Lecture 12: Comparative Anatomy Musculature Basics I Flashcards
1
Q
Dumb question to start off on, but what sort of movements involve muscular contractions?
A
- Motor actions (movement of the skeletal system)
- Contractions of the heart and vessels
- Actions in the intestines
- Many other specific movements of and within the body
2
Q
What are the 3 main ways that muscle tissue can be classified?
A
- Muscle tissue can be classified on the basis of a number of its characteristics:
- Appearance:
- Striated
- Smooth
- Arrangement of nucleus (nuclei):
- Multinucleated (Syncytium)
- Mononucleated
- Function:
- Voluntary
- Involuntary
-The most common classification system is based on microscopic appearance and with what organs it is associated.
3
Q
Describe skeletal muscle
A
- Also referred to as striated or voluntary
- Subunits (muscle fibers) of skeletal muscle have a striated or banded appearance when viewed under magnification.
- Skeletal muscle is generally under the voluntary control of its owner.
- Skeletal muscle is typically attached directly or indirectly to the skeletal system.
- Skeletal muscle fibers develop embryologically from many mononucleated cells (myoblasts) that fuse into long fibers which become peripheral and multinucleated
- See Slide 7
4
Q
Describe smooth muscle
A
- Also referred to as visceral or involuntary
- Smooth muscle is not striated.
- Smooth muscle is generally involuntary –you cannot control its contractions.
- Smooth muscle consists of groups of spindle-shaped mononucleated cells with centrally located nuclei.
- Smooth muscle is most commonly associated with viscera –especially the gut tube and other hollow structures.
5
Q
Describe cardiac muscle
A
- Found only in the heart
- Cardiac muscle shares characteristics with both skeletal and smooth muscle.
- It is striated.
- It is involuntary.
- It consists of chains of individual cells that are both mononucleated and striated.
- A major characteristic of cardiac muscle are specialized intercellular junctions called intercalated discs.
- See Slide 10
6
Q
Describe the lesser known fourth type of tissue known as branchiomeric muscle
A
- Associated with pharyngeal arches:
- Somewhat of a transition between smooth and striated muscle tissue
- Innervated by cranial nerves
7
Q
Describe the basis for naming muscles
A
- Shape:
- Fusiform or spindle-shaped
- Pinnate:
- Unipennate
- Bipennate
- Multipennate
- See Slide 11 for Description for each pennate type
- Action (extensor, supinator)
- Location (pectoralis, latissimus dorsi)
- Number of heads (biceps, triceps, quadriceps)
- Fiber direction (oblique, rectus)
- Relative size (major, minor, magnus)
- Origin-insertion (sternocleidomastoid)
8
Q
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A
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9
Q
Describe the attachment structure for muscle anatomy
A
- Origin (proximal attachment):
- Usually proximal
- May be fixed with regard to movement
- Insertion (distal attachment):
- Usually distal
- Usually more movable
10
Q
Describe the tendon structure of muscle anatomy
A
- Attachments between muscle fibers and bone.
- Dense collagenous connective tissue.
- Surrounded by peritendineum.
- Bundles of collagen fibers.
- Poorly vascularized.
11
Q
Describe aponeurosis
A
Aponeuroses: Flat, fan-shaped tendons typically giving rise to other tendons
12
Q
Describe the hierarchical structure of skeletal muscle (again)
A
From smallest to largest units:
- Myofilament:
- Types: Myosin (thick filaments) and Actin (thin filaments)
- Organized into: Sarcomeres
- Myofibril: = chain of sarcomeres
- Myofiber: = bundle of myofibrils
- Often referred to as a muscle cell
- Each fiber formed from many fused myoblasts
- Fascicle: = bundle of myofibers
- Muscle: Composed of varying numbers of fascicles
- See Slide 14
13
Q
What are the 3 connective tissue supports surrounding skeletal muscle?
A
- Endomysium:
- Surrounds each muscle fiber
- Lies outside sarcolemma (cell membrane)
- Perimysium:
- Surrounds each fascicle
- Epimysium:
- Surrounds each muscle
- Becomes continuous with tendons
- Attached to periosteum
14
Q
What are the two main components of myofilaments
A
- Actin
* Myosin
15
Q
Describe the actin protein polymer
A
- Thin filamentous protein polymer (F-actin)
- Each filament is made up of two helically wound polymers of G actin.
- Associated molecules: Tropomyosin, & Troponin
16
Q
Describe myosin bundles
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:
- Produces contraction = sliding filament theory of contraction.
17
Q
Describe sarcomeric arrangement
A
- Myosin and actin filaments are organized into cylindrical units that are aligned end-to-end to form the myofibrils.
- Each cylindrical unit is called a sarcomere.
- A myofibril is, therefore, a chain of sarcomeres.
- Sarcomere structure:
- Z-lines: Separate adjacent sarcomeres in a fibril. Composed of Z-actin
- H-band: In middle of each A-band. Composed entirely of myosin. Band width changes during contraction
- I-band: On either side of A band. Split by Z lines
- A-band: Between two I bands in middle of sarcomere. Composed of both myosin and actin. Represents length of myosin chains. Does not change width during contraction
- I-bands: Located on either side of Z-line. Make up ends of each sarcomere. Composed entirely of actin
- A-bands: Located in middle of sarcomere. Composed of both actin and myosin
- See slides 20,22
18
Q
Describe the contraction of a muscle fiber
A
- All-or-none:
- A muscle fiber will either contract completely or not at all.
