6A - stimuli and responses Flashcards
1
Q
how do organisms survive?
A
organisms must respond to changes in their environment
2
Q
what do organisms need to be successful at to survive?
A
-finding favourable conditions for living
-finding food
-avoiding being eaten
3
Q
responses to changes between organisms?
A
responses to change can vary in complexity depending on the type of organism involved and the specific circumstances they are responding to
4
Q
what does responding to changes require?
A
detection
5
Q
what does detection involve?
A
detection involves a stimulus being detected by a receptor cell
6
Q
what is a stimulus?
A
/
7
Q
what is a receptor?
A
receptors detect stimuli and are specific to one type of stimulus
8
Q
what are the different types of receptors?
A
-some receptor cells produce electrical activity in nerve cells in response to stimuli
-other receptor cells secrete substances in response to stimuli
9
Q
what are the parts of the CNS?
A
brain, spine
10
Q
what are the parts of the PNS?
A
neurones
11
Q
the steps of a reflex action:
(simple)
A
detection:
1) a stimulus is detected by a receptor cell
coordination:
2) the nerve impulses sent by receptor cells travel to a coordinator (brain or the spinal cord)
action:
3) from the coordinators, the impulse is conducted to the specific effector (muscle/gland) that will produce the appropriate response (contraction/secretion)
12
Q
why are reflex actions necessary for survival?
A
-it allows rapid response to danger
-instinctive
13
Q
what must reflex actions be?
A
flexible:
after the initial reflex action, the organism can take control of the response and display much more complex behaviour
14
Q
example of flexibility with the red robin:
A
in the case of the red robin, its reflex reaction to seeing a crow is to begin to fly, it is then able to control its direction of flight so that it flies away from the crow
15
Q
define innate:
A
something that is present from birth
16
Q
finding favourable conditions:
(complex organisms vs less complex)
A
for complex organisms like monkeys and wolves, this seems like an easy process
(they possess eyes, ears and nervous systems that allow them to observe and process important information about their environment)
organisms like flatworms that do not possess complex nervous systems are still able to flee from trouble and find ideal living conditions
17
Q
which two ways can mobile organisms respond & why?
A
taxes and kineses
(to stay in a favourable environment)
18
Q
what is kinesis?
A
a non-directional response to a stimulus; once random movements bring organisms back to favourable conditions they stop moving
19
Q
what is the rate of movement affected by during kinesis?
A
by the intensity of the stimulus
20
Q
flatworm structures & kinesis:
A
possess a network of neurones and simple eye-like structures that have light-sensitive cells
↳ they display kinesis when removed from their usual dark environment
21
Q
types of kineses:
A
orthokineses:
speed of movement; this increases in unfavourable conditions
kinokineses:
frequency of movement/rate of turning (this increases in unfavourable conditions)
22
Q
example of kinesis:
A
planarians:
when a stone is overturned, the planarian’s light-sensitive cells detect light, but the planarian has no way of detecting the nearest shaded space, therefore it moves randomly until the eye detects a low level or no light
(the planarian uses kinesis to ensure it is in its favourable environment - darkness)
23
Q
what is taxes?
A
a directional response to a stimulus (towards/away)
or
an innate behavioural response by an organism to a directional stimulus / gradient of stimulus intensity
24
Q
example of taxes: euglena
A
euglena:
-it has chloroplasts for photosynthesis and a flagellum to help it swim
-the flagellum has a receptor close to its base that is sensitive to light
-euglena swims directly towards the light, phototaxis
(this behaviour is highly valuable as it brings the organism towards the light where it can photosynthesise)
25
other examples of taxes:
-moths fly towards light (positive phototaxis)
-fishes dorsal fins must always stay upwards (negative geotaxis)
26
positive taxes =
movement towards a stimulus
27
negative taxes =
movement/growth away from a stimulus
28
why do insects dislike dry areas?
insects need water in their trachea, in dry conditions, they lose water (higher concentration gradient between their trachea and the external environment) which is why they try to move away from dry areas
29
kinesis & temperature / humidity:
-kinesis is important when reacting to less directional stimuli, such as temperature or humidity
-these do not vary in clear gradient
-in a kinesis response, when an organism senses that it has temporarily entered an unfavorable location, it will increase its speed and rate of turning to exit the space
30
baroreceptors
detect changes in pressure
31
why does the method of detecting changes in the environment vary?
it depends on the type of sensory organs of mobile organisms
32
what are the two ways that mobile organisms detect changes in the environment?
