6 - Responding to Change Flashcards
1
Q
What does the Cell body of a neurone contain?
A
Contains cytoplasm, nucleus, mitochandria and ribosomes
2
Q
Dendrites
A
branched extensions of the cell body
3
Q
Axon - size
A
single long fibre, can be as long as a metre and less than a micrometre wide
4
Q
Schwann cells
A
Wrap around the axon many times, providing electrical insulation
5
Q
Myelin Sheath
A
Made of Schwann cells
Rich in Myelin
Not all neurons are myelinated but myelinated neurons transmit nerve impulses faster
6
Q
Nodes of Ranvier
A
Gaps between adjacent Schwann cells where there is no myelin sheath
Gaps are 2-3 micrometres wide and occur every 1-3 mm
7
Q
2 main receptors in the human eye
A
Rod Cells
Cone cells
8
Q
Which eye receptor has a high and which has a low sensitivity to light?
A
Rod - high sensitivity
Cone - low sensitivity
9
Q
Visual acuity
A
the ability to distinguish between 2 close objects
10
Q
Which eye receptor is more numerous?
A
Rod cells
11
Q
How are rod cells distributed?
A
Evenly distributed on the retina but absent in the fovea
12
Q
How are cone cells distributed?
A
Mainly at the fovea - a single point in the retina
13
Q
Pigment in rod cells
A
Rhodospin
14
Q
Pigment in Cone cells
A
Lodospin
15
Q
Rhodospin
A
Pigment in rod cells
Detects light and dark
Monochromatic - only detects one wavelength of light
16
Q
Lodospin
A
Pigment in Cone cells
Detects colour
Trichromatic - divided into 3 types, each detecting different wavelengths of light
17
Q
How is light detected after it has been absorbed by photoreceptor cells?
A
Absorption of light induces a change in the membrane permeability of pigments
Na+ flood into the cell and a generator potential is established
If the generator potential reaches the threshold, a nerve impulse flows along a bipolar neurone
18
Q
Role of dendrite
A
Carries nervous impulses towards a cell body
19
Q
Axon - role
A
Carries nervous impulses away from the cell body
20
Q
Where do motor neurons carry impulses?
A
CNS –> effector organs
21
Q
What maintains resting potential?
A
Sodium-Potassium Pumps
22
Q
What is the neurone membrane impermeable to?
A
Na+
23
Q
What is potential differencee at resting state known as?
A
Resting Potential
24
Q
Hyperpolarisation
A
The periodd after depolarization where the potential difference becomes slightly more negative than the resting potential
25
What happens to ion channels during the refractory period?
Close
26
Where does depolarization take place?
Along the neurone membrane
27
What diffuse sideways along the neurone axon in depolarization?
Na+
28
What is the effect of reaching threshold on sodium ion channels?
Sodium Ion channels open
29
Approximate threshold value of membrane potential, before the membrane becomes depolarised
-55mV
30
Diffusion of sodium ions in a neurone
When an action potential Is generated, there are more Na+ inside the neurone than outside, so some of these diffuse sideways along the neurone axon
31
How does Depolarisation of neurones happen?
Presence of sodium ions creates a change in potential difference further along the neurone membrane. this part of the neurone now becomes depolarised
32
Wave of depolarisation
Sodium diffuse all along the neurone in this way and a wave of depolarisation flows along the neurone
33
How does the refractory period effect the wave of depolarisation?
Makes it travel in just one direction
34
Structure in a neurone which carries nervous impulses away from the body
Axon
35
Resting potential of a neurone
-70mV
36
The refractory period
Period of hyperpolarisation in an action potential
37
Saltatory Conduction
The nervous impulses jumps from one node to the next
38
What happens to the postsynaptic membrane after an inhibitory neurootransmitter binds to the receptor
Hyperpolarisation
39
Summation
The process where neurotransmitters from multiple neurones are summed together to produce a response
40
Spatial Summation
The process where multiple presynaptic neurones form a junction with a single neurone
41
Temporal Summation
The process where multiple nerve impulses arrive at the same synaptic knob within a short period of time
42
Where is a neuromuscular junction between?
Motor neurone + Muscle cell
43
What happens after the arrival of the action potential at the synaptic knob?
The action potential depolarises the membrane
Voltage-gated Calcium ion channels open
Calcium ions diffuse into the synaptic knob
44
What are Cholinergic Synapses?
Synapses which use acetylcholine as a neurotransmitter
45
The name of the gap between the cells at a synapse
The synaptic cleft
46
The effect of an inhibitory neurotransmitter on the postsynaptic cell
It prevents an action potential from being generated in the postsynaptic cell
47
Enzyme that breaks down acetylcholine in the synaptic cleft
Acetylcholinesterase
48
Result of depolarisation of the postsynaptic membrane at a Cholinergic synapse
Generation of an action potential
49
The effect of an excitatory drug on the nervous system
They stimulate the nervous system to produce more action potentials
50
(Negative Feedback) - Causes a change in the body's condition
Stimulus
51
(Negative Feedback) - detects change and relays information the the CNS
Receptor
52
Negative Feedback - counteracts change
Effector
53
Benefits of multiple feedback mechanisms
More control
Faster response
54
How do multiple feedback mechanisms provide more control?
The body can respond to multiple changes away from the optimum
55
How do multiple feedback mechanisms provide a faster response?
The body can respond in more ways to a change away from the optimum
56
2 Reasons for maintaining blood glucose concentration
Meeting respiratory demand
Maintaining Water potential
57
Effect of low glucose levels on respiration
Respiration will slow
58
Effect of low glucose levels on water potential
Decrease water potential of the blood
Water will move out of the tissues into the blood by osmosis, causing dehydration of the cells and cell death
59
Glycogenesis
When blood glucose concentration is too high, the liver cells produce enzymes that convert glucose into glycogen. This glycogen is then stored in liver cells
60
Glycogenolysis
When blood glucose concentration is too low, the liver cells produce enzymes that break down the glycogen stored in cells to glucose
61
Glucogenesis
When blood glucose concentration is too low, liver cells also form glucose from glycerol and amino acids
62
What is blood glucose concentration controlled by?
