muscle structure

• Muscles act in antagonistic pair action. When one contracts the other relaxes. 
• Muscles are attached to bones by tendons. They can only pull not push. 
• Cardiac muscle - area around heart. 
• Skeletal muscle - bulk of body muscle. 
• Smooth muscle - found in wall of blood vessels and gut. 
• Muscles are made out of myofibrils, a single myofibril has a small force and can be grouped together into larger fibres. 
• Cellular muscle structure:

  Individual cells fuse together to eliminate weakness at the ends. They share their nuclei and cytoplasm (sarcoplasm). There are many mitochondria and contain sarcoplasmic reticulum found in the sarcoplasm - store of calcium ions. 
• Myofibril structure:

  Made of two types of protein filaments. 

  • Actin - thin, made of two intertwining strands. 
  • Myosin - thicker, made of long rod shaped fibres with bulbous heads that stick out. 
• Myofibril structure:

  Two other proteins. 

  • Tropomyosin - fibrous strand around actin filament 
  • Troponin - globular filament involved in contraction 

   
• Sarcomeres are functional units within myofibrils. 
• sarcomere: ..

  A) h zone

  B) actin

  C) myosin

  D) z line

  E) a band

  F) i band

  
• I band is light and the A band is dark. 
• H zone is myosin only. 
• I band is actin only. 
• A band is myosin and actin. 
• Neuromuscular junction synaptic transmission:

  • Nerve impulses cause synaptic vesicles to fuse with presynaptic membrane and release acetylcholine 
  • Acetylcholine diffuses across gap to postsynaptic membrane and causes sodium ion channels to open 
  • Sodium ions enter and depolarise membrane 
  • Acetylcholine is broken down by acetylcholinesterase 
  • Acetyl and choline are products and recombined in the neurone 

   
• Neuromuscular junction:

  There are many junctions spread throughout muscles so the entire muscle can be stimulated at the same time. 

   
• Types of muscle fibres:

  •  slow twitch muscles - contract slowly with less powerful contraction over a longer period 
  • Fast twitch muscles - contract faster with powerful contraction over a short period of time. 
• What type of signaling is the neuromuscular junction limited to?

   Only excitatory.
• What type of signaling can cholinergic synapses perform?

  May be excitatory or inhibitory.
• What does the neuromuscular junction link?

  Neurons to muscles.
• What do cholinergic synapses link?

  Neurons to neurons, or neurons to other effector organs.
• Which neurons are involved in the neuromuscular junction?

  Only motor neurons.
• Which neurons are involved in cholinergic synapses?

  Motor, sensory, and intermediate neurons.
• What happens to the action potential at the neuromuscular junction?

  It ends
• What happens to the action potential at cholinergic synapses?

  New action potentials may be generated along another neuron.
• Where does acetylcholine bind in the neuromuscular junction?

  To receptors on the membrane of muscle fibers.
• Where does acetylcholine bind in cholinergic synapses?

  To receptors on the postsynaptic membrane.