-klinotaxes
-tropotaxes
33
klinotaxes
the organism continuously samples the environment to determine the direction of a stimulus
34
tropotaxes
(+ example)
bilateral sense organs are used to determine the stimulus direction, the insect gets equal inputs on both receptors and can move in a straight line towards or away from light
(snakes tongues)
35
types of taxes:
phototaxis, chemotaxis
36
innate behaviour v learned behaviour
depends independently of the environmental context (i) v dependent on the environmental context for development (l)
controlled by genes (i) v not controlled by genes (l)
inherited from parents (i) v not inherited from parents (l)
developed by natural selection (i) v develops by response to an environmental stimuli (l)
37
how can taxes and kinesis be investigated?
-using choice chambers and mazes
-using woodlice and maggots
38
how to distinguish taxes and kinesis during experiments?
-the animals need to be observed during the experiment to see if turning frequency or movement rate changes in different environments
-if movement is directional then the turning frequency would decrease when the organism detects the stimulus
39
steps of a choice chamber investigation for negative phototaxes:
1) one half of the transparent choice chamber is covered in an opaque material to prevent light from entering
2) 30 maggots are placed into the chamber via the hole in the centre of the lid
3) 10 minutes later the number of maggots found in each half of the chamber were counted
4) this is repeated multiple times
40
results of a choice chamber investigation for negative phototaxes:
the results show that there are always more maggots in the shaded half of the chamber at the end of the experiment
41
TOP TIP:
-plants, bacteria, fungi and smaller organisms can’t think like human
-make sure not to use language such as "they want" when answering questions in relation to their responses to the environment
42
what are the three main types of neurones?
-sensory neurones
-relay neurones
-motor neurones
43
what do sensory neurones do?
carry impulses from receptors to the CNS
44
what do relay neurones do?
(intermediate) neurones are found entirely within the CNS and connect sensory and motor neurones
45
what do motor neurones do?
carry impulses from the CNS to effectors (muscles or glands)
46
what do all neurones do?
work together to bring about a response to a stimulus
47
what is a reflex arc?
a pathway along which impulses are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain (goes down the spinal cord)
48
why is a reflex action quick?
it doesn’t involve the brain; quicker than any other type of nervous response
49
examples of reflex actions:
-removing the hand rapidly a hot object
-blinking
-focusing the eye on an object
-controlling how much light enters the eye
50
how is the brain still involved in reflex actions?
an impulse is also sent to the brain, but the brain isn’t involved in coordinating the response
51
detailed steps of a reflex action:
1) the stimulus is detected a receptor
2) the sensory neurone sends electrical impulses to the spinal cord (the coordinator)
3) impulses are passed on to relay neurone in the spinal cord
4) the relay neurone connects to the motor neurone and passes the impulses on
5) the motor neurone carries the impulses to the muscle (the effector)
6) the impulses cause the muscle to contract (the response)
52
detailed reflex actions steps:
(arrows)
stimulus
→
receptor
→
sensory neurone
→ (synapse)
relay neurone
→ (synapse)
motor neurone
→
effector
→
response
53
growth responses in plants:
just like animals, the survival of plants is dependent on their ability to respond to changes in their environment
54
examples of growth responses in plants:
-trees in forests grow very tall so they can reach a light source
-some flowers can close up at night to reduce water loss in a dry environment
55
what do plants not have that most animals do?
plants don’t have a nervous system and so they respond to stimuli differently
56
why do plants grow unevenly?