Homeostasis
63
Normal blood glucose concentartion
90mg 100cm3
64
3 processes ininvolved in controlling blood glucose conc which take place in the liver
Glycogenolysis
Glycogenesis
Gluconeogenesis
65
What type of cells in the pancreas detect high blood glucose levels?
Beta cells
66
2 hormones responsible for restoring blood glucose if the cncentartion is too low
Adrenaline
Glucagon
67
What enzyme is activated upon binding of adrenaline or glucagon to receptors
Adenylate Cyclase
68
What attaches skeletal muscle to bones?
Tendons
69
Agonist
The contracting muscle
70
Antagonist
Relaxing muscle
71
What are muscle fibers?
Long, specialized cells and bundles of muscle fiber make up skeletal muscle
72
Sarcolemma
The membrane of muscle fibres
Folds inwards to the sarcoplasm at certain points
73
What is the membrane of muscle fibres known as?
Sarcolemma
74
The name of the inwards folds of the sarcolemma
Transverse (T) Tubules
75
Importance of T tubules
Initiating muscle contraction
76
Sarcoplasm reticulum
Organelle in the cytoplasm which stores Calcium ions
77
What do muscle fibres contain lots of?
Mitochondria and nuclei
78
Myofibrils
Cylindrical organelles that run along the length of muscle fibres
79
Where are myofibrils located?
At the site of muscle contraction
80
What are myofibrils made up of?
Multiple units which run end-to-end along the myofibril, known as sarcomeres
81
What is the end of the sarcomere known as?
The Z-line
82
2 types of myofilament
Thick myofilament
Thin myofilament
83
What is thick myofilament made from?
Myosin protein
84
What is thin myofilament made from?
Actin protein
85
How are myosin and actin filaments arranged?
In alternating patterns in sarcomeres
86
A-band
Region where myosin and actin filaments overlap
87
H zone
Region with only myosin filaments
88
I-band
Region with only actin filament
89
When is muscle contraction initiated?
When an action potential arrives at a neuromuscular junction from a motor neurone
90
What happens once an action potential arrives at a neuromuscular junction from a motor neurone?
Depolarisation of the sarcolemma which spreads along the T tubules and into the sarcoplasm
91
What does depolarisation of the T tubules stimulate?
Sarcoplasmic reticulum to release Calcium ions into the sarcoplasm
92
What do Calcium ions bind to in muscle contraction?
A protein attached tto tropomyosin
93
What is the effect of Calcium ions binding to a protein attached to tropomyosin?
Protein changes shape, causing tropomysoin to be moved so that it is no longer blocking the actin-myosin binding site
94
What is the bond between actin and myosin known as?
actin-myosin cross bridge
95
Enzyme which hydrolyses ATP
ATP Hydrolase
96
The effect of the influx of Calcium ions into the sarcoplasm
Allows actin and myosin filaments to bind, creating an actin-myosin cross bridge
97
What activates ATP Hydrolase?
Calcium ions
98
What effect does the energy released from ATP hydrolysis have on myosin?
Causes the myosin head to bend
99
What causes the actin filament to be pulled by the myosin head?
The actin-myosin cross bridge
100
What is the effect of the movement of the myosin head on the actin filament?
Causes the actin filament to slide past the myosin filament
101
What happens to the cross bridge and the myosin head after the actin filaments have slid past the myosin filaments?
The cross bridge is broken and the myosin head is no longer attached to the actin filament
102
What happens to the myosin head once it is released from the actin binding site?
It bends back to its original position and the myosin forms a new cross bridge with a binding site further along the actin filament
103
What is the overall result as actin filaments are pulled past the myosin filaments?
shortening of the sarcomere
104
What does shortening of the Sarcomeres cause?
Muscle contraction
105
When is muscle contraction stopped?
When the muscle cells are no longer stimulated
106
What happens to calcium ions once muscle contraction is stopped?
Actively transported back into the sarcoplasm reticulum
107
What is the effect of the removal of Calcium ions on the tropomyosin?
The protein attached to tropomyosin undergoes a conformational change, causing tropomyosin to shift so that it is blocking the actin-myosin binding sites
108
Effect of stopping muscle contraction on the sarcomere
Lengthens
109
Where are calcium ions released from?
Sarcoplasmic Reticulum
110
What causes myosin heads to bend?
Energy released from ATP
111
Where does actin overlap with myosin?
Middle of the sarcomere
112
Sarcomere
Units which run along myofibrils, found at the site of muscle contraction
113
Where are slow twitch fibres found?
Muscles used for posture, such as the back and neck
114
Where are fast twitch fibres found?
Mainly in muscles such as the arms and legs
115
Slow twitch fibres - adaptatiion to functionWhat are slow twitch fibres adapted for?
Endurance and slow movement over long periods of time
116
Size of slow twitch fibres
Long and thin
117
Speed of low twitch fibres
Fatigue slowly and contract slowly
118
What are fast twitch fibres adapted for?
Fast or strong movement over short periods of time
119
Size of fast twitch fibres
Short and wide
120
Speed of fast twitch fibres
Fatiguequickly and contract quickly
121
Energy source for slow twitch fibres
Energy released through aerobic respiration
122
Energy source for fast twitch fibres
Energy released through anaerobic respiration
123
What do slow twitch fibres have lots of?
Mitochondria
Capillaries
Myoglobin
124
What do slow twitch fibres have less of?
Glycogen
Phosphocreatine
Sarcoplasmic reticulum
125
What do fast twitch fibres have lots of?
Glycogen
Phosphocreatine
Sarcoplasmic reticulum
126
What do fast twitch fibres have less of?
Mitochondria
Capillaries
Myoglobin
127
Myoglobin
Pigment which stores oxygen
128
How can organisms increase their chances of survival?
Detecting a change and responding accordingly
129
What can organisms detect changes in?
