5.1.5 - Plant and animal responses Flashcards
What kind of system are plants ?
- Plants are dynamic systems
- Not only photosynthesising and producing food but also responding to their environment in many different ways.
How have plants evolved ?
- To cope with abiotic stress such as a lack of water
- They have a range of adaptations to protect them against the attention of herbivores.
What is a tropism ?
Showing directional growth response to environmental cues such as light and gravity
What is the key limitation to plants ?
They are rooted, not mobile, and do not have a rapid responding nervous system
What kind of system have the plants developed ?
- A system of hormones
- They are produced and released in one part of the plant and transported both through the transport tissues and from cell to cell and have an effect in another part of the plant
What are some of the hormones in plants ?
- Auxins
- Gibberellins
- Ethene
- Abscisic acid (ABA)
What are the roles of auxins ?
- Controls cell elongation
- Prevent leaf fall, abscission
- Maintain apical dominance
- Involved in tropisms
- Stimulate the release of ethene
- Involved in fruit ripening
What are the roles of gibberellins ?
- Cause stem elongation
- Trigger the mobilisation of food stores in a seed at germination
- Stimulate pollen tube growth in fertilisation
What are the roles of ethene ?
- Cause fruit ripening
- Promotes abscission in deciduous trees
What are the roles of abscisic acid (ABA) ?
- Maintains dormancy of seeds and buds
- Stimulates cold protective responses (antifreezing)
- Stimulates stomatal closing
Why are scientists still unsure about some plant hormones ?
- Plant hormones work at very low concentrations, so isolating them and measuring changes in concentration is not easy
- The multiple interactions between the different chemical control systems also make it very difficult for researchers to isolate the role of a single chemical in a specific response
What must happen to the seeds for the plant to start growing ?
They must germinate
What happens when the seed absorbs water ?
The embryo is activated and begins to produce gibberellins.
What do the gibberellins stimulate the production of ?
Enzymes that break down the food stores found in the seed.
Where are the food stores found ?
The food store is in the cotyledons in dicot seeds and the endosperm in monocot seeds
How does the embryo plant use the food stores ?
The embryo plant uses these food stores to produce ATP for building materials so that it can grow and break through the seed coat
What does evidence suggest that gibberellins do regarding genes ?
Gibberellins switch on genes which code for amylases and proteases, the digestive enzymes required for germination
What does ABA act as in relation to gibberellins ?
- It acts as an antagonist to gibberellins
- It is the relative level of both hormones which determines when a seed will germinate
Give an example of an auxin
Indoleacetic acid
What do auxins do ?
- They are growth stimulants produced in plants
- Small quantities can have large effects
Where are auxins made ?
They are made in cells at the tip of roots and shoots, and in the meristems
Where can the auxins move to ?
They can move down the stem and up the root both in transport tissue and from cell to cell
What can auxins stimulate ?
They can stimulate the growth of the main apical shoot
What do auxins affect regarding the cell wall ?
They affect the plasticity of the cell wall, the presence of auxins means that the cell wall stretches more easily
How do auxins stimulate the growth of the main apical shoot ?
- They bind to specific receptor sites in the plant cell membrane, causing a fall in the pH to about 5
- As the cells mature, auxin is destroyed
- As the hormone levels fall, the pH rises so the enzymes maintaining plasticity become inactive
- As a result, the wall becomes rigid and more fixed in shape and size and the cells can no longer expand
What can high concentrations of auxin do ?
They suppress the growth of the lateral roots
What does suppressing the growth of the lateral shoots lead to ?
This results in apical dominance
How does apical dominance arise ?
- Growth in the main shoot is stimulated by the auxin produced at the tip so it grows quickly
- The lateral shoots are inhibited by the hormone that moves back down the stem, so they do not grow as well
- Further down the stem, the auxin concentration is lower and so the lateral shoots grow more quickly
What happens if the apical shoot is removed ?
- The auxin producing cells are removed and so there is no auxin.
- As a result, the lateral shoots, freed from the dominance of the apical shoot, grow faster
How can we reassert apical dominance if the apical shoot is cut ?
- Apply auxin artificially to the cut apical shoot
- Apical dominance is reasserted and lateral shoot growth is suppressed
What do low concentrations of auxin lead to ?
They promote growth
What do high concentration of auxin lead to ?
They inhibit root growth
What do gibberellins affect ?
They affect the length of the internodes
What are the internodes ?
They are the regions between the leaves on a stem
How were gibberellins discovered ?
They were discovered because they are produced by a fungus from the genus gibberella that affects rice
Describe the experiment that led to the founding of gibberellins
- The infected seedling grew extremely tall and thin
- Scientists investigated the rice and isolated chemicals which produce the same spindly growth in the plants
- It was then discovered that plants themselves produced the compound
If plants do not have gibberellins what are they likely to be ?
