Nervous Coordination And Muscles

Question 1

Describe the different kinds of neurones

Answer 1

1. Sensory carry action potentials from receptor cells to CNS 2. Relay neurone carries action potentials between sensory and motor neurones in CNS (lots of short dendrites) 3. Motor neurone carries action potentials from cns to effectors

Question 2

Describe the structure of a myelinated motor neurone

Answer 2

Has a cell Boyd that contains a nucleus and many dendrites, has an axon with a myelin sheath (made from Schwann cells for protection and insulation) and node of ranvier between Schwann cells (for faster conduction). Has axon terminals

Question 3

How is resting potential established in a neurone

Answer 3

Sodium potassium pumps are imbedded into the phospholipid bilayer of the axon. 3na+ are actively transported out of the axon while only 2k+ are actively transported into the axon via the Na+k+ pump. Leak channels transport k and Na+ in an out of axon (facilitated diffusion), Membrane is more permeable to k+ and less to Na+./more channels. This means the inside of the axon is negatively charged and the outside is more positively charged (resting potential) 50-90mv

Question 4

describe the general process of an action potential

Answer 4

1. Arriving stimulus disturbs the resting membrane potential (-70mv) causing NA+ voltage gated channels to open 2. NA+ diffuse into the axon, down its electrochemical/ conc gradient, causing the membrane to depolarise (inside more + than out) 3. When the membrane potential reaches +40mv, NA+ voltage gated channels close and the K+ v.g.c open 4. K+ diffuse out of the axon into the extra cellular fluid, causing membrane to repolarise (inside more - than out) 5. Membrane potential overshoots to -70/-75 mv =hyperpolarisation 6. The K+ v.g.c close and leak channels and Na/k pumps work to restore the resting potential

Question 5

What is an action potential

Answer 5

A change in the membrane potential that spreads along an axon

Question 6

Describe the action potential in an unmyelinated axon

Answer 6

1. The axon membrane is at rest and polarised. Stimulus arrives which disturbs the membrane potential, causing Na+ v.g. Channels to open and NA+ to diffuse in 2. If threshold is reached, an action potential is initiated and depolarisation of the membrane occurs (+ on inside) 3. Local ion movements occur, Na+ diffuse through channel, down conc gradient which creates local electron currents 4. Local electron currents disturb the membrane potential further along the axon (adjacent section), causing Na+ channels to open and Na+ to diffuse in, generating a new action potential. As this next section depolarises, previous repolarises 5. Process repeats and a wave of depolarisation spreads along the length of the axon

Question 7

Describe action potential in myelinated axons

Answer 7

By saltatory conduction 1. Myelin acts as an electrical insulator 2. The action potential jumps between nodes of ranvier, where localised currents arise - means faster conduction and only present in vertebrates

Question 8

What are the factors affecting speed of conduction of an action potential

Answer 8

1. Myelination (travel faster via saltatory conduction as impulse jumps between nodes) 2. Axon diameter (bigger=faster as less resistance to ion flow) 3. Temperature (affect enzymes in sodium potassium pump and ion diffusion in cold blooded as less KE means less collisions and less diffusion)

Question 9

What is the all or nothing principle

Answer 9

A specific level of stimulus (the threshold value) is needed to trigger an action potential so below the threshold, no APs are generated

Question 10

Do action potentials differ in size, if not how does an organism detect the size of a stimulus

Answer 10

All action potentials are the same size so a bigger stimulus doesn’t mean a bigger action potential. Organisms detect the size of stimulus as larger stimuli produce a higher frequency of APs

Question 11

What is the refractory period

Answer 11

During your refractory period, v gated Na+ channels remain closed an can’t be stimulated to open so an action potential can’t occur. During late stage/hyperpolarisation , sodium potassium pumps redistribute ions

Question 12

How does the refractory period separate impulses/ what does a refractory period mean for the axon

Answer 12

As another stimulus won’t trigger an action potential until normal resting potential/ excitability is resorted (means max frequency is 1 per every 6ms) so threshold can’t be reached.

