6B Nervous Coordination Flashcards
What are the three types of muscles?
Smooth muscles, cardiac muscle, skeletal muscles
What are smooth muscles?
They contract without conscious control- found in the walls of internal organs (except the heart, stomach and intestine)
What are cardiac muscles?
They contract without conscious control but is only found in the heart
What are skeletal muscles?
The type of muscles that you can use to move
How are skeletal muscles attached to the bone?
By tendons
Agonist
Contracting muscle
Antagonist
Relaxing muscle
Muscle fibres
Large bundles of long cells
Sarcolemma
Muscle cell’s cell membranes
Sarcoplasm
Muscle Cell’s cytoplasm
T-Tubules
Parts of the sarcolemma that fold into the sarcoplasm that help to spread electrical impulses through the entire of the sarcoplasm so they reach all parts of the muscle fibre
Sarcoplasmic Reticulum
A network of internal membranes that store and release calcium ions
Adaptations of muscle fibres
Lots of mitochondria for ATP, multinucleate (contain many nuclei) and lots of myofibrils
Myofibrils
bundles of thick and thin myofilaments that move past each other to allow for muscle contraction
Myosin
Thick myofilaments
Actin
Thin myofilaments
Dark bands
Myosin and overlapping actin
Light bands
Only contain actin
Sarcomeres
A short unit of myofibril
Z-Line
The end of the sarcomere
M-Line
The middle of the sarcomere
H-zone
Only contains myosin filaments
A-band
Dark band
I-band
Light band
Describe the sliding filament theory
myosin and actin filaments slide over each to make the sarcomeres contract- during contraction, the z-lines get closer together (sarcomeres get smaller)
Describe the myosin filament
Globular head that is hinged so can move back and forth
Describe the actin filament
Have binding sites for the myosin heads
Tropomyosin
Blocks the actin myosin binding site
What happens when an action potential reaches the muscle cell?
It depolarises the sarcolemma. Depolarisation spreads through the t-tubules to the sarcoplasmic reticulum. The sarcoplasmic reticulum then releases calcium ions into the sarcoplasm
How do calcium ions trigger a muscle contraction?
They bind to troponin which is attached to the tropomyosin. Troponin changes shape which causes tropomyosin to leave the actin myosin binding site. Calcium ions also activate the enzyme ATP hydrolase
Actin myosin cross bridge
The bond that is formed when the actin and myosin head bind, after the tropomyosin has been removed
How does ATP aid in muscle contraction?
ATP hydrolase is triggered which breaks down ATP into ADP and Pi. The energy released causes the myosin head to bend, pulling the actin filament along in a rowing action. ATP is the hydrolysed again to break the actin myosin cross bridge. The myosin head then moves to the next binding site
How do muscles return to their resting state?
Calcium ions leave their binding site and move back via active transport into the sarcoplasmic reticulum (this requires ATP again). This causes the tropomyosin molecules to move back into the actin myosin binding site
How do muscles get energy for contraction?
Aerobic respiration, anaerobic respiration, ATP-phosphocreatine (PCr) system
What is APT-phosphocreatine system?
A phosphate group is taken from Pcr and added to ADP. PCr runs out after a few seconds so is used for short bursts of energy
ADP + PCr = ATP + Cr
Why are there higher levels of creatinine in people who exercise more?
Some of the creatine (Cr) is broken down into creatinine and pass from the body via the kidneys. A high muscle mass= higher creatinine levels. High creatinine levels can also indicate kidney damage
What are the two types of skeletal muscles?
Slow twitch and fast twitch
Slow twitch muscles
Contract slowly and can work for a long time without getting tired. Energy is released via aerobic respiration
Fast twitch muscles
Contract very quickly but also get tired quickly. Energy is released through anaerobic respiration and also PCr
What is myoglobin and why so slow twitch muscles have more?
