6: Organisms Response to Changes Flashcards
(136 cards)
1
Q
How do organisms increase their chances of survival?
A
- living organisms (plants and animals) increase survival chance by responding to changes in their internal/ external environment
2
Q
How will organisms react in different environments?
A
- either move away from harmful environments or towards favourable environments
- ensure their conditions are always optimal for metabolism
3
Q
How do plants respond to changes in the environment?
A
tropisms and auxins
4
Q
What is a tropism and auxins?
A
a plant response to a stimulus coming from a certain direction
- they do this by regulating their growth
- towards stimulus: positive tropism
- away stimulus: negative tropism
Auxins- a group of naturally occurring and artificially synthesised plant hormones. They play an important role in the regulation of plant growth. (e.g. IAA)
5
Q
What is phototropism?
A
shoots of plants grow towards the light, as they need sunlight to photosynthesise (response to light)
- shoots show positive phototropism
- roots show negative phototropism
6
Q
What is gravitropism/ geotropism?
A
roots of plants grow down to anchor plants in the soil (response to gravitational pull)
- roots show positive geotropism,
- shoots show negative geotropism
7
Q
What does IAA (indoleacetic acid) do?
A
controls cell elongation in plants, produced in tips of shoots, transported down the shoot causing cells to elongate and plant growth
8
Q
What happens to the shoots and roots in phototropism?
A
SHOOTS- positive phototropism:
- initially, IAA evenly distributes throughout the shoot region
- when light intensity changes, IAA moves to shaded side of the shoot
- greater concentration of IAA builds on shaded side, causing cells on this side to elongate more than those on the light side
- cells elongate faster causing shoot tip to bend towards the light
ROOTS- negative phototropism:
- initially, IAA evenly distributes throughout the shoot region
- when light intensity changes, IAA moves to shaded side of the shoot
- high concentration of IAA inhibits cell elongation on the shaded side of the roots
- cells on shaded side grow slower than the light side, root bends and grows away from the light
9
Q
What happens to the shoots and roots in gravitropism/geotropism?
A
SHOOTS- negative geotropism:
- IAA diffuses from upper to lower side of shoot
- cell elongation causes plant to grow upwards
ROOTS- positive geotropism:
- IAA diffuses to lower side of roots
- inhibits cell elongation causing cells to elongate at a slower rate compared to the top causing roots to grow downwards with gravity
10
Q
How do different factors affect IAA?
A
- tip is removed- light can’t be detected, no IAA produced, shoot won’t bend in any direction
- tip of shoot covered- light can’t be detected, no IAA produced, no cell elongation, shoot won’t bend in any direction
- agar block- plant shoot grows naturally towards light as agar block permeable to IAA
- agar on half block- IAA only diffuse down one side, only that side elongates.
- impermeable barrier- no IAA diffuse, plant doesn’t grow
- impermeable barrier on part- IAA diffuse onto only one side, that cell elongates despite postition of light
11
Q
What is nervous communication?
A
Response to a stimulus (change in environment) coordinated by the nervous system
made of: sensory neurones, CNS, motor neurones, effector
12
Q
How does simple reflex work and triggered?
A
to respond to a stimulus, it must be detected first by receptors (cells/ proteins on surface membrane )
- each receptor is specific to 1 type of stimulus
- when a stimulus is detected by receptor cells an electrical impulse is sent along the sensory neurone
- electrical impulse transmitted to central nervous system
- when the electrical impulse reaches the end of the sensory neurone a chemical (neurotransmitter) is released into the **synapse ** (a gap between 2 neurones)
- this passes on information and the new electrical impulse is generated in the relay neurone in the cns
- cns processes the information and sends impulses along the motor neurone to the effector (muscle/ gland)
13
Q
What is the simple reflex?
A
rapid involuntary response to a stimulus
- as it doesn’t involve brain, we don’t waste time thinking (fast response)
- simple reflexes produce a protective effect
14
Q
why do species have simple responses?
A
- simple mobile organisms
- to keep them in a favourable environment
15
Q
What are the 2 types of simple responses?
A
tactic & kinetic
16
Q
What is a tactic response?
A
- directional movement in response to a stimulus and involves the organism either moving towards something (positive tatic response) or away from something (negative tactic response)
- eg.phototaxis (light), thermotaxis (temperature) and chemotaxis (chemicals)
17
Q
What is a kinetic response?
A
- non-directional movement in response to stimulus
- woodlice show kinetic response to humidity
- in high humidity, they’ll move slowly and turn less often so they’ll stay where they are
- when air gets drier, woodlice will move faster and will turn more often do they will move into a new area
- this increses their chances of survival with a high humidity as this will reduce water loss and conceal them from predators
18
Q
What is a receptor?
A
- can either be cells or proteins on cell surface membrane of cells that detect different stimuli
- CNS detects changes to internal and external environments through receptors
- receptors specific to different specific stimuli
- transducers: change in stimulus detected by sensory neurone, converting change in energy to nervous impulses (generator potential)
19
Q
What is resting potential?
