Module 6: Response to Stimuli Flashcards
stimuli definition
a change in the internal or external environment
why do organisms need to respond to stimuli
for survival
- predators
- prey awareness
- homeostasis
how do simple organisms respond to stimuli
taxis and kinesis
what is taxis?
directional response to a stimuli
-towards or away from
what is kinesis?
non-directional movement from an unfavourable area to a favourable area
organism moves rapidly and randomly in unfavourable area until they reach the favourable area where they move slowly and less randomly
spends more time in favourable area, less time in unfavourable area
example of response to stimuli in plants
tropism
what is tropism?
directional growth in plants in response to a stimuli towards= positive and away=negative light=photo, water=hydro, gravity=geo shoots show positive photo roots show positive hydro and geo controlled by IAA
what controls tropisms?
Indoleacetic Acid (IAA) example of an auxin
what does IAA stand for?
Indoleacetic Acid
what is a plant growth factor?
equivalent to animal hormones
difference: made by cells throughout the plant, only affects cells locally, affects growth
effects of IAA?
promotes growth in the shoot
inhibits growth in the root
how does positive phototropism in the shoot take place?
normally the shoot tip produces IAA, sending it down both sides of the plant, causes shoot to grow forwards
if light is present on one side the IAA will redistribute to the shaded side
causes the shaded side to grow faster
shoot bends towards the light
how does negative geotropism in the shoot take place?
if gravity is present on one side, IAA will redistribute to the same side
causes the same side to grow faster
shoot will bend away from gravity and towards the light
how does positive geotropism/hydrotropism in the root take place?
if gravity/water is present on one side, IAA will redistribute to the same side
causes the same side to grow slowly, opposite side grows faster
so the root bends towards the gravity/water
evidence for tropism (positive phototropism in the shoot)
removing/covering the shoot tip prevents tropism (tip causes tropism)
placing micin which prevents movement of chemicals inhibits tropism (tropism caused by movement of chemicals)
placing gelatine which prevents movement of electrical signals doesn’t effect tropism (not affected by electrical signals)
if shoot tip is moved to one side that side grows faster and shoot bends the other way (IAA promotes growth in the shoot)
when in light/darkness the overall levels of IAA remain the same (light doesn’t break down or inhibit IAA but redistributes it)
response to stimuli in mammals?
uses nervous system and hormonal system to coordinate response to stimuli
job of the nervous system?
coordinate response to certain stimuli
response is fast, short-acting and localised
pathway of the nervous system
stimuli receptor sensory spinal cord brain spinal cord motor neurone effector response
role of a receptor
detects stimuli
coverts stimuli energy into nerve impulse
acts as a transducer by converting one type of energy into another
each stimuli has specific receptor
uses stimuli energy to send Na+ ions into the start of the sensory neurone
examples of receptors
Pacinian corpuscle
Retina of the eye
Pacinian corpuscle role
touch receptor that responds to pressure
found in skin, fingers and toes
apply pressure, corpuscle is compressed, stretch-mediated Na+ channels are opened, Na+ ions move into the start of the sensory neurone q
structure of the pacinian corpuscle
layers of connective tissue (lamellae) blood capillary to increase O2 supply neurone ending viscous gel for protection and to determine pressure intensities sensory neurone capsule for protection
how does the retina of the eye work
retina detects light so the brain can generate an image, made of rod and cone cells
cone cells
iodopsin pigment which is only broken down at high light intensities (3 different pigments: green,red,blue)
produces a coloured image
one cone cell connects to one bipolar neurone which connects to one sensory neurone (no retinal convergence)
as one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli is detected therefore high visual acuity
where are rod cells most numerous
everywhere except fovea
located in periphery of the retina
where are cone cells most numerous
fovea
20:1 ratio
where light intensity is the highest
rod cells
rhodopsin pigment which is broken down at low light intensities
a few rod cells connect to one bipolar neurone which connects to one sensor neurone
retinal convergence can occur so can detect low light intensity
a few rod cells per bipolar neurone per sensory neurone the stimuli are merged together therefore low visual acuity
what is retinal convergence
additive effect of low light intensities
what is the central nervous system CNS
made of brain and spinal cord
brain= analyses and coordinates response to stimuli
spinal cord= connects brain to sensory and motor neurones
what is the peripheral nervous system PNS
made of the sensory and motor neurone
neurone transmits nerve impulse
sensory takes nerve impulse from receptor to CNS
motor neurone takes nerve impulse from CNS to effector
sensory has cell body in middle and dendron and axon
motor has cell body at the start and only has a long axon
2 types of motor neurone
voluntary- somatic
involuntary-autonomic
somatic motor neurone
supplies to skeletal muscle
under conscious control
autonomic motor neurone
supplies to cardiac muscle, smooth muscle,glands
under subconscious control
what can autonomic motor neurones be divided into?