They are likely to have stems that are a lot shorter
What does a short plant stem lead to ?
It reduces waste and also makes the plant less vulnerable to damage by weather and harvesting
How do most plant hormones work ?
They work by interacting with other substances
What does hormones working together lead to ?
Very fine control over the responses of the plant that can be achieved
What is synergism ?
When different hormones work together, their effect can be larger than if they were on their own
What is antagonism ?
When two different hormones work against each other, the balance of them will determine the response of the plant
What are some examples of abiotic stresses ?
- Changes in day length
- Cold and heat
- Lack of water / excess water
- High winds
- Changes in salinity
What adaptations may plants have for a hot/dry/windy environment ?
- Thick cuticles
- Hairy leaves
- Sunken stomata
- Wilting response
What adaptations may a plant have for an aquatic environment ?
They may develop aerenchyma
How do seasonal changes affect the amount of photosynthesis possible ?
As light and temperature affect the rate of photosynthesis, seasonal changes have a big impact on the amount of photosynthesis possible.
When is leaf loss in deciduous plants as a response to abiotic stress likely to take place ?
Amount of glucose required for respiration > amount of glucose produced by photosynthesis
When do deciduous trees lose all of their leaves ?
In the winter and they remain dormant until the days lengthen and temperatures rise again in spring
What is photoperiodism ?
The response to a lack of light in the environment of plants
Which plant responses are affected by the photoperiod ?
- Breaking of the dormancy of the leaf buds so they open
- The timing of the flowering in a plant when tubers are formed in preparation for overwintering
Which pigment is responsible for sensitivity to day/dark length ?
Phytochrome
What are the two forms of phytochrome ?
- Pr
- Pfr
How do the two forms of phytochrome differ ?
Each absorbs a different type of light and the ratio of Pr to Pfr changes depending on the levels of light
What does the lengthening of the dark period trigger ?
- Abscission or leaf fall
- Period of dormancy during the winter months
What do falling light levels lead to the fall in ?
Concentrations of auxin
What do falling light levels trigger the plant to produce ?
Ethene
What is the abscission zone ?
- It is at the base of the leaf stalk
- It is made up of two layers that are sensitive to ethene.
What does ethene trigger to happen in the abscission zone ?
- It initiates gene switching in these cells resulting in the production of new enzymes
- These enzymes weaken and digest the cell walls in the outer layer of the abscission zone
What is the separation layer ?
The area that the enzymes have weaken, in the outer layer of the abscission zone
What does the separation layer cause to happen in the plant ?
- The vascular bundles which carry materials into and out of the cell are sealed off
- The fatty material is deposited in the cells on the stem side of the separation layer
What does the separation layer form when the leaf falls ?
- A waterproof protective scar
- It prevents the entry of pathogens
How does the leaf separate from the plant ?
- Cells deep in the separation zone respond to hormonal cues by retaining water and swelling, putting more strain on the already weakened outer layer.
- Then further abiotic factors such as low temps or strong winds finish the process - the strain is too much and the leaf separates from the plant
What is another way that plants respond to abiotic stresses ?
Stomatal control
What does stomatal control refer to ?
The opening and closing of the stomata to conserve/lose water
Which hormone controls the opening and closing of the stomata ?
ABA
When do leaf cells release ABA ?
Under abiotic stress
What do scientists now believe regarding ABA ?
That the roots also provide an early warning of water stresses through ABA
What do the plant roots produce when the levels of soil water fall ?
They produce ABA
Where is ABA transported once it is produced by the plant roots ?
It is transported to the leaves where it binds to the receptors on the plasma membrane of the stomatal guard cells
What does ABA activate ?
ABA activates changes in the ionic concentration of the guard cells, reducing the water potential and therefore turgor of the cells.
What does reduced turgor lead to in the guard cells ?
As a result of reduced turgor, the guard cells close the stomata and water loss by transpiration is greatly reduced
What is herbivory ?
The process by which herbivores eat plants
What are some physical defences plants have developed to prevent herbivory ?
- Thorns
- Barbs
- Spiny leaves
- Inedible tissue
- Hairy leaves
- Stings
What are some chemical defences plants have developed to prevent herbivory ?
- Tannins
- Alkaloids
- Terpenoids
What group are tannins a part of ?
Phenols
What is the role of tannins ?
- They bind to the digestive enzymes produced in the saliva and inactivate them
- They are toxic to insects
What is the taste of tannin like ?
They have a bitter astringent taste
What are alkaloids ?
They are a large group of bitter tasting nitrogenous compounds
What do alkaloids act as ?