A
- if no stimulus, then receptors in nervous system are in their resting state
- membrane of receptors has ion channels and ion pumps, allowing ions to move in and out of the cell
- inside of cell more negative than the outside (as more +ions outside)
- difference in charge means there’s a potential difference across the membrane
20
Q
What is generator potential?
A
- if a stimulus is detected, membrane of receptor becomes excited and more permeable
- allows more ions to enter the cell, changing the potential difference across the membrane so generator potential generated
21
Q
What is an action potential?
A
- generator potential must reach threshold to be passed onto sensory neurone
- if generator potential big enough, it triggers an action potential (nervous impulse)
- ACTION POTENTIALS ARE THE SAME SIZE SO STRNGTH OF STIMULUS MEASURED BY FREQUENCY
22
Q
What is the pacinian corpuscle?
A
mechanoreceptors that detect mechanical stimuli (e.g. pressure and vibration)
- found in skin and soles of feet
- contain end of sensory neurone (sensory nerve ending) wrapped in layers of connective tissue (lamellae)
- plasma membrane of sensory neurone ending has special type of sodium ion (stretch mediated sodium ion channels)
23
Q
How does the pacinian corpuscle detect changes?
A
- when stimulus detected, lamellae become deformed and press on sensory nerve ending (no longer in resting potential)
- causes cell membrane of sensory neurone to stretch, deforming ion channels
- causes stretch mediated sodium ion channels to open so sodium ions diffuse in
- influx of sodium ions changes potential difference of membrane and depolarises it, creating generator potential
- if reached threshold level, it’ll trigger an action potential, which is passed onto the central nervous system
24
Q
What are photoreceptors?
A
receptors in the eye that detect changes in light
- located on the retina (innermost layer of the eye)
- light enters eye through pupil and focused onto retina
- amount of light entering eye controlled by muscle of iris
- fovea is area of retina contaning lots of photoreceptors
- nerve impulses from photoreceptors cells are carried from retina to brain by the optic nerve (a bundle of neurones
- where optic nerve leaves the eye is the blind spot (as no receptors there)
25
What are the 2 types of photoreceptors?
- **Rods-** sensitive to light intensity, lead to images being seen in black and white (monochromatic)
- **Cones-** respond to different wavelengths of light, allowing us to perceive images in full colour
- both photoreceptors connected to the optic nerve by **bipolar neurones**
26
How do we see?
- when light enters the eye, it hits the photoreceptors, the light energy is absorbed and converted into electrical energy (**generator potential**)
- light bleaches the pigment in these cells (**rhodopsin in rods, iodopsin in cones**) breaking them down and causing a chemical change,
- altering permeability of cell surface membrane to sodium ions
- threshold level generates action potential
- action potential sent along **bipolar neurone**, which connects to photoreceptor to the optic nerve, sending impulses to the brain
27
What do rod cells do?
- don't distinguish between wavelengths of light, **only intensity** (monochromatic)
- more **numerous** than cone cells in retina around peripheral (outside)
- used to detect light at very low light intensities, very sensitive to light intensity
- light detected must exceed threshold to trigger generator and action potential
- as many rod cells connected to single sensory neurone
28
What is spacial summation in rod cells?
- if generator potential of each rod cell is very low, they all accumulate to create a larger generator potential and reach the threshold
- create an action potential
29
What is visual acuity?
- the ability to distinguish between 2 points close together
- rod cells provide **low visual acuity**, so the brain can't distinguish between seperate sources of light that've been detected
- as only one action potential travelling to the brain due to summation
30
What do cone cells do?
- packed **close together in the fovea** , distinguish between wavelengths of light (colours, **trichromatic vision**), perceive images in full colour depending on proportion
- 3 types, each w/ different optical pigment, each sensitive to dofferemt wavelengths of light (**blue,green,red**)
- very sensitive to light intensity, only respond at high light intensities (**as each cone cell connected to 1 sensory neurone**)
- to generate an action pot., generator pot. from **each individual cone cell needs to exceed threshold level**
- as each cone cell has its own sensory neurone, each trigger has own action potential, 2 impulses and so easily distinguish (though less sensitive to light int., higher visual acuity)
31
What are the 2 types of nervous system?
- **central nervous system (CNS)-** made of brain and spinal cord
- **peripheral nervous system-** made of neurones connecting CNS to body
32
What is the peripheral nervous system split into?
- **somatic-** controls conscious activity (e.g. walking/talking)
- **autonomic-** controls unconscious activity (e.g. breathing/ digestion)
autonmomic split into sympathetic and parasympathetic
- sympathetic- flight or fight response
- parasympathetic- calm body rest and digest
33
How is our heart rate controlled by our autonomic nervous system?