A red coloured protein that stores oxygen for aerobic respiration
Describe a neurone at its resting potential
Outside of membrane is positively charged compared to the inside- more positive-. Potential difference is -70mV. The resting potential is maintained by a sodium potassium pump and potassium channels in the membrane of the neurone
Describe the sodium potassium pump of a neurone at resting potential
The active transport of 3Na+ out for every 2K+ in. This creates a sodium electrochemical gradient. Potassium ions can move back out via facilitated diffusion through the potassium channels
Describe the changes in potential difference during an action potential
A stimulus excites the neurone, causing the opening of the sodium ion channels. This makes the neurone less negative. Once a threshold is reached (-55mV) voltage gated sodium ion channels open. (depolarisation). At a P.D of +30mV the Na+ channels close and the K+ channels open (repolarisation). K+ ions overshoot as they are too slow to close- hyperpolarisation. The ion channels reset and the sodium potassium pump returns the membrane to its resting potential
Describe how an action potential moves down the neurone
As a wave of depolarisation- Na+ ions diffuse sideways, causing Na+ channels of the next region of the neurone to open
Describe the refractory period and why it is important
Ion channels can’t be opened- acts as a time delay. This means action potentials won’t overlap, there’s a limit to the frequency that action potentials can be transmitted, and so action potentials are unidirectional
What are the three factors that affect the speed of conductions of the action potentials?
Myelination, axon diameter, temperature
How does myelination affect the speed of conduction of an action potential?
They have a myelin sheath which acts as an electrical insulator. Depolarisation only happens at the nodes of Ravnier, where Na+ channels are concentrated, this means the cytoplasm of the neurone can help the action potential jump to the nodes (salatory conduction)
What is the myelin sheath made from?
Schwann cells
Salatory Conduction
The cytoplasm of the neurone can conduct enough electrical charge to depolarise the next node, so the impulse “jumps” from node to node
How does axon diameter affect the speed of conduction of action potentials?
Quicker with bigger diameters because there’s less resistance to the flow of ions, so depolarisation reaches other parts of the cell membrane quicker
How does temperature affect the speed of conduction of action potentials?
Ions diffuse faster at higher temperatures do to having more kinetic energy
Synapse
The junction between two neurones
The synaptic clef
The tiny gap between the cells at the synapse
Where is the synaptic knob
On the presynaptic neurone
What does the synaptic knob contain?
Synaptic vesicles filled with chemicals called neurotransmitters
What happens when an action potential reaches the presynaptic neurone?
The action potential triggers the release of the neurotransmitter into the synaptic clef
What does the neurotransmitter do?
It diffuses across the synaptic clef and binds to the specific receptors on the postsynaptic neurone, which triggers an action potential
Why are impulses across the synapse unidirectional?
The specific receptors for the neurotransmitter are only on the postsynaptic neurone
How and why is the neurotransmitter removed from the synaptic clef?
The are taken back into the presynaptic neurone or broken down by enzymes to stop the response- prevent constant stimulation.
What are synapses called that use acetylcholine?
Cholinergic synapses
Describe the second messenger model that is used to transport ACh across the synaptic clef
An action potential arrives at the synaptic knob of the presynaptic neurone. The action potential stimulates the opening of voltage-gated calcium ion channels. Calcium ions diffuse into the synaptic knob. The Ca2+ ions cause the vesicles to move to and then fuse with the presynaptic membrane. The vesicles then release ACh into the synaptic clef
Exocytosis
The vesicles releasing the neurotransmitter into the synaptic clef
Describe how the neurotransmitter binds to the receptors and creates an action potential
The neurotransmitter binds to the specific receptors on the post synaptic membrane. Na+ ions open in the postsynaptic membrane. The influx of Na+ ions causes depolarisation, and an action potential is triggered if the threshold is reached
What enzyme is used to break down ACh in the synaptic clef? and describe the process
Acetylcholinesterase then the products are reabsorbed into the presynaptic neurone and is used to make more ACh
What are excitatory neurotransmitters
Depolarise the postsynaptic membrane, making it fire an action potential (if the threshold is reached)
What are inhibitory neurotransmitters?
Hyperpolarise the postsynaptic membrane, preventing it from firing an action potential
Summation
The effect of neurotransmitter released from many neurones is added together
Spatial Summation
Many neurones connect to one neurone
Temporal summation
Two or more nerve impulses arrive in quick succession from the same presynaptic neurone- more neurotransmitter is released into the synaptic clef
Neuromuscular junction
a synapse between a motor neurone and a muscle cell
How can drugs affect the action of neurotransmitters?
Some have the same shape, so are complementary to the receptors- so more receptors are activated
Some block receptors so they can’t be activated by neurotransmitters
Inhibit the enzyme that breaks down the neurotransmitter- more neurotransmitters to bind to the receptors
Stimulate the release of the neurotransmitter from the presynaptic neurone
Some inhibit the release of neurotransmitters
