Section 6 - 15 Nervous coordination and muscles

Question 1

Define - potential difference

Answer 1

The difference in electrical potential between two points

Question 2

Define - Polarised

Answer 2

The term used to describe a cell that has a difference in electrical potential across its membrane

Question 3

Define - diffusion

Answer 3

The movement of a substance from an area of high to low concentration

Question 4

Define - facilitated diffusion

Answer 4

The movement of a substance from an area of high to low concentration using a protein carrier

Question 5

Define - active transport

Answer 5

The movement of a substance from an area of low to high concentration, requires energy

Question 6

Define - leakage channel proteins

Answer 6

Proteins involved in the active transport of substances across membranes

Question 7

Define - Voltage-gated channel proteins

Answer 7

An ion channel found in plasma membranes, they open and close as the potential difference of membranes changes

Question 8

Define - protein pumps

Answer 8

An ion channel found in plasma membranes, their permeability to ions remains relatively constant

Question 9

Explain the structure of a myelinated motor neurone

Answer 9

• 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

Question 10

Explain the structure of a non-myelinated motor neurone

Answer 10

• 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

Question 11

What is the nerves resting potential?

Answer 11

• potential difference = -65mv
• polarised
• inside is more negative
• more positively charged outside
• potassium ions inside
• sodium ions outside
  *

Question 12

How do nerves maintain a resting potential?

Answer 12

• 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.

Question 13

What are the stages of action potential being reached within the nervous system?

Answer 13

• stimulate
• depolarisation
• repolarisation
• hyperpolarisation
• restoration of resting potential

Question 14

Explain the stimulate stage of creating an action potential

Answer 14

• causes voltage gated soidum channels to open and sodium ions to diffuse into neurons
• This makes the inside less negative - depolarisation

Question 15

Explain the depolarisation stage of creating an action potential

Answer 15

• 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

Question 16

Explain the repolarisation stage of creating an action potential

Answer 16

• VGSC closed and VGPC are opened
• Means potassium diffuses out of the cell causing the membrane to become more negative

Question 17

Explain the hyperpolarisation stage of creating an action potential

Answer 17

• more potassium ions inside so too negative
• must become more positive

Question 18

Explain the restoration of resting potential stage of creating an action potential

Answer 18

• VGPC shut
• Sodium potassium pump restores resting potential
• -65mv

Question 19

Explain what is meant by a refractory perious

Answer 19

• Period of time after an action potential occurs where another action potential is impossible
• VGSC closed and cannot reopen

Question 20

Why is the refractory period important?

Answer 20

• 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

Question 21

What is the all or nothing principle?

Answer 21

• An action potential only occurs once a threshold has been reached
• All action potentials are the same size

Question 22

What are the factors that affect the rate of impulse transmission?

Answer 22

• 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.

Question 23

Explain the passage of impulses along a cholinergic synapse

Answer 23

1. AP arrives
2. Causing voltage-gated calcium channels to open
3. Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane
4. Assycholine bonds to a receptor on postsynaptic after diffusing across the synaptic cleft
5. Cause sodium ions protein channels to open
6. Sodium ions diffuse into the postsynaptic cell (AP generated)
7. Acetylcholinesterase hydrolysis acetylcholine to ethanoic acid and chlorine so can diffuse back across the cleft
8. ATP released from mitochondria recombining the chlorine and ethanolic acid to acetylcholine at presynaptic cell

Question 24

What does acetylcholine hydrolyse into to more back across the synaptic cleft?

Answer 24

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.

Question 25

What are the two types of synapse?

Answer 25

* **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

Question 26

What are the two types of summation?

Answer 26

* **Spatial** - multiple synapses to one postsynaptic cell * **Temporal** - One synapse but more powerful so more action potentials.

Question 27

What are the similarities/differences between **neuromuscular junctions** and **cholinergic synapses**?

Answer 27

* 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

Question 28

Explain the stucture of a skeletal muscle

Answer 28

* 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**

Question 29

What is a myofibril and what is it made of?

Answer 29

* made of **sacromeres** * Sarcomeres made of protein filaments - **myofilaments** * Two types of filaments: 1. thin = **actin** 2. thick = **myosin**

Question 30

What are the two types of myofilaments?

Answer 30

Thin = actin thick = myosin

Question 31

State the gross structure of a sarcomere

Answer 31

* **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

Question 32

What is tropomyosin?

Answer 32

Forms the long thin threads that wound around actin filaments

Question 33

Explain the changes in the sarcomere during a muscular contraction

Answer 33

* Sacromere shortens as the I band slides into H band * I shorter * H shorter * Sarcomere shorter * A no change

Question 34

What is a neuromuscular junction?

Answer 34

* 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**

Question 35

What is a motor unit?

Answer 35

all muscle fibres supplied by single motor neurone

Question 36

How does a myofibril contract?

Answer 36

1. **Action potential** occurs in **muscle fibres** as sodium channels have been opened 2. **T-Tubles** (extend cell membrane) - carry a **wave of excitation** in sarcoplasmic reticulum 3. **Activated calcium channels** in SR 4. Allows **calcium ions to diffuse** into the saccroplasm

Question 37

What do the T-tubules do?

Answer 37

* In muscular contractions * Entends cell membrane * carrying wave of excitation in sarcoplasmic reticulum

Question 38

What is the sliding filament theory of muscular contraction?

Answer 38

1. Calcium ions cause **tropomyosin** molecules to move to **expose binding** **sites** on **actin** 2. **myosin head** bound to ATP attach to actin forming **actinomycin** **cross bridge** 3. Head uses **energy** **from** **hydrolysis** of ATP to **change angle** **pulling actin filament** along and releasing a molecule of ADP 4. ATP molecule **attaches to myosin head** causing **detachment** 5. ATP **hydrolysed** to ADP **provides energy** to **myosin head to return** to original pattern

Question 39

What are slow-twitch fibre characteristics?

Answer 39

* 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

Question 40

What are fast-twitch fibre characteristics?

Answer 40

* 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

Question 41

Why is important fast-twitch fibres have a store of phosphocreatine?

Answer 41

* 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.