The science behind the munchies

According to a growing pool of research, there is evidence to suggest the munchies are brought on by getting high — to some degree. A 2014 study published in Nature Neuroscience and reported by Smithsonian Mag found certain senses like smell and taste became more acute in mice after THC was introduced to their system. The THC may be tricking your brain.

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Autonomic nervous system

Structure and Function of the Sympathetic and Parasympathetic nervous system

The main function of the autonomic nervous system (ANS) is to assist the body in maintaining a relatively constant internal environment. For example, a sudden increase in systemic blood pressure activates the baroreceptors (those are receptors that detect physical pressure) which in turn modify the activity of the ANS so that the blood pressure is restored to its previous level [1].

The ANS is often regarded as a part of the motor system and is responsible for involuntary action and its effector organs are smooth muscle, cardiac muscle and glands. Another system, the somatic (meaning around the body) nervous system, is responsible for voluntary action in which skeletal muscle is the effector.

The ANS can further be divided into 3 parts: sympathetic, parasympathetic and enteric nervous systems [1][2], with the enteric nervous system sometimes being considered a separate entity [2]. Both parasympathetic and sympathetic nervous systems coexist and work in opposition with each other, ultimately maintaining the correct balance; the activity of one being more active depending on the situation. In a normal resting human, the parasympathetic nervous system dominates, while in a tense and stressful situation, the sympathetic nervous system switches to become dominant.


Figure 1. Structure and function of the central nervous system

This article will be focused on sympathetic and parasympathetic activity from the perspective of:

  1. Anatomy
  2. Biochemical

The sympathetic division provides your “fight or flight” whereas the parasympathetic division helps you to “rest and digest”

Anatomy

Higher centers that control autonomic function include the pons, medulla oblongata and hypothalamus [3].

  1. The pons contains the micturition (urination) and respiratory center.
  2. The medulla oblongata contains the respiratory, cardiac, vomiting, vasomotor and vasodilator centres [4].
  3. The hypothalamus contains the highest concentration of autonomic centres [4]. It contains several centres that control autonomic activities, including heat loss, heat production and conservation, feeding and satiety, as well as fluid intake [4].


Figure 2. Locations of the autonomic control centres of the brain

All 3 structures receive input from certain sources by stimulation of nerve fibres resulting from chemical changes in blood composition like blood pH, blood glucose level, blood osmolarity and volume [4]. Notably, the hypothalamus receives input from cerebral cortex and the limbic system, a system that helps control emotional behaviour [3].

Autonomic promoter neurons are neurons that are found in the brain stem, hypothalamus or even cerebral hemispheres that project to preganglionic neurons (discussed below), where they form synapses with these neurons (5). Hence, input from the higher centres can be relayed to the motor neurons (preganglionic and then postganglionic neurons) which subsequently innervate different body tissues. Changes in the input from these centres could result in responses in those tissues.

The primary functional unit of the sympathetic and parasympathetic nervous system consists of a 2 neuron motor pathway (Figure 3), containing a preganglionic and postganglionic neurons, arranged in series.(2) The two synapse in peripheral ganglion. This clearly distinguishes autonomic motor nervous system and somatic nervous system. The somatic nervous system project from the CNS directly to innervated tissue without any intervening ganglia.(6)


Figure 3. Diagram showing the primary functional unit of the ANS

Sympathetic nervous system

Sympathetic preganglionic neurons mainly are concentrated in the lateral horn in the thoracic (T1-12) and upper lumbar (L1 &2) segments of the spinal cord (Figure 4).

The preganglionic axons leave the spinal cord in 3 ways:
  • Through the paravertebral ganglion
    • The preganglionic axon may synapse with postganglionic neurons in this ganglion or some axon may travel rostrally or caudally within the sympathetic trunk before forming synapse with a postganglionic neurons in a different paravertebral ganglion.
  • Through the prevertebral ganglion
    • Some preganglionic axons pass the paravertebral ganglion (no synapse occur) and form synapse with postganglionic neurons in prevertebral ganglion, also known as collateral ganglion.
  • Directly to the organs without any synapse
    • Some preganglionic axons pass through the sympathetic trunk (no synapse) and end directly on cells of the adrenal medulla, which are equivalent to postganglionic cell.

Parasympathetic nervous system

The parasympathetic preganglionic neurons are located in several cranial nerve nuclei in the brain stem and some are found in the S3 and S4 segments of the sacral spinal cord (Figure 4). The parasympathetic postganglionic neurons are located in cranial ganglia, including the ciliary ganglion, the pterygopalatine, submandibular ganglia, and the otic ganglion. Other ganglia are present near or in the walls of visceral organs. Similarly, the preganglionic neurons form synapse with the postganglionic neurons in the ganglia.


