Topic 6- Responding to changes in environment Flashcards
what is a stimulus?
change in the internal or external environment of an organism
what is a receptor?
detects the stimulus to coordinate a response
what is taxis?
directional response to a stimulus
positive- towards
negative- away
what is kinesis?
non- directional response to stimulus
central nervous system
made of brain and spinal cord
peripheral nervous system
pairs of nerves originating from the brain or spinal cord
sensory neurones
carry nerve impulses from receptors to CNS
motor neurones
carry nerve impulses away from the CNS to receptors
voluntary nervous system
carries nerve impulses to body muscles and is under conscious control
autonomic nervous system
carries nerve impulses to glands, smooth muscle and cardiac muscle and is carried out subconsciously
simple reflex arc
stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response
importance of reflex arcs
1) involuntary meaning brain is left to carry out more complex responses
2) protect body from harm
3) fast due to very few synapses
pacinian corpuscle
detects mechanical pressure (mechanoreceptor)
at resting potential when sodium ion channels are too narrow for Na+ to pass through
when pressure is applied, the layers are distorted and stretch-mediated sodium ion channels open
influx of Na+ depolarises the membrane producing a generator potential therefore producing an action potential
where are rod and cone cells found?
fovea (cone)
retina (rod)
rod cells
~ higher density
~ cannot distinguish between different wavelengths meaning colour can’t be seen
~ multiple rod cells attached to one bipolar neurone leading to retinal convergence
~ higher chance of threshold being reached
~ help us to see when light is low
~ contain rhodopsin
~ low visual acuity
cone cells
~ three types each responding to different wavelengths meaning we can see in colour
~ lower density
~ each cone cell attached to a bipolar neurone leading to high visual acuity
~ contain pigment iodopsin
~ can only respond to high light intensity
sympathetic nervous system
stimulates effectors
fight or flight response
parasympathetic nervous system
inhibits effectors
conserving nearby and replenishing the body’s reserves
why is the heart myogenic?
contraction initiated from inside rather than by nervous impulses
sequence of steps that control heart rate
1) wave of electrical excitation spreads from SAN across atria causing them to contract
2) atrioventricular septum prevents wave crossing into ventricles
3) wave of excitation enters AVN
4) AVN conveys wave between ventricles through purkyne tissue which makes up the bundle of His
5) wave conducted down to base of ventricles where it’s released from the purkyne tissue causing ventricles to contract
what part of the brain controls changes to heart rate?
medulla oblongata
centre that increases heart rate- linked to SAN by sympathetic nervous system
centre that decreases heart rate- linked to SAN by parasympathetic nervous system
chemoreceptors
found in aorta and carotid artery
detect changes in blood pH
process of blood pH control
1) carbon dioxide conc. increases meaning blood pH decreases
2) detected by chemoreceptors which increases impulses to the centre in the medulla oblongata which increases heart rate
3) increases frequency of impulses via sympathetic nervous system to the SAN which will increase heart rate
4) increased blood flow removes more carbon dioxide so blood pH rises to normal
baroreceptors
detect blood pressure
in aorta and carotid arteries
process when blood pressure is high
barocreceptors send more impulses to centre of medulla oblongata that decrease heart rate
sends impulses via parasympathetic nervous system to SAN decreasing the heart beats
two types of coordination in animals
nervous system- transported by neurones, fast, short-lived
hormonal system- transported by blood, slow, long-lasting
myelinated neurones
- cell body
- dendrons —> dendrites
- axon
- myelin sheath made of schwann cells
- nodes of ranvier
- impulses move by saltatory conduction making them faster than non-myelinated neurones
resting potential
charge inside axon is at -70mV (polarised)
3Na+ actively transported out of axon
2K+ actively transported into axon
Na+ channel closed
action potential
stimulus of sufficient size causes threshold level (-55mV) to be reached
Na+ channels open causing an influx of Na+ (depolarisation)
once potential difference of around +40mV has been reached, Na+ channels close
repolarisation
K+ channels open
hyperpolarisation
temporary overshoot of electrical gradient meaning inside is more negative then normal
K+ channels close
factors affecting speed of conduction
myelin sheath
diameter of axon
temperature
all-or-nothing principle
any stimulus, of any strength, that is at threshold level will create an action potential of the same size
refractory period
Na+ channels are closed for a period of time
ensures action potentials go in one direction
produces discrete impulses
limits number of action potentials
synapse structure
presynaptic and postsynaptic neurones
synaptic cleft
synaptic vesicles
neurotransmitters
Na+ channels
Ca2+ channels
unidirectionality of synapses
synapses can only pass information in one direction- from presynaptic to postsynaptic neurone
spatial summation
many presynaptic neurones release enough neurotransmitters to exceed threshold level in the postsynaptic neurone
temporal summation
single presynaptic neurone releases neurotransmitter many times over a very short period.
