Organisms respond to changes in their internal and external environments Flashcards
what is sensitivity
ability of a living organism to detect changes in the environment (stimuli), and respond appropriately to them. many of these are automatic, fast and innate. these are reflexes
the order of the reflex arc
stimulus - receptor - sensory neurone - cell body - synapse - relay neurone - motor neurone - effector (muscle/gland)
what is a tropism
a growth response in a plant. they are controlled by specific growth in factors e.g. auxins
phototropism
plant shoots are +ve trophic (grow towards light). the growth is controlled by the auxin-indoleacetic acid which is made in the shoot tip and moved down into the growing region of the shoot
how does phototropism work
Auxin moves to the dark side of the shoot. the auxin promotes growth by interfering with the hydrogen bonds in the cell wall. his makes the cellulose more flexible, allowing elongation and division of the cell
gravitropsim/ geotropism
roots are +ve gravitropic - they grow towards gravity. this is due to the presence of dense organelles called amyloplasts
how deos gravitropiam work
as amyloplasts move to the bottom of the roots, they take the IAA with them. In the roots, the IAA inhibits growth and division
define taxis
a directional movement response. a positive taxis, movement towards stimulus
define kinesis
a non-directional movement. the rate of movement and frequency of turns increases as the stimulus is less favourable
what is the Pacinian corpuscle
pressure receptor in the skin of mammals. it is a series of membranes (lamellae) around the end of an axon (nerve cell)
what are within the membranes of the Pacinian corpuscle
stretch-mediated channel protein, which opens when pressure is applied. this allows facilitated diffusion of the Na+ between the lamellae and into the axon
what does the movement of ions across the membrane change
the membrane potential or potential difference
the effect of the change in potential difference
If sufficient Na+ cross the membrane and create a big enough change in potential difference to pass a threshold. then, a generator potential is achieved and a nerve impulse (action potential) is produced.
what are the two types of photoreceptors in the retina
- cone cells
- rod cells
what do cone cells provide
colour vision with high visual acuity. however, they only function in higher light intensity
what are the three types of cone cells
- red sensitive
- blue sensitive
- green sensitive
what is the trichromate theory of colour vision
red, blue, green-sensitive cone cells detect and respond to different wavelengths of light. the combination gives us colour perception
what are rod cells
detect low light intensity but only provide black-and-white vision with low visual acuity
where do we get our highest visual acuity
our fovea only has cone cells and they connect to just one neurone which means that the brain knows exactly where on the retina the light is focused.
where do we get low visual acuity
in rod cells, as many rod cells connect to one neurone so our brain does not know exactly where the light is focused
what happens in low light intensity with rod cells
the generator potentials produced in rod cells can summate, enabling the threshold to be passed and an action potential produced
cells respiring
when cells respire they produce CO2, which diffuses into blood plasma where it forms a carbonic acid
H2O + CO2 <=> H2CO3
this reaction is catalysed by carbonic anhydrase
H2CO3 dissociates into
H+ and HCO3-. The H+ diffuse into red blood cells and binds to haemoglobin, making haemoglobinic acid. this breaks H and ionic bonds temporarily altering the tertiary structure of haemoglobin, forcing oxygen to dissociate from it - bohr effect
what are the two parts of the nervous system
central nervous system
- brain
- spinal cord
peripheral nervous system
- neurones
receptor
peripheral nervous system
- somatic (voluntary)
- autonomic (involuntary)
-sympathetic - fight & flight
-parasympathetic - rest and digest
chemoreceptors
detect changes in blood pH are found in the aorta, carotid artery and the medulla (brain)
what happens when blood pH falls
chemoreceptors generate more frequent action potentials, that go to the cardioregulatory centre in the medulla (brain). this sends more frequent action potentials along sympathetic nerves that release excitatory neurotransmitters onto the sino-atrial node, increasing heart rate
what happens when blood pH increases
chemoreceptors send less frequent action potentials to the cardioregulatory centre. this sends more frequent action potential along parasympathetic nerves, releasing inhibitory neurotransmitters onto the sino atrial node, decreasing heart rate
what are baroreceptors
these detect blood pressure in the aorta and medulla. when blood pressure is too high they slow the heart rate, and vice versa
features of motor neurone
- dendrites
- nucleus
- cell body
- Schwann cells
- axon
- myelin sheath
- node of Ranvier
- motor end plate
what is a resting potential
when a neurone is “at rest” and is not transmitting an action potential
the resting potential for all neurones
- NA+/K+ pump actively transports 3x Na+ out of the axon while actively transporting 2x K+ into it.
