organisms respond to changes in their internal and external environments Flashcards
1
Q
What is a stimulus?
A
Detectable change in the environment
- detected by cells called receptors.
2
Q
What are the two main structures of the nervous system?
A
- Central nervous system (CNS) = brain and spinal cord;
- Peripheral nervous system = receptors, sensory and motor neurones.
3
Q
What is a simple reflex arc?
A
Stimulus (touching hot object) -> receptor -> sensory neurone -> coordinator (CNS / relay neurone) -> motor neurone -> effector (muscle) -> response (contraction).
4
Q
What is the importance of simple reflexes?
A
- rapid - short pathway: only 3 neurones + few synapses
- autonomic - unconscious
- protect from harmful stimuli
5
Q
What is tropism?
A
- Response of plants to stimuli via growth
- can be positive (growing towards stimulus) or negative (growing away from stimulus)
- controlled by specific growth factors (IAA).
6
Q
What is phototropism?
A
Response of plants to light.
7
Q
What is gravitropism?
A
Response of plants to gravity.
8
Q
What is hydrotropism?
A
Response of plants to water.
9
Q
What is indoleacetic acid (IAA)?
A
Type of auxin (plant hormone) that controls cell elongation in shoots and inhibits growth of cells in roots.
- made in tips of roots/shoots
- can diffuse into other cells
10
Q
How does phototropism occur in shoots?
A
Shoot tip produces IAA which diffuses to other cells; IAA accumulates on shaded side of shoot, stimulating cell elongation and causing the plant to bend towards light.
- ( positive phototropism)
11
Q
How does phototropism occur in roots?
A
Root tip produces IAA; IAA concentration increases on lower (darker) side, inhibiting cell elongation, causing root to bend away from light. (negative)
12
Q
How does gravitropism occur in shoots?
A
Shoot tip produces IAA which diffuses from upper side to lower side in response to gravity, stimulating cell elongation and causing the plant to grow upwards.
- negative gravitropism
13
Q
How does gravitropism occur in roots?
A
Root tip produces IAA; IAA accumulates on lower side in response to gravity, inhibiting cell elongation and causing the root to bend downwards.
- positive gravitropism
14
Q
What is taxis?
A
Directional response by simple mobile organisms, moving towards favourable stimuli (positive taxis) or away from unfavourable stimuli (negative taxis).
15
Q
What is kinesis?
A
When an organism changes its speed of movement and rate of change of direction in response to a stimulus.
16
Q
What are receptors?
A
Cells that respond to specific stimuli; stimulation leads to establishment of a generator potential, causing a response.
17
Q
What is a Pacinian corpuscle?
A
Receptor that responds to pressure changes, occurring deep in skin mainly in fingers and feet.
- sensory neurone wrapped with layers of tissue
18
Q
How does a Pacinian corpuscle detect pressure?
A
When pressure is applied, stretch-mediated sodium ion channels are deformed, allowing sodium ions to diffuse into the sensory neurone, increasing membrane potential and establishing a generator potential.
19
Q
What are rod cells?
A
Photoreceptor cells concentrated at the periphery of the retina, containing rhodopsin pigment
- do not detect colour
- connected in groups to one bipolar cell
20
Q
What are cone cells?
A
- concentrated on the fovea, fewer at periphery of retina
- 3 types containing different iodopsin pigments
- detect coloured light
- one cone connects to one neurone
21
Q
How do rods and cones differ in sensitivity to light?
A
Rods are more sensitive to light; cones are less sensitive.
22
Q
How do rods and cones differ in visual acuity?
A
Cones provide higher visual acuity; rods have lower visual acuity.
23
Q
What is visual acuity?
A
Ability to distinguish between separate sources of light;
- higher visual acuity means more detailed, focused vision.
24
Q
How do rods and cones differ in colour vision?
A
Rods allow monochromatic vision (black and white); cones allow colour vision.
25
Why do rods have high sensitivity to light?
Rods are connected in groups to one bipolar cell
- retinal convergence
-spatial summation
- stimulation of each individual- cell alone is sub-threshold but because rods are connected in groups more likely threshold potential is reached
26
Why do cones have low sensitivity to light?
One cone connects to one neurone
- no retinal convergence
- requiring higher light intensity to reach threshold potential.
27
Why do rods have low visual acuity?
Rods are connected in groups to one bipolar cell
- retinal convergence
- spatial summation
- many neurones only generate 1 impulse / action potential -> cannot distinguish between separate sources of light
28
Why do cones have high visual acuity?
One cone connects to one neurone, allowing the brain to receive distinct impulses from adjacent cones.
- can distinguish between seperate sources of light
29
Why do rods have monochromatic vision?
Rods contain one type of pigment (rhodopsin).
30
Why do cones provide colour vision?
- 3 types of cone cells with different optical pigments
which absorb different wavelengths of light
- red-sensitive, green-sensitive and blue-sensitive cones
- stimulation of different proportions of cones gives greater range of colour perception
31
myogenic
When a muscle (cardiac muscle) can contract and relax without receiving signals from nerves.
32
What is the sinoatrial node?
