Chapter 24: Neurologic System

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The neurologic system is arguably the most complex, intimidating network in the entire human body.

Oh, absolutely.

It's terrifying at first.

Right, because one minute change in a patient's pupil can literally mean the difference between life and death.

It really can.

So welcome to our deep dive.

If you're listening to this right now, you are likely a nursing student stepping into this incredibly high stakes territory.

And we are thrilled to be your guides today.

We really are.

And I know it's an intimidating system, but the beauty of it is how intensely logical it becomes once you understand the wiring.

Yeah, the wiring is everything.

Exactly.

So today we're essentially serving as your personal one -on -one tutors.

We're drawing all our insights directly from chapter 24 of your physical examination and health assessment textbook.

And we're going to approach this the exact same way you'd approach a real patient at the bedside.

Right, starting from the ground up.

Exactly.

So before we even touch someone, we have to understand the underlying anatomy.

That knowledge tells us what questions to ask during the interview.

Because the history informs the physical exam.

Yes.

And then we use all those hands -on findings to make clinical decisions, document them safely and ultimately protect our patients.

So let's bypass the middle school biology definitions of just the brain and spinal cord and jump right into the big stuff.

The central nervous system versus the peripheral nervous system.

Okay, so CNS and PNS.

Right.

CNS is your brain and spinal cord.

The PNS is everything else out in the periphery.

Your 12 cranial nerves, your 31 spinal nerves.

They carry sensory or afferent messages to the CNS and motor or efferent messages out to the muscles.

The front arrives, efferent exits.

That's how I always remembered it.

That's a great trick.

Let's talk about the cerebral cortex.

This outer layer of gray matter is divided into four very specific lobes.

And honestly, these are non -negotiable for your exams.

Totally non -negotiable.

They're the foundation.

Think of the frontal lobe as the command center.

It controls your personality, behavior, emotions, and higher intellectual function.

And it has the pre -central gyrus, right, for voluntary movement.

You got it.

Then, moving back, you have the parietal lobe.

Its post -central gyrus is the primary center for processing sensation.

Okay.

And then at the very back of the head is the occipital lobe, which is your primary visual receptor.

And finally, tucked right by in the ear is the temporal lobe.

That one handles hearing, taste, and smell.

I've always found the specialized language centers within those lobes to be the most fascinating part of this whole map.

Oh, they're incredible.

You've got Wernicke's area and Broca's area, but they do completely different things.

Very different.

And the clinical presentation of damage to either one is just striking.

So Wernicke's area is in the temporal lobe, and it's responsible for language comprehension.

So understanding what is being said.

Exactly.

If a patient suffers a stroke in this area, in their dominant hemisphere, the developed receptive aphasia, they can hear you talking, but the words hold zero meaning to them.

Wow.

So it would be like you or me suddenly being dropped into a room where everyone is speaking a language we've never even heard.

Exactly like that.

They hear the sound, but there's no meaning attached to it.

That is so wild.

How does that contrast with Broca's area?

So Broca's area is up in the frontal lobe, and it mediates motor speech.

If that area is injured, the result is expressive aphasia.

Expressive.

So they can't get it out.

Right.

The patient understands your questions perfectly.

They know exactly what they want to say back to you.

But when they try to actually speak,

the physical motor output is compromised, and they can only produce these garbled sounds.

Man, that has to be an incredibly frustrating, isolating experience for a patient.

It really is.

Just knowing that helps us approach them with so much more empathy.

Let's look a little deeper.

Below the cortex, at the subcortical structures, you've got the basal ganglia, which control automatic associated movements, like the way your arms naturally swing when you walk.

Yep.

And the thalamus, which acts as the main relay station for sensory pathways.

And we can't forget the hypothalamus.

That is essentially your vital function control board, right?

Managing temperature, heart rate, blood pressure, sleep, appetite.

All the vital stuff.

And below that, sitting under the occipital lobe, is the cerebellum.

