nervous coordination of muscles

Question 1

what are the two main forms of coordination in animals as a whole

Answer 1

-the nervous system and the hormonal system

Question 2

how does the nervous system work

Answer 2

the nervous system uses nerve cells to pass electrical impulses along their length

Question 3

how does the nervous system stimulate their target cells

Answer 3

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

Question 4

what are the responses produced in nervous systems

Answer 4

• they are short-lived
• restricted to a localised area
• the effect is temporary and reversible
• transmission is by neurones and is rapid

Question 5

what is an example of a nervous coordination

Answer 5

a reflex action such as the withdrawal of the hand from an unpleasant stimulus

Question 6

what does the hormonal system produce

Answer 6

it produces chemicals (hormones) that are transported in the blood plasma to their target cells

Question 7

what allows the target cells to respond to the receptors

Answer 7

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

Question 8

what kind of responses are produced from the hormonal system

Answer 8

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

Question 9

what are the features of the hormonal system

Answer 9

1. communication is by chemicals called hormones
2. transmission is by the blood system
3. hormones travel to all parts of the body, but only target cells respond
4. response is widespread
5. response is slow
6. response is often long-lasting

Question 10

what ate the features of the nervous system

Answer 10

1. communication is by nerve impulses
2. transmission is by neurones
3. transmission is very rapid
4. nerve impulses travel to specific parts of the body
5. response is localised
6. response is short-lived
7. effect is usually temporary and reversible

Question 11

what are neurones

Answer 11

neurones (nerve cells) are specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another

Question 12

what are the mammalian motor neurones made of

Answer 12

a cell body

dendrons

an axon

Schwann cells

a myelin sheath

nodes of Ranvier

Question 13

what is a cell body

Answer 13

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

Question 14

what are dendrons/dendrites

Answer 14

they are extensions of the cell body which subdivides into smaller branched fibres, called dendrite that carry nerve impulses towards the cell body

Question 15

what is an axon

Answer 15

it is a single long fibre that carries nerve impulses away from the cell body

Question 16

what are schwann cells

Answer 16

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

Question 17

what is a mylein sheath

Answer 17

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

Question 18

what are nodes of ravier

Answer 18

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

Question 19

what are the different classifications if neurones

Answer 19

sensory neurones

motor neurones

intermediate/relay neurones

Question 20

what are resting potenitals

Answer 20

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

Question 21

what is the voltage of the resting potentials

Answer 21

about -70mV because there are more Na+ and K+ ions outside the neuron and so the inside of the neuron is negative

Question 22

how is resting potentials maintained

Answer 22

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

4. 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

Question 23

how is an action potential maintained

Answer 23

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

Question 24

what is repolarisation

Answer 24

when the potential of a neuron is returning back to its negative state as the k+ ion are leaving

Question 25

what is hyperpolarisation

Answer 25

this is when temporarily, the potential/ the charge of the neuron drops below the resting potential pump therefore returns a neuron back

Question 26

what is the all or nothing principle

Answer 26

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

Question 27

what is the refractory period

Answer 27

it is the period in an action potential when the axon can’t be depolarisation to initiate another action potential

Question 28

why is the refractory period important

Answer 28

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

Question 29

what are non - mylelinated neurons

Answer 29

neurons with no mylein sheath

Question 30

what is the transmission of potentials in non-mylinated neurons

Answer 30

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

Question 31

what is the transmission of potentials in mylinated neurons

Answer 31

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

Question 32

what are the factors affecting the speed of conduction

Answer 32

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

Question 33

what is the structure of the synapse

Answer 33

the synapse is the junction between a neurone and another neurone

Question 34

it contains acetylcholine

describe the transmission of a cholinergic synapse

Answer 34

it is called cholinergic because it has the neutrotransmitter acetylchloline (Ach)

1. 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)
2. the diffusion of calcium ions into the synaptic knob leads to vesicles containing acetylcholine (neurotransmitter) fuse with the presynaptic membrane
3. acetylcholine ir released into the synaptic cleft by exocytosis
4. acetylcholine diffuses across the synaptic cleft to the post - synaptic membrane and ninds to cholinergic receptors

