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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.