When you hear the term emotional fitness, what comes to mind? Maybe being capable of avoiding everyday “negative” emotions? You know, the ones we all prefer not to experience like stress, frustration, disappointment, or anger?

But emotions aren’t something we can simply choose to opt out of. They’re signals our body is constantly responding to whether we are consciously aware of them or not. Our senses and emotions are processed by our nervous system. This is the body’s communication system. It sends information back and forth between our brains, body, and environment.

In this article, we’ll explore emotions from a more practical lens. This foundation helps us develop the BS filtering skills we need. Especially if we start exploring metaphysical perspectives like the law of vibration. We’ll need a healthy level of discernment. Without it, the information out there can lack grounding and even get misleading.

I’ll also explain the term emotional fitness and offer practical ways to build it. The goal is simple: to understand and work with our emotional intelligence system. This creates more balance, resilience, and intention in how we live our lives.

Let’s get into it.

What is Emotional Fitness?

I noticed that most of us think emotional fitness is focusing on “feeling a wide range of emotions without spiraling.” That’s not wrong, but it’s incomplete.

Based on what I’ve learned, emotional fitness isn’t about never feeling stressed. It isn’t about constant happiness or building endless tolerance for pressure either.

The true marker of emotional fitness is how well our nervous system can move through stress and return to balance. From a neuroscience perspective, emotional resilience is about the nervous system’s ability to regulate after stress. This makes emotional fitness easier to observe and harder to fake.

Because it shows up physically:

• In the body.
• In our breathing.
• In muscle tension.
• In how our heart rate speeds up or slows down.

All of this is our nervous system processing information.

Over time, these responses add up. They shape how we handle stress and respond to challenges. They affect how connected we feel to ourselves, to others, and to our body day to day.

That’s why emotional fitness isn’t just about controlling emotions or forcing ourselves to be happy. It’s about learning how to support the nervous system so healthier emotional patterns can form.

What Are Emotions and Why Do They Matter?

Emotions matter because they give us information in the form of sensations and feelings. They help us assess what’s happening around us and inside of us faster than conscious thought. If you think about it, they are the driving force of our behavior and motivate us to take action.

At their core, emotions act like internal signals that point to safety or threat and show what draws us in. They also alert us to what needs attention or distance. Think about touching something hot. You don’t stop to analyze it. You pull your hand away quickly.

That reaction happens because the nervous system processes information before conscious reasoning kicks in. Emotional responses work the same way. They are fast, protective, and often automatic.

Thoughts & Beliefs Influence Emotional Responses

Our thoughts and beliefs shape how our nervous system responds to what we experience. In psychology, how we interpret a situation is known as cognitive appraisal. This interpretation helps us decide the emotional and physical reaction we have to it.

That’s why two people can face the same event but experience very different emotions. This happens because of how they think about it. For example, if someone believes public speaking will embarrass them their nervous system can trigger a racing heart! This can happen before they even start.

While another person interprets it as a chance to connect even though they feel the stress response. Yet, it arouses excitement to speak instead. One person thinks of public speaking as a threat to run from. While the other views it as a challenge to work through. This happens because the brain continually evaluates stimuli and meaning.

Emotions Form Patterns, Baseline, and Chronic stress

Our nervous system is constantly integrating information from our body, our environment, our thoughts, and beliefs. Based on that data, it shapes emotional responses that guide behavior.

Over time, it also learns from repeated experiences, forming emotional patterns that influence how we react in similar situations. This is why chronic stress can make seemingly small problems feel overwhelming. Nothing about the situation has to change, but our internal state has.

Eventually, these learned patterns shape what many of us experience as our emotional “baseline” or default emotional state. They influence how emotions are processed, how long they linger, and how strongly they show up. They also affect physical health, mental clarity, and overall stability.

Ultimately, emotions matter because they shape how we experience life. And the nervous system is doing that shaping…quietly, constantly, and often outside of our awareness.

A Brief History on Emotions and the Nervous System Connection

It’s helpful to understand how emotions were historically perceived. Because that history explains why many of us grew up disconnected from their value.

For much of Western history, emotions were studied primarily as mental experiences. Physical health was treated as a separate domain. The mind and body were conceptualized as distinct systems.

Early, psychoanalytic thinkers like Carl Jung explored emotional patterns, archetypes, and unconscious processes. Yet, emotions were still viewed primarily through a mental lens. And what the body was doing in response often remained secondary.

