Topic 6A - Stumili and Response Flashcards
CNS and PNS
Central nervous system : brain and spinal cord
Peripheral nervous system : any nerves outside CNS
Define nerve
A nerve is a bundle of nerve cells (neurone)
Function of autonomic and voluntary nervous system?
THIS COMES UNDER MOTOR NERVOUS SYSTEM ( of PNS)
Auto: subconscious control (electrical impulses to glands, smooth muscles, and cardiac muscles).
Smooth muscles are in the eyes, digestive tract, respiratory system etc.
Voluntary: carries e. impulses to body muscles under conscious control
Function of nerve cell / neurone?
The 3 types?
Transmits signals (electrical and technically chemical)
Sensory, relay, motor
examples of effectors ?
glands, muscles
Dendrites and their function
(More numerous than axon terminal end)
To receive infe frem other neurones and transmit e. signals to cell body
Neurone: cell body function
Maintain call & its functions - contains nucleus (genetic info and directs protein synthesis)
Axon and its function
A nerve fibre that carries e. impulses from cell body to axon terminal
Axon terminal function?
transmit signals to other neurones/ skeletal muscle
Myelin sheath and its function?
layer of fatty insulating layer covering the axon.
To insulate nerve from others to prevent impulses interfering with others. Also, to speed up conduction of nerve impulses along the avon.
Name for gaps between myelin sheath
Node of Ranvier
Desc. nervous communication pathway
STIMULUS
receptors > sensory neurone > (CNS and then relay neurone) > motor neurone > effector
brings about RESPONSE
How does the number of neurones affect how quickly a response is brought about?
More synapses electrical impulse has to travel across in the form of neurotransmitters
Reflex?
> How does body respond to a sharp pin?
> possible to override reflexes
(reflex arc)
Fast and subconscious responses help survival, such as coughing, pupil reflex, and gagging
pin as stimulus detected by receptor (named) > sensory neurone > … until effector of muscles castrats to pull away
Reflex?
> How does body respond to a sharp pin?
> possible to override reflexes
(reflex arc)
Fast and subconscious responses help survival, such as coughing, pupil reflex, and gagging
pin as stimulus detected by receptor (named) > sensory neurone > … until effector of muscles castrats to pull away
Difference between autonomic VS voluntary that is related to the comms pathway
Autonomic → relay neurone passes through spinal cord while voluntary → passes through brain
3 characteristics of the nervous response
Localised: targeted electrical impulses where neurotransmitters are secreted directly into cells (no widespread impact on body, unlike some hormones)
Short- lived: quick as neurotransmitters removed after response
Rapid: fast electrical impulses (much faster than other chemicals, like hormones in blood) travel via interconnected neurones
role of receptors
detect stimuli (and they are specific and complementary!)
note about role of neurones
When mentioning specific ones, say where electrical impulses are carried from and where to
e.g from CNS to effectors
role of relay neurone
connect sensory to motor neurone via spinal cord (or brain if voluntary) where this intermediary neurone is located
examples of receptors
barro/ photo/ chemo/ thermo/ mechano receptors or ones on the surface of pancreas cells
- they can be proteins or cells themselves (double check this)
What is the word used to desc. receptors that link them to generator potentials?
Transducers: converting energy from stimulus in their environments into e. impulses.
This nervous impulse is known as a generator potential, past threshold = action potential → response
What are Pacinian Corpuscles? Where are they found and why?
Pacinian Corpuscles are sensory receptors (a type of mechanoreceptor) and contain a sensory neurone, and they detect changes in pressure / vibrations.
Deep in the skin most in fingers and soles of feet - also in joints, ligaments, tendons to know which way joints are changing direction
Where are stretch-mediated sodium ion channels, and why do they have this name?
Pacinian Corpuscles > in the cell- surface membrane of sensory nerve cell.
They have this name as their permeability to sodium ions changes when their shape changes (stretched membrane).
resting potential
Difference in electrical charge maintained across the membrane of me aton ga neurone when not stimulated > aka polarised membrane.
