NERVOUS SYSTEMNERVOUS SYSTEMLecture 1Lecture 1

OVERVIEWOVERVIEW

andand

NEUROHISTOLOGYNEUROHISTOLOGY

ANATOMICAL ORGANIZATION of the ANATOMICAL ORGANIZATION of the NERVOUS SYSTEMNERVOUS SYSTEM

NervousSystem

CNS PNS ANS

BRAIN

SPINALCORD

CRANIALNERVES

SPINALNERVES

SYMPATHETIC

PARA-SYMPATHETIC

Central Nervous System (CNS)Central Nervous System (CNS)

Definition:Definition:

Unpaired, bilaterally symmetrical structures Unpaired, bilaterally symmetrical structures extending along the longitudinal axis of the extending along the longitudinal axis of the midsagittal plane of the body.midsagittal plane of the body.

Structures arising directly from the neural tube.Structures arising directly from the neural tube.

Includes:Includes:

BrainBrain

Spinal cordSpinal cord

Peripheral Nervous System (PNS)Peripheral Nervous System (PNS)

Definition:Definition:

Made up of transmission pathways Made up of transmission pathways carrying information between the CNS and carrying information between the CNS and external/internal environments.external/internal environments.

Afferent (sensory) pathways:Afferent (sensory) pathways:Carry information to the CNS.Carry information to the CNS.

Efferent (motor) pathways:Efferent (motor) pathways:Carry information from the CNS.Carry information from the CNS.

Peripheral Nervous System (PNS)Peripheral Nervous System (PNS)

Includes:Includes:Cranial nerves (12 pairs).Cranial nerves (12 pairs).

Spinal nerves (31 pairs).Spinal nerves (31 pairs).

Autonomic Nervous System (ANS)Autonomic Nervous System (ANS)

May be considered a subdivision of the May be considered a subdivision of the PNS.PNS.

Entirely motor.Entirely motor.

Innervates smooth muscle and glands Innervates smooth muscle and glands (viscera).(viscera).

ANS SubdivisionsANS Subdivisions

Sympathetic system (fight or flight):Sympathetic system (fight or flight):Also called thoracolumbar.Also called thoracolumbar.

Parasympathetic system (feed or breed):Parasympathetic system (feed or breed):Also called craniosacral.Also called craniosacral.

Parts of a NeuronParts of a Neuron

Cell body:Cell body:

Trophic unitTrophic unit

PerikaryonPerikaryonDendrites:Dendrites:

Receptive unitReceptive unitAxon:Axon:

Conductive unitConductive unit

Cell Body DefinitionCell Body Definition

That part of a neuron that encloses the That part of a neuron that encloses the nucleus and other organelles necessary to nucleus and other organelles necessary to maintain and repair the neuron.maintain and repair the neuron.

Cell Body OrganellesCell Body Organelles

NucleusNucleusGolgi apparatusGolgi apparatusRERRER

Ribosomes (=Nissl substance)Ribosomes (=Nissl substance)

Dendrites (Characteristics)Dendrites (Characteristics)

Branches off the cell body that carry information Branches off the cell body that carry information to the cell body.to the cell body.

Usually several to many.Usually several to many. Relatively short.Relatively short. Often branched.Often branched. Have receptors for neurotransmitters.Have receptors for neurotransmitters. Conduct local potentials.Conduct local potentials.

Axon CharacteristicsAxon Characteristics

Carries information to another neuron or Carries information to another neuron or muscle cell.muscle cell.

Often relatively long.Often relatively long.Single (one per neuron).Single (one per neuron).Conducts action potential Conducts action potential

Axon CharacteristicsAxon Characteristics

Ends in short branched processes called Ends in short branched processes called telodendria.telodendria.

May have collateral branches.May have collateral branches.Cell membrane (= axolemma).Cell membrane (= axolemma).Cytoplasm = (axoplasm).Cytoplasm = (axoplasm).

Axon CharacteristicsAxon Characteristics

Covered by neurolemma:Covered by neurolemma:Made up of Schwann cells.Made up of Schwann cells.

Often myelinated:Often myelinated:Myelin is formed by Schwann cells.Myelin is formed by Schwann cells.

Note: axon is the only part of a neuron that Note: axon is the only part of a neuron that is ever myelinated.is ever myelinated.