In the early 20th century, physiology began to enter the conversation. Researchers like Walter Cannon identified the “fight-or-flight” response, linking emotional stress to activation of the sympathetic nervous system.

Later, Hans Selye introduced the concept of the General Adaptation Syndrome, demonstrating how chronic stress affects the body over time. These discoveries shifted the narrative.

Patterns of anxiety, grief, and chronic tension weren’t staying confined to the mind. They were linked to measurable changes in sleep, digestion, immunity, cardiovascular strain, and pain perception. This led to interest in stress physiology, psychosomatic medicine, and mind-body research.

Interestingly, many holistic and integrative health traditions were already working from this assumption. For example, Traditional Chinese Medicine and Ayurveda both recognize that emotional states are linked to physiological processes within the body. While their terminology differs from modern neuroscience, the underlying principle is similar, emotional experiences are embodied. In somatic psychology and Western integrative therapy, practitioners often use language like the “emotional body” to describe this mind–body connection.

Today, the mind-body connection is finally understood through neuroscience and physiology. Emotions are recognized as biopsychological processes regulated by the nervous system, involving brain activity, neural signaling, hormones, and bodily responses.

The Link Between Emotions & The Nervous System

Emotions are not just thoughts in our mind. We acknowledge them as signals mediated through the nervous system. Now, let’s dive a little deeper.

Our nervous system is constantly collecting information from our body in the form of felt experience. It also gathers data from our environment, including physical sensations from our five senses or stress levels. Safety cues and past experiences are collected as well. This information travels to the brain through neural pathways where it’s integrated and interpreted as a complex, sensory rich experience.

When our body senses, the nervous system sends signals to the brain. If the brain interprets those signals as a threat to safety, it produces emotions like fear. The nervous system sends signals back to the body. This communication can travel between neurons, glands, or muscles, using neurotransmitters and other signaling molecules. This can increase heart rate, tighten muscles, or change breathing patterns so it can prepare for self-preservation.

This communication works both ways:

• Body → brain: sensations inform felt experience
• Brain → body: interpretations shape felt responses

That’s why emotions show up physically. Tight shoulders. A knot in the stomach. Shallow breathing. These sensations create urgency so we can adjust course.

When the nervous system is regulated, the stress response moves through the body, completes its cycle, and returns to calm. When it’s dysregulated, stress lingers. Emotions feel more intense. The body stays stuck in survival.

This isn’t a personal flaw. It’s just how the process is designed to work.

The Autonomic Nervous System

The autonomic nervous system plays a central role in emotional responses.

It has two primary branches:

• The sympathetic nervous system (SNS): activates the stress response
• The parasympathetic nervous system (PSNS): activates rest, recovery, and restores balance

When you experience emotions like fear, anxiety, or anger, the sympathetic nervous system activates. This prepares the body for action by increasing heart rate, sharpening focus, redirecting blood flow to muscles, and mobilizing energy.

When you feel calm, safe, or content, the parasympathetic nervous system becomes more active. Heart rate slows, digestion improves, breathing deepens, and the body shifts toward recovery.

It’s important to note that sympathetic activation is not “bad.” It’s necessary.

Your body uses this same system during exercise. When lifting heavy weights, sprinting, or pushing through a challenging workout, the sympathetic nervous system activates to meet the demand. Recovery happens when the parasympathetic system restores balance. Like between reps or sets.

Emotional fitness works the same way. Activation isn’t the problem. The inability to return to balance and recover is.

Sensations, Emotions & Thoughts

Sensations and emotions are often used interchangeably, but there’s a distinction. Understanding the difference makes everything that follows much easier to grasp. Thoughts also play a role in how emotions are formed.

Sensations 

Our body experiences raw physical sensations. These are signals from the nervous system’s sensory receptors, which are specialized cells in the body. They detect things in our internal and external environment. These receptors pick up data through our senses like touch, sight, pressure, temperature, and pain.

They also detect internal changes like heart rate or tension. Sensations can also show up as experiences like a tight chest, shallow breathing, warmth, or a knot in the stomach. They normally happen before we consciously think about what’s going on.

Emotions 

Emotions are more complex than simple sensations. They are embodied felt responses that emerge after the brain interprets sensory data and meaning has been assigned to it.

