Previous ib exam Essay Questions: Nerves & Muscles



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Previous IB Exam Essay Questions: Nerves & Muscles

Use these model essay question responses to prepare for essay questions on your in class tests, as well as the IB Examination, Paper 2. These questions have appeared on recent IB examinations, exactly as shown below. Following each question is the markscheme answer which was used to evaluate student answers on the examination paper.




1. Outline the general organization of the nervous system.  4 marks

  • formed of central nervous system

  • brain and spinal cord

  • peripheral nervous system divdided into volumtary and autonomic nervous systems

  • autonomic nervous system consists of sympathetic and parasympathetic nervous system

  • voluntary nervous system has motor and sensory neurons

2. Draw a diagram to show the structure of a motor neuron.  5 marks

  • cell body drawn and labelled with a nucleus shown inside (reject if cell body not drawn at end of axon)

  • axon drawn at least three times as long as the diameter of the cell body and labelled

  • Schwann cells / mylin sheath drawn and labelled

  • gaps in the myelin sheath drawn and labeled

  • at least five dendrites drawn leading to the cell body labelled

  • at least two motor end plates / boutons / synaptic knobs / synaptic terminals drawn and labelled

3. Outline the changes that lead to the depolarization of an axon as an action potential travels along a neuron.  5 marks

  • local currents / ions diffuse from adjacent depolarised section of axon

  • resting / membrane potential reduced

  • voltage-gated ion channels affected

  • sodium channels open

  • sodium diffuses in / moves in rapidly

  • therefore fewer positive charges outside and more inside / inside becomes positive relative to outside / membrane polarity reversed

  • before depolarisation outside was positive relative to inside

  • when some sodium gates open entry of Na+ causes more sodium gates to open

  • membrane potential rises from -70mV to +40 mV ( -+ 10 mV)

(Award no marks for statements about potassium movement and repolarisation)

4. Explain how the nerve impulse passes along a neuron.  8 marks

  • in resting potential

  • sodium is pumped out by the active transport and potassium in

  • a concentration gradient builds up electrical potential / voltage

  • negative inside compared to outside

  • when impulse passes / action potential

  • must pass threshold level

  • sodium channels open and ions diffuse into neuron

  • membrane depolarized

  • potassium diffuse out across membrane through ion channels

  • active transport of ions once more

  • slower in un-myelinated neuron than in myelinated

  • an action potential in one part of the neuron causes the action potential to develop in the next section

5. Explain how a non-mylenated neuron can maintain a resting potential and undergo an action potential.  9 marks

  • resting potential is a charge difference across the membrane / -70mV

  • inside negative compared to the outside

  • active transport of ions across the membrane / pumps using ATP

  • positively charged sodium ions / Na+ are pumped out

  • fewer K+ are pumped in / 2 K+ compared to 3 Na+

  • neurone contains negatively charged organic ions

  • membrane allows little / no diffusion of ions

  • to create action potential sodium ion channels open

  • sodium ions move into the neurone

  • therefore there is depolarisation / membrane polarisation is reversed

  • this causes similar changes further on along the neurone

  • reference to diffusion of ions / local currents

  • potassium ion channels open after the sodium ion channels

  • potassium diffuses out causing some repolarisation

6. Explain how a nerve impulse is transmitted from a neuron to a muscle.  8 marks

  • impulse reaches the motor end plates / synaptice knobs / boutons / synaptic terminals

  • synaptic vesicles contain neurotransmitter / acetylcholine

  • calcium enters through the presynaptic membrane

  • calcium causes the vesicle to move to and fuse with the membrane / causes exocytosis

  • neurotransmitter / acetycholine released into the synaptic cleft

  • crosses / diffuses across the synoptic cleft to the muscle fibre membrane / postsynaptic membrane

