Neuron Action Potential

Neurons are made of dendrites, an axon, and a soma, not mentioning the added compenets of myelin and such. Neurotransmitters bind to neurons via dendrites and act as a chemical signal. This bond opens ion channels, allowing charged ions in and out of the cell. This makes the chemical signal into an electric one. If a neuron is recieving enough neurotransmitters, it generates an action potential, which moves down the axon as a signal and releases neurotransmitters. The charge of a cell is based on the difference in charges between ions inside and outside of the cell. Inside the cell is a negative enviornment, with potassium and negatively charged ions within. The outside, on the other hand, has sodium, chloride, and calcium, making it more positive than the inside of the cell. This charge is the resting membrane potential. The process of sending a signal is as follows: Neurotransmitters bind to receptors on dendrites, opening ligon-gated ion channels and allowing certain ions in. Ligon = Neurotransmitters. Sodium then flows in and the cell is depolarized, meaning it is made less negative due to the shift in ions. There are many kinds of channels for different ions to flow in and out. The net influx of positive charge is the excitatory post-synaptic potential, while the net influx of negative charge is the inhibitory post-synaptic potential. If there are enough bonds from the neurotransmitters or depolarization, the cell reaches its threshold potential. This triggers all voltage-gated sodium channels to open up. This creates action potential, which is the neuron firing. The cell then becomes positively charged. The sodium voltage gates have an inactivation gate, which stops inflow by blocking the channel and pushing away positive ions. Potassium voltage gated channels open slower than sodium channels, and only open once those are inactivated. The potassium gated channels release potassium ions and stay open longer, repolarizing the cell. There is a dip in the charge that goes below the typical base charge, meaning the cell is hyperpolarized. This is the relative refractory period, and in this state, K+ channels stay open while Na+ gates are closed (can be opened with stronger stimulus). This only occurs immediately after firing and the cell eventually closes its K+ channels and keeps the cell balanced and ready for the next stimulus.

Cerebral Hemispheres

Surrounding the cerebral hemispheres is the cerebral cortex. It's composed of six layers of cell bodies that make up gray matter. From this gray matter, myelinated axonal processes extend into the cerebral hemispheres, making up white matter. In the brain, gray matter surrounds white matter. In the spinal cord, it is the opposite. The surface of the cerebral hemispheres is made of a series of elevations called Gyri, and a series of folds called Sulci. These increase the surface area of the brain. There are four lobes per hemisphere: frontal, parietal, occipital, and temporal. The parietal and frontal lobes are seperated by the central sulcus. The parietal and occipital lobes are seperated by the parieto-occipital sulcus. The temporal lobe is seperated from the frontal lobe by the lateral sulcus. Within the cerebral hemispheres is the ventricular system. It's derived from the inner lumen of the developing nueral tube, and adapts to the growing shape of the brain. It starts inferior and lateral to the corpis callosum.

The Heart (basic anatomy)

The heart consists of four chambers -- the right and left ventricles and the right and left atria. From the outside of the heart, the auricles are visible, most notably on the right atrium when looking from an anterior view. The auricles lay atop the atria. Below the atria are the ventricles . These are the lower chambers of the heart and contract after the atria (I will get into the hearts nervous anatomy in another post). Dividing the two halves of the heart (right and left) is the septum. Blood enters the right atrium through the superior and inferior vena cavas. It moves out of the right atrium through the tricuspid valve and into the right ventricle. It then moves out of the right ventricle and into the pulmonary artery through the pulmonary valve. This is how the blood is oxygenated, as the pulmonary artery takes the blood through the lungs and returns it to the heart via the pulmonary veins that empty into the left atrium. You can guess what happens next: the now-oxygenated blood moves into the left ventricle via the mitral valve. Finally, the blood leaves the ventricle and goes through the aortic valve into the aorta, and is then spread throughout the body.

The Knee