5.5 - B - Plant And Animal Responses Flashcards
1
Q
Why do plants need to respond to their environment?
A
To avoid abiotic stress
To maximise photosynthesis or to obtain more light/water/minerals
To ensure germination occurs in suitable conditions
Herbivory
2
Q
How do plants respond to their environment?
A
Higher temps - more waxy later - reduce evaporation
Very windy - more lignification - reduce water loss
Drought - root growth slows - save energy, stomata close - reduce water loss
Herbivory - release chemicals
3
Q
List the 3 chemical defences to herbivory
A
Tannins
Alkaloids
Pheromones
4
Q
What are tannins?
A
They are toxic to microorganisms and larger herbivores. In leaves, they are found in the upper epidermis and make the lead taste bad. In roots, they prevent infiltration by pathogenic microorganisms.
5
Q
What are alkaloids?
A
They are derived from amino acids. In plants, scientists think they are a feeding deterrent to animals, tasting bitter, they are located in growing tips and flowers, and peripheral cell layers of stems and roots.
6
Q
What are pheromones?
A
Chemicals released by one individual and which can affect the behaviour or physiology of another
7
Q
What are tropisms?
A
Directional growth responses or plants to a stimulus in which the response is determined by the direction of the external stimulus
8
Q
List the 4 types of tropisms
A
Phototropism
Geotropism
Chemotropism
Thigmotropism
9
Q
Define phototropism
A
Shoots grow towards sunlight, which enables them to photosynthesise
10
Q
Define geotropism
A
Roots grow towards the pull of gravity. This anchors them in the soil and helps them to take up water, which is needed for support (to keep cells turgid), as a raw material for photosynthesis and to help cook the plant. There will also be minerals, such as nitrate in the water, needed for the synthesis of amino acids.
11
Q
Define chemotropism
A
On a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place.
12
Q
Define thigmotropism
A
Shoots of climbing platen, such as ivy, wind around other plants or solid structures to gain support.
13
Q
What is the difference between a positive tropic response and a negative tropic response
A
Positive - when a plant moves towards the stimulus
Negative - when a plant moves away from the stimulus
14
Q
Define thigmonasy
A
The nastic response of a plant or fungus to touch or vibration
15
Q
List the 5 plant hormones
A
Cytokinins Abscisic acid Auxins Gibberellins Ethene
16
Q
What do cytokinins do?
A
Promote cell division
Delay leaf senescence
Overcome apical dominance
Promote cell expansion
17
Q
What does abscisic acid do?
A
Inhibits seed germination and growth
Causes stomatal closure when the plant is stressed by low water availability
18
Q
What do auxins do?
A
Promote cell elongation
Inhibit growth of side-shoots
Inhibit leaf abscission
19
Q
Define leaf abscission
A
Leaf fall
20
Q
What do gibberellins do?
A
Promote seed germination and internodal growth of stems
21
Q
What does ethene do?
A
Promotes fruit ripening
22
Q
List the 3 ways hormones move around the plant
A
Active transport
Diffusion
Mass flow in the in phloem sap or in the xylem vessels
23
Q
What are auxins?
A
Plant hormones which are responsible for regulating plant growth
24
Q
Define apical dominance
A
Inhibition of lateral buds further down the shoot by chemicals produced by the apical bug at the tip of a plant shoot
25
Give 3 similarities of plant and mammalian hormones
Hormones bind to receptors causing a cascade of events/enzyme reactions. This may involve switching on / off genes only present/needed in small concentrations/quantities (to have an effect).
They may have effect on more than one location/target tissue.
There is an idea that hormone effect may involve interaction of more than one hormone.
26
Give 4 differences between plant and mammalian hormones
Mammalian hormones are made in endocrine glands versus plant hormones which are made in many plant tissues.
Mammalian hormones move in blood versus plant hormones which move in the xylem or phloem or from cell to cell.
Mammalian hormones act on a few specific target tissues versus plants which act on most tissues. They can also act in cells where produced.
Mammalian hormones act more rapidly.
