W9 Muscular System Flashcards
Name the three different types of muscle?
Can you give an example of this?
- Skeletal - Bicep
- Cardiac - Heart
- Smooth- Small intestine
What are the functions of smooth muscle?
- Digestion
- Breathing
- Circulation
Smooth muscle have what kind of shape?
- It has a fusiform shape (tapered at both ends)
Does smooth muscle have voluntary or involuntary contraction?
- Smooth muscle has involuntary (slow wave motions)
How many nucleus’ does smooth muscle have?
- Smooth muscle only has one centrally located nucleus
What does Cardiomyocytes mean?
- Cardiomyocytes is just another word for cardiac muscle cells
What does cardiac muscle look like?
- It is narrower and shorter than skeletal muscle
How many nucleus’ and mitochondria’s does cardiac muscle have?
- It has one nucleus
- It has loads of mitochondria!
What supports the synchronised contraction of cardiac tissue?
- Intercalated disks
What are intercalated disk and give the 4 distinct parts of them?
- They are the ‘gap’ between cells membranes (allows electrical impulse from cell to cell)
1. Z line of sarcomere (longitudinal structure of the tissue)
2. Desmosome - Structural support
3. Fascia adherent - mechanical support
4. Gap junction - electrical synapses
Can you describe what skeletal muscle looks like?
- Elongated muscle cell/myocytes (long structures)
- It has multi nuclei
- Striated (banded pattern (proteins))
What are the four characteristics of a skeletal muscle?
- Excitability
- Capacity to muscles to respond to stimuli - Contractibility
- Ability to shorten to produce force - Extensibility
- Can be stretched to a limited degree beyond normal length - Elasticity
- Ability to recoil to original resting length following stretch
What are the four functions of skeletal muscle?
- Movement/locomotion
- Posture
- Stabilisation
- Generation of heat
- Shivering
- By-product
What causes indirect movement of skeletal muscle?
What is the insertion and origin of this?
Tendons/Aponeurosis
- Immobile Bone (Origin)
- Moveable Bone (Insertion)
What causes direct movement of skeletal muscle?
What is the insertion and origin of this?
- Epimysium of muscle fused to Periosteum of bone
- Epimysium of muscle fused to Perichondrium of cartilage
- What is myofibril?
- It contains two different types of filament. What are they and what do they contain?
- It is a combination of proteins
- Thick filement
Mainly myosin - Thin filement
Actin troponin & tropomyosin
What does Titin do?
- It keeps thick & thin filament aligned resist muscle from over stretching and recoil muscle to resting length after stretching
What does nebulin do?
- Anchoring actin to Z disc
What does Dystrophin do?
- Anchoring protein
- Actin to membrane via protein complex (sarcolemma)
- Muscular dystrophy: weakening & breakdown of skeletal muscle
Can you name the three different filaments in the sarcomere?
- Actin - thin
- Titin - elastic
- Myosin - thick
What line separates each sarcomere?
The Z line separates each sarcomere
What are the two components of a motor unit?
- Alpha-motorneuron
2. Muscle fibre innervated by the AMN
What are the three types of motor unit?
- Slow = type 1 fibres
- Fatigue resistant = type 2a fibres
- Fast fatiguing = type 2x fibres
What is Henneman’s size principle?
- Motor units are activated in a sequence (1>2a>2x) which depends on the motor neuron size of the motor unit.
What are some of the characteristics of type 1 fibres?
- Slow contraction speed
Adapted for aerobic respiration: - High myoglobin content
- Large aerobic metabolism capacity and blood supply
- High mitochondrial density and content/activity of oxidative enzymes
What are some of the characteristics of type 2 fibres?
What are the two type 2 fibres?
- Fast contraction speed
Adapted for anaerobic respiration: - Less blood supply, myoglobin & mitochondria
- High content of glycogen & glycolic enzymes
1. Type 2a: fast oxidative fibres
2. Type 2x: fast glycolic fibres
What are the components of transverse tubules?
- Dihydropyridine Receptor (DHP) acts as a gate keeper
- Voltage gated calcium channel
- L type calcium channel - Ryanodine Receptor
- Which is mechanically coupled with actin
What are Calsequestrin?
Glycoproteins
What happens after the release of calcium?
- Ca2+ binds to troponin (Tn-C) on the thin filament
- Shifts tropomyosin off myosin binding sites
- Enables myosin to bind to actin
How many steps does the sliding filament mechanism have?
- There are 5 steps
Sliding filament mechanism:
- Can you describe Step 1?
Summary: The active site becomes exposed
- At rest ATP molecules bind to myosin heads and having the enzyme ATPase on the myosin head hydrolyses ATP into ADP
- This reaction releases energy that “cocks” the myosin head (pointing away from M-line) into a extended high energy position (ADP & Pi remain attached)
Sliding filament mechanism:
- Can you describe Step 2?
Summary: Cross-bridge formation
- “Cocked” myosin binds to active site on actin molecules (exposes E-C coupling process)
- This is called the Cross-bridge.
- Pi is released making bond stronger
Sliding filament mechanism:
- Can you describe Step 3?
Summary: Pivoting of myosin head
- Myosin releases ADP which bends myosin head and tugging actin along with it towards centre of sarcomere
- This is called a Power Stroke
Sliding filament mechanism:
- Can you describe Step 4?
Summary: Cross-bridge detachment
- A new ATP molecule binds to myosin head to release myosin from actin
Sliding filament mechanism:
- Can you describe Step 5?
Summary: Myosin reactivation
- ATP hydrolysis (by ATPase) cocks the myosin head again
- Steps 3-5 are repeated (cross-bridge cycle) at a new active actin site further down the actin filament to shorten the sarcomere
Where does the sliding filament mechanism occur?
It occurs in the sarcomere between the actin and myosin
What is Calsequestrin?
Calmodulin is a glycoprotein
- It allows large quantities of calcium to be stored in the sarcoplasmic reticulum
What does MLCK stand for?
Myosin light-chain kinase
Calcium Kinetic Influencers:
- What decreases the activation metabolism of Ryanodine receptors (RyR)?
- K+ & Na+
- Increase Mg2+
- Pi
- Ca2+
Contraction phase:
What receptor allows calcium to travel from the transverse tubules to the sarcoplasmic reticulum?
- DHP or Dihydropyridine Receptor controls the voltage gated calcium channel
- If open it can feed the actin in the sarcomere with calcium
Contraction phase:
- What happens after calcium has accumulated in large quantities in the calsequestrin?
- The calcium heads to the thin actin filament
-
Contraction phase:
What happens during excitation contraction coupling?
(This is the process after calsequestrin)
- So after calsequestrin the calcium heads towards the actin
- Myosin binding sites are then exposed because of the calcium
- Calcium sits in a specific location inside the actin
Contraction phase:
How does the sarcomere change during a contraction phase?
(Specify on the bands & zones)
- Actin slides over myosin
- This pulls the Z line closer together
- The A band stays the same
- The I band decreases
- The H zone disappears
Contraction phase:
- What is Calmodulin?
- What is Calmodulin’s job role?
- Calmodulin is a modulated protein
- When calcium is released it binds to calmodulin
- This then activates MLCK which increases the myosin ATPase activity
- Therefore, creating muscle tension in a specific area
Relaxation phase:
- What three components does calcium have to travel through to exit the filament?
- Sarco(endo)plasmic Ca2+ - ATPase which is released after the contraction
- This travels through the membrane proteins
- Lastly, it travels through the calcium & sodium exchange
- This releases calcium into the extracellular fluids