-some plants grow against gravity or towards light
-a seedling will bend and grow towards the light, this occurs because there is more growth on the shaded side than on the illuminated side
57
what is a tropism?
growth response towards a stimulus
58
what is a phototropism?
a growth response to light
59
what is a gravitropism?
a growth response to gravity
60
what can tropisms be?
positive or negative, causing the plant to grow towards or away from the stimulus
61
what does the growth response of plants rely on?
chemical substances that are released in response to a stimulus (specific growth factors)
62
what do specific growth factors act similarly to?
the hormones that are found in animals
63
the speed effects of specific growth factors:
not as quick as that of an electrical nervous system but it still occurs at a substantial
speed
↳ phototropic responses have been detected in plant shoots within minutes of being exposed to light
64
specific growth factors in flowering plants:
move from the growing regions to other tissues, where they regulate the growth in response to a directional stimulus
65
what was the first specific growth factor to be discovered in plants?
indoleacetic acid (IAA)
66
where is IAA synthesised?
at the tips of roots and shoots, it mainly affects the elongating region of a plant
67
where is the elongating region of a plant found?
just prior to the tip/area of cell division
(meristem)
68
where does IAA move & what does it do?
it moves into the elongating region & binds to the protein receptors on the cell membranes
69
what does IAA do at the elongating region?
(simple)
-it lowers the pH by releasing hydrogen bonds
-the lowered pH breaks some of the bonds found between the microfibrils in cellulose cell walls
-this causes the cell wall to loosen and allows the cells to be more easily stretched when the turgor of the cells increases (by an increase of water being stored in the vacuole)
70
IAA & stimulus:
-by affecting the cell elongation of a root or shoot IAA influences the growth of the plant towards the stimulus
-for example, if the shaded side of a plant experiences greater cell elongation then that side of the plant will grow faster, causing it to bend towards the light
71
how does growth in meristems occur?
**in three stages:**
1) cell division by mitosis
2) cell elongation by absorption of water
3) cell differentiation
72
IAA & controlling growth by elongation
(steps)
1) IAA molecules bind to a receptor protein on the cell surface membrane
2) IAA stimulates ATPase proton pumps to pump hydrogen ions from the cytoplasm into the cell wall (across the cell surface membrane)
3) this acidifies the cell wall (lowers the pH of the cell wall)
4) this activates expansins (proteins), which loosen the bonds between cellulose microfibrils
5) at the same time, potassium ion channels are stimulated to open
6) this leads to an increase in potassium ion concentration in the cytoplasm, which decreases the water potential of the cytoplasm
7) this causes the cell to absorb water by osmosis (water enters the cell through aquaporins) which is then stored in the vacuole
8) this increases the internal pressure of the cell, causing the cell wall to stretch (made possible by expansin proteins)
9) the cell expands
73
which parts of a plant does phototropism affect?
shoots and the top of a stem
74
phototropism and IAA:
-the concentration of IAA determines the rate of cell elongation within the region of elongation
-if the concentration of IAA is not uniform on either side of a root/ shoot then uneven growth can occur
75
the steps of phototropism using IAA:
**in shoots, the higher concentrations of IAA result in a greater rate of cell elongation**
1) experiments have shown that IAA moves from the illuminated side of a shoot to the shaded side
2) the higher concentration of IAA on the shaded side of the shoot causes a faster rate of cell elongation
3) this causes the shoot to bend towards the light
76
which part of a plant does gravitropism affect?
roots
77
how do plants detect gravity?
-columellar cells near the root tip possess heavy organelles called amyloplasts
-amylopasts are densely packed with starch and so they sink to the bottom of the cell
-when a root is moved from the vertical plane to the horizontal plane these organelles fall to where the bottom of the cell is
78
steps of gravitropism in plants:
(using lAA)
-IAA is actively transported to the region in the root tip where the amyloplasts have
sunk
-the larger concentration of lAA at the lower side of the root inhibits cell elongation
-as a result, the lower side grows at a slower rate than the upper side of the root
-this causes the root to bend downwards
79
receptor cells & stimuli:
-humans possess a wide range of receptor cells that can detect and respond to a large variety of stimuli
-this allows for an organism to differentiate between the different external and internal environmental conditions
80
what does each receptor respond to?
each receptor will only respond to a specific stimulus
81
the sense of touch:
-through their sense of touch, humans are able to distinguish between many different sensations
-all the different sensations are detected by different types of receptors found within the skin
82
in any area of the skin, what is present?
a range of different receptors
83
are receptor amounts the same in all parts of the skin?
the number of receptors present can vary in different areas of the skin
84
example of receptor differences in hands:
-the fingertips have a very large number of receptors
-the back of fingers have a much lower number of receptors
85
why do humans have a wide range of receptor cells?
they can detect and respond to a large variety of stimuli (eg: temperature, taste, sound, heat and light)
↳ this is highly beneficial as it allows for an organism to differentiate between the different external and internal environmental conditions
86
what do the different receptors have?
different structures and positions within the skin
87
what are pacinian corpuscles?
a type of receptor found deep in the skin
88
where are pacinian corpuscles found?