- membrane is differentially permeable - no Na+ channels are open, K+ channels are. K+ moves by facilitated diffusion out of the axon
- there are more +Ve ions outside the cells, than inside. this has a membrane potential of -70Mv
the action potential
- due to a stimulus, Na+ channels opens. Na+ moves by facilitated diffusion into the axon. the bigger the stimulus the more channels open
what happens when the threshold is met in an action potential (describing the graph)
- many more voltage-gated Na+ channels open, allowing Na+ into the axon by facilitated diffusion
- membrane is depolarized and the membrane potential is +40Mv (AP)
- Na+ channels close and K+ open. K+ moves out the axon by facilitated diffusion, repolarising the membrane
- K+ channels are slow to close, more K+ leaves the axon than necessary. membrane is hyperpolarised before the Na+/K+ pump can restore the resting potential - aka refractory period
what is the refractory period
the brief time of hyperpolarisation ensures that the action potential remains discreet and unidirectional
The all-or-nothing principle
this states that an action potential is approximately 40mV, it doesn’t change according to the strength of the stimulus
effect of a stronger stimulus
stronger stimulus will generate a higher frequency of action potential, than a weaker stimulus
what is the speed of conduction of an impulse
refers to how quickly the impulse is transmitted along a neurone
What factors are the speed of conduction affected by
- presence/ absence of myelin sheath (acts as insulation)
- diameter of the axon
- Temperature
speed of conduction in unmyelinated neurones
the speed of conduction is very slow, as depolarisation must occur along the whole membrane of the axon
why the speed of conduction is faster in myelinated neurones
myelin increases the speed which action potentials travel:
- myelin sheath is formed from Schwann cells
- parts of the axon that are surrounded by myelin sheath, depolarisation and action potentials can’t occur, as myelin sheath stops the diffusion of Na+ and K+
- Action potentials only occur at the nodes of Ranvier (small uninsulated sections of the axon)
how are the nodes of ranvier involved in the speed of action potential
- local circuits of current that trigger depolarization in the next section of the axon membrane exist between the nodes of Ranvier
- Schwann cells means action potentials ‘jump’ from one node to the next (aka saltatory conduction)
- Saltatory conduction allows the impulse to travel much faster (up to 50x) than in an unmyelinated axon
the different nodes involved in myelination
- node at refractory period
- node at action potential
- node becomes depolarised
- node at resting potential
node at refractory period
- membrane becoming repolarised
- Na+ channel proteins closed
- K+ channel proteins open
node at action potential
- membrane fully repolarised (+30mV)
- all Na+ channel proteins open
- K+ channel proteins closed
node becoming depolarised
- membrane potential moving towards threshold level
- Na+ channels starting to open but many are still closed
- K+ channel proteins closed
node at resting potential
- membrane potentia aournd -70mV
- Na+ channel proteins closed
- K+ channel proteins closed
diameter effect on the conduction of speed
impulse will be conducted at a higher speed along neurones with thicker axons than with thinner axons
reasons why thicker axons have a high speed of conductions
- Thicker axon membrane has a greater surface area, which the diffusion of ions can occur
- increases the rate of diffusion of Na+ and K+ through protein channels, which increases the rate that depolarisation and action potentials occur
- also have a greater volume of cytoplasm (contains ions). This reduces their electrical resistance so action potentials push into the next section faster
temperature
as temperature increases so does the kinetic energy, increasing the rate of facilatated diffusion of K+ and Na+ during an action potential
features of cholinergic synapse
- pre-synaptic knob
- axon
- Ca2+ carrier proteins
- vesicles with acetycholine
- synaptic cleft
- acetycholine receptors
- post synaptic membrane
The cholinergic synapse
Transmission of action potential
- action potential arrives at the synaptic knob and opens Ca2+ channels
- Ca2+ moves by facilitated diffusion into the synaptic knob
- Ca2+ stimulates vesicle to move to the membrane, fuse and release acetylcholine (ACH) by exocytosis
- ACH diffuses across the synaptic cleft, it binds to specific complimentary receptors
- Receptors are part of ligand-gated Na+ channels that open when ACH binds
- Na+ enters the post-synaptic neurone by facilitated diffusion, depolarising the membrane
the cholinergic synapse
how the membrane is repolarised
- ACH is hydrolysed by acetylcholinesterase into acetate and choline
- acetate and choline are actively transported back into the pre-synaptic knob and reformed into ACH
- Ca2+ in the synaptic knob is actively transported out
what do synapses do
Synapses allow control of the nervous system and can form in several different arrangements
spacial summation
where all presynaptic knobs release ACH together is the threshold passed post synaptic membrane.
