Started my work on Datura while developing the surface realm Plas

Putting both of them together at the same time 

In chapter two check it out!

⋆˚𝜗𝜚˚⋆

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A Sci-Fi World

The story is about an alien civilization populated by a race called the Laminae who live in two worlds.

One world is called Organelle, its design comes from biology. The other, is Lamina, Also based on biology, with all the processes reversed.

Life in the two worlds has a few rules:

When you cross over from Organelle into Lamina you lose all memory of Organelle, the place becomes a mystery and so do you! Everything that Organelle was built on, flows in the opposite direction. When you return to Organelle, your memories of Organelle are restored. The same rule applies to travelling from Lamina.

The only clue to the mystery of the other side is one of three items: a single photo, a drawing, or a local folktale. 

The goal is to come up with accurate speculation of the other side. This expands the territory and brings new things into existence to enrich the culture. If the speculation is entirely correct that part of the world has the potential to be immortal.

If, however, the people create falsehoods then they lose territory as that part of the world and that part of their identity becomes a fabrication.

If this happens it will be the end of the world and they will die 

Allowing yourself to be deceived will kill you

It begins with a scientific explanation of a few subjects in biology with a lot to unpack.

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My Vision

From the beginning I had a vision.

To see what a society built on biology looks like. World building has always been present, but I had no story. I went into this project knowing very little of biology, but I want to know enough that I have spent seven months researching.

My first attempt at a story was about a world based on the parts of a cell. A story about a world living under a corrupt regime and an unlikely hero. One, unlike the others able to see past all the brainwashing that the regime as done to the people. As she gets people to start thinking for themselves, she begins to organize a rebellion to overthrow the government and liberate the people.

Oh! my things have changed!

While I have recently started over I’m happy with the outline and the plot. I have a lot more knowledge about biology and I still have more to do. 

But, I’m ready to get started

⋆˚𝜗𝜚˚⋆

They Do Not Think Like Us

𖤓

Getting to know the characters 

The characters are part of a race called the Laminae

The characters are put together from  something called Grey Matter. A butterfly shaped area in the spinal cord called Laminae, or Lamina.

⟁

Knowing the Characters 

When a Laminae enters the world, they fuse themselves with the world, to truly become a part of it.

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To become a traveller, the primary purpose of the Laminae, they must be shown the way.

There are five realms for her to fuse herself with. Then, the world, and her identity develop together 

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Datura Nightshade

♀

•°•°•❈•°•°•

Her First Day:

𖤓

Morning:

Datura’s beginning is on the surface realm Plas. Where she is to learn her potential 

She will use the acquired skills to defend herself and the realm of Plas from potential threats 

Her life begins in the core of her soul, it is marked by a glowing white spot in the middle of her chest.

Light is exchanged between the Laminae, because of this spot 

Light can fire from this spot for a distance to another person, to send necessary informatin Their mind will absorb this information in the form of visual effects. 

This however can only happen within the realm they are currently in 

Lamina I, the most superficial layer of the spinal dorsal horn, is a critical site for processing sensory information

from nociceptors

Nociceptors act as the body's first line of defense against potentially damaging stimuli

Nociceptors are activated by noxious stimuli such as intense heat, cold, pressure, or chemicals released during tissue damage

They act as a critical alarm system, alerting the brain to potential or actual tissue damage

Datura’s beginning is on the surface realm Plas. Where she is to learn her potential 

She will use the acquired skills to defend herself and the realm of Plas from potential threats 

projection neurons:

a type of neuron in the central nervous system (CNS) that transmit information to distant regions of the brain or spinal cord

She is to handle the messages from other realms, from far away travellers 

They have long axons

the function of axons is to carry electrical impulses that are the means of communication within the brain and between the brain and the rest of the body

that extend from their cell bodies to distant targets

Their axons project to areas outside the structure they originate from, unlike interneurons which project locally within the same structure

𖤓

Afternoon:

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Types of Mechanoreceptors:

