • CT = endocardium & epicardium
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  31. Intercalated Discs
    • specialized end-to-end junctions between individual cardiac muscle cell
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    • little dark lines in between the ends of cells
    • can see BRANCHING
    • can see centered nuclei (unlike skeletal, whose nuclei are pushed to the periphery)
  32. Image Upload
    A: Intercalated Disc (~Fascia Adherens), which is analagous to the zonula adherens; exists perpendicular to long line of cell & provides STRENGTH

    B: on the lateral surface that’s parallel to the long line of the cell is where most cell-cell communication (gap junctions) occur; this is where the external lamina is DISCONTINUOUS for COMMUNICATION

    desmosomes exist in BOTH places

    Image Upload
  33. What is critical for cardiac muscle contraction?
    the parallel gap junctions
  34. cardiac muscle has LESS robust smooth ER for T tubule activation
    • called a diad (sarcoplasmic reticulum + T tubule because there's less smooth ER surrounding T tubules (plasma membrane invaginations)
    • LESS efficient than skeletal muscle but that's okay because cardiac muscle has GAP JUNCTIONS for communication
    • it can also spontaneously contract
  35. Endocrine Cells
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    • specialized myocardial (muscle) cells that can contract & secrete ANF (Atrial Natriuretic Factor) to surrounding cardiac cells (small black dots = granules)
  36. ANF (Atrial Natriuretic Factor)
    hormone released by endocrine cells in cardiac muscle that acts as a vasoDilator in response to ↑ BP, ↑ Na+, & Angiotensin II (a vasoconstrictor)
  37. Purkinje fibers
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    • specialized myocardial cells that can contract & conduct impulses/signals (contract so they do contain myofibrils)
    • exist just deep of the endocardial surface near lumen of ventricles where blood is
    • are rich in glycogen (cells look filled with space)
  38. Smooth Muscle
    • Image Upload
    • non-striated
    • involuntary (under autonomic control)
    • discontinuous external lamina
    • fewer CT investments (CT = epimysium & endomysium only)
    • many gap junctions
    • found throughout hollow organs of body (eg. GI tract, blood vessels, bladder, & arrector pili in skin)
    • often see both longitudinal and cross-sectional view in the same section
    • lacks true sarcomeres
  39. Image Upload
    • dense body
    • smooth muscle cells have similar contractile units as skeletal/cardiac striated
    • except instead of being anchored on a Z line, smooth muscle contractile elements are anchored on spots known as dense bodies
  40. The Different Ways Smooth Muscle Contract
    • 1. electrically: via gated Ca2+ channels
    • used by single (common BVs, GI tract) & multiunit (restricted trachea, large elastic arteries, iris) smooth muscle
    • -atypical neuromuscular junction: neurotransmitters released at 10- 200μ from muscle = slow excitation

    2. mechanically: receptors in smooth muscle that facilitate stretching; stimulates mechano-sensitive ion channels ("myogenic" response) - NOT a nerve response

    3. hormonally: form a synapse-like structure (eg. oxytocin stimulates uterine contractions
  41. Caveolae
    • indentation in smooth muscle cells which allow propagation of nerve impulses and Ca 2+ activated channels throughout a smooth muscle
    • analogous to T tubules in striated muscle
  42. Leiomyomas
    benign tumors of smooth muscle
  43. muscle repair
    satellite (stem) cells reside in external lamina; activated in damage or injury, proliferate, and replace damaged muscle cells
  44. skeletal muscle repair
    satellite cells are stimulated to proliferate in response to disease (eg. muscular dystrophy) or damage (eg. small tears from excessive weight training)
  45. weight lifting causes ___________, not ________
    • weight lifting causes hypertrophy, not hyperplasia
    • you're increasing cells' SIZE, not their number
  46. cardiac muscle repair
    • satellite cell replacement as well as limited mitosis
    • most repair is fibrotic - fibrous scar that can hinder how the heart beats
    • limited though: most you start with is what you end with
  47. smooth muscle repair
    actively proliferates in throughout life in response to damage or physiological needs (e.g. uterine expansion during pregnancy)
  48. afferent, efferent
    • afferent: TO the cell body (dendrites)
    • efferent: AWAY from the cell body (axons
  49. Peripheral Nerve Anatomy
    • Motor Nerve: single neuron, whose cell body lies in the CNS
    • Sensory Nerve: single neuron, whose cell body lies in the dorsal root ganglion
    • Autonomic Nerve: two neurons; 1st neuron’s cell body is in the CNS, it synapses with a second neuron cell body in the autonomic (motor) ganglion, that 2nd neuron goes on to innervate muscle
    • any nerve in the body are MIXED
    • can distinguish Motor & Sensory nerves from Autonomic ones because they’re myelinated while Autonomic nerves are not
  50. Nerve cross-section from most central to most outside
    axon → myelin → endoneurium / Schwann cell cytoplasm (neurilemma)
  51. All axons throughout the body are surrounded by schwann cells
  52. Nuclei within a peripheral nerve will correspond to SCHWANN CELL NUCLEI
  53. Myelin: multiple layers of Schwann cell plasma membrane that insulates the axon
  54. 1 Schwann cell will myelinate a single axon
    • multiple axons will NOT be myelinated by a single Schwann cell
    • however because neuron axons are so long, it takes multiple Schwann cells to myelinate the entire length of one axon
  55. Inside the axon are:
    • microtubules
    • intermediate filaments (neurofilaments)
    • mitochondria
    • [NO mention of microfilaments]
  56. Reticular fibers (type III collagen) make up most of the endoneurium
  57. Neurokeratin
    • residual protein components after the lipid parts have leeched out
    • when you look at preps you don’t necessarily only see only an empty space where the myelin has been leeched out, but you also see wispy material that represents leftover protein from the neurilemma (Schwann cell cytoplasm)
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    • wispy material surrounding the axon where the myelin used to be
  58. Node of Ranvier
    • junction between 2 myelinating Schwann cells
    • only place where there’s depolarization (saltatory conduction)
    • have myelin on Sensory & Somatic Motor neurons because you want those pathways to be as FAST as possible
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  59. Schmidt-Lanterman Incisure/Cleft
    • gap that exists in the myelin where the Schwann cell neurilemma (plasma membrane) & axon are connected (communicate)
    • Schwann cells don’t JUST myelinate the axon, they’re also a source of support for it
    • communication between the Schwann cell & axon are called Schmidt-Lanterman Incisures
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    • appear at oblique angle
    • there’s a continuous cytoplasmic pathways from the Schwann cell all the way to the axon
    • can also see it as a “gap” between circles of myelin around an axon
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  60. Ganglia
    clusters of neuron cell bodies in the peripheral nervous system
  61. Sensory Ganglion
    • dorsal root ganglion will contain only a cell body, NO synapsing
    • pseudounipolar neurons
    • will have pretty complete ring of satellite cells surrounding neuron cell bodies - complete because sensory neurons don’t have any dendrites that can extend out & disrupt that ring of satellite cells
    • central nucleus
    • Image Upload
  62. Autonomic Motor Ganglion
    • enteric looks markedly different from symp/parasymp
    • will contain synapsing
    • multipolar neurons (have a ton of processes that STICK OUT)
    • have many dendrites present, which disrupts the ring of satellite cells
    • eccentric nucleus
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  63. Myenteric (Auerbach’s) Plexuses
    • see neurons between 2 layers of smooth muscle cells running up/down & into/out of the plane
    • this arrangement of smooth muscle is characteristic of peristalsis
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Card Set:
7 Muscle, ~8 Nerve
2016-09-26 00:24:04
MedFoundationsI Histology Exam2
Histology Exam 2
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