Speaker 1: Welcome back today. We're going to be talking about the
central and peripheral nervous systems. So the CNS central nervous
system is the brain and the spinal cord. The P
and S is all the nerves. Outside the CNS, they
go to the rest of their body. The somatic nervous
system controls voluntary movement, and the autonomic regulates involuntary functions.
We'll get into those a little bit more later on.
Sympathetic system triggers the fight or flight, while the parasympathetic
promotes rest and digest. So you see a threat, whether
physical or non physical, the sympathetic nervous system kicks in
and back to the HPA access. If you remember that,
the parasympathetic nervous system relaxes, so it's after your calming down.
Meditation will also activate parasympathetic The Bell Mangendi law Bell
mcgendy is m A G E n die law is
the dorsal spinal nerves can very sensory input and the
ventral nerves vd N t r L carry the motor output.
So the dorsal spines are carrying the sensory input. Basically
they're receiving the information from the body. So your hand
touches a hot stove that sends a message to the dorsals,
the dorsal spinal nerves, but they call the afferent a
F F, E, R, E, N T nerves. The other one,
the ventral nerves, carry motor put output out, so they
send back a message to your hand to move it
off the stove, and those are the efferent efferent nerves
E F, F, E, R, N T. That's basically the
Bell mcgindy law. Then we go to action potentials. There
are all nothing electrical signals that propagate along axons, so
action potentials all are non electrical signals that propagate along axons.
Neuroplasticity underlies learning and recovery, so long term potentiation LTP
strengthens connects while LTD weakens them. Autonomic overactivation is central
to anxiety, so the ones that regulate in voluntary functions.
You can see where anxiety can be causing involuntary activity
in the body, while pain signals involve spinal thalamic pathways.
So the nervous system is a communication network. That's the
important thing about the nervous system. There's one part relay,
one part highway, and one part surveillance, so it doesn't
just send messages, and it integrates them, interprets them, and
turns them into behavior, memory, or emotion. So we have
a panic attack or something that starts somewhere in the system.
The central nervous system includes the brain and spinal cor
like we mentioned, and it's in case invertebrate or bone
and protected by cerebral spinal fluid. The cerebral spinal fluid
and the blood brain barrier also protect the brain and
spinal cord. It's the command center. It interprets sensory data,
issues motor commands, stores memory, and orchestrates everything from breathing
to complex decision making. The brain is obviously divided into
the cery broom, brainstem, as cerebellum. As we've learned before
to those three areas. The frontal lobes manage planning and inhibition, language,
and movement. We talked about that while back. The parietal
lobes into great sensory input, touch, pain, temperature, and spatial awareness.
The temporal lobes process auditory input and store long term memory.
If you remember, the temporal lobe also is Wernicky's area.
The frontal lobe is broken over in the excipital lobes.
It handles visual processing, olympic structures like the amignalant hippocampus,
regulated motion, and memory. The brain stem controls automatic functions,
so you're thinking about heartbeat, breathing, alertness, things you don't
have to think about. The cerebellum coordinates movement, balance, and
procedural learning. Procedural learning could be things like riding a bike.
Spinal cord a thick cord of nerve tissue extending from
the brain stem. It's segmented and relays messages between the
brain and the body. The white matter, if you remember that,
transmits the signals rapidly in the myelinated axons, gray matter
processes them. It's organized into dorsal, which means posterior and
ventral anterior roots. So dorsal's posterior ventral is anterior, which
brings us to one of the areas in the triple
p that you'll need to remember is the Bell mcgendi law. Again,
sensory in motor out, so you're taking the information from
the senses, processing it, and then sending a message back out.
The Bell mcgendi law explains this. Spinal nerve organization. Right,
we talked about dorsal roots carry sensory afferent information into
the spinal cord while the ventral roots carry motor efforent
commands out to the muscles. If you have damage to
the dorsal root, it means numbness or sensory loss. If
you have damage to the ventral route, this can cause
weakness or paralysis. Right, because there's no message, there's no
signal or a weak signal going out to the muscles
and to the dorsal root. You won't feel anything because
there's numbness or sensory loss that there's a dorsal root issue.
The distinctions distinction helps in localizing lesions, so it helps
the medical professionals or understand the reflex arc which bypass
the brain entirely. So the peripheral nervous system now this
includes all nerves outside the brain and spinal cord. It's
the link between the central nervous system and the rest
of the body. And it's subdivided into somatic nervous system
and autonomic. As we talked about earlier, it control soomatic
controls the voluntary movement, It transmits sensory information. It operates
through cranial which there are twelve of them, and spinal nerves.
When you reach for your phone or feel cold air
in your skin, this is the system at work, the
autonomic Again regularly, it's heart rate, digestion, respiratory rate, pupil dilation,
and it's also subdivided into sympathetic and parasympathetic nervous systems.
Sympathetic to the fight, flight or freeze. Parasympathetic calms the body, rest, digest,
and restore. Let's look how it affects different parts of
your body. So sympathetic dilates pupils increases heart rate, inhibits
GI gastrointestinal motility, movement, lungs broncho dilation, so it expands it.
