Lecture 12 Flashcards
(63 cards)
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
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
3
Q
Muscle appearance
A
Striated or Smooth
4
Q
Arrangement of nuclei of muscle tissue
A
Multinucleated (syncytium)
Mononucleated
5
Q
Function of muscle tissue
A
Voluntary
Involuntary
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
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
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
9
Q
Branchiomeric muscle
A
Associated with pharyngeal arches:
- somewhat of a transition between smooth and striated muscle tissue
- innervated by cranial nerves
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
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
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
13
Q
Gross structure of muscle tissue: aponeuroses
A
-Flat, fan-shaped tendons typically giving rise to other tendons
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
15
Q
Myofilament
A
1) Myosin (thick filaments)
2) Actin (thin filaments)
- Organized into sarcomeres
16
Q
Myofibril
A
Chain of sarcomeres
17
Q
Myofiber
A
Bundle of Myofibrils
- often referred to as a muscle cell
- each fiber formed from many fused myoblasts
18
Q
Fascicle
A
Bundle of myofibers
19
Q
Muscle
A
Composed of varying numbers of fascicles
20
Q
Endomysium
A
Surrounds each muscle fiber
Lies outside sarcolemma (cell membrane)
21
Q
Perimysium
A
Surrounds each fascicle
22
Q
Epimysium
A
Surrounds each muscle
Becomes continuous with tendons
Attached to periosteum
23
Q
Myofilaments (2)
A
Actin and Myosin
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
25
Myosin
- 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
26
Z-lines
Separate adjacent sarcomeres in a fibril
Composed of Z-actin
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I-bands
Located on either side of the Z-line
Make up ends of each sarcomere
**Composed entirely of actin
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A-bands
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*
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H-band
In middle of each A-band
***Composed entirely of myosin
*Band width changes during contraction*
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Contraction of a myofiber
All or none:
| -a muscle fiber will either contract completely or not at all
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Contraction of a myofiber: AP sequence
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
Myofiber growth
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
Motor units
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
Myofiber type
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)
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Dark, slow myofibers
- 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
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Light, fast fibers
- 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
True or false: muscles usually have a mix of fibers
True
38
Muscles predominantly composed of dark fibers
Soleus
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Muscles predominantly composed of light fibers
Gastrocnemius
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Phasic fibers
Found in all vertebrate groups
Not multiply innervated ; Each phasic fiber innervated by 1 motor neuron
Do propagate AP
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Tonic fibers
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
Which of the following do not propagate an AP?
A) Dark, slow fibers
B) Light, fast fibers
C) Phasic fibers
D) Tonic fibers
D) Tonic fibers
43
Muscle contraction
A response to a stimulus
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Types of muscle contraction
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
The result of muscle contractions depends on many variables, including:
- 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
Stability of a bone at a given time is determined by:
Contractions of muscles acting as stabilizers
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Agonist
Muscle doing the desired action
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Antagonist
Muscle that opposes the agonist
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Synergistic
Muscle the eliminates unwanted action by the agonist
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Fixator
Muscle that stabilizes base of attachment of agonist
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Unjointed
Muscle that crosses only 1 joint
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Multijoint
Muscle that crosses more than 1 joint
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Insufficiency
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
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Agonist muscles
- Agonist muscle is a mover when its contraction contributes to the desired movement of a joint
- Classified as prime movers and assistant movers
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Prime agonist mover
Muscle whose primary function is to cause the particular movement, and one which makes a strong contribution to that movement
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Assistant agonist mover
Has the ability to assist in the movement but is only of secondary important to the movement
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Stabilizer (fixator) muscles
Will stabilize the segment (bone) on which another segment (bone) moves
-when a muscle acts as a stabilizer, it usually contracts isometrically
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Neutralizer (synergistic) muscles
Nullify one or more actions of another muscle
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Pure neutralizer muscle
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
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Multi-joint muscle
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
Deltoid muscle
Classified as flexors, extensors, and abductors
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Active insufficiency
(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
Passive insufficiency
(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
