stimuli and response Flashcards
(63 cards)
1
Q
stimulus
A
a change in the envo which can be detected
2
Q
receptor
A
cell/protein on cell membrane that detects a stimulus
3
Q
coordinator
A
connects incoming info with appropriate effector
4
Q
effector
A
part of an organism that carries out a response to the stimulus
5
Q
response
A
the change brought about to the organism as a result
6
Q
taxis
A
- directional
- behavioural response
- in an organism that can move
- e.g. maggots move away from light= negative phototaxis to be in a more favourable envo
7
Q
kinesis
A
- behavioural response
- in an organism that moves
- involves a change in speed of random movement
- e.g. woodlice move faster in low humidity to increase their chance of moving to a more favourable envo
8
Q
tropism
A
- response in plants
- directional
- e.g. phototropism
9
Q
growth response in plants
A
- carried out by growth factors- hormone like chemicals which speed up/slow down plant growth. Moved around plant by diffusion to where it is needed.
- produced in growing regions of the plant e.g. shoot tips
10
Q
Auxins
A
important growth factor
stimulate growth of shoots by cell elongation
high conc of auxins in roots inhibit growth
11
Q
IAA
A
indolacetic acid, type of auxin which moves around the plant to control tropisms. Travel to areas where it is needed by diffusion/active transport.
results in diff parts of the plant with diff conc of IAA. uneven distribution of IAA= uneven growth
12
Q
features of a nervous response
A
- travel via electrical impulses
- via nerves/neurones
- quick
- specific
- effects short-lived
13
Q
feautures of a hormonal response
A
- chemicals
- via blood
- slow
- general
- effects last longer
14
Q
nervous organisation
A
peripheral nervous system- made up of all the neurones that connect the CNS to the rest of the body
motor nervous system- made up of voluntary and autonomic system
voluntary- controls conscious activities e.g. running
autonomic- controls unconscious activities e.g. breathing
15
Q
reflex
A
when your body carries out a response without consciously making a decision to respond.
- fast(fewer synapses)
- automatic( occurs without thinking)
- fixed (same reflexes since birth)
- help to protect from danger
16
Q
receptors
A
- specific to one type of stimulus only
- they are transducers, convert energy from one form into another
17
Q
pacinian corpuscle
A
- mechanorecpetor
- found on skin
- end of sensory neurone attached to middle of pacinian corpuscle
- at rest , Na channels in membrane of pacian corpuscle are closed.
- when pressure is applied the membrane stretches and channel is opened
- influx of sodium ions creates a generator potential. If generator potential is past a certain threshold then an action potential is triggered= electrical impulse across neurone
18
Q
Photoreceptors in the eye
A
- found in retina
- fovea= most sensitive part of retina due to highest number of photorecpetors
- blindspot-where optic nerve attaches to retina, no photorecpetors here so not sensitive to light
- 2 types of cell: cones and rods
19
Q
how is an electrical impulse generated in the eye?
A
- light enters eye and hits photorecpetors on retina. Receptors contain optical pigment which light breaks down
- This causes a chemical change which alters the permeability of the membrane to sodium ions= generator potential= if it exceeds threshold then action potential= electrical impulse along bipolar neurone
- bipolar neurone connects photoreceptors to optic nerve= take simpulse to brain
- rods= peripheral parts of retina, give info in black and white
- cones= conc in fovea, give info in colour
20
Q
sensitivity
A
rods are more sensitive because many rods are connected to one neurone so many weak generator potentials can add up to reach threshold and generate action potential
cones are less sensitive because each cone cell is connected to one neurone so more light is needed to reach threshold and generate an action potential
21
Q
visual acuity
A
rods = low visual acuity , many rods connected to one neurone so brain doesn’t get 2 separate info but rather one electrical impulse. cones= high visual acuity= cone cells close together so 2 action potentials generated so 2 separate info to the brain to distinguish between 2 points
22
Q
sympathetic nervous system
A
prepares body for action fight/flight mode
23
Q
parasymathetic nervous system
A
responses that restore normal body function e.g. rest/digest mode
24
Q
Why is the heart myogenic?
