Chapter 3.6 Response To Change In Conditions Flashcards
Why do plants need to respond to the environment?
- prevent water loss
- reproduce
- increase chance of survival
- maximise photosynthesis
-reduce damage
Types of stimuli that a plant can respond to
Plants respond to; light, gravity and water to avoid abiotic stress
Also respond to predication by producing chemical toxins
How do plants respond to change in stimulus?
Plants change orientation of roots/leaves/stems to favourable conditions
By producing growth factors called tropism from growing regions to other tissues, where they regulate growth in response to stimuli
How do plants respond to light
+ what is it called
Stems respond to light by moving towards it = positive phototropism
Roots respond to light by moving away from= negative phototropism
How do plants respond to gravity
+what is it called
Stems respond by moving upwards = negative geotropism
Roots respond by moving downwards = positive geotropism
What is the growth factor produced by plant in response
Auxin (IAA) is the plant hormone which acts as growth factor
Describe the process of IAA synthesis and movement into shoot in plant response
1) IAA is synthesised in cells in shot tip (as stimuli detected by specific receptor proteins)
2) IAA diffuses down shoot equally on all sides
Describe the effect of different concentrations of IAA on cells in plants in response to light stimuli
3) light on 1 side causes IAA to be transported to shaded side
4) concentration of IAA increases on shaded side causing elongation of cells
5) IAA activates proteins in plasma membrane H+ ion breaks H bond between cellulose microfibrils = easier for cell wall to expand. Elastin enzymes in cell wall break bonds between cellulose microfibrils allowing cell walls to stretch
6) on shaded side, there is greater elongation of cells, causing the shoot to bend towards light
What type of response are taxes and kineses?
Simple innate responses that can maintain a Mobile organism in a favourable environment
Def of taxis response
Movement of whole organism in response to direction of a stimulus
E.g
Some move directly towards (positive taxis) or away (negative taxis) to stimulus
Def of kinesis response
Non-directional response in which rate of movement is related to the intensity of stimulus, not directional
What are the 2 types of kinesis response
Orthokinesis - change in rate of movement
Klinokinesis - change in the rate of turning
Outline the reflex arc
Stimuli, sensory receptor, sensory neurone, relay neurone, motor neurone, effector, response
Why are reflexes important
1- involuntary as do not require decision making (adv of simple organisms)
2- brain is not overloaded with situations in which response is always the same
3- some responses are still sent to brain and can be over ridden if needed
They protect body from handful stimuli ^survival
They are effective from birth so don’t have to be learned
They are fast, because the neurone pathway is short with very few synapses
2 parts of the nervous system
The central nervous system (CNS) and Peripheral nervous system (PMS)
(Brain and spinal cord). (All other peripheral nerves originating from brain and spinal cord)
What are nerves
Nerves are organs - a group of neurones (tissue cells) as well as other tissues such as blood vessels and connective tissue
Def of nerve impulse
A self-propagating wave of electrical disturbances which travels a long the surface of a neurone membrane
What cells secrete myelin around axon
Myelin is secreted by Schwann Cells which surrounds the axon in a spiral structure
How does myelin help axon
+ what is node of ranvier
It is an electrical insulator that prevents ions leaking out of axon and in a jointing cells
Node of ranvier = gaps between myelinated axon
What is happening at resting potential
At resting potential = state of membrane when no impulse passed along it
Inside of axon is - ively charnged with respect to outside
There is a potential difference of -70mV
Membrane is said to be polarised
How is resting potential established?
1) active transport of Na+ & K+ by Na/K pump
As 3 Na moved to 2K there is more + charge outside cell than inside
2) Facilitated diffusion of Na+ & K+ by channel protein molecules
Ions tend to diffuse back through channel proteins however membrane = more permeable to K+ so more K+ moves back out of axon than Na+ in
What transport proteins do neurone membranes contain
- sodium potassium pumps
- voltage gated Na+ & K+ channels
-carrier which allow facilitated diffusion of ions - at synapses there are also Ligond gated and Ca2+ gated channels
How is an action potential generated
Axon membrane contains Na/K voltage gated channels
At resting potential channels = closed
When potential difference reaches threshold value (-50mV)
Voltage gated Na+ channels open = Na+ moves into axon
Potential difference +40mV membrane is depolarised
How is depolarisation generated
Na+ voltage gated channels close at +30mV
K+ voltage gated channels open & K+ flow out of axon
Causing potential difference to be ^ negative
The Na/K pump begins again channels close resting potential restored
K+ channel remain open after repolarisation = more -time (hyperpolarised)
Outline the change in charge produced by nerve cell in
Resting potential , threshold, depolarisation, repolarisation
Resting potential
-70mV
Threshold
-50 mV
Depolarisation
+40 mV
Repolarisation
-90mV
What is refractory period
Period following action potential, the axon is not excitable
Why is the refractory period important
Necessary as allows proteins on voltage sensitive ion channels to restore original polarity.
