Chapter 15: Control and co-ordination Flashcards
what are the nervous and endocrine systems two examples of?
communication systems. They respond to changes in internal and external environments
what is the node of Ranvier?
the gap between two Schwann cells.
in which direction does the conduction of a nerve impulse travel?
from the cell body to the terminal branches
describe the function of sensory receptor cells
- detect changes in their surroundings
- energy transducers: they convert energy into different forms
give an example of a sensory receptor cell
Pacinian corpuscles- they detect pressure changes in the skin
describe the action of Na/K pumps
- 3x Na moved OUT
- 2x K moved IN
- the inside of the axon is more negative than the outside so the cell membrane is polarised
define ‘polarised membrane’
a membrane with a potential difference across it
define ‘depolarisation’
the loss of polarisation across a membrane
define ‘generator potential’
a small depolarisation caused by Na+ entering the cell
what is the ‘refractory period’?
the period after each action potential where it is impossible to stimulate the cell membrane to reach another action potential
what is the purpose of the refractory period?
it ensures that action potentials are only transmitted in one direction
how are action potentials transmitted?
- the temporary depolarisation causes a ‘local circuit’ between the depolarised and resting regions
- these local circuits depolarise and create APs in adjoining regions
what are the consequences of the refractory periods?
- action potentials do not merge
- there is a minimum time between action potentials
- the length of the refractory period determines the frequency of impulses
compare the speed of impulses in myelinated vs non-myelinated cells
myelinated = 100-120 ms-1 non-myelinated = 2-20 ms-1
how does myelin speed up the rate?
- insulates the axon
- Na+/K+ cannot flow through the sheath
- action potentials can only occur in the nodes of Ranvier
- local circuits exist between nodes, so APs ‘jump’ to nodes
define ‘saltatory conduction’
- the propagation of action potentials along myelinated axons from one node to the next
what is contained within the pre-synaptic knob?
- mitochondria
- smooth ER
- vesicles containing acetylcholine
- voltage-gated Ca2+ ion channels
describe the Na+ channels in the post-synaptic knob
- 5x polypeptide molecules
- 2x molecules have a receptor specific to acetylcholine
- it fits in the receptor
- this stimulates the Na+ channels to open
how is the signal transmitted across the synapse?
- AP arrives at knob and Ca2+ channels open
- Ca2+ diffuses into knob, causing vesicles to move to and fuse with the presynaptic membrane
- acetylcholine is released by exocytosis
- acetylcholine molecules diffuse across cleft and bind to Na+ channels
- Na+ channels open and Na+ diffuses into neurone
- generator potential is created. A threshold potential is reached, so a new action potential is generated in the post-synaptic neurone
describe acetylcholinesterase
- found in synaptic cleft
- hydrolyses acetylcholine –> ethanoic acid + choline
- stops the transmission of APs
- the products are recycled and recombined using ATP
how do muscles contract?
- tropomyosin and troponin on the actin prevents myosin from binding
- upon muscle contraction, they change shape and the myosin heads can bind to actin
- the myosin heads tilt and pull the actin. The muscle contracts
- ATP hydrolysis causes the release of myosin heads
describe the roles of the synapses
- ensure one-way transmission
- allow integration of impulses (the brain is not overloaded)
- allow the interconnection of pathways
what are the T-tubules?
deep infoldings into the interior of the muscle
describe the structure of a microfibril
made of two filaments:
- thick = myosin
- thin = actin
describe the structure of myosin
- fibrous protein
- globular head
- the molecules line up with their globular heads all pointing away from the M line
describe the structure of actin
- globular protein
- link together to form a chain
- tropomyosin is twisted around the actin
- troponin is attached to the actin at regular intervals
describe the adaptations of a venus flytrap
- stimulation of a single hair does not result in closure
- the gaps between the hairs allow small, unwanted insects to crawl out
describe how auxins control growth
- stimulates cells to pump H+ into the cell wall
- the cell walls are acidified
- bonds between cellulose fibres and the matrix weaken
- the cells can absorb water, so stretch
describe how the height of plants is partially controlled by genes
- Le (dominant allele) = tall
- le (recessive allele) = short
- Le codes for a functioning enzyme in the gibberellin synthesis pathway
describe how seeds germinate
- water uptake into the seed
- embryo synthesises gibberellin in response to water uptake
- aleurone layer synthesises amylase in response to gibberellin