External environment
Internal environment
130
3 components involved in coordinating a response
Stimulus
Receptors
Effectors
131
Phototropism
Growth in response to direction of light
132
Phototropism in roots and shoots
Shoots are positively phototropic as they grow towards light
Roots are negatively phototropic as they grow away from light
133
Directional responses in plants
They regulate growth in response to a direction stimuli
Directional growth responses are called tropisms
134
Tropisms
Directional growth responses
135
Gravitropism
Growth in response to direction of gravity
136
How do roots and shoots show gravitropism?
Shoots are negatively gravitropic as they grow upwards, away from the gravitational pull
Roots are positively gravitropic as they grow downwards, towards the gravitational pull
137
Indoleacetic acid (IAA)
A type of auxin that controls the tropic response in plants
138
How is IAA transported around the plant?
Short distances by diffusion or active transport
Longer distances in the phloem
139
What happens when a plant detects directional stimuli?
IAA is transported to different parts of the plant, creating an uneven distribution of IAA
140
What happens when the distruvtion of IAA is uneven?
A directional growth response occurs
141
Phototropism in shoots
Shoots are positively phototropic
If a shoot is exposed to an uneven light source, IAA is transported to the more shaded part
A higher concentration of IAA in the shaded parts cause cells in the shaded area to elongate
Cell elongation causes the shoot to bend towards the light
142
Phototropism in roots
Roots are negatively phototropic
If a root is exposed to an uneven light source, IAA is transported to the more shaded part
A higher concentration of IAA in the shaded parts inhibits cell elongation on the shaded part
The root bends away from the light
143
Gravitropism in shoot
Shoots are negatively gravitropic
If a shoot is exposed to an uneven gravitational pull, IAA is transported to the underside
A higher concentration of IAA in the underside causes cells in the underside to elongate
Cell elongation causes the shoot to bend away from the gravitational pull
144
Gravitropism in roots
Roots are positively gravitropic
If a root is exposed to an uneven gravitational pull, IAA is transported to the underside
A higher concentration of IAA in the underside inhibits cell elongation on the lower side
The root bends towards the gravitational pull
145
2 ways in which simple animals respond to change
Taxes
Kineses
146
Taxes
A positively or negatively directionl stimulus
147
Kineses
The stimulus is non-directional
148
Why are damp / humid environments more favourable for wodlice?
Reduce water loss
149
Reflexes
Automatic response to stimuli
150
How reflexes work
Quick and automatic
Help an organism respond quickly to a harmful stimulus
The information is not processed in the brain and no decision is made about the response
151
3 types of neurone involved in the reflex arc
Sensory
Relay
Motor
152
Reflex arc in response to heat
Thermoreceptors in the skin detect a heat stimulus
Sensory neurone carries impulse from thermoreceptors to relay neurone in the spinal cord
Relay neurone carries impulse to motor neurone
Motor neurone carries impulses to effector
Arm moves away from hot object
153
What does IAA stand for?
Indoleacetic acid
154
2 important features of receptors
Specificity
Generatpr potentials
155
Specificity of receptors
Only respond to specific stimuli
This means that a receptor which responds to light will not respond to temperature or pressure
156
Generator potentials in Receptors
Receptors connect with sensory neurones. When stimulated, the receptor creates a generator potential in the sensory neurone
157
Pacinian Corpuscle
Mechanoreceptor found in the skin
Mechanoreceptors respond to changes in pressure to establish a generator potential
158
What does the pacinian corpuscle consist of?
Concentric rings of connective tissue that surrounds a sensory neurone
159
Resting state of the Pacinian Corpuscle
The charge inside the neurone is more negativ than the outside (-70mV)
This is because there are more Na+ ions outside the neurone than inside
160
Potential difference
Difference in charge across the cell membrane
161
What happens when pressure is applied to the pacinian corpuscle?
The rings of connective tissue apply pressure on the sensory neurone
The sensory neurone has stretch-mediated Na+ channels, these channels normally retsrict the movement of Na+ ions
Applied pressure causes the stretch-mediated Na+ channels to open
162
Generator potential in the pacinain corpuscle
Na+ ions flood into the sensory neurone through the open Na+ channels
there are now more Na+ ions insode the neurone than outside, so the charge inside the neurone becomes more positive than the outside, changing the potential difference
The generator potential has been established
163
Action Potential in the Pacinian corpuscle
If the generator potential reaches the threshold level (about -50mV) then an action potential is produced in the sensory neurone
164
Sensitivity to light in rod and cone cells
Rod cells - highly sensitive to light
Cone cells - less sensitive to light
165
Visual acuity
The ability to distinguish between close objects or 2 points
166
Visual acuity in rod and cone cells
Rod cells - low visual acuity
Cone cells - high visual acuity
167
Number and distribution of rod cells
Highly numerous
Evenly distributed on the retina but absent in the fovea
168
Number and distribution of cone cells
Fewer cells than rod cells
Distributed mainly at a single point in the retina called the fovea
169
What do photoreceptors synapse with?
A bipolar relay neurone
170
What does each bipolar neurone synapse with?
A ganglion cell - sensory neurone
171
How do axons of ganglion send a signal to the brain?
Leave the eye via the optic nerve to send a signal to the brain
172
What are differences in sensitivity to light due to?
Differences in how rod and cone cells connect to bipolar neurones
173
How do cone cells form a synapse?
Each cone cell synapses with a single bipolar neurone
Sufficient light must stimulate the cone cell to generate an action potential in the bipolar neurone
174
How do rod cells form synapses?
Several rod cells synapse with the same bipolar neurone
Light stimulating a single rod cell may not be sufficient to generate an action potential in the bipolar neurone
175
Spatial Summation
Several rod cells synapse with the same bipolar neurone
This means that the cumulative stimulation of more than one rod cell can create an action potential in the bipolar neurone
176
What does spatial summation result in?
Retinal Convergence - the idea that several rod cells generate a signal in a single sensory neurone
177
Steps involved in the detection of light
1. light is absorbed by pigments in photoreceptor cells
2. Generator potential is created in pigment cells
3. Nerve impulse flows along a bipolar neurone
178
Sinoatrial node - location
Wall of the right atrium
179
Sinoatrial node - role
Acts as a pacemaker by transmitting waves of electrical activity along the walls of the atria at regular intervals
180
Effect of the electrical waves from the SAN
Cause the left and right atria to contract together
This forces blood into the ventricles
181
Why can wavs of electrical activity not pass from the atria to the ventricles?