Located in the right atrium, known as the pacemaker - releases a wave of depolarisation across the atria, causing muscle contraction.
33
What is the atrioventricular node?
- Located near the border of the right/left ventricle within the atria
- releases another wave of depolarisation after a short delay when it detects the first wave from the SAN.
34
What is the Bundle of His?
Runs through the septum and can conduct and pass the wave of depolarisation down to the Purkyne fibres in the walls of the ventricles.
35
What are Purkyne fibres?
- in the walls of the ventricles
- they spread the wave of depolarisation from the AVN across the bottom of the heart
- the muscular walls of ventricles contract from bottom up
36
What is the role of non-conductive tissue in the heart?
Located between the atria and ventricles, it prevents the wave of depolarisation from travelling down to the ventricles, causing a slight delay in contraction so that ventricles fill before contraction
37
Why is there a short delay between SAN and AVN waves of depolarisation?
Ensures enough time for atria to pump all blood into ventricles
- ventricle becomes full
38
What is the role of the medulla oblongata?
Controls heart rate via the autonomic nervous system, using sympathetic and parasympathetic systems to control SAN rhythm.
39
What are chemoreceptors?
Located in the carotid artery and aorta, they respond to pH / CO2 concentration changes.
40
What are baroreceptors?
Located in the carotid artery and aorta, they respond to pressure changes.
41
What is the response to high blood pressure?
- Baroreceptor detects high blood pressure
- impulse sent to medulla
- more impulses sent to SAN along parasympathetic neurones (releasing noradrenaline)
- heart rate slowed
42
What is the response to low blood pressure?
Baroreceptor detects low blood pressure, sends impulse to medulla, which sends more impulses to SAN along sympathetic neurones ( releasing adrenaline), increasing heart rate.
43
What is the response to high blood pH?
- Chemoreceptor detects low CO2 conc / high pH
- impulse sent to medulla
- more impulses sent to SAN along parasympathetic neurones (releasing noradrenaline)
- heart rate slowed so less CO2 removed and pH lowers
44
What is the response to low blood pH?
- Chemoreceptor detects low CO2 conc / high pH
- impulse sent to medulla
- more impulses sent to SAN along sympathetic neurones (releasing adrenaline)
- heart rate increases to deliver blood to heart to remove CO2
45
What is resting potential?
- The difference between electrical charge inside and outside the axon when a neuron is not conducting an impulse
- more positive ions (Na+/K+) outside axon compared to inside
- inside the axon is -70mV.
46
How is resting potential established?
- Sodium potassium pump actively transports 3 Na+ out of the axon, 2 K+ into the axon
- membrane more permeable to K+ (more channels and always open)
- K+ diffuses out down conc. gradient - facilitated diffusion membrane less permeable to Na+ (closed Na+ channels) - higher conc. Na+ outside
47
What is action potential?
When the neurone's voltage increases beyond the -55mV threshold, generating a nervous impulse due to increased membrane permeability to Na+.
48
action potential stimulus
Voltage-gated Na+ channels open, making the membrane more permeable to Na+, which diffuses into the neurone, increasing the voltage.
49
What happens during depolarisation in action potential?
When a threshold potential is reached, an action potential is generated
- more voltage-gated Na+ channels open
- Na+ move by facilitated diffusion down conc. gradient into axon
- potential inside becomes more positive
50
What happens during repolarisation in action potential?
Na+ channels close, K+ voltage-gated channels open, allowing K+ to diffuse out of the neuron down conc-gradient , causing the voltage to rapidly decrease.
51
What happens during hyperpolarisation in action potential?
- K+ channels slow to close -> overshoot in voltage
- too many K+ diffuse out of neurone
potential difference decrease to -80mV
- sodium-potassium pump returns neurone to resting potential
52
What is the all or nothing principle?
If depolarisation does not exceed -55 mV, action potential is not produced; any stimulus that triggers depolarisation to -55mV will always peak at the same maximum voltage.
53
What is the importance of the all or nothing principle?
Ensures animals only respond to large enough stimuli, preventing overwhelming responses to every small change in the environment.
54
What is the refractory period?
After an action potential has been generated, the membrane cannot be stimulated as Na+ channels are recovering and cant be opened
55
What is the importance of the refractory period?
- Ensures discrete impulses produced - action potentials separate and cannot be generated immediately
- unidirectional - cannot generate action potential in refractory region
- limits number of impulse transmissions - prevent overwhelming
56
What factors affect the speed of conductance?
Myelination, axon diameter, and temperature.
57
How does myelination affect speed?
With myelination - depolarisation occurs at Nodes of Ranvier only -> saltatory conduction
- impulse jumps from node-node
- in non-myelinated neurones, depolarisation occurs along full length of axon - slower
58
How does axon diameter affect speed?
Increased diameter reduces ion leakage, increasing speed of conductance.
59
How does temperature affect speed?
- Increases speed of conductance
- increases rate of movement of ions as more kinetic energy (active transport/diffusion)
- higher rate of respiration as enzyme activity faster so ATP is produced faster - active transport faster
60
What is saltatory conduction?
