chapter 15 - nervous coordination and muscles

Question 1

What is a cell body

Answer 1

It’s contains the organelles found in a typical animal cell including the nucleus, proteins, neurotransmitters, chemicals.

Question 2

What is a dendron

Answer 2

They are extensions of the cell body which subdivide into smaller branched fibers called dendrites. They carry nerve impulses towards the cell body.

Question 3

What is an axon

Answer 3

An axon is a conductive long fiber that carries nervous impulses away from the cell body and along the motor neurone.

Question 4

What is a schwann cell

Answer 4

It’s wraps around the axon, to form the myelin sheath, which is a lipid. providing electrical insulation. it does not allow charged ions to pass through it. Nodes of ranvier are gaps between the myelin sheath. They also carry out phagocytosis and play a part in nerve regeneration.

Question 5

What is a relay neuron/intermediate neurone

Answer 5

They transmit impulses between neurons for example from sensory to motor neurons.

Question 6

Describe the process of maintaining the resting potential

Answer 6

Sodium ions are actively transported out of the axon by the sodium potassium pump. Whilst potassium ions are actively transported into the axon. via ATP

Three sodium’s move out, two potassium move in producing and electrochemical gradient

Sodium diffuses in and potassium diffuses out the axon along a concentration gradient.

However the membrane is more permeable to potassium, so more potassium ions transported out of the axon, this results in a resting potential of -70 mV. In this condition the axon is said to be polarized.

Question 7

Describe the process of an action potential

Answer 7

At resting potential some potassium voltage gated channels remain open but sodium voltage gated channels are closed.

A stimulus causes some voltage gated sodium ion channels to open. Sodium ions than diffuse into the cell, causing a change in potential difference. If depolarization is large enough to reach the threshold value more sodium channels open so there is a large influx of sodium ions by diffusion. if Depolarization reaches +40 mV this creates an action potential [all or nothing response]

Sodium ion channels close, voltage gated potassium channels open and potassium ions diffuse out of the cell restoring the potential difference with respect to the outside of the cell.

The potential difference over shoots :-) as potassium channels are leaky. Both sodium and potassium voltage gated channels close and the sodium potassium pump restores the resting potential [ATP].

Question 8

And an action potential cannot occur during the restoration of the resting potential, explain why this is beneficial

Answer 8

It’s ensures action potential’s only travel in one direction

It produces separate discrete impulses

It limits the number of action potential’s

Question 9

Describe the transmission of an action potential in a non-myelinated neurone

Answer 9

The transmission acts like a Mexican wave. When depolarization occurs voltage gated sodium ion channels open further down the axon. By the time de-polarization has spread/occurred part of the neuron has been re-polarized.

Question 10

Explain the transmission of an action potential in a myelinated neurone

Answer 10

Action potential’s only occur at the nodes of ranvier. So action potential’s jump from node to node which is quicker. This is called saltatory conduction

Question 11

List three factors that affect the speed at which an action potential travels/speed of conductance.

Answer 11

Myelination: this increases the speed of saltatory conduction

Axon diameter: wider the axon/larger the diameter the faster the speed of conductance. This is due to less leakage of ions from a large axon [leakage means that membrane potential’s are harder to maintain] K+ ions

Temperature: high temperatures increase the speed of impulse as proteins are enzymes and have more kinetic energy at high temperatures that for work at a faster rate.

Question 12

describe the all or nothing principal

Answer 12

If depolarization is below the threshold value, there is an insufficient number of opened sodium channels therefore less sodium ions enter the cell. This prevents for depolarization of the axon. an action potential dosent occur.

If the threshold value is reached, an action potential is generated. Action potential’s are always the same size regardless of the strength of the stimulus. For example deep polarization of the axon because at the same voltage

Question 13

If the action potential’s are always the same size regardless of the strength of the stimulus how does an organism perceive the size of a stimulus. Give two examples

Answer 13

By the number of impulses passing in a given time, the larger the stimulus the more impulses that are generated in a given time.

By having different neurons with different threshold values the brain interprets the number and type of neuron the pass is in process as a result of the given stimulus on there by determines its size.

Question 14

What is a synapse

Answer 14

it is the point where one neurone communicates with another or with an effector

Question 15

what is a neurotransmitter

Answer 15

They are chemicals transmit information from one neurone to another

Question 16

What is the synaptic cleft

Answer 16

gap where two neurones are separated

Question 17

What is the presynaptic neuron

Answer 17

the neuron that releases the Neurotransmitter

Question 18

what is a synaptic knob

Answer 18

ending of an axon /ending of the presynoptic neuron

Question 19

what are synaptic vesicles

Answer 19

where the Nero transmitter is stored

Question 20

What does Unidirectional mean in terms of a synapse

Answer 20

Synapses can only pass information in one direction. from the presynaptic neuron to the post synaptic neuron

Question 21

What is summation

Answer 21

Low frequency action potential’s often lead to the release of insufficient concentrations of neural transmitter. However to generate an action potential there is a rapid build up of neurotransmitter in the synapse this is called summation.