Due to a collection of non-conducting tissues
This creates a delay to ensure the atria are empty before the ventricles begin to contract
182
What does the wave of electrical activity pass through after atria contraction?
Through the atrioventricular valve, to the bundle of His
183
Bundle of His
A collection of conducting tissue that transmits the electrical activity to the apex of the heart and around the ventricle walls along fibres called the purkyne fibres
184
What happens as the waves of electrical activity pass along the Purkyne fibres?
The ventricles contract together
Blood is forced out of the ventricles and out of the heart
185
How does the SAN act as a pacemaker?
By transmitting waves of electrical activity along the walls of the atria at regular intervals
186
2 main receptors in controlling heart rate
Chemoreceptors
Baroreceptors
187
Chemoreceptors
Sensitive to changes in CO2 concentration
Found in the aortic body, in the wall of the atria
Found in the carotid body, in the wall of the carotid artery in the neck
188
Effect of increased CO2 concentration on heart rate
Heart rate increases
189
Baroreceptors
Sensitive to changes in blood pressure
Found in the walls of various arteries but particularly in the carotid sinus
190
Where do chemoreceptors and baroreceptors send a signal to when stimulated?
Medulla Oblongata
191
Cardiovascular Centre
Region in the medulla which modifies heart rate
192
2 regions of the cardiovascular centre
Cardio-inhibitory centre
Cardio-acceleratory centre
193
Nerve impulses from the cardiovascukar centre
Sent from these centres along the autonomic nervous system to the sinoatrial node
194
High blood pressure
Detected by baroreceptors
Impulses are sent from the medulla along parasympathetic neurones to the sinoatrial node
Acetylcholine is released
Heart rate slows down and blood pressure decreases
195
Low blood pressure
Detected by baroreceptors
Impulses are sent from the medulla along sympathetic neurones to the SAN
Noradrenaline is released
Heart rate rises and blood pressure increases
196
Low CO2 / High O2
Detected by chemoreceptors
Impulses are sent from the medulla along the parasympathetic neurones to the SAN
Acetylcholine is released
Heart rate slows down and CO2 levels increase / O2 levels decrease
197
Low O2 / High CO2
Detected by chemoreceptors
Impulses are sent from the medulla along sympathetic neurones to the SAN
Noradrenaline is released
Heart rate rises and O2 levels increase / CO2 levels decrease
198
Which neurotransmitter is released in response to Low O2 / High CO2
Noradrenaline
199
In which artery walls are baroreceptors mainly found?
Carotid artery
200
Relay Neurones
Intermediate neurones
Recieve impulses from a sensory neurone and relay them to motor neurones
201
Role of dendrites
Carry nervous impulses towards a cell body
202
Role of axons
Carry nervous impulses away from the cell body
203
How is resting potential maintained?
Sodium-potassium pumps in the neurone membrane
204
How d positive ions build up outside of the cell?
Na-K pumps
3Na+ ions are actively transported out of the neurone by the pumps for every 2K+ that are transported in
205
Potassium ion channels in the neurone membrane
Membrane is permeable to K+ ions
When K+ ions are transported into neurones, they can diffuse back out
The neurone membrane is also impermeable to Na+ ions so the ions cannot diffuse back into the cell after they have been transported out
206
When do Na+ ion channels in the cell membrane open?
When the cell is stimulated
207
What happens if the potential difference rises above the threshold value (-55mV)
The membrane will become depolarised
208
More sodium channels open in the depolarised membrane
Sharp increase in potenttial difference to about +30mV
209
All-or-nothing Principle
If the potential difference reached the threshold, depolarisation will always take place and the change in potential difference will always be the same
If the stimulus is stronger, action potentials wil be produced more frequently but their size will not increase
210
What happens after the neurone membrane hs depolarised to 30mV?
Na+ ion channels close and K+ ion channels open
K+ ions are transported back out of the neurone and the potential difference becomes more negative
Repolarisation
211
Hyperpolarisation
Short period after repolarisation of a neurone where the potential difference becomes slightly more negative than the resting potential
Prevents the neurone from being restimulated instantly
212
Refractory period
Period of depolarisation preventing the neurone from being restimulated instantly
213
What happens after the refractory period?
The K+ ion channels close and the membrane returns to its resting potential
214
Action potential
The process where a neurone is depolarised and returns to resting potential
215
Stages in depolarisation of neurone cell membrane
Stimulation
Depolarisation
Repolarisation
Hyperpolarisation
216
How does the refractory period affect the wave of depolarisation?
Makes it travel in one direction
217
Why does the myelin sheath act as elctrical insulator?
It is impermeable to Na+ and K+
218
Saltatory conduction
Nervous impulses jump from one node to the next
219
Effect of temperature on nerve impulse
An increase in temp increases KE
Ions move across the membrane more rapidly when they have more KE
220
Effect of axon diameter on nerve impulse
Giant axons are found in the giant squid and allow it to have a rapid escape response
Greater axon diameter means there is a greater surface area for the movement of ions across the cell membrane
221
Synaptic cleft
Gap between cells
When an action potential reaches a synapse, it must be transmitted across the synaptic cleft
222
Presynaptic neurone
The neurone before the synapse
When an action potential reaches the end of the neurone, it is transmitted across the presynaptic membrane to the postsynaptic membrane or to an effector cell
223
Synaptic Knob
The end of the axon of the presynaptic neurone
Swelling which contains synaptic vesicles
location where the nerve impulse is transmitted across the synaptic cleft
Contains lots of mitochondria, as it needs lots of energy to synthesise neurotransmitters
224
Synaptic Vesicles
Located in the synaptic knob
Contain neurotransmitters, which fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft
225
Neurotransmitters
Chemicals that allow an action potential to be transferred across a synapse
When NTs are released from the synaptic vesicles into the synaptic cleft, they bind to specific receptors on the postsynaptic membrane
226
Postsynaptic membrane
Membrane of the postsynaptic neurone or effector cell
Receptors on postsynaptic membrane have a complementary shape to NTs released from the synaptic knob
When NTs bind to their receptors, the action potential continues
Contains only receptors, ensuring the nerve impulse moves in only one direction
227
Excitatory Neurotransmitters
Generate an action potential in the postsynaptic cell
When the NTs bind to the receptors on the postsynaptic membrane, the membrane is depolarised
228
Inhibitory Neurotransmitters
Prevent an action potential from being generated in the postsynaptic cell
When the NTs bind to the receptors on the postsynaptic membrane, the membrane is hyperpolarised
229
Example of excitatory neurotransmission
Acetylcholine binds to receptors on the postsynaptic membrane in the CNS, establishing an action potential
230
Example of inhibitory neurotransmission
Acetylcholine binds to receptors on the postsynaptic membrane in the heart, K+ ions channels are opened in the membrane
This prevents an action potential from being established
231
What happens to the postsynaptic membrane after an inhibitory NT binds to the receptors?