Encapsulated mechanoreceptors:

being enclosed or surrounded by a barrier to protect or contain something within

These are specialized receptors with accessory structures, including:

something that is supplementary or additional to the primary function or structure, providing assistance or support but not being essential

Meissner's corpuscles

rapidly adapting mechanoreceptors found in the dermal papillae of glabrous skin, responsible for detecting fine touch, low-frequency vibrations, and the sensation of flutter

Pacinian corpuscles

Their primary function is to detect vibration and deep pressure, making them essential for sensing touch, especially at high frequencies

Merkel's disks

specialized sensory receptors in the skin that detect light touch and fine details

and Ruffini's corpuscles

Ruffini corpuscles in the fingers monitor the slippage of objects along the skin surface, allowing for fine adjustments in grip

These are simple, non-encapsulated nerve endings that respond to various stimuli, including mechanical ones

Mechanoreceptors allow us to perceive the texture, shape, and movement of objects in contact with us

chemical receptors (chemicals released during injury)

Chemoreceptors are sensitive to specific chemicals and substances, such as oxygen, carbon dioxide, and hydrogen ions, in the blood or other bodily fluids

When chemoreceptors detect a change in chemical composition, they send signals to the brain, which then initiates adjustments to breathing, heart rate, or other physiological functions to restore normal levels

thermoreceptors

Thermoreceptors convert temperature changes into electrical signals (action potentials) that are transmitted to the central nervous system

Cold Thermoreceptors: Respond to temperatures below a certain threshold, often increasing firing rate with cooler temperatures

Warm Thermoreceptors: Respond to temperatures above a certain threshold, often increasing firing rate with warmer temperatures

and pruriceptors

𖤓

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Evening:

histamine receptors: 

H1R

The H1R is involved in various physiological processes, including the stimulation of:

nitric oxide formation

Nitric oxide synthases (NOS) are enzymes that catalyze the formation of:

NO

NO is a free radical

These molecules can damage various cellular components, including DNA, proteins, and lipids, potentially leading to oxidative stress and contributing to the development of various diseases

meaning it has an unpaired electron. This characteristic gives it a unique ability to interact with other molecules and participate in signaling pathways

from l-arginine

While L-arginine is a precursor to NO

The enzyme nitric oxide synthase (NOS) converts L-arginine into NO

In the context of allergic reactions, it contributes to symptoms like itching, swelling, and skin rashes

H4R

H4R plays a role in the movement of immune cells to sites of inflammation

are expressed in itch-sensing dorsal root ganglia (DRG) neurons and mediate histamine-induced itch

𖤓

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Night:

While traditionally viewed as a relay station, recent research shows that lamina I neurons are involved in more complex signal processing,

including local interactions and the distribution of information within the spinal cord

Lamina I primarily relays information about pain, temperature, and itch from the periphery to the brainstem and thalamus

It contains a mix of projection neurons (PNs)

that relay information to higher centers and local circuit neurons (LCNs)

that process information within the spinal cord

LCNs play a crucial role in modulating the intensity and distribution of sensory signals

While projection neurons make up only a small fraction of the neurons in lamina I, they are important for transmitting information to other brain regions.

Many lamina I PNs also have local axon collaterals that target other spinal cord regions, contributing to the distribution of information within the cord

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Datura’s Design

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Dorsal Horn

The dorsal horn contains various types of neurons, including primary afferent fibers

projection neurons:

a type of neuron in the central nervous system (CNS) that transmit information to distant regions of the brain or spinal cord

They have long axons

the function of axons is to carry electrical impulses that are the means of communication within the brain and between the brain and the rest of the body

that extend from their cell bodies to distant targets

Their axons project to areas outside the structure they originate from, unlike interneurons which project locally within the same structure

Spinoparabrachial projection neurons:

a type of spinal cord neuron that project to the parabrachial nucleus (PBN) in the brain

SPBNs receive input from other neurons in the spinal cord, including

Neurotransmitters can be either excitatory or inhibitory, with excitatory neurotransmitters promoting nerve firing and inhibitory ones reducing it

excitatory

Glutamate is the primary excitatory neurotransmitter in the central nervous system, playing a crucial role in learning and memory

