nervous coordination of muscles Flashcards
what are the two main forms of coordination in animals as a whole
-the nervous system and the hormonal system
how does the nervous system work
the nervous system uses nerve cells to pass electrical impulses along their length
how does the nervous system stimulate their target cells
They stimulate their target cells by secreting chemicals, known as NEUROTRANSMITTERS directly onto them
This results in rapid communication between specific parts of an organism
what are the responses produced in nervous systems
- they are short-lived
- restricted to a localised area
- the effect is temporary and reversible
- transmission is by neurones and is rapid
what is an example of a nervous coordination
a reflex action such as the withdrawal of the hand from an unpleasant stimulus
what does the hormonal system produce
it produces chemicals (hormones) that are transported in the blood plasma to their target cells
what allows the target cells to respond to the receptors
the target cells have specific receptors on their cell surface membranes and the change in the concentration of hormones stimulates them
This results in a slower, less specific form of communication between parts of an organism
what kind of responses are produced from the hormonal system
The responses are long-lasting and widespread
an example of hormonal coordination is the control of blood glucose concentration, which produces a slower response but has a more long term and more widespread effect
what are the features of the hormonal system
- communication is by chemicals called hormones
- transmission is by the blood system
- hormones travel to all parts of the body, but only target cells respond
- response is widespread
- response is slow
- response is often long-lasting
what ate the features of the nervous system
- communication is by nerve impulses
- transmission is by neurones
- transmission is very rapid
- nerve impulses travel to specific parts of the body
- response is localised
- response is short-lived
- effect is usually temporary and reversible
what are neurones
neurones (nerve cells) are specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another
what are the mammalian motor neurones made of
a cell body
dendrons
an axon
Schwann cells
a myelin sheath
nodes of Ranvier
what is a cell body
it contains all the usual cell organelles, including a nucleus and large amounts of rough endoplasmic recticulum.
This is associayed with the production of proteins and neurotransmitters
what are dendrons/dendrites
they are extensions of the cell body which subdivides into smaller branched fibres, called dendrite that carry nerve impulses towards the cell body
what is an axon
it is a single long fibre that carries nerve impulses away from the cell body
what are schwann cells
shwann cells which surround the axons protecting it and providing electrical insulation
They also carry out phagocytosis (the removal of cell debris) and play a part in nerve regeneration
Schwann cells wrap themselves around the axon many times, so that layers of their membranes build around it
what is a mylein sheath
a mylein sheth, which forms a covering to the axon and is made up of the membranes of the Schwann cells
These membranes are rich in a lipid known as mylein
Neurones with a mylekun sheath are called myelinated neurones
what are nodes of ravier
these are constrictions between adjacent Schwann cells where there is no myelin sheath
The constrictions are 2-3 micrometres long and occur every 1-3 mm in humans
what are the different classifications if neurones
sensory neurones
motor neurones
intermediate/relay neurones
what are resting potenitals
it is the difference in electrical charge between the outside and inside of the neuron when an impulse isn’t being conducted
this means there is no stimulus to send impulses
what is the voltage of the resting potentials
about -70mV because there are more Na+ and K+ ions outside the neuron and so the inside of the neuron is negative
how is resting potentials maintained
1) by sodium-potassium pump, which involves active transport and therefore ATP (active transport of the sodium and potassium ions)
2) 2 K+ions are pumped into the neuron via the sodium - potassium pump and 3 Na_ ions are transported out of the neuron
3)because the K_ ions are transported into the neuron, this creates a concentration of K+ ions inside the neurone and also a concentration gradient of Na+ ions outside the neuron.
Therefore, the K+ ions can diffuse out of the neuron again creating a negative resting potential
- the sodium potassium pump becomes less permeable to sodium ions and so they can’t be transported back into the neuron. This meant that the resting potential is maintained at -70mV
how is an action potential maintained
1) when an impulse is received from receptors, sodium ion channels open, so Na+ ions enters the neuron, this causes them to become depolarised.
Therefore, the charge becomes more positive.
