Stimuli and response- BP Flashcards
What is a Stimuli?
a change in the internal or external environment
Why do Organisms need to Respond to Stimuli?
for survival (predator/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 favourable area where they move slowly and less randomly
so 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, away = negative
light = photo, water = hydro, gravity = geo
shoot shows positive phototropism and negative geotropism
root shows positive geotropism and positive hydrotropism
controlled by a Plant Growth Factor = Indoleacetic Acid (IAA) - auxin
What is a Plant Growth Factor?
equivalent to animal hormones
What are the affects of IAA?
- promotes growth in the shoot
- inhibits growth in the root
How does positive phototropism in the shoot take place?
normally: shoot tip produces IAA, sending it down both sides causing the shoot to grow forwards
if light is present on one side, the IAA redistributes to the opposite side (shaded side)
this causes the opposite side to grow faster
so the shoot bends towards the light
How does negative geotropism in the shoot take place?
if gravity is present on one side, the IAA redistributes to the same side
this causes the same side to grow faster
so the shoot bends away from gravity towards the light
How does positive geotropism/hydrotropism in the root take place?
if gravity/water is present on one side, the IAA redistributes to the same side
this causes the same side to grow slowly, so the opposite side grows faster
so the root bends towards the gravity/water
Evidences for Tropism (positive phototropism in shoot)?
- removing or covering shoot tip prevents tropism [tip causes tropism]
- placing micin (prevents movement of chemicals e.g. IAA) across shoot inhibits tropism [tropism caused by movement of chemicals]
- placing gelatine (prevents movement of electrical signals) across shoot does not affect tropism [tropism not caused by movement of electrical signals]
- if shoot tip is moved to one side, that side grows faster and the shoot bends the other way [IAA promotes growth in shoot]
- when in light or darkness the overall levels of IAA remain the same [light does not inhibit or breakdown IAA but rather redistributes it]
Response to Stimuli in Mammals?
uses Nervous System, Hormonal System (nervous and hormonal systems coordinate response to stimuli)
Job of Nervous System?
- coordinate response to certain stimuli
- response is fast, short acting, localised
Pathway of Nervous System?
stimuli to receptor to sensory neurone to spinal cord to brain to spinal cord to motor neurone to effector for response
What does a Receptor do?
detects stimuli & converts stimuli energy into nerve impulse (acts as a transducer – converts one type of energy into another)
each type of stimuli has a specific receptor
uses stimuli energy to send Na+ ions into the start of the sensory neurone
2 examples of receptors: Pacinian Corpuscle, Retina of Eye
What does a Pacinian Corpuscle do?
touch receptor
found in skin, fingers and toes
responds to pressure/touch
How does the Retina of the Eye work?
detects light so the brain can generate an image
detected by retina (located at back of eye)
made of Cone and Rod cells
Properties of Cone Cells in Retina?
made of Iodopsin Pirgment which is only broken down at high light intensity
one cone cell connects to one bipolar neurone which connects to one sensory neurone (therefore no summation of light can take place so only detects high light intensity)
but because one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli can be distinguished = high visual acuity
Properties of Rod Cells in Retina?
made of Rhodopsin Pigment which can be broken down at low light intensity
a few rod cells connect to one bipolar neurone which connects to one sensory neurone (therefore summation of light can take place so can detect low light intensity)
but because a few rod cells connect to one bipolar neurone which connects to one sensory neurone, the stimuli will be merged together = low visual acuity
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
a neurone transmits a nerve impulse
sensory neurone takes nerve impulse from receptor to CNS
motor neurone takes nerve impulse from CNS to effector
sensory neurone has its cell body in the middle and has a dendron and axon
motor neurone has its cell body at the start and only has a long axon
What are the 2 different types of Motor Neurone?
Voluntary (Somatic) and Involuntary (Autonomic) Motor Neurones
Somatic supplies skeletal muscle = under conscious control
Autonomic supplies cardiac muscle, smooth muscle, glands = under subconscious control
Autonomic can be divided into Sympathetic and Parasympathetic (have opposite effects)
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, 2 K+ ions in
K+ channel allowing K+ ions to diffuse out
(K+ ions 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)
the membrane potential reaches +40mV
then the Na+ channels close, the 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 (the 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 threshold and an AP to occur
- this process continues along the neurone
- an AP will always move along the neurone to the end
why does AP not move back?
