3 - Muscle and Movement Flashcards
What are the four major tissue types in the body
Muscle tissue
Connective tissue
Epithelial tissue
Nervous tissue
What are the three types of muscle tissue
Skeletal
Cardiac
Smooth muscle
Where is skeletal muscle found
Attached to bones and some facial muscles connected to the skin
Where is cardiac muscle found
In the walls of the heart
Where is smooth muscle found
In the walls of hollow visceral organs (excluding the heart), and in multiunit muscle such as the intrinsic eye muscles, airways, and large arteries
What is the structure of skeletal muscle cells
Long, cylindrical, multinucleated cells with visible striations
What is the structure of cardiac muscle cells
Branching chains of cells, usually uni- or binucleated, with striations
What is the structure of smooth muscle cells
Spindle-shaped (fusiform), uninucleate, and lack striations
Do skeletal muscle cells have gap junctions
No
Do cardiac muscle cells have gap junction
Yes, located at intercalated discs
Do smooth muscle cells have gap junctions
Yes, in single unit smooth muscle
Do skeletal muscle cells have individual neuromuscular junctions
Yes
Do cardiac muscle cells have individual neuromuscular junctions
No
Do smooth muscle cells have neuromuscular junctions
No, in single unit smooth muscle
Yes, in multiunit smooth muscle
How is skeletal muscle contraction regulated
Voluntarily controlled via axon terminals of the somatic nervous system
How is cardiac muscle contraction regulated
Involuntarily regulated by an intrinsic conduction system, autonomic nervous system, hormones, and stretch
How is smooth muscle contraction regulated
Involuntarily regulated by autonomic nerves, hormones, local chemical signals, and stretch
What are the three main ways to classify muscle types
By striations, control (voluntary/involuntary), and location (situation)
What is the function of cardiac muscle
Found in the heart, responsible for rhythmic, repeated contractions to pump blood
How is smooth muscle controlled
Phasic smooth muscle: via action potentials (e.g. peristalsis in the GI tract)
Tonic smooth muscle: via electrical, chemical, or mechanical signals (e.g. in blood vessels)
What is peristalsis and which muscle type performs it
Wave-like contractions in the digestive tract using phasic smooth muscle
What controls skeletal muscle contraction
Motor units—groups of motor neurons and the muscle fibres they innervate
What are slow-twitch muscle fibres
Use oxygen for fuel, fire slowly, support endurance activities like long-distance running
What are fast-twitch muscle fibres
Use anaerobic metabolism, fire rapidly, suited for short bursts of strength or speed, but fatigue quickly
What are skeletal muscle cells also called
Myocytes or muscle fibres—long, cylindrical cells with actin and myosin filament
How are myocytes structurally arranged
Aligned along a single axis for contraction
Neuromuscular Transmission (Steps)
- Arrival of action potential
- Depolarisation of presynaptic membrane and opening of Ca2+ voltage gated channels
- Increase intracellular Ca2+ leads to release of Ach from synaptic vesicles
- Binding of Ach to its receptors on ligand-gated cation channels
- Activation of Ach gated ion channels in the end plate membrane
- Increase of Na+ and k+ conductance via ligand gated non-selective cation channels leads to the generation of end plate potential (EPP)
- Generation of the EPP leads to generation of action potential of electrically excitable skeletal sarcolemma
Sliding Filament Theory
- Rise of intracellular Ca2+
- Binding of Ca2+ to troponin moves tropomyosin away from myosin binding sites on actin
- Cross bridge formation
- Power stroke
- Cross bridge detachment
- Reactivation of myosin head
- Repositioning of energised myosin head
Name the main contractile proteins in muscle
Myosin (thick filaments) and actin (thin filaments)
What do the regulatory proteins tropomyosin and troponin do
Tropomyosin: Blocks myosin binding sites in the absence of Ca²⁺
Troponin: Binds Ca²⁺ and shifts tropomyosin to expose binding sites
What are the key structural proteins in skeletal muscle
Titin (elasticity), nebulin, dystrophin, and desmin
What processes require ATP in skeletal muscle
Myosin cross-bridge cycling, Ca²⁺ pumping into the SER, Na⁺/K⁺ pump
What are the sources of ATP for muscle contraction (and durations)
- Preformed ATP (1–2 seconds)
- Phosphocreatine (4–6 seconds)
- Glycolysis (approx. 1 minute)
- Oxidative phosphorylation (long term, 95% of ATP)
What is an isometric contraction
Muscle tension increases, but fibre length stays the same (no movement)
What is an isotonic contraction
Muscle tension remains constant, but fibre length changes (movement occurs)
How is force transferred in the musculoskeletal system
Muscles act through tendons and work in antagonistic pairs—one contracts, the other relaxes
Smooth Muscle Contraction Mechnism
- Intraceilar Ca2+ comes in
- Ca2+ binds to calmodullin
- Ca2+ calmodulin complex binds to myosin light-chain kinase
- Myosin light-chain kinase uses ATP to phosphorus ate myosin cross bridges
- Phosphorylated cross bridges bind to action filaments
- Cross-bridge cycle produces tension and shortening