- cardian muscles are **myogenic** (contract and relax without signals and nerves)
- patterns of contractions control heartbeat, process starts with **sinoatrial node (SAN)**
- mass of tissue in wall of right atrium (**pacemaker, same as SAN**), sets the rhythm of the heartbeat, send out waves of electrical activity to atria wall, causing muscles in atria to contract, forcing blood into the ventricles below
- band of **non-conducting collagen tissue** prevents wave of electrical energy from being passed directly from atria to the ventricles
- wave of electrical activity transferred to **atrioventricular node**
- to esure the atria have empties before ventricles contract, there;s a **delay** before AVN reacts
- AVN responsible for passing waves of electrical activity onto the **bundle of His (in septum)**
- group of muscle fibres responsible for conducting wave of electric activity between ventricles to **heart apex**
- splits into fine tissue (**purkyne tissue**)
- causes wave of electrical activity into muscular ventricle walls
- causes them to contract simultaneously from bottom up, forcing blood out through the pulmonary artery and aorta above
34
What is the role of the heart and brain in controlling heart rate?
- **SAN generates electrical impulses** that cause **cardiac muscles to contract**
- rate of SAN fires unconsciously controlled by brain (**medulla oblongata**)
- animals need to alter heart rate in response to change in internal stimuli
- detected by **pressure receptors** and **chemical receptors**
35
What receptors are used in maintaining heart rate?
- **baroreceptors-** detect pressure. found in aorta and carotid arteries (major arteries in the neck). stimulated by high and low blood pressure
- **chemoreceptors-** detect chemicals. found in aorta, carotid arteris and medulla. monitor O2 levels in the blood (and CO2 and pH, indicate O2 levels)
36
What occurs in the heart when there's a change in blood pressure?
- **high b.p.-** baroreceptors detect change, impulse sent to medulla by **parasympathetic neurones**, secrete **acetylcholine** neurotransmitter to bind to SAN, cardiac muscles cause **heart rate to slow, reducing b.p.**
- **low b.p.-** baroreceptors detect change, impulse sent to medulla by **sympathetic neurones**, secrete **noradrenaline** neurotransmitter to bind to SAN, cardiac muscles cause **heart rate to speedm up, increasing b.p.**
37
What occurs in the heart when there's a change in O2 blood concentration?
| CO2/ pH change
- **high blood O2-** chemoreceptors detect change, impulse sent to medulla by **parasympathetic neurones**, secrete **acetylcholine** neurotransmitter to bind to SAN, cardiac muscles cause **heart rate to decrease, returning O2, Co2 and pH levels to normal**
- **low blood O2-** chemoreceptors detect change, impulse sent to medulla by **sympathetic neurones**, secrete **noradrenaline** neurotransmitter to bind to SAN, cardiac muscles cause **heart rate to increase, returning O2, Co2 and pH levels to normal**
38
What is a neurone?
nerve cells, responsible for conducting electrical impulses (action potentials) around the body
39
What are the 3 types of mammalian neurone?
- **sensory-** transmit nerve impulses from receptors (e.g. skin/eyes) to relay (intermediate) neurone or directly to the motor neurone
- **relay-** transmits impulses between sensory to motor neurone (in CNS)
- **motor-** transmits impulses to effector (e.g. muscles/ glands)
40
What are the sturctures of the 3 mammalian neurones?
- **sensory-** receptor, axon, cell body centre, myelin sheath
- **relay-** dendrites, cell body at top, axon
- **motor-** cell body top, nodes of ranvier, axon, shwann cells
| bottom -> top
41
What is the cell body?
- contains organelles (cells)
- including nucleus and large amounts of rough endoplasmic reticulum, for protein/ neurotransmitter production
42
What is the dendrons?
- extensions of cell body
- divide to form **dendrites** (small branches)
- dendrites are able to conduct electrical impulses from multiple neurones, carrying electrical impulses to the cell body
43
What is the axon?
- a single, long fibre carrying electrical impulses away from the cell body
- some **myelinated** neurones have a myelin sheath (made of **schwann cells**) rich in myelin
- this protects the axon and provides electrical insulation
44
What is the nodes of ranvier?
- exposed parts of axon between schwann cells where there's no myelin sheath
- occur every 1-3mm along the length of the myelinated neurone
45
How do ions move through nerve cells?
- can't move by simple diffusion as they're charged
- require use of carrier and channel proteins, need **facillitated diffusion**
- also may require active transport for energy
46
What are the 5 stages of the movement of nerve impulses?
1. resting potential
2. action potential
3. peak action potential
4. hyperpolarisation
5. repolarisation
47
What is resting potential (1)?
| Nerve Impulses
- **neurone isn't stimulated**, membrane is polarised
- inside of axon less positively charged than the outside, creating Na+ **electrochemical gradient**, maintaines by sodium, potassium pump
- Na/K pump, pumps 3Na+ ions out, 2K+ ions in
- some voltage gated K+ ion channels are open, K+ ions diffuse back out of the cell
- voltage gates Na+ channels closed
- active process, requires ATP to pump ions in and out of neurone cytoplasm
48
What is action potential (2)?