Hyperpolarisation
232
Neuromuscular Junction
Synapse between a motor neurone and a muscle cell
233
What happens once an action potential arrives at the synaptic knob at the end of a motor neurone in a neuromuscular junction?
The action potential depolarises the membrane of the synaptic knob, causing voltage-gated Ca 2+ ion channels to open
Ca 2+ ions dissue into the synaptic knob
234
Effect of increased Ca 2+ ion concentration inside the synaptic knob
Synaptic vesicles move and fuse with presynaptic membrane
Acetylcholine is released into the synaptic cleft via exocytosis
235
What receptors does acetylcholine bind to on the postsynaptic membrane?
Nicotinic Cholinergic Receptors
236
Effect of binding of acetylcholine in a neuromuscular junction
Binding of the neurotransmitter opens sodium ion channels in the postsynaptic muscle cell
237
Na+ ions diffuse into the cell
The membrane becomes depolarised
If the potential difference reaches the threshold value, an action potential is generated and flows along the motor cell
238
What is a neuromuscular junction between?
Motor neurone + muscle cell
239
Cholinergic Synapses
Synapses which use acetylcholine as a neurotransmitter
240
What are cholinergic synapses between?
2 neurones
241
Type of response in a cholinergic synapse vs neuromuscular junction
Cholinergic synapse - Inhibitory or excitatory
Neuromuscular junvtion - always excitatory
242
Depolarisation of the post synaptic membrane of the cholinergic synapse vs neuromuscular junction
Cholinergic synapse - action potential
Neuromuscular junction - muscle contraction
243
Acetylcholinesterase
Enzyme that breaks down acetylcholine after it has bound to receptors on the postsynaptic membrane
244
Where is acetylcholinerase located in cholinergic synapses vs neuromuscular junction?
Cholinergic synapse - synaptic cleft
Neuromuscular junction - clefts postsynaptic membrane
245
3 ways in which excitatory drugs work
Mimic neurotransmitters
Inhibit enzymes
Release of neurotransmitters
246
How do excitatory drugs mimic neurotransmitters?
Drugs with a similar shape to the neurotransmitter can bind to receptors on the postsynaptic membrane to produce an action potential
Agonists
247
Example of an excitatory agonist drug
Nictotine can bind to cholinergic receptors in the brain to mimic acetylcholine
248
How can excitatory drugs inhibit enzymes?
Bind to enzymes to prevent the breakdown of a neurotransmitter
The NT would continue to generate an action potential in the postsynaptic membrane
249
Example of an excitatory drug inhibiting enzymes
Nerve gas inhibits acetylcholinesterase and stops the breakdown of acetylcholine
This causes loss of muscle control
250
How do excitatory drugs release NTs?
Drugs can cause presynaptic neurones to release NTs
More NTs will activate more receptors and an action potential is more likely to be created
251
2 ways in which inhibitory drugs work
Block Calcium ion channels
Block receptors
252
Inhibitory drugs blocking calcium ion channels
Drugs can block calcium ion channels in the presynaptic membrane
Blocking calcium ion channels would prevent the release of neurotransmitters from the presynaptic neurone
253
Inhibitory drugs blocking receptors
Drugs can block receptors on the postsynaptic membrane
If the receptors are blocked, NTs cannot bind and an action potential is not generated in the postsynaptic neurone
Antagonists
254
Example of an antagonist inhibitory drug
Curare blocks nicotinic cholinergic receptors causing muscle paralysis
255
Effect of an inhibitory NT on the postsynaptic cell
It preventtts an action potential from being generated in the postsynaptic cell
256
Effect of acetylcholinesterase
Breaks down acetylcholine so that is can be reabsorbed by the presynaptic neurone and reused to synthesise more acetylcholine
257
What is the result of depolarisation of the postsyanaptic membrane at a cholinergic synapse?
Generation of an action potential
258
What attaches skeletal muscles to bones?
Tendons
259
What do skeletal muscles consist of?
Many bundles of muscle fibres
260
What are muscle fibres?
Long, specialised cells
261
Name of the membrane of muscle fibres
Sarcolemma
262
Sarcolemma
The membrane of the muscle fibres
Folds inwards to the sarcoplasm at certain points
The inwards folds are called Transverse (T) Tubules
263
Importance of T tubules
Initiating muscle contraction
264
Calcium ion store in the sarcoplasm
Sarcoplasmic reticulum
265
What do muscke fibres have lots of?
Mitochondria and nuclei
266
Myofibrils
Cylindrical organelles that run along the length of muscle fibres
Site of muscle contraction
267
What are myofibrils made up of?
