Foundations in human physiology structure function and permeability of cells

One or more cells constitute all forms of life. Cells can only develop from pre-existent cells. The smallest form of life is cell. The human cell consists of an outer plasma membrane which encloses the minute organelles dispersed within the cytoplasm. These organelles include endoplasmic reticulum, Golgi apparatus, mitochondria, ribosome, chromosomes, nucleus, lysosome, vacuoles and centrioles. A typical human cell (Carone, 2001) The outer cell membrane is made up of lipid molecules and provides the passage for interaction of cells with each other. Different kinds of human cells have distinct structures that aid in the functioning of their particular activity, such as the axons of nerve and brain cells which transmit signals out across distances to other cells via neurotransmitters. The neurons are specially adapted to perform this function as the axons are as long as one meter in length and the nerve impulse is transmitted from one neuron to another. The various functions performed by human cells include enzyme production, movement, transmission of electrical impulses and demolishing invaders. Among the various cells constituting the human body five main are: epithelial, nerve or neuron, connective, adipose and muscle cells. The four main selected to be explained in the given text include epithelial cells, neuron, connective and adipose cells (Marieb Hoehn, 2010). Nerve Cells Nerve cells or neurons are specialized cell often referred as the structural and functional unit of nervous system. A characteristic neuron consists of a cell body known as soma, an axon and dendrites. The thin structures arising from the cell body are dendrites that frequently extend for hundred micrometres and forming multiple branches thus forming a complex called dendritic tree. An axon on the other hand is a peculiar cellular extension that originates from the axon hillock and travels as far as one meter (Chudler, 2012). A typical Neuron (Chudler, 2012) Synapse is a specialized connection of these neurons with other cells that facilitates chemical signal. Neurons communicate by electrical and chemical (via neurotransmitters like GABA, dopamine and glutamate) synapses in a process referred as synaptic transmission. Action potential is the basic process that activates synaptic transmission, a disseminating electrical signal that is produced by tapping the electrically impulsive membrane (the myelin sheath) that encloses the axon of the neuron. This is also known as a wave of depolarization. Neurons are the central part of the nervous system consisting of the spinal cord, the brain and peripheral ganglia. A great number of these specialized neurons exist and are classified on the basis of their function as sensory, motor and inter-neurons. The inter-neurons connect other neurons within the spinal cord or brain while the motor neurons transmit the response generated from brain and spinal cord to the organs. Sensory neurons respond to light, sound, touch, taste and legion other stimuli impacting the epithelial cells of the sensory organs (Levitan Kaczmarek, 2001). Dorsal root ganglion The sensory neurons cell bodies are settled outside the spinal cord and brain in ganglia or in the sensory organs. Ganglia situated along specific cranial and spinal nerves accommodate the sensory neurons

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