sympathetic and parasympathetic
how does the pacinian corpuscle respond to pressure
pressure is applied PC changes shape causes the membrane to stretch the stretch-mediated sodium channels widen Na+ ions diffuse in generator potential is established
intensity of pressure on pacinian corpuscle
if you increase the frequency of stimulus, increases frerquency of nerve impulse
maintained stimulus doesn’t generate multiple impulses
intermittent stimuli will generate multiple responses
what controls your heart beat
sinoatrial node (SAN) atrioventricular node (AV)
heart beat regulation process
- Electrical impulse from SAN spreads across atria, it contracts
- Atrioventricular septum is non-conductive tissue so stops this impulse travelling to ventricles
- Electrical activity travels to AV node
- Pause and wait for ventricles to fill
- AV sends impulse down bundle of His
- Bundle of His conducts impulse through AV septum to bottom of ventricle
- Smaller Purkinje fibres continue throughout ventricle walls, ventricles contract from base up
importance of purkinje fibres
smaller branching network which sends nerve impulse to cells in ventricles of heart
examples of things controlled by sympathetic nervous system
primary role is to stimulate fight/flight
heightens awareness, stimulates effectors, helps to cope with stress
examples of things controlled by parasympathetic nervous system
primary role is to rest and digest
state of relaxation, conserving energy, inhibits effectors to slow activity
What is a nerve impulse
Movement of an action potential along a neurone
Action potential= change in membrane potential (charge’ in one section of the neurone)
Changes from negative (polarised) to positive (depolarised) back to negative (repolarised/hyperpolarised)
What is resting potential
Membrane potential of neurone at rest
Is -65mV
Polarised
Caused by having more positive ions outside neurone compared to inside
Involves Na+/K+ pump, pumping 3 Na+ ions out and 2K+ ions in
K+ channel allowing K+ ions to diffuse out (K+ will eventually stop diffusing out due to a positive potential outside)
What happens during an action potential
Stimuli causes Na+ ions to enter the start of the neurone
Makes membrane potential less negative
If it reaches threshold (-50mV), Na+ channels open
Therefore more Na+ ions diffuse into the neurone, therefore membrane potential becomes positive (depolarised)
Membrane potential reaches +40mV
Then the Na+ channels close, K+ channels open
Therefore K+ ions diffuse out, therefore membrane potential becomes negative (repolarised)
Too many K+ ions move out so the membrane potential becomes more negative than Normal (hyperpolarised)
One action potential= depolarisation, repolarisation, hyperpolarisation
How does an action potential move along a neurone
By local currents
If the stimuli energy is large enough and enough Na+ ions enter the start of the neurone, threshold will be reached and an AP will occur (1st AP is called a generator potential)
Na+ ions that move in during depolarisation of the generator potential diffuse along the neurone causing the next section to reach the threshold and an AP to occur
Process continues along the neurone
Why does an action potential not move back ?
