Muscles Flashcards
Describe the organisation in skeletal muscle
Smallest- largest
1. Muscles fibres - group together
2. Fasciculi - groups of muscle fibres
3. Perimysium - groups of Fasciculi
4. Epimysium
Describe the cell structure of skeletal muscle fibres?
- Long muscle fibres
-Multinucleated cells with nucleus outside cell of the periphery
What are the functions of skeletal muscle?
- Move and stabilise the skeleton
- Form sphincters in digestive and urinary tracts
- Involved in respiration
What are the different types of muscle fibres?
- (A) Aerobic Type1 - contain myogoblin and can retain O2, used for longer movements
- (An) Anaerobic - lots of glycogen for anaerobic respiration, used for short burst movements
- (I) intermediate - use both anaerobic and aerobic
How are skeletal muscle innervated?
Somatic motor neurone
Each motor neurone innervates a number of fibres this is called a motor unit
What is a motor unit?
Group of muscle fibres innervated by a single neurone
How does size of motor units effect control?
- For fine control the motor unit size is smaller, giving the body more control for exact movements e.g. eye motor unit size = 20
Strength control - larger motor units to generate power e.g. biceps = 1000 muscle fibres
What is the neuromuscular junction?
Where the neurone and muscle meet and synapse happens passing along the signal
What happens at the neuromuscular junction?
- Nerve signal passes down neurone
- Signal opens voltage-gated Ca2+ channels
- The increase of Ca2+ causes vesicles containing ACh (neurotransmitter) to move to the border and fuse with the synaptic cleft
- Exocytosis happens and ACh leaves the axon
How does ACh enter the post-synaptic membrane after leaving the axon?
- ACh binds to nicotinic ACh receptors (each receptor needs 2 molecules of ACh) this opens the ions channels and creates a potential at the surface .
- this is a ligand gated ion channel - Na+ enters the membrane this causes depolarisation
What happens once the post synaptic membrane is depolarised?
- Action potential moves down T-tubules and activates DHP voltage gated receptors
- DHP receptor acts as a plug but when activated the plug is pulled out of the CA2+ channel
- Ca2+ moves out of sarcoplasmic reticulum into the membrane
What is Ca2+ needed for?
Needed for contraction of muscle fibres
What is the role of the sarcoplasmic reticulum?
Provides the membrane with CA2+ ions that enter through a Ca2+ ion channel
What makes up a sarcomere?
A sarcomere extends from one Z band to another Zband
It contains:
A. A band
B. I band
How does the sliding filament theory work?
- Relaxed state - Tropomyosin covering the binding site
- Ca2+ realised from sarcoplasmic reticulum - Ca 2+ binds with tropomyosin and uncovers the binding site, and myosin head bings with actin
- Power stroke - ADP and Pi is realised and the energy released causes the myosin head to pivot and pull the actin filament with it
- The ATP created binds to the myosin head and the head dis-attaches from the actin filament
- ATP splits in ADP and Pi - ready for the next contraction