Question 13

What are the benefits of having a refractory period

Answer 13

Is ensures all action potentials are propagated in only 1 direction, it ensures action potentials are separated and it limits the number of action potentials do there is a maximum strength of stimulus that can be detected

Question 14

Draw out a synapse and pre and post neurones (with labels)

Answer 14

Should include: ca2+ channels, vesicles, neurotransmitters, smooth ER, mitochondria, protein receptors, sodium channels, the synapse

Question 15

Describe the transmission across a cholinergic synapse (without breakdown of AcH)

Answer 15

1. Arrival of depolarisation/ AP at the end of the presynaptic neurone causing Ca2+ channels to open and ca2+ diffuse in, down conc gradient 2. Influx of ca2+ causes vesicles to move to and fuse with the presynaptic membrane and release acetylcholine into the synapse 3. AcH diffuses across the synapse and binds to protein receptors on the postsynaptic membrane 4. This causes Na+ channels to open and Na+ diffuse into the post neurone, leading to depolarisation

Question 16

Describe the breakdown of acytylecholine

Answer 16

Acetylcholinesterase hydrolyses AcH into choline and ethanoic acid/acetate. Choline diffuses back across the synapse into pre neurone. ATP from mitochondria combines choline and acetate to AcH

Question 17

What are the 2 ways to get rid of neurotransmitters from the synaptic cleft

Answer 17

1. Breakdown using an enzyme and the products can be taken back into the pre 2. Pump NT back into pre using transport proteins

Question 18

Why is the signal across a synapse is unidirectional

Answer 18

Neurotransmitters are only released/ made in the presynaptic neurone and protein receptors are only on the post synaptic membrane

Question 19

Describe the process of inhibitory synapses

Answer 19

1. The presynaptic neurone releases neurotransmitter (e.g GABA) which diffuses and binds to chloride ion protein channels and opens them so cl- enter the post synaptic neurone, down conc gradient 2. Binding opens k+ channels and k+ diffuse out of the post neurone, into the synapse 3. Combined effect of gain of negative ions and loss of positive, makes inside of post more negative (hyper polarisation) so it is less likely a new AP is created (as more Na+ needed)

Question 20

Describe spatial summation

Answer 20

When A number of different presynaptic neurones together release enough NT to exceed the threshold value to trigger an AP at the Postsynaptic neurone

Question 21

Describe temporal summation

Answer 21

When a single presynaptic neurone releases neurotransmitter many times over a short period. If conc of NT exceeds threshold, an AP is triggered at the post synaptic neurone. / high frequency of APs lead to an accumulation of enough NT to reach threshold

Question 22

Describe the general act of summation

Answer 22

On their own, some neurones might not release a sufficient amount of NT. however they may be sufficient though summation, through a buildup of NT, to reach a threshold to tigger an AP and post synaptic neurone

Question 23

How may drugs affect synapses

Answer 23

They may stimulate the nervous system by creating more APs on excitatory post synaptic neurones (may do this by mimicking a NT, stimulating release of more NT or inhibiting the enzyme that breaks down Nt) or they may inhibit the nervous system by creating fewer APs in post (may do this by inhibiting release of excitatory NT, increasing inhibitory Nt or blocking post receptors)

Question 24

What is meant by antagonistic muscles and how do they operate

Answer 24

When muscles contract, they shorten and pull on incompressible bone. Skeletal muscles work in Paris, when one contracts, the other relaxes

Question 25

What is the neuromuscular junction

Answer 25

A synapse between a motor neurone and skeletal muscle. The NT AcH binds to receptors of muscle cell membrane, stimulating contraction

Question 26

What are differences between cholinergic synapse and neuromuscular junction

Answer 26

NmJ: only excitatory, between motor neurone and muscle, only has motor neurones, the end of a neural pathway, AcH binds to receptors on muscle. Cholinergic: can be excitatory or inhibitory , found between neurones, other neurones involved, other APs may be produced, AcH binds to receptors on Post

Question 27

Similarities between cholinergic synapse and neuromuscular junction

Answer 27

Both use AcH as NT, both stimulated by AP on pre, both use enzymes to break down NT

Question 28

The gross and microscopic structure of skeletal muscle

Answer 28

Gross: muscle, muscle bundles microscopic: muscle fibre, myofibril, sarcomere

Question 29

Describe the ultrastructure of a myofibril (and draw and label it!)