27
Explain the commercial uses of auxins
Cuttings of plants are dipped in rooting powder containing low
concentrations of auxin (promotes root growth)
Weedkiller ‐ promotes rapid shoot growth ‐ plant can't support itself and falls and dies
Can help make seedless fruits
28
How do levels of auxin affect cytokinins?
High levels of auxin inhibit cytokinins' effects
| Low levels of auxin allows cytokinins to promote lateral bud growth
29
What are the commercial uses of cytokinins?
Prevent yellowing of lettuce leaves (senescence)
In tissue culture (artificial cloning of plants) cytokinins added to promote many side shoots ‐ can be grown into new plants ‐ hgiher production of new plants
30
What are the commercial uses of gibberellins?
Elongate internodal cells in stalks of grapes ‐ grapes spread out and get bigger
Elongation of internodal cells in sugar cane ‐ more sugar
Beer production needs malt. Gibberellins added to encourage barley
seed to make amylase so starch ‐‐> maltose. Germination then
stopped by drying.
31
What are the commercial uses of ethene?
Spraying fruit with an ethene based compound can:
> speed up ripening in bananas and other fruits
> promote fruit abscission in cherries and other fruits
Cold conditions, little oxygen and high carbon dioxide prevents ethene
synthesis and can prevent fruit ripening during shipping
32
Define action potential
The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.
33
What is the mammalian nervous system split into?
Central nervous system
| Peripheral nervous system
34
What is the central nervous system split into?
Brain
| Spinal chord
35
What is the peripheral nervous system split into?
Sensory system
| Motor system
36
What is the motor system split into?
Somatic nervous system
| Autonomic nervous system
37
What is the autonomic nervous system?
The part of the nervous system responsible for controlling the involuntary motor activities of the body
38
What is the CNS?
The central nervous system
| The central part of the nervous system composed of the brain and spinal chord
39
What is the PNS?
The peripheral nervous system
| The sensory and motor nerves connecting the sensory receptors and effectors to the CNS
40
What is the somatic nervous system?
The motor neurones under conscious control
41
What must a communication system enable?
Detection of changes in the environment
Cell signalling to occur between all parts of the body
Coordination of a range of effectors to carry out responses to the sensory input
Suitable responses
42
Describe the structure of the brain in respect to the CNS
It contains about 86 billion neurones. Much of the brain is composed of relay neurones, which have multiple connections enabling complex neural pathways. Most of these cells are non-myelinated cells and the tissue looks grey. It’s also known as grey matter.
43
Describe the structure of the spinal chord in respect to the CNS
It has many non-myelinated relay neurones making up the grey cell matter. It also contains large numbers of myelinated neurones making up an outer region of white matter. These myelinated neurones carry action potentials up and down the spinal cord for rapid communication over long distances.
It’s protected by the vertebral column.
44
What is the role of the PNS?
To ensure rapid communication between the sensory receptors, the CNS and the effectors.
45
Describe the structure of the PNS
It’s composed of sensory and motor neurones. These are usually bundled together in a connective tissue sheath to form nerves.
46
Explain the structure of the somatic nervous system
It consists of motor neurones that conduct action potentials from the CNS to the effectors that are under voluntary (conscious) control, such as the skeletal muscles. These neurones are mostly myelinated, so that responses can be rapid. There is always one motor neurone connecting the CNS to the effector.
47
Explain the structure of the autonomic nervous system
It consists of motor neurones that conduct action potentials from the CNS to effectors that are not voluntary control. There are at least 2 neurones involved in the connection between the CNS and the effector. These neurones are connected at small swellings called ganglia.
48
What does autonomic mean?
Self-governing
49
What can the autonomic system be divided into?
The sympathetic system
| The parasympathetic system
50
What does the sympathetic system do?
Prepares the body for activity
| Fight or flight
51
What does the parasympathetic system do?
Conserves energy
| Rest and digest
52
What type of systems are the sympathetic and parasympathetic systems?
Antagonistic - the action of one system opposes the action of the other.