- Action-potential Sequence:
- An action potential arrives at the sarcolemma from a motor neuron.
- Synaptic plate is the intervention point between the axon and the sarcolemma.
- Action potential is conducted from sarcolemma into the interior of the myofiber via T-tubules.
- Action potential carried by T-tubules causes the release of calcium ions from the sarcoplasmic reticulum cisternae.
- Calcium ions initiate mechanism by which actin and myosin filaments slide over one another resulting in a contraction.
19
Q
Describe myofiber growth
A
- After birth, the number of myofibers cannot be increased.
- The number of myofibrils can be increased; therefore:
- The mass of a myofiberand a muscle may be increased.
- Lost muscle tissue will be replaced by scar tissue (fibrous connective tissue).
20
Q
What are motor units?
A
- A single nerve cell (neuron) may innervate 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.
- See slide 25
21
Q
Briefly describe the two types of myofibers
A
- Myofiber type is determined by innervating neuron.
- Therefore, all the myofibers in a single motor unit will be of the 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)
22
Q
Describe the Dark, Slow Fiber
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.
23
Q
Describe the light, fast type of muscle fiber
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.
24
Q
What are the characteristics of myofiber types?
A
- Muscles usually have a mix of fibers.
- Some muscles are almost entirely of one fiber type or another:
- Muscles predominantly composed of dark fibers: Soleus
- -Muscles predominantly composed of light fibers: Gastrocnemius
25
Compare phasic fibers to tonic fibers
* Phasic fibers:
- Found in all vertebrate groups.
- Not multiply innervated
- Do propagate action potential
* Tonic fibers:
- Found in non-mammalian vertebrates.
- Involved in slow, sustained postural activities.
- Single nerve cell innervates many fibers:
- - (= motor unit) but each fiber is innervated by more than one nerve cell.
- Contract slowly.
- Do not propagate an action potential.
26
Describe the muscle contraction types
- A contraction is a response to a stimulus.
- Types of contraction:
- - Isometric: Length of muscle does not change.
- - Isotonic: Length of muscle does change:
- - Muscle gets shorter = Concentric.
- - Muscle gets longer = Eccentric.
27
What are examples of muscle names based on each type?
* Shape: Deltoid, Trapezius
* Origin-insertion: Coracobrachialis, Sternocleidomastoid
* Function: Pronator teres, Extensor digitorum
* Relative size: Adductor magnus, Adductor brevis
* Fiber arrangement: Rectus abdominis, Rectus cervicus
* Location: Pectoralis, Latissimus dorsi
28
Describe the fiber arrangement types in musculature
- Straight: Example: rectus abdominis
- Fusiform: Example: biceps brachii
- Unipennate: Example: palmar interosseous muscles
- Bipennate: Example: dorsal interosseous muscles
- Multipennate: Example: deltoid muscle
29
Describe the types of muscle action
* The result of a muscle contraction 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.
* For example, when the muscle contracts, it pulls toward the middle, exerting equal force on attachments at both ends in an attempt to pull them toward each other.
- Which bone moves depends on the relative stability of the bones at that particular time.
- Stability of a bone at a given time is determined by contractions of muscles acting as stabilizers.
30
What are terms related to muscle function
- Agonist: Muscle doing the desired action.
- Antagonist: Muscle that opposes the agonist.
- Synergist: Muscle that eliminates unwanted action by the agonist.
- Fixator: Muscle that stabilizes base of attachment of agonist.
- Unijoint: Muscle that crosses only one joint.
- Multijoint: Muscle that crosses more than one joint.
- 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.
31
Describe agonists, antagonists, and stabilizers
* Agonist (mover) muscle is a mover when its contraction contributes to the desired movement of a joint.
- Agonist muscles are classified as prime movers and assistant movers.
- The prime mover is a muscle whose primary function is to cause the particular movement, and one which makes a strong contribution to that movement.
- An assistant mover has the ability to assist in the movement but is only of secondary importance to the movement.
* Antagonists oppose the movement of an agonist.
* 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.
32
Describe the terms neutralizer, and multi-joint muscles
* Neutralizer (synergistic) muscles nullify one or more actions of another muscle.
- A pure neutralizer will cause the opposite motion of the prime mover without assisting in the movement.
- The triceps is a pure synergist 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.
* A multi-joint muscle is one that extends across more than one joint and potentially can contribute to movement at each joint that it crosses.
- Multi-joint muscles do not allow complete range of motion in all joints at one time.
33
Give muscle examples of flexors, extensors, and abductors
* Muscles that pass anterior to the axis of a joint are flexors:
- Examples: deltoid, biceps.
* Muscles that pass posterior to the axis of a joint are extensors:
- Examples: deltoid, triceps.
* Muscles that pass lateral to a joint are abductors:
- Example: deltoid.
* Muscle flexors can shorten about one-half of total length.
34
Describe active muscle insufficiency
* 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.
35
Describe Passive Muscle Insufficiency
* Passive insufficiency (involves passive elements):
- Occurs when the inactive antagonist muscle is of insufficient length to allow a force to complete the full range of motion available.
- Mostly applies to multi-joint muscles.
