Topic 6A - Stimuli and response ARN * Flashcards
nervous communication responses in plants and animals receptors control of heart rate
why do organisms respond to changes in their external environment?
they increase their chance of survival
e.g. avoiding harmful environments
what is a stimulus?
any change in internal or external environment
what do receptors do?
detect stimuli
they can be cells or proteins on cell surface membranes. there are loads of different types of receptors that detect different stimuli
what are effectors?
cells that bring about a response to a stimulus, to produce an effect.
effectors include muscle cells and cells found in glands
how do receptors interact with effectors?
receptors communicate with effectors via the nervous system or the hormonal system or both
what is the nervous system?
a complex network of cells called neurones
it coordinates responses to different stimuli
what are the 3 main types of neurone?
sensory neurones
motor neurones
relay neurones
what do sensory neurones do?
transmit electrical impulses from receptors to the CNS
what is the CNS?
the central nervous system - the brain and spinal cord
what do motor neurones do?
transmit electrical impulses from the CNS to effectors
what do the relay neurones do?
transmit electrical impulses between sensory neurones and motor neurones
what happens when a signal reaches the end of a neurone?
chemicals called neurotransmitters take the info across to the next neurone, which sends an electrical impulse
what happens at the CNS?
it processes the info and sends impulses along motor neurones to an effector
what is the chain of events in a nervous system?
stimulus receptors detect sensory neurone relay neurone in CNS motor neurone effectors response
electrical impulses are sent between each one
what is the peripheral nervous system?
made up of the neurones that connect the CNS to the rest of the body
made up of somatic and autonomic nervous system
what is the nervous system split into?
the CNS
the peripheral nervous system
what is the somatic nervous system?
it controls conscious activities
what is the autonomic nervous system?
it controls unconscious activities split into sympathetic and parasympathetic nervous system
what is the sympathetic nervous system?
it gets the body ready for action
the fight or flight system
what is the parasympathetic nervous system?
it clams the body down
the rest and digest system
what is a reflex?
where the body responds to a simulus without making a conscious decision to respond
why are simple reflexes good?
info travels fast from receptors to effectors. this helps organisms protect the body because they’re rapid
what is a reflex arc?
the pathway of neurone linking receptors to effectors in a reflex
why is a simple reflex arc simple?
it only involves 3 neurones
sensory, relay and motor
what does it mean if a relay neurone is involved in a simple reflex?
its possible to override the reflex
what properties does a reflex arc have?
localised
short-lived
rapid
what does it mean in the nervous system is localised?
when an electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto target cells
what does it mean the the nervous system is short lived?
neurotransmitters are quickly removed once they’ve done their job
what does it mean in the nervous system is rapid?
electrical impulses are really fast, so the animal can react quickly to stimuli
how do flowering plants increase their chances of survival?
by responding to changes in their environment
how do plants respond to changes in their environment?
they sense the direction of light to grow towards it
sense gravity, so roots and shoots grow in right direction
climbing plants have sense of touch to climb things
what is a tropism?
the response of a plant to a directional stimulus by regulating their growth
what is a positive tropism?
growth towards the stimulus
what is a negative tropism?
growth away from the stimulus
what is phototropism?
the growth of a plant in response to light
shoots are positively phototropic
roots are negatively phototropic
what is gravitropism?
the growth of a plant in response to gravity
shoots are negatively gravitropic
roots are positively gravitropic
how do plants respond to directional stimuli?
using specific growth factors (hormone-like chemicals that speed up or slow down plant growth)
where are growth factors produced?
in the growing regions of the plant and move to where they’re needed in the other parts of he plant
what are auxins?
growth factors that stimulate the growth of shoots by cell elongation
high concentrations inhibit growth in roots
what is cell elongation?
where cell walls become loose and stretchy (plasticity increases), so the cells get longer
what is IAA?
indoleacetic acid
its an important auxin (growth factor) that’s produced in the tips of shoots in plants
how is IAA transported?
by diffusion or active transport
via phloem for long distances
it is moved around the plant to control tropisms
what does IAA do in phototropisms?
it moves to more shaded parts of roots and shoots causing uneven growth
what does IAA do in shoots in phototropism?
IAA conc. increases on shaded side
cells elongate and the shoot bends towards the light
what does IAA do in roots in phototropism?
IAA conc. increases on shaded side
growth is inhibited so the root bends away from the light
what does IAA do in gravitropisms?
IAA moves to the underside of shoots and roots, so there’s uneven growth
what does IAA do in shoots in gravitropism?
IAA conc. increases on the lower side
cells elongate so the shoot grows upwards
what does IAA do in roots in gravitropism?
