Presentation on theme: "Chapter 5 Nerve Cells Chris Rorden University of South Carolina"— Presentation transcript:
1Chapter 5 Nerve Cells Chris Rorden University of South Carolina Norman J. Arnold School of Public HealthDepartment of Communication Sciences and Disorders
2Around 100 billion neurons in the brain initially Nerve cellsAround 100 billion neurons in the brain initiallyAdult stage 15 billionMeans of communication in the nervous systemExcitatory and inhibitory in nature
4Neurons Three parts Soma: body with nucleus Dendrite: receives inputs Axon: sends informationSignal 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
5Soma Protoplasm Nucleus - DNA Cytoplasm Protein filled liquid Microscopic Organellesneurofibrilmitochondria – powerhouse of the celllysosomes – digest worn out organellesRibosomes – Create proteinsNissl bodiesGolgi complex – Package ProteinsEndoplasmic reticulum - system of tubes for transport of materials within cytoplasm
6Firing requires oxygen and glucose Metabolic activityFiring requires oxygen and glucoseConstant supply is required (via capillaries of vascular system).If supply is disrupted:Meaningful neural activity will cease immediatelyNeurons will die within hours if supply is not restored
7Intracellular transport Proteins generated and degraded in the soma.Proteins must be moved to axons/synapseProteins transported via Microtubules in AxonAnterograde 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
8Nucleus Control Center Contains DNA Contains Nucleolus Engaged in Protein SynthesisContains RNA - Code for Enzyme for Synthesis of Specific Enzymes Needed
9Nuclear structures and functions Neurofibrils: Channels for Communication in Cell. These filaments repel each other, so their development enlarges the diameter of the axon and dendriteMitochondria: Contain Enzymes for Metabolism: creates ATP, used for chemical energy.Free Ribosomes: Synthesize ProteinsLysosomes: Intracellular Digestion (break down waste)Nissl Bodies: Amino Acids to ProteinsGolgi Complex: Protein Secretion and its Transportation (post office of the cell)
10Neural communication Dendrites: Axons Afferent: influenced by other neurons/receptors.Branching and shortAxonsEfferent: influence other neurons/receptors.Dependent on electrical signal at axon hillockEnd in axon terminals with synaptic knobs that release neurotransmitters.
11Myelin Sheath Myelin Sheath Multilayer Lipid (fatty) Material Insulates Nerve FiberAnalogy: plastic insulation on wire in houseRegulationSpeed: Signals can jump between nodesEfficiency: Escape of Electrical EnergySegmented: nodes of Ranvier with internodes
12Normally, chemical signal is relatively slow down an axon. Saltatory conductionNormally, chemical signal is relatively slow down an axon.However, in myelinated segments the signal can jump between nodes.Facilitates Speed of Fiber (120 msec/m)
13Glial cells for myelin In CNS: In PNS: Oligodendroglia: single cell can support Myelin sheaths for up to 50 axonsMultiple SclerosisIn PNS:Schwann cells: each covers only about 1mm, so many cells per axon.Can RegenerateInjury to Motor PathwaysAmputation
14Synapse Connection Between Neurons Three Parts Knob (Axon; presynaptic)Contain VesiclesFilled with Neurotransmitters Released when NecessaryChemically Stimulate Receiving Nerve Cell BodySynaptic Cleft: gap between one neuron and the next.2/100,000mm WideReceptive Sites (Receiving Cell Axon or Dendrite; postsynaptic)Prozac – a selective serotonin (5HT) reuptake inhibitorInterferes with 5HT presynaptic reuptake pumpIncreases concentration of 5HT in synaptic cleft
15Action PotentialsWhen 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 responseAfter firing, neuron must wait a while before it can fire again.
16Classified By Number of Processes Types of neuronClassified By Number of ProcessesMultipolar – many dendrites, one axon (brain)Bipolar – retina, smell, facial nerveUnipolar – dorsal spine
17Axonal Length Types Golgi Type I Golgi Type II Axons range from feet to inches.E.G. Motor cortexGolgi Type IIAxons are very shortE.G. interneurons
18MCQHow do cooks keep chicken from tasting dry?Soften meat with a hammer (tenderizing)Soak in water before cooking (hydrating)Soak in salty water before cooking (brining)Cook in boiling water (boiling)
19Brining Brine has more salt than inside meat: salt diffuses into cell. Diffusion is the movement of molecules from a region of higher concentration to one of lower concentration by random molecular motion.The increased salinity of the cell fluid causes the cell to absorb water from the brine via osmosis.Osmosis is the diffusion of a solvent (frequently water) through a semi-permeable membrane.
20The cell membrane maintains gradients 3 Sodium ions (Na+) are pumped out of the cell2 Potassium ions (K+) are pumped into the neuronThis creates gradientsCell is negatively charged relative two outsideCell has less sodium than outsideCell has more potassium than outsideThe cell membrane maintains gradients
21GradientIf a sodium channel is opened, sodium will rush in (due to diffusion). Cell will depolarize.If a potassium channel is opened, K+ will rush in.Na+Na+Na+Na+Na+Na+K+Na+K+Na+K+K+K+Na+Na+Na+