A
the heart can contract and relax without receiving signals from nerves. pattern of contraction leads to a regular heartbeat
25
How does the heart beat?
1. The SAN in the right wall of the atrium sends out regular waves of electrical activity to the atrial walls.
2. The atria contract.
3. Between atria and ventricles there is a band of non conducting collagen tissue. This prevents electrical activity being passed directly to ventricles.
4. therefore electrical activity transferred from SAN to AVN.
5. AVN conducts electricity to bundle of His (muscle fibres which conduct electricity from ventricles to apex of heart) . Bundle of His split into finer muscle fibres = purkyne tissue
6. slight delay before AVN reacts to ensure the atria have contracted.
7. Ventricles contract from bottom up
26
How is electrical activity of the SAN controlled?
controlled by medulla oblangata.
heart rate needs to alter depending on certain stimuli so medulla oblangata sends nerve impulses down sympathetic/parasympathetic nerve to SAN to control the rate at which SAN generates electrical impulses
27
how does body respond to high blood pressure?
baroreceptors in aorta/carotid artery detect high bp, send impulses down sensory neurone to medulla oblangata . Medulla processes info and sends impulses down parasympathetic nerve to SAN. secrete acetyl choline which binds to receptors on SAN. effector= cardiac muscles which decrease heart rate
28
How does body respond to high levels of CO2 and low levels of O2?
chemoreceptors (aorta,carotid arteries, medulla) detect low O2 levels. send impulses via sensory neurone to medulla oblangata . processes info and sends impulses down sympathetic neurone to SAN. Secrete nor adrenaline which binds to receptors on SAN. effector= cardiac muscle= heart rate increases to restore normal levels
29
resting potential
axon membrane consists of many different gated/ungated ion channels.
1. sodium potassium pump= actively transports 3Na+ ions out and 2K+ ions in using ATP.
2. gated Na+ channels= closed, membrane isn't permeable to Na+
3. ungated K+ channels= open, allow facilitated diffusion of K+ out of membrane. doesn't reach equillibrium
4. gated K+ channels= closed
the outside of the membrane is positively charged compared to the inside of the membrane therefore it is polarised
30
graph of an action potential
1. resting potential- maintained by sodium potassium pump.
2. generator potential-weak stimulus causes some Na+ channels open and depolarisation happens but doesn't reach threshold so no action potential triggered.
3. depolarisation- greater stimulus causes Na+ channels to open. Sudden influx of Na+ ions in the membrane cause nearby voltage gated Na+ channels to open so more Na+ diffuses in . Therefore impulse travels as a wave of depolarisation across the membrane
4. Repolarisation- VG sodium channels close, VG potassium channels open and K+ diffuses out
5. hyperpolarisation- slight delay in VG K+ channels closing so the membrane becomes more negative than resting potential
6. sodium potassium pump restores resting potential
31
refractory period
between repolarisation and resting potential.
period where another action potential cant be started as ion channels are recovering and cant be opened.Makes nerve impulses:
- discrete- dont overlap, pass as separate impulses
- unidirectional- travels one way only
32
All or nothing nature
All action potentials, once the threshold has been reached, have the same change in voltage no matter how big the stimulus is.
If the threshold isn't reached then an action potential isn't triggered.
the bigger a stimulus, the greater the frequency in action potentials
33
myelination
some neurones have a myelin sheath= made up of schwann cells and acts as an electrical insulator. The Na+ channels are concentrated at the nodes of Ranvier= pieces of bare membrane. the cytoplasm of the nerve cell can conduct enough electrical charge to depolarise the next node of Ranvier. In a myelinated neurone depolarisation only happens at the nodes of Ranvier= saltatory conduction= fast compared to a non-myelinated neurone where depolarisation has to occur across the whole membrane
34
other factors affecting conduction
1. Axon diameter= greater diameter= less resistance to flow of ions= faster conduction
2. Temperature= higher temp= ions more KE so diffuse faster. After 40 degrees enzymes begin to denature so rate decreases.