53
Explain the difference in the number of nerves between the sympathetic and parasympathetic systems
Sympathetic - consists of many nerves leading out of the CNS, each leading to a separate effector.
Parasympathetic - consists of a few nerves leading out of the CNS, which divide up and lead to different effectors.
54
Explain the difference in where the ganglia are located between the sympathetic and parasympathetic systems
Sympathetic - just outside the CNS
| Parasympathetic - in the effector tissue
55
Explain the difference in the length of the ganglia between the sympathetic and parasympathetic systems
Sympathetic - short pre-ganglionic neurones. Long post-ganglionic neurones (variable in length, dependent upon the position of the effector)
Parasympathetic - long pre-ganglionic neurones (variable in length, dependent upon the position of the effector). Short post-ganglionic neurones.
56
Explain the difference in what is used as the neurotransmitter between the sympathetic and parasympathetic systems
Sympathetic - noradrenaline
| Parasympathetic - acetylcholine
57
Explain the difference in the when the systems are most active between the sympathetic and parasympathetic systems
Sympathetic - most effective at times of stress
| Parasympathetic - most effective during sleep or relaxation
58
Lost 5 effects of the sympathetic nervous system
```
Increase heart rate
Dilated pupils
Increases ventilation rate
Reduces digestive activity
Orgasm
```
59
List 5 effects of the parasympathetic nervous system
```
Decreases heart rate
Constricts pupils
Reduces ventilation rate
Increases digestive activity
Sexual arousal
```
60
What is a ganglion?
A structure containing a number of nerve cell bodies, typically linked by synapses, and often forming a swelling on a nerve fibre.
61
What are the 4 main parts of the human brain?
Cerebrum
Cerebellum
Hypothalamus and pituitary complex
Medulla oblongata
62
What is the cerebrum?
The learners part of the brain. It organises most of our higher thought processes, such as conscious thought and memory.
It is divided into 2 cerebral hemispheres.
63
What is the cerebellum?
A region of the brain which coordinates balance and fine control of movement.
64
What is the hypothalamus?
Part of the brain that coordinates homeostatic responses?
65
What is the pituitary gland?
An endocrine gland at the base of the brain, below but attached to the hypothalamus; the anterior lobe secretes many hormones; the posterior lobe stores and releases hormones made in the hypothalamus.
66
How are the 2 cerebral hemispheres connected?
Via major tracts of neurones called the corpus callosum
67
What does the outermost layer of the cerebrum consist of?
A thin layer of nerve cell bodies called the cerebral cortex
68
List 5 functions of the cerebrum
Conscious thought
Conscious actions (including the ability to override some reflexes)
Emotional responses
Intelligence, reasoning, judgement and decision making
Factual memory
69
What are the 3 subdivisions of the cerebral cortex and why is it subdivided?
Sensory area
Association areas
Motor areas
For specific activities and body regions
70
What do sensory areas in the cerebral cortex do?
Sensory areas receive action potentials indirectly from sensory receptors. The size of the region allocated to receive input from different receptors correlates to the sensitivity of the area that inputs are received from.
71
What do association areas in the cerebral cortex do?
Association areas compare sensory inputs with previous experience, interpret what the input means, and judge an appropriate response.
72
What do motor areas in the cerebral cortex do?
Motor areas send action potentials to various effectors (muscles and glands). The sizes of the regions allocated to deal with the different effectors correlates to the complexity of the movements needed in the parts of the body. Motor areas on the left side of the brain control the effectors on the right side of the body and vice versa.
73
How many neurones does the cerebellum contain?
Over half of all the neurones in the brain
74
How does the cerebellum carry out its functions?
It must receive information from many sensory receptors and process the information accurately. The sensory receptors that supply information to the cerebellum include the retina, the balance organs in the ear and spindle fibres in the muscles - these give information about muscle length and joints.
75
List 4 muscular movements that the cerebellum coordinates the fine control of
Maintaining body position and balance, such as when riding a bicycle.