- They act as drugs
- Affecting the metabolism of animals that take them in and sometimes poisoning them
Give some examples of alkaloids
- Caffeine
- Morphine
- Nicotine
- Cocaine
How does caffeine protect a plant ?
- Caffeine is toxic to fungi and insects
- Caffeine produced by coffee bush seedlings spreads through the soil and prevents the
germination of the seeds of other plants
How does nicotine protect a plant ?
- Nicotine is a toxin produced in the roots of tobacco plants
- It is transported to the leaves and stored in vacuoles to be released
when the leaf is eaten
What are terpenoids ?
They are toxins to insect and fungi that might attack the plant
What is pyrethrin ?
It acts as an insect neurotoxin that interferes with the nervous system
What is citronella ?
It is a terpenoid that acts as an insect repellent
What is a pheromone ?
A pheromone is a chemical made by an organism which affects the social behaviour of other members of the same species
What are VOC’s ?
- They act like pheromones between themselves and other organisms, particularly insect.
- They diffuse through the air in and around the plant
What can VOC’s do ?
They can alert neighbouring plants to produce VOC’s before they are attacked
When are VOCs made ?
They are usually only made when the plant detects attack by an insect pest through chemicals in the saliva of the insect
What may VOC’s elicit ?
Gene switching
What are tropisms ?
Plant growth responses to stimuli
What is phototropism ?
The growth of plants in response to light which comes from one direction
What is geotropism ?
The response to gravity
What is chemotropism ?
The response to chemicals
What is thigmotropism ?
The response to touch
What is the direction of the response related to ?
It is related to the direction from which the stimulus comes
What is used to research tropisms ?
Germinating seeds
Why are germinating seeds used to research tropisms ?
This is because they are easy to work with and manipulate as they are growing and responding rapidly, this means that any changes will show up quickly
What are coleoptiles ?
The seedlings of monocotyledonous plants
What causes phototropism ?
The movement of auxins across the shoot or root if it is exposed to light that is stronger on one side than another
What happens to the plant if it is grown in bright, all round light in normal conditions of gravity ?
They grow upwards
What will happen if the plant grows in an even but low light ?
- They grow upwards
- They will grow faster and taller than in bright lights
What will happen if plants are exposed to light which is right on one side than another ?
The shoot of the plant will grow towards that light and the roots, if exposed, will grow away from it
What are shoots said to be (phototropism) ?
- Positively phototropic
- They receive as much light as possible, allowing as much photosynthesis to take place
What are roots said to be (phototropism) ?
Negatively phototropic
Where does auxin move in unilateral light ?
It moves laterally across the tip of the shoot away from the light
What does a higher concentration of auxin on the non illuminated side cause ?
It stimulates cell elongation and growth on the dark side, resulting in observed growth towards the light
What happens when you remove the unilateral stimulus, once the shoot is growing towards the light ?
The transport of auxin stops and the shoot then goes straight towards the light
What hormone is responsible for the elongation of the internodal plant in the dark ?
Gibberellins
When do levels of gibberellins fall ?
Once the stem is exposed to light
What is etiolation ?
The rapid upward growth which tales place in a plant grown in the dark
What are etiolated plants like ?
- They are thin and pale
- This is because the plant is deprived of the chlorophyll developed in the leaves
What are shoots like (geotropism) ?
- Negatively geotropic
- Shoot grows upwards
What are roots like (geotropism) ?
- Positively geotropic
- Shoot grows downwards
What are geotropism’s also know as ?
Gravitropism’s
What hormone is involved in the ripening of climacteric fruit ?
Ethene
What are climacteric fruit ?
Fruits that continue to ripen after they have been harvested
Give some examples of climacteric fruit
- Bananas
- Tomatoes
- Mangoes
- Avocados
What are non climacteric fruit ?
Fruits that do not produce large amounts of ethene and do not ripen much after picking
What is the ripening linked to ?
A peak of ethene production which triggers a series of chemical reactions including a greatly increased respiration rate
How can you see the effect of ethene on climacteric fruit ?
- It can easily be seen if a bunch of green bananas is put in a bag with a single ripe banana.
- The bunch with the ripe banana with ripen faster, even if the temperature is exactly the same in both cases.
When are climacteric fruit harvested ?
They are harvested when they are fully formed but long before they are right
What is the unripe fruit like ?
It is hard and much less easily damaged during transport compared to the ripe versions
What is done when the fruit is needed for sale ?
- They are exposed to ethene gas under controlled conditions
- This ensures that each batch of fruit ripe at the same stage to be put on sale
What does the careful control of the ripening prevent ?
It prevents a lot of wastage of fruit during transport and increases the time available for them to be sold
What can the application of auxin to shoots lead to ?
