Regulation and reproduction Flashcards
What is membrane potential?
- electric charge difference
- across membrane
What is resting potential?
- imbalance of positive and negative charges across membrane (-70mV)
- no signal
- inside negative, outside positive
What causes resting potential?
- inside
- K+
- protein anions (-)
- outside
- Na+
- Cl-
- sodium-potassium pumps (ATP needed)
- for every 3Na+, 2K+ are pumped
- more Na+ on the outside
- for every 3Na+, 2K+ are pumped
- leakages
- voltage gated channels = open at certain electrical potential value
- closed are leaky
- more K+ leaks outside
- closed are leaky
- voltage gated channels = open at certain electrical potential value
How do voltage-gated channels work?
- Na+
- open at threshold potential (depolarisation)
- Na+ in
- close at action potential
- K+
- open at action potential (repolarisation)
- K+ out
- close after reaching resting potential again
How is action potential propagated?
- ion movement depolarises one part
- Na+ inside move from depolarised part to not yet depolarised
- Na+ outside move the opposite direction
- difference = -50mV (threshold potential reached) - impulse initiated at one terminal
- passed at other terminal
What is axon hillock?
- junction between cell body and axon
- plasma membrane composition changes
- voltage-gated channels
- plasma membrane composition changes
- initiates electric impulse
- small amounts of Na+ accumulate there
What is depolarisation?
- Na+ in axon hillock
- charge grows inside neurone
- plasma membrane depolarisation
- threshold potential is reached (-55mV)
- voltage-gated channels open
- Na+ inside
- more Na+ channels open = positive feedback
- charge changes to 40mV = action potential
- Na+ inside
- voltage-gated channels open
What is repolarisation?
- at action potential
- Na+ closes — K+ open
- K+ outside
- charge drops
- K+ and Na+ at wrong sides
What is hyperpolarisation?
- K+ channels close
- slow
- potential inside drops further than resting state
What happens at the absolute refractory period?
- after action potential
- Na+ channels can’t open
- no action potential
- prevents backflow
What happens at relative refractory period?
- hyperpolarisation
- harder to reach threshold potential
- stronger stimulus needed (more Na+)
How is action potential propagated forward?
- depolarisation
- opens channels in next part of axon
- signal goes forward
- opens channels in next part of axon
- local currents
- Na+ inside the cell (depolarised part) move to the polarised part
- Na+ outside the cell (polarised) moves to depolarised part
- this prevents signal from going backwards
- reduces concentration gradient (easier to reach -55mV)
What is myelin?
- coats nerve fibres
- phospholipid bilayer
- Schwann cells deposit myelin
- 20 or more layers
- Schwann cells deposit myelin
- gap: node of Ranvier
- saltatory conduction
- impulse jumps from node to node
- quicker
- impulse jumps from node to node
What is a synapse?
- space between the axon terminals of one nerve and dendrites of the other
- or muscles and glands
- fluid-filled gap = synaptic cleft (20nm)
How does a signal move?
- neurotransmitters send signals across synapses
- from signal to receiver cell
- receptors on post-synaptic cell
- diffusion
- from signal to receiver cell
What are the steps of synaptic transmission?
- impulse propagated along pre-synaptic neuron
- reaches axon terminal
- depolarisation of membrane
- voltage-gated channels of Ca2+ open
- Ca2+ inside
- voltage-gated channels of Ca2+ open
- Ca2+ influx causes vesicles with neurotransmitters to move
- fuse with membrane
- neurotransmitter is released to synaptic cleft
- exocytosis
- neurotransmitters bind to post-synaptic receptors
- Na+ channels open
- Na+ into the cell
- threshold potential
- Na+ into the cell
- neurotransmitter degraded by enzyme or back into pre-synaptic membrane by a transporter or reuptake pump
How are neurotransmitters in axon terminal?
- produced in cell body
- in vesicles
- transported to axon terminal
- in vesicles
What happens after synaptic transmission?
- vesicles fuse with pre-synaptic membrane
- enlarged
- neurotransmitter reuptake
- endocytosis
What is a motor neurone?
- from central nervous system (CNS) to muscles
- elongated axon - connected to muscle
- neuromuscular junction
- chemical synapse
- neurotransmitter: acetylcholine (cholinergic)
- chemical synapse
- neuromuscular junction
How is acetylcholine produced?
- pre-synaptic cell
- combining choline (diet) with acetyl group (aerobic respiration)
How does cholinergic synapse work?
- acetylcholine is released after Ca2+ influx
- ACh binds to Na+ channel receptors
- threshold potential
- shortly bounded: only 1 action potential
- acetylcholinesterase (in synaptic cleft) breaks ACh down into choline and acetate
- choline is reabsorbed by pre-synaptic neuron
- back into ACh
How is knowledge about synaptic transmission applied?
- neuronal and mental diseases
- Selective Serotonin Reuptake Inhibitor (SSRI) = antidepressants
- neuroactive toxins
- neonicotinoids (pesticide)
What are neonicotinoids?
- similar to nicotine
- binds acetylcholine receptors
- insects
- acetylcholinesterase doesn’t break it down
- irreversible
- paralysis and death
- not toxic to humans
- more cholinergic synapses in CNS of insects
- bind less strongly to receptors
- imidacloprid = commonly used pesticide
- harmful for honeybees
What are hormones?
- chemical messengers
- produced by endocrine glands
- homeostasic regulation
- modification of activity of tissues
- transported by blood
- slower but long lasting effects
What are the differences between nervous and endocrine system?
- nerve impulse vs chemical messenger
- neurons vs blood
- fast vs slow
- carried to specific cells vs throughout body
- muscles / glands vs range of organs affected
What are different types of hormones?
~ steroids
- receptors in nucleus
- action by transcription regulation
- affect gene expression
- slow
> peptides
- receptors in plasma membrane
- act by signalling cascade
- affect chemical processes and gene expression
- fast
> proteins, glycoproteins, amines or tyrosine derivatives
How do steroid hormones work?
- cross through plasma and nuclear membrane
- bind to receptors
- ex. sex hormones
- form receptor-hormone complex
- serves as transcription factor (promotion or inhibition)
- produced from cholesterol
- calciferol: intestinal cell membrane
- complex affects expression of calcium transport protein calbindin
- absorption of calcium
- complex affects expression of calcium transport protein calbindin
- cortisol binds in cytoplasm and enters nucleus
- in liver cell: gluconeogenesis
- conversion of fats and proteins into glucose
- decreases expression of insulin receptor
- in pancreas
- in liver cell: gluconeogenesis
How do peptide hormones work?
- bind to membrane receptors
- triggers cascade reaction, edited by second messengers
- hydrophilic so cannot pass the membrane
What is an example of second messengers?
- water soluble — spread signal fast
- Ca2+ and cyclic AMP (cAMP)
How does epinephrine signalling work?
- epinephrine mediates “fight or flight” (first messenger)
- supply of glucose (energy) needed
- in liver binds to G-protein couple receptor
- activation of G-protein
- uses GTP as energy to activate enzyme adenylyl cyclase
- ATP —> cAMP
- uses GTP as energy to activate enzyme adenylyl cyclase
- activation of G-protein
- cAMP (cyclic adenosine monophosphate) activates protein kinase enzymes
- glycogen breakdown and inhibit glycogen synthesis