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HBA > WEEK 8 - MUSCULAR SYSTEM > Flashcards

WEEK 8 - MUSCULAR SYSTEM Flashcards

1
Q

Types of muscular tissue 1

A

Muscle type: skeletal
Location: skeleton
Function: move bones
Appearance: multi-nucleated and striated
Control: voluntary

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2
Q

Types of muscular tissue 2

A

Muscle type: cardiac
Location: heart
Function: pump blood
Appearance: One nucleus, striated and intercalated discs
Control: Involuntary

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3
Q

Types of muscular tissue 3

A

Muscle type: smooth
Location: various organs
Function: various functions
Appearance: One nucleus, no striations
Control: Involuntary

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4
Q

Functions of Muscular Tissue

A
  1. Producing body movement
    – Move bones and joints to execute movements such as walking, running, writing.
  2. Stabilising body positions
    – Maintain standing or sitting through contraction of postural muscles while awake.
  3. Storing and moving substances within the body
    – Smooth muscle contractions move food through GI tract, propel urine and sperm. Smooth muscle rings called sphincters prevent outflow of contents of hollow
    organs (e.g. stomach and bladder) to allow for temporary storage.
  4. Generating heat
    – Muscular contraction leads to thermogenesis.
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5
Q

Properties of Muscle

A
  • Electrical excitability
  • Able to respond to stimuli by producing electrical signals.
    Autorhythmic electrical signals arising in muscular tissue itself (cardiac) or chemical stimuli (neurotransmitters, hormones)
  • Contractility
  • Ability to contract forcefully when stimulated by an action potential.
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6
Q

Properties of muscles cont.

A
  • Extensibility
  • Ability to stretch (within connective tissue limits) without being damaged. Smooth muscle is subject to greatest stretch, while cardiac is stretched during filling phase.
  • Elasticity
  • Returns to its original length and shape after contraction or extension.
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7
Q

Skeletal Muscle Structure

A
  • Tendons
    – Connects skeletal muscle to bone
  • Fascia
    – Covers and separates individual muscles
  • Epimysium
    – Outer sheath (under fascia) that surrounds muscle
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8
Q

Skeletal Muscle Structure cont.

A
  • Perimysium
    – Surrounds individual fascicles
    – Fascicles are subunits of skeletal muscle
  • The strings in stringy meat
  • Composed of many microscopic muscle fibres/cells
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9
Q

Skeletal Muscle Structure cont.

A
  • Endomysium
    – Very thin sheath surrounding individual fibres
    – Binds fibres together within a fascicle
  • Connective tissue of skeletal muscle is continuous
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10
Q

Microscopic Anatomy

A
  • Sarcolemma
    – The cell membrane of a muscle fibre
  • Sarcoplasm
    – The cytoplasm of muscle cell
  • Myofibril
    – Rod-like contractile element
  • Spans the cell length
  • Comprises most of the volume of muscle
  • Myofilaments
    – Include the thick filament MYOSIN & the thin filament
    containing ACTIN, TROPONIN & TROPOMYOSIN
    – Causes the striated appearance of skeletal muscle
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11
Q

Arrangement of Sarcomere

A
  • Z disc: Separates one sarcomere from the next
  • A-Band: Dark middle part of sarcomere that extends the
    entire length of thick filaments and includes parts of thin
    filaments that overlap
  • I-Band: Light area that contains remainder of thin but not thick filament.
  • H-Zone: Narrow region in centre of A band that contains
    thick filaments but no thin
  • M-Line: Region in centre of H-zone that contains proteins that hold thick filaments together at the center of sarcomere.
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12
Q

Myofilaments

A
  • Thick Filament – Myosin
  • Globular head contains:
    – ATP binding site
    – Actin binding site
    – ATPase
  • The myosin heads form “cross bridges”
    – Attaches to actin during muscle contraction
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13
Q

Myofilaments cont.

A
  • Thin Filament - Actin
    – Makes up thin filaments
    – Two actin chains are wound around each other
    – Has binding sites for myosin to attach during contraction
  • Tropomyosin
    – Long, thin protein associated with actin
    – Blocks myosin binding sites on actin during muscle relaxation
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14
Q

Myofilaments cont.