Judging the position of objects and limbs while moving about or playing sport.
Tensioning muscles in order to use tools and play musical instruments effectively.
Coordinating contraction and relaxation of antagonistic skeletal muscles when walking and running.
76
What connects the cerebrum and the cerebellum?
The pons
77
Explain how the hypothalamus controls temperature regulation
It detects changes in core body temperature. However, it also receives sensory input from temperature receptors in the skin. It will initiate responses to temperature change that regulate body temperature within a narrow range. These responses may be mediated by the nervous system or by the hormonal system (via the pituitary gland)
78
Explain how the hypothalamus controls temperature regulation
It contains osmoreceptors - these monitor water potential in the blood. When the water changes, the osmoregulatory centre initiates responses that bring about a reversal of this change. The responses are mediated by the hormonal system via the pituitary gland.
79
State the 2 lobes of the pituitary gland
The posterior lobe
| The anterior lobe
80
What does the posterior lobe do?
It’s linked with the hypothalamus by specialised neurosecretory cells. Hormones such as ADH, which are manufactured in the hypothalamus, pass down the neurosecretory cells and are released into the blood from the pituitary gland.
81
What does the anterior lobe do?
It produces it’s own hormones, which are released into the blood in response to releasing factors produced by the hypothalamus. These releasing factors are hormones that need to be transported a short distance from the hypothalamus to the pituitary gland. Hormones from the anterior lobe control a number of physiological processes in the body, including response to stress, growth, reproduction and lactation.
82
What does the medulla oblongata control?
| How does it do this?
Non-skeletal muscles (the cardiac muscles and involuntary smooth muscles) by sending action potentials out through the autonomic nervous system.
83
List 3 centres the medulla oblongata contains for regulating several vital processes
The cardiac centre - this regulates heart rate
The vasomotor centre - this regulates circulation and blood pressure
The respiratory centre - this controls the rate and depth of breathing
84
What type of information do the centres of the medulla oblongata receive?
What do they coordinate and how?
They receive sensory information and coordinate vital functions by negative feedback
85
What is the knee jerk reflex?
A reflex action that straightens the leg when the tendon below the knee cap is tapped
86
What is a reflex action?
A response to changes in the environment that do not involve any processing by the brain to coordinate the movement. The nervous pathway is as short as possible so that the reflex so fast as fuck.
87
What are the 3 neurones that most reflex pathways consist of?
Sensory neurone
Relay neurone
Motor neurone
88
What type of reflex is the blinking reflex and why?
Cranial reflex - the nervous pathway passes through part of the brain
89
What is it called when the receptor and the effector are in the same place?
A reflex arc
90
What is the corneal reflex?
Blinking due to a foreign object touching the eye
91
What is the optical reflex?
Blinking due to sudden bright light
92
List 4 sudden changes in the environment that blinking may be stimulated by
A foreign object touching the eye (the corneal reflex)
Sudden bright light (the optical reflex)
Loud sounds
Sudden movements close to the eye
93
Explain how the cornea reflex is carried out
This reflex is mediated by a sensory neurone from the cornea, which enters the pons. A synapse connects the sensory neurone to a relay neurone, which passes the action potential to the motor neurone. The motor neurone passes back out of the brain to the facial muscles, causing the eyelid to blink. This is a very short and direct pathway, so the corneal reflex is very rapid - it takes about 0.1 seconds. The corneal reflex usually causes both eyes to blink, even if only one cornea is affected.
94
Explain how the corneal reflex can be overridden by conscious control
The sensory neurone involved also passes action potential to myelinated neurones in the pons. These myelinated neurones carry the action potential to the sensory region in the cerebral cortex to inform the higher centres of the brain that the stimulus has occurred. The higher parts of the brain (cerebral cortex) can send inhibitory signals to the motor centre in the pons. The myelinated neurones carrying impulses to and from the cerebral cortex transmit action potentials much more rapidly than the non-myelinated relay neurone in the pons. Therefore, the inhibitory action potentials can prevent the formation of an action potential in the motor neurone.
