The stomach , small intestine , and large intestine (colon) comprise the gastrointestinal (GI) tract. They are primarily responsible for the absorption of water and nutrients. Anatomically speaking, each of the GI organs has a different part to play.

The stomach is a muscular organ that is primarily responsible for the digestion of food and to break it down to smaller particles. It produces hydrochloric acid to digest protein.

Here is that part of the GI tract in which food stays longer due to its function of breaking down food. However, it also has the capacity to absorb nutrients.

The small intestine on the other hand is a hollow muscular organ that is primarily responsible for the absorption of nutrients. However, like any GI organ, it shares some functions with the stomach especially in the digestion of food.

For example, the first part of the small intestine called the duodenum has the end of the bile duct which secretes pancreatic juices and bile in order to further break down nutrients.

The absorption is facilitated because of the villi vascularity where nutrients are absorbed to the blood stream.

Finally, the large intestine is primary responsible for absorption of water and resorption of nutrients in the lower part of the GI tract. It is divided into three parts: ascending, transverse, and descending.

Further, there are connecting parts which includes the cecum (connecting the small intestine and the colon) and the sigmoid colon connecting to the rectum . Any residuals will be expelled.

Ligaments join two bones and are responsible for the stability of joints. If a ligament has no elasticity and is not stretchy, joints cannot be moved.

As shown in the image, tendons attach muscles to bones. Unlike ligaments, tendons are not flexible, and if stretched too far, will stiffen.

Ligaments are meant to help you slowly and progressively increase flexibility, and moving too fast or suddenly will cause your ligament to tear. Ligaments, therefore, by being only slightly flexible, offer protection by limiting movement.

Excessive stretching, as mentioned above, can damage ligaments and in the process decrease the stability of joints.

[Referred, see more - https://nianow.com/story/2012/02/awareness-of-ligaments-and-tendons-sensing-stability

For common ligament injuries, see https://www.visiblebody.com/blog/common-ligament-injuries-and-disorders ]

Sensory receptors of hearing are hair cells, present on basilar membrane of cochlea. Sensory organ present on basilar membrane for hearing is formed by hair cells and the tissue is called Organ of Corti.

Cochlea is a coiled structure. It is a bony tube on the outside, and a membranar tube is there on the inside. There is perilymph inside bony labyrinth and endolymph within membranar labyrinth.

Perilymphatic space within bony labyrinth is divided in two parallel canals: scala vestibuli and scala tympani, due to presence of endolymphatic canal scala media (also called cochlear duct).

SV and ST are connected at the tip of cochlear coil by a connecting passage named helicotrema. SV and SM are separated by Reissner's membrane while ST and SM are separated by Basilar membrane. Organ of Corti is located on basilar membrane and it is immersed in endolymph of scala media.

Sound waves are amplified before it reach oval window. The vibrations are transferred from SV to ST via helicotrema. As the basilar membrane vibrates, sensory hair cells of organ of Corti get stimulated. Nerve impulse generated at the base of organ of Corti will reach brain via auditory nerve.

(https://d2gne97vdumgn3.cloudfront.net/api/file/3Uf4OxpQS7afCoD6ZJZi)

The brain (and spinal cord) is surrounded by a protective sheath called the meninges which is made up of three layers:

1. The outermost dura mater is a thick durable fibro-elastic membrane that contains large blood vessels that subdivide into capillaries in the pia mater.
2. The middle arachnoid mater is called that because it resembles a spider's web in appearance. It is composed of fibrous tissue and cushions the brain (and spinal cord).
3. The innermost pia mater is a thin delicate membrane that adheres to the surface of the brain (and spinal cord) and provides nourishment to the brain through the blood capillaries that infuse it.

Anatomy (from the Greek ana [up] and tomia [cut]) is that branch of science that studies the structure of living beings - usually by dissection and separation of its parts.

The anatomy of the human heart reveals four chambers: two atria (singular: atrium) and two ventricles. The atria are the smaller, upper chambers while the ventricles are the larger, lower chambers.

The right atrium is connected to the right ventricle by an opening controlled by a valve known as the tricuspid valve. The left atrium is connected to the left ventricle by an opening controlled by the mitral valve. The valves serve to prevent the reverse flow of blood.

The right atrium receives blood from two major veins - the superior vena cava and the inferior vena cava which drain blood from the upper and lower parts of the body respectively. This blood is de-oxygenated blood. The right atrium pumps this blood through the tricuspid valve into the right ventricle from where it is pumped via the pulmonary artery to the lungs for oxygenation. The pulmonary valve between the right ventricle and the pulmonary artery keeps the blood flow unidirectional.

Oxygenated blood is received from the lungs via the pulmonary veins into the left atrium which then pumps it through the mitral valve into the left ventricle. The left ventricle pumps this blood through the aortic valve into the aorta which transports it across the body.

According to the American Academy of Sleep Medicine there is a wide range of potential causes, including anxiety, caffeine, stress and strenuous activities in the evening. However, most hypnic jerks occur essentially at random in healthy people.

Another hypothesis is evolutionary, stretching back to our primate ancestors. A study at the University of Colorado has suggested that a hypnic jerk could be "an archaic reflex to the brain's misinterpretation of muscle relaxation with the onset of sleep as a signal that a sleeping primate is falling out of a tree. The reflex may also have had selective value by having the sleeper readjust or review his or her sleeping position in a nest or on a branch in order to assure that a fall did not occur."

During an epilepsy and intensive care study, the lack of a preceding spike discharge measured on an epilepsy monitoring unit, along with the presence only at sleep onset, helped differentiate hypnic jerks from epileptic myoclonus.

According to a study on sleep disturbances in the Journal of Neural Transmission, a hypnic jerk occurs during the non-rapid eye movement sleep cycle and is an "abrupt muscle action flexing movement, generalized or partial and asymmetric, which may cause arousal, with an illusion of falling". Hypnic jerks are more frequent in childhood with 4–7 per hour at the age ranging from 8 to 12 years old, and it decreases toward 1–2 per hour at 65 to 80 years old.

Sources:
Wikipedia
Medical College of Wisconsin, Sleep: A Dynamic Activity
Jump up ^ National Institute of Neurological Disorders and Stroke, Brain Basics: Understanding Sleep
Jump up ^ Why You Sometimes Feel Like You're Falling And Jerk Awake When Trying To Fall Asleep by Lauren F Friedman, Business Insider, May 21, 2014
Jump up ^ Basics of Sleep Behavior: NREM and REM Sleep
Jump up ^ A Case of the Jerks by Kaitlyn Syring, University Daily Kansan, February 28, 2008
Jump up ^ "Why You Sometimes Feel Like You're Falling And Jerk Awake When Trying To Fall Asleep". Retrieved 2016-07-17.
Jump up ^ Fisch, Bruce J. Epilepsy and Intensive Care Monitoring: Principles and Practice. New York: Demos Medical, 2010.
^ Jump up to: a b Askenasy, J. J. M. (2003). "Sleep Disturbances in Parkinsonism" (PDF). Journal of Neural Transmission. Springer-Verlag. 110: 125–50. doi:10.1007/s007020300001.