Unit 6 - Organisms respond to changes in their internal and external environments Flashcards
Tropism
A plants growth response to an external stimulus
Types of tropisms
Gravitrophism
Hydrotrophism
Phototrophism
How does IAA move through plant
Via phloem (Mass transport)
Then diffusion/ active transport through cells
Two types of responses in animals and definitions
Taxis- An organism moves towards/ away from a directional stimulus
Kinesis- Movement affected by a non-directional stimulus
Nervous response cycle
Stimulus–> Receptors—> CNS —–> Effectors —-> Response
Two parts of nervous system
Central nervous system
Peripheral nervous system
Two types of peripheral nervous system
Somatic
Autonomic
Two types of autonomic nervous system + description
Sympathetic- ‘Fight or flight’
Parasympathetic- ‘Rest + Digest’
Benefits of reflexes
-Rapid
- Prevent tissue damage
- Don’t require conscious thought
What is the resting potential difference
-70 mV
Steps in an action potential being generated
1- Resting potential
2- Depolarisation pt 1 (stimulus)
3- Depolarisation pt 2 (Channels open)
4- Repolarisation
5- Hyperpolarisation then return to resting potential
What is a stimulus
A detectable change in the environment
What is a reflex?
The body responds to a stimulus without mkaing a consious decision to respond.
What are pacinian corpuscles
Pressure recpetors in the skin that detect mechanical stimuli
How does the brain portray light?
- Light enters the eye and hits the photoreceptors
- This is absorbed by light-sensitive optical pigments
- Light bleaches the pigments, causing a chemical change and altering the membrane permability to sodium ions
- A generator potential is created and if it reaches the threshold, a nerve impulse is snet along a bipolar neurone.
Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain.
What are the two photoreceptors and where are they found?
- Rods - peripheral parts of the retina
- cones - closely packed together in the fovea
Are rods very sensitive?
Yes - Rods are very sensitive to light and work well in dim settings
This is beacuse many rods join to one neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential.
Are cones very sensitive?
No - Cones are less sensitive than rods beause one cone joins to one neurone. This means it takes more light to reach the threshold and trigger the action potential.
Do rods have high visual acutity?
No - Rods give low visual acuity because many rods join to the same neurone which means light from two points close together cannot be told apart.
Do cones have high visual acuity?
Yes - Cones give high visual acuity beacuse cones are close together and one cone joins one neurone.
Produces multiple different impulses to brain
Step 1 - Stimulus- Pacinian corpuscle
A stimulus excites the neurone cell membrane causing stretch mediated sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ions electrochemical gradient. This makes the inside of the neurone less negative.
Step 2 - Depolarisation
If the potential difference reaches the threshold (around -55mV), more voltage gated sodium channels open. More sodium ions diffuse rapidly into the neurone.
Step 3 - Repolarisation
At a potential difference of around +33 mV the sodium ion channels close and the voltage gated potassium channels open.
The membrane is more permeable to potassium ions so potassium ions diffuse out of the neuron down their concentration gradient.
Step 4 - Hyperpolarisation
Potassium ion channels are slow to close.
This means there is a slight overshoot where too many potassium ions diffuse out the neurone.
The potential difference becomes more negative than the resting potential (< -70mV)
Step 4 - Hyperpolarisation
Potassium ion channels are slow to close.
This means there is a slight overshoot where too many potassium ions diffuse out the neurone.
The potential difference becomes more negative than the resting potential (< -70mV)
Step 5 - Resting potential
The voltage-gated ion channels are closed.
Sodium potassium pump pumps sodium out and potassium in in the ratio 3:2
Potassium ion channels open so potassium diffuses back out of membrane down electrochemical gradient
Wave of depolarisation steps
- When an action potential occurs, come of the sodium ions that enter the neurone diffuse sideways
- This causes sodium ion channels in the next region to open and sodium ions diffuse into that part
- This causes a wave of depolarisation to travel along the neurone
What is the refactory period?
It is a time delay between action potentials where ion channels are recovering and cant be opened.
Why is the refactory period important?
- Action potenials dont overlap - pass on discrete impulses
- There is a limit to the frequency at which nerve impulses can be transmitted
- Action potentials are unidirectional
All or nothing theory for action potentials
- Once the threshold is reached an action potential will always fire with the same change in voltage, no matter how big the stimulus is.
- A bigger stimulus won’t cause a bigger action potenial but will cause them to fire more frequently.
What 3 factors affect the speed of conducation of action potentials?
- Myelination
- Axon diameter
- Temperature
How does temperature affect the speed of conducation of action potentials?
- Diffusion occurs faster at higher temperatures, increasing the speed of conduction.
- Only increases up to around 40C, as proteins start to denature.
- If plasma membrane proteins and enzymes denature there is NO conduction!
How does myelination affect the speed of conduction of action potenials?