- It stimulates the production of roots
- This makes it much easier to propagate new plants from plant cuttings
What is a cutting ?
It is a small piece of the stem of a plant, usually with some leaves on
What can happen when you place a cutting in hormone rooting powder ?
It increases the chances of roots forming and of successful propagation taking place
What is micropropagation ?
Micropropagation is when thousands of new plants are grown from a few cells of the original plant.
What do plant hormones control in micropropagation ?
They control the production of the mass of new cells and then the differentiation of the clones into tiny new plants
What are weeds ?
Weeds are plant that grow where they are not wanted
What do weeds interfere with ?
Weeds interfere with crop plants, competing for life, space, water and minerals
What have scientists developed as an effective weed killer ?
Scientists have developed synthetic dicot auxins which acts as a very effective weed killer.
How do synthetic dicot auxins kill weeds ?
- If synthetic dicot auxins are applied as weedkiller, they are absorbed by the broadleaved plants and affect their metabolism.
- The growth rate increases and becomes unsustainable, so they die.
What else can auxin be used for ?
Auxin can be used in the production of seedless fruit
What else can ethene be used for ?
- Ethene is used to promote fruit dropping in plants such as cotton, walnuts, and cherries
What else can cytokinins be used for ?
Cytokinins are used to prevent ageing of ripened fruit and products such as lettuces, and in micropropagation to control tissue development
What else can gibberellins be used for ?
Gibberellin can be used to delay ripening and ageing in fruit, to improve the size and shape of fruits, and in beer brewing to speed up the malting process
What else can gibberellins be used for ?
Gibberellin can be used to delay ripening and ageing in fruit, to improve the size and shape of fruits, and in beer brewing to speed up the malting process
What is the mammalian nervous system split into, structurally ?
- Central nervous system
- Peripheral nervous system
What is the CNS ?
- This consists of your brain and spinal cord
- Relay neurones
What is the PNS ?
- This consists of all the neurones that connect the CNS to the rest of the body
- Including sensory and motor neurones
What is the mammalian nervous system split into, functionally ?
- Somatic nervous system
- Autonomic nervous system
What is the Somatic Nervous System ?
- This system is under conscious control
- It is used when you voluntarily decide to do something
Where does the input come from in the somatic nervous system ?
Sense organs
Where does the output go to in the somatic nervous system ?
Skeletal muscles
What does the somatic nervous system carry ?
It carries impulses to the body’s muscles
What is the Autonomic Nervous System ?
- This system works constantly
- It is under subconscious control and it is used when the body does something automatically without you deciding to
What is the autonomic nervous system said to be ?
Involuntary
Where does the input come from in the autonomic nervous system ?
Internal receptors
What does the autonomic nervous system carry ?
It carries nerve impulses to glands, smooth muscles and cardiac muscle
What is the autonomic nervous system split into, functionally ?
- Sympathetic nervous system
- Parasympathetic nervous system
What falls under the sympathetic nervous system ?
- If the outcome increases activity
- e.g. increase in heart rate
Give an example of a neurotransmitter in the sympathetic system
Noradrenaline
What falls under the parasympathetic nervous system ?
- If the outcome decreases activity
- e.g. fall in heart rate or breathing rate
Give an example of a neurotransmitter in the parasympathetic system
Acetylcholine
What are the structures that protect the brain ?
Skull and the meninges
What are the 5 main areas of the brain ?
- Cerebrum
- Cerebellum
- Medulla oblangata
- Hypothalamus
- Pituitary gland
What is the role of the cerebrum ?
Controls voluntary actions, such as learning, memory, personality and conscious thought
What is the role of the cerebellum ?
Controls unconscious functions such as posture, balance and non voluntary movements
What is the role of the medulla oblangata ?
Used in autonomic control, it controls heart rate and breathing rate
What is the role of the hypothalamus ?
Regulatory centre for temperature and water balance
What is the role of the pituitary gland ?
Stores and releases hormones that regulate many body functions
What are the three different ways that the brain can be imaged ?
- MRI
- fMRI
- CT scan
What does the cerebrum do ?
It receives sensory information, interprets it, sends impulses along motor neurones to effectors and produces and appropriate response
What is the cerebrum responsible for ?
It is responsible for coordinating all of the body’s voluntary responses as well as some involuntary ones
What does the cerebrum being convoluted lead to ?
It increases its surface area and therefore its capacity for complex activity
What is the cerebrum split into ?
Into two hemispheres
What do the two hemispheres of the cerebrum control ?
- Controls one half of the body
- It has discrete areas which perform certain functions
What is the outer layer of the cerebral hemispheres called ?