| Nerve Impulses
- when stimulus detected
- energy from stimulus transduced, **voltage gated Na+ ion channels open**
- Na+ ions diffuse back into the neurone, down Na+ electrochemical gradient
- triggers reversal in potential difference across the membrane, causing **generator potential**
- if stimulus reaches the **threshold**, more voltahe gated Na+ ion channels open, causing influx of Na+ ions reentering by diffusion
- can **depolarise** membrane (due to reverse in charge), inside more positive than outside, generating **action potential**
49
What is peak action potential (3)?
| Nerve Impulses
- when pd across the membrance reaches 40mV
- voltage gated Na+ ion channels close again, **decreasing permeability** to Na+ ions
- other voltage gated K+ ion channels open, more K+ ions diffuse back into the cell, **repolarising it**
50
What is hyperpolarisation (4)?
| Nerve Impulses
- voltage gated K+ ion channels that opened are slow to close
- therefore there's a **slight overshoot in the no. of K+ ions diffusing out**
- causes membrane to become hyperpolarised
- as inside of axon **more negative** than outside, more negative than **resting potential**
51
What is repolarisation (5)?
| Nerve Impulses
- closeable voltage gated K+ ion channels close, **Na/K pump reestablishes resting potential** of -70mV across the membrance
- cell surfave membrane **repolarised**
52
What is the refractory period?
- after action potential membrane of axon **unable to be excited straight away**
- as ion channels recovering (Na+ ion channels closed due to repolarisation, K+ ion channels closed due to hyperpolarisation)
- this is known as the **refractory period**
53
How does the refractory period show the action potential is unidirectional?
- acts as **time delay** between 1 action potential and the next
- ensures action potentials don't overlap, able to pass as seperate impulses
- means there's a **limit to the frequency** where nerve impulses can be transmitted
54
Why do waves of depolarisation take longer in non-myelinated neurones?
- when an action potential is generated, some Na+ ions that enter the neurone diffuses sideways along it, in **myelinated neurone**
- causes sodium ion channels in next part of neurone to open, allowing Na+ ions to diffuse into that part
- causes a wave of depolarisation along length of neurone ina a **non-myelinated neurone**, this happens along the entire length of the axon membrane (takes longer)
55
What is saltory conduction?
- in a **myelinated** neurone, depolariation will onlyoccur at the **nodes of ranvier**, as the Na+ ion channels on axon membrane are exposed
- cytoplasm in the neurone is able to conduct enough of an electrical charge in order to depolarise the next node
- allowd electrical impulse to jump sideways from one node to the other **(saltory conduction)**
- much faster then depolarisation in a non-myelinated neurone
56
What factors affect the speed of conduction in a neurone?
- **myelination-** affects speed of conduction of action potential along neurone length
- **diameter of axon-** thicker diameter, less resistance to flow of ions in the cytoplasm
- **temperature-** higher temp., increased rate of diffusion of ions, faster speed of condctuction. at 40C, proteins denature, so speed of conduction decreases
57
What is a synapse?
a junction between 2 or more neurones, or between neurones and effector cells
58
What is the structure of the synapse?
- gap between neurones- **synaptic cleft**
- neurone before synaptic cleft- **presynaptic neurone**
- neurone after synaptic cleft- **postsynaptic neurone**
59
What is the structure of the presynaptic neurone?
- ends in swollen portion: synaptic knob w/ vesicles containing chemicals (neurotransmitters)
- lots of mitochondria, large amounts of endoplasmic reticulum, needed formanufacturing neurotransmitters
60
What is the structure of the postsynaptic neurone?
- has receptor sites on membrane, complementary to the specific neurotransmitter
- when action potential reaches the end of the neurone, an electrical impulse is transferred onto the next neurone by these neurotransmitters (e.g. acetylcholine)
- ensures nerve impulses/ action potentialis unidirectional, only travels in one direction
61
What are the types of synapses?
- **cholinergic synapse**- junction between 2 neurones
- **neuromuscular junction**- junction between presynaptic neurone andmuscular (effector)
- both involve neurotransmitter **acetylcholine**
62
How does an electrical impulse travel through a cholinergic synapse?
1. when an **action potential** reaches the end of the **presynaptic neurone**, causes Ca2+ voltage gates ion channels to open
2. Ca2+ ions diffuse across cell membrane into presynaptic knob by **facillitated diffusion**
3. influx of Ca2+ ions causes **vesicles w/ neurotransmitters ACh** to fuse w/ the membrane of the presynaptic knob
4. neurotransmitter released into synaptic cleft by **exocytosis which diffuses across the synaptic cleft**
5. Ach binds to **complementary receptor site**s (Na+ ion protein channels) present on membrane of post-synaptic neurone
6. influx of Na+ions into post-synaptic neurone **generates new action potential due to depolarisation**, conducted along the length of the neurone towards the synaptic knob at the end of that neurone
63
Why is acetylcholine later removed from the synaptic cleft?
- binding of ACh to receptor sites could triggeer continuous action potentials to be generated in the post synaptic neurone
64
How is ACh removed from the synaptic cleft?
