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BIO 132 Neurophysiology Lecture 2 Neurons Lecture Goals: Understanding the basic function of the nervous system. Understanding the parts of a neuron. Neuron – A specialized cell of the body that can communicate information quickly by using ionic currents and chemical signals called neurotransmitters. Nerve - Many neurons that are bundled together and covered by a connective tissue sheath. Nervous System – The entire network of interconnecting neurons. Overall function of the nervous system: To control motor output of the body based on sensory information it detects from both the internal and external environments of the body. There are ~100 billion neurons in the brain. (Current population is less than 7 billion people.) Each neuron can make one to thousands of connections with other neurons. Glial cells are support cells of the nervous system There are ~10 times as many glial cells as there are neurons. Used to nourish, insulate, direct growth of neurons. Neuron Morphology Parts of a typical neuron: Dendrites Cell body Axon Axon terminal Cell Body (soma) Contains most of the cellular machinery of the neuron (nucleus, ER, mitochondria, golgi complex, etc). Is where most the synthesis of new cellular products occurs. Cell body Dendrites Means “tree” in Latin. Main site where input is received from other neurons. Dendrites Axon Long projection from cell body that carries an ionic signal, called an action potential, to other neurons. Can be very short or very long (up to 6 feet in humans). Can send off many branches (collaterals). Axon Axon Terminal Is at the end of each axon. Contains vesicles filled with neurotransmitter. Forms a connection with another neuron, called a synapse. Axon terminal Classifying Neurons There are several conventions for classifying neurons: By neurites (projections from the cell body). By dendrite shape. By connections. By neurotransmitter released Classification By Neurites Unipolar neuron - A single neurite (projection from cell body: Bipolar – Two neurites (both part of the axon) Multipolar – Many neurites (usually one axon and many denrites) Classification By Connections Primary sensory – dendrites detect external stimuli. Stimuli Motor - makes a direct connection with skeletal muscle. Interneuron - only makes connections with other neurons. (Most numerous type) Classification By Neurotransmitter Based on the type of neurotransmitter released. Examples: Cholinergic Acetylcholine (ACh) Noradrenergic Norepinephrine (NE) GABAergic GABA Glutamatergic Glutamate (Glu) Dopaminergic Dopamine (DA) Classifying Glia Astrocytes Most numerous Fill the space between neurons Envelope synapses to limit the spread of neurotransmitters Regulate chemical content of extracellular fluid Remove neurotransmitters from synapse Myelinating glia – insulate axons from ion leakage Oligodentrites Found in Central NS and spinal cord Can wrap around several axons Schwann cells Found in peripheral NS Wrap around a single axon