Cerebral cortex
What occurs in the cerebral cortex ?
- The most sophisticated processes occur here, such as reasoning and decision making
- They occur in the frontal and prefrontal lobe of the cortex
What is the size of the sensory area like ?
It is in proportion to the relative number of receptor cells present in the body part
What are association areas ?
They are areas where information is passed so it can be analysed and acted upon
What is the size of the motor area like ?
It is in proportion to the relative number of motor endings in it
What is the main region in the brain that controls movement ?
Primary motor cortex located at the back of the frontal lobe
What happens at the base of the brain ?
Impulses from each side of the body cross, therefore the left hemisphere receives impulses from the RHS of the body and the left hemisphere receives impulses from the LHS of the body
What is the cerebellum concerned with ?
- The control of muscular movement, body posture and balance
- Coordinates movement
What happens if the cerebellum becomes damaged ?
A person suffers from jerky and uncoordinated movements
What is the role of the cerebellum ?
- Receives information from the organs of balance in the ears and information about the tone of muscles and tendons
- It then relays this information to the areas of the cerebral cortex that are involved in motor control
What does the medulla oblangata contain ?
Important regulatory centres of the autonomic nervous system
What does the medulla oblangata control ?
- Ventilation and breathing rate
- Swallowing and coughing
- Peristalsis
What is the hypothalamus ?
Main controlling region for the autonomic nervous system
What are the two centres of the hypothalamus ?
- Sympathetic
- Parasympathetic
What are the functions of the hypothalamus ?
- Controlling complex patterns of behaviour; feeding, sleeping and aggression
- Monitoring the composition of blood plasma, such as conc of water and blood glucose
- Producing hormones
Where is the pituitary gland found ?
Found at the base of the hypothalamus
What are the two sections of the pituitary gland ?
- Anterior pituitary gland
- Posterior pituitary gland
Where is the anterior pituitary gland ?
Front section of the pituitary gland
What is the role of the anterior pituitary gland ?
- Produces 6 hormones
- Including FSH, involved in reproduction and growth hormones
Where is the posterior pituitary gland ?
Back section of the pituitary gland
What is the role of the posterior pituitary gland ?
- Stores and releases hormones produced by the hypothalamus
- ADH
What is a reflex ?
An involuntary response to a sensory stimulus
What is a reflex action ?
When the body responds to situations without conscious thought
What is the reflex arc ?
The pathway of neurones involved in a reflex action
What is the order of things in the reflex arc ?
- Receptor
- Sensory neurone
- Relay neurone
- Motor neurone
Describe what happens in the reflex arc
- The receptor detects the stimulus and creates an action potential in the sensory neurone, this then carries the impulse to the spinal cord
- The relay neurone then proceeds to connect the sensory neurone to the motor neurone within the spinal cord or brain
- The motor neurone then carries the impulse to the effector which carries out an appropriate response
What is the knee jerk reflex ?
Spinal reflex, this means that the neural circuit only goes up to the spinal cord and not the brain
What acts as a stimulus in the knee jerk reflex ?
- When the patella is tapped, it stretches the patellar tendon
- This is the stimulus
What does the stretching of the patellar tendon lead to ?
- It initiates a reflex arc that causes the extensor muscle on the top of the thigh to contract
- A relay neurone inhibits the motor neurone of the flexor muscle, causing it to relax
- At the same time, a relay neurone inhibits the motor neurone of the flexor muscle, causing it to relax.
- This contraction coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick
What does the absence of the knee jerk reflex indicate ?
It indicates nervous problems and multiple oscillation of the leg may be a sign of a cerebral disease
What does the knee jerk reflex used for ?
It is used by the body to help maintain posture and balance, allowing you to remain balanced with little effort or conscious thought
When does the blinking reflex occur ?
When the cornea is stimulated
What is the purpose of the blinking reflex ?
Its purpose is to keep the cornea safe from damage due to foreign bodies entering the eye
What other way can a blinking reflex occur ?
- When sounds greater than 40-60 dB are heard
- Very bright light
What is the corneal reflex ?
Reflex thats main aim is to protect the cornea from damage, does this by blinking
What is the optical reflex ?
Blinking as a reaction to over bright light to protect the lens and the retina
What does the blinking reflex come under ?
- It is a cranial reflex
- This is because it occurs in the brain and not the spinal cord
Fully explain the blinking reflex
- Stimulus triggers an impulse along a sensory neurone
- Impulse passes through a relay neurone in the lower brain stem
- Impulse is then sent along branches of the motor neurone to initiate a motor response to close the eyelids
What does it indicate if the blinking reflex is present ?
The lower brain stem is functioning
What does it indicate if the corneal reflex is present ?