Multiple units which run end-to-end, called sarcomeres
268
Z-line
End of the sarcomere
269
Myofilaments
Sarcomeres are made up from 2 types of myofilaments
The 2 filaments slide past each other, causing muscles to contract
270
Protein in thick myofilaments
Myosin protein
271
Protein in thin myofilaments
Actin protein
272
A-band
Overlapping region of thick myosin and thin actin filaments
273
H-Zone
Region with only thick myosin filament
274
M-line
Middle of the sarcomere where thin actin filaments and thick myosin filaments overlap
275
I-band
Region with only thin actin filaments
276
Redox behaviour of aldehydes
Oxidised to carboxylic acids
Reduced to primary alcohols
277
Redox behaviour of ketone
cannot be oxidised but can be reduced to secondary alcohols
278
Test for an aldehyde
Benedicts and Fehlings will turn blue to brick red in the presence of an aldehyde but do nothing with a ketone
Tollens reagent - silver mirror with an aldehyde, stays clear with a ketone
279
What is the carbonyl group (=O) present in?
Aldehydes
Ketones
Carboxylic acids
Amides
280
How are carbonyls reduced to alcohols?
Hydride reduction - nucelophilic addition-elimination
H- acts as a nucleophile, from sodum borohydride (NaBH4 -)
281
Why can sodium borohydride reduce carbonyls?
The alcohol is less reactive
282
Product of the nucleophilic addition of a cyanide ion to a carbonyl
Hydroxynitrile
283
Nucleophilic addition of CN
Adding CN to a carbonyl results in a hydroxynitrile
You must add acid at the end to put a proton on the oxygen anion
If the reactant is assymetric, you get enantiomers
284
KCN hazards
KCN - irritant
Produced HCN when wet - respiratory inhibitor
285
Sliding Filament Theory
Explains how mucle contraction is coordinated in myofibrils
286
Stages of sliding filament theory
Depolarisation of the sarcolemma
Contraction of the sarcomeres
Muscle contraction
Muscle relaxation
287
When is muscle contraction initiated in sliding filament theory?
Muscle contraction is initiated when an action potential arrives at the muscle cells
The action potential depolarises the sarcolemma
288
Effect of the depolarisation of the sarcolemma in sliding filament theory
Depolarisation of the sarcolemma causes the myosin and actin filaments to slide over each other
The sliding movement causes the sarcomeres to contract
289
Muscle contraction in sliding filament theory
There are multiple sarcomeres along the length of myofibrils
As many sarcomeres contract simultaneously, the muscke fibres contract
Contraction of the muscle fibres causes the whole muscle to contract
290
Muscle relaxation in sliding filament theory
After the muscle has contracted, the sarcomeres relax
The filaments slide back over each other and the muscle relaxes
291
What allows sliding filament theory to take place?
Globular heads on myosin filaments, which allow myosin and actin filaments to bind together and slide past each other
292
Binding sites on myosin head
2 binding sites
One can bind to actin
One can bind to ATP
293
Binding site on actin filaments
Actin-myosin binding site, where the actin filament binds to the myosin filament
294
Tropomyosin
Protein located on actin filaments
Blocks the actin-myosin binding site when muscle fibres are at rest
When muscle fibres are stimulated, the tropomyosin protein is moved so that myosin heads can bind to the actin-myosin binding site
295
What happens when actin and myosin bind?
They can slide past each other to cause muscle contraction
296
How does aerobic respirationmake ATP?
Oxidative phosphorylation
297
How does anaerobic respiration make ATP?
Glycolysis and lactate fermentation
298
Phosphocreatine
A molecule which can supply ATP for muscle contraction
Donates phosphate to ADP to produce ATP
During low periods of muscle activity, ATP can be used to phosphorylate creatine back to phosphocreatine
Anaerobic and no lactate is produced, but phosphocreatine is in short supply
299
What causes actin and myosin filaments to slide over each other?
Depolarisation of the sarcolemma
300
Effect of calcium ions binding to a protein attached to tropomyosin
Causes the protein to change shape
altering the protein causes tropomyosin to be moved
The actin-myosin binding site is no longer blocked
301
Name of the bond between actin and myosin
Actin-myosin cross bridge
302
What happens when Calcum ions activate ATP hydrolase?
ATP is split into ADP and inorganic phosphate
303
Use of energy released when calcium ions activate ATP hydrolase
Causes the myosin head to bend
The movement of the head causes the actin filament to slide past the myosin filament
The actin filament is pulled by the myosin head because of the actin-myosin cross bridge
304
What happens after the actin filament has slid past the myosin filament?
The actin-myosin cross bridge is broken and the actin filament is no longer attached to the myosin head
305
What happens once the actin-myosin cross bridge is broken?
The myosin head bends back to its original position after it is released from the actin binding site
The myosin forms a new cross bridge with a binding site further along the actin filament
306
Whay happens if action potentials are no longer stimulating the muscle cells?
The release of Ca 2+ ions by the sarcoplasmic reticulum will stop
The Ca 2+ ions are transported back into the SR by active transport
307
Effect of removal of Ca 2+ ions
The protein attached to tropomysoin undergoes a conformational change
The protein changes shape, causing tropomyosin to shift so that it is blocking the actin-myosin binding sites
Myosin heads can no longer bind to actin filaments
308
When does the sarcomere lengthen?
When actin filaments return to resting
309
Where are slow twitch fibres found?
In muscles used for posture such as the back and neck
310
Where are fast twitch fibres found?
Mainly in muscles such as the arms and legs
311
Slow twitch fibres adaption to function
Adapted for endurance and slow movement over long periods of time
Muscle fibres are long and thin
The muscles fatigue slowly and contract slowly
312
Fast twitch fibres adaption to function
Adapted for fast or strong movement over short periods of time
Muscle fibres are short and wide
The muscles fatigue quickly and contract quickly
313
Energy source of slow twitch fibres
Energy released through aerobic respiration
314
Energy source for fast twitch fibres
Energy released through anaerobic respiration
315
Negative feedback
The mechanism that restores systems to the original level
316
Steps in negative feedback
Receptors detect change
Effectors counteract change
317
Benefit of multiple negative feedback mechanisms
More control
Faster respose
318
How does negative feedback increase body temperature?
Shivering
Vasoconstriction
319
How does glucose concentartion affect blood water potential?
An increase in blood glucose concentration will decrease the water potential of the blood
320
What are increases in blood lucose levels monitered by?
Pancreas
321
Glycogenesis
When blood glucose concentration is high, liver cells produce enzymes to convert glucose into glycogen.
