histology of the nervous system

cells in the neuron

• nucelus

• cytoplasm - contains chromatophilic substance (nissl substance)

• neuron proceses - dendrites and axon

neurone functions

• sensory neurones - transmit changes in body to brain (afferent)

• interneurones - lie between sensory and motor neurones, process, store and retrieve information

• motor neurones - efferent neurones that send signals to muscles and glands

types of neurones

• unipolar and pseudounipolar - body with single axon that divides into central and peripheral branches (peripheral - sensitive to environmental stimuli, central - conveys environmentally induced excitation into CNS)

• bipolar - have dendrites and axon, afferent neurones that convey sensory info to the CNS

• multipolar - many dendrites with a single axon, efferent motor neurones that convey signals from CNS to effectors

types of synapses

• axo-dendritic - axon communicates with a dendrite of another neuron. It is a form of neuron-to-neuron synaptic signalling

• axo-somatic - axon communicates with the cell body or soma of another neuron

• axo-axonic - when an axon communicates with another axon

• dendro-dendritic - where one dendrite communicates with another dendrite

describe neuroglia cells

• small cells with an ectodermal origin

• important role in neuronal development, activity, plasticity and recovery from injury

describe astrocytes (neuroglia- CNS)

• pale, largest among the glial nuclei, have fibrous and protoplasmic types

• fibrous - long, slender, branched, in the white matter

• protoplasmic - shorter, highly branched, in the grey matter

• astrocytes processes - end feed, glial limiting membrane and pial-glial membrane

• provide support to neurones, store glycogen and release glucose

• insulate synapses and release substances that modulate synapse sensitivity

• important in the immune system - act as antigen present cells to T-lymphocytes

describe the oligodendrocytes (neuroglia- CNS)

• small, spherical and densely staining nuclei

• few branches relative to other cells

• grey matter - perineuronal satellite cells, growth factor providers

• white matter - myelin sheaths around axons, biogensis and maintenance of myelin sheaths

describe the microglia (neuroglia- CNS)

• mesodermal origin

• small, elongated chromophilic nuclei

• synthesis and release trophic factors

• cytotoxic defence properties

• transform into macrophages

• important role in viral infection, autoimmunity and neurodegenerative disorders

describe pericytes (neuroglia - CNS)

• associated with CNS capillaries (part of BBB)

• contractile abilities

• phagocytic

describe ependymal cells (neuroglia - CNS)

• epithelial cells that line the ventricular cavities within the brain and central canal of the spinal cord

• secrete substances - spinal fluid

• located in brain ventricles

• cover surfaces of choroid plexus villi and produce cerebrospinal fluid by active secretion of sodium

describe tanycytes (neuroglia - CNS)

• modified ependymal cells, hypothalmic walls of third ventricle

• basal process - make contact with capillaries and neurones

• play a role in hypothalamic hormone release into hypothalamic pituitary portal system, act as sensors in feedback mechanisms and play a role in transfer of hypothalamic hormones from CSF to blood

what are ganglionic gliocytes

• satellite glial cells

what cells are involved with the neuroglia in the CNS

• astrocytes

• oligodendrocytes

• microglia

• pericytes

• ependymal

• tanycytes

what are neurolemmocytes (shwann cells - neuroglia - PNS)

• produce myelinate for the myelin sheath

• enclosed within the basal lamina

• can phagocytose in event of nerve damage

• create nodes of ranvier for saltatory conduction

• glial cell wrapped around an axon

what does the histological central nervous tissue include

• brain

• spinal cord

• optic nerve

• retina

• embryological origin

• white matter - collection of axons (tracts)

• grey matter - cell bodies located (bundles of cell bodies that are also called nuclei, also contain neurophil)

6 layers of the central nervous tissue

• molecular layer

• external granular layer - small interneurons

• external pyramidal layer - pyramidal (triangular) neurones

• internal granular layer - smaller satellite neurones

• internal pyramidal layer - medium/large neurones

• fusiform - spindle shaped neurones

layers of the cerebellum

• grey matter (cerebellum cortex)

• molecular layer

• purkinje cell layer - contains climbing fibres

• granular cell layer (adjacent to white matter) - contains mossy fibres

describe the thalamus

• deeper part of cerebrum

• no white or grey matter distinction

• relay of sensory information

describe the hippocampus

• part of the limbic system (emotional control)

• split into left and right

• two interlocking parts of grey matter - hippocampus proper and dentate gyrus (top part of s-shape is hippocampus proper, bottom is dentate gyrus)

• s-shape in transverse section

layers of the hippocampus

• external plexiform layer (hippocampus proper)

• stratum oriens (hippocampus proper)

• pyramidal layer (hippocampus proper)

• stratum lucidum (hippocampus proper)

• stratum radiatum/lacunosum

• molecular layer (dentate gyrus)

• granular layer (dentate gyrus)

• polymorphic layer (dentate gyrus)

describe the brainstem

• uniform grey matter (no white and grey matter distinction)

• fundamental to basal body activity, respiratory activity and consciouness

describe the spinal cord

• white matter is on outside

• grey matter is on inside and contains dorsal sensory horns (top) and ventral motor horns (bottom)

• middle canal contains ependymal cells

describe the meninges (more detailed)

• cover brain, spinal cord and optic nerve

• contain cerebrospinal fluid

• dura mater - thick and strong, thick collagen bundles and elastic fibres, inner surface lined by multiple layers of fibrocytes which arachnoid membrane adhere - little space

• spinal dura mater - surrounded by epidural space, fibres are orientated parallel to long axis of spine

• cranial dura mater - contains internal lamina (same as spinal dura mater) and external lamina (continuos with periosteum of cranial bone)

• arachnoid mater - outer layer of flattened fibrocytes, contain collagen fibre bundles, arachnoid villi penetrate walls of venous sinuses that expand to allow drainage of spinal fluid back into the blood when pressure increases

• pia mater - vascular layer, contain collagen fibres, elastic network, fibrocytes and lymphocytes, astrocyte processes involved

structure of meninges (less detailed)

• dura mater

• spinal dura mater

• cranial dura mater

• arachnoid mater (arachnoid villi)

• pia mater

describe the peripheral nervous tissue

• contain myelinated axon, nerve fibres, axon and myelin sheath

• afferent fibres - sensory

• efferent fibres - motor

• contain individual nerve fibre bundles

describe the peripheral nerves

• hundreds of axons, each with myelin sheath and all organised into fascicles enveloped by connective tissue

• endoneurium - fibrocytes and collagen fibres surrounding individual bundles of neurolemmocytes

• perineurium - fibrous tissue surrounding the nerve fascicle

• epineurium - fibrous tissue surrounding multiple fascicles

• contain blood vessels

ganglia role in peripheral nervous tissue

• neurone cell bodies

• spinal ganglia located in dorsal spinal roots and ganglia in cranial nerve roots are referred to as sensory ganglia - bodies from primary afferent neurones

• afferent neurones are unipolar except in sense organs

• autonomic ganglia - innervate visceral organs