Neurons

Neurons The human body is made up of trillions of cells. Cells of the nervous system, called nerve cells or neurons. The human brain has approximately 100 billion neurons, more in the spinal cord, peripheral nervous system and sensory organs. These system’s basic building blocks, are specialized to carry "messages" through an electrochemical process. * Nafly Hussain *

Neurons come in many different shapes and sizes, can be quite large such as corticospinal neurons (from motor cortex to spinal cord) or primary afferent neurons (neurons that extend from the skin into the spinal cord and up to the brain stem), can be several feet long * Nafly Hussain *

Neurons are similar to other cells in the body because,, Neurons are surrounded by a cell membrane. Neurons have a nucleus that contains genes. Neurons contain cytoplasm, mitochondria and other organelles. Neurons carry out basic cellular processes such as protein synthesis and energy production. * Nafly Hussain *

Neurons are different from other cells in the body because,, Neurons have specialized extensions called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body. Neurons communicate with each other through an electrochemical process. Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters). * Nafly Hussain *

STRUCTURE OF A NEURON * Nafly Hussain *

Dendrites of another neuron The Neuron Node of Ranvier Cell Body Dendrites Axon Myelin Sheath Synaptic knobs Axon of another neuron Dendrites of another neuron * Nafly Hussain *

Synapse- space between the axon of one neuron and the dendrite of another cell (they do not touch) * Nafly Hussain *

Dendrites are short branching processes from the cell body Axon is a projection from the cell body and it is few millimeters to one meter in length & covered with the myelin sheath Myelin have an insulating sheath Supports, insulates & nourishes the axon and helps maintain chemical balance Nodes of Ranvier allow passage of the electrical signal through ion channels which helps the transmission very fast. The cell body is responsible for the nutrition and maintenance of the entire cell. * Nafly Hussain *

Inside of a neuron! * Nafly Hussain *

FUNCTION OF A NEURON * Nafly Hussain *

How Neurons Carry the Message Only neurons are involved in transmission of electrical signals. Within a nerve cell, message is an electrical signal = action potential Cascading membrane depolarization creates the movement of the action potential as a nerve impulse rapid, all or none impulses in myelinated neurons, gaps at regular intervals allow regeneration of the action potential Between nerve cells the message is carried chemically * Nafly Hussain *

Direction of neural impulse DENDRITES -----> CELL BODY (with nucleus) -------> AXON * Nafly Hussain *

The direction of a neural impulse is always from dendrites to cell body to axon. All of the life functions of the neuron take place in the cell body. Here nutrients are assimilated, broken down and used to maintain the existence of the entire cell. Part of the material in the cell body makes up the nucleus, which directs the life functions of the neuron. The dendrites are sensitive to external stimuli & possess chemically regulated ion gates which respond to stimulation by neurotransmitters. Then transfer it as a neural impulse through the cell body to the axon The axon has voltage regulated ion gates and therefore is responsible for carrying an impulse to another neuron or effectors. * Nafly Hussain *

At the end of the axon, the axon terminus, is the secretory region where the neurotransmitters are released into the synapse. The function of the axon is to propagate the neural impulse along its entire length. The destination may be a muscle, a gland, or, more commonly, the dendrites of another neuron. The neural impulses sometimes travel as fast as 390 feet per second and are seldom as slow as 10 feet per second as they travel to the hair like end of the axon. Neurons are the oldest and longest cells in the body. You have many of the same neurons for your whole life. Although other cells die and are replaced, many neurons are never replaced when they die. * Nafly Hussain *

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The End * Nafly Hussain *