- enzyme **Acetyl Choliersterase** hydrolyses ACh to acetyl and choline
- acetyl and choline diffuses from the** synaptic cleft across the membrane and back into the presynaptic knob**
- ATP produced by mitochondria used to **combine acetyl and choline to reform ACh, stored in vesicles** in the presynaptic knob for future use
- as there's no more Ach to bind to receptor sites,Na+ ion channels close
65
What are the types of neurotransmitters?
- inhibitory (e.g. GABA)
- excitory (e.g. ACh)
66
How does an excitory neurotransmitter work?
| ACh
- e.g. Acetylcholine
- **depolarises the post-synaptic neurone, generating an action potential**
- no more acetylcholine so Na+ ion protein channels close
67
How does an inhibitory neurotransmitter work?
| GABA
- e.g. GABA
- when GABA binds to receptor sites, membrane of post-synaptic neurone becomes **hyperpolarised, preventing an action potential from being generated**
- causes K+ ion channels in post synaptic neurone to open, allowing K+ ions to diffuse out
68
How can acetylcholine also act as an inhibitory neurotransmitter?
- inhibitory when it bonds to complementary receptor sites on postsynaptic neurone at synapse at the heart
- causes K+ ion channels to open, allowing more K+ ions to diffuse out of the cell, depolarising the neurone
69
What is summation and when is it required?
- if a small amount of neurotransmitter is released into the synaptic cleft, may not reach threshold in postsynaptic neurone to trigger action potential
- **summation-** when neurotransmitters are added together from many neurones to trigger an action potential
70
What is spacial summation?
- when 2 or more presynaptic neurones release neurotransmitters **onto the same postsynaptic neurone**
- **accumulation of neurotransmitters enough to trigger action potential** in postsynaptic neurone, even if a small amount of neurotranmsitter is released from each presynaptic neurone
71
What is temporal summation?
- when 2 or more nerve impulses arrive **in quick succession to each other** from the same presynaptic neurone
- as more and more neurotransmitters are released into the synaptic cleft, **accumulation** of this makes it **more likely to generate an action potential** in the postsynaptic neurone
72
What is the neuromuscular junction?
- a type of cholinergic synapse, between the motor neurone and muscles
- still uses neurotransmitter ACh
73
How is the neuromuscular junction different to cholinergic synapse?
- both **unidirectional** due to neurotransmitter receptors only being on postsynaptic membrane
- in **N.m. only excitatory** neurotransmitters, cholinergic inhibitory and excitatory
- **N.m. only connects motor neurone to muscles**, **cholinergic connects 2 neurones**
- **N.m. is the end point for the action potential**, cholinergic connects action potentials
- in N.m., ACh binds tp receptors on **muscle fibre membranes**, not post-synaptic
- in N.m.,** membrane folded forming pleats that store AChase**
- N.m. has **more ACh receptor**
74
Explain the effects of drugs with the same shape as neurotransmitters on synapses
- can also bind to complementary receptor sites (act as **competitive inhibitor**)
- e.g. endorphins bind to receptors on brain cells, block pain, morphine can also **mimic this effect**
- these are called **agonists**
75
Explain the effects of drugs that block the receptor
sites on synapses
- preventing the synapses from **being activated**
- these are called **antagonists**
76
What can other drugs do at synapses?
- some drugs **inhibit enzymes that breakdown the neurotransmitter**
- some drugs (e.g. amphetamines and cocaine) stimuate the release if a neurotransmitter from the presynaptic neurones, so **no more receptors activated**
- some drugs (e.g. GABA) **inhibit the release of neurotransmitters** from the presynaptic neurone, **fewer receptors activated**
77
What are muscles?
- effector organs that respond to nervous impulses
- contract and relax to bring about movement
78
What are the types of muscles?
- **smooth-** **involuntary** muscles (contract without conscious control) | found **in walls of internal organs** (e.g. intestines, not the heart)
- **cardiac-** exclusively found in **heart (involuntary)** | **myogenic-** contract and relax without electrical impulses
- **skeletal-** (a.k.a. striated, striped or voluntari muscle) muscles contract and relax under our **conscious control** for movement | skeletal muscles attatched to bones by **tendons** | bones attatched to other bones by **ligaments**
79
How are skeletal muscles antagonistic?
- act in pairs (one relaxes, the other contracts)
- contracting- **agonist** | relaxing- **antagonist**
- bones are incompressible, act as levers, give muscles something to pull against
80
What is the structure of the skeletal muscles?
- made up of large bundles of long cells (**muscle fibres**)
- cell membrane of muscle fibre cells= **sarcolemma** (may fold inwards across muscle fibres and stick into sarcoplasm, forming **transverse T tubules**)
- transverse T tubules spread electrical impulses throughout the entire sarcoplasm so it reaches all the muscle fibre
- network of internal membrane (**sarcoplasmic reticulum**) run through the sarcoplasm and stores/releases Ca2+ ion for muscle contractions
- muscle fibres have **mitchondria** to release ATP for contraction
- lots of **nuclei (multinucleated)** and lots of long cylindrical organelles (**myofibrils**)
- made up of **myofilaments** and are highly specialised for **contraction**
81
What is the structure of myofibrils?