When the outside is more positive overall.
depolarisation of membrane
where an influx of positive sodium ions, making the inside of the cell more positive than outside
generator potential
depolarisation of the membrane as result of stimulus being detected and converted into an electrical impulse by the receptor
threshold
the minimum level for a generator potential to reach & turn into an action potential
action potential
change in electric change across the membrane across the membrane of axon when neurone is stimulated
At rest, can you desc. the charges of the neurone
The membrane is polarised and the nearone has a resting potential which is where the outside of the cell is more positive (as the inside has a negative charge generally)
Desc. how a generator potential is created in the Pacinian Corpuscle, which is a type of mechanoreceptor.
- At (polarised) rest, stretch - mediated sodium ion channels of neurone membrane are too narrow to let in sodium DOWN CONC GRADIENT (facilitated diffusion)
- Pressure changes the shape of P. Corpuscle and membrane becomes stretched and this opens stretch mediated sodium ion channels.
- Sodium ions enter neurone and membrane is depolarised
- This generates a generator potential, if it reaches threshold value then action potential (electrical impulse)
Why is a threshold value needed?
So nervous system isn’t overwhelmed with unimportant stimuli, to only acknowledge change in environment
- an adaptation due to continuous pressure (e.g. standing) so adapted to have less frequent action potentials
How might a person’s perception of touch be affected by drugs that block stretch- mediated sodium ion channels?
Pressure normally deforms the membrane, the drugs stop Na from diffusion down gradient as channels won’t open, and so no generator potential or then action potential > person won’t perceive touch
Name of 2 photoreceptors in the eye, and what stimuli do they detect?
Rod and come cells in the retina - wavelength and light intensity
Fovea
Indent in the retina - most sensitive part as where come cells are in abundance
What is the blind spot?
Area with no photoreceptors, near nerve ending
How are nervous impulses carried from retina te brain?
Sensory neurones to optic nerve carries the e. impulses
photoreceptor that allows you to see in colour, and how many colour receptors are there?
Cone cells: red, green and blue
What happens when you look at something purple?
Red and blue photoreceptors (cones) are both stimulated in different proportions, they give trichromatic vision
photoreceptors that let you see in black and white?
Rod cells
How does a photoreceptor convert light into an electrical impulse?
- Light wavelengths enter, hits the photoreceptor, and is absorbed by LIGHT-SENSITIVE OPTICAL PIGMENTS
- The light bleaches the pigments and causes a chemical change - the photoreceptor membrane becomes more permeable to sodium ions (enter by facilitated diffusion, depolarising the membrane)
- Generator potential created, and if threshold reached, a nerve impulse is sent along to the bipolar neurone … then to the optic (a sensory) nerve, which takes impulses to the brain
photoreceptors are also…
nerve cells, just like the nerve cell (aka machanoreceptor) in the
Pacinian Corpuscle
What are the light - sensitive optical pigments called? (2)
Rhodopsin in Rod cells, and iodopsin in cone cells
Tell me some info about cone cells.
- There are less cones than rod cells and are concentrated in the centre of the fovea.
- iodopsin pigment can be bleached by light, and as these photoreceptors/ nerve cells they are transducers, they are responsible for changing light energy into electrical impulses by undergoing chemical changes
- work best in bright light
- 3 types : red, blue, green
- one cone to one bipolar neurone
Tell me some info about rod cells
- monochromatic vision, black /white
- many to one bipolar neurone called retinal convergence, so more sensitive to bright light ( work best in dim light, due to the fact it only takes a few weak generator potentials to activate action potential )
- rhodopsin pigment
- concentrated on outer edges of retina / peripheral
Explain why cone cells have high visual acuity and lower sensitivity to light / spatial sensitivity
They give high visual acuity as they are close together and one cone to one bipolar neurone. When light from two points hits two cones (iodopsin requires high light intensity to breakdown and so probably why you can’t see colours too well in dim light), 2 action potentials from each cone go to the brain via the optical nerve - so can distinguish between 2 close points, resolution.
