The Nervous System

the rest of the body bows down before the nervous system

the nervous system works by Sensory Input → Integration → Motor output

Here is a chart of how the nervous system is organized

All of the nervous system is mainly made up of nervous tissue

  • Neurons

  • Glial cells

    • Astrocytes are the most abundant glial cells, found in the central nervous system

    • Microglial cells are kind of thorny and also found in the CNS are your main defense against any invaders

    • Ependymal cells line the barriers of the brain and spinal cord and are what make and manage cerebrospinal fluid(CSF)

    • Oligodendrocytes… insulation

Peripheral nervous system glial cells

  • Satellite cells(like astrocytes.. “pit crew”)

  • Schwann cells (like oligodendrocytes.. insulation)

Types of neurons

  • Multipolar neurons - multiple dendrites

  • Bipolar - one dendrite

  • Unipolar - one process

  • Sensory carry info to the CNS, most are unipolar

  • Motor carries info away from the CNS to the rest of the body, most are multipolar

  • Interneurons carry info around the CNS; mostly multipolar

Part 2 - Sack of Batteries

neurons use real electricity, they are like small batteries

A polarized neuron is at rest

  • high potassium inside, high sodium outside

  • the resting rate is -70mV

IONS are just electrically charged cells

ION CHANNELS are what allow sodium and potassium to pass through the membrane, they are what opens at action potential

An action potential happens when the positively charged sodium ions enter the neuron and create a charge that goes above -55mV.

This causes the voltage gated sodium channels to all open in a chain like reaction down the neuron into the axon, which creates depolarization with all of the positively charged sodium ions coming into the neuron

When the inside of the neuron hits +30mV, all of the sodium gates close and potassium starts getting pumped out, this is repolarization.

the sodium-potassium pump is actively moving 3 sodium out and 2 potassium in after this happens in order to re balance the neuron

Axons that are coated with MYELIN have higher conduction velocities

Part 3 - Synapses

The synapse is the meeting point between two neurons

  • Chemical synapses are much slower, more abundant, precise, and selective

  • An electrical synapse is a type of connection between two neurons where electrical signals pass directly from one cell to another through gap junctions. These junctions allow ions and small molecules to flow freely between cells, enabling very fast and synchronized communication

The presynaptic terminal is the end of an axon that sends the message. it connects an axon to a dendrite

  • Holds synaptic vesicles which are plasma membranes holding packets of neurotransmitters

  • the synaptic cleft is the tiny gap between the terminal and the receiving neuron

the synaptic terminal has voltage gated calcium channels instead of sodium

calcium stimulates the synaptic vesicles(plasma membranes which hold neurotransmitters inside)

the synaptic vesicles then move and fuse with the plasma membrane that walls the synaptic terminal and release the neurotransmitters inside of them

they then move across the synaptic cleft and bind to receptors on the dendrite of the other neuron

they can either be excitatory or inhibitory

  • An excitatory neurotransmitter polarizes the postsynaptic neuron

  • An inhibitory neurotransmitter hyperpolarizes the postsynaptic neuron

Part 4 - Central Nervous System

the brain is directly connected to the spinal cord, and the spinal cord governs basic muscle reflexes and patterns, while the brain is responsible for thinking, feeling, and remembering.

Cerebellum - Coordinates muscular activity

Brain Stem - Relays information between the body and the higher regions of the brain.

The three main regions of the brain stem regulate many of the key involuntary functions of the body

  • Midbrain - receives and processes sensory information to make u react without thinking

  • Pons

  • Medulla Oblongata

Diencephalon(Reptilian/Caveman brain)

  • Thalamus

  • Hypothalamus - regulates homeostasis, alertness, and reproductive activity

  • Epithalamus

  • Mamillary body

  • Limbic System - center for strong emotions, like fear

Telencephalon(Cerebrum) - made up of grey(outside) and white matter(inside)

  • Frontal lobe - governs muscle movement, motor skills, and cognitive functions that require conscious thinking

  • Occipital lobe - processes bright visual cues

  • Parietal lobe - processes sensations of touch, pain, and pressure

  • temporal lobe - helps sort out auditory information

    • The limbic system is also here

      • Amygdala - social and sexual behavior

      • Hippocampus - short term memory

DEVELOPMENT

Neural Tube

  • Prosencephalon

    • Telencephalon

    • Diencephalon

  • Mesencephalon

  • Rhombencephalon

    • Metencephalon

    • Myelencephalon

Part 5 - Peripheral Nervous system

the peripheral nervous system outs your brain in touch with your outside environment. It has different types of sensory nerve receptors.