Acetylcholine is excitatory at the neuromuscular junction, causing muscle contractions

Norepinephrine and dopamine are also excitatory, with roles in arousal, alertness, and motivation

Norepinephrine acts as both a neurotransmitter, transmitting signals between nerve cells, and a hormone, influencing bodily functions

Neurotransmitters are chemical messengers in the body that allow neurons (nerve cells) to communicate with each other and other cells. They transmit signals, or messages, across the synapse, the tiny gap between neurons or between neurons and other cells

Dopamine is a neurotransmitter in the brain, often called the "feel-good" hormone, involved in the reward system, motivation, and movement

Other excitatory neurotransmitters include

serotonin:

Serotonin is synthesized from the amino acid tryptophan.

Tryptophan is an essential amino acid

a polar aromatic amino acid:

Tyrosine (Tyr):

Contains a hydroxyl group (-OH) on its aromatic ring, allowing it to participate in hydrogen bonding

Tryptophan (Trp):

Has a complex indole ring structure that includes a nitrogen atom, making it polar and capable of hydrogen bonding

the precursor to serotonin and melatonin. Its structure consists of an α-amino group:

an α-carboxylic acid group

and a unique indole side chain

making it a polar molecule

with a non-polar aromatic beta carbon substituent

epinephrine:

Epinephrine is both a neurotransmitter and a hormone, but it acts mainly as a hormone. Epinephrine, also known as adrenaline, plays an important role in your body's fight-or-flight response

histamine:

Histamine is released by mast cells and basophils in response to allergens, pathogens, or injury, triggering an immune response

glycine:

Glycine is a key inhibitory neurotransmitter, particularly in the spinal cord and brainstem, playing a crucial role in motor and sensory functions. It also contributes to the function of excitatory neurotransmitter:

NMDA receptors:

a glutamate receptor and a crucial ion channel in neurons. It plays a significant role in synaptic plasticity, memory formation, and learning

particularly during development

Excitatory neurotransmitters, like glutamate, bind to receptors on the postsynaptic neuron's membrane, triggering depolarization and increasing the likelihood of an action potential

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inhibitory interneurons:

Inhibitory interneurons are neurons that release inhibitory neurotransmitters

Inhibitory neurotransmitters are chemicals that reduce the likelihood of a nerve cell firing and sending signals. These neurotransmitters act as "off switches," calming the nervous system and preventing excessive stimulation

primarily GABA, to suppress the activity of other neurons

GABA reduces neuronal excitability and can produce a calming, relaxing sensation

GABA is involved in controlling nerve cell activity, particularly those associated with anxiety, stress, and fear

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Corticofugal projection neurons:

They connect the cerebral cortex to subcortical areas, forming tracts like the corticothalamic, corticostriatal, corticorubral, corticotectal, corticobulbar, and corticospinal tracts

Callosal projection neurons:

also known as interhemispheric commissural pyramidal neurons, are specialized neurons that connect the two cerebral hemispheres via the corpus callosum, the largest white-matter tract 

Modulatory projection neurons:

a type of neuron that extends axons to distant regions of the central nervous system (CNS) and exert modulatory (metabotropic) effects on target neurons, often alongside more traditional (ionotropic) actions

associative projection neurons:

neurons that project their axons within the same hemisphere to connect different cortical areas

commissural projection neurons:

Commissural projection neurons establish connections between the two sides of the brain, allowing for communication and coordination between them

corticofugal projection neurons:

are involved in the formation of several important brain circuits, including the corticothalamic, corticostriatal, corticorubral, corticotectal, corticobulbar, and corticospinal tracts

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peripheral sensory neurons

a type of neuron that detects stimuli in the body and transmits them to the central nervous system. 

