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Histology Exam 3 > Exam 3Skeletal Muscle Composition and the NMJ > Flashcards

Exam 3Skeletal Muscle Composition and the NMJ Flashcards

1
Q

3 types of muscles

A

Cardiac, Skeletal, Smooth

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2
Q

Characteristic of Skeletal muscle

A

Multinucleated cells
Cells appear striated at the microscopic level due to orientation of contractile proteins
Contraction provides voluntary movement

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3
Q

Connective tissue laters of Skeletal Muscle

A

Epimysium, perimysium, endomysium

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4
Q

Epimysium

A

An external sheath of DENSE connective tissue, surrounds the entire muscle.
Septa of this tissue extend inward, carrying the larger nerves blood vessels and lymphatics of the muscle

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5
Q

Perimysium

A

A thin connective tissue layer that immediately surrounds each bundle of muscle fibers termed a fascicle. Each fascicle of muscle fibers makes up a functional unit in which the fibers work together. Nerves, blood vessels, and lymphatics penetrate the perimysium to supply each fascicle.

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6
Q

Endomysium

A

A very thin, delicate later of reticular fibers and scatter fibroblasts within fascicles surrounding the external lamina of individual muscle fibers. In addition to nerve fibers, capillaries form a rich network in the endomysium bringing oxygen to the muscle fibers

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7
Q

Function of collagen in CT layers of muscle

A

serve to transmit the mechanical forces generates by the contracting muscle cells/fibers

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8
Q

Function of CT

A

Nourishment via rich capillary and lymphatic network
Protection/organization
Transmit forces along muscle fibers (through collagen)

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9
Q

Muscle components

A 
Myofilaments
Myofibrils
Muscle Fiber
Muscle fasciculus
Whole Muscle
Myotendinous junction
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10
Q

Myofilaments

A

Protein polymers responsible for contraction (e.g., actin and myosin)

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11
Q

Myofibrils

A

grouping of myofilaments within a muscle cell

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12
Q

Muscle fiber

A

muscle cell, made up of myofibrils

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13
Q

Muscle fasciculus/fascicle

A

bundle of muscle fibers

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14
Q

Whole muscle

A

many fascicles bundled together

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15
Q

Cardiac muscle characteristics

A

composed of irregularly branched cells bound together longitudinally by intercalated discs and shows strong, involuntary contractions

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16
Q

Smooth muscle

A

Composed of grouped, fusiform cells with weak involuntary contractions

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17
Q

Myotendinous junction

A

connection of muscle and tendon
Infoldings of cell membrane of muscle fibers
Provides insertion sites for collagen fibers of tendon into muscle fibers

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18
Q

Sarcomere

A

functional unit of muscle

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19
Q

Components of a sarcomere

A

Thick (myosin) and thin (actin) myofilaments, Titin

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20
Q

Titin functions

A

assists with transmission of force during contraction, limits range of motion of sarcomere in tension, provides passive tension in resting muscle, maintains appropriate positions of actin and myosin (binds Z-disc to M-line)

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21
Q

Sarcomere landmarks

A

Z-line (disk)- boundaries of a sarcomere *actin attaches here
I-band: area of actin molecules only (straddles Z-lines; Z-lines bisect I-band)
A-band: area of myosin and actin overlap
H-band (H-zone): area of myosin only
M-line: anchors central area of myosin within each sarcomere; contains kinase - enzyme that adds high energy phosphates to ADP to make ATP

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22
Q

Myofilaments of skeletal muscle

A

small proteins responsible for muscle contraction (actin and myosin filaments)
Number of myofilaments increases with training hypertrophy while number of muscle fibers is unaltered

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23
Q

Thick filament

A

Myosin

24
Q

Light chain of Myosin

A

Consists of area of ATPase function (globular head)

Serves as connection sites for actin

25
Q

Globular head

A

Heavy chain; just beyond the neck/light chain; Functions as an ATPase - enzyme that energizes the process of muscle contraction by facilitating hydrolysis of ATP to release energy

26
Q

Heavy chain of myosin

A

Consist of helixes of filamentous protein polymers

27
Q

thin filament

A

Actin

28
Q

Actin

A

Globular protein polymer, bound to myosin at cross-bridges (on light chain of myosin)
Globular proteins polymerized into long chains

29
Q

Tropomyosin

A

Filamentous protein that exists within the “grooves” of actin filaments

30
Q

Troponin

A

Complex of three proteins
TnT - binds tightly to tropomyosin
TnC - contains a calcium binding site
TnI - inhibits tropomyosin from uncovering binding sites on actin

31
Q

Sarcoplasmic Reticulum

A

SER of muscle cells is specialized as a storage area for calcium ions; has terminal cisterns adjacent to T-tubules

32
Q

Transverse tubules

A

invaginations of the sarcolemma that create a network of membranous tubules at each sarcomere of muscle fibers

33
Q

Triad

A

complex of two terminal cisterns of SR and one t-tubule; area where sarcolemma depolarization is transmitted to the membrane of the SR

