Chapter 11

Dr Tamily Weissman, Department of Molecular and Cellular Biology, Harvard University

Functions of the Nervous SystemMaster controller and communicator for

the body

Sensory input (to brain)Sensors External or internal info

IntegrationImmediate contextExperience

Motor output (from brain)Effector organsMuscle or gland response

See yellow light

Foot to brake or gas

Process options

Human Nervous System Divisions

Integration & command Info in & out

NeurogliaCNS

Astrocytes Most abundant & versatile Exchange b/w blood & neurons;

migration; environment controlMicroglia

Immune cells of CNSEpendymal cells

Circulate CSF & cushioningOligodendrocytes

Produce multiple myelin sheathsPNS

Schwann cells Produce a single myelin sheath

Satellite cells Similar to astrocytes

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

Neurons

http://www.mind.ilstu.edu/curriculum/neurons_intro/imgs/neuron_types.gif

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 (soma) Nissl bodies (rough ER) Nuclei vs ganglia

Processes Dendrites

Input; dendritic spines; graded potentials

Axons Axon hillock (trigger zone) Myelin sheath and nodes of Ranvier Axon terminals (secretory region) and Lack Nissl bodies and Golgi

Anterograde and retrograde transport Axolemma and axoplasm

Tracts vs nervesWhite vs gray matter

Classification of NeuronsStructural

classificationMultipolar: 3+

processes; 99% of all neurons, major in CNS

Bipolar: 2 processes; rare, located in sense organs

Unipolar : short, divided process (peripheral and central processes); mainly in PNS

Functional classificationSensory (afferent):

message to CNSMotor (efferent):

message from CNS Interneurons

http://www.unisanet.unisa.edu.au/Resources/101766/Online%20Brain%20Development%20course/Pics/Photo%201g.gif

NeurophysiologyResting membrane potential

Positive charge outside, negative charge inside

Separation of charges creates PE Measured in millivolts (mV) -70 mV in the plasma membrane of neurons

Cell said to be polarizedFlow of charge (ions) is the current

K+ flows out, Cl- flows in more readily than Na+ inNa+/K+ pump maintains negative intracellular

environmentPlasma membrane provide resistance

Ohm’s law: current = (voltage/resistance) More volts (potential difference) = more movement Greater resistance = less movement

Ion ChannelsProteins spanning PM controlling flow

Leak channelsGated channels

Chemical respond to NT Voltage respond to potential change Mechanical respond to physical change/deformation

Ions move down an electrochemical gradientConcentration Charge

Graded PotentialsShort lived and localDepolarizations or hyperpolarizationsDecrease in magnitude w/distance,

decrementalVaries with strength of stimuli

Point of stimulus only place ions can pass (+) ions toward (-) areas and (-) ions to (+) areasInside (+) ions move from stimuli site to

neighboring (-) areasOutside (+) ions move toward stimuli site

Action PotentialsRapid reversal of membrane

potentialAll-or-nothing

Graded until threshold reachedMagnitude independent of strength

Carry informationDepolarization

Positive feedback maintainsRepolarization Hyperpolarization

Returning electrical conditionsNa+/K+ pump

Returns ionic conditionsRefractory periods

Absolute vs relative

Propagation of an APLocal currents depolarize membrane

at stimuli site and disperseOrigin enters a refractory period

Local changes can produce another APMyelinated axons allow speed

conduction and allow regenerationSaltatory conduction

at nodes of RanvierAxon diameter

Larger = fasterDegree of myelination

w/o = continuousconduction; AP immediately= slow

w/ = prevents leaks; fasterchange

SynapsesTypes

Presynaptic neuron sendsPostsynaptic neuron receives

ClassificationAxodendriticAxosomaticAxoaxonic

FunctionElectrical synapses allow ion

flow b/w gap junctions Electrical only

Chemical synapses release and receive NT’s b/w pre- and postsynaptic neurons Electrical chemical electrical

Transmission at a SynapseAP opens Ca2+ channels

in presynaptic neuronCa2+ influx causes

synaptic vesicle fusion and NT exocytoic release

Binds to postsynaptic neuron Postsynaptic ion

channels change EPSP or IPSP

Temporal summation Spatial summation

Actions of NT in synaptic cleft ended Degradation Reuptake Diffusion

http://anthropologynet.files.wordpress.com/2008/01/neuron-synapse.png

Neurotransmitter ClassesAcetylcholine (Ach): skeletal muscles (excitatory)Biogenic amines

Dopamine (DA): movement (both)Norepinephrine (NE) & epinephrine (Epi): feel good NT’s

(both)Serotonin (5-HT): mood, sleep, appetite & anger (inhibitory)Histamine: immune response & wakefulness (both)

Amino acidsGABA (inhibitory)Glutamate (excitatory)

PeptidesEndorphins and enkephalins: natural opiates (inhibitory)Substance P: perception of pain (excitatory)

Dissolved gasesNO: synthesized on demand; relaxation of smooth muscle

(Viagra)

Nervous System DisordersPolio: destroys motor neurons in CNSRabies: inflames the brainMultiple sclerosis: destruction of myelin

slows AP conduction, axons unaffectedTay-Sachs: harmful accumulation in brain

tissueShingles: viral infection in skin sensory

neuronsNumbing and prickling: slowed blood flow

to areas impair nerve impulses