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Speaker 1: Welcome back today. We're going to be talking about the

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central and peripheral nervous systems. So the CNS central nervous

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system is the brain and the spinal cord. The P

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and S is all the nerves. Outside the CNS, they

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go to the rest of their body. The somatic nervous

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system controls voluntary movement, and the autonomic regulates involuntary functions.

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We'll get into those a little bit more later on.

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Sympathetic system triggers the fight or flight, while the parasympathetic

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promotes rest and digest. So you see a threat, whether

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physical or non physical, the sympathetic nervous system kicks in

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and back to the HPA access. If you remember that,

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the parasympathetic nervous system relaxes, so it's after your calming down.

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Meditation will also activate parasympathetic The Bell Mangendi law Bell

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mcgendy is m A G E n die law is

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the dorsal spinal nerves can very sensory input and the

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ventral nerves vd N t r L carry the motor output.

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So the dorsal spines are carrying the sensory input. Basically

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they're receiving the information from the body. So your hand

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touches a hot stove that sends a message to the dorsals,

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the dorsal spinal nerves, but they call the afferent a

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F F, E, R, E, N T nerves. The other one,

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the ventral nerves, carry motor put output out, so they

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send back a message to your hand to move it

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off the stove, and those are the efferent efferent nerves

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E F, F, E, R, N T. That's basically the

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Bell mcgindy law. Then we go to action potentials. There

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are all nothing electrical signals that propagate along axons, so

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action potentials all are non electrical signals that propagate along axons.

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Neuroplasticity underlies learning and recovery, so long term potentiation LTP

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strengthens connects while LTD weakens them. Autonomic overactivation is central

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to anxiety, so the ones that regulate in voluntary functions.

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You can see where anxiety can be causing involuntary activity

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in the body, while pain signals involve spinal thalamic pathways.

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So the nervous system is a communication network. That's the

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important thing about the nervous system. There's one part relay,

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one part highway, and one part surveillance, so it doesn't

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just send messages, and it integrates them, interprets them, and

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turns them into behavior, memory, or emotion. So we have

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a panic attack or something that starts somewhere in the system.

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The central nervous system includes the brain and spinal cor

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like we mentioned, and it's in case invertebrate or bone

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and protected by cerebral spinal fluid. The cerebral spinal fluid

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and the blood brain barrier also protect the brain and

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spinal cord. It's the command center. It interprets sensory data,

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issues motor commands, stores memory, and orchestrates everything from breathing

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to complex decision making. The brain is obviously divided into

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the cery broom, brainstem, as cerebellum. As we've learned before

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to those three areas. The frontal lobes manage planning and inhibition, language,

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and movement. We talked about that while back. The parietal

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lobes into great sensory input, touch, pain, temperature, and spatial awareness.

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The temporal lobes process auditory input and store long term memory.

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If you remember, the temporal lobe also is Wernicky's area.

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The frontal lobe is broken over in the excipital lobes.

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It handles visual processing, olympic structures like the amignalant hippocampus,

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regulated motion, and memory. The brain stem controls automatic functions,

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so you're thinking about heartbeat, breathing, alertness, things you don't

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have to think about. The cerebellum coordinates movement, balance, and

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procedural learning. Procedural learning could be things like riding a bike.

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Spinal cord a thick cord of nerve tissue extending from

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the brain stem. It's segmented and relays messages between the

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brain and the body. The white matter, if you remember that,

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transmits the signals rapidly in the myelinated axons, gray matter

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processes them. It's organized into dorsal, which means posterior and

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ventral anterior roots. So dorsal's posterior ventral is anterior, which

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brings us to one of the areas in the triple

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p that you'll need to remember is the Bell mcgendi law. Again,

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sensory in motor out, so you're taking the information from

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the senses, processing it, and then sending a message back out.

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The Bell mcgendi law explains this. Spinal nerve organization. Right,

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we talked about dorsal roots carry sensory afferent information into

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the spinal cord while the ventral roots carry motor efforent

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commands out to the muscles. If you have damage to

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the dorsal root, it means numbness or sensory loss. If

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you have damage to the ventral route, this can cause

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weakness or paralysis. Right, because there's no message, there's no

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signal or a weak signal going out to the muscles

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and to the dorsal root. You won't feel anything because

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there's numbness or sensory loss that there's a dorsal root issue.

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The distinctions distinction helps in localizing lesions, so it helps

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the medical professionals or understand the reflex arc which bypass

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the brain entirely. So the peripheral nervous system now this

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includes all nerves outside the brain and spinal cord. It's

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the link between the central nervous system and the rest

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of the body. And it's subdivided into somatic nervous system

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and autonomic. As we talked about earlier, it control soomatic

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controls the voluntary movement, It transmits sensory information. It operates

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through cranial which there are twelve of them, and spinal nerves.

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When you reach for your phone or feel cold air

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in your skin, this is the system at work, the

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autonomic Again regularly, it's heart rate, digestion, respiratory rate, pupil dilation,

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and it's also subdivided into sympathetic and parasympathetic nervous systems.

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Sympathetic to the fight, flight or freeze. Parasympathetic calms the body, rest, digest,

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and restore. Let's look how it affects different parts of

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your body. So sympathetic dilates pupils increases heart rate, inhibits

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GI gastrointestinal motility, movement, lungs broncho dilation, so it expands it.