e.g. rod cells in the eyes
temporal summation
These synapses only trigger an action potential on the post synaptic membrane if the frequency of action potential is high enough in the presynaptic knob.
e.g. in cone cells
What are the 3 main muscle types
- striated/ skeletal
- cardiac - myogenic
- smooth - autonomic
Neuromuscular junction features
- motor neurone
- sarcolemma
- synaptic knob
- trasnverse tubules
- sarcoplasmic reticulum
What is a striated muscle
makes up the muscles in the body that are attached to the skeleton. it is made up of muscle fibre
Different names of the muscle fibres to the equivalent parts of a normal cell:
- Cell surface membrane
- Cytoplasm
- Endoplasmic reticulum
Cell surface membrane = sarcolemma
Cytoplasm = sarcoplasm
Endoplasmic reticulum = sarcoplasmic reticulum (SR)
The sarcolemma features
- many deep tube-like projections that fold in from its outer surface these are transverse system tubules or T-tubules
- they run close to the SR
Muscle fibres structure
- organised arrangment on contractile portions in the cytoplasm
- surrounds by a cell surface membrane
- contian many nuclei
what are Myofibrils
They are located in the sarcoplasm. each myofibril is made up of two types of protein filament
- thick filaments made of mysoin
- thin filamesn made of acton
part of myofibril
H band
only thick myosin filaments present
Sarcoplasmic reticulum contians
it stores calcium ions
part of myofibril
I band
only thin actin filaments present
part of myofibril
A band
contains areas where only myosin filaments are present and areas where myosin and actin filaments overlap
part of myofibril
M line
attachment for myosin filaments
part of myofibril
Z line
attachment for actin filaments
part of myofibril
sacromere
the section of myofibril between two z lines
sliding-filament of theory
- Tropomyosin protein is wrapped around the actin, blocking myosin binding sites
- Ca2+ is released from SR, changing the shape of tropomyosin, reveals binding sites
- The myosin head an ADP and Pi attached to it
- This is released when it binds to the actin, forming an actin myosin cross bridge
sliding-filament of theory
2
- myosin head changes shape, pulling the actin along - power stroke
- ATP binds, allowing the myosin head to detach from the actin
- Myosin head contains ATPase - this hydrolyses the ATP into ADP + Pi. The energy released is used to rest the myosin and head - recovery stroke
sliding - filament of theory
3
- sarcomere, H zone, I band shortens. A band stays the same size
- Ca2+ are actively transported back to the SR, and the muscle relaxes
the phosphocreatine system (PCR)
This utilities phosphocreatine to quickly phosphorylate ADP into ATP
ADP + PCR -> ATP + creatine
fast muscle fibres features
- short contraction- relaxation cycle
- Fewer capillaries
- ATP is supplied mostly from anaerobic respiration
Fewer, smaller mitochondria present - large store of Ca2+ in sarcoplasmic reticulum
- large amount of glycogen and phosphocreatine present
- faster rate of ATP hydrolysis in mysoin heads
- Fatigue rapidly due to greater lactate formation
Slow muscle fibres features
- long contraction-relaxation cycle
- denser network of capillaries
- ATP supplied from aerobic respiration
- many large mitochondria present
- small store of Ca2+ in sarcosplasmic reticulum
- small amounts of glycogen present
- Slower rate of ATP hydrolysis in myosin heads
- Faitgues more slowly due to reduced lactate formation
what does homeostasis use
Physiological control system to maintain the internal environment between restricted limits
what is negative feedback
when a stimulus causes a response that reverses the effect of the stimulus
what is positive feedback
when a stimulus causes a response that exaggerates the effect of the stimulus
process of blood glucose increasing
