Section 6 - 15 Nervous coordination and muscles Flashcards
Define - potential difference
The difference in electrical potential between two points
Define - Polarised
The term used to describe a cell that has a difference in electrical potential across its membrane
Define - diffusion
The movement of a substance from an area of high to low concentration
Define - facilitated diffusion
The movement of a substance from an area of high to low concentration using a protein carrier
Define - active transport
The movement of a substance from an area of low to high concentration, requires energy
Define - leakage channel proteins
Proteins involved in the active transport of substances across membranes
Define - Voltage-gated channel proteins
An ion channel found in plasma membranes, they open and close as the potential difference of membranes changes
Define - protein pumps
An ion channel found in plasma membranes, their permeability to ions remains relatively constant
Explain the structure of a myelinated motor neurone
- Voltage gated sodium and potassium channels only found on the node of Ranvier
- Action Potential only happens at the node of ranvier
- The action potential jumps from node to the next as the sheath is highly insulated
Explain the structure of a non-myelinated motor neurone
- Action potential fires as voltage gated sodium channels are open and the threshold is reached
- The action potential means more voltage gated sodium channels are opened
- Only one direction as refractory period so voltage gated sodium channels close
What is the nerves resting potential?
- potential difference = -65mv
- polarised
- inside is more negative
- more positively charged outside
- potassium ions inside
- sodium ions outside
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How do nerves maintain a resting potential?
- Aim to main the inside more negative
- At sodium-potassium pump - active transport 3 sodium out and 2 potassium in - going against the conc gradient
- Increased sodium conc outside - leakage channel proteins closed preventing facilitated diffusion
- Increased potassium conc inside - diffuse out the cell as leakage channel proteins are open
- Overall more positive ions outside the cell so positive outside and negative inside.
What are the stages of action potential being reached within the nervous system?
- stimulate
- depolarisation
- repolarisation
- hyperpolarisation
- restoration of resting potential
Explain the stimulate stage of creating an action potential
- causes voltage gated soidum channels to open and sodium ions to diffuse into neurons
- This makes the inside less negative - depolarisation
Explain the depolarisation stage of creating an action potential
- If enough voltage gated sodium channels are opened then enough sodium entered the cell to reach threshold
- threshold = -55mv
- This allows more SGSC to open and active potential occurs
- AP membrane = +40mv
Explain the repolarisation stage of creating an action potential
- VGSC closed and VGPC are opened
- Means potassium diffuses out of the cell causing the membrane to become more negative
Explain the hyperpolarisation stage of creating an action potential
- more potassium ions inside so too negative
- must become more positive
Explain the restoration of resting potential stage of creating an action potential
- VGPC shut
- Sodium potassium pump restores resting potential
- -65mv
Explain what is meant by a refractory perious
- Period of time after an action potential occurs where another action potential is impossible
- VGSC closed and cannot reopen
Why is the refractory period important?
- Ensures action potentials are only propagated in one direction
- produces discrete impulses - so the brain can distinguish between the action potentials
- limits the number of action potentials
What is the all or nothing principle?
- An action potential only occurs once a threshold has been reached
- All action potentials are the same size
What are the factors that affect the rate of impulse transmission?
- Myelin sheath - if neuron has a sheath then increased transmissions
- The diameter of the axon - larger diameter = faster transmission as there is fewer leakage of ions
- Temperature - higher = more diffusion so faster impulses
- Saltatory conduction - Electrical signals travel faster in axons that are insulated with myelin - The leap.
Explain the passage of impulses along a cholinergic synapse
- AP arrives
- Causing voltage-gated calcium channels to open
- Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane
- Assycholine bonds to a receptor on postsynaptic after diffusing across the synaptic cleft
- Cause sodium ions protein channels to open
- Sodium ions diffuse into the postsynaptic cell (AP generated)
- Acetylcholinesterase hydrolysis acetylcholine to ethanoic acid and chlorine so can diffuse back across the cleft
- ATP released from mitochondria recombining the chlorine and ethanolic acid to acetylcholine at presynaptic cell
What does acetylcholine hydrolyse into to more back across the synaptic cleft?