-in the skin of fingers, soles of the feet as well as in joints, tendons and ligaments
-they are found at the ends of sensory neurone axons
89
how do pacinian corpuscles work?
they respond to changes in pressure
↳ when these receptors are stimulated by pressure on the skin it leads to the establishment of a generator potential
90
the structure of the pacinian corpuscle:
-they are made of many layers of membrane separated by a gel (can look like an onion)
-the gel between the layers contains positively charged sodium ions (Na+)
91
pacinian corpuscle & pressure
-the section of axon surrounded by layers of membrane contains stretch-mediated sodium ion channels which open when sufficient pressure is applied
-when pressure receptors are stimulated by pressure on the skin (stretch mediated sodium ion channels are deformed) a generator potential is established
92
why are there so many different receptor types?
because receptors detect and respond to a specific stimulus
93
how does the establishment of a generator potential occur in the pacinian corpuscle? (steps)
1) the lamellae deform, pressing on the sensory neurone ending.
2) this stretches the neurone's membrane, causing it to change shape
3) this opens stretch-mediated sodium ion (Na+) channels in the membrane, increasing its permeability to Na+
4) Na+ diffuses into the neurone, depolarising it and resulting in a generator potential.
5) If this signal reaches the threshold, an action potential is triggered.
94
what is the eye?
a sense organ containing receptors that are sensitive to light intensity and colour
95
what are receptors?
groups of specialised cells that can generate an electrical impulse in a sensory neurone
96
which two types of receptor cells do eyes contain?
**rod cells** - sensitive to light intensity
**cone cells** - sensitive to different wavelengths of visible light (colour)
97
where are cone & rod cells located?
in the retina
98
are there more cone or rod cells?
significantly more rod cells
99
what is the purpose of the eye?
to receive light and focus it onto the retina at the back of the eye
100
what are the structures of the eye?
-cornea
-iris
-lens
-retina
-optic nerve
-pupil
-ciliary muscles
-suspensory ligaments
-sclera
101
what is the cornea?
-where light rays enter the eye
-transparent lens that refracts light as it enters the eye
102
what is the iris?
controls how much light enters the eye
103
what is the lens?
a transparent disc that can change shape to focus light onto the retina
104
what is the retina?
it contains light receptor cells
105
what is the optic nerve?
a sensory neurone that carries impulses between the eye and the brain
106
what is the pupil?
a hole that allows light to enter the eye
107
what is the sclera?
the white layer of the eye that covers the eye ball
108
what are the ciliary muscles?
a ring of muscles around the lens which relaxes and contracts to change the shape of the lens
109
what are suspensory ligaments?
they work with the ciliary muscles to change the shape of the lens
110
how does the iris control how much light enters the eye?
-in a dark room, the iris expands allowing the pupil to dilate (widen) so more light can enter the eye
-when in bright sunlight, the iris contracts causing the pupil to get smaller, so less light can enter the eye
111
what do light receptor cells contain?
optical pigments that absorb light and then break down
112
which optical pigments do rod and cone cells contain?
-rod cells contain rhodopsin
-cone cells contain iodopsin
113
pigments & generator potentials:
the breakdown of optical pigments results in a generator potential being produced
114
which conditions lead to the breakdown of each optical pigment?
-rhodopsin within rods breaks down in dim light
-iodopsin within cones breaks down in bright light only
115
what do different receptors have?
different sensitivities to light:
sensitivity refers to the amount of light required to stimulate the receptor
116
sensitivity of rod cells:
-rods are very sensitive to even low light intensities
-they allow humans to distinguish between light and dark objects when light is very dim
(they do not allow humans to see in colour)
117
sensitivity of cone cells:
-cones are less sensitive to light
-they are sensitive to different wavelengths of light
-there are three cone types found in human eyes, each contains a different optical pigment
118
each pigment is…
sensitive to light of a different wavelength
119
the three types of cone cells:
**red-sensitive cones**
are sensitive to wavelengths of light that correspond to the colour red
**blue-sensitive cones**
are sensitive to wavelengths of light that correspond to the colour blue
**green-sensitive cones**
are sensitive to wavelengths of light that correspond to the colour green
120
how are humans able to see all colours?
