4.1 Neuromuscular Function

A single motoneuron & the muscle fibres which it innervates (supply with nerves)

Dendrite, cell body, nucleus, axon, motor end plate, synapse and muscle

• Link neuron to neuron - allows information to flow between nerves

• Contains the nucleus but does not incorporate the dendrites or axon

• Membrane-enclosed organelle • Has the cell’s DNA • Controls the cell

• Main component of nerve signal transmission • Has a cover made of myelin (protein) • makes sure electrical signal is insulated • has Nodes of Ranvier (gaps) - aids in transmission of info

• Where the neuron meets the muscle fibre

• Gap between neuron and muscle fibre - Transmission of electrical nerve signals happens across

• Transmission of electrical nerve signal stimulates muscle (to contract)

Chemicals that are used for communication between a neurone at the synapse and another cell

• Acetylcholine (ACh) is the primary neurotransmitter for the motor neurons that innervate skeletal muscle • Muscular contractions start w/ electrical impulse • generated either voluntarily by brain or by reflex • Electrical impulses travel along motoneuron through motor end plate • When a signal reaches the synapse, neurotransmitter ACh is released • ACh changes electrical state of muscle & causes signal called the action potential to travel along muscle fibres • When nerve is no longer stimulated, ACh is removed by cholinesterase • Cholinesterase (enzyme) is present in synaptic cleft + rapidly breaks down ACh into acetate + choline • necessary to allow a neuron to return to its resting state after activation

• Contracted state of sarcomere: • H-zones disappear • I-band narrows • light bands shorten • A-band remains the same • dark bands remain the same

SKELETAL MUSCLE ⇒ MUSCLE FIBRES ⇒ MYOFIBRILS ⇒ MYOFILAMENTS

• Relaxed muscle - regulatory protein tropomyosin binds protein sites on actin • Motor neuron sends a signal to muscle fibre to contract ⇒ sarcoplasmic reticulum releases calcium ions • Calcium ions bind to a protein called troponin & causes it to change shape ⇒ tropomyosin moves + unblock actin’s binding sites • Myosin heads bind to site & swivel towards centre of sarcomere • moving actin filament a small distance • ATP causes breaking of cross-bridges • when ATP attaches to myosin head ⇒ head detaches from binding site • ATP hydrolyses ⇒ ADP + phosphate • Hydrolysis provides energy for myosin head to cock • cock: swivel outwards away from centre of sarcomere • New cross-bridges are formed by myosin binding to actin’s binding site adjacent to ones previously occupied • each head binds to a site one position further from centre of sarcomere • Energy stored in myosin head when cocked causes it to swivel inwards towards centre ⇒ moving actin a small distance

• slow nerve transmission speeds • small muscle forces • can maintain contractions for a long time ⇒ fatigue resistant e.g. walking, jogging

• high in glycogen content depending on training status • enzymes necessary for producing energy without oxygen • can be broken down to quickly generate glucose for glycolysis

• fast neural transmission times • stronger contraction forces • fatigue resistant e.g. swimming, cycling

• fastest contraction times • largest forces • can not maintain contractions for a long time ⇒ fatigue at a high rate e.g. sprinting, jumping, throwing, weightlifting