- contain bundles of thick and thin myofilaments
- thick filament- **myosin** | thin filament- **actin**
- each myofibril made up of short sections (**sarcomeres**)
82
What are the zones and bands within the myofibril?
- dark bands (**A band**)- myosin and actin filaments overlap
- light bands (**I band**)- only actin filaments
- end of each sarcomere (**Z line**)
- middle of each sarcomere (**M line**)
- between dark bands by M line (**H zone**)- only myosin filaments
| pattern of bands under the microscope
83
What is the sliding filament theory used to explain?
- what happens in the muscles contractions
- when actin and myosin filaments slide over each other, the sarcomere contracts
- simultaneous contraction of lots of sarcomeres causes muscle fibres to contract
84
What happens to the sarcomere and myofibrils when the muscle fibres contract?
- **I band** (actin only) shortens
- **H zone** (myosin only) shortens
- **Z line** (end of each sarcomere) comes closer together
85
What is the structure of the actinomyosin bridge when muscles are at rest?
- **myosin filament** has hinged globular head, allowing it to move back and forth **each myosin head has binding site for actin and ATP**
- **actin filaments have binding sites for mysoin head** (actin-myosin binding sites)
- contain another protein (**tropomyosin**) found between actin filaments helping them move past each other
- **when muscles resting, tropomyosin blocks actin-myosin binding site**
- as myosin head can't bind to actin myosin binding site, **actin and myosin filaments unable to slide over each other**
86
What is the sliding filament theory (muscle contraction)?
1. when an **action potential** from motor neurone stimulates the muscle cell, it **depolarises the sarcolemma** (depolarisation spreads through transverse T tubules to sarcoplasmic reticulum, storing Ca 2+)
2. Ca2+ ions released into sarcoplasmm **trigerring muscle contractions**
3. Ca2+ ions **bind to tropomyosin on actin filament, causing tropomyosin to change shape, pulling tropomyosin out of actin myosin binding site, exposing the binding site**
4. **myosin head binds to binding site, forming actin-myosin cross bridge bond**
5. Ca2+ ions activate ATP hydrolase (hydrolyses ATP -> ADP + Pi to **provide energy for muscle contraction**
6. energy allows myosin head to bend to side (**powerstroke**), pulling actin filament over it (in order for cross bridge to br broken and allow to return myosin to resting, **another ATP provides energy to break actin-myosin cross bridge**
7. **myosin head detaches and reattacks position of actin filament**
8. process repeats itself
87
Why is lots of energy required when muscles contract?
- when muscles contract, lots of energy is needed, ATP used quickly
- in order to provide enough ATP for exercise, it can be produced by:
- aerobic respiration, anaerobic respiration and the ATP phosphocreatine (PCr) system
88
How is ATP provided in aerobic respiration?
- most ATP generated in oxidative phosphorylation (mitochondria)
- only carried out w/ sufficient oxygen supply
- good for **long periods, low intensity excercise**
89
How is ATP provided in anaerobic respiration?
- ATP produced in glycolysis, produces pyruvate
- pyruvate -> lactate by lactate fermentation, builds up quick in muscles, causing muscle fatigue
- useful for **short periods of hard excercise**
90
How is ATP provided in ATP phosphocreatine (PCr) system?
- uses ATP and phosphocreatine
- **provides immediate ATP production** by phosphorylating ADP, adding P from PCr
- PCr runs out fast, used in **short bursts of vigorous excercise**
- ATP PCr system is anaerobic, no lactate formed, **creatine broken into creatinine removed from the body by the kidney**
91
What are the 2 types of muscle fibres?
skeletal muscles made of 2 fibres
- fast twitch
- slow twitch
92
How do slow twitch muscle fibres work?
- **contract slowly, work for long time before getting tired**
- useful for endurance activities and maintaining posture
- energy **released slowly by aerobic respiration**
- lots of mitochondria, found near edge of muscle fibres
- short diffusion pathway for O2, to diffuse from blood vessels to mitochondria
- rich in myoglobin, protein that stores O2, so appears reddish
93
How do fast twitch muscle fibres work?
- **contract quickly, get tired quickly**
- useful for short bursts of speed and power, found in high proportions of muscles for fast movement
- energy **released quickly by anaerobic respiration**, using glycogen
- have PCr stores to generate energy quickly when needed
- few mitochondria and blood cells
- very little myoglobin, don't store as much O2, whiter colour
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What is homeostatis?
the maintainance of the stable internal environment within restricted limits, regardless of changes to the external environment
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Why do we need homeostatis?
- for survival
- despite external factors (e.g. temperature, water potential of blood, blood glucose conc.)
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What do control mechanisms in any self-regulating system of homeostatis involve?
- **optimal point-** point where system operates best
- **receptors-** detects changes from optimal point
- **coordinator-** co-ordinates these changes, sends electrical impulses to required effectors
- **feedback mechanism**
- **effectors-** bring about change to return to optimal point
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What is negative feedback?