First, the body senses something. This can be a a sound, a facial expression, a memory, a physical shift. Those signals travel to the brain.

The brain evaluates them for relevance and safety. And that’s when emotions emerge. In this way, emotions are not just feelings. They are the result of thoughts or physical sensation filtered through interpretation.

You can think of emotions as a chemical and neurological cocktail that produces coordinated patterns of sensation in the body.

They signal whether something feels safe, threatening, exciting, or meaningful. In doing so, they organize our physiological and behavioral response to what we’re experiencing.

Emotions show up as recognizable patterns like fear, anger, sadness, calm, joy, elation. Each preparing us to respond in a specific way.

Example: A Loud Noise

Imagine hearing a loud noise behind you: Your body reacts first. Sensory receptors pick up the sound. These are sensations, raw signals from the body.

Almost instantly, your brain interprets those sensations. If the noise is recognized as a threat, a corresponding emotional response is triggered. 

Emotions like fear or alertness kicks in and prepares you to react. You can notice extra sensations like your shoulders tense, your heart race, or your breath catch.

In short: Your body senses first and emotions emerge once those sensations are interpreted. It happens very quickly, but that’s how sensations and emotions work together.

Thoughts

Thoughts can also trigger emotions when the brain interprets them as meaningful. A memory, worry, or imagined scenario can signal the body to respond, creating emotional sensations we experience. But not every thought creates emotion. Only the thoughts the brain interprets as relevant or significant enough to engage the body.

What Dysregulates the Nervous System

The nervous system doesn’t become dysregulated randomly. It responds to experiences (especially repeated ones) that signal threat, unpredictability, or lack of safety.

You can probably relate to some of the common factors that dysregulate the nervous system, these include:

• Chronic stress (work pressure, financial strain, care-giving, burnout)
• Unprocessed emotional experiences where the body didn’t get what it needs to return to calm
• Chronic exposure to toxic or unpredictable behavior (criticism, emotional volatility, manipulation, boundary violations)
• Lack of emotional or physical safety, past or present
• Ongoing suppression of emotions instead of healthy expression or regulation

Picture this: a stressful experience occurs and activates the SNS. But the nervous system doesn’t get what it needs to trigger the PSNS and return to balance. The stress response stays unfinished. The body stays on alert.

Over time, the nervous system starts to treat similar situations as threats. It can even treat similar people or environments as threats, even when danger isn’t there. This is not a conscious choice. It’s a protective pattern designed to keep you safe.

Overtime, this can become a unconscious pattern. The nervous system learns to stay vigilant so the conscious mind can keep functioning. The result can look like heightened anxiety, emotional reactivity, shutdown, or lack of trust.

This doesn’t mean something is “wrong” with you. It means your nervous system adapted to survive.

Emotional fitness is not about blaming the past or diagnosing our behaviors. It’s about recognizing how the nervous system learns patterns. And learning how to intentionally retrain it toward safety and regulation.

Nervous Systems Regulate With Each Other

The nervous system doesn’t regulate in isolation. It’s constantly responding to its environment, including the nervous systems (people) around it.

This process is known in neuroscience as emotional contagion. Emotional and physiological states influence others through tone of voice, facial expression, posture, and behavior. This happens automatically, often without conscious awareness.

Emotional contagion doesn’t need direct interaction. Simply being near a dysregulated person can induce stress responses. This can happen through subtle cues like tension, posture, breathing, or emotional intensity. The nervous system registers these signals automatically as part of its safety-scanning process.

Co-regulation

Because of this, co-regulation can occur in both supportive and destabilizing ways. Being around calm, consistent, and emotionally aware people can help our nervous system settle. Prolonged exposure to dysregulated, unpredictable, or emotionally volatile people can dysregulate us in return. It activates stress responses and keeps our body on alert.

This isn’t a matter of intention or blame. It’s how our nervous systems communicate through nonverbal signaling. This includes mechanisms linked to the mirror neuron system.

Emotional fitness includes learning to recognize which environments and relationships support regulation. And which ones do not.

How Emotions are Part Of Our Intelligence System

Emotions work as our internal guidance system. One way to think about them is like dashboard lights in a car. Each signal exists for a reason, letting us know what’s happening beneath the surface.