These neurons are located in the peripheral nervous system (PNS) and play a crucial role in various bodily functions, including sensing external stimuli, maintaining homeostasis, and even regulating the immune system

Primary afferent fibers: These neurons receive sensory input from the body

They receive sensory information from various receptors in the body:

mechanoreceptors

sensory receptors that respond to mechanical stimuli

Cutaneous Mechanoreceptors: 

These are located in the skin and include:

Meissner's corpuscles:

specialized nerve endings in the skin, responsible for detecting fine touch, low-frequency vibrations, and the sensation of flutter

They are rapidly adapting receptors, meaning they respond best to changes in stimulus rather than sustained pressure

Pacinian corpuscles:

Pacinian corpuscles are rapidly adapting mechanoreceptors that detect vibration and deep pressure

Merkel's disks:

They are composed of Merkel cells and associated Aβ-afferent nerve endings

Ruffini's corpuscles:

encapsulated nerve endings

thermoreceptors

Thermoreceptors help the body regulate its temperature by sending information about the surrounding temperature to the brain's hypothalamus, which acts as the body's "thermostat"

nociceptors

specialized sensory nerve endings that detect potentially harmful stimuli, alerting the brain to the risk of injury or damage and initiating pain perception

chemoreceptors

specialized sensory cells that detect and respond to chemical stimuli in the environment or within the body, triggering a response

Peripheral Chemoreceptors:

Found in the carotid bodies and aortic arch, these receptors primarily detect changes in blood oxygen, carbon dioxide, and pH. They send signals to the brainstem to regulate breathing and blood pressure

Central Chemoreceptors:

Located in the brainstem, these receptors respond to changes in the concentration of hydrogen ions (H+) in the cerebrospinal fluid, effectively detecting changes in blood carbon dioxide

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Interneurons

connecting primary afferent fibers to projection neurons

They outnumber both sensory and motor neurons

They act as a "middleman" between sensory neurons (afferent) and motor neurons (efferent), and also connect to other interneurons, forming intricate neural circuits

𖤓

When someone crosses over into Lamina they take on a new personality and way of thinking. 

The biology process is reversed and they become someone totally different

𖤓

Datura in Lamina

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Lamina I, the most superficial layer of the spinal dorsal horn, is a critical site for processing sensory information

She does not actively analyze everything, but instead, puts her energy into dressing to match the energy and emotions felt. She likes to put that energy on display in her own way.

Nociceptors act as the body's first line of defense against potentially damaging stimuli

When something terrible happens, she is there to fight it off

They detect noxious stimuli and initiate pain signals that lead to withdrawal reflexes and the experience of pain

When she is in pain, she will often withdraw, and express that pain in her self expression until she is able to see what is the source, and the cause. 

Nociceptors can be categorized based on the type of stimulus they detect, such as high-threshold mechanoreceptors (intense pressure)

When it is time to be serious, Datura looks to establish a neutral environment. One without labels is what she thinks is right, she believes that an environment is not black and white, but instead a spectrum

Types of Mechanoreceptors:

Encapsulated mechanoreceptors:

being enclosed or surrounded by a barrier to protect or contain something within

What was once contained inside is brought to the surface, Datura believes that containing your true self is like keeping a bird in a cage. Sad, a bit cruel and a waste of potential.

These are specialized receptors with accessory structures, including:

something that is supplementary or additional to the primary function or structure, providing assistance or support but not being essential

She loves to take something that seems very complex and strip it down to its basics, to understand what she believes to be its core nature 

Meissner's corpuscles

rapidly adapting mechanoreceptors found in the dermal papillae of glabrous skin, responsible for detecting fine touch, low-frequency vibrations, and the sensation of flutter

Pacinian corpuscles

Their primary function is to detect vibration and deep pressure, making them essential for sensing touch, especially at high frequencies

She is able to pick up on the emotion of the room, influencing her to quickly adapt as much as she can, while choosing to adapt to the lightest of frequencies, as she attempts to get close to being on the same frequency as everyone else. If she is getting mostly negative energy she will look for the highest frequency available and try to match it.

Merkel's disks

specialized sensory receptors in the skin that detect light touch and fine details

and Ruffini's corpuscles

Ruffini corpuscles in the fingers monitor the slippage of objects along the skin surface, allowing for fine adjustments in grip

Sometimes she can misinterpret the level of seriousness in a situation and later come to realization that she has possibly underestimated the situation or the people around her. While she usually is in tune with the emotions of those around her she occasionally misunderstands. Nobody is perfect.