95
What type of reflex is the knee jerk reflex and why?
Spinal reflex - the nervous pathway passes through the spinal chord rather than through the brain
96
State the neurones that knee jerk reflex nervous pathway consist of
Sensory neurone
| Motor neurone
97
Why can’t the brain inhibit the knee jerk reflex?
There is no relay neurone
98
What is the value of the knee jerk reflex?
It coordinates leg movement and balance
99
Which is faster: the optical reflex or the corneal reflex?
The corneal reflex
100
What is adenyl cyclase?
An intracellular enzyme, which is activated by other certain hormones
101
What is cyclic AMP (cAMP)?
A secondary messenger released inside cells to activate a response
102
Explain how the optical reflex works
The stimulus is detected by the retina and the reflex is mediated by the optical centre in the cerebral cortex.
103
How do dilate pupils have survival value?
Allows more light to enter the eyes, making the retina mire sensitive
104
How does an increased heart rate and blood pressure have survival value?
Increases the rate of blood flow to deliver more oxygen and glucose to the muscles and to remove carbon dioxide and other toxins
105
How does constricting arteriolar to the digestive system and skin and dilating those to the muscles and liver have survival value?
Diverts blood flow away from the skin and digestive system towards the muscles.
106
How does increasing blood glucose levels have survival value?
Supplies energy for muscular contraction
107
How does increasing metabolic rates have survival value?
Converts glucose to useable forms of energy such as ATP
108
How does contracting erector pili muscles in the skin have survival value?
It makes hairs stand up - this is a sign of aggression
109
How does increasing ventilation rate and depth have survival value?
Increases gaseous exchange so that more oxygen enters the blood and supplies aerobic respiration
110
How does having endorphins (natural painkillers) be released in the brain have survival value?
Wounds inflicted on the mammal do not prevent activity
111
Explain the role of the brain in coordinating responses
Receptors sense the threatening stimulus.
Action potential sent to sensory centres in the cerebrum and then to association centres which coordinate the response.
The cerebrum stimulates the hypothalamus in response to the threat.
The hypothalamus stimulates the sympathetic nervous system and the anterior pituitary gland.
112
Explain the role of the sympathetic nervous system in coordinating responses
It increases the activity of effectors via nervous impulses for rapid responses.
It stimulates the adrenal medulla to release adrenaline (which brings about responses in effectors) for longer responses.
113
Describe the mechanism of adrenaline action
Adrenaline acts as a first messenger by travelling through the blood and binding to receptors on the cell surface membrane of its target cells.
The binding causes a G-protein on the membrane to activate the enzyme adenyl cyclase which converts ATP into cyclic AMP (this is the second messenger) which brings about the effect in the cell.
114
Describe the release of hormones from the anterior pituitary gland
The hypothalamus secretes releasing hormones into the blood. These pass down a portal vessel to the pituitary gland and stimulate the release of tropic hormones from the anterior part of the pituitary gland. These stimulate activity in a variety of endocrine glands.
115
What are releasing hormones also known as?
Releasing factors
116
Where is CRH from? What does it do? What does it stand for?
Corticotropin-releasing hormone - from the hypothalamus.
It causes ACTH to be released. ACTH passes around the blood system and stimulates the adrenal cortex to release a number of different (corticosteroid) hormones. As a result, more glucose is released from glycogen stores. New glucose may also be produced from fat and protein stores.
117
What does ACTH stand for?
Adrenocorticotropic hormone
118
What does TRH stand for and what does it do?
Thyrotropin-releasing hormone.
It causes the release of TRH which stimulates the thyroid gland to release more thyroxine. This acts on nearly every cell if the body, increasing the metabolic rate and making cells more sensitive to adrenaline.
119
What does TSH stand for?
Thyroid-stimulating hormone
120
What are 4 important roles of circulation?
Transport of oxygen and nutrients, such as glucose, fatty acids and amino acids to the tissues.
Removal of waste products, such as carbon dioxide from the tissues to prevent accumulation that may become toxic.