- The myelin sheath acts as an electrical insulator.
- Prevents action potentials in the part of the axon covered by the myelin.
- Action potential jumps from node to node (saltatory conduction). i.e. depolarisation is not required all the way along the axon.
- Increases speed of conduction.
How does the Axon diameter affect the speed of conduction of action potenials?
- The greater the diameter of an axon, the faster the speed of conductance.
- There is less resistance to the flow of ions in the cytoplasm of wider axons.
- Ions therefore reach other parts of the neurone faster.
What does myogenic mean?
It can contract and relax without receiving signals from nerves
What and where is the sinoatrial node?
- It is located in the right atrium and is like a pacemaker.
- It sets the rhythm of the heartbeat by sending out regular waves of electrical actvity.
It causes the right and left atria to contract at the same time.
What and where is the atrioventricular node?
- It is loacted near the border of the right and left ventricle but still within the artia.
- It is reposnsible for passing on waves of electrical activity on to the bundle of His.
(There is a slight delay beore the AVN reacts to make sure the atrira have emptied before the ventricles contract)
What and where is the bundle of His?
- Runs through the septum
- It is a group of muscle fibres responsible for conducting waves of electrical activity between the ventricles to the apex of the heart.
What and where is the purkyne tissue?
- In the walls of the ventricles
- It carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from the bottom up.
What is the medulla oblongata?
The medulla oblongata in the brain controls the heart rate, via the autonomic nervous system
What are the baroreceptors?
They are pressure receptors in the aorta and the carotid arteries. They’re stimulated by high and low blood pressure.
What does the refractory period ensure
Impulses don’t overlap
They travel in one direction
All or nothing principle
When a threshold is met an action potential fires
This is the same size regardless of the size of the stimulus
A larger stimulus will cause the action potential to fire more frequently
Factors which affect speed of an action potential transmission
Myelination
Axon diameter
Temperature
Transmission of an action potential across a synapse steps
- An action potential at the synaptic knob causes an increase in permeability to calcium
- Calcium diffuses in via voltage-gated calcium ion channels
- This causes synaptic vesicles to fuse with the presynaptic membrane releasing acetylcholine
- Acetylcholine binds to receptors on the postsynaptic membrane opening voltage-gated sodium ion channels
- The influx of ions causes depolarisation of the membrane
- If this reaches the threshold then an action potential is generated
- The acetylcholine is hydrolysed by acetyl cholinesterase on the postsynaptic membrane and the products are reabsorbed into the synaptic knob.
Key differences for neuromuscular junction
-They have more chemoreceptors for Ach
- THey have more wells containing ACh esterase
- Each impulse causes an action potential
Excitatory neurone
Depolarise the postsynaptic neurone
Use Ach
Inhibitory neurone
Hyperpolarise postsynaptic neurone
Use GABA
Spatial summation
Many to one (neurones)
Result bases on combination of neurones
Temporal summation
1 to 1
Result based on frequency of impulse
3 types of muscle
Smooth- Involuntary
Cardiac muscle- Involuntary
Skeletal (Striated)- Voluntary
What is the sarcolemma + role
The cell membrane
Allows transmission of impulse into sarcoplasmic reticulum
What is the sarcoplasm
The cell cytoplasm
Sarcoplasmic reticulum
Endoplasmic reticulum of muscle cells
Releases calcium ions- stimulating muscle contraction
Two types of myofilaments
Actin
Myosin
What do dark bands contain
Mainly myosin- some actin
What do light bands contain (I bands)
Just actin
What happens (each band) during contraction
A bands stay the same
I bands and H zones get shorter
Muscle contraction process
1- At rest, tropomyosin blocks myosin binding sites- actin cannot bind
2- Ca2+ is released binding to troponin causing tropomyosin to be moved out of the way
3- Actin binds to mysosin then releases ADP + Pi causing the myosin heads to change angle
4- Free ATP binds to myosin head changing its shape so the actinomyosin cross bridge is broken
5- ATP on the myson is hydrolysed causing myosin to return to its original position
6-The myosin binds to actin and the process repeats
Aerobic respiration advantages
- Lots of ATP produced overall
- Good for long periods of low intensity exercise
Advantages anaerobic respiration
- Rapid ATP production
- Lactate produced which causes fatigue
- Good for short periods of hard exercise
Phosphocreatine as an energy release
- ATP generated very quickly
- Runs out after a few seconds
Slow twitch muscle properties
Slow contraction
Fatigue slowly
Slow energy release
Rich in myoglobin
More, larger mitochondria
Smaller store of calcium ions in tubules
More blood capillaries
Fast twitch muscle properties
- Fast contraction
- Fatigue quickly
- Fast energy release
- Less rich in myoglobin
- Fewer smaller mitochondria
- Larger store of calcium ions in tubules
- Fewer blood capillaries around fibres
How IAA works
Steps of depolarisation of a Pacinian copuscle
No pressure- Excess of NA+ ions outside of Axon
Pressure is applied- Layers are distorted and stretch-mediated sodium ion channels to open
Sodium ions move in by facilitated diffusion
Generator potential established
The influx of sodium ions causes depolarisation of the membrane
If enough generator potential is established-IE threshold is met, an action potential will be generated.
