THE NERVOUS SYSTEM

I. IntroductionA.Functions of N.S.

1.Sensory input 2.Integration 3.Homeostasis 4.Mental activity 5.Control of

skeletal muscles

I. I. IntroductionIntroductionB. Divisions of the N.S.

Central N.S.Central N.S. Peripheral Peripheral N.S.N.S.

BraiBrainn

Spinal Spinal CordCord

AutonomiAutonomicc

SomatiSomaticcParasympathParasympath

eticeticSympathetSympatheticic

EfferentEfferent AfferenAfferentt

Sympathetic NSSympathetic NSFight or Flight• Dilates pupils• Reduces saliva,

mucus, peristalsis, intestinal motility, urine secretion

• Increases heart rate, glycogen to glucose conversion

Parasympathetic Parasympathetic NSNSDigest & Rest

• Constricts pupils• Reduces heart

rate• Increases mucus

production, gastric juice production, digestion, urine production, intestinal tract motility, peristalsis

II. Histology of the N.S.II. Histology of the N.S.

A.Neurons – 1. Basics

– nerve cells– functional unit of

n.s.

Neurons are not Neurons are not nerves!nerves!

A. Neurons 2. Structure.Structure.

 a. Cell bodyCell body b. DendritesDendrites

receive incoming signals towards cell body

A. Neurons

2. StructureStructure  c. AxonsAxons

transmit signals away from cell body

c. c. AxonsAxons• Myelin SheathMyelin Sheath -

membrane "insulation" around axons

• Nodes of Nodes of RanvierRanvier - gaps between myelin

2. Structure

c. c. AxonsAxons• Nissil bodiesNissil bodies -

rough endoplasmic reticulum... Lots of protein synthesis

• Synaptic vesiclesSynaptic vesicles - stores neurotransmitter at axon terminal

2. Structure

Structural Classification of Neurons

II. Histology of the N.S.B.B.Neuroglia – Neuroglia – nonexcitablenonexcitable;;

help & support neurons

OF THE CNSOF THE CNS

1.1.Astrocytes Astrocytes - "nurse" cells; nourish & protect neurons; form blood brain barrier

2.2.Oligodendrocytes Oligodendrocytes - form myelin in CNS

II. Histology of the N.SII. Histology of the N.S..B.B.Neuroglia – Neuroglia – nonexcitablenonexcitable;;

help & support neurons

OF THE CNSOF THE CNS 3.3.Microglia Microglia - provide

immune protection in CNS.

4.4.Ependymal cells Ependymal cells –circulate cerebrospinal fluid

II. Histology of the N.S.

B.Neuroglia – OF THE PNSOF THE PNS5.5.Schwann CellsSchwann Cells - form

myelin in peripheral nerves

6.6.Satellite CellsSatellite Cells – surround and support neurons of the ganglia

C. Nerves and Ganglia1.1.NervesNerves

a.bundles of nerve cell axons and/or dendrites in periphery of body.

b.Functional classification• Sensory (afferent) Sensory (afferent)

nervesnerves carry incoming signals from sense receptors towards CNS.

C. Nerves and Ganglia1.1.NervesNerves

b. Functional classification• Motor (efferent) nerves Motor (efferent) nerves

– carry outgoing (away from CNS) signals to muscle & glands.

• Interneurons nervesInterneurons nerves – connect motor and sensory neurons

C. Nerves and Ganglia2.2.Ganglia.Ganglia.

Ganglia are bundles of nerve cell bodies in periphery of body.

II. Histology of the N.S.D.Gray & White Matter

1.1.White MatterWhite Matter• Made of mylinated

processes

2.2.Gray MatterGray Matter• Unmylinated processes

and cell bodies

II. Histology of the N.S.

D.Gray & White Matter3. Location3. Location Spinal

cord gray matter forms H in center surrounded by white matter

II. Histology of the N.S.D.Gray & White Matter

3. Location3. LocationBrain central white matter with a superficial gray matter covering

III. Neurophysiology A.Membrane Properties

1.When at rest, the neuron has more + charges outside than inside

2.This electric imbalance called the restingresting membrane potentialmembrane potential

Resting PotentialResting Potential

A. Membrane Properties3. Resting Potential ion 3. Resting Potential ion

distribution distribution • Lg # NaLg # Na++ outside; K outside; K++ inside inside

A. Membrane Properties

4.4. Changes in ion Changes in ion distributiondistribution

• Stimulation of membrane opens ion ion channels (pores)channels (pores)

• When this occurs it is When this occurs it is called an called an Action Action PotentialPotential

III. Neurophysiology B.Action Potentials

1.Are a specialized kind of electric signal generated only by neurons and muscle cells

2.are self-propagating 3.are all-or-none events.

