The Nervous The Nervous System: Neural System: Neural

TissueTissue

IntroductionIntroduction– Nervous system = control center & Nervous system = control center &

communications networkcommunications network– FunctionsFunctions

Stimulates movementsStimulates movements Maintains homeostasis (with endocrine system)Maintains homeostasis (with endocrine system)

Organization of the Organization of the Nervous SystemNervous System

– Central nervous system (CNS)Central nervous system (CNS) Brain & spinal cordBrain & spinal cord

– Peripheral Nervous System (PNS)Peripheral Nervous System (PNS) Afferent (Sensory) SystemAfferent (Sensory) System Efferent (Motor) SystemEfferent (Motor) System

– Somatic Nervous SystemSomatic Nervous System– Autonomic Nervous SystemAutonomic Nervous System

Sympathetic Nervous SystemSympathetic Nervous System Parasympathetic Nervous SystemParasympathetic Nervous System

The Nervous SystemThe Nervous System

Organization of the Organization of the Nervous SystemNervous System

Histology of Nervous Histology of Nervous TissueTissue

– 2 types of cells2 types of cells NeuronsNeurons

– Structural & functional part of nervous systemStructural & functional part of nervous system– Specialized functionsSpecialized functions

Neuroglia (glial cells)Neuroglia (glial cells)– Support & protection of nervous systemSupport & protection of nervous system

Neuroglia of CNSNeuroglia of CNS

NeuronsNeurons– FunctionFunction

Conduct electrical impulsesConduct electrical impulses– StructureStructure

Cell body Cell body – Nucleus with nucleolus Nucleus with nucleolus – CytoplasmCytoplasm

Cytoplasmic processesCytoplasmic processes– DendritesDendrites– AxonAxon

Review of Neuron Review of Neuron StructureStructure

Anatomy of a NeuronAnatomy of a Neuron

Nerve Fibers of the PNSNerve Fibers of the PNS– An axon and its sheathsAn axon and its sheaths

Myelinated axon Myelinated axon – Axon is surrounded by a myelin sheathAxon is surrounded by a myelin sheath

Unmyelinated axonUnmyelinated axon– Axon has no myelin sheathAxon has no myelin sheath

MyelinMyelin– White matter of nerves, brain, spinal cordWhite matter of nerves, brain, spinal cord– Composed primarily of phospholipidsComposed primarily of phospholipids– ProductionProduction

Developing Schwann cells wind around axonDeveloping Schwann cells wind around axon– FunctionFunction

Increases speed of impulse conductionIncreases speed of impulse conduction Insulation and maintenance of axonInsulation and maintenance of axon

Schwann Cells and Schwann Cells and Peripheral AxonsPeripheral Axons

MyelinMyelin– Nodes of RanvierNodes of Ranvier

Unmyelinated gaps between segments of myelinUnmyelinated gaps between segments of myelin Impulses “jump” from node to nodeImpulses “jump” from node to node

A Myelinated AxonA Myelinated Axon

Nerve Fibers of the CNSNerve Fibers of the CNS– UmyelinatedUmyelinated– MyelinatedMyelinated

Production of myelin is from oligodendrocytesProduction of myelin is from oligodendrocytes Nodes of Ranvier are less numerousNodes of Ranvier are less numerous

Nerve Fibers of the CNSNerve Fibers of the CNS

Classification of NeuronsClassification of Neurons– Functional – based on the direction of impulse Functional – based on the direction of impulse

transmissiontransmission Sensory neuronsSensory neurons Motor neuronsMotor neurons Interneurons (association)Interneurons (association)

Functional Classification of Functional Classification of NeuronsNeurons

NervesNerves– Bundles of cell processes of afferent and Bundles of cell processes of afferent and

efferent neuronsefferent neurons– Functional unit = nerve fiberFunctional unit = nerve fiber

Nerve ImpulseNerve Impulse– A change in charge that travels as a wave along A change in charge that travels as a wave along

the membrane of a neuronthe membrane of a neuron– Depends on the movement of K+ and Na+ Depends on the movement of K+ and Na+

across the nerve cell membrane. across the nerve cell membrane.

Resting NeuronResting Neuron– Sodium ions are in large concentration along Sodium ions are in large concentration along

the outside of the cell membranethe outside of the cell membrane– Potassium ions are in large concentration along Potassium ions are in large concentration along

the inside of the cell membranethe inside of the cell membrane

Resting PotentialResting Potential

Action PotentialAction Potential– Requires a stimulus of adequate strengthRequires a stimulus of adequate strength– Membrane is disturbedMembrane is disturbed– Sodium ions flow inward, potassium ions flow Sodium ions flow inward, potassium ions flow

outwardoutward Action potentialAction potential

– The disturbance at the point of stimulation is The disturbance at the point of stimulation is enough to disturb adjacent portion of membrane. enough to disturb adjacent portion of membrane.

– The action potential moves along the membrane. The action potential moves along the membrane.

Action PotentialAction Potential

Back to Resting PotentialBack to Resting Potential– Potassium and sodium ions are actively Potassium and sodium ions are actively

transported back across the membranetransported back across the membrane– Membrane is at rest againMembrane is at rest again

Neurons Exhibit Neurons Exhibit ConductivityConductivity

– The ability to transmit an impulse to another The ability to transmit an impulse to another neuron or tissue.neuron or tissue.

– Action potentials can be transmitted across Action potentials can be transmitted across synapses.synapses. Junction between 2 neuronsJunction between 2 neurons Uses neurotransmittersUses neurotransmitters Transmission is one way onlyTransmission is one way only

SynapseSynapse

Neural Regeneration after Neural Regeneration after InjuryInjury

– Axon & myelin sheath distal to the injury Axon & myelin sheath distal to the injury deterioratedeteriorate

– Scwann cells form a cord, grow into the cut, and Scwann cells form a cord, grow into the cut, and unite the stumps.unite the stumps.

– The axon forms buds and grows along the cord The axon forms buds and grows along the cord of Schwann cellsof Schwann cells

– The axon continues to grow into the distal The axon continues to grow into the distal stump and is enfolded by Schwann cells.stump and is enfolded by Schwann cells.

– (Rate of 1mm/day)(Rate of 1mm/day)

Neural RegenerationNeural Regeneration

Neural RegenerationNeural Regeneration

Neural RegenerationNeural Regeneration

Neural RegenerationNeural Regeneration