15 - Nervous coordination and muscles Flashcards
Describe the roles of calcium ions and ATP in the contraction of them myofibril. (7)
- Ca2+ diffuse into myofibrils from reticulum
- Ca2+ moves tropomyosin
- Exposure of actin binding sites
- Myosin heads bind to actin binding site
- Hydrolysis of ATP causes myosin heads to bend
- Pulling actin molecules
- Attachment of new ATP molecule to each myosin head causes myosin heads to detach
Describe the structure of a myelinated motor neurone.
Cell body > Axon, with myelin sheath and nodes of Ranvier between Schwann cells > axon terminal
How is a resting potential established?
- membrane permeable to K+ but not to Na+
- sodium-potassium pump moves two K+ into axon and three Na+ out of axon
- axon more negative internal than external due to electrochemical gradient of ions
- -65mV relative potential
Describe an action potential.
- Neurone recieves impulse causing Na+ to enter cell
- If this is above threshold, voltage-gated sodium channels open, causing action potential (positive feedback and delopolarisation)
- afte maximum relative potential (40mV) reached, voltage-gated sodium channels close and voltage-gated potassium channels open, causing repolarisation
- Hyperpolarisation causes more negative relative potential than resting potential
Describe the all-or-nothing principle.
When the threshold is reached, all action potentials depolarise to the same voltage, irrelevant of the size of stimulus
How are action potentials transmitted in non-myelinated axons?
When depolarisation occurs, voltage-gated sodium channels open further down the axon
How are action potentials transmitted in myelinated axons?
Action potentials only occur at Nodes of Ranvier
Charge diffuses along axon
Describe the refractory period and its importance.
- A period in which an axon cannot be depolarised to initiate a new action potential
- Limits frequency of action potentials
- Ensures action potentials are discrete and unidirectional
Give three factors wich affect the speed of action potential conductance.
- Myelination and saltatory conduction
- Axon diameter
- temperature
Describe the process of transmission across a choligernic synapse.
- Action potential arrives at pre-synaptic knob
- Voltage-gated calcium channels open
- Ca2+ diffuses into knob
- Synaptic vesicles fuse with membrane
- Neurotransmitter (acetylcholine) released into synaptic cleft
- Neurotransmitter diffuses across cleft, and binds to receptors on post-synaptic membrane
- Action potential continues as Na+ channels open
- Acetylcholinesterase breaks down acetylcholine, which diffuses back into pre-synaptic knob
How does an inhibitory synapse work?
- Diffused nerotransmitter causes opening of chloride or potassium channels
- Causes hyperpolarisation
what is spatial summation?
action potentials from multiple presynaptic neurones are added together in a post-synaptic neurone
what is temporal summation?
multiple action potentials from one single presynaptic neurone are added together to a post-synaptic neurone, over time
Describe 5 differences between a cholinergic synapse, and a neuromuscular junction.
- neuromuscular is only excitaory, synapse is excitatory and inhibitory
- neuromuscular links neurones to muscle, where synapse links neurones to other neurones or effectors
- action potential ends at neuromuscular, whereas it continues to other neurones in a synapse
- only motor neurones feature in a neuromuscualr junction, whereas intermedate, motor and sensory neurones can be involved in synapse
- in neuromuscular, acetylcholine binds to receptors on muscle fibre membrane, in a synapse it binds to receptors on membrane of post-synaptic neurone
How do muscles allow movement?
Antagonistic pairs against an incompressible skeleton to allow movement