Question 22

spatial summation

Answer 22

When different presynaptic neurons Release enough neurotransmitter to exceed the threshold value of the post synaptic neuron. then an action potential is triggered.

Question 23

temporal summation

Answer 23

a single presynaptic neuron Releases enough neurotransmitter many times over a very short period, if the concentration of neurotransmitter exceeds the threshold value of the post synaptic neuron then a new action potential is triggered.

Question 24

What is an inhibitory synapse

Answer 24

Some synapses make it less likely that a new action potential will be created on the post synaptic neuron.

Question 25

Describe the process of an inhibitory synapse

Answer 25

The presynaptic neuron releases inhibitory neurotransmitter, which binds to chloride ion proteins channels on the post synaptic neuron. This causes chloride protein channels to open.

Chloride ions move into the post synaptic neuron by facilitated diffusion.

Potassium ions protein channels are open due to the binding of inhibitory neurotransmitter.

potassium ions move out of the post synaptic neuron and into the synapse.

Inside of the postsynaptic membrane is now relatively more negative

Membrane potential goes to -80 mV compared to the usual -65 mV [resting potential]

This is called hyper polarization, it is less likely of a new action potential as a large influx of sodium ions is now needed.

Question 26

Describe the process of an excitatory synapse

Answer 26

Neurotransmitter is made only in the presynaptic neuron

neurotransmitter is stored in synaptic vesicles. When an action potential reaches the synaptic knob the membranes of these vehicles fuse with the presynaptic membrane to release the neurotransmitter.

Neurotransmitter diffuses across the synaptic cleft and binds to specific receptor proteins on the post synaptic neuron.

The neurotransmitter binds with the receptor proteins and this leads to a new action potential in the post synaptic neuron. Synapses that produce a new action potential in this way are called excitatory synapses.

Question 27

What are the main two affects of drugs on synapses

Answer 27

They stimulate the nervous system by creating more action potential’s in the postsynaptic neuron’s, [by mimicking Neurotransmitter]

They inhibit the nervous system by creating fewer action potential’s in the post synaptic neuron [by inhibiting the release of neurotransmitters]

Question 28

Describe the process of a cholinergic synapse

Answer 28

the Neurotransmitter is a chemical called acetylcholine.

The arrival of an action potential in the presynaptic neuron causes calcium ion protein channels to open calcium ions enter the synaptic knob by facilitated diffusion.

The influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane releasing acetylcholine into the synaptic cleft.

Acetylcholine then diffuses across the synaptic cleft quickly, and binds to sodium ion protein channels on the membrane of the postsynaptic neuron.

It causes sodium ion protein channels to open, allowing sodium ions to diffuse into the postsynaptic neuron. along a concentration gradient

Acetylcholinesterase Hydrolyses acetylcholine into choline and ethanoic acid(acetyl). Which diffuses back across the synaptic cleft and into the presynaptic neuron [recycling]. Furthermore the rapid breakdown of acetylcholine also prevents the regeneration of a new action potential in the post synaptic neurone.

This leads to discrete transfer of information across a synapse.

Question 29

Describe the structure of a skeletal/striated muscle

Answer 29

Separate cells fuse together into muscle fibers. These muscle fibers share nuclei and cytoplasm [sarcoplasm] within the soccer plasm there is a large concentration of mitochondria and endoplasmic reticulum]

If a muscle was made up of individual cells joined end to end this wouldn’t be efficient as the junction between adjacent cells would be a point of weakness and would reduce the overall strength of the muscle.

Question 30

What is actin

Answer 30

Part of a myofibril which is thinner and has two stands twisted around one another.

Question 31

What is myosin

Answer 31

part of a myofibril. thicker and has long shaped rod tails with bulbous heads that project to the side

Question 32

Describe slow twitch muscle fibers

Answer 32

Are used during endurance activities, because they contract slowly and can work for long periods of time

They have a large number of mitochondria
They have a high concentration of myoglobin
They have an excellent blood supply

This allows for aerobic respiration in the tissue making slow twitch muscle fibers slow to fatigue, however the ATP generation is slower than in fast twitch fibers making the contractions of slow twitch fibers weaker.

Question 33

Describe fast twitch muscle fibers

Answer 33

They are used for short bursts of activity because the contractions are powerful and quick

They respire anaerobically and store a lot of phosphocreatine in the cytoplasm.

The lactate produced by anaerobic respiration causes fast twitch fibers to become fatigued quickly.

Question 34

What is phosphocreatine

Answer 34

Phosphocreatine [in muscle cells] transfer a phosphate ion to ADP, so ATP can be formed

ADP + phosphocreatine = ATP + creatine

Question 35

why is a neuromuscular junction important in muscles

Answer 35

it is where a motor neuron meets a skeletal muscle fibre. There are many junctions along the muscle because if there were only one junction it would take time for a wave of contraction to travel across the muscle and not all fibers would contract simultaneously and the movement would be slow. So there are many neuromuscular junction‘s spread throughout the muscle, this ensures that contraction of a muscle is rapid and powerful when it is simultaneously stimulated by an action potential.

