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Anatomy and Physiology > Muscular Tissue and Skeletal Muscles > Flashcards

Muscular Tissue and Skeletal Muscles Flashcards

1
Q

Muscle Types

A

o Skeletal
o Cardiac
o Smooth

  • Skeletal and smooth muscle cells are elongated
  • Contraction and shortening of muscles are due to the movement of microfilaments
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2
Q

Skeletal Muscle

A
  • Most skeletal muscle fibres are attached by tendons to bones
  • Skeletal muscle cells are large, cigar shaped and multinucleate
  • Striated Muscle (due to stripes)
  • Voluntary Muscle (under conscious control, stimulated by nerve activity)
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3
Q

Skeletal Muscle Layers

A
  • Endomysium (enclose a single muscle fibre)
  • Perimysium (wraps around a fascicle of muscle fibres)
  • Epimysium (covers the entire skeletal muscle, composed of fibrous tissue)
  • Fascia (on the outside of the epimysium)
  • Sarcolemma (cell membrane of muscle fibre)
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4
Q

Epimysium

A
  • Blends into a connective tissue attachment

Tendons (cordlike structures)
 Mostly collagen fibers
 Often cross a joint because of their toughness and small size

Aponeuroses (sheetlike structures)
 Attach muscles indirectly to bones, cartilage, or connective tissue coverings

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5
Q

Skeletal Muscle Fibre Types

A

Slow Twitch (type I) fibres

Fast Twitch (type II) fibres (produce more force, fatigue more rapidly) 
o	Type IIa fibres (intermediate contraction rate) 
o	Type IIb fibres (fastest contraction)
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6
Q

Smooth Muscle

A
  • No striations
  • Involuntary (no conscious control)
  • Spindle-shaped fibres that are uninucleate
  • Contractions are slow and sustained (without muscle becoming fatigued)
  • Found main in the walls of hollow visceral organs, bladder and respiratory passages (visceral muscle)
  • Arranged in layers
  • Moving food through the digestive system, emptying the bladder, changing diameter of blood vessels
    o Food is propelled through a process called peristalsis
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7
Q

Cardiac Muscle

A
  • Striations
  • Involuntary (under control of ANS)
  • Found only in the walls of the heart
  • Uninucleate
  • Branching cells joined by gap junctions called intercalated discs
    o Arrangement allows simultaneous contraction of neighbouring cells
  • Contracts at a steady rate set by pacemaker cells
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8
Q

Skeletal Muscle Functions

A
  • Maintain posture and body position (postural muscles are continually contracting)
  • Stabilise joints
  • Generate heat
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9
Q

Types of Muscle Contractions

A

Isotonic Contractions
o Myofilaments can slide past each other during contractions
o Muscle shortens, and movement occurs
o Example: bending the knee, lifting weights, smiling
o Concentric Isotonic = shortening of the muscle (muscle tension is greater than the resistance)

Isometric Contractions
o Muscle filaments are trying to slide, but the muscle is pitted against an immovable object
o Tension increases, but muscles do not shorten
o Example: pushing your palms together in front of you

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10
Q

Organisation of the Sarcomere

A

Myofilaments produce banding (striped) pattern
 Thick filaments = myosin filaments
 Thin filaments = actin filaments

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11
Q

Thick Filaments = Myosin Filaments

A

o Composed of the protein myosin
o Contain ATPase enzymes to split ATP (ADP and P) to release energy for muscle contractions
o Possess projections known as myosin heads (binding site for ATP)
o Myosin heads are known as cross bridges when they link thick and thin filaments during contraction

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12
Q

Thin Filaments = Actin Filaments

A

o Composed of the contractile protein actin
o Actin is anchored to the Z-disc

Small spherical molecules bind together to form a fibrous strand
 Some action molecules contain an actin binding site  myosin head attaches to these sites during contraction to form a cross bridge