Figure 4. Anatomy of the ANS and how its nuerons innervate tissues

After knowing how nerves connect from the CNS to PNS and to different organs, we will now consider some of the neurotransmitters that are being released at different nerve terminals. It is the binding of these neurotransmitters to the receptors on the effectors that leads to biochemical and physiological changes. Some of the neurotransmitters in use are:

  • For the synapse between pre and postganglionic neurons mentioned above, the neurotransmitter that is released by the preganglionic axon terminal, is acetylcholine. The corresponding receptors are found on the postsynaptic membrane of postganglionic nerves and are nicotinic receptors.
  • Parasympathetic postganglionic nerve terminals also release acetylcholine.
  • Sympathetic postganglionic nerve terminals release mostly noradrenaline
  • The adrenal medulla receives direct stimulation from sympathetic preganglionic innervation, releases mainly adrenaline (80%) and some noradrenaline into the blood stream. In this case, both adrenaline and noradrenaline act as hormones as they are transported via blood circulating system to target organs instead of neuronal pathway.
  • Strangely, for the sympathetic postganglionic nerves that innervate the sweat glands, the nerves release acetylcholine (normally only by parasympathetic postganglionic nerve) instead.

1. H.P.Rang, J.M.Ritter, R.J.Flower GH. RANG & DALE’S Pharmacology. In: 8th ed. ELSEVIER CHURCHILL LIVINGSTONE; 2016. p. 145.

2. Bruce M. Koeppen BAS. BERNE & LEVY PHYSIOLOGY. In: 6th ed. MOSBY ELSEVIER; 2010. p. 218.

3. Cholinergic transmission [Internet]. 2015. Available from: http://www.dartmouth.edu/~rpsmith/Cholinergic_Transmission.html

4. Bruce M. Koeppen BAS. BERNE & LEVY PHYSIOLOGY. In: 6th ed. MOSBY ELSEVIER; 2016. p. 44.

list of personality types and stuff

MBTI
http://www.16personalities.com/free-personality-test

Love Language
http://www.5lovelanguages.com/profile/

Hogwarts House
http://www.thealmightyguru.com/Reviews/HarryPotter/Docs/Quiz-House.html

Divergent Fractions 
http://divergentthemovie.com/aptitudetest

Enneagram
http://similarminds.com/cgi-bin/similarminds.pl

Alignment 
http://www.wizards.com/default.asp?x=dnd%2Fdnd%2F20001222b

5 Temperaments
http://personality-testing.info/tests/O4TS/

Big 5 Sloan 
http://similarminds.com/bigfive.html

Zodiac Sign (are you most like?)
http://www.zimbio.com/quiz/uW1gJfWu9ED/Zodiac+Sign

Right Vs. Left Brained
http://similarminds.com/brain.html

Hunger Games Districts
http://www.zimbio.com/quiz/2xNP21CNXf2/Hunger+Games+District+Live

Dark Side Vs. Light Side
http://www.buzzfeed.com/gregpgleason/are-you-more-the-light-or-the-dark-side-of-the-for-1ldcq

Element Bending 
http://www.buzzfeed.com/awesomer/which-element-would-you-bend#.bqow9Z6Y8D

Percy Jackson Cabin 
https://www.boombox.com/c/quiz/116605/d03d4b6c-d85f-4c0e-a1c3-c9155e973ce5

Superhero Team
http://moviepilot.com/quizzes/3484362

2

Most animals have smooth brains. The brains of humans (and a handful of animals we consider pretty intelligent – dolphins, chimps, elephants, pigs) start out smooth in the early days of gestation and get more and more wrinkled through infancy.

A wrinkled brain makes sense - folding means you can have a really big cortex but the different parts of the brain won’t be as far apart. But how do brains become wrinkled? Is it programmed somehow - does some genetic code determine the pattern of folds?

A new study from Harvard says no - its just simple physics. They created a 3D model of a smooth fetal brain and coated it with an elastomer gel “cortex.” When they immersed this brain in a special solution, the gel swelled, mimicking brain growth.

Lo and behold, the brain began to buckle, creating folds similar to size, shape and location of a real brain.

Image credit: Mahadevan Lab/Harvard SEAS

Since I get asked a lot about where to learn more about the human brain and behaviour, I’ve made a masterpost of books, websites, videos and online courses to introduce yourself to that piece of matter that sits between your ears.

Books

  • The Brain Book  by Rita Carter
  • The Pyschology Book (a good starter book)  by DK
  • Thinking, Fast and Slow  by Daniel Kahneman
  • Quiet: The Power of Introverts in a World That Can’t Stop Talking  by Susan Cain
  • The Man Who Mistook His Wife for a Hat  by Oliver Sacks
  • The Brain: The Story of You  by David Eagleman
  • The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science  by Norman Doidge
  • This Is Your Brain on Music  by Daniel Levitin
  • The Autistic Brain by Richard Panek and Temple Grandin (highly reccomended)
  • Sapiens: A Brief History of Humankind  by Yuval Noah Harari (not really brain-related, but it is single handedly the best book I have ever read)

Websites

Videos & Youtube Channels

Online Courses

2

New brain implant could move paralyzed limbs with just a thought

It’s called a stent-electrode recording array, and it has been used for the last few years for neurological conditions, according to a paper by University of Melbourne researchers. But a 39-person team from 16 of the university’s departments think it could be used to make people walk again. But wait it gets even better.

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