Unit 3 - Muscle - (Course Notes) Important Terms and Concepts Flashcards

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1
Q

What is muscle?

A

Tissue specialized to convert biochemical reactions into mechanical work

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2
Q

Muscle Function

Two main functions:
i. Motion
ii. Force

A
  • Can only contract
  • Cannot expand - except when physically pulled by antagonist muscle group
  • Generate heat & contribute to body temperature homeostasis
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3
Q

Muscle Types

Three types of muscle in the human body:
i. Skeletal
ii. Smooth
iii. Cardiac

A

i. Skelatal:
-attached to bones→ control movement
-contract in response to signal from somatic motor neuron→ cannot contract on its own, no hormonal influence

ii. Smooth: no striations
-primary muscle of internal organs & tubes (bladder, stomach, blood vessels)
-influences movement of materials through body

iii. Cardiac: has striations
-found only in the heart→ pump to move blood around the body

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4
Q

Skeletal Muscle

Characteristics

A

~40% of body weight, responsible for positioning and movement of skeleton
- attached to bones via tendons
- composed of dense regular connective tissue → collagen (cable-like fibres made of protein)

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5
Q

Skeletal Muscle

Structure

A

-outer connective tissue → epimysium
-contains bundles of muscle tissue called “fascicles”
-fascicles contain muscle fibres

fascicles are covered by perimysium → a connective tissue sheath

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6
Q

Skeletal Muscle

Muscle Fibres

(muscle cells)

A

-muscle fibres are found within each fascicle
-covered by an innermost connective sheath → endomysium
-within the muscle fibres are a large number of myofibrils → the functional units of skeletal muscle
-muscle cells contain many glycogen granules (energy storage), and mitochondria (ATP synthesis) → in the cytosol

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7
Q

Structure of a Muscle Fibre

A

-long, cylindrical cell
-several hundred nuclei on the surface
-cell membrane called “sarcolemma”
-majority of space is taken up by myofibrils → contractile and elastic protein bundles
-have a special ER (sarcoplasmic reticulum, stores calcium)

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8
Q

Sarcoplasmic Reticulum

A

-series of branching tubes called T-tubules (transverse tubules)
-transverse tubules have a lumen continuous with the ECF
-closely associated with terminal cisternae (sequester Ca 2+)
-one T-tubule with flanking terminal cisternae (called a “triad”)
-T-tubule allow for rapid action potential diffusion into muscle fibre

sequester- isolate or hide away

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9
Q

General Term

  1. Muscle cell
  2. Cell membrane
  3. Cytoplasm
  4. Modified ER
A

Muscle Equivalent:
1. Muscle Fibre
2. Sarcolemma
3. Sarcoplasm
4. Sarcoplasmic Reticulum

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10
Q

Organization of the Myofibril

Characteristics

A

-myofibrils occupy most of the space in a muscle
-highly organized→ consist of bundles of contractile elastic proteins
A. Contractile proteins→actin & myosin
B. Regular proteins→ troponin & tropomyosin
C. Accessory proteins→ nebulin (aligns this filament) & titin (elastic protein that returns stretched muscle to relaxed)

Titin’s primary functions are→ stabilize the thick filament, center it between the thin filaments, prevent overstretching of the sarcomere, and recoil the sarcomere like a spring after being stretched.

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11
Q

Organization of the Myofibril

Contractile Proteins

i. Myosin
ii. Actin

A

i. Myosin
-motor protein→ two coiled protein molecule with a head and tail (chains)
-thick filament→ 250 myosin molecules joined
-arranged with heads at the ends and tails together

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12
Q

Organization of the Myofibril

Contractile Proteins

i. Myosin
ii. Actin

A

ii. Actin
-subunits G-actin (globular actin)
-G-actin subunits polymerize, form a chain (F-actin, “filamentous actin”)
-two “F-actin” chains twist together (forms basis of thin filament)
-coiled F-actin associates with regulatory proteins→ Troponin and Tropomyosin (regulate muscle contraction, forms completed thin filament)

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13
Q

Organization of the Myofibril

The Sarcomere

myofibrils have striations
(skeletal muscle = striated muscle)

Sarcomere- one repeated pattern of myofibril unit

A

-a sarcomere is made up of thick and thin filaments→ has striations

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14
Q

Organization of the Myofibril

The Sarcomere

myofibrils have striations
(skeletal muscle = striated muscle)

Sarcomere- one repeated pattern of myofibril unit

A

Z-line (disks)→ site of attachment for thin filaments
-one sarcomere→ made of two Z discs & filaments between them

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15
Q

Organization of the Myofibril

The Sarcomere

myofibrils have striations
(skeletal muscle = striated muscle)

Sarcomere- one repeated pattern of myofibril unit

A

I band (isotropic band) → region containing only thin filaments
-Z disc runs through the middle of the I band → each half of I band is part of a different sarcomere

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16
Q

Organization of the Myofibril

The Sarcomere

myofibrils have striations
(skeletal muscle = striated muscle)

Sarcomere- one repeated pattern of myofibril unit

A

A band (anisotropic band) → region contains thick and thin filaments
-thick and thin filaments overlap at outer edges of A band
-center is occupied by thick filaments only

17
Q

Organization of the Myofibril

The Sarcomere

myofibrils have striations
(skeletal muscle = striated muscle)

Sarcomere- one repeated pattern of myofibril unit

A

H zone (part of A band) → region sontaining only thick filaments
-central region is lighter than outer edges

18
Q

Organization of the Myofibril

The Sarcomere

myofibrils have striations
(skeletal muscle = striated muscle)

Sarcomere- one repeated pattern of myofibril unit

A

M line - the center of the sarcomere → site of attachment for thick filaments

19
Q

What is the effect of not having T-tubules?

Smooth muscle

A
  • No direct coupling of AP (action potential) to calcium release from SR through DHP receptor-ryanodine receptor coupling (skeletal muscle)
  • Calcium entering through cell membrane causes calcium release from the SR
20
Q

How do the properties of myosin contribute to the characteristics of smooth muscle as a whole?

A
  • contract slow & for longer periods of time (than skeletal or cardiac muscle)
  • due partly to slower myosin ATPase activity
  • longer actin and myosin filaments allow longer contractions and allow smooth muscle to be stretched yet still be able to contract