Bladder inhibits urination and salivation decreases. So this is where
you get really thirsty. When the sympathetic nervous system is
kicking in for a while, especially the parasympathetic will constrict
the pupils, make them smaller, decrease heart rate, stimulate GI
motility to lead to diarrhea or other issues, so that
broncho constrictions, so it constricts your lungs harder to breathe.
Bladder remotes urination and then salivation is increased. And what
you'll see a lot of significance right after UH an
event that kicks in your sympathetic nervous system. When you
kick your parasympathetic nervous system, it's restoring everything back to normal.
So when I said Brocco constriction of lungs, it isn't
a bad thing. It's actually trying to return it back
to normal. The push pull balance is just it's not
only physiology though, it's psychology, right, So in anxiety it's
orders if you think about it, Sympathetic overactivation does what
what It manifests into a rapid heart rate, tight chest,
disruption in the GI and hypervigilance. So what you're really
you're doing here when you're doing therapies, you're trying to
downregulate the sympathetic nervous system and activate the parasympathetic system
through brief breathwork, grounding or vagal stimulation. And the vegus
nerve is one of the cranial nerves, one of the twelve.
It kind of hits the brake on the sympathet nervous system.
Action potentials and synaptic transmission neurons communicate using electrical impulses
called action potentials. These are all or none signals that
travel along the axon when the neurons threshold potential is reached.
So let me explain a little bit more. It's not
going to be super in depth because they're not going
to get into that in the exam like that, so
we'll just kind of cover some of the basics. Resting
potential is when the neuron is polarized the negative seventy millivolts.
Depolarization is when sodium na plus channels open, rushing positive ions.
In repolarization as potassium K plus exits, restoring the charge
the negative charge, and then the refractory periods neuron briefly
cannot fire again. So the resting potential is already negative.
You're depolarize it by making it positive, and you're repolarize
it by making it negative. The speed of conduction is
increased by myelin and myolin, if you remember, is a
fatty insulating layer produced by glial cells. Gaps in mylin
called nodes of red and allow for slitary conduction, where
the signal jumps between these nodes, similar to skipping stones
across water. At the synapse, the electrical signal becomes chemical.
Neurotransmitters are released from presynaptic vesicles, cross the synaptic left
and bind to receptors on the post synaptic neuron. This
process can either excite or inhibit the next neuron. Disruptions
here are central to psychiatric illness. Think about this for
a second. Schizophrenia is linked to dopamine. We talked about
that as dopamine dysregulation. Depression is linked to impaired serotonin transmission.
So many of the psychotropic or psycho the medications work
by alerting the synaptic chemistry or altering I'm sorry, altering
the chemic street, blocking reuptake, mimking neurotransmitters, or inhibiting degradation.
If you remember with the MLIES neuroplasticity, it's learning and adaptation.
Neuroplasticity is the brain's ability to change its structure and
function based on experience. This happens in multiple forms. The
famous heavy in learning the quote. The famous quote is
Neurons that fire together, wire together, strengthening of synapses that
are used repeatedly long term potentiation. You enhanced synaptic strength
following repeated stimulation, especially in the hippocampus. It underlies learning
and memory. LTD decreased its long term depression, decreased synaptic
strength after under use. This happens a lot as an adolescent.
It helps true unnecessary connection. Neuroplasticity explains how therapy works,
how new habits form, and how people recover from trauma.
It's also why in early intervention matters. Young brains are
very plastic, but even adults can rewire. This is something
we've learned about a decade or two ago that we
can still create new neurons and new rewiring. Plasticity is
seen as an exposure therapy for trauma rewires fear circuits
in the amigla and prefunnel cortex. Stroke rehab builds new
motor pathways, and CBTE changes patterns of thought and emotion
by neural connectivity. Last thing we'll be covering is pain,
the pain pathways and perception. Pain isn't just a sensation.
What happens. It's an experience that has processed through the
spinal thomic tract, which carries no susceptive or pain signals,
as well as temperature signals from the body to the
relay station that we learned the thalmas. Remember the thalmus
it's the relay station, so the pain and temperature signals
go to the thalmis and then the selma seta somatosensory
cortex on top of the brain. There are two types
of pain fibers a delta fast sharp pain like a
paper cut, sea fiber, slow dull burning pain. Chronic pain
involves central sensitization and form of maladaptive plasticity where the
brain amplifies pain signals even in the absence of injury,
and this is tied to mood, memory, and stress, highlighting
the biocycle sol model that occurs with pain. So the
more we understand the nervous system, the better we can
understand both behavior and dysfunction at their root. Every psychiatric
symptom is a story of neural pathways either firing too much,
too little, or out of sync. So that's it for today.
Tomorrow we're going to be covering biological bases of major
psychological disorders, so we'll be looking at depressions, schizophrenia, anxiety, bipolar,
and ADHD to see what the biology says about those
psychiatric issues. Thanks for listening.