Neurons are one of two types of nerve cells. Depending on their functions, there are afferent, efferent, and interneurons. Nerves are structures from neurons and neuroglia (“helper” cells) transmitting signals throughout the body. Myelin is a substance forming an electrically insulating layer. It surrounds axons of neurons. Grey matter is responsible for processing information. It consists of unmyelinated neural cells. White matter consists of myelinated cells and transfer signals between the brain and spinal cord. CNS consists of the brain and spinal cord. PNS includes all nerve structures outside the brain and spinal cord. Somatic NS includes voluntary efferent neurons while autonomic NS consists of involuntary efferent neurons.
Meninges occur in the following order: dura matter, arachnoid matter, and pia matter. They protect CNS from mechanical damage.

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Reflex arc consists of a receptor, sensory neuron, interneuron, motor neuron, and effector.

The eye consists of gel substance surrounded by three tissue layers: fibrous (protection), vascular (blood circulation), and nervous (detect and transmit visual information) tunics. Two cavities are divided by lens: the anterior chamber and vitreous chamber.

Three regions of the ear are an outer ear, middle ear, and inner ear. Through the external auditory canal, sound reaches eardrum and transfers to vibration to reach the inner ear which converts it into neuron signals. The cochlea is a spiral-shaped cavity containing organ of Corti. Vestibule and semicircular canals are responsible for equilibrium detection. Canals detect dynamic equilibrium while vestibule detects movement in planes (forwards, backward, right, left).

Systemic circulation transfers oxygenated blood to the tissues of the body from the left side of the heart. Pulmonary circulation transfers deoxygenated blood to the lungs. Then it receives oxygen and returns to the left side of the heart.

The heart consists of four chambers: ventricles and atria. They are responsible for oxygenation of blood. Coronary arteries deliver oxygenated blood to the myocardium. Four valves regulate blood flow between atria and ventricles (mitral valves) and out of the ventricles (aortic valves). Three layers constitute heart wall: epicardium, myocardium, and endocardium.

Cardiac muscle cells and conducting fibers constitute the conducting system of the heart. They initiate impulses and transfer them to all regions of the heart. Electrocardiogram measures these signals. P-wave – upper chambers, QRS complex – lower chambers, ST-segment – the contraction of a ventricle with no electricity flow. T-wave – lower chambers prepare for the next contraction.

Types of blood pressure: systolic (heart is pumping) and diastolic (rest stage between beats). Blood pressure is measured in millimeters of mercury; the systolic number is followed by the diastolic number.

Arteries supply blood directly from the heart, capillaries distribute blood between body cells, veins return blood from the capillaries to the heart.

Vasodilation is blood vessels widening and blood flow increasing caused by parasympathetic nerve impulses. Vasoconstriction is narrowing blood vessels restricting blood flow. It is caused by sympathetic nerve impulses.

    References
  • Inner body (Anatomy explorer). 2017, Howtomedia.Inc, http://www.innerbody.com/