Fundamentals of the Nervous System Chapter 11 Dr Tamily Weissman, Department of Molecular and Cellular Biology, Harvard University
Fundamentals of the Nervous System
Chapter 11
Dr Tamily Weissman, Department of Molecular and Cellular Biology, Harvard University
Functions of the Nervous System• Master controller and communicator of the body
• Sensory input (to CNS)– External or internal sensors
• Integration– Immediate context– Experience
• Motor output (from CNS)– Muscle or gland response
See yellow light
Foot to brake or gas
Process options
http://images.google.com/imgres?imgurl=http://www.dmacc.edu/instructors/rbwollaston/Nervous_system/neuroglia_of_CNS.gif&imgrefurl=http://www.dmacc.edu/instructors/rbwollaston/Chapter_8_Nervous_System.htm&usg=__2YxucQKrJmUKtfkBty-PZGw_y1A=&h=386&w=371&sz=9&hl=en&start=1&sig2=zDo9CPoP08kpEikUtueyXw&um=1&tbnid=7Kr6pqq0qPkVQM:&tbnh=123&tbnw=118&prev=/images%3Fq%3Dneuroglia%26hl%3Den%26sa%3DG%26um%3D1&ei=NGVTSvmkE8yjmQels_CgCQ
Neuroglia
• CNS– Astrocytes
• Connect neurons to capillaries• Guide growing neurons
– Microglia: immune functions– Ependymal cells: circulate CSF– Oligodendrocytes: produce
multiple myelin sheaths• PNS– Schwann cells: produce myelin – Satellite cells: similar to
astrocytes
Neurons
http://www.pspnperak.edu.my/biologit5/Abd%20Razak%20b.%20Yaacob/Portfolio/BBM/Audio/saraf/Neuron%208.gif
• Structural unit of the nervous system
• Cell body – Nissl bodies – Nuclei vs ganglia
• Processes– Dendrites
• Graded potentials– Axons
• Axon hillock • Axon terminals • Axolemma and axoplasm• Myelin sheath and nodes of Ranvier
• White vs gray matter
– Tracts vs nerves
Classification of Neurons
http://www.unisanet.unisa.edu.au/Resources/101766/Online%20Brain%20Development%20course/Pics/Photo%201g.gif
• Structural classification– Multipolar: mainly in
CNS– Bipolar: sense organs– Unipolar : mainly in PNS
• Functional classification– Sensory are afferents– Motor are efferents– Interneurons
Ion Channels• Proteins spanning PM controlling flow– Leak channels– Gated channels• Chemical (ligand) respond to NT• Voltage respond to change in polarization• Mechanical respond to physical change/deformation
• Ions move down an electrochemical gradient
Resting Membrane Potential
• Polarization creates potential energy
• Changes allow cellular communication– Current from flow of
charge (ions) • K+ leaks out and Na+ leaks in• Na+/K+ pump maintains
– Resistance regulates
Graded Potentials
• Varies with stimuli– Short, localized, and decremental• Depolarization (-70mV to -55mV)• Hyperpolarization (-70mV to -100mV)
– Summation can initiate action potentials (APs)
http://www.colorado.edu/intphys/Class/IPHY3430-200/image/figure4-8.jpg
Action Potentials (AP’s)
• Depolarization – Positive feedback maintains– Threshold = all or nothing response
• Repolarization – Returning electrical conditions
• Hyperpolarization– Na+/K+ pump returns ionic
conditions• Refractory periods– Absolute– Relative
Propagation of an Action Potential
Unmyelinated
Myelinated
• Self-generating • Refractory period ensures
one-way movement• Conduction speed– Axon diameter– Degree of myelination• Continuous conduction w/o
myelin• Saltatory conduction at
nodes of Ranvier• Multiple sclerosis
Synapses• Types– Presynaptic neuron sends– Postsynaptic neuron
receives
• Classification– Axodendritic– Axosomatic– Axoaxonic
• Function– Electrical synapses – Chemical synapses
Chemical Transmission
• AP reaches axon terminal
• Ca2+ signals NT release• NT binds postsynaptic
neuron– EPSP (depolarize)– IPSP (hyperpolarize)
• Ending transmission– Degradation– Reuptake– Diffusion http://anthropologynet.files.wordpress.com/2008/01/neuron-synapse.png
Neurotransmitter Classes• Acetylcholine (ACh): skeletal muscles• Biogenic amines
– Dopamine (DA)– Norepinephrine (NE) & epinephrine (Epi)– Serotonin (5-HT)– Histamine
• Amino acids– GABA – Glutamate
• Neuropeptides– Endorphins– Substance P
• Dissolved gases– NO: synthesized on demand; relaxation of smooth muscle (Viagra)