Transport of urea from the liver to the kidneys.
Distribute heat around the body or deliver it to the skin to be radiated away.
121
List 3 ways heart action can be modified by
Raising or lowering the heart rate. This is the number of beats per minute.
Altering the force of the contractions of the ventricular walls.
Altering the stroke volume (volume of blood pumped per beat).
122
Define myogenic muscle
Muscle that generates its own bear at regular intervals
123
What is heart rate controlled by at rest?
| What is the typical frequency of excitation?
The SAN
| 60-80 per minute
124
What are the excitation waves altered by?
They are altered by the cardiovascular centre in the medulla oblongata. Nerves from here supply the SAN. These nerves are part of the autonomic nervous system.
125
How are the frequency of excitation waves altered?
The nerves do not initiate a contraction, but can affect the frequency of contractions by:
Action potentials sent down the accelerans nerve cause the release of the neurotransmitter noradrenaline at the SAN. This increases heart rate.
Action potentials sent down the vagus nerve release the neurotransmitter acetylcholine, which reduces heart rate.
126
What type of nerve is the accelerans nerve?
A sympathetic nerve
127
How does heart rate change due to environmental factors?
Input from sensory receptors is fed to the cardiovascular centre in the medulla oblongata. Some inputs increase heart rate, others decrease it. This ensure the SAN always reacts appropriately.
128
List 4 sensory inputs to the cardiovascular system
Stretch receptors in muscles
Chemoreceptors
Carbon dioxide concentration in the blood
Stretch receptors in the walls of the carotid sinus
130
Explain how stretch receptors in muscles act as a sensory input to the cardiovascular centre
Stretch receptors in the muscles detect movement of the limbs. These send impulses to the cardiovascular centre, informing it that extra oxygen may soon be needed. This leads to an increase in heart rate.
131
Explain how chemoreceptors act as a sensory input to the cardiovascular centre
It’s found in the carotid arteries, the aorta and brain. They monitor the pH of the blood. When we exercise, our muscles produce more carbon dioxide. Some of this reacts with the water in the blood plasma to produce carbonic acid. This reduces the ph of the blood, which affects the transport of oxygen. The change in pH is detected by the chemoreceptors, which send action potentials to the cardiovascular centre. This will tend to increase heart rate.
132
Explain how carbon dioxide concentration in the blood acts as a sensory input to the cardiovascular centre
When we stop exerting, the concentration of carbon dioxide in the blood falls. This reduces the activity of the accelerator pathway. Therefore, the heart rate declines.
133
Explain how stretch receptors in the walls of the carotid sinus act as a sensory input to the cardiovascular centre
They monitor blood pressure. The carotid sinus is a small swelling in the carotid artery. An increase in blood pressure is detected by these stretch receptors. If pressure rises too high, the stretch receptors send action potentials to the cardiovascular centre, leading to a reduction in heart rate.
134
What are the 3 types of muscle?
Cardiac muscle
Smooth (involuntary) muscle
Skeletal (striated) muscle
135
What is the neuromuscular junction?
The structure at which a nerve meets the muscle; it is similar in action to a synapse
136
What are muscles composed of?
Cells arranged to form fibres.
| These fibres can contract to become shorter, which produces a force.
137
How is muscle contraction achieved?
By interaction between 2 protein filaments in the muscle cells. Muscle cannot elongate without an antagonist. Therefore, muscles are usually arranged in opposing pairs, so that one contracts as the other elongates. In some cases, the antagonist may be elastic recoil or hydrostatic pressure in a chamber.
138
What are the 2 protein filaments found in muscle cells?
Actin
| Myosin
139
Describe the cells that create smooth muscle
Individual cells
Tapered at both ends (spindle shaped)
At rest, each cell is approx. 500 micrometers long and 5 micrometers wide
Each cell contains a nucleus and bundles of actin and myosin
140
Describe features of smooth muscle
It contracts slowly and regularly
It does not tire quickly
It is controlled by the autonomic nervous system
141
Where is smooth muscle found?