- previous section has just finished an AP
- therefore it is in refractory period
- Na+ channels cannot be opened
- it is hyperpolarised
- therefore threshold cannot be reached
How does the Size of Stimuli affect a Nerve Impulse?
- does not affect size of AP (AP is all or nothing
- reach threshold = get AP [all]
- do not reach threshold = no AP [nothing])
- larger stimuli increases the frequency (number) of APs
What affects Speed of Nerve Impulse?
- temperature = higher temp, higher kinetic energy, faster rate of diffusion of ions (faster nerve impulse)
- axon diameter = wider diameter, neurone less leaky (faster nerve impulse)
- myelination = schwann cells wrap around axon, insulates axon preventing AP, therefore AP only occurs in gaps – called node of ranvier, so AP jumps from node to node = saltatory conduction (faster nerve impulse)
What is a Synapse?
connection between 2 different neurones
sends nerve impulse across the gap (synaptic cleft) using neurotransmitters (e.g. acetylcholine)
What are the Properties of Synapses?
- unidirectionality = AP/nerve impulse travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors
- filters out low level stimuli = low level stimuli do not release enough neurotransmitter, therefore not enough Na+ ion channels open, therefore not enough Na+ ions enter postsynaptic neurone for threshold to be reached, therefore no AP produced
- summation = low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, can be temporal or spatial
- inhibitory = normal synapses are excitatory (cause AP), some can be inhibitory – prevent action potential from occurring by making postsynaptic neurone hyperpolarised
what are the two types of summation?
temporal
spatial
What is a Reflex?
- a rapid involuntary response to a stimuli
- does not use the brain
- the sensory neurone connects directly to motor neurone
(stimuli to receptor to sensory neurone to relay neurone to motor neurone to effector for response) - ensures less damage done and does not require learning
How is Heart Rate controlled?
the heart is myogenic, its heart beat is initiated by the SAN
the 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 sympathetic nerves to SAN to increase HR and sends impulse in parasympathetic nerves to SAN to decrease HR
How does Exercise affect Heart Rate?
exercise = muscle contraction, which requires respiration
therefore, waste product CO2 is released into blood
this lower pH of blood (acidic)
this is detected by chemoreceptors in carotid arteries
sends impulses to medulla oblongata
then medulla oblongata sends impulses 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, 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)
how does a synapse transmit nerve impulses between 2 neurones?
AP arrives in end of presynaptic neurone
Ca2+ channels open
Ca2+ ions enter presynaptic neurone
causes vesicles containing neurotransmitter to move to presynaptic membrane
vesicle binds to membrane releasing neurotransmitter into cleft
neurotransmitter diffuses across cleft
binds to complementary receptors on postsynaptic membrane
Na+ channels open, Na+ ions enter
if threshold is reached, AP occurs
structure of pacinian corpuscule?
structure = corpuscle (several layers of tissue) wrapped around the start of a sensory neurone
process of pacinian corpuscle?
- pressure applied
- corpuscle compressed
- stretch-mediated Na+ channels opened
- Na+ ions move into the start of the sensory neurone
cone vs rod cells?
Cone Cells detect high light intensity only, produces colour image, with high visual acuity
Rod Cells can detect low light intensity, produces black and white image, with low visual acuity
Cone Cells located in centre of retina (fovea) – site of high light intensity
Rod Cells located in periphery of retina
how does synapse 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 vesicle and actively transport Ca2+ ions out
difference between plant growth factor and human hormone?
- made by cells throughout the plant
- only affects cells locally
- affects growth
what is spatial summation?
a low level stimuli from a few presynaptic neurones add together
what is temporal summation?
low level stimuli present for extended period of time
what are the 3 main purposes of a refractory period?
- AP propagated in one direction only
- impulses produced are discrete
- limits the number of action potentials
saltatory conduction?
propagation of a nerve impulse along myelinated axon in which the AP jumps from one node of ranvier to another