The individual can not be declared as brain dead
Why are reflexes essential for survival ?
They avoid the body being harmed or they reduce the severity of the damage
How do reflexes increase your chances of survival ?
- They are involuntary responses
- They do not have to be learnt
- They are extremely fast
- They are what we could consider everyday actions
How does the fact that reflexes are involuntary responses increase your chance of survival ?
The decision making regions of the brain are not involved and therefore the brain is able to deal with more complex responses
How does the fact that reflexes dont have to be learnt increase your chance of survival ?
They are present at birth and therefore provide immediate protection
How does the fact that reflexes are extremely fast increase your chance of survival ?
- The reflex arc is very short
- Only involves one or two synapses, which are the slowest parts of nervous transmission
How does the fact that reflexes are extremely fast increase your chance of survival ?
- The reflex arc is very short
- Only involves one or two synapses, which are the slowest parts of nervous transmission
What do the nervous and endocrine systems work together to do ?
To detect and respond appropriately to stimuli
What happens in the fight or flight response ?
When there is a dangerous situation, the body automatically triggers a series of physical responses
What is the intention of the flight or fight response ?
Help mammals survive by preparing the body to either run or fight for life, hence the name of the response
Which two systems does the hypothalamus communicate with when a threat is detected ?
Sympathetic nervous system
Adrenal-cortical system
Which system detects a threat ?
Adrenal-cortical system
What does the sympathetic system use to initiate body reactions ?
Neuronal pathways
What does the adrenal cortical system use to initiate body reactions ?
Hormones in the bloodstream
What does the sympathetic nervous system do when the fight or flight response is activated ?
- It sends out impulses to smooth muscles and glands
- It tells the adrenal medulla to release adrenaline and noradrenaline
What does the hypothalamus stimulate in the adrenal cortical system ?
It stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH)
What does ACTH do ?
ACTH travels in the bloodstream to the adrenal cortex, where it activates the release of many hormones that prepare the body to deal with a threat
Why does the heart rate increase ?
To pump more oxygenated blood around the body
Why do pupils dilate ?
To take in as much light as possible for better vision
Why do arterioles in the skin contract ?
More blood to major muscle groups, brain, heart, and muscles of ventilation
Why do blood glucose levels increase ?
Increase respiration to provide energy for muscle contraction
Why do smooth muscles of the airway relax ?
To allow more oxygen into the lungs
Why do non essential systems shut down ?
To focus resources on emergency functions
What is adrenaline’s main function in the fight or flight response ?
- To stimulate liver cells to undergo gluconeogenesis and glycogenolysis
- This increases the glucose in the blood stream
- This allows respiration to increase so more energy is available for muscle contraction
What type of hormone is adrenaline ?
Non lipid soluble
Because adrenaline is non lipid soluble, how does it enter a liver cell ?
Adrenaline binds with receptors on the surface of a liver cell membrane and triggers a chain reaction inside the cell
Explain the secondary messenger model of adrenaline
- When adrenaline binds to its receptor, the enzyme adenylyl cyclase (which is also present in the cell membrane) is activated.
- Adenylyl cyclase triggers the conversion of ATP into cAMP on the inner surface of the cell membrane in the cytoplasm.
- The increase in cAMP levels activates specific enzymes called protein kinases which phosphorylate, and hence activate, other enzymes.
- In this example, enzymes are activated which trigger the conversion of glycogen into glucose.
What is the first messenger ?
Adrenaline
What is the secondary messenger ?
cAMP
What is the cascade effect ?
At each stage, the number of molecules involved increases so the process is said to have a cascade effect
What system controls the heart rate ?
Autonomic nervous system
What part of the brain is responsible for controlling the heart rate ?
Medulla oblangata
What are the two centres in the medulla oblangata ?
- One that increases heart rate
- One that decreases heart rate
How does one of the centres in the medulla oblangata increase heart rate ?
- It sends impulses through the sympathetic nervous system
- These impulses are transmitted by the accelerator nerve
How does one of the centres in the medulla oblangata decrease heart rate ?
- It sends impulses through the parasympathetic nervous system
- These impulses are transmitted by the vagus nerve
What are the two types of receptors that affect heart rate ?
- Chemoreceptors
- Baroreceptors
What do chemoreceptors detect ?
- Detect changes in levels of particular chemicals
- Such as CO2
Where are chemoreceptors located ?
- Aorta
- Carotid artery
- Medulla
What are chemoreceptors sensitive to ?
Changes in the pH level of the blood
What does a high CO2 in the blood lead to ?
pH of the blood decreases because HCO3 is formed when CO2 interacts with H2O in the blood
What does a decrease in blood pH lead to ?