Axon OrganellesAxon Organelles

MitochondriaMitochondria

NeurofilamentsNeurofilaments

NeurotubulesNeurotubules

Axonal TransportAxonal Transport

Anterograde:Anterograde:Transports vesicles from cell body to end Transports vesicles from cell body to end

of of axon.axon.

KinesinKinesinRetrograde:Retrograde:

Transports vesicles from end of axon Transports vesicles from end of axon toward toward cell body.cell body.

Cytoplasmic dyneinCytoplasmic dynein

Axonal TransportAxonal Transport

Slow transport:Slow transport:1-5 mm/day1-5 mm/day

Fast transport:Fast transport:200-400 mm/day200-400 mm/day

General TerminologyGeneral Terminology

Nerve:Nerve:Bundle of fibers in the PNS.Bundle of fibers in the PNS.

Tract:Tract:Bundle of fibers in the CNS.Bundle of fibers in the CNS.

Commissure:Commissure:Tract in the CNS that crosses from one Tract in the CNS that crosses from one

side side to the other.to the other.

General TerminologyGeneral Terminology

Nucleus:Nucleus:Aggregation of dendrites and nerve cell Aggregation of dendrites and nerve cell

bodies in the CNS.bodies in the CNS.Ganglion:Ganglion:

Aggregation of dendrites and nerve cell Aggregation of dendrites and nerve cell bodies in the PNS.bodies in the PNS.

General TerminologyGeneral Terminology

White matter:White matter:Areas of myelinated axons.Areas of myelinated axons.

Gray matter:Gray matter:Areas of unmyelinated axons, cell Areas of unmyelinated axons, cell bodies, bodies, and dendrites.and dendrites.

SynapseSynapse

Definition:Definition:Composite structure that allows two neurons Composite structure that allows two neurons

or a neuron and a muscle cell to “talk” to each or a neuron and a muscle cell to “talk” to each other.other.

Synapse ComponentsSynapse Components

Presynaptic membrane:Presynaptic membrane:With synaptic vesicles filled with With synaptic vesicles filled with

neurotransmitters.neurotransmitters.Synaptic cleft:Synaptic cleft:Postsynaptic membrane:Postsynaptic membrane:

With receptors for neurotransmitters.With receptors for neurotransmitters.Monosynaptic pathways.Monosynaptic pathways.Polysynaptic pathways.Polysynaptic pathways.

Reflex ArcReflex Arc

Afferent (sensory) pathways:Afferent (sensory) pathways:

Somatic.Somatic.

Visceral (splanchnic).Visceral (splanchnic).Efferent (motor) pathways:Efferent (motor) pathways:

Somatic.Somatic.

Visceral (splanchnic).Visceral (splanchnic).Association neurons (interneurons).Association neurons (interneurons).

Neuroglial CellsNeuroglial Cells

Schwann cells Schwann cells AstrocytesAstrocytesMicroglial cellsMicroglial cellsOligodendrocytesOligodendrocytesEpendymal cellsEpendymal cells

Schwann CellsSchwann Cells

Derived from neural crest cells.Derived from neural crest cells.

Myelinate axons in the PNS.Myelinate axons in the PNS.

AstrocytesAstrocytes

Derived from neural crest cells.Derived from neural crest cells. Function to physically support neurons.Function to physically support neurons. Channel materials between capillaries and Channel materials between capillaries and

neurons (= Blood-brain barrier).neurons (= Blood-brain barrier). Support and guide neurons during embryonic Support and guide neurons during embryonic

building of cerebral cortex.building of cerebral cortex. Act as sinks for ions (i.e., KAct as sinks for ions (i.e., K++).). Remove neuroactive and potentially toxic Remove neuroactive and potentially toxic

substances.substances.

Microglial CellsMicroglial Cells

Derived from embryonic mesenchyme.Derived from embryonic mesenchyme.

May transform into phagocytes within May transform into phagocytes within CNS.CNS.

OligodendrocytesOligodendrocytes

Derived from neural crest cells.Derived from neural crest cells.

Function to myelinate axons within CNS.Function to myelinate axons within CNS.

Ependymal cellsEpendymal cells

Derived from neural crest cells.Derived from neural crest cells.

Line ventricles of brain.Line ventricles of brain.