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Histo > Muscle > Flashcards

Muscle Flashcards

(47 cards)

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1
Q

All muscle tissues are involved in what two functions?

A

Movement

Heat production

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2
Q

All muscle tissue contractions depend on myofilaments, which are composed of

A

Thin filaments - actin

Thick filaments- myosin

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3
Q

Satellite cells

A

Unfused prescursor myoblasts/ stem cells that persist in muscle; They fuse with present muscle fibers to support growth with additional nuclei

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4
Q

Why do skeletal muscles have limited regeneraitive capacity?

A

Skeletal muscle cells DO NOT undergo mitosis; they have satellite cells with limited capability to divide & repair

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5
Q

Organization of skeletal muscle

A

Fascicle > Muscle fibers > Myofibrils > Myofilaments > Thin & Thick filaments

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6
Q

Muscle fibers (aka muscle cells) are bound by

A

Connective tissue (epimysium, perimysium, endomysium)- not cell junctions

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7
Q

Fascicle

A

Group of muscle cells held together by perimysium

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8
Q

Visible characteristics of skeletal muscle

A
  • Polygon shaped cross-section; Rectangular longitudinal section
  • Peripheral nuclei
  • Striated
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9
Q

Epimysium- what is its composition and function?

A

Dense irregular connective tissue that ensheaths the entire muscle and carries vascular and nerve supply

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10
Q

Endomysium wraps around

A

Each individual muscle fiber/ cell

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11
Q

Thick filaments

A
  • Myosin II: 2 heavychains, 4 light chains
    • Light chains contain actin, ATP binding sites, ATPase, and motor activity
  • Lined up tail-to-tail to form bipolar thick filaments
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12
Q

What’s the black stuff?

A

Mitochondria

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13
Q

Thin filaments- F-actin, tropomyosin, troponin

A

Tropomyosin masks myosin-binding sites on F-actin

Ca+ binds torponin C to pull off tropomyosin, exposing the myosin-binding sites for the thick filament

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14
Q

A sarcomere (contractil eunit of skeletal muscle) is either

A

Distance between 2 adjacent Z lines

I band + A band

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15
Q

A band composition

A

Full length of thick filaments with some overlap from thin filaments

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16
Q

I band composition

A

Only thin filaments

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17
Q

H band composition

A

Only thick filaments; appears lighter because it lacks thin filaments

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18
Q

M line function

A

Holds thick filaments in place and links them to one another

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19
Q

What happens in muscle contraction

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A

Sarcomere shortens, so

  • Z lines brought closer
  • I band shortens
  • H band shortens
  • A stays teh same*
20
Q

Sliding filament theory

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A
  1. ATP-myosin hydrolyzes -> binds actin
  2. Pi is released -> conformational change (cock)
  3. ADP is released -> power stroke
  4. New ATP binds -> release actin
21
Q

Transverse tubules

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A

Invaginations of the plasma membrane at A-I band junctions that propagate impulses down into all levels of the muscle cell

Serves as voltage-sensor proteins

22
Q

Sarcoplasmic reticulum

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A

Terminal cisternae; stores Ca2+ via gated Ca2+ release channels

Two of these and 1 T-tubule form a triad together

23
Q

Dystrophin

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A

Links actin to endomysium through dystrophin-associated glycoprotein complex

Ensures that shortening of myofibers is transmitted to surrounding connective tissue, resulting in muscle contraction

24
Q

Rigor mortis

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A

Lack of ATP –> can’t release actin, so there’s no detachment and muscles stiffen

25
Motor unit of skeletal muscle
Motor neuron (from ventral horn of spinal cord) + all the muscle fibers it innervates Less muscle fibers, finer movement
26
Neuromuscular junction (motor-end plate)
Where synapse occurs between motor nerve and muscle fiber; point of contact between axon & muscle fiber
27
Initiation of contraction
1. **Action potential** arrives 2. Synaptic transmission at **neuromuscular junction** 3. Propagation of AP along **sarcolemma** 4. **Hyperpolarization of T-tubules** 5. Conformational change of **voltage-sensor proteins** 6. Gated **Ca++-release channels** open 7. Ca++ released into **sarcoplasm** from SR 8. **Troponin** binds Ca++ 9. **Myosin-actin i**nteraction
28
**Myasthenia gravis**
Autoimmune disorder attacking **Ach receptors** on post-synaptic sarcolemma. (The body tries to fix this by digesting affected receptors, but replaces them with less responsive receptors.) --\> **ptosis**
29
Fiber types of skeletal muscle
* **Type I** : slow oxidative; fatigue resistance; red * **Type IIa**: fast oxidative; glycolytic; intermediate * **Type IIb**: fast glycolytic; fatigue-prone; white
30
Sprinting is associated with what type of fiber?
Type IIb Fast glycolytic; fatigue prone
31
**Contrasting red (type I) vs white (type II) fibers**- Vascularity, size, SR mitochondria, myoglobin, etc
Type I is smaller and has less SR, but is otherwise more rich in everything else
32
Myotendinous junction
Where the connective tissues surrounding skeletal muscle fibers become continuous with the dense collagenous (**Type I collagen**) tissue of tendon
33
Sensory Receptors vs Golgi Tendon Organs
**Sensory receptors** penetrate the muscle spindle itself to detect stretch/tension of extrafusal muscle fibers and relay it to the CNS --\> maintain posture & regulate opposing muscle groups **GTO**: Encloses **sensory axons** penetrating among the collagen bundles in **tendons at the myotendinous junction** to send info about stretch and tension to the CNS
34
What is the cursor pointing at?
**Muscle spindles** are located in the connective tissue island between muscle fascicles
35
Visible characteristics of cardiac muscle
* Branching * Intercalated discs * Central nuclei
36
Cardiac muscle is held together by
**Gap junctions** **demosomes**: intermediate filaments for cell adhesion **Adhering junctions** to actin filaments of sarcomeres
37
How to differentiate between skeletal and cardiac muscle on a cross section?
Cardiac = centrall located nuclei
38
Contracitle apparatus of smooth muscle
* **Myosin filaments** (side-polar) and **actin filaments** * But no troponin, no specific patterns (like sarcomeres) * **Dense bodies-** bind to intermediate filaments (vimentin, desmin), actin, and the membrane * Similar to Z-discs * **Caveolae**: dyad * Similar to T-tubule system * **Gap junctions** Actin anchors to dense bodies, which also attach IF to the sarcolemma
39
Regeneration of smooth muscle
High proliferative capacity (hyperplasia) Arises from vascular pericytes
40
Side-polar thick filament of smooth muscle
41
3 ways to initiate smooth muscle contraction
Mechanical (stretching) Depolarization (neuronal) Chemical (vasopressin, angiotensin II , etc)
42
Visible characteristics of smoth muscle
* longitudinal * fusiform, small * no striations * corkscrew-shape dnucleus when contracted * central nucleus * cross-section * central nucleus with little cytoplasm * variable nuclear profile
43
Regulation of smooth muscle contraction by calcium
Note: no troponin involved
44
How to differentiate between smooth muscle and dense irregular connective tissue?
Smooth muscle has more cells & nuclei; whereas, in dense irregular connective tissue has more collagen, less cells
45
White matter vs gray matter of spinal cord
White matter of spinal cord - no neurons Gray matter of spinal cord - neurons
46
**Muscle spindles**
Encapsulated proprioreceptors that help control body posture and coordinate the action of opposing muscles; consists of * Connective tissue capsule * Intrafusal muscle fibers * Sensory nerve fibers penetrating those fibers
47
What kind of muscle is this
Nuclei are peripheral -\> skeletal

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