- Heart rate increases
- Blood flows more quickly to the lungs
- CO2 can be exhaled
What does a low CO2 in the blood lead to ?
pH of the blood rises
What does an increase in pH of the blood lead to ?
- Reduction in the frequency of the nerve impulses being sent to the medulla oblangata
- This reduces the frequency of impulses being sent to the SAN via the sympathetic nervous system
- Heart rate decreases
What do baroreceptors detect ?
Changes in blood pressure
Where are baroreceptors located ?
- Aorta
- Vena Cava
- Carotid arteries
What happens if the blood pressure is too high ?
- Impulses are sent to the medulla oblangata which decreases heart rate
- The medulla oblangata sends impulses along the parasympathetic neurones to the SAN which decreases heart rate
- This then reduces blood pressure back to normal
What happens if the blood pressure is too low ?
- Impulses are sent to the medulla oblangata which increases heart rate
- The medulla oblangata sends impulses along sympathetic neurones to the SAN which increases the heart rate
- This increases blood pressure back to normal
What else influences heart rate ?
Hormones
What is released in times of stress ?
- Adrenaline
- Noradrenaline
How do adrenaline and noradrenaline increase heart rate ?
Increase the frequency of impulses produced by the SAN
What are the three types of muscles in the body ?
- Skeletal
- Cardiac
- Smooth
What are skeletal muscles ?
- Make up the bulk of the body muscle tissue
- Cells responsible for movement
What are cardiac muscles ?
Myogenic, contract without the need for a nervous stimulus, causing the hear to beat in a regular rhythm
What are smooth muscles ?
- Found in walls of hollow organs
- Found in walls of blood vessels and the digestive tract
Fibre appearance - skeletal
Striated
Control - skeletal
Voluntary
Arrangement - skeletal
Regularly arranged so muscle contracts in one direction
Contraction speed - skeletal
Fast
Length of contraction - skeletal
Short
Structure - skeletal
- Muscle shows cross striations
- Fibres are tubular and multinucleated
Fibre appearance - cardiac
Specialised striated
Control - cardiac
Involuntary
Arrangement - cardiac
Cells branch and interconnect resulting in simultaneous contraction
Contraction speed - cardiac
Intermediate
Length of contraction - cardiac
Intermediate
Structure - cardiac
- Does have striations but are much fainter than skeletal muscles
- Fibres are branched and uninucleated
Fibre appearance - smooth
Non striated
Control - smooth
Involuntary
Arrangement - smooth
No regular arrangement - different cells can contract in different directions
Contraction speed - smooth
Slow
Length of contraction - smooth
Can remain contracted for a relatively long time
Structure - smooth
- No cross striations
- Fibres are spindle shaped and uninucleated
What are skeletal muscles made out of ?
Muscle fibres
What is the plasma membrane of a muscle fibre called ?
Sarcolemma
How many nuclei does a muscle fibre have ?
Has many nuclei
How long are the muscle fibres compared to other cells ?
- They are much longer than normal cells
- This is because they are formed as a result of many individual embryonic muscle cells fusing together
Why are muscle fibres stronger than other cells ?
- They are made up of many muscle ells that are fused together
- If they weren’t fused together then the junction between adjacent cells would’ve been seen as a point of weakness
What is the cytoplasm within a muscle fibre called ?
Sarcoplasm
Why do parts of the sarcolemma fold inwards to create T tubules ?
- They help to spread the electrical impulses through the sarcoplasm
- Ensures that the whole of the fibre received the impulse to contract at the same time
Why do muscle fibres have lots of mitochondria ?
To provide the ATP that is needed for muscular contraction
What is the name of the ER in the muscle fibres ?
Sarcoplasmic reticulum
What is the role of the Sarcoplasmic Reticulum ?
Contains the calcium ions needed for muscle contraction
What are myofibrils ?
Long cylindrical shaped organelles made of proteins that are specialised for contraction
How are myofibrils arranged ?
Lined up in parallel to provide maximum force when they all contract together
What are the two types of protein filament that make up myofibrils ?
- Actin
- Myosin
What is actin ?
- The thinner filament
- Consists of two strands twisted around each other
What is myosin ?
- The thicker filament
- Consists of long rod shaped fibres with bulbous heads that project to one side
Why do myofibrils have a striped appearance ?
They have alternating light and dark bands
What are light bands ?
- They are the region where the actin and myosin filaments do not overlap
- Also known as I bands
What are dark bands ?
- These are areas where there are thick myosin filaments
- The edges are particularly dark because this is where the myosin overlaps with the actin
- Also known as A bands
What is the Z line ?
Line at the centre of each light band
What are sarcomeres ?
- Distance between adjacent Z lines
- Functional unit of the myofibril
What happens to the sarcomere as the muscle contracts ?