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Bladder inhibits urination and salivation decreases. So this is where

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you get really thirsty. When the sympathetic nervous system is

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kicking in for a while, especially the parasympathetic will constrict

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the pupils, make them smaller, decrease heart rate, stimulate GI

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motility to lead to diarrhea or other issues, so that

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broncho constrictions, so it constricts your lungs harder to breathe.

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Bladder remotes urination and then salivation is increased. And what

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you'll see a lot of significance right after UH an

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event that kicks in your sympathetic nervous system. When you

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kick your parasympathetic nervous system, it's restoring everything back to normal.

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So when I said Brocco constriction of lungs, it isn't

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a bad thing. It's actually trying to return it back

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to normal. The push pull balance is just it's not

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only physiology though, it's psychology, right, So in anxiety it's

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orders if you think about it, Sympathetic overactivation does what

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what It manifests into a rapid heart rate, tight chest,

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disruption in the GI and hypervigilance. So what you're really

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you're doing here when you're doing therapies, you're trying to

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downregulate the sympathetic nervous system and activate the parasympathetic system

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through brief breathwork, grounding or vagal stimulation. And the vegus

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nerve is one of the cranial nerves, one of the twelve.

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It kind of hits the brake on the sympathet nervous system.

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Action potentials and synaptic transmission neurons communicate using electrical impulses

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called action potentials. These are all or none signals that

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travel along the axon when the neurons threshold potential is reached.

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So let me explain a little bit more. It's not

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going to be super in depth because they're not going

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to get into that in the exam like that, so

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we'll just kind of cover some of the basics. Resting

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potential is when the neuron is polarized the negative seventy millivolts.

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Depolarization is when sodium na plus channels open, rushing positive ions.

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In repolarization as potassium K plus exits, restoring the charge

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the negative charge, and then the refractory periods neuron briefly

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cannot fire again. So the resting potential is already negative.

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You're depolarize it by making it positive, and you're repolarize

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it by making it negative. The speed of conduction is

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increased by myelin and myolin, if you remember, is a

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fatty insulating layer produced by glial cells. Gaps in mylin

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called nodes of red and allow for slitary conduction, where

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the signal jumps between these nodes, similar to skipping stones

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across water. At the synapse, the electrical signal becomes chemical.

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Neurotransmitters are released from presynaptic vesicles, cross the synaptic left

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and bind to receptors on the post synaptic neuron. This

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process can either excite or inhibit the next neuron. Disruptions

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here are central to psychiatric illness. Think about this for

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a second. Schizophrenia is linked to dopamine. We talked about

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that as dopamine dysregulation. Depression is linked to impaired serotonin transmission.

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So many of the psychotropic or psycho the medications work

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by alerting the synaptic chemistry or altering I'm sorry, altering

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the chemic street, blocking reuptake, mimking neurotransmitters, or inhibiting degradation.

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If you remember with the MLIES neuroplasticity, it's learning and adaptation.

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Neuroplasticity is the brain's ability to change its structure and

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function based on experience. This happens in multiple forms. The

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famous heavy in learning the quote. The famous quote is

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Neurons that fire together, wire together, strengthening of synapses that

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are used repeatedly long term potentiation. You enhanced synaptic strength

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following repeated stimulation, especially in the hippocampus. It underlies learning

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and memory. LTD decreased its long term depression, decreased synaptic

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strength after under use. This happens a lot as an adolescent.

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It helps true unnecessary connection. Neuroplasticity explains how therapy works,

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how new habits form, and how people recover from trauma.

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It's also why in early intervention matters. Young brains are

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very plastic, but even adults can rewire. This is something

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we've learned about a decade or two ago that we

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can still create new neurons and new rewiring. Plasticity is

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seen as an exposure therapy for trauma rewires fear circuits

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in the amigla and prefunnel cortex. Stroke rehab builds new

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motor pathways, and CBTE changes patterns of thought and emotion

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by neural connectivity. Last thing we'll be covering is pain,

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the pain pathways and perception. Pain isn't just a sensation.

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What happens. It's an experience that has processed through the

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spinal thomic tract, which carries no susceptive or pain signals,

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as well as temperature signals from the body to the

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relay station that we learned the thalmas. Remember the thalmus

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it's the relay station, so the pain and temperature signals

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go to the thalmis and then the selma seta somatosensory

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cortex on top of the brain. There are two types

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of pain fibers a delta fast sharp pain like a

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paper cut, sea fiber, slow dull burning pain. Chronic pain

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involves central sensitization and form of maladaptive plasticity where the

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brain amplifies pain signals even in the absence of injury,

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and this is tied to mood, memory, and stress, highlighting

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the biocycle sol model that occurs with pain. So the

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more we understand the nervous system, the better we can

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understand both behavior and dysfunction at their root. Every psychiatric

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symptom is a story of neural pathways either firing too much,

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too little, or out of sync. So that's it for today.

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Tomorrow we're going to be covering biological bases of major

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psychological disorders, so we'll be looking at depressions, schizophrenia, anxiety, bipolar,

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and ADHD to see what the biology says about those

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psychiatric issues. Thanks for listening.