These are simple, non-encapsulated nerve endings that respond to various stimuli, including mechanical ones

Mechanoreceptors allow us to perceive the texture, shape, and movement of objects in contact with us

She will pursue friendships and relationships, as she learns more details about the person she tries harder to win them over by looking at features of their character that many people miss about that person 

chemical receptors (chemicals released during injury)

Chemoreceptors are sensitive to specific chemicals and substances, such as oxygen, carbon dioxide, and hydrogen ions, in the blood or other bodily fluids

She can, at times, ignore her health and often her body will punish her as a result 

thermoreceptors

Thermoreceptors convert temperature changes into electrical signals (action potentials) that are transmitted to the central nervous system

Different social cues, or signals, she will process in own way. Her interpretation greatly affects the type of comfort (there’s more than one way of being comfortable) and if it is on a level that she can handle 

Cold Thermoreceptors: Respond to temperatures below a certain threshold, often increasing firing rate with cooler temperatures

Warm Thermoreceptors: Respond to temperatures above a certain threshold, often increasing firing rate with warmer temperatures

and pruriceptors

histamine receptors: 

H1R

The H1R is involved in various physiological processes, including the stimulation of:

nitric oxide formation

Nitric oxide synthases (NOS) are enzymes that catalyze the formation of:

NO

NO is a free radical

These molecules can damage various cellular components, including DNA, proteins, and lipids, potentially leading to oxidative stress and contributing to the development of various diseases

When there are problems that contribute to stress, leading to the inability to make proper judgments, or impacting the decisions because of a clouded mind, it makes Datura’s behaviour unstable.

meaning it has an unpaired electron. This characteristic gives it a unique ability to interact with other molecules and participate in signaling pathways

How she expresses herself when she is feeling this way hints to others she is under stress. She uses her creativity in how she dresses and presents herself to better explain what she is feeling than with words alone. When something is difficult to understand with words, it’s easier for her to express it creatively.

This is her way of communicating when she feels misunderstood 

from l-arginine

While L-arginine is a precursor to NO

L-arginine is a semi-essential amino acid meaning those that the body can typically produce, but may require additional intake under certain conditions, such as illness, growth, or stress

She is for the most part able to show to others that she is going through some challenges. Sometimes it’s difficult to express in words alone. She is capable of solving her own issues but at times she needs to be understood 

The enzyme nitric oxide synthase (NOS) converts L-arginine into NO

She feels the need to be understood which fuels her to express herself in ways to explain her struggles in a way that people can see

In the context of allergic reactions, it contributes to symptoms like itching, swelling, and skin rashes

H4R

H4R plays a role in the movement of immune cells to sites of inflammation

Her self expression can at times make her a target 

are expressed in itch-sensing dorsal root ganglia (DRG) neurons and mediate histamine-induced itch

While traditionally viewed as a relay station, recent research shows that lamina I neurons are involved in more complex signal processing, 

Her ways are carefully calculated but not in the way that is acceptable to those who wish to hold on traditional views 

including local interactions and the distribution of information within the spinal cord

What she is trying to express is that it’s not about using art just to tell people something you already know it can be used in other ways 

Lamina I primarily relays information about pain, temperature, and itch from the periphery to the brainstem and thalamus

Her ways are often viewed as dark or negative 

It contains a mix of projection neurons (PNs) 

that relay information to higher centers and local circuit neurons (LCNs)

They act as the final output neurons of a brain structure, summing local information and relaying it to other parts of the nervous system

They have long axons that extend from their cell bodies to distant targets

Their axons project to areas outside the structure they originate from, unlike interneurons which project locally within the same structure

She is quite good at taking what is in her environment and relaying it to future situations. Her long term memory is excellent.

She is able to distinguish solutions in one situation to suit another by looking at the basic nature of what is around her.

that process information within the spinal cord

LCNs play a crucial role in modulating the intensity and distribution of sensory signals

While projection neurons make up only a small fraction of the neurons in lamina I, they are important for transmitting information to other brain regions.