Feelings like joy, ease, or calm often signal alignment or onward movement. Discomfort, tension, or emotional pain usually signal that something needs attention or adjustment. Unfortunately, these signals don’t come to us in neat, logical language. They show up as sensations, moods, or reactions. For many of us, they can be hard to explain or even acknowledge because we aren’t emotionally aware.

Nonetheless, confusing emotions still serve a purpose in our lives. They force us to slow down and prompt us to reassess our choices. Yet, if our nervous system is regulated, these signals are much easier to spot and manage. We have the clarity and emotional bandwidth to be patient, dissecting them without becoming overwhelmed.

But if our emotional signals are ignored or suppressed, it’s like driving with warning lights flashing. Over time, this clouds our decision-making, increases stress, and begins to affect our physical health.

Ironically, this is what actually influences most us to take the journey toward emotional fitness! Unprocessed emotional stress finally catches up to us and forces us into awareness!

How Emotional Patterns Form (Habits, Thoughts, and Feelings)

So now we know emotions don’t just pass through us and disappear. They leave an imprint on the nervous system, especially when the same emotional response happens over and over again.

Each time we have an emotional or sensory experience, our nervous system responds to it. Neurons in the brain fire together to process what’s happening. When the same neurons fire repeatedly, the connection between them strengthens. Over time, this creates familiar emotional and thought patterns.

Our brain is made up of billions of neurons that communicate through connections. When we repeat certain thoughts, emotions, or behaviors, those patterns form stronger neural pathways. But if we introduce new responses and practice them consistently, the brain begins forming new connections. These are sometimes described as new “branches” between neurons.

In simple terms:

• What we practice, our nervous system strengthens
• What we stop reinforcing, our nervous system gradually weakens

This applies to thought and emotional patterns just as much as physical habits.

Neuroplasticity: The Nervous System Can Change

Neuroplasticity is the nervous system’s ability to adapt based on experience. In other words, what we repeatedly think and do forms emotional reactions that eventually become more automatic responses.

This is how habits form. Not just physical habits, like our bench press, but emotional ones too, like discomfort with intimacy.

If stress, self-criticism, or emotional shutdown have been frequent responses, the nervous system learns to default to them. Not because they’re helpful, but because they’re familiar. Your body is designed to conserve energy, and familiar patterns need less effort.

The same is true for healthier patterns. When calm, curiosity, or emotional regulation are practiced repeatedly, the nervous system begins forming new neural pathways. Neurons create new connections, sometimes described as new “branches,” that support different emotional responses. This is why emotional fitness is trainable.

We’re not trying to remove emotions or change our personality. We’re teaching our nervous system new healthier options. Over time, those options become more accessible, and our emotional responses feel less reactive and more intentional.

This is what change actually looks like at the emotional level. Not overnight transformation, but repeated moments of awareness, regulation, and choice.

Emotional Fitness Is a Key Part of the 5 Pillars of Lifestyle Fitness

The five pillars (nutritional, physical, mental, emotional, and spiritual fitness) don’t work separately. The nervous system connects them all.

Emotional fitness influences digestion, movement, thought patterns, and our sense of awareness, connection, and discernment. When emotional regulation improves, the other pillars become easier to support. This is why emotional fitness sits at the center of holistic well-being.

The Emotional Domino Effect

Emotions often act as the bridge between our body, mind, and sense of meaning. A shift in one area can quickly ripple into the others.

For example, imagine being in a high-stress work environment. Chronic stress can dysregulate the nervous system, which then shows up across multiple pillars:

• Mental: racing thoughts, negativity, or difficulty concentrating
• Emotional: anxiety, irritability, or emotional overwhelm
• Physical: muscle tension, fatigue, headaches, or digestive issues
• Nutritional: impaired digestion, making it harder to extract nutrients
• Spiritual: feeling disconnected, ungrounded, or a lacking discernment

Nothing about this experience is random, the body is responding as an interconnected system.

Now consider a different scenario. You’re facing a challenging life event. Instead of suppressing your emotions, you support your nervous system with regulating practices. As those emotional patterns start to shift:

• your mood feels lighter and more manageable (emotional)
• your body becomes more resilient to stress (physical)
• your thoughts feel clearer and less reactive (mental)
• you gain a new sense of perspective (spiritual)

This is the domino effect in action. When emotional fitness is supported, it doesn’t just improve how we feel, it helps stabilize the entire system.

