Topic 6-organisms respond to changes in environment Flashcards
What are receptors?
Cells that detect change in the environment (a stimulus)
What are four types of environmental stimuli?
Chemical, thermal, electromagnetic, mechanical
Why do organisms respond to environment?
To increase chance of survival by keeping them in their favourable environmental conditions
What are the 3 simple responses? (not requiring conscious effort)
taxis, kinesis and tropisms (in plants)
What is taxis?
Simple response when an organism moves its entire body toward or away from a stimulus to be in favourable conditions.
What is positive taxis and what is negative taxis?
To move toward the stimulus is positive, to move away from it is negative. E.g. positive chemotaxis would be moving towards a chemical stimulus
Kinesis
simple response- When an organism is moving and changes it speed of movement and rate of direction suddenly, (not toward or away from a stimulus) to move back into favourable conditions, its non directional
Tropism
Simple plant response, the plant grows in response to a directional stimulus, positive if toward, negative if its away from the stimulus (can be light, gravity or water)
What is positive phototropism?
Plant grows towards light
What are growth factors?
hormone like substances in plants, stimulate cell expansion and division
What is IAA
Indoleacetic acid, a growth factor and type of auxin produced in tips of shoots and roots and diffuses
What is positive phototropism in shoots?
IAA diffuses to shady side causing cell elongation so the plant bends toward the light
Why do roots exhbit negative phototropism?
To anchor the plant into the soil
how do roots exhibit negative phototropism?
IAA will diffuse to the shady side (always) causing cell growth to be inhibited, so the plant grows away from the light
How does gravitropism work in shoots?
IAA diffuses from tip to lower side of shoot, where it causes elongation stimulating growth upwards, so negative gravitropism
What is positive gravitotropism in roots?
similar to shoots, it diffuses from tip to to lower side but causes cell growth inhibition, causing the plant to grow downwards which is positive gravitropism (IAA always diffuses to shady side and from top to bottom, it just causes growth in shoots and inhibition in roots)
Outline 2 differences between nervous and endocrine system- communication and and transmission
Nervous system is communication by nerve impulses, endocrine is by hormone chemicals. Nervous system transmission is by neurones, endocrine system transmission of hormones is by blood
Outline 3 differences between nervous and endocrine systems- speed of transmission and response, location
Nervous system transmission and response is very fast, endocrine transmission and response is very slow. nerve impulses travel to specific parts of the body, hormones travel to all parts of the body but only target cells respond.
Two major divisions of nervous system
Central+peripheral
what does central nervous system contain
Brain, spinal cord- a column of tissue surrounded by verbretal column for protection
What neurons does peripheral nervous system contain
Sensory neurones (cells that carry impulses from receptors to the CNS), motor neurones (cells that carry impulses from CNS to effectors) and
What are the two divisions of peripheral nervous system?
Autonomic (automatic) controls impulses to glands, cardiac tissue, smooth muscle, it is subconcious)
what order do neurons go in the reflex arc?
Sensory—>relay—>motor
sensory (receptors ->CNS) relay (perceives signal and sends message to effector via motor neuron)
3 advantages of reflex arcs
Fast (as short as 2 synpases), involuntary (more complex responses can be made), and protect the body from harmful stimuli.
difference between nerve impulse and neuron?
the neurons are the cells, nerve impulses are electrical signals
describe and explain the structure of a neurone (4)
Dendrites carry nerve impulses to cell body, Schwann cells surround axon for insulation, axon carries nerve impulses from
the receptor to the axon terminal, cell body has large amounts of rough ER for production of proteins and neurotransmitters
What type of receptor is the pacinian corposcule?
Pressure receptor
What does the pacinian corposcule do?
responds to changes in pressure and converts to an electrical signal
where in the body are the pacinian corpasules?
deep in the skin in fingers and feet mostly
describe structure of pacinian corpascule
a sensory neuron wrapped in layers of tissue and gel called a capsule
Theres a sensory neurone in the pacinian corpascule right, and theres a plasma membrane in the sensory neurone, identify one feature of the plasma membrane?
It has channel proteins
what channels does the sensory neurone have?