the combined effect of all three pigments allows humans to observe all the other colours that are on the visible spectrum
121
what is acuity?
the ability to distinguish two separate points
122
when are receptors stimulated & unstimulated?
receptors that are hit by light rays become stimulated and those that are not hit by light rays remain unstimulated
123
what happens when a receptor is stimulated?
it can send impulses to the brain →
the brain is then able to interpret the pattern of impulses to form an image
124
are cone and rod cells directly connected to the central nervous system?
there’s no direct connection between rods and cones and the central nervous system
125
what do rod and cones connect to?
-there are synapses connecting the rods and cones to bipolar neurone
-the bipolar neurones connect to ganglion cells via synapses
-the ganglion cells have axons that extend to the optic nerve which is directly connected to the brain
126
what does the high number of receptors on the retina mean?
-due to the high number of receptors on the retina, it is not possible for there to be individual connections between each receptor and the brain
-the way that rods and cones are connected to the optic nerve affects visual acuity
127
what is visual acuity?
the resolution or amount of detail that is perceived in an image
128
how is visual acuity measured?
it is measured by how far apart two spots of light need to be in order to be seen separately
129
rods & visual acuity:
**rod cells provide lower visual acuity**
-multiple rod cells synapse with a single bipolar cell → multiple bipolar cells synapse with a single ganglion cell (connects to the optic nerve)
-the brain is not able to interpret which impulses are sent by specific rods
-if multiple rod cells connected to the same bipolar cell detect light, only one impulse from the bipolar cell is sent
↳ therefore, the brain receives a general, unspecific, understanding of the fields of vision that are light or dark
130
cones & visual acuity
**cone cells provide higher visual acuity**
a single cone cell synapses with a single bipolar cell → a single bipolar cell synapses with a single ganglion cell (connects to optic nerve)
-if two cones are stimulated to send an impulse the brain is able to interpret these as two different spots of light
-as cone cells detect only one of three colours (red, green or blue) the brain will receive information about the colour of light detected by the stimulated cone cell and where this light is
-this is because the brain knows which bipolar cell connects to which cone cell
131
EXAM QUESTIONS ABOUT SPOTS OF LIGHT
!!
132
summation of rod cells:
-there’s a benefit to how the rods are connected to the optical nerve
-each rod is very sensitive to light however a single stimulated rod is unlikely to produce a large enough generator potential to stimulate the bipolar cell for the conduction of nerve impulses
-when a group of rods are stimulated at the same time the combined generator potentials are enough to reach the threshold and stimulate the bipolar cell for the conduction of nerve impulses onwards towards the optic nerve
(this additive effect of rods is known as summation)
133
what does summation produce?
-summation produces a less sharp image but enables organisms to see in much dimmer light than cones allow
-nocturnal animals tend to have mostly or solely rods present in their eyes
134
what is control of the heartbeat?
myogenic -the heart can initiate its own contractions without the need for nervous stimulation
135
what is the bpm of the heart?
around 60 times per minute
136
extra parts of the heart
(heart action)
-SAN
-AVN
-bundle of His
-purkyne fibres
137
what is the SAN?
a group of cells in the wall of the right atrium
138
what is the AVN?
a region of conducting tissue between atria and ventricles
139
what is the bundle of his?
a collection of conducting tissue in the septum of the heart
140
what does the bundle of his divide into?
two conducting fibres (the purkyne fibres) which spread around the ventricles
141
the stages of heart rate control:
(detailed)
1) the SAN initiates a wave of excitation that causes the atria to contract
2) a region of non-conducting tissue prevents the depolarisation spreading straight to the ventricles
3) instead, the depolarisation is carried to the atrioventricular node (AVN), a region of conducting tissue between atria and ventricles
4) after a slight delay, the AVN is stimulated & passes the stimulation along the bundle of His (this delay means that the ventricles contract after the atria)
5) the bundle of his divides into two conducting fibres, called purkyne fibres, and carries the wave of excitation along them
6) the purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart
7) this makes the ventricles contract and blood is forced out of the pulmonary artery and aorta
142
stages of heart control
(simple)
1) the SAN sends out a wave of excitation
2) the atria contract
3) the AVN sends out a wave of excitation
4) the purkyne fibres conduct the wave of excitation
5) the ventricles contract
143
explain the roles of the sinoatrial node, the atrioventricular node and the purkyne fibres in a heartbeat.