In the walls of tubular systems, such as the digestive system and blood vessels.
142
How is smooth muscle arranged?
In longitudinal and circular layers that oppose each other
143
What is cardiac muscle?
Muscle that forms the muscular walls of the heart
144
Explain the structure of cardiac muscle and the cells it consists of.
What does this cause?
The individual cells form long fibres, which branch to form cross-bridges between the fibres. When the muscle contracts, the arrangement ensures that the contraction is a squeezing action rather than one-dimensional.
The cells are joined by intercalated discs. These are specialised cell surface membranes fused to produce gap junctions that allow free diffusion of ions between cells. Actions potentials pass easily and quickly along and between the cardiac muscle fibres.
Low free diffusion of ions between the cells.
145
What do the cross-bridges in cardiac muscle help to ensure?
That electrical stimulation spreads over the walls of the chambers.
146
Describe features of cardiac muscle
It contracts and relaxes continuously throughout life
It can contract powerfully
It doesn’t fatigue easily
147
What parts of the heart are modified to carry electrical impulsesL
What do these coordinate?
Purkyne fibres
| These coordinate the contraction of the chamber walls
148
What does cardiac muscle appear as when viewed under a microscope?
Striated (striped)
149
Where does skeletal muscle occur?
At the joints in a skeleton
150
How do contractions of the skeletal muscle cause movement
By bending or straightening the joint
151
What is the difference between skeletal and smooth muscle?
Skeletal muscle is voluntary
| Smooth muscle is involuntary
152
How are skeletal muscles arranged?
In pairs called antagonistic pairs. When one contracts, the other elongates.
153
Discuss the fibres formed from skeletal muscle cells
Approx 100 micrometers in diameter.
| Each fibre is multinucleate and is surrounded by the sarcolemma.
154
Define multinucleate
Containing many nuclei
155
What is the muscle cell membrane known as?
Sarcolemma
156
What is the muscle cell cytoplasm known as?
Sarcoplasm
157
How is the sarcoplasm specialised?
It is specialised to contain many mitochondria and an extensive sarcoplasmic reticulum.
158
What are the contents of the fibres arranged into a number of?
Microbibrils
159
What are microfibrils divided into?
A chain of subunits called sarcomeres.
160
What do sarcomeres contain?
Actin and myosin
161
What are the dark bands called?
A bands
162
What are the light bands called?
I bands
163
What is in the I band?
Pure actin
164
What is in the A band?
Both myosin, actin and the H zone
165
What is in the H zone? Where is the H zone?
In the A band
| Pure myosin
166
What are the skeletal muscle’s contractions stimulated by?
The somatic nervous system
167
Explain the 5 stages of the stimulation of contraction
Action potentials arrive at the end of the axon and open calcium ion channels allowing calcium ions to flood into the axon tip.
Vehicles of acetylcholine move towards the membrane and fuse.
Acetylcholine molecules diffuse across the gap and bind to receptors on the sarcolemma.
Sodium ion channels open and sodium ions enter the muscle fibre causing depolarisation.
The wave of depolarisation passes along the sarcolemma and down transverse tubules.
168
Define depolarisation
A change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell.
169
What are transverse tubules?
Extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cell (also known as T-tubules).
170
Explain what a motor unit is
Some motor neurones stimulate single muscle fibres. However, many motor neurones divide an connect to several muscle fibres. All these muscle fibres contract together, providing a stronger contraction. This is called a motor unit.
171
What does EMG stand for?
| What are they used for?
Electromyography.
| It is a diagnostic procedure used to assess the health of muscles and the nerve cells that control them (motor neurons).
172
What is creatine phosphate?
A compound in muscle that acts as a store of phosphates and can supply phosphates to make ATP rapidly
173
What are the light bands held together by?
The Z line
174
What are aligned to make up the light band?
Thin filaments
175
What make up the dark band?
Thick filaments
176
What is the middle of the dark band with no overlap called?
The H zone
177
What is the distance between 2 Z lines called?
