Nervous Coordination + Contraction of Skeletal Muscles

• Explain how a resting potential is maintained across the axon membrane in a neurone?

  1. Higher concentration of potassium ions inside and higher concentration of sodium ions outside the neurone
  2. Membrane more permeable to potassium ions
  3. Sodium ions actively transported out and potassium ions in
• Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon?

  1. Myelination provides electrical insulation
  2. In myelinated axon, saltatory conduction
  3. In non-myelinated axon, depolarisation occurs along whole/ length of axon
• A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV. Explain why?

  1. Less ATP produced
  2. Less active transport
  3. No net movement of sodium and potassium ions
• Describe the sequence of events involved in transmission across a cholinergic synapse. Do not include details on the breakdown of acetylcholine in your answer?

  1. Depolarisation of presynaptic membrane
  2. Calcium channels open and calcium ions enter synaptic knob
  3. Synaptic vesicles fuse with presynaptic membrane and release acetylcholine
  4. Acetylcholine diffuses across synaptic cleft and attaches to receptors on the postsynaptic membrane
  5. Sodium ions enter postsynaptic neurone leading to depolarisation
• Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine. Dopamine stimulates the production of nerve impulses in postsynaptic neurones. Describe how?

  1. Dopamine diffuses across synapse
  2. Attaches to receptors on postsynaptic membrane
  3. Stimulates entry of sodium ions and depolarisation
• GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA causes negatively charged chloride ions to enter postsynaptic neurones. Explain how this inhibits postsynaptic neurones?

  1. Inside of postsynaptic neurone becomes more negative
  2. More sodium ions required to reach threshold
  3. For depolarisation
• When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob. Describe how?

  1. Depolarisation of membrane causes calcium channels to open
  2. Calcium ions enter by facilitated diffusion
  3. Causes synaptic vesicles to fuse with presynaptic membrane
• Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane. Do not include the roles of calcium ions and tropomyosin in your answer?

  1. Myosin head attaches to actin and bends (performs power stroke)
  2. Pulls mitochondria along the actin
  3. Next myosin head attaches to actin and bends
• Explain the banding pattern of a single sarcomere?

  1. Light/I band only actin
  2. H zone/band only myosin
  3. Darkest/overlapping region actin and myosin
• Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction?

  1. Less tropomyosin moved from binding site
  2. Fewer actinomyosin bridges being formed
  3. Myosin head does not move
• Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration?

  1. Regenerates NAD
  2. So glycolysis continues
• Explain the role of glycogen granules in skeletal muscle?

  1. To be hydrolysed to glucose
  2. For respiration
• During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction. Suggest how?

  1. Low pH changes shape of calcium ion receptors
  2. Fewer calcium ions bind to tropomyosin
  3. Fewer tropomyosin molecules move away
  4. Fewer binding sites on actin revealed
  5. Fewer myosin heads can bind
• Describe the roles of calcium ions and ATP in the contraction of a myofibril?

  1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum
  2. Calcium ions cause movement of tropomyosin on actin, exposing the binding sites on the actin
  3. Myosin heads attach to binding sites on actin
  4. Hydrolysis of ATP on myosin heads causes myosin heads to bend, (bending) pulling actin molecules
  5. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach from actin sites.
• ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use?

  1. Releases relatively small amount of energy
  2. Energy is released instantaneously (is readily available)
• What is the role of ATP in myofibril contraction?

  1. Reaction with ATP allows binding of myosin to actin
  2. Provides energy to move myosin head
• Describe and explain how taking creatine supplements and 'carbohydrate loading' can improve performance of different types of muscle fibres during different types of exercise?

  1. Fast fibres using during short-term/intense exercise
  2. Slow fibres used during long-term exercise
  3. Creatine used to form phosphocreatine
  4. Phosphocreatine combines with ADP to form ATP
  5. Carbohydrates stored as glycogen
  6. Glycogen hydrolysed to glucose and used in respiration