35
synapse
The junction between one neurone and another neurone/ effector cell
The gap between the 2 neurones is known as the synaptic cleft.
36
Features of a synapse
presynaptic neurone has synaptic vesicles containing neurotransmitter. This is found in the swelling known as the synaptic knob.
receptors are only found on the post synaptic membrane ensuring impulses are unidirectional.
contains an enzyme to break down the neurotransmitter so the impulse doesn't keep happening.
synapses that use acetylcholine=cholinergic synapse
37
How does a cholinergic synapse work?
1. Action potential arrives at presynaptic neurone and this stimulates VG Ca2+ ion channels to open and Ca2+ ions diffuse into the presynaptic knob.
2. This stimulates the synaptic vesicles to move towards the membrane and bind to the membrane and fuse with it. The vesicles release neurotransmitter into the synaptic cleft = exocytosis
3. neurotransmitter binds to specific receptors called cholinergic receptors and this causes sodium channels to open and depolarisation. If the threshold is reached then an action potential is created.
4. Remaining Acetylcholine is hydrolysed by an enzyme(Acetylcholineesterase = AchE) into ethanoic acid and choline which is reabsorbed into the presynaptic neurone.
5. ATP is required to form acetylcholine again and package it into vesicles
synapse has lots of mitochondria= ATP
lots of rough ER= to manufacture neurotransmitter
38
excitatory neurotransmitters
they always cause depolarisation of the postsynaptic membrane and an action potential is generated if the threshold is reached.
39
inhibitory neurotransmitters
they hyperpolarise the postsynaptic membrane( making it more negative than resting potential) and therefore an action potential can't happen.
40
summation
when the effect of many neurones joined to one neurone/ one neurone being stimulated a lot in a short period of time is added together
41
spatial summation
sometimes many neurones are connected to one neurone. They may all release small amounts of neurotransmitter but this may be enough to reach threshold and start an action potential in the next neurone. If more inhibitory neurotransmitter released it may not cause depolarisation
42
temporal summation
high frequency of weak impulses increases the amount of neurotransmitter in the synaptic cleft which makes an action potential more likely
43
Neuromuscular junction
synapse between motor neurone and muscle cell. Use acetylcholine and receptor on muscle cell=nicotinic cholinergic recpetors.
differences between normal synapse and NMJ=
1. post synaptic membrane has a lot more folds which create more clefts so more spaces to store AchE
2. post synaptic membrane has more receptors than any other synapse.
3. acetyl choline is always an excitatory neurotransmitter at a NMJ. response is generated in a muscle cell.
44
drugs and neurotransmitters
| effect of drugs with same shape
-some drugs= same shape as neurotransmitters = mimic their actions at receptors= more receptors are activated
45
effect of antagonists
block receptors so fewer receptors can be activated by neurotransmitters
46
Effect of drugs inhibiting the enzyme
inhibit the enzyme that breaks down neurotransmitter . more neurotransmitter in the synaptic cleft to bind to receptors and they're there for longer
47
effect of drugs which inhibit neurotransmitters
inhibit release of neurotransmitter from pre synaptic neurone so fewer receptors are activated.
48
effect of drugs which stimulate neurotransmitter
stimulates the release of neurotransmitter from the presynaptic neurone so more receptors are activated
49
skeletal muscle
attached to bones via tendons and under voluntary conscious control
ligaments attach bones to other bones( go around joints)
pairs of skeletal muscle contract and relax to move bones at a joint. The bones of the skeleton are incompressible
muscles that work together to move a bone= ANTAGONISITIC PAIR
contracting muscle= agonist relaxing muscle= antagonist
50
sarcolemma
cell membrane of muscle fibres
51
transverse(T) tubules
bits of the sarcolemma fold inwards and stick into the sarcoplasm.
help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
52
sarcoplasmic reticulum
network of internalmembranes which run through sarcoplasm. It stores and releases Ca2+ that are needed for muscle contraction.
