The neuron – Synaptic transmission and psychopharmacology
Reflex arc
Reflex – automatic muscular response to a stimulus
Sensory neuron (afferent) excites interneuron which then excites the motor
neuron activating a muscle. = Circuit is called reflex arc
Sherrington’s evidence for synaptic delay
Direct communication = 40 seconds
Sherrington pinched a dog’s foot and found the dog flexed (raided foot) after a
long delay.
The speed of conduction through a reflex arc is slower – 15 m/sec. The delay
occurs at the synapse.
Communication between neurons
Neurons not physically connected (tiny gap)
, Presynaptic neuron – delivers message
Postsynaptic neuron - receives message
Presynaptic membrane –
Contains vesicles with neurotransmitters
Membrane has high concentration of Ca ++ channels, Ca ++ is more
concentrated outside
When an action potential occurs calcium will go inside because of the
concentration gradient.
Synaptic cleft – 20 to 40 nm gap
Separates the pre and post synaptic membrane.
Contains extra cellular fluid
Neurotransmitters diffuse here.
Postsynaptic membrane
Contains specialised proteins (receptors) for neurotransmitters
The receptors control ion channels (e.g., sodium, chloride and
potassium) + cause hyper or depolarisation
Graded potential
What causes an action potential?
Temporal summation – several impulses from one neuron over time
Spatial summation – info coming in from many connections (impulses
from several neurons at the same time)
Sum of postsynaptic effects determines what happens … if action
potential occurs.
Reflex arc
Reflex – automatic muscular response to a stimulus
Sensory neuron (afferent) excites interneuron which then excites the motor
neuron activating a muscle. = Circuit is called reflex arc
Sherrington’s evidence for synaptic delay
Direct communication = 40 seconds
Sherrington pinched a dog’s foot and found the dog flexed (raided foot) after a
long delay.
The speed of conduction through a reflex arc is slower – 15 m/sec. The delay
occurs at the synapse.
Communication between neurons
Neurons not physically connected (tiny gap)
, Presynaptic neuron – delivers message
Postsynaptic neuron - receives message
Presynaptic membrane –
Contains vesicles with neurotransmitters
Membrane has high concentration of Ca ++ channels, Ca ++ is more
concentrated outside
When an action potential occurs calcium will go inside because of the
concentration gradient.
Synaptic cleft – 20 to 40 nm gap
Separates the pre and post synaptic membrane.
Contains extra cellular fluid
Neurotransmitters diffuse here.
Postsynaptic membrane
Contains specialised proteins (receptors) for neurotransmitters
The receptors control ion channels (e.g., sodium, chloride and
potassium) + cause hyper or depolarisation
Graded potential
What causes an action potential?
Temporal summation – several impulses from one neuron over time
Spatial summation – info coming in from many connections (impulses
from several neurons at the same time)
Sum of postsynaptic effects determines what happens … if action
potential occurs.