Question 36

Why is it important that all muscle fibers are supplied by single motor neuron

Answer 36

Because muscle fibers can act together as a single functional unit known as a motor unit. This arrangement get control over the force that the muscle exacts for example, if only a slight forces needed only a few units are stimulated. If a greater force is required a large number of units are stimulated.

Question 37

similarities of a neuromuscular junction and a cholinergic synapse

Answer 37

They have neurotransmitters are both transported by diffusion

they have receptors That’s cause an influx of sodium ions

They use a sodium potassium pump to repolarise the axon

They use enzymes to break down the neurotransmitter

Question 38

What are some differences between the neuromuscular junction and a cholinergic synapse

Answer 38

NMJ is only exitatory whereas a CS is inhibitory or excitatory

NMJ acetylcholine binds to receptors on the membrane of muscle fibers
CS Acetylcholine binds to receptors on the membrane of the post synaptic neuron

NMJ action potentials end here, CS a new action potential could be produced (post synaptic neuron)

NMJ only motor neurons are involved. CS intermediate, motor, sensory neurons could be involved

Question 39

What is some evidence for the sliding filament theory

Answer 39

I hands shorten / become narrower

Z Lines move closer together and the sarcomere shortens

The H zone becomes narrower

Question 40

What is the only band that stays the same during contraction of a skeletal muscle

Answer 40

A band

Question 41

describe the sliding filament theory

Answer 41

An action potential travels to the muscle fibers via T tubules which are in contact with the sarcoplasmic reticulum

Calcium ion channels open and calcium ions diffuse into the sarcoplasm

Calcium ions bind to troponin

This causes a confirmational change which causes Tropomyosin to move and expose the myosin binding site on the actin filament.

Myosin attaches to actin ( actin-myosin cross bridge)

Myosin heads change shape pulling Actin filaments along, releasing a molecule of ADP.

ATP attaches to myosin causing it to change shape again and detach from actin

ATPase enzymes activated by calcium ions and are released into the sarcoplasmic reticulum. enzyme breaks down ATP forming ADP (attaches to myosin again) allowing My son had to return to their original position

Myosin heads are now detached and can attach to another binding site further down the actin filament, the process than repeats.

as long as calcium ions are released into the SR, the process repeats. This results in actin filaments in one sarcomere being pulled in opposite directions towards each other.

calcium ions use active transport to go back into the SR, using energy from hydrolysis of ATP. This allows for tropomyosin to block the binding sites once again myosin heads cannot bind. Causing the muscles to relax.

Question 42

During the sliding filament theory (muscle contraction) if there are anaerobic conditions ATP cannot be regenerated from ADP. (respiration) How can muscle contraction still occur anaerobically

Answer 42

Phosphocreatine is stored in the muscle and acts as a reserve supply of phosphate, which can immediately combine with ATP to form ATP. The phosphocreatine store is replenished using phosphate from ATP when the muscle is relaxed.

Question 43

what is more evidence for the sliding filament theory that does not involve the bands

Answer 43

Myofibrils appear darker when actin and myosin overlap. If the sliding filament theory is correct there will be more overlap in the contracted muscle.

During relaxation they’ll be less overlap

Question 44

Why is the membrane more permeable to potassium ions [maintaining the resting potential]

Answer 44

Because that are more potassium ion channels than sodium ion channels. Therefore more potassium ions can diffuse out.

most of the potassium ion channels remain open whereas not all of the sodium ion channels are open. Most of the sodium ion channels open when only there is a high enough voltage.

Question 45

Why is it that the impulse only travels in one direction over a synapse

Answer 45

The vesicles are only found in the presynaptic neuron. this means that newer transmitter is only released from one side.

The receptors are only on the post synaptic neuron membrane therefore the impulse can only travel in one direction

Question 46

Why in the post synaptic neurone is the neurotransmitter broken down quickly and recycled

Answer 46

This allows the sodium ion channels to close And reestablish a resting potential in the postsynaptic neuron. The quick breakdown of neurotransmitter prevents regeneration of a new action potential in the post synaptic neuron. This leads to a discrete transfer of information across the synapse.

Question 47

what are myosin and actin

Answer 47

proteins

Question 48

describe the sliding filament theory ADP/ATP part

Answer 48

ADP and Pi are attached to myosin head when first bound.

the angle created from myosin actin cross bridge created TENSION pulling actin filament along the myosin. ADP is released when this happens.

ATP can bind to myosin changing it’s shape. and detaching it from actin.

ATPase activated by calcium ions allows ATP to form ADP and pi

this releases enough energy for the myosin head to reach original position.

Question 49

when does the process of sliding filament stop

Answer 49

when actin gets as close together as possible. no more contraction can occur

or until you run out of ATP.

The muscles remain stimulated and contracted when that is a plentiful supply of calcium ions and ATP

Question 50

Why does a wider axon diameter increase the speed of conductance

Answer 50

Why the axon diameter means that There is a less leakage of ions from the axon therefore increasing the speed of conductance

Question 51

Why does a higher temperature increase the speed of conductance

Answer 51

The ions diffuse faster

The enzymes involved in respiration work faster. There is more ATP produced therefore the sodium potassium pump can work at a faster rate increasing the speed of conductance