  • binds to receptor sites

  • causes depolarisation of the muscle fibre membrane / postsynaptic membrane

  • by opening sodium gates

  • threshold of stimulation must be reached / all or nothing effect

  • enzyme / acetylcholinesterase breaks down the neurotransmitter / acetylcholine

  • depolarisation causes sarcoplasmic reticulum to release calcium ions

  • calcium ions cause / enable muscle contraction

7. Describe the principles of synaptic transmission in the nervous system.  6 marks

  • nerve impulse reaches pre-synaptic knob / membrane

  • calcium ions / Ca+2 enter pre-synaptic neuron / knob

  • vesicles with neurotransmitter / acetylcholine release contents

  • neurotransmitter diffuses across synapse / synaptic cleft

  • binds to receptors on post-synaptic neuron / membrane

  • sodium ions / Na+ enter post-synaptic neuron / sodium channels open

  • depolarization / action potential / nerve impulse (in post synaptic neuron)

  • calcium ions / Ca+2 pumped back into synaptic cleft / synapse

  • neurotransmitter broken down

8. Explain the process of synaptic transmission.  7 marks

  • presynaptic neurons pass stimulus / potential to postsynaptic neurons

  • presynaptic neuron releases neurotransmitter into synaptic cleft

  • process involves exocytosis

  • exocytosis requires Ca+2 entry into presynaptic neuron

  • neurotransmitter binds with postsynaptic membrane receptor

  • neurotransmitter binding can cause postsynaptic membrane ion channel to open / increase / change permeability of post-synaptic membrane

  • increase / change permeability of post-synatic membrane

  • open channel allows specific ions to enter / exit post-synaptic membrane

  • depolarization / hyperpolarization can result in / initiate action potential

  • outcome depends on type of postsynaptic receptor and type of channel opened ; reference to excitatory and inhibitory synapses

  • Na+ passing to the inside of the post-synaptic neuron (usually) causes depolarization

  • Cl- passing to the outside of the post-synaptic neuron (usually) causes hyperpolarization

  • (some) neurotransmitters are destroyed by enzymes

Accept any of the above points if accurately illustrated in a diagram.

9. Describe the roles of structures at the elbow joint, including nerves, muscles and bones, in movements of the human forearm.  8 marks

  • labelled diagram showing, biceps, humerus, radius, ulna

  • cartilage reduces friction

  • synovial fluid lubricates the joint

  • capsule / capsular ligament seals the joint

  • ligaments prevent dislocation / restrict the range of movement / attach bones to one and another

  • motor neurones stimulate muscles to contract

  • bones provide a firm anchorage for muscles

  • bones act as levers / change the torque / size / direction of forces

  • tendons attach muscle to bone

  • biceps and triceps are antagonistic

  • biceps is the flexor / bends the elbow and triceps is the extensor / straightens the elbow joint

  • biceps is attached to the radius and triceps is attached to the ulna

Accept any of the above points if clearly drawn and correctly labelled in a diagram.

10. Describe the roles of nerves, muscles and bones in producing movement.  6 marks

  • motor neurones carry impulses / messages to muscle

  • nerves / neurones stimulate muscles to contract

  • neurones control the timing of muscle contraction

  • muscles provide the force for / cause movement

  • muscles are attached to bone by tendons

  • bones act as levers

  • joints between bones control the range of movement

  • antagonistic muscles cause opposite movements

11. Draw a labelled diagram to show the structure of a sarcomere.  5 marks

Award 1 for each structure clearly drawn and correctly labelled.

  • sarcomere – clearly indicated between Z lines;

  • Z lines;

  • actin filaments attached to Z line;

  • myosin filaments with heads;

  • (two) light bands;

  • dark band;

12. Explain the process of muscle contraction.  9 marks

  • muscles contraction due to sliding filaments

  • actin and myosin filaments slide over each other

  • diagram / description of interdigitation of filaments

  • action potential / stimulation causes calcium release in muscle fibres

  • from the endoplasmic / sarcoplasmic reticulum

  • calcium activates troponin

  • troponin binds to tropomyosin / troponin and tropomyosin change shape

  • tropomyosin moves exposing binding sites on actin

  • myosin heads bind to actin / cross bridges formed between actin and myosin

  • myosin heads / crossing bridges push actin filaments (inwards)

  • myosin heads detach / cross bridges break

  • myosin heads move back and reattach / ratchet mechanism

  • ATP used (to break cross bridges)

  • actin and myosin overlap more

  • sarcomere becomes shorter

  • myofibril / muscle fibre consists of many sarcomeres


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