Because previous section has jus finished an action potential
It is in the refractory period (Na+ channels can’t be opened) and is hyperpolarised (therefore threshold can’t be reached)
How does the size of the stimuli affect a nerve impulse
Doesn’t affect the size of the action potential (AP is all or nothing, react threshold then get AP, doesn’t reach then no AP)
Larger stimuli increases the frequency of APs
What affects the speed of a nerve impulse
Temperature
Axon diameter
Myelination
How does temperature affect the speed of a nerve impulse
Higher temp
Higher kinetic energy
Faster rate of diffusion of ions
Faster nerve impulse
How does axon diameter affect the speed of a nerve impulse
Wider diameter
Nerueone less leaky
Faster nerve impulse
How does myelination affect the speed of a nerve impulse
Schwann cells wrap around the axon Insulates axon preventing AP AP only occurs in gaps Called node of ran viler So AP jumps from node to node= saltatory conduction (faster nerve impulse)
What is a synapse
Connection between 2 different neurons
Sends nerve impulses across the synaptic cleft using neurotransmitters (acetylcholine)
AP arrives in the end of the presynaptic neurone
Ca2+ channels open
Ca2+ ions enter presynaptic neurone
Cause vesicles containing neurotransmitter to move to presynaptic membrane
Vesicles binds to membrane releasing neurotransmitter into cleft
Neurotransmitter diffuses across the cleft
Binds to the complementary receptors on postsynaptic membrane
Na+ channels open, Na+ ions enter
If threshold is reached then action potential occurs
Synapse, how does AP return to rest
Enzyme used to breakdown neurotransmitter e.g. acetylcholinesterase breaks down acetylcholine into ethanoic acid and choline, diffuses back into presynaptic neurone, ATP used to reform neurotransmitter into vesicles and actively transport Ca2+ ions out
What are the properties of synapses
Unidirectionality
Filters out low level stimuli
Summation
Inhibitory
Unidirectionality of synapses
AP/nerve impulses travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors
Filters out low level stimuli (synapses)
Low level stimuli don’t release enough neurotransmitter, not enough Na+ ion channels open, not enough Na+ ions enter postsynaptic neurone for threshold to be reached, no AP produced
Summation (synapses)
Low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, temporal or spatial
Temporal
Low level stimuli present for an extended period of time
Spatial
Low level stimuli from a presynaptic neurone add together
Inhibitory
Normal synapses are excitatory (cause AP), some can be inhibitory- prevent action potential from occurring by making postsynaptic neurone hyperpolarised
What is a reflex
Rapid involuntary response to a stimuli
Doesn’t use the brain
Sensory connected to the motor neurone to intermediate to effector for response
Less damage is done and doesn’t require learning
How is heart rate controlled
Heart is myotonic, heart beat is initiated by the SAN
Medulla oblongata in the brain can increase or decrease heart rate
Receives nerve impulse from chemoreceptors (respond to blood pH) in the carotid arteries and pressure receptors (respond to blood pressure) in the carotid arteries and aorta
Sends impulse in the sympathetic nerves to SAN to increase HR and send impulse in parasympathetic nerves to SAN to decrease HR
How does exercise affect heart rate
Exercise= muscle contractions, require respiration
Waste product CO2 released into blood
Lower pH of blood (acidic)
Detected by chemoreceptors in carotid arteries
Sends impulses to medulla oblongata to SAN via the sympathetic nerves causing the heart rate to increase
Benefit= increase blood flow to lungs to remove CO2 and take in O2
How does low blood pressure affect heart rate
If a person moves from lying/sitting to standing the blood pressure falls (reducing blood flow to the brain)
This is detected by pressure receptors in the carotid arteries and aorta
Sends impulses to medulla oblongata
Then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase
Benefit= increasing heart rate leads to an increase in blood pressure (so enough blood can reach the brain)
Different types of muscles
Skeletal
Smooth
Cardiac
Role of skeletal muscle
Moves the body skeleton
When muscle contracts (shortens)
Tendons pulls on joints causing movement
Structure of skeletal muscle
Basic structure- sarcomeres Many sarcomeres-myofibril Many myofibrils-muscle fiber Many muscle fibres- bundle Many bundles-whole muscle
Sarcomeres
Made up of actin and myosin
When sarcomere contracts the whole muscle contracts/shortens by sliding filament mechanism
Actin
Thin
Tropomyosin wrapped around it
Myosin
Thick
Has heads
Muscle fibre
Surrounded by a membrane called sarcolemma
Contains myofibrils, fluid called sarcoplasm and tubes called sarcoplasmic reticulum
Locations in a sarcomere
A band= location of myosin [no change in contraction]
I band= location between the myosin [shortens in contraction]
H zone= location between the actin [shortens in contraction]
Z line= end line of sarcomere [moves closer together in contraction]
What occurs in sliding filament mechanism
How the sarcomere shortens
Myosin head pulls actin inwards