The sarcomere shortens
What is the H zone ?
- Lighter coloured region found in the centre of each dark band
- Only myosin filaments present here
What happens to the H zone as the muscle contracts ?
The H zone decreases
What is the sliding filament model ?
The model used to describe muscular contraction
What happens during contraction ?
Myosin filaments pull the actin filaments inwards towards the centre of the sarcomere
What does contraction result in ?
- Light band becomes narrower
- Z lines move closer together, shortening the sarcomere
- The H zone becomes narrower
Why does the dark band (h zone) remain the same width ?
The myosin filaments themselves have not shortened, but now overlap the actin filaments by a greater amount
What does the simultaneous contraction of lots of sarcomeres lead to ?
- Myofibrils and muscle fibres contract
- This results in enough force to pull on a bone and cause movement
What do the heads on the myosin molecule being hinged allow them to do ?
Allows them to move back and forward
What is on the head of a myosin molecule ?
Binding site for each actin and ATP
What do the tails of a myosin molecule form ?
Aligned together to form the myosin filament
What do actin filaments have binding sites for ?
- Myosin heads
- These are actin-myosin binding sites
What are the binding sites often blocked by ?
The presence of another protein called tropomyosin that is help in place by the protein troponin
What does tropomyosin do ?
Blocks the actin myosin binding sites
What is the role of troponin ?
Holds the tropomyosin in place
What are the active sites like when the muscle is relaxing ?
They are blocked by tropomyosin
What does the binding sites being blocked mean ?
The myosin can then not bind to the actin and the filaments cannot slide past each other
What happens when a muscle is stimulated to contract ?
Myosin heads form bonds with actin filaments known as actin-myosin cross-bridges
What happens when the actin-myosin cross-bridges are formed ?
- The myosin heads flex in unison
- This pulls the actin filament along the myosin filament
What happens once the myosin heads flex ?
The myosin then detaches from the actin and its head returns to its original angle, using ATP
What causes muscle contraction ?
Triggered when an action potential arrives at a neuromuscular junction
Why is it better to have numerous muscular junctions rather than one ?
- Contraction of the muscle would not be powerful
- Contraction of the muscle would be much slower, wave of contraction would have to travel across the muscle to stimulate the individual fibres to contract
What is a motor unit ?
- All the muscle fibres that are supplied by a single motor neurone
- They act as a single unit
What is the stimulation of motor units like if a strong force is needed ?
Large number of motor units are stimulated
What is the stimulation of motor units like if a weak force is needed ?
Small number of motor units are stimulated
What happens when an action potential reaches a neuromuscular junction ?
Stimulates calcium ion channels to open
What happens once calcium channels are open ?
- Calcium ions diffuse from the synapse to the synaptic knob
- They then cause synaptic vesicles to leave the presynaptic neurone - exocytosis
What happens once acetylcholine is released by the synaptic vesicles ?
- Binds to receptors on the sarcolemma
- This opens sodium ion channels
- Results in depolarisation
How does the depolarisation of the sarcolemma travel into the muscle fibre ?
Through the t tubules
What are the t tubules in contact with ?
The sarcoplasmic reticulum
What does the sarcoplasmic reticulum contain ?
Stored calcium ions which it actively absorbs from the sarcoplasm
What happens when the action potential reaches the SR ?
- Stimulates calcium ion channels to open
- Calcium ions diffuse down their concentration gradient flooding the sarcoplasm with calcium ions
What do the calcium ions do once in the sarcoplasm ?
They bind to troponin causing it to change shape
What happens once the troponin changes shape ?
It pulls on the tropomyosin moving it away from the binding sites on the actin filament
What happens once the binding sites have been exposed ?
Myosin head binds to the actin filament forming an actin-myosin cross-bridge
What happens once the myosin heads are attached to the actin filament ?
- The myosin head flexes, pulling the actin filament along
- ADP is released from the myosin head
- ATP molecule can now bind to the myosin head
- This causes the head to detach from the actin filament
What do the calcium ions in the sarcoplasm lead to ?
They activate the ATPase activity of the myosin
What does the activation of ATPase lead to ?
- This hydrolyses the ATP to ADP and Pi, releasing energy
- This allows the myosin heads to return to their original position
What does the myosin head going back to its original position allow ?
It can now attach to another actin-myosin binding site further along the actin filament and the cycle is repeated
What actually causes the actin filament to be pulled ?
- The breaking and forming of the myosin-actin bridges
- This shortens the sarcomere and causes the muscle to contract
What is energy required for in muscle contraction ?
- Movement of myosin heads
- Enabling the SR to actively reabsorb calcium ions from the sarcoplasm