Advantage:
Nerve impulse flow in 1 direction
Action potential separated, with no overlap
> brain uses frequency of impulses to determine strength of stimulus
More frequent impulse = strong stimulus
Advantages of the refractory period
1) nerve impulses flow in 1 direction
2) action potential separated with no overlap
In unmeyleinated neurones how are nerve impulses transmitted
Depolarisation of 1 area of membrane sets up local current which stimulates the next patch to open Na+ channels
Speed of nerve impulse transmission through unmyleinated neurone compared to myelinated neurone
Speed = 1-3 ms-1 unmyleinated
Speed = up to 120 ms-1 myleinated
How are nerve impulses sent through myelinated neurones
In myelinated neurones, depolarisation occurs only at node of ranvier . Action potential jumps from 1 node to next ( known as saltatory conduction )
How does saltatory conduction effect re polarisation
Metabolically increases efficient as less ions move across membrane so less energy expended restoring resting potential
Factors that affect nerve impulse speeds
1) myelination
2) temperature
3) axon diameter
How does myelination affect nerve impulse speeds
Myelinated axons shoe saltatoy conduction (jumps between nodes)
= increases speed of transmission
not all organisms have this as size is dependent for example smaller organisms have less far for impulses to travel so don’t have myelination compared to larger ones
How does temperature affect nerve impulse speeds
Higher temps = fast the speeds
Ions have more kinetic energy so diffusion rates increase
However in excessive temps channel proteins can denature or membrane fluidity becomes disrupted
warm blooded animals have higher impulse speeds
How does axon diameter affect nerve impulse speeds
Larger diameter = faster the speed
Marine invertebrates who live in temps develop thick axons to increase speed of response
How is action potential started in receptor cells
1) nerve impulse created by altering permeability of membrane to Na+ ions
2) when gated Na+ channels open Na+ moves into cell
3) small influx of Na+ causes generator potential
4) if enough Na+ enters, threshold potential will be reached and an action potential generated
What is generator potential
The small influx of Na+ caused by altered permeability of membrane to Na+ at receptor cells
Examples of receptor cells
Pacinian corpuscles
Baroreceports
Chemoreceptors
Photoreceptors
Compare the rod and cone cells for
- number of them in the eye
- distribution of them
Rods
- there are many more rods
- highest density outside fovea and on perifory
Cones
- fewer cones
- highest destiny around fovea
What pigment is in rod cells
Rhodopsin
What pigment is in cone cells
Iodopsin
Compare rod and cone cells for
- convergence (defining shapes)
- visual acuity ( level of detail in image created)
Rods
- have higher convergence, as multiple rods per bipolar cell and multiple bipolar per ganglion
- lower visual activity
Cones
- lower convergence as 1 cone per bipolar cell-polar cell and ganglion
- higher visual activity due to this individual cells
Label the structure of the eye
Label the rod and cone cells diagram
Compare rods and cone cells for
-sensitivity to light
- wavelengths of light they detect
Rods
- very sensitive to light and stimulated in low light conditions
- detect in black and white
Cones
- not sensitive to light so required bright light to work
- colour spectrum
The role of receptors
-detect change in internal/external environment
- energy transducers ( covert 1 from of energy to another)
- adapted to detect changes in particular forms of energy
- transfer energy of stimulus into electrical energy for impulse
How are receptors classified by
1) the stimulus they detect
2) their structure (simple primary or complex secondary)
3) source of stimulation (external or internal)
How do receptor cells generate an action potential
1)Receptor cells are the same as other neurones when in their resting potential and how it is generated
2) when stimulus detected, the cell surface membrane becomes more permeable to Na+ (and other ions)allowing more ions to move into cell
3) this change in potential difference due to stimulus = generator potential
bigger stimulus = more channels open = more ion movement in
4) if generator potential is enough to reach threshold then action potential is formed
What are the layers of connective tissue around Pacinian corpuscles called + label the Pacinian corpuscle
Lamellae
How do Pacinian corpuscles in the skin work to generate an action potential when detect pressure change
When Pacinian corpuscles are stimulated the lamellae deforms and presses on the sensory nerve ending.