Cones less sensitive as no summation - an action potential only generated in bright light as one cone to one bipolar neurone, so takes more light for the threshold to be reached
Explain why rod cells have low visual acuity and higher sensitivity to light / lower spatial sensitivity
Work best in dim light as many rods joined to one bipolar neurone, so many weak generator potentials combine to reach theshold - summation.
ONLY 1 ACTION POTENTIAL by each bipolar neurone no matter how many of the3 ADJACENT rods stimulated
Low visual acuity as many to one means light hitting 2 separate rods can’t be told apart, info sent to brain via optical nerve as one point, low resolution > retinal convergence
(rhodopsin must be easily broken down by low and mostly bright light)
How many rods to a bipolar neurone?
3 usually
Shape of rod and cone cells
rods- like a rod, round
cones- sharp cone ends
explain these 2 scenarios
1 Why are things in black and white and blurred at night
2 Why is your peripheral vision not very clear
- Rods stimulated as more sensitive to light and so action potentials fired in dim light in monochromatic vision, and because usually 3 rods to one bipolar neurone → low visual acuity
- only rod cells at the ends of the retina which have low visual a. (explain why)
important point about Pacinian Corpuscle
must explain that pressure first causes the membrane to become deformed
note
most of the time you will have to use comparative language when writing about cones, and compare to rods
Desc. Pacinian Corpuscle structure
The sensory nerve ending is covered by many layers of lamellae (connective tissue with gel in between)
- can talk about stretch - mediated … if you want
What is the autonomic system split into? (This is the automatic nervous system of the motor system)
- what word can desc. these 2 systems?
Parasympathetic and sympathetic, they are called antagonistic > when one in action, the other relaxes.
The heart is controlled by the autonomic
What is the parasympathetic nervous system (PSNS)?
Para: slow down, it also takes longer to say it than sympathetic.
- inhibits effectors
- sIows activity
- controls actions when under resting conditions
- conserves energy
What is the sympathetic nervous system (SNS)?
- s: speed
- stimulates effectors
- controls conditions when under stress / activity
The heart muscle especially is known as myogenic,meaning?
A myogenic heart is a heart that generates its own contractions and rhythm without needing external stimuli,
HOWEVER, the rate of the heart beating is controlled by the autonomic nervous system.
- opportunity to review year 12 work on heart and diastole and ventricular/ atriole systoles
Silly Ants Have Pants
SAN
AVN
(Bundle of) His
Purkyne fibres
Why doesn’t the bundle of His only carry the wave of excitation to the apex of the heart and contract there.
Essentially, saying that the Purkyne tissue / fibres exist to carry the wave all up the base of ventricles to allow as much muscle contraction as possible to allow all blood to be pumped whatever distance
Explain the route of electrical activity in the heart
- A wave of excitation/ depolarisation is sent out from SAN (sinoatrial node in right atria) across both atria, causing to contract - ATRIOLE SYSTOLE
- Wave of e. enters AVN (atrioventricular node in right atria) and sends out another wave after short delay to the conducting tissue Bundle of His
- it has to travel this way because the (insulating) atrioventricular septum stops waves from going atria to ventricles - Bundle conducts wave down septum to the apex of the heart where it branches off into Purkyne tissue fibres - bottom of heart starts contracting first
- Purkyne tissue releases and carries wave up the muscle ventricle walls from apex and up - contracts, ventrical systole
how is the RATE (as heart is myogenic) of the SAN controlled?
- important Q
The rate at which waves of excitation are fired are subconsciously controlled by the coordinator in the brain called the medulla oblongata
Why might your heart rate need to increase or decrease
- need to respond to internal stimuli (more info on other cards)
- exercise to deliver useful stuff to respiring cells or to return HR to resting rate
What are the 2 parts of the medulla oblongata and do they do?
One centre that is connected to the SAN via the sympathetic nervous system (it increases the heart rate by sending more electrical impulses)
Another centre is also connected to the SAN via the parasympathetic nervous system (decreases HR by sending more e. impulses down this pathway)
What are the 2 receptors that When stimulated impact which centre in the medulla responds?
Where are these 2 receptors and how do they reach the brain?
Barroreceptors detect pressure changes in the blood, in WALL of aorta and carotid artery .