The glycogen is then store in liver cells
322
Glycogenolysis
When blood glucose concentration is too low, the liver cells produce enzymes that break down the glycogen stored in the cells to glucose
323
Gluconeogenesis
When blood glucose concentration is too low, liver cells form glucose from glycerol and amino acids
324
Effect on an increse in blood glucose concentration on the cells in the body
Water diffuses out
325
What detects high insulin levels?
Beta cells in the pancreas
326
Where are beta cells located?
Islets of langerhan
327
How do beta cells respond to high blood glucose concentration?
Secreting insulin, which travels in teh blood to the liver and muscle cells
328
What does insulin bind to?
Receptors on the muscle cell membranes
329
Effect of insulin binding to muscle cell membranes
The muscle cell insert more glucose channel proteins in the cell membrane, causing
The rate of uptake by muscle cells to increase
The rate of respiration in muscle cells to increase
330
How does glycogenesis happen?
Insulin binds to receptors on the liver cell membranes
The liver cell produces enzymes that convert glucose to glycogen
331
Where is glycogen stored?
Liver Cells cytoplasm
332
Stages in action of insulin to decrease blood glucose levels
Detection of high blood glucose levels in beta cells
Secretion of insulin from beta cells
Binding of insulin to muscle and liver cells
Glycogenesis
333
What is low blood glucose concentration detected by?
Alpha cells in islets of langerhan
334
How do alpha cells respond to low blood glucose concentartion?
Secreting glucagon into the blood, which travels in the blood to liver cells
335
How does glycogenolysis happen?
Glucagon binds to receptors on the liver cell membranes
The liver cells produce enzymes that convert glycogen to glucose
336
How does gluconeogenesis happen?
Binding of glucagon to liver cells also causes the release of enzymes that form glucose from glycerol and amino acids
337
Adrenaline response to low glucose levels
Secretion of adrenaline from adrenal gland
Adrenaline binds to receptors on liver cell membrane
Activates glycogenolysis
Inhibits glycogenesis
Promotes secretion of glucagon from pancreas and inhibits secretion of insulin
338
When insulin binds to receptors on the muscle cells, what 2 processes take place?
Rate of glucose uptake increases
Rate of respiration increases
339
What does adrenaline bind to?
Receptors on liver cell membrane
340
2 hormones responsible for restoring normal levels of blood glucose if the concentration is too low
Glucagon
Adrenaline
341
What enzyme does the binding of adrenaline or glucagon activate?
Adenylate Cyclase
342
Role of adenylate cyclase
ATP --> cAMP
343
Role of cAMP
Activates protein kinase A
344
Role of protein kinase A
Triggers a cascade of reactions that result in glycogenolysis
345
Prrrimary messengers
Do not enter a cell
Exert an action on the cell membrane by binding to receptors and triggering a change within a cell
This change can be the actovation of another molecule or it may initiate a reaction
346
Secondary Messengers
Initiate and coordinate responses that take place inside a cell
Usually activated by the binding of a primary messenger to a cell surface receptor
347
cAMP - stages
Adrenaline or glucagon bind to receptors on the cell membranes of liver cells
This activates adenylate cyclase, which converts ATP --> cAMP
cAMP activates protein kinase A, which triggers a cascade of reactions that result in glycogenolysis
348
Diabetes Mellitus
A chronic health condition where sufferers cannot properly control their blood glucose concentration.
Type I diabetes sufferers cannot produce insulin
349
Cause of Type I diabetes
Beta cells in the pancreas are attacked by the immune system
The beta cells become damaged and can no longer produce insulin
350
Hyperglycaemia
Eating causes the blood glucose concentration to increase
People with type I diabetes cannot produce insulin to counteract the increased levels of glucose so the blood glucose level remains high
Hyperglycaemia can lead to death if it is not treated
351
Type I diabetes treatment
Insulin therapy
Too much insulin can cause a fall in glucose levels called hypoglycaemia so insulin must be carefully monitered
352
Type II diabetes
Either don't produce enough insulin or don't respond to insulin
Usually develops in later life
353
Causes of Type II diabetes
Correlated with obesity, lack of exercise, age and family history
Develops when beta cells in the pancreas no longer produce enough insulin or when the muscle nd liver cells stop responding to insulin
354
Type II diabetes - Treatment
Eating a healthy diet and exercising
Medication to lower glucose levels, or sometimes insulin injections
355
Health advice for type II diabetes
A balanced diet that is low in salt, fat and sugar
Regular exercise
356
WHO recommendation for the food industry to help combat the rise in obesity and diabetes
Reducing levels of sugar, saturated fats and salts in processed food products
Developing healthy, alternative products
Having clear and simple labelling on food items showing nutritional contents
Promoting and market healthier foods, especially to children
357
What will happen to the blue colour of Benedicts reagent as glucose concentration increases?
Become darker
358
Where does osmoregulation take place?
Kidneys
The kidneys absorb more or less water accrding to the water potential
359
Osmoregulation
The control of the water potential in the blood
360
Blood water potential is too high
More water must be lost by excretion to return the water potential to normal
The blood reabsorbs less water from the kidneys
The urine is more dilute and water potential in the blood decreases
361
Low blood water potential
Less water must be lost by excretion to retutn the water potential to normal
The blood reabsorbs more water from the kidneys
The urine is more concetrated and water potential in the blood increases
362
Nephron
Functional unit of the kidney and each kidney has several million
The structure of the nephron is important for osmoregulation
363
Bowmans capsule
Beginning of the tubules that make up the nephron
The capsule surrounds a network of capillaries, know as the glomerulus
364
Role of the Bowmans capsule
The first step of filtration of the blood to form urine takes place in the Bowman's capsule.
This produces glomerular filtrate
365
How does blood flow in and out of the glomerulus?
In - Afferent arteriole
Out - Efferent arteriole
366
Afferent vs efferent arteriole
The afferent arteriole is much wider than the efferent arteriole. This means that blood pressure in the capillaries is very high
367
PCT - Proximal Convoluted Tube
Site of selective reabsorption
After the golemrular filtrate has been produced in the Bowman's capsule, glucose and water are reabsorbed into the bloodstream through the PCT
368
What happens once the glomerular filtrate has been produced in the Bowman's capsule?