This causes the sensory- neurone’s cells membrane to stretch, deforming the stretch-mediated sodium channels .
Na + channels open and Na+ diffuses in creating a generator potential. If generator potential reaches the threshold it triggers and action potential
Label the structure of the eye
Sclera
Fovea
Retina
Optic nerve
Blind spot
Vitreous humour
Suspensory ligament
Lense
Pupil
Iris
Ciliary muscle
Cornea
How does the iris change size of the pupil
1) in bright light
2) in dim light
1) in bright light
-circular muscles contract
- radial muscles relax
- pupil constricts
2) in dim light
- circular muscles relax
- radial muscles contract
- pupils dilate
Where are photoreceptors found in the eye
Both photoreceptors are found embedded into the retina and fovea
Higher conc. of cones in the fovea
Higher conc. of rods in the retina
How do photoreceptors work to generate an action potential
Light enters the eye, hit the photoreceptors and is absorbed by light sensitive optic pigment
1) light bleaches the pigment, causing chemical change and altering the membrane permeability to Na+
2) a generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone.
(Bipolar neurone connects photoreceptors to the optic nerve which then take impulse to the brain)
Label the structure of the synapse
Pre-synaptic membrane
Mitochondria
Synaptic vesicle
Synaptic cleft
Neurotransmitter (acetylcholine)
Post synaptic membrane
Synaptic knob
Voltage gated Na+ and Ca+ channels
Liganded gated Na+ channels
Acetyl choline Esterase
Process of transmission across cholinergic synapse
1) action potential arrives in synaptic knob (presynaptic membrane)
2) Ca2+ enter pre-synaptic cell from synaptic cleft by facilitated diffusion
3) Ca2+ causes vesicle of acetylcholine fuse with pre-s membrane
4) acetylcholine released by exocytosis and diffuses across cleft
5) acetylcholine binds to receptor proteins on post-s membrane
6) Na+ channel open leading to depolarisation of post-s membrane
7) if sufficient Na+ diffuses in = threshold reached action potential is induced in post-s neurone
8) acetylcholine is hydrolyses by enzyme acetylcholinesterase to choline and ethanoic acid
Adaptions of the synapse and synaptic membranes
Mitochondria
- makes/regenerates neurotransmitters
- makes vesicles
-Na+/k+ pump to generate resting potential
Synaptic cleft
-short diameter gap = short diffusion pathway
Vesicles of neurotransmitters
- acetylcholine, noradrenaline, dopamine, adrenaline
How is neurotransmitters released to synaptic cleft
1) Action potential arrives at synaptic knob in presynaptic membrane opening Ca2+ channels
2) Ca2+ enters pre-synaptic by facilitated diffusion
3) Ca2+ causes vesicles of acetylcholine to fuse with pre-synaptic membrane
4) this releases acetylcholine by exocytosis to synaptic cleft
How does acetylcholine cause action potential in the post-synaptic cleft
1) Acetylcholine binds to receptor proteins on post-synaptic membrane
2) Na+ channels open = depolarisation of membrane
3) if threshold reached action potential induced and membrane changes permeability to Na+ causing influx making membrane positive
How is a synapse adapted to prevent acetylcholine to keep biding to receptors
Post-synaptic membrane contains the enzyme acetylcholinesterase
This hydrolyses acetylcholine after impulse into choline ad ethanoic acid
These products re-enter the pre-synaptic cell and are re-synthesised back into acetylcholine
(This process requires ATP)
Def of summation
Rapid build-up of neurotransmitters in the synapse to help generate an action potential
What are the types of summation
Temporal summation
- one neurone releases more than 1 nerve impulse so neurotransmitter repeatable releases until threshold reached
Spatial summation
- multiple presynaptic neurones release their neurotransmitters to the same postsynaptic combining to reach threshold
What is temporal summation
Two or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely because more neurotransmitter released into the synaptic cleft.
What is spatial summation
Two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone. The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach threshold
Is it true that neurotransmitters can be both excitatory and inhibitory
It is true
Neurotransmitters can be excitatory, inhibitory or both.
How do excitatory neurotransmitters work + give an example
Excitatory neurotransmitters depolarise the postsynaptic membrane, making it fire and action potential if the threshold is reached
+
E.g acetylcholine is an excitatory neurotransmitter at cholinergic synapses in the CNS and at neuromuscular junctions
How do inhibitory neurotransmitters work
+ give an example
Inhibitory neurotransmitters hyperpolarise the postsynaptic membrane (making the potential difference more negative preventing it from firing an action potential
+
E.g GABA is an inhibitory neurotransmitter that bind to receptors it causes k+ channels to open on the postsynaptic membrane, hyperpolarising the neurone
Acetylcholine is an inhibitory neurotransmitter at cholinergic synapse in the heart. When it binds to receptors here it also causes K+ channels to open ..