Question 35

describe the trasnmission of a cholinergic synapse

Answer 35

it is called cholingergic because it was the neutrotransmitter acetylchloline (Ach)

1. 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)
2. the diffusion of calcium ions into the synaptic knob leads to vesicles containing acetylcholine (neurotransmitter) fuse with the presynaptic membrane
3. acetylcholine ir released into the synaptic cleft by exocytosis
4. acetylcholine diffuses across the synaptic cleft to the post - synaptic membrane and binds to cholinergic receptors
5. Na+ channels on the post synaptic membrane open and Na+ diffuses into the post - synaptic neuron, causing depolarisation
6. if the threshold is reached, an action potential is formed
7. acetylcholine removed from synaptic cleft and degraded by acetylcholine esterase to prevent a continuous impulse. An enzyme substrate complex is formed
8. the products formed from the degradation of acetycholine transferred into presynaptic neuron and Na+ channels close, allowing post- synaptic neuron to reach resting potential

Question 36

how can cholinergic synapses be inhibitory

Answer 36

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

Question 37

what is summation

Answer 37

summation occurs within synapses.

It is the rapid build ip of neurotransmitters to help generate action potential

Question 38

what are the two types of summation

Answer 38

temporal

spatial

Question 39

what is temporal summation

Answer 39

this is when 1 neuron releases neurotransmitters repeatedly over a short period so the threshold value is exceed

Question 40

what is spatial summation

Answer 40

this is when many neurons collectively stimulate an action potential by combining the neurotransmitters they release to exceed the threshold value

Question 41

how are neuromuscular junctions different

Answer 41

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

Question 42

how do skeletal muscles work

Answer 42

they act in antogontastic pairs e.g. when one muscle contracts, the other releases

this creates movement

Question 43

what are muscle fibres made up of

Answer 43

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

Question 44

what is the structure of a muscle fibre

Answer 44

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

Question 45

what is a sacromere

Answer 45

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

Question 46

what is the sliding filament theory

Answer 46

1. Action potentials travel to muscles fibres and depolaries the sacromere via T tubules, causing release of calcium ions from the sacroplasmic reticulum (Ca2+)
2. Calcium ions bind to tropomyosin molecules causes the tropomysoin molecules to move, exposing the myosin binding site on the actin filament
3. This leads to actin and myosin head to bind specifically to the myosin head. This forms an actin myosin cross bridge formed upon attachment
4. ATP is hydrolysed by ATP to detach the myosin head, allowing reattaching at a further site.
   The sacrament shortens, causing muscle contractions
5. When the impulse stops, calcium ions actively transported back into the sacroplasmic reticulum
6. This allows tropomyosin to block the actin filament from binding to myosin, so muscle contractions stop

Question 47

what are myosin and actin filaments

Answer 47

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

Question 48

what are slow-twitch muscle fibres

Answer 48

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

Question 49

where are the mitochondria found in slow-twitch muscles

Answer 49

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

Question 50

what are slow-twitch muscles good for

Answer 50

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

Question 51

what colour are slow-twitch muscles

Answer 51

slow-twitch muscles are red in colour as they are rich in myoglobin, which is a red colour protein that stores oxygen

Question 52

what are fast-twitch muscles

Answer 52

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

Question 53

how is energy released in fast-twitch muscles

Answer 53

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

Question 54

what colour are fast-twitch muscles

Answer 54

They don’t have much myoglobin either so they cant store much oxygen - this gives them more of a whitish colour

Question 55

where are fast-twitch muscles in high proportion

Answer 55

they are found in muscles you use in fast movement such as the legs, arms and eyes

Question 56

what is the ATP phosphocreatine system (PCr)

Answer 56

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

Question 57

what kind of system is PCr

Answer 57

it is anaerobic and it is galactic (as in it does not form any lactate)

Question 58

what is the reaction for the phosphorylation of ADP by PCr

Answer 58

ADP + PCr → ATP + Cr (creatine)

Question 59

what happens to some of the creatine produced

Answer 59

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