Nervous coordination Flashcards
What are the 7 parts of a nerve cell?
Nucleus, cell body, dendrites, axon, Schwann cells, nodes of Ranvier, axon terminal
How is the resting potential of a neurone achieved?
Sodium-potassium pump moves 3 Na+ out of the neurone and 2 K+ into the neurone via active transport
Membrane is more permeable to K+ than Na+
Some K+ diffuses out of the neurone
Higher conc. of Na+ outside and higher conc. of K+ inside the neurone
What is the voltage of the resting potential of a neurone?
-70mV
How is an action potential achieved?
- Na+ channels open and Na+ ions diffuse in which causes depolarisation
- If depolarisation exceeds threshold, action potential created
- Na+ channels close and K+ channels open
- K+ ions diffuse out which causes repolarisation
- Eventually hyperpolarisation occurs so K+ channels close
- Sodium-potassium pump restores resting potential
Refractory period definition
Time during which no new action potentials can be generated
What are the 3 reasons why refractory periods are important?
- Allows action potentials to travel in one direction
- Produces discrete impulses
- Limits the maximum frequency of action potentials
Explain the all or nothing principle
Action potential is an all or nothing response and is always the same size - if threshold is reached you get an action potential, if not reached there is no action potential
How does the brain determine the strength of a stimulus?
Stronger stimulus = greater frequency of action potentials to the brain
Explain propagation of an action potential along an UNMYELINATED neurone (3 steps)
- Action potential occurs at section of axon membrane
- Voltage gated Na+ channels in membrane, adjacently in front of action potential, detect depolarisation and open, also forming an action potential
- Action potential moves forward in one direction - refractory period behind action potential prevents impulse from being conducted backwards
Explain propagation of an action potential along a MYELINATED neurone (4 steps)
- Myelin insulates axon, preventing ion movements
- Depolarisations only take place at nodes of Ranvier
- Saltatory conduction occurs
- Less depolarisations along whole length of axon membrane
What 3 ways can speed up the conduction of action potentials?
- Myelination - allows saltatory conduction
- Higher temp. - increases kinetic energy of ions so they diffuse faster through membrane
- Greater axon diameter - reduces resistance to ion flow
What are the 8 parts which make up a synapse?
- Pre-synaptic neurone
- Post-synaptic neurone
- Mitochondrion
- Synaptic vesicle
- Synaptic cleft
- Neurotransmitter receptor
- Ca2+ channel
- Neurotransmitter reuptake pump
What are the 6 steps to the transmission of an impulse across a CHOLINERGIC synapse?
- Action potential depolarises pre-synaptic membrane
- Voltage-gated Ca2+ channels open and Ca2+ ions diffuse in
- Ca2+ causes synaptic vesicles to fuse with pre-synaptic membrane and release ACh into synaptic cleft
- ACh diffuses across synaptic cleft and binds to receptors on post-synaptic membrane
- Na+ channels open and Na+ diffuses into post-synaptic neurone, depolarising it and causing action potentials
- Acetylcholinesterase hydrolyses ACh so Na+ channels close and no more action potentials are generated
What does summation do?
Increases the amount of neurotransmitter released to increase depolarisation so it is more likley to reach threshold
Explain spatial summation
More than one pre-synaptic neurone releasing neurotransmitter onto one post-synaptic neurone
Explain temporal summation
Several action potentials arrive in a short time from ONE pre-synaptic neurone to ONE post-synaptic neurone, increasing neurotransmitter
What is unidirectionality and what 2 things enable synapses to have this?
Action potentials travel in one direction
- Neurotransmitter is only released from the pre-synaptic neurone
- Receptors are only on the post-synaptic neurone
What effect does Cl- channels on the post-synaptic membrane have and how does this lead to synapse inhibition?
Makes the post-synaptic neurone more negative, more Na+ needed to reach threshold for an action potential
What are 3 differences between cholinergic synapses and neuromuscular junctions?
- Cholinergic synapses are neurone to neurone whilst neuromuscular junctions are neurone to muscle fibre
- Cholinergic synapses can be excitatory or inhibitory whilst neuromuscular junctions can only be excitatory
- Cholinergic synapses have less ACh receptors on the post-synaptic membrane whilst neuromuscular junctions have more ACh receptors on the muscle fibre