What is a synapse called where inhibitory neurotransmitters released by pre-synaptic membrane
Inhibitory synapses
What is a neuromuscular junction
Specialised cholinergic synapse between motor neurone and muscle cell.
Label the structure of neuromuscular junction
Include:
- motor neurone
- presynaptic membrane
- vesicles containing ACh
- ACh (acetylcholine)
- AchE (breaks down ACh
- post synaptic membrane (also called motor end plate)
- nicotine cholinergic receptors
- AChE stored in clefts
- muscle fibre
How does action potential extend at a neuromuscular junction
Basically in the same way as cholinergic synapse
1) ACh released from vesicle in presynaptic membrane
diffuses across synaptic cleft
Binds to cholinergic receptors on post synaptic membrane
Triggers Na+ move in until threshold reaches
ACh is broken down by enzyme acetylcholinesterase (AChE)
Differences between neuromuscular junction and cholinergic synapse
Neuromuscular
Only excitatory
Connects motor neurone to muscle
End point for the action potential
Acetylcholine binds to receptors on muscle fibre
Postsynaptic membrane folded to from clefts that store AChE
More receptors than other synapses
Cholinergic
Inhibitory and excitatory
Connects two neurones which could be sensory, relay or motor
New action potential generated in the next neurone
Acetylcholine binds to receptors on postsynaptic
No folds and clefts in the postsynaptic membrane
Less receptors than neuromuscular junctions
What are the 3 types of muscle
smooth muscle
- contract without conscious control
cardiac muscle
- contracts without conscious control but only found in the heart
skeletal muscle
- type of muscle that you use to move
(can also be called striated, striped or voluntary muscle)
What are skeletal muscles attached to to allow use to move
Skeletal muscles are attached to bones by tendons. Ligaments attach bone to bone. This allows arm to move
What does it mean if muscles act in antagonistic pairs
When one muscle in the pair contracts that other muscle in the pair relaxes.
Label the structure of skeletal muscle fibre
Ways in which toxins can distrust the synapse transmission
Inhibition of Na+ channels (poison dart frog)
Block Ca2+ channels. (Pufferfish)
Cause massive release of acetylcholine (black widow spider)
Block acetylcholine release (botulinum toxin)
Bind to acetylcholine receptors (snakes)
Inhibit acetylcholinesterase (nerve gases)
How can excitatory drugs work on. The synapse
+ give example of a drug for each mechanism
Mimic the neurotransmitter
- amphetamines mimic noradrenaline
- nicotine mimics acetylcholine
Stimulate release of neurotransmitters
- canine stimulates more Ca2+ ions to be uptakes
Slows/stop enzyme action to break down neurotransmitter
- nerve gases
How do inhibitory drugs work on the synapse
+. Give example of drug for each mechanism
Prevent the release of neurotransmitters
- botulinum toxin
Block action of transmitter at receptor sites
- snake venoms
What are the types of synapses
Excitatory - induce an action potential
Inhibitory - makes action potential less likely
Neuromuscular junctions - between motor neurone and muscle cells
Function of synapses
- allow single impulse along one neurone to be transmitted to number of different neurones at a synapse
- a stimulus Crete multiple simultaneous response
- number of different impulse can combine at the synapse (spatial summation)
- multiple stimuli from different receptors to interact to produce 1 response
The 2 types of effector junctions
1- neuromuscular junction (motor effector)
2- neuroglandular junction ( secretory effector)
What is neuromuscular junction
Specialised synapse between motor neurone and a skeletal muscle fibre
What are synaptic boutons in neuromuscular junctions
Synaptic boutons are extensions of the motor neurone that release neurotransmitter ACh, for role in muscle contraction
What separates the synaptic boutons from the end plate in a neuromuscular junction
The synaptic cleft
What does the end plate of neuromuscular junction contain
The end-plate constrains junction all folds with numerous ligand-gated ion channel receptors for neurotransmitters like acetylcholine
Describe the significance of acetylcholine in the neuromuscular junction
Acetylcholine is released when an action potential travels down the motor neurone binds to receptors in the muscle membrane’s junction all folds causing muscle depolarisation = muscle contraction
How does the neuromuscular junction lead to muscle contraction?
Released of ACh triggers opening of ion channels = depolarisation leading to opening of V-gated Na+ channels = action potential