pancrease relelases insulin. beta cells in the islets of Langerhans produce insulin and release it into the bloodstream- endocrine function. Insulin binds to complementary receptors on muscle and liver cells. This stimulates the addition of more GLUT-4 (glucose transporter proteins) into the plasma membrane. This allows facilitated diffusion of glucose into muscles and liver cells. To maintain the conc gradient, the insulin stimulates glycogensis (glucose-forming glycogen)
process of blood glucose decreasing
Alpha cells of the islets of Langerhans release glucagon. Glucagon binds to the complimentary receptors on the liver cells, stimulating glyocgenolysis (glycogen to glucose) and gluconeogenesis (amino acids & lipids to glucose)
the second messenger model
(Adrenaline works similarly to glucagon as it increases blood glucose levels)
Adrenaline binds to complimentary receptors on liver cells, it activates an enzyme called adenylate cyclase. This enzyme catalyses the hydrolysis of ATP into cAMP (cyclic adenosine monophosphate). The cAMP is the second messenger. It activates the enzyme protein Kinase A, which stimulates glycogneolysis
Type 1 diabetes
what is it?
treatment?
different types of insulin?
- when the pancreas fails to produce sufficient insulin to control blood glucose levels
- treated with blood tests, insulin injections after meals and a diabetes appropriate diet
- The insulin used by diabetics can be fast-acting or slow-acting, allowing for a different level of control
Type 2 diabetes
- pancreas produces insulin but receptors have reduced in number or no longer respond to it. This occurs in the liver and fat storage tissues
- this leads to an uncontrolled high blood glucose concentration
- β cells produce larger amounts of insulin which damages them
- a sugar and fat-controlled diet and exercise are sufficient treatments
- Obesity is a major risk factor
Diabetes and blood pressure
- high blood glucose concentration lowers the water potential of the blood. more water moves from tissues into blood vessels by osmosis
- theres a larger volume of blood within the circulatory system which causes blood pressure to increase
what is the kidney made of
many nephrons
The five features of the kidney that is involved in osmoregulation
- Renal capsule
- Proximal convoluted tubule
- loop of henle
- Distal convoluted tubules
- collecting duct
osmoregulation
1. renal capsule - ultrification
Blood arrives at the glomerulus (capillary bed) under relatively high pressure from the afferent arteriole. Pressure increases in the glomerulus. This leads to ultrafiltration. Large proteins, cells and some water remain in the blood, the dissolved glucose, amino acids, inos, urea, and most of the water is filtered through the basement membrane and the podyctyes of the renal capsule. this form filtrate
osmoregulation
2. Proximal convoluted tubules - selective reabsorption
In the PCT, all of the glucose and amino acids are reabsorbed into the blood by active transport. some ions are reabsorbed by facilitated diffusion, some by active transport depending on the needs of the body. Some water is reabsorbed by osmosis.
osmoregulation
3. loop of Henle
Water is recovered into the medulla (then the blood) from the descending limb of the loop of Henle. The further into the medulla you go, the more concentrated the salt solution, so the water potential lowers, maintaining a water potential gradient. The ascending limb is impermeable to water, but Na+ are actively transported out into the medulla, helping to maintain the water potential gradient
osmoregulation
4. Distal convoluted tubules
in the DCT, the ion balance of the body is restored. any inos that the body is deficient in are recovered back into the blood by active transport.
osmoregulation
5. collecting duct
The urine in the collecting duct passes on more through the medulla. if the body needs to recover more water from the urine, it will occur here. Dehydration is detected by osmroeceptros in the hypothalamus, and the response is the release of ADH (anti-diuretic hormone). ADH stimulates the addition of aquaporins (channel proteins for water) to the collecting duct. This will allow the reuptake of more water and result in a smaller volume of concentrated urine