Label structure of eye
Label myelinated neurone
Myogenic stimulation of the heart steps
SAN sends out a wave of excitation
Atria contract
AV node sends out a wave of excitation after a delay
Purkyne tissue conducts wave of excitation down the septum and to the apex
Ventricles contract from the apex
Genrating resting potential
3 Sodium ions pumped out of cell
2 potassium ions pumped in
Sodium ion channels open
Potassium ion channels closed
K+ diffuse out-
More positive outside cell
More negative inside
How to tell if something is a negative feedback mechanism
The level is brought back yo
How to tell if positive feedback mechanism
Effectors will amplify the change
Factors which affect blood glucose concerntration
Eating food containing carbohydrates
Falls after exercising
Response when blood glucose levels too high
Pancreas detects change in blood glucose levels
Beta cells are stimulated and release insulin into blood
Insulin increases permeability of muscle cells to glucose
It also increases glycogenesis and decreases glycogenolysis within the liver
Insulin also increases rate of respiration of glucose in muscles
Response when blood glucose levels too low
Alpha cells secrete glucagon
Liver stimulated to increase glycogenolysis
Enzymes are activated which stimulate gluconeogenesis
Glucagon also decreases rate of respiration of glucose in cells
Effect of adrenaline on blood glucose concerntration
Adrenaline binds to receptors on cell membrane of liver cells
Activates glycogenolysis
It inhibits glucogenesis
it activates glucagon secretion and inhibits insulin secretion
Second messenger model
Adrenaline/ Insulin/ Glucagon bind to cell surface receptors
This activates adenylate cyclase
This converts ATP into adenylate cyclase
This activates protein kinase which causes a chain reaction
How does insulin increase uptake of glucose into muscle cells
When insulin levels low, transporters are stored in vesicles inside cells
When insulin binds, it triggers movement of channel proteins to cell surface membrane
Glucose can be transported into the muscle by facilitated diffusion
Type 1 diabetes cause and treatment
Immunse system attacks B cells- no production of insulin
Treated by insulin therapy and controlling diet
Type 2 diabetes cause and treatment
- Insulin receptors on membrane of cell dont respond properly to insulin
- Treated by losing weight/ regular exercise
Glucose lowering medications/ Insulin therapy
Process of ultrafiltration
Afferent arteriole has larger lumen than efferent arteriole
This results in a high hydrostatic pressure of blood movig through bowmans capsule
The hydrostatic pressure forces out water and small ions
Large molecules such as proteins stay in blood
Adaptation of proximal convoluted tubule
Microvilli
Provide a large surface area for reabsorbtion of molecules
How are molecules reabsorbed in proximal convoluted tubule
They are absorbed via active transport
Urine contains…
Water and dissolved salts
Urea
Hormones and excess vitamins
Urine doesnt contain…
Protein and blood cells
Glucose as it is reabsorbed back into the blood
Process of reabsorbtion of water in loop of Henle
- Thick ascending limb is impermeable to water and sodium ions are pumped out by active transport- this creates a water potential gradient down the medulla
- Because of the lowered water potential- water moves out of the descending limb by osmosis into the medulla- to be absorbed by the capillary network
- Near bottom of ascending limb Na+ ions diffuse out into medulla- maintaining high Na+ concerntration at bottom of medulla
- These three steps massively decrease water potential in medulla- as a result, water moves out of the collecting duct by osmosis
Steps when dehydrated
- Water potential in blood drops
- Change is detecteed by osmoreceptors in hypothalamus
- Posterior pituitary gland is stimulated to release more ADH into blood
- More ADH means DCT and collecting duct become more permeable and absorb more water by osmosis
What is the name of the membrane in the glomerulus?
Basement membrane
Describe function of myelin sheath
Schwann cells are electrical conductors
Ions cannot move through
Depolarisation only occurs at nodes of ranvier
Increases speed of impulses due to saltatory conduction
Draw the Structure of sarcomere
ok
Which organ releases hormones involed in blood glucose regulation
Pancreas
Describe what happens during selective reabsorbtion
What detects low water potential in blood
Osmoreceptors in the hypothalamus
What secretes ADH
Pituitary gland
Advantages of second messenger model
Each molecule of hormone can produce lots of cAMP
These activate large numbers of enzymes
Blood glucose concerntration raised very quickly
Why is leaching less likely to occur with natural fertiliser
Made of organic matter
Must be decomposed by saprobionts
Less likely to be leached as it isnt released too quickly