I always like to think of it as the brain's automatic pilot.

Automatic pilot.

I like that.

Yeah.

Because it doesn't initiate a movement.

But once the frontal lobe decides to move, the cerebellum coordinates it, smooths it out, and maintains your balance entirely below your conscious awareness.

And finally, the brain stem connects it all down to the spinal cord.

Midbrain, pons, and medulla.

And the medulla is where a very important crossing of motor fibers happens.

Yes.

Let's talk about that crossing, because it feels like a concept that trips up a lot of students.

It's called crossed representation.

We visualize this using the homunculus, right?

The homunculus is such a great visual.

It's this distorted map of how the brain perceives the body.

Because of that crossing of fibers in the medulla, the left cerebral cortex receives sensory information from and controls motor function to the right side of the body.

And vice versa.

Left controls right, right controls left.

Exactly.

And understanding that cross is the only way you can accurately interpret clinical findings.

Like why a stroke on the left side of the brain causes weakness on the right side of the body.

Right.

It's foundational.

So if we trace those pathways down the spinal cord, the sensory side has two main routes.

The anterolateral, or spinothalamic tract,

handles pain, temperature, and crude touch.

And then you have the posterior, or dorsal, columns.

Those conduct vibration.

Proprioception, which is your sense of where your body parts are in space.

And stereognosis.

Stereognosis is identifying an object using only fine touch, right?

I got it.

Like feeling a key in your pocket and knowing it's a key without looking.

On the descending motor side, impulses travel down the corticospinal, or pyramidal tract, for highly skilled, purposeful movements like riding.

And the extrapure middle tract handles gross automatic movements like walking.

Exactly.

Here is where I want to pause because this next distinction is a massive clinical concept for any nursing student.

Upper motor neurons versus lower motor neurons.

Why is it so crucial to know the difference?

It all comes down to where the damage is and how the muscle responds.

Upper motor neurons, or UMNs, live entirely within the central nervous system.

So brain and spinal cord.

Right.

Diseases that affect them are things like stroke or multiple sclerosis.

When a UMN is damaged, you typically see spasticity, meaning the muscle tone is overly rigid and reflexes are hyperactive.

Okay, so UMN means spastic and hyperactive.

What about lower motor neurons?

Lower motor neurons are the final common pathway out to the muscle itself.

Think of diseases like polio or the severed spinal cord injury.

When an LMN is damaged, the muscle loses this connection entirely.

So it goes limp.

Exactly.

It results in flaccidity, a limp ragdoll tone, and absent reflexes.

So a healthy reflex arc actually requires five intact components.

A functioning sensory nerve, a synapse in the spinal cord, an intact motor nerve fiber, the neuromuscular junction, and a competent muscle.

Perfect summary.

Now we've mapped out this incredibly intricate wiring in a healthy adult.

But does this wiring look the same across a patient's entire lifespan?

What does this look like in a newborn?

It looks very different.

An infant's neurologic system isn't completely developed at birth.

Their movements are directed primarily by primitive reflexes.

Because they don't have that myelin yet.

Exactly.

As they grow, their cerebral cortex develops and their neurons grow that insulating layer of myelin.

As myelination progresses, those primitive reflexes are suppressed and disappear and they're replaced by localized purposeful movements.

And on the other end of the lifespan, in the aging adult, there's a normal generalized atrophy with a steady loss of neurons.

But we really have to be careful not to dismiss pathology as just getting older.

Right.

Your textbook has a really good breakdown of this.

Table 24 .1, it compares normal aging versus the warning signs of Alzheimer's disease.

That table is a fantastic tool for practice.

Normal aging might mean a patient forgets a word but remembers it later.

Or maybe they get a little irritated when their routine is disrupted.

Which happens to all of us.

Exactly.

But Alzheimer's is characterized by forgetting recently learned information entirely, experiencing severe mood swings, and on imaging, showing asymmetric and focal brain atrophy.