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13
Q

Nerve Stimulus and Action Potential

A

Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
o Otherwise cannot develop tension/n

  • Motor Unit (one motor neuron and all the skeletal muscle cells stimulated by that neuron)
  • Motor Neuron – nerve that stimulates skeletal muscle (under voluntary control)
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14
Q

Neuromuscular Junction

A
  • Association site of axon terminal of the motor neuron and sarcolemma of muscle
  • Size of motor unit determines degree of control (inverse relationship)
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15
Q

Events at the Neuromuscular Junction

A
  • Axon connects the motor neuron of a cell body with the muscle fibres
  • Axon then branches into the axon terminals
    o Axon terminals than branch out to separate muscle fibers
  • Nerve impulse reaches axon terminal -> neurotransmitter released and diffused across the synaptic cleft
    o Neurotransmitters (ACh) than attach to receptors on the muscle fiber sarcolemma
    o ACh make sarcolemma temporarily permeable to ions
  • Ion channels open
    o Positive sodium ions rapidly enter the fibre
    o Positive potassium ions rapidly exit the fibre
     Net Effect = Positive Charge in the fibre (more sodium enter than potassium leave)
  • Change in charge triggers the opening of more channels on the membrane
    o Only allow entry of additional sodium ions (temporarily more permeable to sodium)
     Generates electrical charge (action potential)
     Action potential spreads from one end of the fiber to another
  • Enzyme acetylcholinesterase breaks down ACh to acetic acid and choline
  • Ion channels close and muscle contraction ends
  • Muscle fibers return to resting state
    o When potassium ions diffuse out of the cell
    o Sodium-potassium exchange pump moves ions back to original positions
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16
Q

Neurotransmitter

A
  • Chemical released by nerve upon arrival of nerve impulse in the axon terminal
  • Acetylcholine (Ach) is the neurotransmitter that stimulates skeletal muscle
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17
Q

Synaptic Cleft

A
  • Gap between nerve and muscle filled with interstitial fluid
  • Although very close, the nerve and muscle do not make contact
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18
Q

Sliding Filament Theory

A

o Calcium ions bind to regulatory proteins on thin filaments and expose myosin-binding sites
 Allows the myosin heads on the thick filaments to attach

o Each cross bridge pivots
 Causes the thin filaments to slide toward the center of the sarcomere

o Contraction occurs, and the cell shortens

o During a contraction
 Cross bridge attaches and detaches several times
 Calcium ions released allow the myosin heads to attach to the actin filaments

o ATP provides the energy for the sliding process (continues as along as calcium ions are present)
o Variation in force and speed (regulated by variation in frequency and amount of action potentials)

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19
Q

Cross Bridge Cycle

A
  • Initiated when calcium ions released from sarcoplasmic reticulum bind to troponin
    o Binding causes troponin to change shape
  • Tropomyosin moves away from the myosin binding sites on actin
    o Allows myosin head to bind actin -> form a cross bridge
    o Myosin head must be activated before a cross bridge cycle can begin
  • Cycle will repeat if actin remain exposed
    o Through repetitions -> thin myofilaments are pulled towards each other -> sarcomere shortens
  • Cycle will end when calcium ions are actively transported back into the sarcoplasmic reticulum
    o Troponin returns to its original shape
    o Allows tropomyosin to cover the myosin binding site on actin
20
Q

Four Main Stages of Cross Bridge Cycle

A

Step 1: Cross Bridge Formation

  • Activated myosin head binds to actin  forms cross bridge
  • Inorganic phosphate is released
  • Bond between myosin and actin becomes stronger

Step 2: Power Stroke
- ADP is released and activated myosin head pivots
• Slides thin myofilament toward the center of the sarcomere

Step 3: Cross Bridge Detachment
- Another ATP binds to myosin head
• Link between myosin head and actin weakens
• Myosin head detaches

Step 4: Reactivation of Myosin Head
- ATP is hydrolysed to ADP and inorganic phosphate e
• Energy reactivates the myosin head -> returning it to the cocked position

