Unit 15: Control & Coordination (JW) Flashcards
Describe endocrine system
endocrine glands -> ductless glands
- in good blood supply -> secrete hormones into bloodstream as soon as possible
Define and describe hormones
Hormones = cell-signalling molecules secreted to bloodstream
- only affect cells with receptors that the hormone can bind to
- water-soluble -> cannot cross phospholipid bilayer of CSM
- binds to receptor -> which activates 2nd messenger to transfer signal throughout cytoplasm
Extra: steroid hormones and their properties?
other hormones such as testosterone, oestrogen & progesterone are steroid hormones
- lipid soluble
- can cross phospholipid bilayer
- bind to receptors in cytoplasm/nucleus of target cells
compare the features of the nervous system and the endocrine system
- Impulse vs hormone
- Electrical vs. chemical
- Neurone vs blood
- Muscle/gland vs target organ (organs, tissue, cells)
- Faster vs slower
- Specific vs widespread
- Short-term vs long-lasting
- CSM vs CSM/within cell
Both: (similarities)
- Involve cell signalling
- Involve signal molecule binding to receptor
- involve chemicals
Describe the function of 3 diff types of neurone
Sensory neurone - transmit impulse from receptor to intermediate neurone
Motor neurone - transmit impulse from intermediate neurone to effector/muscle/gland
intermediate neurone - connect sensory & motor neurone
outline the role of sensory receptor cells
detect stimuli, e.g. light, heat
act as transducers by converting stimuli energy to electrical energy
produces receptor potential
Passes impulse to sensory neurone
Describe structure of motor neurones
- Dendrites -> dendron -> to cell body in centre
- Nucleus in cell body
- Many mito & rER
- 1 long axon
- Synaptic knobs furthest from cell body
- Schwann cells
- Nodes of Ranvier
Describe structure of sensory neurones
nucleus in, cell body / soma ;
(long) dendron ;
3 (short) axon ;
4 many mitochondria (in cell body) ;
5 many, RER / ribosomes or presence of Nissl’s granules (in cell body) ;
6 synaptic, knobs / terminals / boutons ;
7 Schwann cells / myelin sheath ;
8 nodes of Ranvier
describe the sequence of events that results in an action potential in a sensory neurone
Na+ ions enter chemoreceptor cell through microvilli
CSM depolarised
receptor potential > threshold
Ca2+ channels open, Ca2+ enter cytoplasm
vesicles move towards and fuse with presynaptic membrane
released to synaptic cleft by exocytosis
diffuses across synaptic cleft
binds to receptors on sensory neurone
Na+ enters sensory neurone
depolarisation
such that receptor potential > threshold potential
Describe how a resting potential is set up and maintained in a myelinated neurone
Na+ moves out of, cell and K+ moves into cell ;
3 Na+ for every 2 K+ ;
by, active transport / use of ATP ;
sodium-potassium pump / Na+ K+ pump ;
against concentration gradient ;
K+ diffuses out of cell and Na+ diffuses into cell ;
by facilitated diffusion / diffusion through (ion) channels ;
membrane more permeable to K+ / more K+ goes out than Na+ in ;
inside of, cell / membrane, more negative than outside ; ora
membrane / cell, polarised / repolarised ;
(resting potential is), –60 mV / –65 mV / –70 mV ;
AVP ; e.g. ion movement only at nodes of Ranvier
Describe refractory period
Neurone is unresponsive as it is recovering
until repolarisation occurs and resting potential is established, axon membrane undergoes refractory period
when resting potential close to being reestablished, K+ close, Na+ open -> responsive to depolarisation again
describe and explain the rapid transmission of an impulse in a myelinated neurone
- Schwann cells wrap around axon
- myelin sheath insulates axon
- Ions cannot pass through
Na+ channels only occur at nodes of Ranvier
depolarisation only occurs at nodes - APs occur at nodes of Ranvier only
- Longer circuits/currents
- APs must jump from node to node (saltatory conduction)
- Faster transmission of impulses (approx 50x faster)
1 way transmission
Explain the importance of the refractory period in determining the frequency of impulses
Ensures AP are discrete events - prevent merging into one another
So, 1 way transmission = establish minimum time between APs occuring only at 1 place along neurone
Ensures new APs are generated ahead, rather than behind original AP - as region behind is recovering from AP that has just occurred
Length of refractory period determines maximum frequency of impulse transmission
Describe the structure of a cholinergic synapse and explain how it functions, including the role of calcium ions
AP reaches presynaptic neurone =
Ca2+ channels open = Ca2+ enters presynaptic neurone
causes vesicles containing ACh to move towards & fuse with presynaptic membrane
ACh released to synaptic cleft by exocytosis
ACh diffuses across synaptic cleft
binds to receptors on postsynaptic membrane
Na+ channels open = Na+ enter = Postsynaptic neurone
Depolarised
Acetylcholinesterase breaks down ACh
Explain the role of acetylcholinesterase in a synapse.
Enzyme that breaks down ACh = ACh leaves the binding site = recycles ACh too
Depolarisation stops in postsynaptic neurone = so stops continuous APs
