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NERVOUS SYSTEM Lecture 1. OVERVIEW and NEUROHISTOLOGY. ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM. Central Nervous System (CNS). Definition: Unpaired, bilaterally symmetrical structures extending along the longitudinal axis of the midsagittal plane of the body.

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Nervous system lecture 1





Central nervous system cns
Central Nervous System (CNS)

  • Definition:

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

    Structures arising directly from the neural tube.

  • Includes:


    Spinal cord

Peripheral nervous system pns
Peripheral Nervous System (PNS)

  • Definition:

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

  • Afferent (sensory) pathways:

    Carry information to the CNS.

  • Efferent (motor) pathways:

    Carry information from the CNS.

Peripheral nervous system pns1
Peripheral Nervous System (PNS)

  • Includes:

    Cranial nerves (12 pairs).

    Spinal nerves (31 pairs).

Autonomic nervous system ans
Autonomic Nervous System (ANS)

  • May be considered a subdivision of the PNS.

  • Entirely motor.

  • Innervates smooth muscle and glands (viscera).

Ans subdivisions
ANS Subdivisions

  • Sympathetic system (fight or flight):

    Also called thoracolumbar.

  • Parasympathetic system (feed or breed):

    Also called craniosacral.

Parts of a neuron
Parts of a Neuron

  • Cell body:

    Trophic unit


  • Dendrites:

    Receptive unit

  • Axon:

    Conductive unit

Cell body definition
Cell Body Definition

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

Cell body organelles
Cell Body Organelles

  • Nucleus

  • Golgi apparatus

  • RER

    Ribosomes (=Nissl substance)

Dendrites characteristics
Dendrites (Characteristics)

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

  • Usually several to many.

  • Relatively short.

  • Often branched.

  • Have receptors for neurotransmitters.

  • Conduct local potentials.

Axon characteristics
Axon Characteristics

  • Carries information to another neuron or muscle cell.

  • Often relatively long.

  • Single (one per neuron).

  • Conducts action potential

Axon characteristics1
Axon Characteristics

  • Ends in short branched processes called telodendria.

  • May have collateral branches.

  • Cell membrane (= axolemma).

  • Cytoplasm = (axoplasm).

Axon characteristics2
Axon Characteristics

  • Covered by neurolemma:

    Made up of Schwann cells.

  • Often myelinated:

    Myelin is formed by Schwann cells.

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

Axon organelles
Axon Organelles

  • Mitochondria

  • Neurofilaments

  • Neurotubules

Axonal transport
Axonal Transport

  • Anterograde:

    Transports vesicles from cell body to end of axon.


  • Retrograde:

    Transports vesicles from end of axon toward cell body.

    Cytoplasmic dynein

Axonal transport1
Axonal Transport

  • Slow transport:

    1-5 mm/day

  • Fast transport:

    200-400 mm/day

General terminology
General Terminology

  • Nerve:

    Bundle of fibers in the PNS.

  • Tract:

    Bundle of fibers in the CNS.

  • Commissure:

    Tract in the CNS that crosses from one side to the other.

General terminology1
General Terminology

  • Nucleus:

    Aggregation of dendrites and nerve cell bodies in the CNS.

  • Ganglion:

    Aggregation of dendrites and nerve cell bodies in the PNS.

General terminology2
General Terminology

  • White matter:

    Areas of myelinated axons.

  • Gray matter:

    Areas of unmyelinated axons, cell bodies, and dendrites.


  • Definition:

    • Composite structure that allows two neurons or a neuron and a muscle cell to “talk” to each other.

Synapse components
Synapse Components

  • Presynaptic membrane:

    With synaptic vesicles filled with neurotransmitters.

  • Synaptic cleft:

  • Postsynaptic membrane:

    With receptors for neurotransmitters.

  • Monosynaptic pathways.

  • Polysynaptic pathways.

Reflex arc
Reflex Arc

  • Afferent (sensory) pathways:


    Visceral (splanchnic).

  • Efferent (motor) pathways:


    Visceral (splanchnic).

  • Association neurons (interneurons).

Neuroglial cells
Neuroglial Cells

  • Schwann cells

  • Astrocytes

  • Microglial cells

  • Oligodendrocytes

  • Ependymal cells

Schwann cells
Schwann Cells

  • Derived from neural crest cells.

  • Myelinate axons in the PNS.


  • Derived from neural crest cells.

  • Function to physically support neurons.

  • Channel materials between capillaries and neurons (= Blood-brain barrier).

  • Support and guide neurons during embryonic building of cerebral cortex.

  • Act as sinks for ions (i.e., K+).

  • Remove neuroactive and potentially toxic substances.

Microglial cells
Microglial Cells

  • Derived from embryonic mesenchyme.

  • May transform into phagocytes within CNS.


  • Derived from neural crest cells.

  • Function to myelinate axons within CNS.

Ependymal cells
Ependymal cells

  • Derived from neural crest cells.

  • Line ventricles of brain.