Stretch mediated sodium channels
when do the stretch mediated sodium channels open in the sensory neurone of the pc?
when pressure is applied and they are stretched
what are 2 features of neurones?
specific to a certain stimulus, sodium channels will only open for that stimulus.
do rod cells process colour?
only of very low light levels, many rod cells connect to 1 sensory neurone, this is retinal convergence
do cone cells process colour?
yes
how rod cells work
- the pigment (from very low light that is absorbed) in rod cells must be broken down by light energy to help trigger the generator potential. once enough pigment is broken down in the bipolar cells the rod cells will connect with the sensory neurones?
what connects to a bipolar cell
multiple rod cells (they connect via synapses) to a single bipolar cell
what can cause an action potential in the bipolar cell
if light, in very low light intensity, hits one rod cell it causes an action potential in the bipolar cell which is sent to the brain
where is the visual resolution of cone cells highest?
fovea
what are cells called that detect change in the environment?
receptors
are receptors specific to what stimuli they respond to?
yes they are specific and only respond to certain stimuli
what are the 3 receptors (to know)?
-pacinian corposcule
-rod cells
-cone cells
what is the structure of pacinian corposcule?
-sensory neurone wrapped in tissue and gel layers
what type of receptor is pacinian corposcule?
Pressure receptor
what proteins are in the plasma membrane and the connective tissues of a pacinian corposcule?
channel proteins
what is the overall charge of a human body
neutral, equal amount of positive and negative charge in total
is the body equally charged?
no
some parts are more positive or negatively charged than others
what is potential energy?
-when there is a barrier (e.g. a cell membrane) between positive and negative energy, this creates attraction which generates potential energy (cells can use this energy), this is measured in voltage
what is resting membrane potential?
-so, i know that an energy potential is created from the attraction when two oppositely charged forces are seperated by a barrier
-So for neurons, the electrical charge inside the cell is different to outside of it, this creates the resting membrane potential, the energy potential from the difference
what is voltage
the measure of potential energy created by the attraction of two opposite forces
What is the unit for resting membrane potential
millivolts, because the difference isn’t very large so there isn’t significant energy potential
why is there a resting membrane potential in the neuron?
more positive ions outside of the cell than inside the cell, so the inside of the cell is more negative in comparison, creating attraction and generating potential energy measured in millivolts
what are some examples of positive ions outside of the neuron cell membrane
Na+, K+
is the inside of the neuron more positively or negatively charged?
negative, there are more positive ions on the outside
In mV, what is the resting membrane potential of a neuron cell?
-70 mV (the potential energy generated by this difference in charges)
what is the term to describe a cell with a negative membrane potential?
Polarised
is a neuron more positive outside or inside?
outside is more positive because there are positive ions, e.g. Na+, K+
what does it mean if a cell is polarised?
it has a negative membrane potential
why is it -70 resting membrane potential not positive?
because it is the negative charge of inside the cell
what helps to maintain resting membrane potential in neurones?
sodium potassium pump (a carrier protein in the cell membrane)
what is the sodium potassium pump?
A bouncer of a very exclusive club. Potassium is chilling inside the cell, but sodium keeps trying to come in and crash the party. the bouncer, the sodium potassium pump, it has to kick out 3 potassiums for every sodium it lets in.
how does the sodium potassium pump help maintain resting membrane potential?
-it controls how much positive ions can go in and out
how many sodium ions are moved out of the cell and how many potassium ions are moved in?
Three sodiums move out, 2 potassiums move in. This creates an electrochemical gradient
what is the electrochemical gradient in a neuron?
because more potassiums are being let in than sodium is being let out, a gradient is created
how does the electrochemical gradient work of a cell?
-K+ and Na+ are both positive
-Theres more Na+ on the outside and more K+ on the inside
-K+ is trying to leave the negative inside of the cell, Na+ is trying to go into the cell
-Chemical is the same, its moving down conc. gradient
-together, it makes sodium move outside and potassium move inside
what does it mean that the cell membrane is more permeable to potassium?
-potassium can easily move in and out of the cell, but sodium can’t, this is because there is more potassium channels than sodium channels
-this causes loads of potassium to leak out of the cell overtime, creating a net positive charge outside of the cell (there is still positive ions inside but a lot more K+ outside)
what are the 6 stages of an action potential being generated in a neuron?
