Muscle Contraction Flashcards
Suggest the consequences to sarcomere when the protein, Ca2+ATPase, found in the sarcoplasmic reticulum is inhibited. (Ca2+ATPase pumps calcium ions from the cytoplasm into the sarcoplasmic reticulum when the fibre is no longer stimulated.)
Ca2+ remains in the cytoplasm; Ca2+ bound to troponin; tropomyosin does not cover binding sites on actin; myosin-actin cross bridges remain; sarcomere shortened/contracted
Describe the role of calcium ions in a cholinergic synapse.
Ca2+ diffuses into synaptic knob through voltage-gated calcium ion channels; vesicles containing acetylcholine fuse with presynaptic membrane; exocytosis of acetylcholine
Motor neurones and sensory neurones have different roles in nervous coordination
Contrast the structure and function of sensory neurones and motor neurones.
Motor:
Transmit impulses from CNS to effector;
Cell body at end of neurone / axon;
Cell body in CNS / brain / spinal cord;
Long axon OR axon;
Dendrites attached to cell body
Sensory:
Transmits impulses from receptors / sense organs to CNS;
Cell body in middle of neurone OR cell body not at end of neurone / axon;
Cell body in (dorsal root) ganglion;
Short axon OR axon and dendron;
Dendrites attached to dendron
Explain the importance of the myelin sheath in the transmission of action potentials.
Insulator / ions cannot pass through it;
Depolarisation / action potentials occur at nodes of Ranvier only;
Longer local circuits / currents;
Action potential jumps from node to node;
Transmission / conduction faster
…produces saxitoxin, a neurotoxin that causes muscle paralysis by acting on voltage-gated sodium ion channels in neurones. Saxitoxin can kill whales.
Suggest how saxitoxin results in the death of a whale.
Sodium ions do not enter neurones / axons / nerve cells;
Neurones cannot depolarise OR cannot generate / transmit impulses / action potentials;
Reason for death
Eugenol can be used to relieve toothache. ( Eugenol inhibits movement of sodium ions through the cell surface membranes of sensory neurones ).
Suggest and explain how the action of eugenol may reduce pain.
Reduced entry of Na+ into sensory neurone;
Eugenol prevents opening of sodium ion channels;
No / reduced depolarisation of sensory neurone membrane;
Receptor potential / threshold potential not reached;
No / fewer action potentials / impulses;
May affect sodium-potassium pump;
Resting potential not restored;
Action potential / impulses do not reach brain
Describe the difference between the action potential in a motor neurone and the action potential in a striated muscle fibre.
41/ON/22 Q9
Resting potential higher in motor neurone;
-70mV (motor) vs -90mV (muscle);
Smaller change in membrane potential / smaller depolarisation;
110mV (motor) vs 130mV (muscle);
Action potential / depolarisation takes less time / is faster;
Action potential 2.7ms (motor) vs 4ms (muscle) OR depolarisation 1ms (motor) vs 2ms (muscle);
Hyperpolarisation / refractory period occurs in motor neurone
Explain what is happening in the striated muscle fibre during the latent phase.
T-tubules depolarised;
Ca2+ diffuse out of sarcoplasmic reticulum;
Ca2+ bind to troponin;
Tropomyosin expose binding sites;
For myosin on actin;
Cross-bridges form / myosin head binds to actin
Suggest why the relaxation phase shows a gradual decrease in muscle tension.
Cross bridges break / myosin heads detach at different times
Describe and explain the transmission of an action potential in a myelinated neurone.
Sodium channels open;
Na+ enter neurone;
Membrane potential becomes positive / depolarised;
Sodium ion channels close;
Potassium ion channels open;
K+ leaves cell;
Membrane potential becomes negative / repolarised;
Myelin sheath / Schwann cells insulates / stop ion movement;
Action potential / depolarisation only occurs at nodes of Ranvier;
Fast transmission of action potential / impulse;
One-way transmission of action potential
