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So today we're going to talking with the micturition reflex otherwise known as
the urination process
and it's somewhat complex because it actually involves both a local
and a central reflex so we'll get right to it.
What happens is when you have urine that fills the bladder
It activates receptors that are found in the walls of the bladder.
What this does is it activates an afferent neuron
that goes from the walls in the bladder to the level up the sacral spinal cord.
From there an
efferent neuron is activated which then goes back
to the walls of the bladder. And that's a motor neuron
so it causes the urinary bladder and the walls to actually contract. What this does
is increases pressure within the urinary bladder.
While that happens, however, an
interneuron that synapses on that primary
afferent neuron we first talked about goes
up the spinal cord to the brain. What it tells the brain is that
the bladder is full now this is where the central reflex occurs.
So what happens is that interneuron that's sent to the brain synapses
on another neuron. So it goes from
an area called the thalamus to an area called the cerebral cortex.
And what that does
is it relays the information or that sensation that the bladder's full.
So it tells us: okay we're about to urinate.
From there what happens is when appropriate
your brain or your motor cortex will send a signal
back to the region
the bladder to the external urinary sphincter.
And that is a voluntary process
in which that allows the external urinary sphincter to relax.
And that's what causes the urination because you already have
a local reflex causing an increase in pressure
within the bladder so once you have
that voluntary relaxation of the external sphincter it
allows for your in to leave the bladder
and we eliminate it from our body.