- Resting potential
- Stimulus
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Resting potential
how does a neuron respond to a stimulus?
-Small change in environment or signal from another cell.
-If stimulus is strong enough to reach the threshold of -55 mV is reached, an action potential is generated
-This triggers voltage gated sodium ion channels to open.
-Because the sodium channels are open, all the sodium will rapidly diffuse into the neuron
-Now because there is so much Na+ inside, the inside of the cell becomes much more positive, so the membrane potential goes from -70 to +40 mV
-This is called depolarisation, the charge has completely switched
-Repolarisation: So it cant stay in this super positive membrane potential permanently, so now the potassium channels open, and all the K+ ions diffuse out, this makes it negative again
-Hyperpolarization, the potassium channels are slow to close, the membrane potential drops to about -80 mV
what are cells with a negative charge called?
depolarised
what are cells with a positive charge called?
polarised
After an action potential has been generated in the cell body of a neuron, what is the next step?
it must move down the axon of the neuron (to carry the impulse to other neurons)
what are the two categories of neurons?
myelinated and unmyelinated
what is myelin sheath made of?
schwann cells
What is the purpose of the myelin sheath?
provides electrical insulation and allows for faster transmission of impulse
what are the gaps between schwann cells in the myelin sheath called?
nodes of ranvier
how does movement of an action potential work in unmyelinated neurons?
its like a mexican wave, sodium rushes in, potassium rushes out, and it repeats, all the way down the neuron. This is a slow process, its like the manual way of doing it, a relay race of depolarisation all the way down the axon, no skipping.
why is the refractory period especially important in unmyelinated neurons?
ensures the action potential travels in the right direction down the axon and not back towards the cell body.
how does movement of an action potential work in a myelinated neuron?
the action potential travels down the neuron, but because the myelin sheath provides insulation, depolarisation only happens at each node of ranvier (gap between schwann cells). This is saltatory conduction. Its a lot faster than unmyelinated, it has a VIP ticket to skip along the nodes, a fast pass down the axon
what are some causes of myelin sheath damage and what are the effects?
-Causes of damage to the myelin sheath include stroke, infections, or metabolic disorders.
-Effects of this are slower responses or jerky movements.
-There is less or no saltatory conduction, so like unmyelinated, depolarisation must occur all the way down the axon
-So nerve impulses take longer to reach the neuromuscular junction and muscle contractions may be delayed
-Also depolarisation can leak into other neurons, causing the wrong muscle fibres to contract
how does size of stimulus affect action potential?
if the stimulus is large, the frequency of action potentials will increase, however the charge doesnt go above +40, no matter how big the stimulus is
what is multiple sclerosis?
autoimmune disease damaging the myelin sheath of neurons
what are 3 factors that affect the speed of conductance in a neuron?
-Myelination and saltatory conduction
-Temperature
-Axon diameter
what are schwann cells made of?
lipids
how does axon diameter affect speed of conductance?
-Wider diameter is higher speed of conductance, because there is less resistance within the cells and a greater surface area for the ions to move (they can zoom through there is less congestion, the action potentials can speed through on a wider road. Its a motorway instead of a narrow country lane)
-Therefore the action potential travels more quickly
Does higher temperature increase or decrease rate of conductance?
Increases it for 2 reasons:
-Rate of diffusion of Na+ and K+ increase because they have more kinetic energy
-There is more ATP being produced for active transport in the sodium potassium pump
-however enzymes will denature above the optimum temp
Explain how a resting potential is maintained across the axon membrane in
a neurone (3)
- Potassium ions diffuse out of the neuron sodium ions diffuse in
Explain why the speed of transmission of impulses is faster along a
myelinated axon than along a non-myelinated axon. (3)
- Myelination provides electrical insulation, in saltatory conduction depolarisation occurs at the nodes of ranvier
what are the gaps between neurons called
synapses, the gap between the axon of one neuron and the dendrite of another
how do action potentials move across the synapse?
they cant just jump across, they have to go across in the form of neurotransmitters
what is the definition of a neurotransmitter
a molecule that can diffuse across a synapse to trigger an action potential in the post synaptic neurone
these are usually held in vesicles until the axon terminal
what is the axon terminal?
the end of a neuron
what are the stages of synaptic transmission?
- 2.
3.
4.
5.
