Contraction of skeletal muscles

Energy Needed for Contraction 1. Aerobic Respiration (oxidative phosphorylation) Majority of ATP comes from this process. Glucose is the starting molecule along with oxygen. 2. A high energy molecule called creatine phosphate is present in myofibrils (only place in your body). Used to make ATP quickly during prolonged exercise by phosphorylation 3. Anaerobic Respiration due to a lack of oxygen, glucose can only be partially broken down into a small amount of ATP. The left over “glucose” is found in the form of lactic acid.

Motor Unit is composed of –Motor neuron – type of neuron that stimulates muscle tissue –Muscle fibers – many fibers attach to one motor neuron Range from as far as 10 to as many as 2000! The place where the nerve meets the muscle is called the Neuromuscular junction

Axon terminal Synaptic cleft (Synapse) Sarcolemma The nerve cell never touches the myofibril (muscle cell)

How Does the Nerve communication with the Myofibril Synaptic vesicles tiny sacs within the axon terminal release chemicals called neurotransmitters into the synaptic cleft. The specific neurotransmitter released at a neuromuscular junction is called acetylcholine (ACh) Protein receptors in the membrane

The Real Deal synapse Axon terminal Vesicle containing ACh sarcolemma

Keep in mind: If a stimulus causes a myofibril contraction, then threshold has been reached When ever a threshold is reached, the myofibril will contract to the fullest extent. (it can’t be stopped) This is called the All or none principle ****contraction of an entire muscle is different and will be discussed later.

Neuromuscular Junction 1. When ACh binds with the ACh receptors on the sarcolemma, protein channels open causing the diffusion of molecules (Ach is almost immediately broken down by acetylcholinesterase) 2. Sodium(Na+) begins to rush into the myofibril and potassium (K+) begins to trickle out, this causes a change in the overall charge of the membrane, which will quickly fix itself back to normal (resting potential) 3. A muscle action potential begins. This means that the current of Na+ and K+ will continue to travel down the sarcolemma.

4. The action potential travels down t-tubule membranes deep into the myofibril causing the sarcoplasmic reticulum to release stored Ca The Ca + binds to proteins (tropomyosin and troponin) found on the actin which begin what is known as “the sliding filament theory”

(Steps of the Sliding filament theory) 6. The Ca + attached to the proteins on the actin cause it to change shape, which exposes myosin binding sites (where myosin heads can attach to actin) 7. Using ATP for energy, the myosin heads attached to the binding sites on the actin 8. The myosin swivels and pulls the actin filament. 9. As the myosin head swivel, the ADP is released and the myosin head returns to its original position.

Action potential to t-tubules and release of calcium from the sarcoplasmic reticulum eature=related Nurses version eature=related Human body, pushing the limits R=1

Sliding