21
Q

Special Functional Properties of Skeletal Muscles

A

Special functional properties of skeletal muscles
o Extensibility (ability of muscle cells to be stretched)
o Elasticity (ability to recoil and resume resting length after stretching)
o Irritability / responsiveness (ability to receive and respond to a stimulus)
o Contractility (ability to forcibly shorten when an adequate stimulus is received)
 Unique to muscle tissue

22
Q

Graded Responses

A
  • Increase in voltage -> more motor units contract
    o Tension within each contraction increases till point of maximum muscle contraction is reached
     All motor units are stimulated
     Known as recruitment
  • Muscles fiber contraction ‘all-or-none’ meaning it will contact to its fullest when stimulated adequately
    o If stimulus is not sufficient, muscle will not contract
  • Within a whole skeletal muscle
    o Not all fibers may be stimulated during the same interval
  • Different combinations of muscle fiber contractions may give differing responses
  • Graded responses – different degrees of skeletal muscle shortening
23
Q

Production of Graded Responses

A

Graded responses can be produced in two ways:
o By changing the frequency of muscle stimulation
o By changing the number of muscle cells being stimulated at one time

24
Q

Muscle Response to Increasingly Rapid Stimulation

A

Muscle Twitch
o Single, brief, jerky contraction
o Not a normal muscle function

  • In most types of muscle activity, nerve impulses are delivered at a rapid rate
  • As a result, contractions are ‘summed’ (added) together, and one contraction is immediately followed by another
  • When stimulations become more frequent, muscle contractions get stronger and smoother
  • Fused (complete) tetanus is achieved when the muscle is stimulated so rapidly that no evidence of relaxation is seen (tetanic contraction)
  • Contractions are smooth and sustained
25
Q

Muscle Response to Stronger Stimuli

A
  • Muscle force depends upon the number of fibers stimulated
  • Contraction of more fibers results in greater muscle tension
  • When all motor units are active and stimulated, the muscle contraction is as strong as it can get
26
Q

Providing Energy for Muscle Contraction: ATP

A

o Only energy source that can be used to directly power muscle contraction
 Produced continuously

o Stored in muscle fibers in small amounts that are quickly used up
o After this initial time, other pathways must be utilised to produce ATP

27
Q

Direct Phosphoralysation of ADP to CP

A

 CP is only present in muscle fibres
 As ATP use increases, interactions between CP and ADP transfer high energy phosphate group from CP to ADP
• More ATP is created

28
Q

Aerobic Pathway

A
  • Generates majority of ATP during rest and light and moderate exercise

Aerobic respiration
• Glucose and fat broken down -> forms CO2 and water
• Some energy released is stored in bonds of ATP molecules
• Slow and requires a constant supply of oxygen and nutrients

29
Q

Anaerobic Glycolysis and Lactic Acid Formation

A
  • Breakdown of glucose -> pyruvic acid and ATP are produced
  • If oxygen is present -> pyruvic acid used in aerobic respiration to produce more ATP
  • If activity is intense, or oxygen and glucose are low -> slow aerobic pathways cannot produce ATP fast enough to maintain muscle contractions
    • Pyruvic acid produced during glycolysis -> converted to lactic acid
30
Q

Types of Body Movements

A
  • Muscles are attached to no fewer than two points
    o Origin – attachment to an immovable or less movable bone
    o Insertion – attachment to a movable bone
  • When the muscle contracts
    o The insertion moves toward the origin
  • Body movement occurs when muscles contract across joints
31
Q

Flexion

A
  • Decreases the angle of the joint (generally in sagittal plane
  • Brings two bones closer together
  • Typical of bending hinge joints (e.g., knee and elbow) or ball-and-socket joints (e.g., the hip)
32
Q