Chemoreceptors detect chemical (pH) changes in the blood, in Aorta and carotid artery.
- connect to medulla oblongata via sensory neurone.
Medulla Oblongata acts as …
Co-ordinator to bring about response
What exactly are chemoreceptors detecting?
the levels of carbonic ACID - it’s produced when CO² reacts with water,… and the MORE of it, the lower the pH as it’s acidic so you’ll want to get rid of some CO²
(could maybe acknowledge lactic acid also brings pH down)
What is the effector of the motor nervous system
the heart muscles (not really SAN)
why is there a slight delay before the AVN reacts and sends aware of excitation?
To make sure the atria have emptied before the ventricles contract
Describe the response to low blood pressure (6)
- Barroreceptors (aorta and carotid artery) detect a decrease in blood pressure, they are stimulated
- So, increased frequency of electrical impulses to the medulla oblongata along SENSORY NEURONES
- Medulla processes and sends more e. impulses along sympathetic NEURONES to SAN RECEPTORS!
- Noradrenaline is secreted from the neurone to bind to SAN receptors
- This makes the SAN send out more frequent waves of depolarisation
- Cardiac muscles are the effectors and contract faster, ^ HR to bring blood pressure back up.
The opposite for high blood pressure :
remember that the SAN is the only part that really changes when it comes to frequency of events
What are the 2 neurotransmitters involved in the motor nervous system?
sympathetic: norADRENALINE
parasympathetic: acetylcholine
Explain the response to high pH levels /
or LOW CO² Ievels / high O² levels
(6)
high pH due to alkaline conditions, not enough CO being converted into carbonic acid
(so likely that in comparison, there’s a lot of oxygen)
- Chemoreceptors (aorta and carotid artery) detect high pH
- More frequent e. impulses sent along sensory neurones to the medulla oblongata
- Medulla process and sends more frequent e. impulses down parasympathetic neurones to SAN
- Acetylcholine released from neurones and binds to receptors on SAN
- The SAN responds by sending out less frequent waves of excitation/ depolarisation
- Cardiac muscles contract slower, and HR decreases so that less CO² is removed by the lungs and pH starts to lower again
CAREFUL with this question, take time thinking and vice versa for low pH, which can also be caused by lactic acid … all about CO² being removed more or less
tip
If the question says high pH or high blood pressure,
always think the heart rate has to decrease and do the opposite
tip (2)
high pH… so need to higher CO²
- heart rate counteracts stimuli, heart rate will decrease
low pH… so need to lower CO²
pH in the blood needs to be kept fairly neutral because…
could denature enzymes in cells or proteins in the blood (haemoglobin)
cardiac output equation
ml/min
HR × stroke volume
What’s the effect of exercise on cardiac output (mention of myogenic heart/
^ muscular activity
^ CO² produced
↓ pH
… chemoreceptor… ^ HR via sympathetic
synapse
a junction where 2 neurones meet
resting potential
difference in charge across a nerve / receptor membrane
generator is change in potential and depolarised is certain threshold where inside of membrane becomes a higher charge
stimulus
a change to normal conditions / action will produce a response
response
reaction to a stimulus to increase chance of survival
Kinesis
non-directional & random movement as a response to conditions (could include rate of turning)
Taxis
Like a taxi with directions…
Directional response/ movement in response to stimulus.
The direction of stimulus affects response (e.g. phototaxis)
- Simple organisms like woodlice have simple and automatic responses that keep them in favourable environments
Tropism
Growth response to directional stimulus
Auxin
A level example: IAA (indoleacetic acid, don’t need to know).
Hormone released in small quantities - controls plant cell elongation
Growth factor
Factors affecting growth (light intensity , gravity, presence of substance/ mineral ions)
note
organisms increase chances of survival by responding to changes in their external & internal environment (temp)
How do Woodlouse respond to light intensity increasing in the environment
(they also respond to humidity and temp as they like cold, moist conditions)
seek shade
- to avoid dessication in low humidity environments and avoid predators
Desc. how you would investigate how woodlice respond to light, given:
- fine mesh
- a petri dish and a divider
- lid to dish
- RP 10 on maze with worms
Create a choice chamber w equipment.