Somatic motor neurone connects to the skeletal muscle via a neuro-muscular junction
One motor neurone connects to a few muscle fibres=motor unit (benefit=simultaneous muscle contraction and can control strength of contraction/0
Releases acetylcholine that binds to complementary receptors on the muscle I really membrane (sarcomere)
Na+ channels open, Na+ ions enter the muscle fibre causing depolarisation
Wave of depolarisation travels through sarcoplasmic reticulum
Causes release of Ca2+ ions into the sarcoplasm
Moves tropomyosin on the actin
Exposes binding sites on the actin
Myosin heads now bind to the actin (forms actin-myosin cross bridge)
Power stroke occurs, myosin pulling the actin inwards
ATP attaches to myosin head so it detaches
ATP broke down by ATPase to release energy
Causes myosin head to go back to its original position
So it reattaches, pulling actin further inwards
Role of Ca2+ ions and ATP in muscle contraction
Ca2+ ions causes the tropomyosin to move exposing binding sites on actin
Ca2+ ions stimulate ATPase
ATP causes myosin head to detach
ATP releases energy so myosin head returns to original position
ATP actively transports Ca2+ ions back into sarcoplasmic reticulum when the muscle is relaxed
2 types of muscle fibres
Fast twitch and slow twitch
How do fast twitch muscle fibres work
Provide powerful but short lasting contractions
Found in biceps and sprinters
Adapted for anaerobic respiration
Has thicker myosin for powerful contractions
Contains more enzymes for anaerobic respiration
Contains phosphocreatine, provides phosphate to ADP to reform ATP
How do slow twitch muscle fibres work
Provide less powerful by long lasting contractions
Found in thigh muscles ad marathon runners
Adapted for aerobic respiration
Has a rich blood supply
Contains many mitochondria
Contains glycogen
Contains myoglobin (stores oxygen)
role of the hormonal system
coordinates response to certain stimuli
involves chemical messengers released by endocrine glands into the blood (exocrine glands release substances into open spaces)
protein hormones bind to complementary receptors on target cells, activates enzymes that convert ATP into cyclic AMP in the cell, cyclic AMP makes changes in the cell (2nd messenger system) e.g. insulin
lipid hormones enter cells by simple diffusion and cause direct changes e.g. oestrogen
control of blood glucose levels
if high= should be in cells for respiration, lowers blood water potential
if low=not enough to supply cells of the brain, also increases blood water potential
controlled by pancreas
contains islets of langerhans made of alpha and beta cells
alpha=glucagon production
beta= insulin production
high blood glucose levels
occurs after a meal
insulin is released
most cells in the body have complementary receptors
cause increase in glucose channels and carriers
glucose taken up and used in respiration
in muscle and liver cells, glucose converted into glycogen for storage (glycogenesis)
in liver cells glucose converted into fat
glycogenesis
glucose converted to glycogen for storage
low blood glucose levels
occurs after starvation or exercise
glucagon is released
only liver cells have complementary receptors
converts glycogen into glucose (glycogenolysis)
converts fats and amino acids into glucose (gluconeogenesis)
glucose released into the blood
glycogenolysis
converts glycogen into glucose
gluconeogenesis
converts fats and amino acids into glucose
diabetes
loss of control of blood glucose levels
normally high hyperglycaemia
2 types
symptoms= tiredness, increased urination, thirst
diagnosis of diabetes
high blood glucose levels on random testing and blood glucose levels remain high following a fasting blood glucose test
2 types of diabetes
type 1
type 2
type 1 diabetes
typically at a young age
person doesn’t make insulin
beta cells damaged by an autoimmune disorder
treatment=insulin injections
type 2 diabetes
typically at middle age
person makes insulin but the cells are less sensitive
caused by obesity and diet high in simple sugars
treatment= diet and exercise, drugs, insulin injection
homeostasis
maintenance of a constant internal environment (blood and tissue fluid) in animals
control: body temp, blood pH, blood glucose levels, blood water levels, blood salt levels, blood pressure
homeostasis and negative feedbac k
the response to change is to oppose the change to bring levels back to normal
body temp increases- response to bring back to normal
positive feedback
the response to change is to continue the change
e.g. Na+ ions entering a neurone stimulating more to enter in depolarisation
why do organisms need to maintain a constant body temperature
maintain optimum temp for enzyme activity
endotherms
animals that maintain a strict constant internal body temperature irrespective of external environmental temperature (mammals)
ectotherms
animals internal body temperature maintained more generally and varies with changes in external environment
benefits of being endotherm
can maintain activity over a range of settings
benefit of ectotherm
require less food/energy
how is internal body temperature controlled
anatomical,behavioural, physiological changes