Rather than the generalized even shrinkage we see in normal aging.

Right.

And speaking of modern context, the text also discusses the evidence -based guidelines around COVID -19.

We're seeing long -term neurological effects in survivors.

Like anosmia.

That's the complete loss of smell, right?

Yes.

And persistent cognitive issues like brain fog and short -term memory loss, even in patients who are never hospitalized.

That's so important to screen for now.

So now that we understand the anatomy and how it changes, let's transition into the patient's room for the health history interview.

Because the wiring we just discussed directly dictates the questions you need to ask.

Let's start with headaches.

Almost everyone gets them.

But what transforms a routine headache complaint into a drop -everything red flag?

If a patient says, this is the worst headache of my life, you immediately shift gears.

That's a huge red flag.

Huge.

That requires an emergency referral to screen for a possible hemorrhagic stroke or a ruptured aneurysm.

You also need to ask detailed questions about head injuries to screen for concussions.

Which happens when a direct blow causes the brain to rapidly shift inside the skull, creating a sheer injury to those nerve fibers.

Exactly.

Another common complaint is feeling dizzy.

But patients use that word to describe wildly different sensations.

How do we differentiate normal dizziness from true vertigo?

You have to ask them to describe the exact sensation.

Dizziness is a feeling of being lightheaded or swimming.

True vertigo is a powerful rotational spinning sensation.

So you specifically ask, does the room seem to spin around you or do you feel like you are spinning inside the room?

Yes.

True vertigo points away from a simple blood pressure drop and indicates an issue with inner ear disease or a lesion in the brain stem.

Got it.

And if a patient has a history of seizures, we need to map out the entire timeline.

We ask about an aura.

Right.

An aura is a subjective warning sensation, a specific sound, a visual flash, a strange smell that tells them a seizure is coming.

And crucially, we ask about the postictal phase.

What exactly are we looking for there?

The postictal phase is the period immediately following the seizure.

You want to know if they fall into an unarousable deep sleep, if they wake up confused, or if they have profound muscle weakness.

Okay.

So as we document all these subjective complaints, we have to translate the patient's words into clinical terminology.

Let's decode some of these.

Pariesis versus paralysis.

Pariesis is partial paralysis or weakness.

Paralysis is the absolute loss of motor function.

Parastesia.

An abnormal sensation like burning or pins and needles tingling.

Dysmetria.

That's the inability to control the distance, power, and speed of a movement, like overreaching for a cup.

And finally, dysarthria versus dysphagia.

Dysarthria is a physical difficulty forming words due to muscle weakness.

Dysphagia is a difficulty with language comprehension or expression itself.

Perfect.

So now that we know what to ask, let's move to the objective data, the physical exam.

You might do a quick screening on a well person or a complete exam on someone with specific concerns.

And the most intimidating part of the complete exam for students is usually testing the 12 cranial nerves.

Yes.

Instead of just listing them, let's systematically walk through how to test them in practice.

Grouping them helps immensely.

It really does.

Let's start with cranial nerve, the olfactory nerve.

You test this by having the patient close their eyes and you present familiar odors like coffee or peppermint to each nostril.

And an abnormal finding is anosmia.

Right.

Next, let's group the nerves that control the eyes.

Nerves two, three, four, and six.

Cranial nerve two is the optic nerve.

You test that using a Snellen chart for visual acuity and testing peripheral visual fields.

And nerves the third, four, and six, the oculomotor, trochlear, and abducens, they control the physical movement of the eye and the pupils.

We test this by checking for perla.

Pupils equal, round, reactive to light and accommodation.

We also test extraocular movements by having the patient track our finger through the six cardinal positions of gaze, looking for nystagmus.

Which is that rapid back and forth oscillation of the eyes.

Now, I saw a very specific warning in the textbook regarding the pupils.

Why is a sudden, unilateral, dilated, and non -reactive pupil considered an absolute emergency?

That is one of the most ominous signs you can encounter.

