1 Nerve Cells

2 Nerve cells Around 100 billion neurons in the brain initially –Adult stage 15 billion Means of communication in the nervous system Excitatory and inhibitory in nature

3 Nerve cells Neurons –Sensorimotor activities –Higher mental functions Neuroglia cells –Support and protect neurons

4 Neurons Three parts 1.Soma: body with nucleus 2.Dendrite: receives inputs 3.Axon: sends information –Signal is transmitted electrochemically down shaft of axon. –Connects to target cells (neurons, muscles, glands) at synapse. –Can either inhibit or excite target cells. –Can be up to x10,000 length of soma

5 Soma Protoplasm –Nucleus –Cytoplasm Protein filled liquid Microscopic Organelles – neurofibril – mitochondria – powerhouse of the cell – ribosomes – lysosomes – Nissl bodies – Golgi com

6 Metabolic activity Firing requires oxygen and glucose –Constant supply is required (via capillaries of vascular system). –If supply is disrupted: Meaningful neural activity will cease immediately Neurons will die within hours if supply is not restored

7 Intracellular transport Proteins generated and degraded in the soma. –Proteins must by moved to axons/synapse Proteins transported via Microtubules in Axon –Anterograde Transport – toward synapse (new proteins, transported by protein kinesin) –Retrograde Transport – toward cell body (recycling, transported by protein dynein) –Suicide Transport (apoptosis, form of retrograde transport) –Microtubules act as tracks for moving proteins

8 Nucleus Control Center Contains DNA Contains Nucleolus –Engaged in Protein Synthesis –Contains RNA - Code for Enzyme for Synthesis of Specific Enzymes Needed

9 Nuclear structures and functions Neurofibrils: Channels for Communication in Cell. These filaments repulse each other, so their development enlarges the diameter of the axon and dendrite Mitochondria: Contain Enzymes for Metabolism: creates ATP, used for chemical energy. Free Ribosomes: Synthesize Proteins Lysosomes: Intracellular Digestion (break down waste) Nissl Bodies: Amino Acids to Proteins Golgi Complex: Protein Secretion and its Transportation (post office of the cell)

10 Neural communication Dendrites: –Afferent: influenced by other neurons/receptors. –Branching and short Axons –Efferent: influence other neurons/receptors. –Dependent on electrical signal at axon hillock –End in axon terminals with synaptic knobs that release neurotransmitters.

11 Myelin Sheath –Multilayer Lipid (fatty) Material –Insulates Nerve Fiber Analogy: plastic insulation on wire in house –Regulation Speed: Signals can jump between nodes Efficiency: Escape of Electrical Energy –Segmented: nodes of Ranvier with internodes

12 Saltatory conduction Normally, chemical signal is relatively slow down an axon. However, in mylinated segments the signal can jump between nodes. –Facilitates Speed of Fiber (120 msec)

13 Glial cells for myelin In CNS: – Oligodendroglia: single cell can support Myelin sheaths for up to 50 axons –Multiple Sclerosis In PNS: –Schwann cells: each covers only about 1mm, so many cells per axon. –Can Regenerate Injury to Motor Pathways Amputation

14 Synapse Connection Between Neurons Three Parts –Knob (Axon; presynaptic) Contain Vesicles Filled with Neurotransmitters Released when Necessary Chemically Stimulate Receiving Nerve Cell Body –Synaptic Cleft: gap between one neuron and the next. 2/100,000mm Wide –Receptive Sites (Receiving Cell Axon or Dendrite; postsynaptic)

15 Action Potentials When a neuron fires, it releases neurotransmitters from terminals into synaptic cleft. Chemical in Neurotransmitter Stimulates or inhibits Postsynaptic Cell (Dendrite, Axon or Cell Body) If the postsynaptic cell receives enough stimulation, this neuron will fire. –Firing is an all-or-none response –After firing, neuron must wait a while before it can fire again.

16 Types of neuron Classified By Number of Processes Multipolar – many dendrites, one axon (brain) –Bipolar – retina, smell, facial nerve –Unipolar – dorsal spine

17 Axonal Length Types Golgi Type I –Axons range from feet to inches. –E.G. Motor cortex Golgi Type II –Axons are very short –E.G. interneurons