-the SAN sends out a wave of excitation and this spreads across both atria, causing atrial systole
-non-conducting tissue prevents the excitation from spreading to the ventricles (so the atria and ventricles don’t contract at the same time)
-the AVN then sends the wave of excitation to the ventricles after a short delay of around 0.1 - 0.2 seconds, ensuring that the atria have time to empty their blood into the ventricles
-the purkyne fibres conduct the excitation down the septum of the heart and to the apex, before the excitation is carried upwards in the walls of the ventricles
-this means that during ventricular systole, the blood contracts from its base and blood is pushed upwards and outwards
144
what does the electrical activity of the heart regulate?
the heart rate
145
which variables can affect heart rate?
-drugs
-caffeine
-alcohol
-sex
-weight
-height
-temperature
-diet
-dehydration
-exercise
146
experiments into heart rate:
-experiments can be designed to investigate the effect of a named variable on an organism's heart rate
↳ when designing experiments investigating a single factor, it is essential to try and control the other variables
-these experiments are commonly done using humans → serious care needs to be taken during these experiments to ensure that no test subjects are harmed
147
limitations of heart rate experiments:
-it is very difficult to ensure that individuals within a sample group are sufficiently similar
-by using the same group for the before and after measurements this is not as much of an issue
-if multiple groups were used, with some consuming caffeine and some not, then this would be a major issue and care would need to be taken to find individuals with a similar life history (same sex, age, weight and height etc.)
148
what part of the brain controls the heart rate?
this cardioregulatory centre in the brain is called the medulla oblongata
149
what is the autonomic nervous system?
it controls automatic involuntary functions
150
what are the two parts of the medulla?
the acceleratory centre, which causes the heart to speed up (CAC)
The inhibitory centre, which causes the heart to slow down (CIC)
151
what are the two centres connected to?
-both centres are connected to the sinoatrial node (SAN) by nerves
-these specific nerves make up the autonomic nervous system (control unconscious activities)
152
the accelatory centre
-once the acceleratory centre has been activated, impulses are sent along the sympathetic nervous system neurones to the SAN
-noradrenaline is secreted at the synapse with the SAN
-noradrenaline causes the SAN to increase the frequency of the electrical waves that it produces
this results in an increased heart rate
153
the inhibitory centre
-once the inhibitory centre has been activated, impulses are sent along the parasympathetic neurones to the SAN
-acetylcholine is secreted at the synapse with the SAN
-this neurotransmitter causes the SAN to reduce the frequency of the electrical waves that it produces → this reduces the elevated heart rate towards the resting rate
154
how is the medulla connected to the SAN?
(which neurotransmitters are secreted?)
the medulla is connected to the SAN by two types of neurone → parasympathetic and sympathetic
**the parasympathetic neurones** secrete acetylcholine, a neurotransmitter that decreases heart rate
**the sympathetic neurones** secrete noradrenaline, a neurotransmitter that increases heart rate.
155
when are the acceleratory and inhibitory centres activated?
exercise causes several internal conditions to change, creating internal stimuli:
-carbon dioxide concentration in the blood increases (pH of blood decreases)
-there is an initial fall in blood pressure caused by the dilation of muscle arterioles
156
what is internal stimuli detected by?
by chemoreceptors and pressure receptors (baroreceptors) located in the aorta and in the carotid arteries
157
what do the carotid arteries do?
they supply the head with oxygenated blood
158
what do chemoreceptors & baro receptors do as a method control?
release nerve impulses that are sent to the acceleratory and inhibitory centres (coordinators)
159
what does the frequency of nerve impulses depend on?
the frequency of the nerve impulses increases or decreases depending on how stimulated the receptors are:
-lower frequency impulses activate the inhibitory centre to slow down the heart rate
-higher frequency impulses activate the acceleratory centre to speed up the heart rate
160
issues of blood pressure changes:
-if blood pressure is too high, this can cause damage to the walls of the arteries and it is important to put mechanisms in place to reduce the blood pressure
-if the blood pressure is too low, there may be an insufficient supply of oxygenated blood to respiring cells
161
when will pH decrease?
