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Comparative Anatomy > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

Muscle activity

A

All movements in the human body involve muscular contractions, including:

Motor actions (movement of skeletal system)

Contractions of heart and vessels

Actions in the intestines

Many other specific movements of and within the body

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2
Q

Muscle tissue classification

A

Muscle tissue is classified on the basis of a number of its characteristics including:

1) Appearance
2) Arrangement of nucleus (nuclei)
3) Function

Most common classification system is based on microscopic appearance and with what organs it is associated

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3
Q

Muscle appearance

A

Striated or Smooth

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4
Q

Arrangement of nuclei of muscle tissue

A

Multinucleated (syncytium)

Mononucleated

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5
Q

Function of muscle tissue

A

Voluntary

Involuntary

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6
Q

Skeletal muscle

A
  • Striated
  • Voluntary
  • Subunits of skeletal muscle have striated or banded appearance when viewed under magnification
  • Skeletal muscle is generally under voluntary control
  • Typically attached directly or indirectly to skeletal system
  • Fibers develop embryologically from many mononucleated cells (myoblasts) that fuse into long fibers which become peripheral and multinucleated
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7
Q

Smooth muscle

A
  • Also referred to as visceral or involuntary
  • Not striated
  • Generally involuntary
  • Consists of groups of spindle-shaped mononucleated cells with centrally located nuclei
  • Most commonly associated with viscera–especially the gut tube and other hollow structures
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8
Q

Cardiac muscle

A
  • Found only in the heart
  • Shares characteristics with both smooth and skeletal
  • Striated
  • Involuntary
  • Consists of chains of individual cells that are both mononucleated and striated
  • Major characteristics are specialized intercellular junctions called intercalated discs
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9
Q

Branchiomeric muscle

A

Associated with pharyngeal arches:

  • somewhat of a transition between smooth and striated muscle tissue
  • innervated by cranial nerves
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10
Q

Basis for muscle names

A

1) Shape: fusiform or spindle-shaped; pinnate (unipennate, bipennate, multipennate)
2) Action: extensor, supinator
3) Location: pectoralis, latissimus dorsi
4) Number of heads: biceps, triceps, quadriceps
5) Fiber direction: oblique, rectus
6) Relative size: major, minor, magnus
7) Origin-insertion: sternocleidomastoid

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11
Q

Gross structure of muscle tissue: attachments

A

Origin (proximal attachment):

  • usually proximal
  • may be fixed with regard to movement

Insertion (distal attachment):

  • usually distal
  • usually more movable
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12
Q

Gross structure of muscle tissue: tendons

A
  • Attachments between muscle fibers and bone
  • Dense collagenous connective tissue
  • Surrounded by peritendineum
  • Bundles of collagen fibers
  • Poorly vascularized
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13
Q

Gross structure of muscle tissue: aponeuroses

A

-Flat, fan-shaped tendons typically giving rise to other tendons

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14
Q

Hierarchical structure of skeletal muscle

A

Smallest—->Largest

1) Myofilament
2) Myofibril
3) Myofiber
4) Fascicle
5) Muscle
6) Endomysium
7) Perimysium
8) Epimysium

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15
Q

Myofilament

A

1) Myosin (thick filaments)
2) Actin (thin filaments)
- Organized into sarcomeres

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16
Q

Myofibril

A

Chain of sarcomeres

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17
Q

Myofiber

A

Bundle of Myofibrils

  • often referred to as a muscle cell
  • each fiber formed from many fused myoblasts
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18
Q

Fascicle

A

Bundle of myofibers

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19
Q

Muscle

A

Composed of varying numbers of fascicles

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20
Q

Endomysium

A

Surrounds each muscle fiber

Lies outside sarcolemma (cell membrane)

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21
Q

Perimysium

A

Surrounds each fascicle

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22
Q

Epimysium

A

Surrounds each muscle

Becomes continuous with tendons

Attached to periosteum

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23
Q

Myofilaments (2)

A

Actin and Myosin

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24
Q

Actin

A
  • thin filamentous protein polymer (F-actin)
  • each filament is made up of 2 helically wound polymers of G actin
  • Associated molecules:
    • -Tropomyosin
    • -Troponin
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25
Q

Myosin

A
  • Bundles of long molecules:
    • -Tail + ATPase head
    • -Head attached to tail via swivel mechanism
  • Heads attach to binding sites on actin filaments
  • Attach-swivel-release- cycles allow myosin and actin to slide along one another in opposite directions:
    • -Producing contraction=sliding filament theory of contraction
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26
Q

Z-lines

A

Separate adjacent sarcomeres in a fibril

Composed of Z-actin

27
Q

I-bands

A

Located on either side of the Z-line

Make up ends of each sarcomere

**Composed entirely of actin

28
Q

A-bands

A

Located in middle of sarcomere between 2 I bands

***Composed of both actin and myosin

Represents length of myosin chains

Does not change width during contraction

29
Q

H-band

A

In middle of each A-band

***Composed entirely of myosin

Band width changes during contraction

30
Q

Contraction of a myofiber

A

All or none:

-a muscle fiber will either contract completely or not at all

31
Q

Contraction of a myofiber: AP sequence

A

1) AP arrives @ sarcolemma from a motor neuron
2) Synaptic plate is the intervention point b/t the axon and the sarcolemma
3) AP is conducted from the sarcolemma into the interior of the myofiber via T-tubules
4) AP carried by T-tubules causes the release of Ca++ from the sarcoplasmic reticulum cisternae
5) Ca++ initiates mechanism by which actin and myosin filaments slide over one another resulting in a contraction