  • thermoreceptors - temperature

  • photoreceptors - light

  • chemoreceptors - chemicals

  • mechanoreceptors - pressure, touch, vibration

  • nociceptors - PAIN

The MOTOR DIVISION is responsible for carrying signals from the CNS to the body

Reflex ARC

Innate/Intrinsic Reaction - a super fast motor response to a starting stimulus

Learned/Acquired reflexes - come from experience

Muscle and tendon spindles are what keep them from over stretching

Part 6 - Autonomic Nervous system intro

the autonomic nervous system regulates your organs, smooth and cardiac muscles, and glands… it does all of this automatically and is inconsistent

  • Sympathetic nervous system is the “lively” part of it and controls the fight or flight response… it is responsible for stress

    • Is located throughout the thoracic spine

    • ganglia is found in the spine, short

  • The parasympathetic nervous system is the “chill” part. Its what makes us feel at peace

    • is located at base of the brain(upper neck) and the tailbone.

    • ganglia is found way outside of the spine, very long

A Ganglia is a cluster of neuron synapses all located in the same place

both parts of the autonomic nervous system require at least two neurons in order to work, unlike the PNS being able to have just one long axon

The sympathetic nervous system is set up in such a way that even a small stress signal sent down one path could trigger a response in many effectors at once. Which is one reason why your reaction to a sudden, stressful event can feel so all-encompassing.

By the same token, the resting and digesting that’s overseen by the parasympathetic system doesn’t require urgent, all-hands-on deck communication. If you need to process a burrito or take a nap or maybe a trip to the bathroom, it can communicate with the organs involved, one on one.

Part 7 - Sympathetic nervous system(aka the stress system)

Our sympathetic nervous systems response to non immediate stresses is largely the same as the response to fighting for survival

The stress response involves two kinds of chemicals:

  • Neurotransmitters(what neurons use to communicate with one another)

  • Hormones - chemical messengers secreted by glands into the bloodstream that regulate vital functions(mood, thirst metabolism, homeostasis, etc.)

THE STRESS RESPONSE (for neurotransmitters)

Your brain sends action potentials down your spinal cord and preganglionic neuronal axons which flow all the way to their ganglia.

When the signals reach the synapses inside the ganglia, the nerve fibers then release a neurotransmitter -- called acetylcholine, aka ACh - a key neurotransmitter used for various functions

So, that acetylcholine crosses the synapse and, if there’s enough of it, it can stimulate action potentials in several neurons on the other end -- in the postganglionic fibers.

And at the end of that second, postganglionic neuron, the fiber releases a different neurotransmitter called norepinephrine which helps carry out the action

preganglionic - ACh

postganglionic - norepinephrine

A substance is a neurotransmitter or a hormone based off of where its at in your body.

Norepinephrine can help increase or decrease bloodflow to certain parts of the body at the same time depending on what’s most important at the moment

^^^weather something restricts or opens more depends on the receptor. norepinephrine receptors are in smooth muscle(organs or blood vessels)

  • alpha receptors cause it to contract - vasoconstriction

  • beta receptors cause it to relax - vasodilation

Part 8 - parasympathetic nervous system(the rest system)

in the parasympathetic nervous system, the postganglionic cell continues to release more ACh rather than norepinephrine

remember that the nerves of the parasympathetic are craniosacral - right under the brain and also in the tailbone. they run right from the brain almost all the way to their effectors, there are 12 of them… they all are sensory, motor, or both

  • 1. Olfactory nerve                                                                        S

  • 2. Optic nerve                                                                               S

  • 3. Oculomotor nerve - controls 4 of 6 eye muscles                       M

  • 4. Trochlear nerve - controls a single eye muscle(looking down)    M

  • 5. Trigeminal nerve - Largest, control face and jaw muscles            B

  • 6. Abducens - controls eye muscle looking side to side                    M

  • 7. Facial nerve - makes facial expressions possible                        B

  • 8. Auditory nerve                                                                              S

  • 9. Glossopharyngeal nerve - tongue                                                B

  • 10. Vagus nerve - heart and digestive tract                                        B

  • 11. Spinal accessory nerve - head and shoulder movement            M

  • 12. Hypoglossal - swallow and talk                                                    M