Glucose and water are reabsorbed into the bloodstream through the PCT
369
Loop of Henle
Produces a low water potential in the medulla of the kidney
The loop of Henle consists of an ascending limb and a descending limb
370
Ascending vs descending limb in the medulla of the kidney
Ascending lumb - impermeable to water
Descending limb - permeable to water
371
How is water reabsorbed into the blood from the kidney?
Through the collecting duct
372
What does the amount of water absorbed by the blood from the kidney depend on?
The water potential of the blood
Low - more water is reabsorbed
High - less water is reabsorbed
373
Where does the formation of glomerular filttrate take place?
Bowman's Capsule
374
Stages of the formation of glomerular filtrate
Pressure filtration
Capillary endothelium
Basement membrane
Podocytes
Glomerular filtrate
375
Pressure filtration in the formation of glomerular filtrate
The branch of capillary that enters the glomerulus is much wider than the branch that exits the glomerulus
This creates a high blood pressure in the glomerulus
The high blood pressure causes the fluid and its solutes in the blood to be forced out of the capillary
376
Capillary endothelium in the formation of glomerular filtrate
The fluid flows through the pores in the capillary endothelium
377
Basement membrane in the formation of glomerular filtrate
The smaller molecules filter through slit pores in the basement membrane. This is a mesh of collagen fibres and glycoprotein
Most proteins and all blood cells are too big to pass through the slit pores
378
Podocytes in the formation of glomerular filtrate
The substances finally pass between the epithelial cells of the Bowman's capsule
The epithelial cells, called podocytes, have finger-like projections that the substances can flow between
379
Glomerular filtrate
The fluid that has filtered from the capillaries to the Bowman's capsule
380
What does the glomerular filtrate contain?
Water
Amino acids
Urea
Glucose
Inorganic ions
381
Sodium-potassium pumps in PCT
Na+ ions are actively transported out of the PCT epithelial cells and into the blood by sodium-potassium pumps
K+ ions are also transported into the epithelium
382
Co-transporter proteins in PCT
Active transport of Na+ ions causes the concentration of Na+ ions inside the epithelial cells to decrease
Na+ ions in the filtrate diffuse into the epithelial cells through co-transporter proteins
Co-transporter proteins allow glucose and amino acids to be transorted into the epithelial cells along with Na+ ions
383
Rebsorption of glucose and amino acids in PCT
As glucose and amino acids are co-transpoerted into teh PCT epithelial cells, their concentration increases inside the cells
Glucose and amino acids diffuse down the concetration gradient into the blood
Blood pressure is relatively high so that substances in the blood are carried away quickly. This maintains a steep concentration gradient
384
Reabsorption of water in PCT
The movement of Na+ ions, glucose and amino acids into the bloodstream causes the water potential in the blood to decrease and increase in the PCT
Water in the PCT diffuses into the blood through osmosis
Any substances that are not reabsorbed are excreted as waste
385
Steps in movement of glomerular filtrate substances from PCT --> blood (selective reabsorption)
Sodium-potassium pumps
Co-transporter proteins
Reabsorption of glucose and amino acids
Reabsorption of water
386
Role of Loop of henle
Creates a region of low water potential and high sodium concentration in the medulla of the kidney
This allows water to be reabsorbed in the collecting duct
387
Role of the top of the ascending limb in the loop of Helne
Na+ ions are actively transported out of the top of the ascending limb in the surrounding tissue fluid in the medulla
This causes the solute concentration of the medulla to increase and the water potential to decrease
The ascending limb in impermeable to water. This means water inside the tubule cannot diffuse out
388
Role of the bottom of the ascending limb in the loop of henle
Na+ ions diffuse out of the bottom of the ascending limb into the medulla
This further increases the solute concentration of medulla
389
Role of the descending limb in the Loop of Henle
The descending limb is permeable to water.
This means that water inside the tubule can diffuse out becaise there is a low water potential in the medulla
The water is reabsorbed by the bloodstream
390
Overall effect of the ascending and descending limb in the Loop of Henle
Create a high solute concentration and low water potential in the tissue fluid surronding the collecting duct
This causes water inside the collecting duct to diffuse into the surrounding tissue fluid by osmosis
The water is then reabsorbed into the bloodstream
391
What does the volume of water reabsorbed by the bloodstream depend on?
The permeability of the collecting duct
392
How does the permeability of the collecting duct vary?
According to the water potential of the blood
High water potential = collecting duct is less permeable to water and less water in absorbed in the blood
393
Antidiuretic Hormone (ADH) - role
ADH controls osmoregulation
ADH influences the permeability of the distal convoluted tubule and collecting duct.
This controls how much water is reabsorbed from he kidney into the blood
394
What monitors blood water potential?
Osmoreceptors in the hypothalamus
395
How do osmoreceptors in the hypothalamus monitor blood water potential?
If the water potential increases, water diffuses into the osmoreceptor cells and the cell swells
If the water potential decreases, water diffuses out of the osmoreceptor cells and the cells shrink
396
Role of posterior pituitary gland
Detects when osmoreceptors shrink and releases ADH into the blood
397
ADH
A hormone that binds to receptors on the cell membrane of epithelial cells of the distal convoluted tube and the collecting duct
398
What happens when ADH binds?
Vesicles containing aquaporins fuse with the cell membrane
399
Aquaporins
Protein channels for water
Increase the permeability of the DCT and collecting duct
This means that more water is reabsorbed into the blood by osmosis
400
What happens if more ADH is in the bloodstream?
More water is reabsorbed from the nephron into the blood
The urine is more concentration
401
Osmorecptor cells
The cells in the hypothalamus that respond to water potential in the blood and trigger a response in the posterior pituitary gland
402
Podocytes
Epithelial cells of the Bowman's capsule
403
Through what process is water reabsorbed into the bloodstream in the proximinal convoluted tube?
Osmosis
404
Which limb of the Loop of Henle is impermeable to water?
The Ascending Limb