- Gaps between myelin sheath are nodes of Ranvier
- action potential can "jump" from node to node via saltatory conduction - action potential travels faster as depolarisation across whole length of axon not required
61
What is a synapse?
Gaps between the end of the axon of one neurone and the dendrite of another, where impulses are transmitted as neurotransmitters.
62
What is the role of calcium ions in synaptic transmission?
- Depolarisation of the pre- synaptic knob opens voltage gated Ca2+ channels and Ca2+ diffuses into synaptic knob. - stimulates vesicles containing neurotransmitter to fuse with membrane and release neurotransmitter into the synaptic cleft via exocytosis
63
Why are synapses unidirectional?
- Receptors only present on the post-synaptic membrane
- enzymes in synaptic cleft break down excess-unbound neurotransmitter - concentration gradient established from pre-post synaptic neurone
- neurotransmitter only released from the pre-synaptic neurone
64
What is a cholinergic synapse?
The neurotransmitter is acetylcholine
- enzyme breaking down acetylcholine = acetylcholine- esterase
- breaks down acetylcholine to acetate and choline to be recycled in the pre-synaptic neurone
65
What is summation?
- Rapid build-up of neurotransmitters in the synapse to help generate an action potential by 2 methods:
spatial or temporal
- required because some action potentials do not result in sufficient concentrations of neurotransmitters released to generate a new action potential
66
What is spatial summation?
Many different neurones collectively trigger a new action potential by combining neurotransmitters to exceed the threshold value.
67
What is temporal summation?
When one neurone releases neurotransmitters repeatedly over a short period of time to exceed the threshold value.
68
What are inhibitory synapses?
Causes chloride ions (Cl-) to move into the post-synaptic neurone and K+ to move out, making the membrane hyperpolarised and less likely to propagate an action potential.
69
What is a neuromuscular junction?
A synapse that occurs between a motor neurone and a muscle, similar to a synaptic junction.
70
What is a myofibril?
Made up of fused cells that share nuclei/cytoplasm (sarcoplasm) and many mitochondria, millions of muscle fibres bringing about movement.
71
What is the role of Ca2+ in sliding filament theory?
- Ca2+ enter from sarcoplasmic reticulum and causes tropomyosin to change shape
- myosin heads attach to exposed binding sites on actin forming actin-myosin cross bridge
- activates ATPase on myosin
- ATP hydrolysed so energy for myosin heads to return to og position
72
What is the role of tropomyosin in sliding filament theory?
- Tropomyosin covers binding site on actin filament
- Ca2+ bind to tropomyosin on actin so it changes shape
- exposes binding site
- allows myosin to bind to actin, forming cross bridge
73
What is the role of ATP in myofibril contraction?
- Hydrolysis of ATP -> ADP + Pi releases energy
- movement of myosin heads pulls actin - power stroke
- ATP binds to myosin head causing it to detach, breaking cross bridge
- myosin heads recocked
- active transport of Ca2+ back to sarcoplasmic reticulum
74
What is the role of myosin in myofibril contraction?
- Myosin heads (with ADP attached) attach to binding sites on actin.
- form actin-myosin cross bridge
- power stroke - myosin heads move pulling actin
- requires ATP to release energy ATP binds to myosin head to break cross bridge so myosin heads can move further along actin
75
What is phosphocreatine?
A chemical stored in muscles that can rapidly regenerate ATP from ADP by providing a Pi group for continued muscle contraction.
76
What are slow-twitch muscle fibres?
- Specialised for slow, sustained contractions (endurance)
- lots of myoglobin
- many mitochondria - high rate aerobic respiration to release ATP
- many capillaries - supply high concentrations of glucose/O2 & prevent build-up of lactic acid e.g. thighs / calf
77
What are fast-twitch muscle fibres?
- Specialised in producing rapid, intense contractions of short duration
- glycogen -> hydrolysed to glucose -> glycolysis
- higher concentration of enzymes involved in anaerobic respiration - fast glycolysis
- phosphocreatine store
e.g., eyelids/biceps
78
What is homeostasis?
Maintenance of a constant internal environment via physiological control systems.
79
What is myoglobin?
A protein that contains many mitochondria for high rates of aerobic respiration to release ATP.
80
What is the role of capillaries in muscle tissue?
They supply high concentrations of glucose and O2 and prevent the build-up of lactic acid.
81
What are fast-twitch muscle fibers specialized for?
Producing rapid, intense contractions of short duration.
82
What is the process of the second messenger model?
- Adrenaline/glucagon bind to specific complementary receptors on the cell membrane
- activate adenylate cyclase
- converts ATP to cyclic AMP (secondary messenger)
- cAMP activates protein kinase A (enzyme)
- protein kinase A activates a cascade to break down glycogen to glucose (glycogenolysis)
83
compare the NMJ with a cholinergic synapse
BOTH= unidirectional
NMJ= excitatory CS= excitatory or inhibitory
NMJ= connects motor neurones- muscles CS= connects 2 neurones
NMJ= end point for action potential CS= new action potential generated in next neurone
NMJ= ach binds to receptors on muscle fibre CS= ach binds to recpetors on post-synaptic membrane
84
pacinian corpsule structure