IAA conc. increases on longer side
growth in inhibited so the root grows downwards
how do simple mobile organisms stay in a favourable environment?
they have simple responses
the response can be tactic or kinetic
what are tactic responses (taxes)?
the organisms move towards or away from a directional stimulus
types:
phototaxis
chemotaxis
what is an example of a taxes?
phototaxis - move away from a light source
helps woodlice survive as it keeps them damp in concealed under stones during the day from predators
what is a kinetic response (kineses)?
randomly changing speed and rate of turning in response to non-directional stimulus
increase rate of turning in unfavourable environments to leave
what is an example of kinesis?
in high humidity woodlice move slowly and turn less often to stay there
in dry areas they move faster and turn more to leave
what is a choice chamber?
a container with different compartments, in which you can create different environmental conditions
what are choice chambers used for?
to investigate how animals, like woodlice, respond to conditions like light intensity or humidity in the lab
how to use a choice chamber to investigate light intensity?
cover 1 half of the lid with black paper, making 1 side dark. put damp filter paper in both sides
place 10 woodlice in centre
after 10 mins count # of woodlice on each side
repeat
what should results of choice chamber for light investigation show?
most woodlice end up on dark side
how to use a choice chamber to investigate humidity?
place damp filter paper on 1 side and a desiccating (drying) agent on the other then do choice chamber experiment
you should find most woodlice are on damp side
what are receptors?
some are cells, some are proteins on cell membranes
how are receptors specific?
they only detect 1 particular stimulus
what does it mean when a nervous system receptor is in its resting state?
its not being stimulated
there’s a difference in charge between the inside and the outside of the cell - generated by K+/Na+ ion pumps and channels, so there is a voltage across the membrane
what is resting potential?
the potential difference when a cell is at rest.
the potential difference of the inside of a neurone relative to the outside is typically -65mV
what is the generator potential?
the change in potential difference due to a stimulus.
when a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference
what is an action potential?
if a generator potential is big enough (reaches threshold level) it will trigger an electrical impulse along a neurone
how is the strength of a stimulus measured?
action potentials are all 1 size, so the strength of the stimulus is measured by the frequency of action potentials.
if the stimulus is too weak the generator potential won’t reach the threshold, so there’s no action potential
what are Pacinian corpuscles?
they are mechanoreceptors - they detect mechanical stimuli e.g. pressure and vibrations and convert them into electrical energy. found in your skin
what do Pacinian corpuscles contain?
the end of a sensory neurone, called a sensory nerve ending.
it’s wrapped in a fluid filled capsule with loads of layers of connective tissue called lamellae
what happens when a Pacinian corpuscle is stimulated?
the lamellae are deformed and press on the sensory nerve ending.
causing it’s cell membrane to stretch, deforming the stretch-mediated sodium ion channels
what happens when the stretch-mediated sodium ions in the Pacinian corpuscle are deformed?
they open and Na+ diffuse into cell, creating greater potential, if it reaches the threshold an action potential is triggered
how do eyes register light?
light enters through pupil and is focused ono retina by the lens
retina contains photoreceptor cells
nerve impulses from receptor cells carried from retina to brain vi optic nerve
how is the amount of light entering your eye controlled?
by the muscles of the iris
what are photoreceptors?
receptors that detect light
what is the fovea?
an area of the retina where there are lots of photoreceptors
what is the optic nerve?
a bundle of neurones, there aren’t any photoreceptors here so it isn’t sensitive to light
its called the blind spot
what happens to light in the photoreceptors?
absorbed by light-sensitive optical pigments
light bleaches pigment causing chemical change and altering membrane permeability to Na+
generator potential created, if it reaches threshold nerve impulse sent along a bipolar neurone
what do bipolar neurones in the eyes do?
connect photoreceptors to the optic nerve, which takes impulses to the brain
what are the 2 types of photoreceptor in the eyes?
rods and cones
they contain different optical pigments making them sensitive to different wavelengths of light
they convert light energy into electrical energy (nerve impulse)
where are rods mainly found?
in the peripheral parts of the retina
where are cones found?
packed together in the fovea opposite to the pupil
what do rods do?
only give information in black and white (monochromatic vision)
what do cones do?
give information in colour (trichromatic vision)
there are 3 types of cones, each containing different optical pigments
red, green and blue-sensitive
when they’re stimulated in different proportions you see different colours
how sensitive are rods?
very sensitive to light, work well in dim light.
many rods join 1 neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential
how sensitive are cones?
less sensitive than rods, work best in bright light.
1 cone joins 1 neurone, so it takes more light to reach the threshold and trigger an action potential
what is visual activity?
the ability to tell apart points that are close together
how good is the visual activity of rods?
rods give low visual activity because many rods join the same neurone, meaning light from 2 points close together can’t be told apart
how good is the visual activity of the cones?
they give high visual acuity because cones are close together and 1 cone joins 1 neurone.
when light from 2 points hits 2 cones, 2 action potential go to the brain, so 2 separate points can be distinguished
what is cardiac muscle?
it is myogenic - it can contract and relax without receiving signals from nerves
what happens in a regular heartbeat?