It means intracranial pressure is rising so high that the brain stem is physically being pushed down.

It's herniating and putting direct, crushing pressure on cranial nerve three.

So that requires immediate, life -saving intervention.

Absolutely.

Moving down the face, we have nerves V and seventh.

Cranial nerve V is the trigeminal nerve.

You palpate the jaw muscles while they clench their teeth for the motor component and lightly touch their forehead, cheeks, and chin with a cotton wisp for the sensory side.

And cranial nerve seventh is the facial nerve.

Yes, and smile, frown, raise their eyebrows, puff out their cheeks.

Now, if you observe facial paralysis here, your knowledge of UMNs versus LMNs is critical.

Yes.

A stroke and upper motor neuron lesion will typically paralyze only the lower half of one side of the face.

The forehead muscles stay intact because of alternative wiring pathways.

But Bell -Pulsey Bell -Pulsey is a lower motor neuron lesion of the nerve itself, and it paralyzes the entire half of the face, including the forehead.

That distinction alone dictates the entirety of the patient's treatment plan.

Exactly.

To finish out the cranial nerves.

Nerve eighth is the acoustic nerve, tested by whispering behind the patient to check hearing.

Nerves, nyex, and ex, glossopharyngeal, and vagus are tested by having the patient say,

ah, the uvula should rise perfectly in the midline, and you assess the gag reflex.

Nerve eight, the spinal accessory, is tested by having them shrug their shoulders against your hands.

And finally, nerve 12, the hypoglossal.

They stick out their tongue, which should be midline, and you ask them to say, light, tight dynamite to ensure lingual speech is clear.

Once the cranial nerves are done, we move to the motor system.

We assess the size, strength, and tone of the major muscle groups.

Normal tone has a mild, even resistance to a passive stretch.

We already discussed flaccidity and spasticity, but we also test cerebellar function here.

Right.

To see how smoothly those muscles work together.

You can test this with rapid alternating movements.

Have the patient sit, place their hands on their knees, and quickly flip their hands palm up, palm down, faster and faster.

Or the finger -to -nose test.

You also assess their gait, watch them walk normally, and then ask them to do tandem walking, walking a straight line, perfectly heel -to -toe.

An inability to maintain balance during tandem walking is a very sensitive indicator for an upper motor neuron lesion or acute cerebellar dysfunction.

And to isolate balance even further, we use the Romberg test.

The patient stands with feet together, arms at their sides, and closes their eyes.

You wait about 20 seconds.

If they lose their balance and sway wildly, that's a positive Romberg sign.

For the sensory system, we are literally testing those tracts we mapped out earlier.

To test the spinothalamic tract, you alternate gently touching them with a sharp pin and a dull object, and they have to identify the sensation.

For light touch, use a cotton wisp.

And to test the posterior column tract, you place a vibrating tuning fork over bony prominences, usually on the toes or fingers.

You also test proprioception by moving their finger up or down and asking them to identify the position with their eyes closed.

We also test tactile discrimination.

Stereognosis is the ability to identify a familiar object, like a key, placed in their hand with their eyes closed.

And graphesthesia is tracing a number on their palm, and they have to read it by feel.

Exactly.

Now for the classic visual of the neuro exam, the reflex hammer.

Yes.

We grade deep tendon reflexes on a four -point scale.

Zero is completely absent, one plus is diminished, two plus is normal, three plus is brisker than average, and four plus is hyperactive, usually accompanied by clonus.

Clonus is a fascinating rhythmic set of rapid muscle contractions.

If you briskly dorsiflex the patient's foot and hold it there, a foot with clonus will visibly and rapidly bounce back and forth against your hand.

It's a hallmark of upper motor neuron disease.

To elicit these reflexes, you walk through striking the biceps, triceps, patellar, and Achilles tendons.

And beyond the deep tendons, we test the superficial plantar reflex.

You take the hard handle of the reflex hammer and draw a light stroke up the lateral side of the sole of the foot, curving inward across the ball like an upside -down J.