Extension

A
  • Opposite of flexion
  • Increases angle between two bones
  • Typical of straightening the elbow or knee
  • Extension beyond 180° is hyperextension (beyond normal anatomical position)
33
Q

Rotation

A
  • Movement of a bone around its longitudinal axis (generally through the transverse plane)
  • Common in ball-and-socket joints
  • Examples: moving the atlas around the dens of the axis
34
Q

Abduction

A
  • Movement of limb away from the midline (along frontal plane)
35
Q

Adduction

A
  • Opposite of abduction

- Movement of a limb toward the midline (along frontal plane)

36
Q

Circumduction

A
  • Combination of flexion, extension, abduction, and adduction
  • Common in ball-and-socket joints
  • Proximal end of bone is stationary
  • Distal end moves in a circle
37
Q

Dorsiflexion

A
  • Lifting the foot (occurs in sagittal plane)

o Superior surface approaches the shin

38
Q

Plantar Flexion

A
  • Pointing the toes away from the head (occurs in sagittal plane)
39
Q

Inversion

A
  • Turning sole of the foot medially (occurs in frontal plane)
40
Q

Eversion

A
  • Turning sole of the foot laterally (occurs in frontal plane)
41
Q

Supination

A
  • Forearm rotates laterally so palm faces anteriorly

- Radius and ulna are parallel

42
Q

Pronation

A
  • Forearm rotates medially so palm faces posteriorly

- Radius and ulna cross each other like an X

43
Q

Opposition

A
  • Moving the thumb to touch the tips of other fingers on the same hand
44
Q

Interactions of Skeletal Muscles in the Body

A
  • Muscles can only pull as they contract (cannot push)
  • Groups of muscles that produce opposite actions lie on opposite sides of a joint
  • When a skeletal muscle develops tension, one of three things can happen:
    o Shorten
    o Remain the same length
    o Lengthen

Agonist
o Major muscles within a certain movement

Antagonist
o Opposes or reverses a prime mover

Synergist
o Aids a prime mover in a movement or reduces undesirable movements

Fixator
o Specialised synergists that hold a bone still or stabilise the origin of a prime mover

45
Q

Fascicle Arrangement to Muscle Structure

A

Circular
o Concentrically arranged fascicles around on opening
o Sphincter = contraction decreases diameter of a passageway

Convergent
o Widespread muscle fascicles over a broad area which converge on a common attachment point
o Often triangular in shape
o Direction of its pull can be manipulated

Parallel
o Length of the fascicles run along the axis of the long axis of the muscle
o Strap-like

Fusiform
o Spindle-shaped muscle with an expanded belly

Pennate
o Muscles resemble a large feather with respect to the tendon
o Have one or more tendons extending through their body
o Fascicles are arranged obliquely to their tendon

Multipennate
o Has branches of tendon within the muscle
o Fascicles arranged on both sides of the tendon branch

Bipennate
o Has muscle fascicles on both sides of the tendon

Unipennate
o Has all muscle fascicles on the same side of the tendon

46
Q

Common Injuries and Disorders of Muscles

A

Strains
o Occur when a muscle is stretched (mild, moderate, or severe)

Contusions
o Bruising or bleeding within a muscle (moderate to severe)

Cramps
o Severe muscle spasms (nutrient deficiency in Ca, Mg, or K and dehydration)

Delayed onset muscle soreness (DOMS)
o Common after unaccustomed activity (microscopic tears in muscle tissue, inflammation, stiffness)

Tendinitis (acute) and tendinosis (chronic = degeneration of a tendon due to microtears)
o Inflammation of a tendon (aging, common sites = shoulder, wrist, Achilles)

Rotational injuries of the shoulder
o Inflammation or muscle tears

Overuse injuries of the elbow
o Inflammation or muscle tears

Shin Splints
o An overuse injury

Whiplash Injuries
o Result from rapid, forceful contractions of neck muscles

Hernia
o Bulging of the abdominal cavity

Anatomy and Physiology (14 decks)

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