For more on the holistic body, please visit: The Holistic Body: How to Sync Body, Mind & Spirit

Training the Nervous System to Support Healthier Patterns

We don’t train the nervous system through willpower or motivation alone. We train it through repetition and consistency. The same way we train a muscle.

Simple practices like slowing your breath and intentionally moving your body can signal safety to the nervous system. Re-framing thoughts or allowing emotions to move through instead of suppressing them also helps. These signals create the conditions needed for new neural connections to form.

This is why emotional fitness is a skill, not a personality trait.

With time and practice, the nervous system can learn:

• calmer responses to stress
• more balanced emotional reactions
• clearer thinking under pressure
• greater emotional resilience

This is neuroplasticity in action and it’s happening whether we’re aware of it or not. Emotional fitness simply makes the process intentional.

Embracing Emotional Fitness: The Real Path To Lifestyle Fitness

Emotions are fundamental aspects of who we are and play a vital role in our overall health and wellness. Whether we experience joy, anger, sadness, or fear, each emotion has a purpose and serves as a form of communication.

Emotions offer valuable insights into how we process information from the external world and what it means to us internally. Embracing emotions involves recognizing them as meaningful experiences. They should be felt and understood. They should not be dismissed, ignored, or rushed to change.

Embracing emotions is about accepting them without judgment and recognizing them as natural, necessary parts of being human.

Embracing vs. Acting on Emotions

It’s important to clarify that embracing emotions doesn’t mean acting impulsively based on how we feel. Feeling angry, for example, doesn’t mean we should lash out at someone.

Instead, embracing emotions involves acknowledging the anger and finding a safe way to process it. By doing this, we can learn to regulate the intensity of our responses. At the same time, we still allow ourselves to feel the full range of our emotions.

This distinction is crucial, as it helps us avoid suppressing emotions, which can lead to long-term negative consequences.

Practical Nervous System Regulation Tools

First, we need to understand what our unique circumstances are. This means what causes our nervous system to become dysregulated in the first. Then, the next step is learning how to guide it back to balance.

At the same time, emotional fitness isn’t built through understanding alone. It’s built through felt experience.

The nervous system learns regulation in two key ways:

• through co-regulation (regulating with others)
• through self-regulation (regulating yourself)

Both are necessary and each one supports the other.

Co-Regulation: Why Safety Starts in Connection

Before we learn how to regulate ourselves, we learn how to regulate with others.

From infancy, the nervous system depends on caregivers to help us calm down, feel safe, and return to balance. That wiring doesn’t disappear in adulthood. Our nervous system is still shaped by connection, presence, and rapport or lack of that.

Healing co-regulation happens when a regulated nervous system helps another nervous system settle. This is biology, not weakness.

When we’re around someone who feels calm and emotionally attentive, our nervous system automatically picks up on cues of safety. Facial expressions, tone of voice, posture, and breathing patterns all send signals. The brain uses these signals to sense and mirror emotional states.

This is why:

• being heard can calm us
• sitting quietly with someone can feel grounding
• a safe presence can reduce stress without needing advice

Our nervous system looks for safety through felt experience, not logic. Though understanding can help reinforce that sense of safety.

Common Forms of Co-Regulation

Co-regulation shows up in everyday life:

• Therapeutic relationships
  A therapist’s rapport and steady presence help retrain the nervous system over time.
• Safe relationships
  Healthy friendships or partnerships, listening without fixing, judging, or escalating help signal safety.
• Nature
  Natural environments that offer consistent, non-threatening sensory data helps settle the nervous system.
• Animals and pets
  Animals like horses often regulate through presence, rhythm, and physical closeness, which can be deeply grounding.

These experiences help the nervous system borrow regulation until it learns how to do it more independently.

Self-Regulation: Building Internal Stability and Choice

Self-regulation is the ability to notice our internal state. We support our nervous system without relying on someone else in the moment.

This matters because self-regulation lets us:

• think clearly under stress
• pause before reacting
• make healthier choices
• seek healthy co-regulation intentionally rather than impulsively

Self-regulation doesn’t mean forcing calm. It means creating enough internal stability to respond instead of react.

