K2 - Histology of Nervous System

Histology of Nervous System

IKA MURTI

HISTOLOGY DEPT.

FK UNSOED

ReferencesJunqueira, LC, Carneiro,J & Kelly RO. Basic Histology. Appleton & Lange.

Young, B & Heath JW. Wheather’s Functional Histology: a text and colour atlas.

Gartner, LP & Hiatt, JL. Color Textbook of Histology, 2nd Edition. WB. Saunders Company

Introduction The most complex system in the body histologically and physiologically Formed by a network of many billion nerve cells (neurons) All assisted by many more supporting glial cells Each neuron has hundreds of interconnections with other neurons → forming a very complex system for processing information and generating responses

Outline

Central nervous system (CNS) Peripheral nervous system (PNS) Classification of receptors

Structural divisions of the nervous systemOrganization Components General description

Central nervous system (CNS)

Brain and spinal cord Overall "command center," processing and integrating information

Peripheral nervous system (PNS)

Nerves and ganglia Receives and projects information to and from the CNS; mediates some reflexes

Nervous System

Organization of the Nervous System

Central Nervous System (CNS)Consists of the brain and spinal cord

- Nucleus = a collection of nerve cell bodies in the CNS- Tracts = bundle of nerve fibers within the CNS

integrating, processing, and coordinating

Peripheral Nervous System (PNS)

Consists of ganglia, cranial nerves, spinal nerves and peripheral receptorsGanglia = a collection of nerve cell bodies in the PNSNerve = bundle of nerve fibers in the PNS

Provides sensory information to the CNSCarries motor commands to peripheral tissues

Functional divisions of the nervous systemOrganization Components General description

Sensory nervous system

Some CNS and PNS components

Includes all axons that transmit impulses from a peripheral structure to the CNS

Somatic sensory Transmits input from skin, fascia, joints, and skeletal muscles

Visceral sensory Transmits input from stomach and intestines (viscera)

Motor nervous system

Some CNS and PNS components

Includes all axons that transmit nerve impulses from the CNS to a muscle or gland

Somatic motor (somatic nervous system) Voluntary control of skeletal muscle

Autonomic motor (autonomic nervous system)

Involuntary control of smooth muscle, cardiac muscle, and glands

Cerebrum Grey matter

◦ Outer part cerebral & cerebellar cortex◦ Gyri & sulci◦ Soma, dendrite, initial segment of axon◦ Non-myelinating glial cell◦ Learning, memory, sensory integration, information analysis,

initiation of motor response

White matter ◦ Inner part◦ Myelinated axon & some unmyelinated axon◦ Oligodendrocyte >>

Cerebral cortex

Molecular layer/plexiform layer ◦ Horizontal cell (of Cajal), neuroglia

Outer granular layer◦ Stellate/granule cell, pyramidal cell,

neuroglia Outer pyramidal layer

◦ Pyramidal cell (small) >>, neuroglia Inner granular layer

◦ Stellate cell, pyramidal cell, neuroglia

Inner pyramidal layer◦ Large pyramidal cell >>, stelate cells,

neuroglia Multiform layer

◦ Martinotti cells◦ Fusiform cells

Important neurons of the cerebrum are pyramidal neurons

The largest motor neurons in the cerebral cortex are those found in the fifth stratum of the cortex

Cerebellum

Coordination & Balance Grey matter

◦ Cerebellar cortex◦ Folding cortex folia◦ Neuronal cell bodies & Glial cell

White matter◦ Medulla ◦ Bundles of myelinated axon

PURKINJE cell

Cerebellar cortex

Molecular layer◦ Dendrite of Purkinje cell◦ Unmyelinated axon◦ Stellate cell◦ Basket cell

(Purkinje cell layer)◦ Inhibitory output (GABA NT)◦ Basket cell

Granular layer◦ Small granule cell :

Golgi cell tipe II◦ Glomeruli (cerebellar islands)

Cerebellar cortex

Purkinje cell

Spinal cord

Unlike the cerebrum and cerebellum, in the spinal cord the gray matter is internal, forming a roughly H-shaped structure that consists

of two posterior (P) horns (sensory) and two anterior (A) (motor) horns all joined by the gray commissure around the central canal

Internal anatomy of the spinal cord : The organization of gray matter and white matter

Grey matter◦ Inner part ◦ Butterfly-shaped◦ Central canal ◦ Anterior horn (motor) ◦ Posterior horn (sensory)◦ Neuronal cell bodies◦ Neuroglial cells

White matter◦ Outer part◦ Axons (mostly myelinated)

A cross section of spinal cord shows the transition between white matter (left) and

gray matter (right)

Comparison of Various Spinal Cord Segments

The skull and the vertebral column protect the CNS Between the bone and nervous tissue are membranes of connective tissue called the meninges

Meninges

Meninges Duramater

◦ Dense connective tissue◦ Periosteal duramater◦ Meningeal duramater◦ Epidural space◦ Subdural space

Arachnoid◦ Trabecular meshwork◦ Subarachnoid space- CSF◦ Arachnoid villi

Piamater◦ Thin layer of loose

connective tissue◦ Close to brain tissue but not

contact◦ Fibroblast

Meninges

Meninges in spinal cord

CLINICAL CORRELATIONS

• Meningiomas : slow growing tumors of the meninges, usually benign, produce clinical effects by compressing the brain and increasing intracranial pressure

• Meningitis : an inflammation of the meninges resulting from bacterial or viral infection in the CSF

BLOOD-BRAIN BARRIER : a system of tight junctions in the endothelial cells of brain capillaries that form a

semi-permeable membrane, allowing only certain substances to

enter the brain

Neuroglia

Blood-Brain Barrier (BBB) is formed by:

1. Astrocyte end feet

2. Basal membran

2. Endothelial cells (of brain capillary)

Most capillaries in the body

Brain capillaries

(BBB)

Astrocyte

Neuron

Oligodendro cyte

Ependyma

Microglia

Blood brain barrier

Choroid plexus

The choroid plexus consists of highly specialized regions of CNS tissue containing ependyma cells and vascularized piamater

that project from specific walls of the ventricles

Choroid plexus

• Section of the bilateral choroid plexus (CP) projecting into the fourth ventricle (V) near the cerebrum and cerebellum

• It is elaborately folded with many finger-like villi

Choroid plexus

each villus is seen to be well-vascularized with capillaries (C) and covered by a continuous layer of ependymal cells (arrow)

The choroid plexus is specialized for transport of water and ions across the capillary endothelium and ependymal

layer and the elaboration of these as CSF

MEDICAL APPLICATION

• A decrease in the absorption of CSF or a blockage of outflow from the ventricles during fetal or postnatal development → hydrocephalus

• Enlargement of the head followed by mental impairment

Peripheral nervous system

Ganglia◦ Cluster of soma◦ Satellite cell

Nerve fiber◦ Bundles of myelinated & unmyelinated axon◦ Supported with connective tissue◦ Motor & sensory nerve fibers

Nerve endings◦ Receptors

Peripheral nervous system

Ganglia Ganglia are typically ovoid structures containing neuronal cell bodies and glial cells supported by connective tissue

A. Dorsal root ganglia/sensory ganglia/spinal ganglia B. Autonomic ganglia

Sensory ganglia

Unipolar cell bodiesreceive afferent impulses that go to the CNS associated with both cranial nerves (cranial ganglia) and the dorsal root of the spinal nerves (spinal ganglia) The large neuronal cell bodies of ganglia are associated with thin, sheet-like extensions of small glial cells called satellite cells

Autonomic ganglia

◦ Sympathetic ganglia◦ Multipolar cell bodies◦ Nuclei eccentric + lipofuchsin granule◦ Less satelite cells

◦ Parasympathetic ganglia◦ Near effector organ

GANGLION CELL

A sensory ganglion (G) has a distinct connective tissue capsule (C) and internal framework continuous with the epineurium and other components of peripheral nerves,

except that no perineurium is present and there is no blood-nerve barrier function. Fascicles of nerve fibers (F) enter and leave these ganglia. X56. Luxol fast blue.

Spinal Ganglion

Higher magnification shows the small, rounded nuclei of glia cells called satellite cells (S) which produce thin, sheet-like cytoplasmic extensions that completely envelope each large neuronal perikaryon, some containing lipofuscin (L). X400. H&E

Sympathetic Ganglion

Immunostained satellite cells form thin sheets (S) surrounding neuronal cell bodies (N). Like the effect of Schwann cells on axons, satellite glial cells insulate, nourish, and regulate the microenvironment of the neuronal cell bodies. X1000. Rhodamine red-labeled antibody against glutamine synthetase

Parasympathetic Ganglion

Nerve fiber & supporting tissue

Nerve fiber◦ Bundles of myelinated & unmyelinated axon

Supporting tissue◦ Epineurium

◦ outer sheath of fibrocollageneous tissue

◦ Perineurium◦ surrounds groups of axons and endoneurium to form a small

bundles (fascicles)

◦ Endoneurium◦ surrounds individual axons and their associated Schwann cells as

well as capillary blood vessels

• Groups of fibers are bound together into bundles (fascicles) by a perineurium

• All the fascicles of a nerve are enclosed by a epineurium

• Each axon is surrounded by an endoneurium

Nerve Sheath

Nerve fibers

Classification of receptors

Structure and location of sensory receptors in the skin and subcutaneous layer

Receptors

MEISSNER’S CORPUSCLE

Mechanoreceptor Capsule (+) Lamellae of fibroblast & Schwann cell

Dermal papilla

MERKEL’S CORPUSCLE

Mechanoreceptor Capsule (-) Merkel cell & Merkel disks Epidermis

Receptors

PACCINIAN’S CORPUSCLE Mechanoreceptor : pressure

Capsule (+) Lamellae of fibroblast + schwann cell

Hipodermis, dermis, periosteum, joints capsule, visceral organs

FREE NERVE ENDINGS

Nociceptor Capsule (-) Branches of unmyelinated nerve fiber

Dermis

Receptors

RUFFINIAN’S CORPUSCLE

Mechanoreceptor Capsule (-) Branches of unmyelinated nerve fiber

Dermis, hipodermis, joints capsule

KRAUSE’S ENDBULB

Mechanoreceptor Capsule (+) Bulb formed by intracapsular fluid

Genitals, conjunctiva, oral cavity, nasal cavity, peritoneum

Receptor

Pacinian corpuscles

Krausse endbulb

Two types of proprioceptors : a muscle spindle and a tendon

organ

In muscle spindles, which monitor changes in skeletal muscle length, sensory nerve endings wrap around the central portion of intrafusal muscle fibers

In tendon organs, which monitor the force of muscle contraction, sensory nerve endings are activated by increasing tension on a tendon

The Golgi tendon organs = neurotendinous organs

Muscle spindle

Free nerve endings

Golgi Tendon Organ

THE SPECIAL SENSES

Sensory organs have special receptors that allow us to smell, taste, see, hear, and maintain equilibrium or balance

Information conveyed from these receptors to the central nervous system is used to help maintain homeostasis

Thank you…………

K2 - Histology of Nervous System

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