34
Q

Sarcoplasmic Reticulum: function

A

Motor neuron creates depolarization of the sarcolemma at the neuromuscular junction;
Depolarization is transmitted from the sarcolemma to the SR via the T-tubule system of the muscle fiber;
SR depolarization stimulates release of calcium from cisterns;
Released Calcium binds to TnC (binding allows cross-bridging between actin and myosin);
At the end of depolarization, calcium is actively returned from the sarcoplasm to the SR

35
Q

Muscle spindles

A

Proprioceptors within striated muscle fibers; used reflexively to maintain appropriate muscle tension for posture and regulation of opposing muscle groups

36
Q

Spindles consist of

A

A CT capsule that surrounds intrafusal muscle fibers (modified muscle fibers): bag fibers (dynamic and static stretch) and chain fibers (static stretch)

37
Q

Spindles monitor…

A

the velocity and degree of muscle stretch and send that information to the CNS (transmit info using 1A and II afferent fibers)

38
Q

Muscle stretch information from sensory fibers of the spindles synapses at…

A

the spinal cord to allow reflexive control of the contractile state of muscles

39
Q

When stretched (quickly) spindles

A

Stimulate reflexive contraction of the muscle to reduce stretch (MSRs)

40
Q

Spindles also stimulate reflexive inhibition…

A

of antagonist muscles to allow agonist muscles to contract without opposition

41
Q

Gamma motorneuron controls

A

the sensitive of the spindles to stretch

42
Q

Golgi tendon organ

A

Sensory nerve ending imbedded in the collagen fibers of the myotendinous junction; monitors the force of contraction of the muscle and sends info to CNS via 1b afferent fibers;
Provides input to CNS about contraction forces to aid in producing appropriate, smooth contractions

43
Q

GTO provides an inhibitory reflex that…

A

protects muscles from creating too much tension (too much tension in a contracting muscle stimulates reflexive relaxation to prevent muscle damage)

44
Q

glycogen

A

polymer of glucose; abundant amount stored within the sarcoplasm and serves as a source of glucose for energy production

45
Q

Myoglobin

A

oxygen binding protein in sarcoplasm; serves as storage site for oxygen for aerobic respiration; concentrated in muscles that maintain activity for prolonged periods

46
Q

Neuromuscular junction

A

site of connection between the nerve fiber of a motorneuron and the muscle fibers of skeletal muscle (also called “motor end plate”); each nerve contains terminal branches allowing it to synapse with up to several hundred muscle fibers (synapse at midpoint of muscle fiber)

47
Q

Synaptic characteristics

A

Synaptic trough: invagination of muscle membrane

Subneural clefts: folds within synaptic trough which increase surface area for NT receptors (Ach)

48
Q

Mitochondria of motorneuron of NMJ

A

within axon terminal of motorneuron; create ATP energy for acetylcholine synthesis and vesicle exocytosis

49
Q

Voltage gated calcium channels of motorneuron on NMJ

A

Opened by spread of action potential to axon terminal; influx of Ca stimulates vesicle release of Ach

50
Q

How is Ach of motorneuron released? Then what happens?

A

exocytosis of synaptic vesicles; Ach moves into synaptic cleft and binds nicotinic receptors located in subneural clefts

51
Q

The post-synaptic membrane of the NMJ

A

muscle fiber

52
Q

characteristics of the post-synaptic NMJ membrane

A

contains synaptic trough and subneural clefts; Ach binding to nicotinic receptor opens Sodium channels that creates local depolarization (end plate potential); most end plate potentials create and action potential in muscle fibers (for fiber contraction); AP propagates in both directions along muscle fiber (moves along t-tubules within fibers)

53
Q

Neuromuscular contraction

A

AP is transmitted along the t-tubules and across each sarcomere within the muscle fiber; along t-tubule stimulates depolarization of SR membrane which results in release of Calcium from the cisterns of the SR; ACh is active at receptors for milliseconds, ACh is released from its receptor and is quickly degraded by acetylcholinesterase; Calcium binds with TnC and initiates attractive forces between actin and myosin of muscle fibers; conformation change in Tn causes tropomyosin to “move” and uncover actin binding sites; Once calcium binds, actin and myosin “bridge” together; actin-myosin then slide along side each other, creaing a muscle fiber contraction; following contraction calcium is released from TnC and then pumped back into the SR in preparation for the next depolarization

54
Q

Myasthenia gravis

A 
Auto-immune disease in which antibodies "attack" (blocks) ACh receptors and render them non functional; disease creates weakness/paralysis due to inability muscle cell to react to nerve impulses; Treatment: Acetylcholinesterase inhibitors that reduce ACh degradation and increase ACh binding to remain functional receptors. 
Nerve gas (sarin) - inhibits acetylcholinesterase and creates tonic muscle contraction
55
Q

Alpha motor neuron

A

extrafusal muscle fibers (skeletal muscle fibers); creates muscle fiber contraction

56
Q

Gamma motor neuron

A

intrafusal muscle fibers (muscle spindle); generates muscle response to sensory input from muscle spindles; causes tightening/relaxation of spindles to alter their sensitivity

57
Q

C-motor neuron

A

autonomic nervous system fibers to smooth muscle

Histology Exam 3 (6 decks)

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