Many lamina I PNs also have local axon collaterals that target other spinal cord regions, contributing to the distribution of information within the cord

She is quite good at pin pointing something in another person that needs to come out and talk about it openly

𖤓

Sage Obsidian

♂

I will provide a brief science explanation for this character who is classified as Laminae II

Laminae II consists of projection neurons (Golgi type I neurons)

Involved in sensory information transmission, Transmit signals from one area of the nervous system to another, such as peripheral nerves and long tracts of the brain and spinal cord.

peripheral nerves

nerves that branch out from the central nervous system (brain and spinal cord) and extend to the rest of the body

They act like wires, transmitting messages back and forth between the brain and various parts of the body

These nerves are responsible for a wide range of functions, from controlling movement and sensation to regulating involuntary functions like breathing and digestion

Have many dendritic branches

the treelike extensions of a neuron that receive signals from other neurons. 

These branches are essential for neuronal communication and function, with their unique branching patterns being highly correlated with the neuron's specific role

including dendritic protrusions and short hair-like appendages

Long axons that extend over considerable distances, allowing for the transmission of signals to different parts of the nervous system

and local interneurons (Golgi type II neurons)

also known as microneurons

also known as microneurons, are characterized by short axons or sometimes lacking axons altogether. 

Axons transmit electrical signals (action potentials) away from the neuron's cell body (soma). 

Many axons are surrounded by a myelin sheath, a fatty insulating layer that speeds up the transmission of electrical signals. 

At the end of an axon are axon terminals (synaptic terminals), which release neurotransmitters to communicate with other cells. 

They are a type of interneuron within the central nervous system, meaning they connect neurons within a specific brain region rather than projecting to distant areas. 

These neurons are crucial for local circuit function and can be either excitatory or inhibitory, contributing to the complex processing of neural information

They are a type of neuron found in the central nervous system, with smaller soma

and fewer dendritic branches compared to Golgi type I neurons.

Type II Golgi neurons

Golgi cells are often inhibitory interneurons

Inhibitory interneurons release GABA, which hyperpolarizes

Hyperpolarization means an increase in the difference in electrical potential across a cell membrane, making the inside of the cell more negative relative to the outside

or inhibits the postsynaptic neuron

A postsynaptic neuron is a nerve cell that receives signals from another neuron through a synapse.

 It's the neuron that "receives" the message after it's been transmitted across the gap between neurons, where chemical signals called neurotransmitters play a role. 

The postsynaptic neuron then processes this input and can potentially generate its own signal

inhibitory interneurons are less likely to fire an action potential

thus reducing the excitatory influence on the target neuron

They help regulate the activity of neuronal circuits by controlling the balance between excitatory

and inhibitory inputs

contributing to the stability and proper functioning of neural networks

GABA is a primary inhibitory neurotransmitter in the central nervous system, acting to calm and regulate brain activity. It's crucial for maintaining a balance between excitatory and inhibitory neurotransmission

Excitatory neurotransmission is the process by which chemical signals from a neuron (the sending cell)

a cell that transmits a signal to another cell, often through the release of chemical messengers. These messengers, known as signaling molecules or ligands, travel to a target cell and bind to receptors on its surface, triggering a response

excite the next neuron (the receiving cell)

a receiving cell (also called a target cell or recipient cell) is a cell that has the ability to receive and respond to signals from other cells or its environment. 

These cells have specific receptors on their surfaces that can bind to signaling molecules, triggering a cascade of events that leads to a cellular response

increasing the likelihood that it will fire an action potential

These chemical messengers bind to receptors on the postsynaptic neuron

leading to depolarization

which means the cell's membrane potential becomes less negative, increasing the likelihood of an action potential

impacting various neurological functions and contributing to the regulation of mood, sleep, and anxiety

──── ·:*¨༺ ♱✮♱ ༻¨*:· ────

Sage’s Design 

──── ·:*¨༺ ♱✮♱ ༻¨*:· ────

Ventral Horn

Sage in Lamina

──── ·:*¨༺ ♱✮♱ ༻¨*:· ────

Lotus Lamb

♀

I will provide a brief science explanation for this character who is classified as Laminae III

Lamina III a layer within the dorsal horn of the spinal cord, specifically the superficial part of the nucleus proprius

The nucleus proprius is a sensory nucleus in the spinal cord's posterior horn, playing a key role in processing sensory information like touch, vibration, and proprioception. 