inhibitory synapses
postsynaptic neurone hyperpolarised due to Cl- moving in and K+ moving out
cholinergic synapses
1) action potential arrives at presynaptic neurone
2) Ca2+ channels open causing an influx (depolarisation)
3) synaptic vesicles move towards membrane and fuse
4) acetylcholine diffuses down conc. gradient in synaptic cleft and binds to receptors on Na+ channels
5) Na+ channels open causing an influx
6) if threshold is reached an action potential is generated
7) acetylcholinesterase hydrolyses acetylcholine into choline and acetyl which diffuses back across
7) prevents action potentials from being continuously generated
8) ATP recombines the 2 products into acetylcholine for future use
neuromuscular junction
works in a similar way to cholinergic synapses except there’s no postsynaptic neurone, just muscles fibres
only excitatory
action potential ends here
What are the 3 changes in the environment that plants respond to?
light (phototropism)
gravity (gravitropism)
water (hydrotropism)
plant growth factors
hormone-like substances released in a response to external stimuli
What does IAA stand for?
indoleacetic acid
what is IAA?
type of auxin
found in the top of shoots (apex)
controls plant elongation
what type of phototropism is found in plants?
positive phototropism (grows towards light)
what type of phototropism is found in roots
negative phototropism
positive phototropism in shoots
1) Cells in the tip produce IAA
2) IAA is initially transported evenly throughout the shoot
3) light causes IAA to move from the light side to shaded side
4) greater concentration of IAA on shaded side
5) IAA stimulates cell elongation
6) shoot grows towards the light
negative phototropism in roots
1) IAA moves away from light side to shaded side
2) IAA inhibits cell elongation
3) Roots grow away from the light
what type of gravitropism is found in shoots?
negative gravitropism
what type of gravitropism is found in roots?
positive gravitropism
negative gravitropism in shoots
1) IAA accumulates on lower side of the shoot
2) stimulates cell elongation
3) shoot grows away from gravity
positive gravitropism in roots
1) IAA accumulates on lower side
2) inhibits cell elongation
3) Root grows towards gravity
acid growth hypothesis
active transport of hydrogen ions from cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate by expansion.
how do neuromuscular junctions work?
same process as cholinergic synapses up to the depolarisation of the sarcolemma
~ depolarisation travels down tubules leading to release of calcium ions from stores in sarcoplasmic reticulum
~ acetylcholine broken down
what are the 3 types of muscles?
cardiac
smooth
skeletal
smooth muscle
found in lining of internal organs
involuntary
non-striated
spindle shape and only have one nucleus
cardiac muscle
in heart
involuntary
specialised striated
single nucleus per fibre
branching
skeletal muscle
attached to skeleton
voluntary
contacts in one direction
run parallel
multinucleated
what are myofibrils?
tiny muscle fibre that makes up an individual muscle
describe the structure of muscle fibres
t-tubules
sarcolemma (cell membrane)
mitochondria (ATP for contraction)
sarcoplasm
myofibrils
sarcoplasmic reticulum
what are sacromeres?
repeating units of myofibrils
hierarchy of muscle organisation
muscles
muscle fibres
myofibrils
protein fibres
what are the two types of muscle fibre?
myosin
actin
slow twitch fibres
contact more slowly
less powerful contractions over a longer period of time
adapted to endurance work
aerobic respiration
darker in colour due to the rich blood supply and large store of myoglobin
fast twitch fibres
contact more rapidly
more powerful contractions over a short period of time
adapted to intense exercise
anaerobic respiration
high concentration of glycogen
store of phosphocreatine which can rapidly generate ATP form ADP