2) if depolarisation reaches the threshold potential (-50mV) voltage - gated sodium ions are activated, leading to an eve higher influx, causing an action potential (+40mV)
3) Voltage - gated Na+ channels close whilst voltage gated K+ channels open, so reporalisation occurs as K+ ions leaves the neuron
4) When most of the L+ ions have left the neuron, this occurs hyperpolarisation so the voltage - gated K+ ion channels close
5) the sodium potassium pump therefore returns a neuron back to its resting potential
what is repolarisation
when the potential of a neuron is returning back to its negative state as the k+ ion are leaving
what is hyperpolarisation
this is when temporarily, the potential/ the charge of the neuron drops below the resting potential pump therefore returns a neuron back
what is the all or nothing principle
once a threshold is reached, each action potential depolarises the axon the same voltage by voltage gates sodium ion channels
this is important in maintaining the rate of nervous impulse
what is the refractory period
it is the period in an action potential when the axon can’t be depolarisation to initiate another action potential
why is the refractory period important
it is important as it limits the frequency of action potentials as we do not want too many action potentials to be fired
it ensures action potentials only travel in one direction and are discrete
what are non - mylelinated neurons
neurons with no mylein sheath
what is the transmission of potentials in non-mylinated neurons
transimission acts like a “mexican wave” because when depolarisation occurs, voltage - gated sodium channels open further down the axon.
By the time depolarisation has spread part of the neuron has already repolarised
what is the transmission of potentials in mylinated neurons
potentials only occur at the Nodes of Ranvier
So action potentials jump from node to node, which is much quicker and is called saltatory conclusion
what are the factors affecting the speed of conduction
myelination increases speed
axon diameter
the wider the axon the faster the impulse.
This is because there is less resistance to the flow of ions than in the cytoplasm of a smaller axon. With less resistance, depolarisation reaches other parts of the neurone quicker
temperature
higher temp increases the speed of impulse once temp passes optimum it denatures
what is the structure of the synapse
the synapse is the junction between a neurone and another neurone
it contains acetylcholine
describe the transmission of a cholinergic synapse
it is called cholinergic because it has the neutrotransmitter acetylchloline (Ach)
- the action potential arrives at the synaptic knob, depolarising it so voltage gated channels ion and calcium ions diffuse into the synpatic knob (via facilitated diffusion)
- the diffusion of calcium ions into the synaptic knob leads to vesicles containing acetylcholine (neurotransmitter) fuse with the presynaptic membrane
- acetylcholine ir released into the synaptic cleft by exocytosis
- acetylcholine diffuses across the synaptic cleft to the post - synaptic membrane and ninds to cholinergic receptors
describe the trasnmission of a cholinergic synapse
it is called cholingergic because it was the neutrotransmitter acetylchloline (Ach)
- the action potential arrives at the synaptic knob, depolarising it so voltage gated channels ion and calcium ions diffuse into the synpatic knob (via facilitated diffusion)
- the diffusion of calcium ions into the synaptic knob leads to vesicles containing acetylcholine (neurotransmitter) fuse with the presynaptic membrane
- acetylcholine ir released into the synaptic cleft by exocytosis
- acetylcholine diffuses across the synaptic cleft to the post - synaptic membrane and binds to cholinergic receptors
- Na+ channels on the post synaptic membrane open and Na+ diffuses into the post - synaptic neuron, causing depolarisation
- if the threshold is reached, an action potential is formed
- acetylcholine removed from synaptic cleft and degraded by acetylcholine esterase to prevent a continuous impulse. An enzyme substrate complex is formed
- the products formed from the degradation of acetycholine transferred into presynaptic neuron and Na+ channels close, allowing post- synaptic neuron to reach resting potential
how can cholinergic synapses be inhibitory
chloride ions move into the the post - synaptic neuron and potassium ions move out into the synaptic cleft
Membrane potential reaches -80mV, causing hyperpolarisation so an action potential would be very unlikely
what is summation
summation occurs within synapses.
It is the rapid build ip of neurotransmitters to help generate action potential
what are the two types of summation
temporal
spatial
what is temporal summation
this is when 1 neuron releases neurotransmitters repeatedly over a short period so the threshold value is exceed
what is spatial summation
this is when many neurons collectively stimulate an action potential by combining the neurotransmitters they release to exceed the threshold value
how are neuromuscular junctions different
they are unidirectional as neurotransmitter receptors are only on the post synaptic membrane
This is because neurotransmitter receptors are only on the post synaptic membrane so the action potential can only travel in one direction
they are only excitatory unlike choligenic which can be inhibitory
connects motor neurones and muscles
they are the end point of the action potential
acetylcholine binds to receptors on muscle fibre membranes instead of post synaptic membranes
how do skeletal muscles work
they act in antogontastic pairs e.g. when one muscle contracts, the other releases
this creates movement
what are muscle fibres made up of
they are made up of myofibrils
if you look at myosin under an electron microscope, you will see a pattern of alternating light bands and dark bands
Dark bands contain the thick myosin filament and some overlapping thin actin filament - these are called A bands
Light bands contain this actin only - these are called I bands
what is the structure of a muscle fibre
skeletal muscles are made up of a large bundle of long cells called muscle fibres
the cell membrane of muscle fibre cells is called the SACROLEMMA
Bits of the SACROMMELA fold inward across the muscle fibre and stick into the SACROPLASM (a muscle cell’s cytoplasm)
These folds are called T tubules and they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
a network of internal membranes called the SACROPLASMIC RETICULUM runs through the sarcoplasm.
