Neuronal Communication Flashcards
what are neurones
transmit electrical impulses rapidly around the body so an organism can respond to changes in its internal and external environment
what is the structure of a neuron
Cell body - nucleus surrounded by a cytoplasm
Dendrons - extensions from cell body - dendrites transmit electrical impulses
Axons - elongates nerve fibres that transmit impulses away from the cell body
what are the types of neurones
Sensory - transmit impulses from sensory receptors to CNS
Relay - transmit impulses between sensory and motor neurones
Motor - transmit impulses to a muscle / gland (effector)
what are myelinated neurones
- myelin sheath made from Schwann cells
- acts as an insulating layer and allows myelinated neurones to conduct the impulse at a faster speed
- nodes of Ranvier allow the impulse to jump
what are sensory receptors
transducers - convert stimulus they detect into a nerve impulse
what are examples of sensory receptors
mechanoreceptors - pressure
chemoreceptor - chemicals
thermoreceptor - heat
photoreceptor - light
what are Pacinian corpuscles
- detect mechanical pressure
- deep within the skin
- stretched mediated sodium channel that transports sodium ions
how do pacinian corpuscles work
- in resting state the stretch mediated sodium ion channels in sensory neurone membrane are too narrow
- applied pressure to pacinian corpuscles changes the shape
- sodium ion channels widen and ions diffuse into the neurone
- influx of sodium ions depolarise the membrane = generator potential
- generator potential creates an action potential
- action potenital is transmitted along neurones to the CNS
what is resting potential
- outside of the membrane is more positively charged
- membrane is polarised as there is a potential difference
- occurs due to the movement of sodium and potassium ions
how is a resting potential created
- Na+ actively transported out of the axon and K+ in by intrinsic protein (sodium potassium pump)
- every 3 Na+ pumped out 2 K+ pumped in
- more Na+ ions outside the membrane than in thee axon cytoplasm
- Na+ diffuses back into the axon down electrochemical gradient
- gated Na+ channels are closed and K+ channels are open
- K+ ions can diffuse out of the axon
- more positively charged ions outside of the axon then inside creating resting potenital
what is an action potential
- caused by the rapid movement of Na+ and K+ ions across the axon membrane through voltage gated ion channels
what are the 5 stages in an action potential
- stimulus
- depolarisation
- repolarisation
- hyperpolarisation
- resting potential
in an action potential what happens at the stimulus
- sodium ion channels open
- voltage gated sodium channels closed
- must meet threshold of excitation
in an action potential what happens at depolarisation
- voltage gated Na+ channels open
- Na+ ions pass into axon down electrochemical gradient
- reduces potential difference
- inside of the axon is less negative
in an action potential what happens at repolarisation
- at +30mv all Na+ voltage channels close
- K+ voltage gated channels open
- K+ ions diffuse out of the axon down the concentration gradient
- returns resting potential
in an action potential what happens at hyperpolarisation
- K+ channels are slow to close
- too many K+ ions diffuse out of the neurone
- potential difference is more negative than the normal resting potential
in an action potential what happens at resting potential
- once al K+ channels are closed the sodium potassium pump restores the resting potential
- Na+ can then repolarise again
what is the all or nothing principle
an impulse is only transmitted if the initial stimulus is sufficient enough to increase the membrane potential above a threshold potential
what is the refractory period
- ensures action potentials are discrete events (separate)
- new action potential are generated ahead
- impulse only travels in one direction
- creates a minimum time between action potentials
what is the speed of conduction
- how quickly an impulse is transmitted along a neurone
- myelination
- diameter of axon
- temperature
how does myelination affect the speed of conduction
- increases the speed that action potentials travel
- depolarisation cannot occur at the myelin sheath
- action potentials only occur at the nodes
- Schwann cells allow the impulse to jump from one node to the next (saltatory conduction)
how does the diameter of the axon affect the speed of conduction
- thick axons = impulse travels at high speeds
- axon membrane has a greater surface area
- increases rate of diffusion of ions which increases the rate of action potentials
- greater volume of cytoplasm reduces electrical resistance and action potential moves faster
how does temperature affect the speed of conduction
- more impactful on ectotherms
- cold conditions slow down nerve impulses
- cold = less kinetic energy available for facilitated diffusion of Na+ and K+ ions
what is the synaptic cleft
gap that separates the axon of one neurone from the dendrite of the next
what is the presynaptic neurone
neurone along which the impulse has arrived
what is the postsynaptic neurone
neurone that receives the neurotransmitter
what are synaptic vesicles
vesicles containing neurotransmitters that fuse with the presynaptic membrane and release contents into the synaptic cleft
what are excitatory neurotransmitters
- result in depolarisation of the postsynaptic neurone
- if meets threshold it triggers an action potential
-acetylcholine
what are inhibitory neurotransmitters
- result in hyperpolarisation of the postsynaptic membrane
- prevents an action potential being triggered
how is an impulse transmitted across a synapse
- action potential reaches the end of the presynaptic neurone
- depolarisation of presynaptic membrane causes calcium ion channels to open
- calcium ions diffuse into the presynaptic knob
- synaptic vesicles with neurotransmitters fuse which presynaptic membrane
- neurotransmitters are released into the synaptic cleft by exocytosis
- neurotransmitters diffuse across the synaptic cleft and binds with receptor molecules on the postsynaptic membrane
- sodium ion channels open
- sodium ions diffuse into the postsynaptic neurone
- triggers an action potential
- neurotransmitters are recycled or destroyed once an impulse is sent
how does transmission occur across a cholinergic synapse
- arrival of an action potential at the presynaptic neurone causes calcium ion channels to open
- calcium ions enter synaptic knob
- influx of calcium ions causes synaptic vesicles to fuse with presynaptic membrane and release ACh into the synaptic cleft
- Ach fuse with receptor sites on the sodium channel in postsynaptic neurone
- Na+ channels open and ions diffuse rapidly along concentration gradient
- influx of Na+ generates action potential in postsynaptic neurone
- ACHnase hydrolyses Ach into choline and acetyl to diffuse into presynaptic neurone
- prevents from continuously generating action potentials
- ATP in mitochondria is used to recombine choline and ethanoic acid into Ach
what is the role of a synapse
- ensures impulses only travel from the presynaptic to the postsynaptic neurone
- allow an impulse from one neurone to be transmitted to a number of neurones
what is summation
effect of multiple impulses can be added together
what is spatial summation
- number on presynaptic neurones connected to one postsynaptic neurone
- each releases neurotransmitters which build up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone
what is temporal summation
- a single presynaptic neurone releases neurotransmitters as a result of an action potential several times
- builds up in the synapse until the quantity is sufficient to trigger an action potential