32
Q

Myofiber growth

A

After birth, the # of myofibers cannot be increased***

The number of myofiBRILS can be increased, therefore:
-the MASS of a myofiber and muscle can be increased

Lost muscle tissue will be replaced by scar tissue (fibrous CT)

33
Q

Motor units

A

A single nerve cell (neuron) may innervated from a few to several hundred myofibers

A neuron and the myofibers it innervates constitute a motor unit

When a neuron fires, all the myofibers in the motor unit contract

All-or-none really refers to a motor unit

34
Q

Myofiber type

A

Determined by innervation neuron
-therefore, all the myofibers in a single motor unit will be same type

Fiber type classification is based mainly on endurance (resistance to fatigue) and speed of contraction

Types:

  • Dark, slow fibers (red fibers)
  • Light, fast fibers (white fibers)
35
Q

Dark, slow myofibers

A
  • Fatigue resistant
  • Contract slowly (slow twitch)
  • Rely on oxidative phosphorylation
  • Have a large number of mitochondria
  • Have a high concentration of myoglobin
  • Have a low concentration of ATPase
36
Q

Light, fast fibers

A
  • Fatigue easily
  • Contract rapidly (fast twitch)
  • Rely on glycolysis
  • Have a small number of mitochondria
  • Have a low concentration of myoglobin
  • Have a high concentration of ATPase (higher the concentration of the enzyme, faster the reaction)
37
Q

True or false: muscles usually have a mix of fibers

A

True

38
Q

Muscles predominantly composed of dark fibers

A

Soleus

39
Q

Muscles predominantly composed of light fibers

A

Gastrocnemius

40
Q

Phasic fibers

A

Found in all vertebrate groups

Not multiply innervated ; Each phasic fiber innervated by 1 motor neuron

Do propagate AP

41
Q

Tonic fibers

A

Found in non-mammalian vertebrates

Involved in slow, sustained postural activities

Single nerve cell innervated many fibers:
=motor unit; but each fiber is innervated by more than 1 nerve

Contract slowly

Do not propagate an AP

42
Q

Which of the following do not propagate an AP?

A) Dark, slow fibers
B) Light, fast fibers
C) Phasic fibers
D) Tonic fibers

A

D) Tonic fibers

43
Q

Muscle contraction

A

A response to a stimulus

44
Q

Types of muscle contraction

A

Isometric:

  • length of muscle does not change
  • ex: pushing against a wall

Isotonic:

  • muscle gets shorter=concentric (pull up)
  • muscle gets longer=eccentric (push up)
45
Q

The result of muscle contractions depends on many variables, including:

A
  • What the muscle is attached to
  • Which end of the muscle is fixed
  • The force of the contraction and the force of the resistance
  • The simultaneous actions of other muscles associated with the same structure
46
Q

Stability of a bone at a given time is determined by:

A

Contractions of muscles acting as stabilizers

47
Q

Agonist

A

Muscle doing the desired action

48
Q

Antagonist

A

Muscle that opposes the agonist

49
Q

Synergistic

A

Muscle the eliminates unwanted action by the agonist

50
Q

Fixator

A

Muscle that stabilizes base of attachment of agonist

51
Q

Unjointed

A

Muscle that crosses only 1 joint

52
Q

Multijoint

A

Muscle that crosses more than 1 joint

53
Q

Insufficiency

A

Inability of a multijoint muscle to contract maximally over all joints crossed simultaneously:

 - Active insufficiency:   
     - refers to the agonist
 - Passive insufficiency:
     - refers to the antagonist
54
Q

Agonist muscles

A
  • Agonist muscle is a mover when its contraction contributes to the desired movement of a joint
    • Classified as prime movers and assistant movers
55
Q

Prime agonist mover

A

Muscle whose primary function is to cause the particular movement, and one which makes a strong contribution to that movement

56
Q

Assistant agonist mover

A

Has the ability to assist in the movement but is only of secondary important to the movement

57
Q

Stabilizer (fixator) muscles

A

Will stabilize the segment (bone) on which another segment (bone) moves
-when a muscle acts as a stabilizer, it usually contracts isometrically

58
Q

Neutralizer (synergistic) muscles

A

Nullify one or more actions of another muscle

59
Q

Pure neutralizer muscle

A

Will cause the opposite motion of the prime mover without assisting in the movement

  • the triceps is a pure synergistic to the biceps elbow flexion, so that the biceps can perform supination of the forearm
  • the pronator teres is a helping synergist for elbow flexion performed by the biceps while it nullifies the supination component of the biceps
60
Q

Multi-joint muscle

A

One that extends across more than just one joint and potentially can contribute to movement at each joint that it crosses
-multi-joint muscles do not allow complete ROM is all joints at one time

61
Q

Deltoid muscle

A

Classified as flexors, extensors, and abductors

62
Q

Active insufficiency

A

(Involves active components)
-The diminished ability of a muscle to produce or maintain active tension

  • The muscle is elongated to a point where there is no overlap between myofilaments
  • The muscle is excessively shortened when all cross-bridges have been formed
  • One-joint muscles are arranged so this won’t occur
63
Q

Passive insufficiency

A

(Involved passive elements)
-Occurs when the inactive antagonist muscle is of insufficient length to allow a force to complete a full ROM available

-Mostly applies to multi-joint muscles

Comparative Anatomy (5 decks)

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