Peripheral Nervous System Flashcards
What are signals for the PNS?
Hormones
Nerves
Muscles
What do action potentials require?
Excitable cells and voltage gated ion channels
What do voltage gated ion channels give rise to? Are they graded or all or nothing?
Positive feedback loop
All or nothing
The strength of an impulse is altered by what?
Number and frequency of action potentials
Most voltage gated ion channels use which ion?
Sodium
When are voltage gated ion channels calcium gated?Are they faster or slower than sodium?
Some smooth muscle
Cardiac cells
Endocrine cells
much slower
Calcium is a second messenger. What does this mean?
It can link with an action potential with intracellular signalling
What is the absolute refractory period? What is the state of the ion channels?
Interval where a secondary action potential cannot be initiated, no matter the stimulation size
All channels inactivated
How many gates are involved in sodium gated ion channels? How many states?
2 gates, therefore 3 states
What are the 3 stages of sodium based action potentials?
Deactivated - low membrane potential, closed
Activated - open
Inactivated - closed for refractory period
What is the relative refractory period?
Second action potential is inhibited but not impossible
Some sodium ion channels inactivated,
Increased K+ conductance
What is a nerve fibre?
Part of a neuron
What is the cell body of a neutron?
Perikaryon
Soma
What are dendrites?
Receiving antenna of a neuron
What are microfilaments and microtubules?
Protein networks which provide transport and structure for neurons
What are nodes of Ranvier/
Gaps in the myelination of an axon
What are terminal buttons?
Part of presynaptic neurone
Release neurotransmitters into the cleft
What is the opposite of saltatory conduction?
Continuous conduction
Non myelinated sheath, depolarisation of adjacent parts of the membrane
Do synapses give graded or all or nothing excitation? Why are they better than the few ions which transport via gap junctions?
Graded
Synchronised and allow communication
Are synapses excitatory or inhibitory?
Both
If excitatory - depolarise membrane more positive, bring to threshold
Inhibitory - hyperpolarises membrane to make it more difficult to reach the threshold
What is EPSP and IPSP
Excitatory post synaptic potentials
Inhibitory post synaptic potentials
What are the 3 ways neurotransmitter can be removed from the synaptic cleft?
Enzyme degradation
Diffusion
Uptake by cells
Are neurotransmitters excitatory or inhibitory? What can they be blocked by?
Both
Agonists, antagonists
What is temporal summation?
One presynaptic neurone to one postsynaptic neurone
What is spatial summation?
Multiple presynaptic neurones to one postsynaptic neurone
What is the neuromuscular junction between? Is it excitatory or inhibitory?
Motor neurone and skeletal muscle
Excitatory - inhibition by CNS
What is the process that takes place in a neuromuscular junction?
Action potential in motor neurone propagated to terminal button, which triggers the opening of calcium channels
Calcium enters terminal button and triggers exocytosis of acetylcholine
Acetylcholine is degraded by acetylcholinesterase to acetate and choline
Choline taken back into presynaptic terminal
What are the similarities between NMJ and a synapse?
Both excitable and separated by cleft
Axon terminals store chemical messenger
Binding of a neurotransmitter leads to ion channels opening and change in membrane potential
Changes in membrane potential are graded
What are the differences between NMJ and a synapse?
Between two neurones, between motor neurone and skeletal muscle
1 to 1 transmission of action potential at neuromuscular junction, whilst at synapse only occurs when EPSP reaches threshold
NMJ always excitatory, synapses can be either