Answer 29

Is made up sarcomeres which contain 2 types of fibrous proteins: actin (which is thinner) and myosin (which is thicker). In the sarcomere, they are arranged like a gate white two Z lines marking the boundaries (z end of alphabet), with thinner actin coming from them each side and thicker myosin in the middle, overlapping. The I band is just actin (thin letter, thin protein), the A band is A bit of both actin and myosin and the H zone is just myosin (thick letter, thick protein)

Question 30

Evidence for contraction of skeletal muscle

Answer 30

The I band and H zone becomes narrower (shorter sarcomere), Z lines move closer together (more overlap) but the A band stays the same lengths

Question 31

The features of slow twitch fibres

Answer 31

Red in colour, high myoglobin conc and high capillary density. Contract slower for longer, have more mitochondria, low reliance on phosphocreatine and fatigue slowly. Most ATP for contraction is generated by oxidative phosphorylation in the mitochondria. They have high 02 consumption and myoglobin in muscles stores 02 to keep AEROBIC respiration going (use glucose and fatty acids)

Question 32

The features of fast twitch fibres

Answer 32

They are white/ place in colour, lower myoglobin conc and capillary density. Rapidly contract with high force, have lower mitochondria and carry out ANAEROBIC respiration. High reliance of PC and fatigue rapidly. They generate most ATP for contraction by glycolysis and consume large amounts of glucose from glycogen in the muscle. They use creating phosphate to release ATP in rapid contraction (pc + ADP= ATP +C)

Question 33

Describe the process of muscle contraction PART 1 (muscle stimulation)

Answer 33

1. An action potential arrives at the presynaptic neurone of the neuromuscular junction (stimulates ca2+ channels to open) 2. Ca2+ diffuse into the neurone, triggering the exocytosis of vesicles containing AcH 3. AcH diffuses across the synapse and binds to receptors on muscle cell surface membrane, causing it to depolarise

Question 34

Describe the process of muscle contraction PART 2 (muscle contraction)

Answer 34

4. Action potentials travel down the T tubules and trigger the opening of calcium ion channels in the sarcoplasmic reticulum (SR) 5. Ca2+ diffuse out of the SR into the cytoplasm and bind to troponin on actin, causing tropomyosin to move and expose myosin binding sites on actin 6. Myosin ADP forms cross bridges with actin filament 7. Myosin pulls actin (power stroke) and releases ADP 8. ATP binds to myosin head, causing it to detach from actin and cross bridge breaks 9. Calcium ions activate ATPase which hydrolyses ATP to ADP + Pi. Hydrolysis provides energy for myosin head to return to original position 10. Multiple cross bridge cycles pull actin towards each other, shortening distance between Z lines

Question 35

How does muscle relaxation occur at the neuromuscular junction

Answer 35

When nervous stimulation ceases, ca2+ are actively transported back into the SR, using energy from hydrolysis of ATP. Reabsorption means topomysosin blocks myosin binding sites on actin so myosin heads can’t form cross bridges and the muscle relaxer

Question 36

How does having multiple sclerosis result in slower responses to stimuli

Answer 36

There is less/no saltatory conduction (AP unable to jump between nodes of ranvier) so depolarisation has to spread along entire length of axon membrane which is slower

Question 37

When a neurone transmits a series of impulses, why does the rate of 02 consumption increase

Answer 37

There is more respiration so more ATP supplied for sodium potassium pump and active transport of ions

Question 38

State why impulse transmission speed in response to touch may be longer than the highest speed expected

Answer 38

Synaptic transmission, time for muscle contraction, time for Na+ channels to open in pacinian corpuscle, person may be distracted, time for coordination or comprehension by Brian