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)