Practical Self-Regulation Tools

These tools work because they communicate safety directly to the nervous system:

• Breath awareness
  Slowing the breath, especially extending the exhale, signals the body to downshift.
• Movement
  Walking, stretching, or structured physical activity gives an outlet for pent up stress, stored in the body.
• Naming the emotion
  Identifying what you’re feeling (“this is anxiety,” “this is frustration”) helps organize the experience.
• Allowing emotions to move
  Feeling an emotion without suppressing it allows it to rise and fall naturally. This is why we feel better after a good cry, it can help finish the stress cycle.
• Pausing before action
  Even a brief pause interrupts automatic patterns and creates choice.
• Meditation: Meditation helps regulate the nervous system by increasing awareness without reaction. This supports a shift from stress toward calm over time.
• For more on meditation: please visit:
  • Meditation: How To Train The Body To Meditate Better
  • Meditation: The Truth About How It Actually Works

These practices are regulating over time, eventually relief becomes more instant.

How Co-Regulation and Self-Regulation Work Together

Healthy co-regulation teaches the nervous system what safety feels like.
Self-regulation helps us access that state independently when we need it.

We don’t choose one over the other. We build both.

The more our nervous system experiences safety in connection, the easier self-regulation becomes. And the more self-regulation we develop, the more intentionally we will lean towards healthy co-regulation. This is emotional fitness in practice.

A Key Clarification About Emotional Regulation

Emotional regulation does not mean calming ourselves down instantly.
It means increasing our capacity to stay aware while our nervous system goes through its natural cycle. Sometimes with support, sometimes on our own.

Worth noting: needing co-regulation doesn’t mean we lack emotional fitness, avoiding it does. Self-regulation alone doesn’t build it either. Balance does.

Summing it Up

Emotional fitness isn’t about eliminating stress or mastering our emotions. Stress is part of being human. Emotions are part of being alive.

What matters is how our nervous system responds and how well it can return to balance.

When we understand emotions as signals rather than problems, we stop fighting our internal experience and start working with it. We learn to recognize when our system needs support, whether that comes through connection, movement, rest, or professional care.

Building emotional fitness doesn’t happen overnight. It happens through small, repeated moments of awareness, regulation, and choice. Over time, those moments reshape our nervous system, creating more resilience, clarity, and stability.

We don’t need to do this perfectly. And we don’t need to do it alone either.

Emotional fitness is the ongoing practice of supporting our nervous system. This support lets us meet life with greater intention, flexibility, awareness, and ease.

A Note on Scope & Professional Support

This article is for educational and informational purposes only. It is not intended to diagnose, treat, or replace professional medical, psychological, or therapeutic care.

Emotional fitness and nervous system regulation are important aspects of well-being, but individual needs vary. If you’re experiencing ongoing emotional distress, trauma, anxiety, or depression, work with a licensed healthcare provider.

Consulting a mental health professional is also strongly recommended for stress-related physical symptoms. They have the resources, skill, and tools necessary to help guide your recovery.

The practices discussed here are meant to support awareness and about regulation. They should never override professional medical advice or delay seeking care when it’s needed.

References

1. National Institute of Mental Health (NIMH)
   Understanding Stress and the Stress Response
   (https://www.nimh.nih.gov/health/topics/stress)
2. Cleveland Clinic
   Autonomic Nervous System
   (https://my.clevelandclinic.org/health/body/21648-autonomic-nervous-system)
3. Harvard Health Publishing
   Understanding the Stress Response
   https://www.health.harvard.edu/staying-healthy/understanding-the-stress-response
4. American Psychological Association (APA)
   Stress Effects on the Body
   https://www.apa.org/topics/stress/body
5. Frontiers in Psychology
   Neuroplasticity and Emotional Regulation
   https://www.frontiersin.org/articles/10.3389/fpsyg.2018.00400/full
6. Greater Good Science Center
   How Emotions Are Made
   https://greatergood.berkeley.edu/article/item/how_emotions_are_made
7. Stanford Medicine
   Neuroplasticity
   https://med.stanford.edu/neuroscience/research/neuroplasticity.html
8. National Institute of Mental Health (NIMH)
   Emotional Contagion
   (https://pmc.ncbi.nlm.nih.gov/articles/PMC8322226/)
9. National Center for Biotechnology Information (NCBI)
   Sensory Receptors and Transduction
   https://www.ncbi.nlm.nih.gov/books/NBK539861/
10. OpenStax
    Anatomy & Physiology – Sensory Processes
    https://openstax.org/details/books/anatomy-and-physiology