III. Neurophysiology C.Action Potentials have 3

Phases1.1.Depolarization Depolarization

• Rapid (1 msec)Rapid (1 msec)• sodium channels open, sodium channels open,

NaNa++ rush in rush in

III. Neurophysiology C.Action Potentials have 3

Phases1.1.Depolarization Depolarization •Ends in an Ends in an overshoot overshoot

(i.e. brief period of (i.e. brief period of time time inside of cell is inside of cell is more more positive than positive than outside)outside)

III. Neurophysiology C.Action Potentials have 3

Phases2.2.Repolarization Repolarization

• Na+ channels close Na+ channels close • K+ channels open and K+ channels open and

K+ rushes out K+ rushes out

III. Neurophysiology C.Action Potentials have 3

Phases2.2.Repolarization Repolarization

• overshoots the overshoots the resting pointresting point

III. Neurophysiology C.Action Potentials have 3

Phases3.3.Undershoot Phase Undershoot Phase

• Membrane is Membrane is hyperpolarized back to the hyperpolarized back to the resting potential resting potential

• KK++ channels close channels close• NaNa++/K/K++ pump reestablishes pump reestablishes

the resting potentialthe resting potential• 3 Na3 Na+ + movedmoved for 2 Kfor 2 K++

NaNa++ / K / K++ Pump Pump Reestablishes Resting Reestablishes Resting

PotentialPotential

III. Neurophysiology D.Nerve Impulse

1.1. Impulse conduction Impulse conduction • Unmyelinated - entire Unmyelinated - entire

membrane surface.membrane surface.• Myelinated fibers - from Myelinated fibers - from

node to nodenode to node

2.2.Action potential spreads Action potential spreads down the fiber to adjacent down the fiber to adjacent areas of membraneareas of membrane

IV. The Synapse

A.DefinedThe junction (cleft) between 2 The junction (cleft) between 2

neuronsneurons

IV. The Synapse B.B. Transmission Transmission

Across a SynapseAcross a Synapse• Impulse Impulse

reaches axon reaches axon terminals terminals (knobs)(knobs)

• synaptic synaptic vesicles release vesicles release neurotransmittneurotransmitterer

IV. The Synapse C.C.Kinds of NeurotransmittersKinds of Neurotransmitters

1.1.Acetylcholine (ACh)Acetylcholine (ACh)• Made from acetic acidMade from acetic acid

2.2.Biogenic AminesBiogenic Amines • Made from amino acidsMade from amino acids• Include: Include:

dopamine, dopamine, epinephrine (adrenaline), epinephrine (adrenaline), norepinephrine norepinephrine

(noradrenaline), (noradrenaline), Serotonin and histamineSerotonin and histamine

C. Kinds of Neurotransmitters

3.3.Amino AcidsAmino Acids4.4.PeptidesPeptides (includes (includes

endorphins)endorphins)5.5.ATPATP6.6.Nitric Oxide (NO)Nitric Oxide (NO)7.7.Carbon monoxide (CO)Carbon monoxide (CO)

Nicotine mimics acetylcholine but can block function by producing sustained depolarization

V. The Reflex ArcA.A.The Pathway The Pathway

1.1.ReceptorsReceptors2.2.Sensory NeuronSensory Neuron3.3.CNS Integration CNS Integration

CenterCenter4.4.Motor NeuronMotor Neuron5.5.EffectorEffector

B.B.ReflexesReflexes1.1.Are rapid, Are rapid,

automatic automatic responses responses

to to stimulistimuli

2.2.A A specific specific stimulus stimulus produceproduces the s the same same motor motor responseresponse