Acetylcholinesterase hydrolysis acetylcholine to ethanoic acid and chlorine so can diffuse back across the cleft
ATP used to recombine when back at the presynaptic cell.
What are the two types of synapse?
- inhibitory - vesicles containing chlorine which bind to potassium making cell more negative and overall less likely for threshold to be reached
- excitatory - vesicles contain acetylcholine which open the VGSC making the cell more positive and more likely for threshold to be reached
What are the two types of summation?
- Spatial - multiple synapses to one postsynaptic cell
- Temporal - One synapse but more powerful so more action potentials.
What are the similarities/differences between neuromuscular junctions and cholinergic synapses?
- A synapse is neurone-neurone.
- Neuromuscular junctions are only ever excitatory whereas a synapse can be excitatory or inhibitory.
- Neuromuscular junctions use T-tubules to carry the signal quickly, synapses don’t
Explain the stucture of a skeletal muscle
- Many bundles of muscle fibres
- Formed by many cells fusing together
- Different to eukaryotic as - sarcoplasm = cytoplasm and sarcolemma = cell membrane
- Lots of mitochondria and endoplasmic reticulum (known as sarcoplasmic reticulum)
- banded appearance due to myofibrils
What is a myofibril and what is it made of?
- made of sacromeres
- Sarcomeres made of protein filaments - myofilaments
- Two types of filaments:
- thin = actin
- thick = myosin
What are the two types of myofilaments?
Thin = actin
thick = myosin
State the gross structure of a sarcomere
- Z disc - actin is anchored
- I band - only actin
- Sarcomere - the distance between Z discs
- A band - length containing myosin and actin
- M line - myosin is attached
- H band - only myosin
What is tropomyosin?
Forms the long thin threads that wound around actin filaments
Explain the changes in the sarcomere during a muscular contraction
- Sacromere shortens as the I band slides into H band
- I shorter
- H shorter
- Sarcomere shorter
- A no change
What is a neuromuscular junction?
- many junctions along muscle so all action potential occur at the same time
- motor unit = all muscle fibres supplied by single motor neurone
- Actyelchlorine released when an action potential reaches the end of the motor neuron - making sodium channels open
- Only excitatory
What is a motor unit?
all muscle fibres supplied by single motor neurone
How does a myofibril contract?
- Action potential occurs in muscle fibres as sodium channels have been opened
- T-Tubles (extend cell membrane) - carry a wave of excitation in sarcoplasmic reticulum
- Activated calcium channels in SR
- Allows calcium ions to diffuse into the saccroplasm
What do the T-tubules do?
- In muscular contractions
- Entends cell membrane
- carrying wave of excitation in sarcoplasmic reticulum
What is the sliding filament theory of muscular contraction?
- Calcium ions cause tropomyosin molecules to move to expose binding sites on actin
- myosin head bound to ATP attach to actin forming actinomycin cross bridge
- Head uses energy from hydrolysis of ATP to change angle pulling actin filament along and releasing a molecule of ADP
- ATP molecule attaches to myosin head causing detachment
- ATP hydrolysed to ADP provides energy to myosin head to return to original pattern
What are slow-twitch fibre characteristics?
- Contract slowly
- less power but a longer period of time
- aerobic respiration
- large story of myoglobin - give dark red colour as highly oxygenated
- Rich supply of blood vessels
- Many mitochondria to produce ATP
What are fast-twitch fibre characteristics?
- contract rapidly
- powerful contract over short periods
- anaerobic respiration
- thick and numerous myosin filaments
- increased conc of glycogen
- increased enzyme for anaerobic respiration
- store of phosphocreatine for rapid generation of ATP
Why is important fast-twitch fibres have a store of phosphocreatine?
- To repidly generate ATP
- Adding a phosphate group to creatine meant ATP is hydrolysis to ADP and energy is released
- This reaction is reversible so ADP can be condensed to produce ATP again.
