neuronal communication Flashcards
Nervous system components
-Sensory receptors
-neurones
-synapses
-CNS
-effectors
Sensory receptors
Convert energy of stimulus to electrical energy (transducers)
-specialised cells that detect changes in stimuli
Receptor cells stimulated
When receptor stimulated potential difference occurs (resting potential)
Pacinian corpuscles
they are mechanoreceptors that detect MECHANICAL stimuli (pressure, vibrations)
Types of energy conversion
Retina - light to electrical
Ear - kinetic to electrical
Muscles - kinetic to electrical
Nerve impulses stages
-stimulus
-threshold
-depolarisation
(+35mv)
-action potential reached
-repolarisation
-refractory period
Threshold
Between -50mv & -55mv
Depolarisation
once threshold is reached the voltage gated sodium ion channels open
-more sodium ions diffuse into neuron
-membrane becomes depolarised
Action potential
between +30mv & +40mv
-sodium channels close and potassium gates open
all or nothing, if nerve impulse does not reach threshold nothing will happen
Repolarisation
membrane is now more permeable to potassium so they diffuse down conc gradient out of membrane
back towards RESTING POTENTIAL
negatively charged on inside
Refractory period
potassium ion channels take a while to close so we go past resting potential (too many move out)
p.d becomes more negative
sodium potassium pump returns it back to normal
Synapse functions
A junction between a neuron and another neuron or an effector cell
– Act as junctions
-Filter out low level stimuli
Synaptic bulb
A swelling at the end of the presynaptic membrane
-many mitochondria
-smooth ER
-vesicles with acetylcholine
Transmission across synaptic cleft
-action potential arrives
-voltage gated calcium ion channels open (on presynaptic)
-calcium ions move into presynaptic bulb
-ca2+ ions cause vesicles containing acetylcholine to move to presynaptic membrane
-vesicles fuse & release AC into synaptic cleft
-AC diffuses across to postsynaptic membrane
-AC binds to receptors
-causes sodium ion channels to open (causing threshold etc)
Acetylcholinesterase
Enzyme found in synaptic cleft
-hydrolyses acetylcholine into ethanoic acid & choline
-choline taken back to presynaptic membrane to reform acetylcholine
Spatial summation
2 or more presynaptic neurons converge to release onto 1 post synaptic neuron
Termporal summation
1 neuron sending 2 or more nerve impulses to postsynaptic neuron
-more chance of action potential to be reached
(multiple signals, 1 response)
Acclimation
Prevent overstimulation & fatigue
-Memory (formation of new neuronal pathways
sensory neuron
transmit nerve impulses from receptor to CNS
relay neuron
transmit nerve impulses between sensory neurons and motor neurons
motor neurons
transmit nerve impulses from CNS to effectors
structure of sensory neuron
cell body central but NOT in axon
-short axon
-short dendrites
structure of relay neuron
cell body central IN axon
-short dendrites
-one axon
structure of a motor neuron
cell body at end of axon
-short dendrites
-one long axon
myelinated neurons
myelinated sheath - wrapped shwann cells
-gaps every 1-3mm - nodes of ranvier
-speeds up impulse as impulse jumps from node to node
(saltatory conduction)
non-myelinated neurons
Still has shwann cells but they DONT wrap around
-slower impulses than myelinated as impulse has to move across entire neuron
Effect of temp on speed of conduction
-Temp, increases kinetic energy (sodium ions diffuse quicker)
- more likely to collide successfully with active site
Effect of axon diameter on speed of conduction
larger = faster impulses