- when changes detected by the control system are **counteracted** by humoral/ nervous system to **reestablish optimal point**
- only works in **small limits**, if change ius too big, effectors can't rectify the change (e.g. temperature: shivering | hypothermia & hyperthermia)
- **reverse changes to bring about a response, restore optimum conditions**
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What is positive feedback?
- **amplifies changes detected (does opposite)**
- further increases level beyond optimum level
- also only works in **small limits**
- e.g. when you cut yourself, platelets activated, chemical reactions release MORE platelets to clot and heal
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Why is positive feedback not involved in homeostatis?
- not involved in stabilising the environment
- or keeping environment constaht
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Why is it important to maintain our body temperature?
internal body temperature needs to be maintained at 37°C to function properly
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What happens when our body temerature falls below 37°C?
- substrate and enzyme have less energy to move
- collide with each other less frequently
- reduces enzyme activity, slowing down the rate of metabolic reactions in the body
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What happens when our body temerature rises above 37°C?
- active site of enzymes can denature
- as molecules within the enzyme have more energy, vibrate faster, breaking hydrogen bonds holding the tertiary structure
- reduces rate of enzyme activity and slows down metabolic reactions in the body
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Why do our pH levels need to remain constant?
- if pH of blood too low or too high, active site of enzyme denatures
- breaks hydrogen bonds, holding tertiary structure, changes shaoe of active site
- as active site has changed shape, enzyme can no longer act as a catalyst
- this reduces rate of metabolic reactions in the body
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What is pH?
- the concentration of H+ ions in solution
- pH= -log10[H+]
- more H+, lower pH, more acidic
- [H+] represents the concentration of H+ ions in the solution in mol/dm³.
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Why is pH using logs?
- logarithmic scale
- easier to compare values as conc. (H+) varies
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Why is it esssential to mainbtain blood glucose levels?
- glucose in blood essentrial for energy for cells
- conc. of blood glucose can affect water potential of the blood (usually 5mmoldm-3)
- if conc. of blood in glucose is too low, cells can't carry out their normal functions as there isn't enough glucose to release energy in respiration
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What happens if there's too much sugar in the blood?
- lower water potential in the blood
- water moves by osmosis from cells to the blood
- cells shrivel and die
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What happens if there's too little sugar in the blood?
- not enough glucose for respiration
- cells can't carry out normal functions
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What are hormones?
- chemical messengers, produced in organs called glands
- released directly into the **bloodstream**, carried around body to target cells
- have complementary receptor/ binding sites on cell surface membrane
- **effective in low concentrations, often have long lasting/ widespread effects, slow to travel**
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What hormones control blood glucose concentration?
- controlled by hormones in the pancreas
- through cells in pancreas, there's a group of hormone producing cells (**islets of langerhans**)
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What cells make up the islets of langerhans?
- **alpha cells-** larger, manufacture and secrete hormone **glucagon**
- **beta cells-** smaller, manufacture and secrete hormone **insulin**
- when hormones released into the bloodstream, carried to target cells of liver **(hepatocytes)** and muscle cells
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What are the processes the liver responsible for carrying out?
- **glycogenesis-** convert glucose -> glycogen
- **glycogenolysis-** break glycogen -> glucose
- **gluconeogenesis-** make glucose from other sources
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What is the role of insulin hormone?
- eating foods containing carbohydrates increases blood glucose concentration
- detected by **beta cells in islets of langerhans** which secrete insulin hormone directly into the blood (pancreas)
- insulin binds to complementary receptor sites of target cells (mucles and hepatocytes)
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What is glucogenesis?
converts glucose -> glycogen
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What is glucogenlysis?
convert glycogen -> glucose
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What is gluconeogenesis?
convert amino acids and glycerol -> glucose
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How does insulin decease blood glucose concentration?
- when it binds to receptors, **increases permeability** of membrane of target cells and changes the **tertiary structure** of glucose transport protein, causeing it to chsnge shape and **allow glucose in by facillitated diffusion**
- when insulin binds to receptors, **increases no. of carrier proteins** responsible for transporting glucose in cell surface membrane
- increase in insulin conc -> vesicles with carrier protein fuse w/ plasma membrane so there's **more transport proteins**
- when it binds to receptors, activates enzymes within liver cells which convert **glucose -> glycogen (glycogenesis) and fat**
- results in low blood glucose conc. through **negative feedback**
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How does insulin affect blood glucose concentration?
- increase **absorption rate** of glucose in cells
- increase **respiration rate** in cells, which uses more glucose, increasing glucose uptake from the blood
- increase rate of **converting glucose -> glycogen (glucogenesis)** in liver and muscle cells
- increase rate of converting glucose -> fat
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What is the role of glucagon hormone?
- when we excercise/ don't eat enough, glucose concentration decreases (as used in respiration)
- decrease detected by **alpha cells in islets of langerhans**, which secrete glucagon directly into the blood from the pancreas
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How does glucagon increase blood glucose concentration?