SAN sends out impulse causing right and left atria to contract
impulse received by AVN
AVN passes on waves of excitation to bundle of His
purkunje tissue carries the waves of electrical activity into muscular walls of ventricles, causing them to contract simultaneously from the bottom up
what is the SAN?
the sinoatrial node, in the wall of the right atrium
its like a pacemaker - sets rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls
how do the venules not contract at same time as atria?
a band of non-conduction collagen tissue prevents the waves of electrical activity from being passed directly from atria to ventricles
what is the AVN?
the atrioventricular node
its responsible for passing the waves of excitation on to the bundle of His, after a slight delay to make sure the atria have emptied before the ventricles contract
what is the bundle of His?
a group of muscle fibres responsible for conducting the waves of excitation between ventricles to apex (bottom) of the heart. the bundle splits into finer muscle fibres in the right and left ventricle walls, called the purkunje tissue
what is the rate at which the SAN fires controlled by?
unconsciously controlled by a part of the brain called the medulla oblongata
why do animals need to alter their heart rate?
to respond to internal stimuli detected by pressure and chemical receptors
what pressure receptors work for the heart?
baroreceptors in the aorta and the carotid arteries. they’re stimulated by high and low blood pressure
what chemical receptors work for the heart?
chemoreceptors in the aorta, the carotid arteries and in the medulla. they monitor the oxygen level in the blood and also carbon dioxide and pH
how does the heart respond to high blood pressure?
baroreceptors detect high blood pressure
impulses sent to medulla
impulse sent along parasympathetic neurones.
these secrete acetylcholine, which bond to receptors on SAN
heart rate slows to reduce pressure to normal
how does the heart respond to low blood pressure?
baroreceptors detect low pressure
impulses sent to medulla
impulses sent along sympathetic neurones
they secrete noradrenaline to bind to SAN
heart speeds up to increase pressure to normal
how does the heart respond to high blood O2/low CO2/ high pH?
chemoreceptors detect chemical changes in blood
impulses sent to medulla
impulse sent along parasympathetic neurones.
these secrete acetylcholine, which bond to receptors on SAN
heart rate decreases to return pH to normal
how does the heart respond to low O2/high CO2/low pH?
chemoreceptors detect chemical changes in blood
impulses sent to medulla
impulses sent along sympathetic neurones
they secrete noradrenaline to bind to SAN
heart increases to return pH to normal
what are the 3 different types of responses?
taxis
kinesis
tropisms
what is positive and negative taxis?
positive - moving towards a stimulus
negative - moving away from a stimulus
what is hydrotropism?
growth in response to water
roots exhibit positive hydrotropism
what is 2,4-D?
a selective weed killer
similar to IAA
works on plants with large leaves and makes them grow so fast that they die
plants don’t have enough resources to support rapid growth
what are the advantages of reflex actions?
rapid protect body tissues innate - don't have to be learned allow escape from predators enable homeostatic control maintain posture/balance allow organism to find suitable conditions involuntary - brain not overloaded with decisions
how does the relay send information through the CNS?
relay neurone is fully inside the grey matter
sensory and motor neurone embed into the grey matter to reach the relay neurone
what is an energy converter called?
a transducer
how does the body respond to a pressure stimulus?
the receptor is the Pacinian corpuscle
sensory neurone
CNS
where is the Pacinian corpuscle located?
on nerve endings that are on the end of dendrites
dendrites are located on the end of a dendron
what is a dendron?
it carries an electrical impulse towards the cell body from the Pacinian corpuscle
what is an axon?
it carries an electrical impulse away from the cell body towards the axon terminals
what is the myelin sheath?
an insulating layer of lipid around nerves
what pumps and receptors are there between the Pacinian corpuscle and the nerve ending?
stretch mediated sodium ion channel protein
Na+/K+ pump (takes in 2 K+ for 3 Na+)
voltage gated Na+ channel
exam technique for generating an action potential:
pressure applied to Pacinian corpuscle
lamellae deform, passing deformation to nerve ending
stretch mediated Na+ channel deforms/opens
Na+ diffuse into neurone
region of neurone begins to depolarise
if threshold is reached (enough Na+ enters) voltage gated channels open, causing complete depolarisation
this is called a generator potential because it triggers a cascade of voltage gated channels to open further down neurone
these self-propagating openings are called an action potential
what does it mean if the neurone becomes depolarised?
the inside of the neurone is usually more negative than the Pacinian corpuscle
depolarisation is when the inside of the neurone becomes less negative
how do rods compare to cones?
rods - cones
rod shaped/ cone shaped
many/ fewer
dark/ light
exam technique for nervous system heart beat:
SAN -> AVN -> Bundle of His/ purkunje fibres
impulses/ electrical activity over atria
atria contract
non-conducting tissue between atria and ventricles
delay at AVN ensures atria empty/ ventricles fill before they contract
ventricles contract from apex upwards