during times of high respiratory rate, due to the production of carbon dioxide or lactic acid
(water + carbon dioxide → carbonic acid)
162
how does the body respond to changes in the pH of blood?
the heart rate is increased so carbon dioxide can diffuse out into the alveoli more rapidly to be removed
(excess acid must be removed from the blood rapidly to prevent enzymes from denaturing)
163
response sequence for low blood pressure:
1 low blood pressure (stimulus)
2) pressure receptors in the wall of the aorta and carotid artery are stretched/stimulated less if low blood pressure
3) more electrical impulses are sent to the medulla oblongata
4) the acceleratory centre sends impulses via the sympathetic nervous system to SAN to increase the frequency of electrical impulses
5) the SAN is then stimulated by noradrenaline
6) there is an increased frequency of waves of excitation from the SAN
(heart rate increases)
164
response sequence for high blood pressure:
1) high blood pressure (stimulus)
2) pressure receptors in the wall of the aorta and carotid artery are stretched/stimulated more
3) more electrical impulses are sent to the medulla oblongata
4) the inhibitory centre sends impulses via the parasympathetic nervous system to SAN to decrease the frequency of electrical impulses
5) the SAN is then stimulated by acetylcholine
6) there is an reduced frequency of waves of excitation from the SAN
(heart rate decreases)
165
response sequence for low pH:
(high carbon dioxide)
1) low pH (stimulus)
2) detected by chemoreceptors in the wall of the aorta and carotid artery
3) more electrical impulses are sent to the medulla oblongata
4) the acceleratory centre sends impulses via the sympathetic nervous system to SAN to increase the frequency of electrical impulses
5) the SAN is then stimulated by noradreline
6) heart rate increases to deliver blood to the heart more rapidly to remove carbon dioxide
166
response sequence for high pH:
(low carbon dioxide/high oxygen)
1) high pH (stimulus)
2) detected by chemoreceptors in the wall of the aorta and carotid artery
3) electrical impulses are sent to the medulla oblongata
4) the inhibitory centre sends impulses via the parasympathetic nervous system to SAN to dencrease the frequency of electrical impulses
5) the SAN is then stimulated by acetylcholine
6) heart rate decreases to return the oxygen, carbon dioxide and pH of the blood to normal levels
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which neurotransmitters can have an accelerators effect?
-noradrenaline
-adrenaline
-thyroxine
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what is adrenaline?
is a hormone produced by the adrenal glands (it is chemically similar to noradrenaline)
169
when is adrenaline released?
during a fight-or-flight response
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why is increased heart rate helpful during fight or flight?
-it allows for a rapid increase in blood supply to respiring muscles
-this means the muscles will have more oxygen and glucose for respiration
-it enables high-intensity activities to be an immediate response
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what is heart rate?
the number of heartbeats per minute
(the autonomic nervous system is responsible for controlling heart rate)
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what is cardiac output?
the term used to describe the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time
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cardiac output of adults at rest:
an average adult has a cardiac output of roughly 4.7 litres of blood per minute when at rest
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how do cardiac outputs vary?
individuals who are fitter often have higher cardiac outputs due to having thicker and stronger ventricular muscles in their hearts
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when do cardiac outputs increase?
when an individual is exercising
this is so that the blood supply can match the increased metabolic demands of the cells
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how is cardiac output calculated?
(CO)
heart rate x stroke volume
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what is heart rate?
the number of times a heart beats per minute (the number of cardiac cycles per minute)
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what is stroke volume?
the volume of blood pumped out of the left ventricle during one cardiac cycle
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it took a woman 1 second to complete a single cardiac cycle. Their stroke volume was measured at 73cm³. calculate their cardiac output, give your answer in dm³.
1 cardiac cycle takes 1 second
to find the number of cardiac cycles completed in a minute, multiply by 60
60 x 1 = 60 bpm
step 2: insert relevant figures into the equation
cardiac output = heart rate x stroke volume
cardiac output = 60 x 73 = 4,380 cm³
CO = 4.38 dm3
180
dm → cm
cm divided by 1000