IV: light intensity
DV: how many woodlice move into chamber w/ lower light intensity
CV: number of woodlice / species or age / time given
Place woodlice on top of mesh to give them choice, sample large of 20.
Increase light intensity in one chamber, at each level of intensity count woodlouse in each chamber.
Plor a graph over time for around 30 mins.
- 10 repeats
- Finding over time, positive correlation between increasing light and number in dark chamber, but already large number in dark at start. As negative phototaxis, going to dark area as close to habitat conditions to survive (as hidden from predators or to not dessicate)
What about the stimulus affects the kinetic response?
The intensity of the stimulus
How do the results vary when 2 different woodlouse are put in 2 different petri dishes, at the same time, where one has damp filter paper and the other is dry?
- where position is recorded and mapped out every 10 seconds
LIKE TATIC, THE RESPONSE IS ALSO AUTOMATIC
Dry: moving rapidly and more random changes in direction as he’s trying to find a more favourable environment to survive
Moist: humidity is at good levels, so direction changes half as many times.
- this response to stimulus was to avoid dessication & improve chance of survival
Name the taxis and why it’s needed:
1. Male moths fly to females producing pheromones
2. Earthworms burrow underground
- positive chemotaxis is so courtship and reproduction can occur = offspring
- positive geotaxis to hide from predators … avoid dessication … ^ chance of survival. THEY MOVE IN THIS WAY FOR more favorable conditions
Name 3 plant responses and why they’re useful, e .g chemotropism.
phototropism: absorb as much light for photosynth.
geotropism: so shoots grow to light, and for roots to know where to go to access waters/ minerals in soil
hydrotropism: greater chance of finding water
What kind of tropisms do shoots display?
positive phototropism, negative geotropism.
- roots opposite
Hormone auxin (diffuses backwards from tip) accumulates in shoots & roots for what?
Shoots: stim growth
Roots: inhibit growth
positive tropism
growth toward stimulus
- directional
Growth factors
Chemicals that slow or quicken rate of growth, auxin is an example
Auxin is produced in … and how does it promote growth?
growing regions called meristems - shoots and roots.
It dissolves/ diffuses backwards away from the tip and stimulates enzymes to increase cell wall plasticity (they get loose and stretchy) - allowing cell elongation
auxin in roots
inhibits growth when in high concentrations
- stimulated in shoots
phototropin
- and how are they responsible in reacting to light stimulus
phototropins are a group of photoreceptors (pigments/ structures sensitive to wavelengths)
Light absorbed/ detected by these receptors - causes a change in the molecules, triggers cascade of cellular reactions.
Auxin is redistributed on shaded side - phototropism
Nature of lAA across the plant
produced in the tips of shoots (or meristem?), diffuses, and moves around via phloem to control tropism over long distances, uneven concentrations means uneven growth
- tip removed = no IAA
Note over short distances now IAA moves by diffusion or active transport
Describe the re-distribution of IAA in response to light in shoots and roots
For both conc redistributed and increases in shaded side
shoots: cells elongate so bends toward light
root: growth inhibited so eventually bends away from light
Describe the re-distribution of IAA in response to gravity in shoots and roots
In response to gravity, both have increased concentrations on lower side.
Shoots: cell elongation to grow upwards (picture in your head)
Roots : growth inhibited so grow down
do some practice Qs on phorctropism experiments, and variables/ control experiments
Might want to be very detailed or how one theory discounts another
Coleoptiles
protection covering emerging shoot tips
what to say instead of plant hormone
growth factor
conclusions generally about phototropism experiment
Light increases growth, but IAA responds to direction and speeds up growth.
IAA can diffuse to parts of shoot needed.
IAA is a chemical and can be blocked from diffusing if there’s a solid physical barrier (e.g. mica proves this as it conducts elec. but not chemicals)
how do auxins affect plant growth?
either allow cell elongation or inhibit growth
response
reaction to increase chance of survival, e.g. hydrotropism