It's located beneath the substantia gelatinosa and spans the length of the posterior horn

Characterized by a gelatinous, pale, and crescent-shaped appearance due to the lack of myelinated fibers

substantia gelatinosa plays a crucial role in the gate control theory of pain

where it modulates sensory signals from primary afferent neurons

Contains various interneurons, including:

islet cells

Islet cells in the spinal cord are specialized neurons located in the substantia gelatinosa (SG), a region in the dorsal horn responsible for processing sensory information

These cells have a distinct morphology, including long, often sagittal-oriented dendrites

Islet cells are primarily inhibitory, releasing GABA, and some also co-localize with glycine, which further contributes to their inhibitory function

central cells

stalked cells

and radial cells

which can be GABAergic or glutamatergic

Contains neurons that receive input from both low-threshold and high-threshold primary afferents. 

It's characterized by the presence of numerous myelinated fibers

and neurons

and it's known to receive input from both low-threshold and nociceptive high-threshold primary afferents

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Lotus’s Design

──── ·:*¨༺ ♱✮♱ ༻¨*:· ────

Dorsal Horn

The dorsal horn contains various types of neurons, including primary afferent fibers

projection neurons:

a type of neuron in the central nervous system (CNS) that transmit information to distant regions of the brain or spinal cord

They have long axons

the function of axons is to carry electrical impulses that are the means of communication within the brain and between the brain and the rest of the body

that extend from their cell bodies to distant targets

Their axons project to areas outside the structure they originate from, unlike interneurons which project locally within the same structure

Spinoparabrachial projection neurons:

a type of spinal cord neuron that project to the parabrachial nucleus (PBN) in the brain

SPBNs receive input from other neurons in the spinal cord, including

Neurotransmitters can be either excitatory or inhibitory, with excitatory neurotransmitters promoting nerve firing and inhibitory ones reducing it

excitatory

Glutamate is the primary excitatory neurotransmitter in the central nervous system, playing a crucial role in learning and memory

Acetylcholine is excitatory at the neuromuscular junction, causing muscle contractions

Norepinephrine and dopamine are also excitatory, with roles in arousal, alertness, and motivation

Norepinephrine acts as both a neurotransmitter, transmitting signals between nerve cells, and a hormone, influencing bodily functions

Neurotransmitters are chemical messengers in the body that allow neurons (nerve cells) to communicate with each other and other cells. They transmit signals, or messages, across the synapse, the tiny gap between neurons or between neurons and other cells

Dopamine is a neurotransmitter in the brain, often called the "feel-good" hormone, involved in the reward system, motivation, and movement

Other excitatory neurotransmitters include

serotonin:

Serotonin is synthesized from the amino acid tryptophan.

Tryptophan is an essential amino acid

a polar aromatic amino acid:

Tyrosine (Tyr):

Contains a hydroxyl group (-OH) on its aromatic ring, allowing it to participate in hydrogen bonding

Tryptophan (Trp):

Has a complex indole ring structure that includes a nitrogen atom, making it polar and capable of hydrogen bonding

the precursor to serotonin and melatonin. Its structure consists of an α-amino group:

an α-carboxylic acid group

and a unique indole side chain

making it a polar molecule

with a non-polar aromatic beta carbon substituent

epinephrine:

Epinephrine is both a neurotransmitter and a hormone, but it acts mainly as a hormone. Epinephrine, also known as adrenaline, plays an important role in your body's fight-or-flight response

histamine:

Histamine is released by mast cells and basophils in response to allergens, pathogens, or injury, triggering an immune response

glycine:

Glycine is a key inhibitory neurotransmitter, particularly in the spinal cord and brainstem, playing a crucial role in motor and sensory functions. It also contributes to the function of excitatory neurotransmitter:

NMDA receptors:

a glutamate receptor and a crucial ion channel in neurons. It plays a significant role in synaptic plasticity, memory formation, and learning

particularly during development

Excitatory neurotransmitters, like glutamate, bind to receptors on the postsynaptic neuron's membrane, triggering depolarization and increasing the likelihood of an action potential

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inhibitory interneurons:

Inhibitory interneurons are neurons that release inhibitory neurotransmitters

Inhibitory neurotransmitters are chemicals that reduce the likelihood of a nerve cell firing and sending signals. These neurotransmitters act as "off switches," calming the nervous system and preventing excessive stimulation

primarily GABA, to suppress the activity of other neurons

GABA reduces neuronal excitability and can produce a calming, relaxing sensation

GABA is involved in controlling nerve cell activity, particularly those associated with anxiety, stress, and fear

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Corticofugal projection neurons:

They connect the cerebral cortex to subcortical areas, forming tracts like the corticothalamic, corticostriatal, corticorubral, corticotectal, corticobulbar, and corticospinal tracts

Callosal projection neurons:

also known as interhemispheric commissural pyramidal neurons, are specialized neurons that connect the two cerebral hemispheres via the corpus callosum, the largest white-matter tract 

Modulatory projection neurons:

a type of neuron that extends axons to distant regions of the central nervous system (CNS) and exert modulatory (metabotropic) effects on target neurons, often alongside more traditional (ionotropic) actions

associative projection neurons:

neurons that project their axons within the same hemisphere to connect different cortical areas

commissural projection neurons:

Commissural projection neurons establish connections between the two sides of the brain, allowing for communication and coordination between them

corticofugal projection neurons:

are involved in the formation of several important brain circuits, including the corticothalamic, corticostriatal, corticorubral, corticotectal, corticobulbar, and corticospinal tracts

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peripheral sensory neurons

a type of neuron that detects stimuli in the body and transmits them to the central nervous system. 

These neurons are located in the peripheral nervous system (PNS) and play a crucial role in various bodily functions, including sensing external stimuli, maintaining homeostasis, and even regulating the immune system

Primary afferent fibers: These neurons receive sensory input from the body

They receive sensory information from various receptors in the body:

mechanoreceptors

sensory receptors that respond to mechanical stimuli

Cutaneous Mechanoreceptors: 

These are located in the skin and include:

Meissner's corpuscles:

specialized nerve endings in the skin, responsible for detecting fine touch, low-frequency vibrations, and the sensation of flutter

They are rapidly adapting receptors, meaning they respond best to changes in stimulus rather than sustained pressure

Pacinian corpuscles:

Pacinian corpuscles are rapidly adapting mechanoreceptors that detect vibration and deep pressure

Merkel's disks:

They are composed of Merkel cells and associated Aβ-afferent nerve endings

Ruffini's corpuscles:

encapsulated nerve endings

thermoreceptors

Thermoreceptors help the body regulate its temperature by sending information about the surrounding temperature to the brain's hypothalamus, which acts as the body's "thermostat"

nociceptors

specialized sensory nerve endings that detect potentially harmful stimuli, alerting the brain to the risk of injury or damage and initiating pain perception

chemoreceptors

specialized sensory cells that detect and respond to chemical stimuli in the environment or within the body, triggering a response

Peripheral Chemoreceptors:

Found in the carotid bodies and aortic arch, these receptors primarily detect changes in blood oxygen, carbon dioxide, and pH. They send signals to the brainstem to regulate breathing and blood pressure

Central Chemoreceptors:

Located in the brainstem, these receptors respond to changes in the concentration of hydrogen ions (H+) in the cerebrospinal fluid, effectively detecting changes in blood carbon dioxide

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Interneurons

connecting primary afferent fibers to projection neurons

They outnumber both sensory and motor neurons

They act as a "middleman" between sensory neurons (afferent) and motor neurons (efferent), and also connect to other interneurons, forming intricate neural circuits

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