In a healthy adult, the toes will curl downward.

But an abnormal response is the Bovinsky sign, where the big toe points dramatically upward and the other toes fan out.

If you see a Bovinsky sign in an adult, it is a definitive marker of UMN disease in the corticospinal tract.

Before we move to critical tear, let's highlight special assessments.

If you have a patient with diabetes, you must screen for peripheral neuropathy using a monofilament.

You gently apply pressure to 10 specific sites on the sole of the foot until the filament bends.

If they can't feel it, they've lost protective sensation.

And for infants, the exam focuses on primitive reflexes.

The rooting reflex, grasp reflex, and moro, or startle, reflex.

You also use the Denver Second tool for milestones.

Now, if you are working in a hospital, particularly in critical care, you will perform the neurologic recheck constantly.

It's an abbreviated exam to monitor for increasing intracranial pressure.

And it hits four key areas.

First, and most importantly, is level of consciousness, or LOC.

A change in LOC is the earliest and most sensitive indicator that something is going wrong.

Ask about person, place, and time.

Second is motor function.

Check commands, bilateral grip strength, and tests for pronator drift.

Have the patient extend both arms forward, palms up, and close their eyes.

If one arm drifts downward in pronates, that indicates mild hemiparesis.

Third is pupillary response.

Use a millimeter scale to check for that we talked about.

And fourth is vital signs, specifically looking for the cushion reflex.

Because, by the time it appears,

the brain is under extreme duress.

It manifests as a sudden, massive elevation in blood pressure with a widening pulse pressure, paired with a decreased, slow, bounding heart rate.

To make sure every nurse grades these patients on the exact same scale, we use the Glasgow Coma Scale, or GCS.

It grades eye opening, verbal response, and motor response.

A fully alert person scores a perfect 15.

A score of 7 or less reflects a cona.

As we pull all this clinical reasoning together, you'll encounter specific abnormalities.

For strokes, understand the mechanism.

Ischemic means a clot is blocking a vessel.

Hemorrhagic means a vessel physically ruptured and is bleeding into the brain.

In comatose patients, look for abnormal posturing.

Decorticate rigidity arms tightly flexed inward to the core indicates a hemispheric lesion.

Decerebrate rigidity arms stiffly extended outward is a much more ominous sign of a brain stem lesion.

You'll also screen for meningeal irritation.

Look for neutral rigidity, which is a stiff neck.

The kernic sign is resistance when extending the knee.

And the Brzezinski sign is when flexing their neck forward causes them to involuntarily pull their hips and knees up in pain.

You might also see frontal release signs in adults with severe brain disease primitive reflexes like snout, sucking, or grasp that have re -emerged.

Finally, all of this has to be documented.

Under subjective, you chart the presence or absence of symptoms.

Under objective, you summarize the exam.

And your assessment is a concise summary.

And for reflexes, nurses use a brilliant visual shorthand,

drawing a stick figure and writing 2 plus at the major joint reflex sites to document normal DTRs concisely.

By mastering the anatomy first, you instinctively know what history questions to ask.

Those answers guide your physical exam, and those maneuvers allow you to pinpoint the deficit.

It's this logical flow that transforms a daunting chapter into the foundation of safe patient care.

Before you go, I want to leave you with a thought on neuroplasticity.

We've talked about how strictly mapped the brain is.

If tissue dies in a stroke, that function is lost.

But how fascinating is it that after a severe injury, the brain can physically rewire itself, transferring lost functions to entirely new, healthy areas?

It completely redefines rehabilitation.

It is the ultimate testament to the resilience of the human nervous system.

To all the nursing students listening, you are entering an incredibly challenging but rewarding field.

The Deep Dive is brought to you by the Last Minute Lecture Team.

We want to extend a warm thank you for studying with us today, and we wish you the absolute best of luck on your neurologic assessment exam.

You're going to do great.