Nervous coordination and muscles

Question 1

what is mammalian motor neurone made up of?

Answer 1

cell body
dendrons (leads to dendrites)
axon
Schwann cells
myelin sheath (rich in myelin lipid)
nodes of Ranvier

Question 2

what are the three neurones and their functions?

Answer 2

sensory - transmit nerve impulses from receptor to an intermediate or motor neurone
motor - transmits nerve impulses from an intermediate or relay neurone to an effector
intermediate or relay - transmits impulses between neurones

Question 3

saltatory conduction?

why is it faster?

Answer 3

action potentials jump from node of Ranvier to node of Ranvier
action potential passed along a myelinated neurone faster than along the axon of an unmyelinated one of the same diameter.
because in unmyelinated, depolarisation has to occur throughout the axon

Question 4

what are three factors that affect the speed at which an action potential travels?

Answer 4

myelin sheath - saltatory conduction
diameter of the axon - greater diameter = faster speed of conductance
temperature - higher temperature = faster nerve impulse (affects rate of diffusion of ions)

Question 5

explain all-or-nothing principle?

Answer 5

threshold value must be met for an action potential to be triggered.”

Question 6

how can an organism perceive the size of a stimulus?

Answer 6

by number of impulses passing in a given time

by having different neurones with different threshold values

Question 7

explain both types of summation?

Answer 7

spatial - number of different presynaptic together release enough neurotransmitter to exceed threshold value of postsynaptic neurone
temporal - single presynaptic neurone releases neurotransmitter many times over a very short period

Question 8

how do inhibitory synapses work?

Answer 8

• presynaptic neurone releases a type of neurotransmitter that binds to Cl- protein channels on postsynaptic and causes it to OPEN
• Cl- ions into postsynaptic neurone by facilitates diffusion
• binding of neurotransmitter causes opening of nearby K+ protein channels
• K+ out of postsynaptic into synapse
• inside of postsynaptic neurone made more negative and outside more positive
• called hyperpolarisation, makes new a.p less likely

Question 9

what are the functions of synapses?

Answer 9

allow a single impulse along one neurone to initiate new impulses in a number of different neurones at a synapse
allow a number of impulses to be combined at a synapse

Question 10

what is the structure of skeletal muscle?

Answer 10

whole muscle > bundle of muscle fibres > single muscle fibre (here, the single myofibrils share a nucleus and and sarcoplasm) > myofibrils (within have sarcomere, which are made up of actin and myosin)

Question 11

what are actin protein filaments?

Answer 11

actin - thinner and consists of two strands twisted around one another

Question 12

what are myosin protein filaments?

Answer 12

myosin - thicker and consists of long rod-shaped tails with bulbous heads that project to the side

Question 13

what is tropomyosin?

Answer 13

it is a protein that forms a fibrous strand around the actin filament

Question 14

what are slow twitch muscles and what are they used for?

Answer 14

contract more slowly than fast twitch and provide less powerful contractions but over a longer period.
adapted to endurance work and are adapted for AEROBIC respiration, in order to avoid a build-up of lactic acid

Question 15

what are the adaptations of slow-twitch muscles?

Answer 15

• have a large store of myoglobin
• rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration
• numerous mitochondria to produce ATP

Question 16

what are fast-twitch fibres and what are they used for?

Answer 16

contract more rapidly and produce powerful contractions but only for a short period
adapted to intense exercise

Question 17

what are the adaptations of fast- twitch fibres?

Answer 17

• thicker and more numerous myosin filaments
• high conc. of glycogen
• high conc. of enzymes involved in ANAEROBIC respiration which provides ATP rapidly
• a store of phosphocreatine, a molecule that can rapidly generate ATP from ADP in anaerobic conditions and so provide energy for muscle contraction

Question 18

what is a neuromuscular junction?

Answer 18

the point where a motor neurone meets a skeletal muscle fibre.
many spread throughout the muscle.

Question 19

what happens at the neuromuscular junction when a nerve impulse is received?

Answer 19

the synaptic vesicles fuse with the presynaptic membrane and release their acetylcholine.

Question 20

what happens to a sacromere when a muscle contracts?

Answer 20

I-band becomes narrower
Z-lines move closer together, sacromere shortens
H-zone becomes narrower
A-band stays the same

Question 21

in the sliding filament mechanism of muscle contraction, how does muscle stimulation occur?

Answer 21

• an a.p reaches many neuromuscular junctions simultaneously, causing Ca2+ protein channels to open and Ca2+ to diffuse into synaptic knob
• Ca2+ canes the synaptic vesicles to fuse with the presynaptic membrane and release their acetylcholine into the synaptic cleft
• acetylcholine diffuses across the synaptic cleft and bunds with receptors on the muscle cell-surface, causing it to DEPOLARISE.

Question 22

in the sliding filament mechanism of muscle contraction, how does muscle contraction occur?

Answer 22

• a.p travels through T-tubules
• tubules are in contact with sarcoplasmjc reticulum, which has actively transported Ca2+ ions from muscle cytoplasm, leading to low Ca2+ conc. in cytoplasm
• a.p opens Ca2+ protein channels on endoplasmic reticulum, Ca2+ diffuse into muscle cytoplasm down conc. gradient
• Ca2+ ions cause tropomyosin molecules that were blocking binding sites on action filament to pull away
• ATP molecules attached to myosin head mean they are in a state to bind to the actin filament and form a cross bridge
• myosin heads change angle, pulling actin filament along as they do so and releasing a molecule of ADP
• an ATP molecule attaches to each myosin head, causing it to become detached from the actin filament
• Ca2+ then activate the ATPass enzyme, which hydrolysed the ATP to ADP, provides energy for myosin head to return to its original position
• myosin head, once more with an attached ADP molecule, then reattached itself further along the actin filament and the cycle is repeated as long as the conc. of Ca2+ in the myofibrils remains high

Question 23

in the sliding filament mechanism of muscle contraction, how does muscle relaxation occur?

Answer 23

• when nervous stimulation ceases, Ca2+ ions are actively transported back into the endoplasmic reticulum using energy from hydrolysis of ATP
• reabsorption of Ca2+ allows tropomyosin to block the actin filament again
• myosin heads are now unable to bind to actin filaments and contraction ceases, muscle relaxes
• force from antagonistic muscles can pull actin filaments out from between myosin

Question 24

what is the the release of energy from ATP used from?

Answer 24

for:
the movement of myosin heads
the reabsorption of Ca2+ into the endoplasmic reticulum by active transport

Question 25

how is a means of rapidly generating ATP anaerobically created?

Answer 25

using phosphocreatine, and partly by more glycolysis

Question 26

how does phosphocreatine work?

Answer 26

it regenerates ATP
is stored in muscle and acts as a reserve supply of phosphate, which is available immediately to combine with ADP to re-form ATP