- when glucagon binds to specific protein receptors on liver, **activates enzymes to convert glycogen -> glucose (glycogenlysis)**
- activates enzymes to convert **amino acids and glycerol -> glucose (gluconeogenesis)**
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What is the role of adrenaline hormone?
- produced in **adrenal glands**
- at times of excitement or stress, **increases blood glucose conc.** by binding to receptors on cell surface membrane of target cells
- activates enzyme cause breakdown of **glycogen -> glucose (glycogenelysis)** in liver cells
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What is the second messenger model?
- a mechanism used by 2 hormones (**adrenaline and glucagon**) in order to regulate blood glucose concentration
- **adrenaline and glucagon** act as first messenger
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How does the second messenger model work?
- **adrenaline** binds to **transmembrane protein** in cell surface membrane of liver cell
- causes protein to **change shape** on the inside of the membrane, enzyme activates **adenylate cyclase (adenylyl)**
- activates enzyme convertd **ATP -> cyclic AMP n(cAMP)**
- **cAMP acts as second messenger**, binds to enzyme **protein kinase**, changing its shape and activating it
- **activated adenylate protein kinase** catalyses the conversion of **glycogen -> glucose (glycogenlysis)**
- glucose can move out of liver into bloodstream by **facillitated diffusion** through carrier proteins
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What are examples of antagonistic hormones?
- hormone **insulin** and **glucagon** as they work in opposite directions
- insulin drecreases blood glucose conc. but glucagon acts to increase blood glucose conc.
- self regulate by **negative feedback** to maintain at optimal point
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What is regular blood glucose concentration and how is it maintained?
- **normal blood glucose concentration- 5 mmol/dm3**
- comes directly from food we eat as glucose, absorbed by **hydrolysing carbohydrates**
- can come from hydrolysis in small intestine of glycogen (glycogenolysis) of gluconeogenesis
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Why do we test for glucose concentration?
- high blood glucose conc. could indicate **diabetes**
- test concentration with a blood or urine sample
- urine shouldn't contain glucose, **conc. of glucose in urine should be low (0-0.8mmol)**
- can use colorimetry & quantitative benedicts to test for presence of glucose
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How do you do a quantitative benedicts test?
- more colourless, higher glucose conc.
- darker blue, less glucose
- **colorimeter** used to measure % of light absorbed of sample
- find serial dilutions of known conc.
- plot calibration curve
- use to fine unknown conc.
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What is the role of the kidneys?
- filters out blood to get rid of waste through urea, contains water potential of our cells
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What is osmoregulation?
the amount of water in our blood that should be regulated/ maintained
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How does osmoregulation work?
- waste products (e.g. urea) excreted from body in solution (w/ water) as urine
- **kidneys** responsible for regulating water potential of bloos so it contains correct amounts of water
- **osmoreceptors in hypothalamus** of brain deters changes in **osmotic pressure** in the blood as it flows through it
- when osmotic pressure of the blood changes, causes **water to diffuse either in or out of the osmoreceptors** so cells either **expand or contract**
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What happens when our body is dehydrated?
- water potential of blood is too low
- **water moves out of cells, causing osmoreceptor cells to shrink**
- sends **signals to other hypothalamus cells** to bring about a response
- ensures **more water is reabsorbed from the tubules in nephron**
- results in **small amount of concentrated urine** (reduces water loss by excretion)
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What happens when our body is over hydrated?
- water potential of blood is too high
- **water moves into osmoreceptor cells, causing them to expand**
- causes **pituitary gland** to release more **ADH** into the blood
- causes **distal convoluted tubule and collecting ducts** to be **less water permeable**
- results in **large amount of dilute urine**
- increases amount of water lost in excretion
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What happens during excretion?
- removal of **metabolic waste** products from the body
- metabolic waste- contains nitrogen containing compounds (e.g. urea)
- **kidney function filters out waste products from blood and reabsorbs any useful solutes** (e.g. glucose)
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What is the structure of the kidney?
- **renal artery** goes from heart -> kidney through capillaries in the cortex
- **renal vein** goes from kidney -> heart
- **cortex-** outer region
- **medulla-** inner region
- **pelvis-** centre region
- - as blood passes through capillaries, substances filtered out of blood into long tubules (**nephron**)
- **nephron** found in both cortex and medulla
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Where is water reabsorbed and how is it controlled?
- regulation of water potential mainly takes place in **loop of Henle, distal convoluted tubule and collecting duct**
- volume of water reabsorbed controlled by **antidiuretic hormones**
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How do antidiuretic hormones work?
- when **osmoreceptors** in the hypothalamus detects a low water potential in the blood, **hypothalamus produces ADH, secreted into the blood by the pituitary gland**
- ADH binds to complementary receptors on the plasma membrane of cells lining **distal convoluted tubule and collecting duct**
- causes **protein channels (aquaporins)** to be insertes into plasma membrane
- **aquaporins make distal conv. tubule and collecting duct walls** more **water permeable**