The SACROPLASMIC RETICULUM stores and releases calcium ions that are needed for muscle contractions
what is a sacromere
a myofibril is made up of many short units called a sacromere
The ends of each sarcomere are marked with a Z line
In the middle of each sarcomere is an M line
The M line is the middle of the myosin filaments
Around the M line is the H zone
The H zone only contains myosin filaments
what is the sliding filament theory
- Action potentials travel to muscles fibres and depolaries the sacromere via T tubules, causing release of calcium ions from the sacroplasmic reticulum (Ca2+)
- Calcium ions bind to tropomyosin molecules causes the tropomysoin molecules to move, exposing the myosin binding site on the actin filament
- This leads to actin and myosin head to bind specifically to the myosin head. This forms an actin myosin cross bridge formed upon attachment
- ATP is hydrolysed by ATP to detach the myosin head, allowing reattaching at a further site.
The sacrament shortens, causing muscle contractions - When the impulse stops, calcium ions actively transported back into the sacroplasmic reticulum
- This allows tropomyosin to block the actin filament from binding to myosin, so muscle contractions stop
what are myosin and actin filaments
myosin filaments have globular heads that are hinged so that they can move back and forth
Each myosin head has a binding site for actin and a binding site for ATP
actin filaments have binding sites for myosin heads called actin myosin-binding sites
Another protein called tropomyosin is found between actin filaments. It helps myofilaments move past each other
what are slow-twitch muscle fibres
slow-twitch muscle fibres contract slowly and can work for a long time without getting tired
energy is released very slowly in aerobic respiration
They have a lot of mitochondria and blood vessels to supply the muscle with oxygen
where are the mitochondria found in slow-twitch muscles
the mitochondria is mainly found near to the edge of muscle fibres, so that there is a short pathway for oxygen from the blood vessel to the mitochondria
what are slow-twitch muscles good for
they are good for endurance activities e.g. long-distance running and maintaining posture
high proportions of slow-twitch muscle fibres are found in the muscles you use for posture such as the muscles in the back and in the calves
what colour are slow-twitch muscles
slow-twitch muscles are red in colour as they are rich in myoglobin, which is a red colour protein that stores oxygen
what are fast-twitch muscles
fast-twitch muscle fibres contract quickly but also get tired quickly
This makes them good for short bursts of energy
energy is released slowly through anaerobic respiration using glycogen in fast-twitch muscles
They also have stores of PCr so that energy can be generated very slowly when needed
Fast-twitch muscles have few mitochondria or blood vessels.
They don’t have much myoglobin either so they cant store much oxygen - this gives them more of a whitish colour
how is energy released in fast-twitch muscles
energy is released slowly through anaerobic respiration using glycogen in fast-twitch muscles
They also have stores of PCr so that energy can be generated very slowly when needed
what colour are fast-twitch muscles
They don’t have much myoglobin either so they cant store much oxygen - this gives them more of a whitish colour
where are fast-twitch muscles in high proportion
they are found in muscles you use in fast movement such as the legs, arms and eyes
what is the ATP phosphocreatine system (PCr)
ATP is made by phosphorylating ADP - adding a phosphate group taken from PCr
PCr is sroed inside cells and the ATP -PCr system generates ATP very quickly
PCr runs out after a few seconds so it’s used during short bursts of vigorous exercise
what kind of system is PCr
it is anaerobic and it is galactic (as in it does not form any lactate)
what is the reaction for the phosphorylation of ADP by PCr
ADP + PCr → ATP + Cr (creatine)
what happens to some of the creatine produced
some of the creatine (Cr) gets broken down into creatinine, which is removed from the body via the kidneys
Creatinine levels can be higher in people who exercise regularly and those with a high muscle mass.
High creatinine levels may also indicate kidney damage