53
Other featuresof muscle fibres
lots of mitochondria= ATP needed for muscle contraction
muscle fibres= multinucleate
have lots of long,cylindrical organelles= myofibrils these are made up of proteins and are highly specialised for muscle contraction
54
myofibrils
made up of myofilaments:
thin actin
thick myosin
move past each other tomake muscles contract
55
sarcomere
a basic unit of skeletal muscle
structure:
A bands= thick myosin filaments and some overlapping thin actin filaments
I bands= contain only thin actin filaments
end of sarcomere= z line
h zone contains myosin only
56
sliding filament theory
myosin and actin filaments slide over one another to make the sarcomeres contract- myofilaments dont contract
simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
sarcomeres return to original length as muscle relaxes
A band = SAME length
I band= SHORTER
H zone= SHORTER
57
myosin
- have globular head which are hinged so they can move back and forth
- each myosin head has a binding site for actin and one for ATP
- actin filaments have binding sites for myosin heads called actin-myosin binding sites
58
tropomyosin
- found between actin filaments
- it helps the myofilaments move past each other
- in a resting muscle the actin-myosin binding site is blocked by tropomyosin therefore myofilaments can't slide past each other because the myosin heads can't bind to the actin-myosin binding site on the actin filament.
59
muscle contraction
1. Action potential from motor neurone stimulates a muscle cell, depolarising the sarcolemma. Depolarisation spreads through the t tubules into the sarcoplasmic reticulum
2. Sarcoplasmic reticulum releases Ca2+ into the sarcoplasm
3. Ca2+ binds to troponin (protein) attached to tropomyosin causing the protein to change shape. This pulls the attached tropomyosin out of the actin myosin binding site on the actin filament
4. binding site is exposed so the myosin head can now bind. This bond is called an actin-myosin crossbridge
5. Ca2+ activates ATP hydrolase to hydrolyse ATP to prvide the energy needed for muscle contraction
6. Energy released from ATP causes the myosin head to bend which ratchets the actin filament forward.
7. Another ATP molecule provides the energy needed to break the actin-myosin crossbridgeso the mysoin head detatches from the actin once its moved
8. myosin head then attaches to a different binding site further along the actin filament. new actin myosin crossbridge is formed and cycle is repeated.
9. many crossbridges form and break rapidly pulling the actin filament along which shortens the sarcomere= muscles contract
10. Cycle will continue as long as Ca2+ present
60
what happens when muscle stops being stimulated?
- Ca2+ leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum (needs ATP too)
- tropomyosin molecules move back so they block the actin-myosin binding sites again
- actin filaments slide back to their relaxed position which lengthens the sarcomere.
61
how is ATP generated continuously during muscle contraction
1. aerobic respiration- oxidative phosphorylation in the mitochondria . good for long periods of low intensity exercise
2. Anaerobic respiration- ATP made rapidly by glycolysis. build up of lactate muscle fatigue, good for short periods of intense exercise
3. ATP phosphocreatine (PCr system)
- ATP is made by phosphorylating ADP- adding a phosphate group taken from PCr
- PCr is stored inside cells and the ATP-PCr system generates ATP very quickly.
- PCr runs out after a few seconds so its used during short periods of vigorous exercise
- ATP PCr system is alactic and anaerobic.
ADP + PCr= ATP + Cr
- some of the Cr broken down into creatinine which is removed from body via kidneys
62
slow twitch
- muscle fibres that contract slowly
muscles used for posture/ endurance activities
- can work for a long time without getting tired
- energy released slowly through aerobic respiration . lots of mitochondria and blood vessels supply muscles with oxygen
- reddish in colour because they're rich in myoglobin= a red coloured protein that stores oxygen
63
fast twitch
- contract very quickly
- muscles used for fast movement e.g. eyes
- good for short busts of power and speed
- get tired very quickly
- energy released quickly through anaerobic respiration using glycogen, few mitochondria/blood vessels
- white in colour because they don't have much myoglobin