A
  • Troponin
    – A protein attached to tropomyosin
    – Three part protein
  • Troponin-T (tropomyosin), Troponin-C (calcium), Troponin-I (inhibitory)
    – The “blocker” of the myosin binding site on actin
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15
Q

The Neuromuscular Junction

A
  • Somatic motor neurons extend from the brain or spinal cord to a group of skeletal muscles
  • Muscle action potentials arise at the neuromuscular junction – the synapse between a somatic motor neuron and skeletal muscle fibre.
  • Motor end plate – the region of sarcolemma opposite the synaptic end bulbs
  • There is a synaptic cleft – neurotransmitter (Acetylcholine)
    1. Release of acetylcholine
    2. Activation of ACh receptors
    3. Production of muscle action potential
    4. Termination of ACh activity
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16
Q

Cross Bridge Cycle

A
  • A single power stroke of all cross bridges would shorten muscle by only approximately 1% of resting length.
  • Muscles can shorten up to ~50-60% of resting length
  • Therefore, contraction cycles must be repeated many times
  • Cross bridges must:
  • detach from actin at conclusion of the power stroke
  • Resume their resting orientation
  • Reattach to actin and repeat the cycle
17
Q

Muscle Relaxation

A
  • AP’s travelling along motor neuron stop
  • No neurotransmitter (ACh) present at neuromuscular junction
  • AP’s in muscle cease
  • Ca2+ actively transported from sarcoplasm into SR
  • Ca2+ no longer bound to troponin
  • Tropomyosin resumes its blocking function
  • Myosin cross bridges cannot reattach to actin, therefore
    contraction ceases & relaxation occurs
18
Q

Steps Involved in Skeletal Muscle Contraction

A
  1. Action potential travels down axon of a somatic motor neuron
  2. Action potential arrives at voltageregulated Ca2+ channels
    * Calcium diffuses into axon terminal
  3. Calcium triggers release of Acetylcholine (ACh) into
    neuromuscular cleft by exocytosis
    * ACh diffuses across neuromuscular cleft & binds nicotinic receptors on motor endplate
19
Q

Steps Involved in Skeletal Muscle Contraction cont.

A
  1. Binding of ACh to receptors opens ion channels in sarcolemma
  2. An endplate potential is created when most importantly Na+
    moves through open ion channels
  3. Endplate Potential
    - A graded depolarisation produced by Ach
    - Equivalent to EPSP produced in neurons
20
Q

Steps Involved in Skeletal Muscle Contraction cont.

A
  1. Endplate potentials cause adjacent muscle membrane to
    depolarise
    * These regions may reach threshold for action potential generation
  2. If AP generated, it spreads quickly along muscle fibre through t-tubule system
  3. AP in t-tubules stimulates release of Ca2+ into sarcoplasm from the SR
21
Q

Steps Involved in Skeletal Muscle Contraction cont.

A
  1. Ca2+ binds troponin (Tn-C) resulting in a positional shift of
    tropomyosin
  2. Exposes binding sites on actin
  3. Myosin cross bridges attach to actin
  4. A conformation change in myosin head results in a power
    stroke
  5. Produces sliding of thin filament over thick filament
    – Sliding Filament Theory
22
Q

MOTOR UNIT RECRUITMENT

A
  • A motor unit consists of a somatic motor neuron and the
    muscle fibers it innervates
  • The strength of a contraction depends on how many motor units are activated.
  • Motor units recruitment is the process in which the number of active motor units increases
  • Weakest motor units are recruited first followed by stronger motor units
  • Motor units contract alternately to sustain contractions for longer periods of time
23
Q

MOTOR UNIT RECRUITMENT CONT.

A
  • Whole muscles contracted in a GRADED fashion
  • Produced by variations in the number of motor units activated
  • Fine neural control over strength of muscle contraction = many small motor units
  • E.g. Muscles that position the eye have an average of 23 fibres per neuron/motor unit
  • Neural control over powerful muscle contraction = large motor units
  • E.g. Gastrocnemius = 1000 fibres per neuron/motor unit
24
Q

Skeletal Muscle Fibre Types

A
  • Classifying muscle fibres based on the
    1. Speed of contraction
  • Fast and slow
    2. Major pathway for forming ATP
  • Oxygen using aerobic or anaerobic glycolysis
  • Slow oxidative
  • Fast oxidative-glycolytic
  • Fast glycolytic

HBA (12 decks)

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