What is this?
How long are these?
A sarcomere
This is the long functional unit of the muscle
At rest, approx 2.5 micrometers long
178
What are the 2 types of protein filaments myofibrils contain?
Thin filaments
| Thick filaments
179
What surrounds both thick and thin filaments?
Sarcoplasmic reticulum
180
Give the zones, lines and bands of a sarcomere in order
Z line, I band, A band (H zone inside A band), A band contd.
| I band, Z lime
181
What are the thin filaments made from?
Actin
182
What does each thin filament consist of?
2 chains of actin subunits twisted around each other
183
What is wound around the actin of the thin filament?
| What is attached to these?
Tropomyosin
| Globular molecules of troponin are attached to the tropomyosin
184
Explain the troponin complex
It consists of 3 polypeptides. One binds to actin, one to tropomyosin and the third to calcium when it is available.
185
What do tropomyosin and troponin do at rest?
Cover binding sites to which the thick filaments can bind
186
What does each thick filament consist of?
A bundle of myosin molecules
187
Explain the structure of a myosin molecule
Each one has 2 protruding heads, which stick out at the end of each molecule. These appears are mobile and can bind to the actin when the binding sites are exposed.
188
What is the muscle contraction hypothesis called?
The sliding filament hypothesis
189
What happens to the bands and zones during contraction?
The light band and the H zone get shorter.
| Therefore, the Z lines move closer together and the sarcomere gets shorter.
190
Explain the 6 steps in the contraction of muscle
When the muscle is stimulated, the action potential passes along the sarcolemma and down the T-tubules into the muscle fibre.
The action potential is carried to the sarcoplasmic reticulum, which stores calcium ions, and causes the release of calcium ions into the sarcoplasm.
The calcium ions bind to the troponin, which alters the shape pulling the tropomyosin aside. This exposes the binding sites on the action.
Myosin heads bind to the actin, forming cross-bridges between the filaments.
The myosin heads move, pulling the actin filament past the myosin filament.
The myosin heads detach from the actin and can bind again further up the actin filament.
191
Explain the 4 steps of the role of ATP in muscle contraction
The myosin head attaches to the actin filament, forming a cross-bridge.
The myosin head tilts backwards, causing the thin filament to slide past the myosin filament. This is the power stroke. During the power stroke, ADP and Pi are released from the myosin head.
After the power stroke, a new ATP molecule attached to the myosin head, breaking the cross-bridge.
The myosin head returns to its original position as the ATP is hydrolysed, releasing the energy to make this movement occur. The myosin head can now make a new cross-bridge further along the actin filament.
192
State the 3 mechanisms involved in maintaining the supply of ATP for muscle contraction
Aerobic respiration in mitochondria
Anaerobic respiration in the sarcoplasm of the muscle tissue
Creatine phosphate in the sarcoplasm
193
Explain how aerobic respiration in mitochondria is a mechanism involved in maintaining the supply of ATP in muscle contraction
Muscle tissue contains a large number of mitochondria in which aerobic respiration can occur. The Bohr effect helps to release more oxygen from the haemoglobin in the blood. However, during intense activity, the rate at which ATP can be produced will be limited by the delivery of oxygen to the muscle tissue.
194
Explain how anaerobic respiration in sarcoplasm of the muscle tissue is a mechanism involved in maintaining the supply of ATP in muscle contraction
Anaerobic respiration can release a little more ATP from the respiratory substrates. However, it leads to the production of lactate (lactic acid), which is toxic. Anaerobic respiration can only last a few seconds before lactic acid build-up starts to cause fatigue.
195
Explain how creatine phosphate in the sarcoplasm is a mechanism involved in maintaining the supply of ATP in muscle contraction
It acts as a reserve store of phosphate groups. The phosphate can be transferred from the creatine phosphate to ADP molecules, creating ATP molecules very rapidly. The enzyme creatine phosphotransferase is involved. The supply of creatine phosphate is sufficient to support muscular contraction for a further 2-4 seconds.
