Neuromuscular Systems

• after a message is sent to the central nervous system:

  1. a message originates and is released from the central nervous system
  2. the message travels from the axon branch to the axon terminal of the muscle, and a motor unit will be recruited (size depending on intensity of movement)
  3. the message is carried through the axon terminal via acetylcholine (ACh) to the sarcolemma of each muscle fibre involved
  4. the ACh causes the sarcoplasmic reticulum to release calcium ions from the terminal cisterna
• after ACh releases calcium ions:

  1. the calcium ions then find their way to attachment sites on troponin, (located on the actin's tropomyosin)
  2. the tropomyosin swivels, exposing the binding sites on the actin filament
  3. the myosin heads attach themselves to the actin
  4. ATP is broken down by ATPase, causing the sliding of actin along the myosin filament
  5. the contraction of the filaments will continue until you decide to stop the activation of the muscle, and as long as calcium is present, contraction will continue
• The neuromuscular system is a general term that refers to the linkage between the muscular and nervous system. It includes the brain, the spinal cord, the muscle fibres, and the neurons connecting them.
• Neuromuscular junctions are points where the nerves that transmit a message directing a muscle to move comes into contact with the muscle. Electrical impulses travel along the nerve pathways to the contact point, where the chemical ACh is released and detected by receptors on the surface of the muscle fibre.
• the reflex arc:

  1. receptor receives initial stimulus
  2. sensory neuron afferent posterior carries the impulse to the spinal column or brain
  3. interneuron interprets the signal and issues an appropriate response
  4. motor efferent anterior neuron carries the response message from the spinal cord to the muscle or organ
  5. the effector organ carries out the response
• Proprioceptors are sensory receptors found in muscles, tendons, joints, and the inner ear that are able to detect the motion or position of the entire body or a limb by responding to stimuli from within the organism; they provide sensory information about the state of muscle contraction, the position of body limbs, and body posture and balance.
• Muscle spindles are sensory receptors within a muscle fibre that primary detect changes in the length of the muscle.
• Golgi tendon organs are sensory receptors found at the end of muscle fibres that merge into the tendon itself and detect changes in muscle tension.
• golgi tendon organs and the tension reflex:

  1. the golgi tendon organ detects tension
  2. the impulse is sent along the sensory neuron afferent posterior
  3. the afferent neuron synapses with the efferent pathways by the interneuron
  4. the impulse is transmitted along the motor efferent anterior neuron
  5. the motor units respond to the impulse, telling the muscle to relax in order to prevent injury
• main steps of action potential:

  1. receptor detects stimulus
  2. if the stimulus reaches above a certain threshold, the receptor will transform the stimulus into a nerve impulse
  3. the nerve impulse travels to the CNS
  4. the CNS initiates a response to the stimulus, which is passed down to effector cells
• Depolarization is when the membrane potential rapidly rises to +40mv, causing the sodium voltage-gated channels to open in the membrane, and sodium ions enter the cell.
• Repolarization is when the potential difference reaches +40mv, and the sodium channels close and potassium channels open, causing large amounts of potassium ions to flow out of the cell, which reduces membrane potential.
• Hyperpolarization or the Refractory Period is when the ouflow of potassium ions causes an overshoot of potential difference, which causes the membrane potential to be more negative than the resting state. To re-establish the right balance of ions, the ATP-driven pump (ATPase), pumps in 2 potassium ions for every 3 sodium ions it pumps out.
• Resting state refers to the neuron returning to its resting membrane potential, where no action potential is generated.