endotherms mainly rely on physiological changes
ectotherms mainly rely on behavioural changes
anatomical adaptations in organisms in warm areas
small body size= large surface area to volume ratio (lose heat)
less fur
less fat
large extremities e.g. hands/ears/feet (lose heat)
anatomical adaptations in organisms in cold areas
large body size= small surface area to volume ratio
more fur
more fat
small extremities
control of body temperature in endotherms
controlled by hypothalamus in brain
receives nerve impulse from peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus
peripheral thermoreceptors monitor changes in the external environment temperature
central thermoreceptors monitor changes in core body temperature (blood supplying major organs)
how does an endotherm warm itself up
reduce blood flow to skin surface= vasoconstriction, smooth muscle in arterioles to skin contract, lumen narrows, less blood to skin surface, less heat lost form blood by radiation
hair on skin stand up= hair erector muscles contract, hair stands up, traps air particles, forms an insulating layer, reduces heat loss
shivering= involuntary contraction of muscle, friction in sliding filament mechanism generates heat and respiration generates heat
increased respiration in liver= generates heat
how does an endotherm cool down
increases blood supply to skin surface= vasodilation, smooth muscle in arterioles to skin relax, lumen widens, more blood to skin surface, more heat lost from blood by radiation
sweating= evaporation of water particles from skin surface using the heat in the blood
structure of kidneys
outer region= cortex
middle region= medulla
role of kidneys
filter blood
removes: urea, excess salts and water (combined=urine)
why remove urea
toxic waste product made from excess amino acids
why remove excess salts and water
maintain correct water potential and pressure in the blood
how do kidneys filter
made up of millions of nephrons
each nephron filters the blood producing urine
structure of nephron
1st= bowmans capsules 2nd= proximal convoluted tubule 3rd= loop of henles 4th= distal convoluted tubule 5th= collecting duct
bowmans capsule
start of nephron
site of ultrafiltration
occurs between specialised capillaries- Glomerulus and Bowmans capsule
glomerulus located in the middle of an arteriole
afferent arteriole before glomerulus is wide, efferent arteriole after glomerulus is narrow
build up of hydrostatic pressure in the glomerulus pushes fluid and small substances from the glomerulus into the bowmans capsule
small substances= glucose, amino acids, salt, urea
only small substances can pass through the 3 layers (endothelium of glomerulus, basement membrane, podocytes of bowmans capsule)
results in glomerular filtrate in bowmans capsule (water + salts/aminoacids/glucose/urea)
job of the rest of nephron is to send all the glucose/amino acids and some of the salts/water back into the blood (reabsorption)
proximal convoluted tubule
second part of nephron
site of selective reabsorption
all glucose/amino acids and some salts/water are sent back to blood (from lumen of PCT, through cells lining PCT, into the blood)
how:
salts (Na+) are actively transported from cells lining PCT into blood
lowers Na+ conc in the cells so Na+ diffuse from lumen of PCT into cells
as Na+ move they pull glucose and amino acids with them via co-transport
glucose and amino acids build up in the cell, then diffuse into the blood
movement of salt/glucose/amino acids lowers water potential in blood so water follows by osmosis
loop of henle
3rd part of nephron
site of further water reabsorption
occurs by hairpin countercurrent multiplier
how:
sodium and chloride ions are actively transported out of the ascending limb of the loop of henle into the surrounding medulla of the kidney
lowers water potential of the medulla
water moves out of the descending limb of loop of henle (and collecting duct) by osmosis in the medulla
water moves into the blood
sodium and chloride ions then diffuse into the descending limb of the loop of henles
so the above process can be repeated
distal convoluted tubule
4th part of nephron
site of further salt reabsorption
corrects required salt balance between blood ad urine
collecting duct
final part of nephron
site of further water reabsorption and osmoregulation
end up being left with urine that is sent into the ureter to the bladder
water reabsorption occurs by hairpin countercurrent multiplier
amount of water being reabsorbed is controlled at this stage (osmoregulation)
(learn what happens if water levels are low and high)
osmoregulation
process by which the hypothalamus controls water potential of the blood
if water levels become low (dehydration)
osmoreceptors in hypothalamus shrink
stimulates release of ADH form posterior part of the pituitary gland
ADH stimulates the cells lining the collecting duct to increase the number of aquaporins (water channels)
so more water moves from the collecting duct back into the blood
less water lost in urine
if water levels become high (overhydration)
less ADH released
less aquaporins in collecting duct
less water moves from collecting duct into the blood
more water lost in urine (reduces overhydration)
