# Nervous Tissue Histology

> Neuron structure with Nissl substance, axoplasmic transport, neuron types, and astrocytes, oligodendrocytes, microglia and Schwann cells for MBBS Anatomy.

- Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/nervous-tissue-histology
- Exam / course: MBBS · Subject: Anatomy
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Nervous Tissue Histology", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/nervous-tissue-histology

## Direct answer

Nervous tissue consists of excitable neurons and supporting neuroglia. A neuron has a cell body (perikaryon) containing Nissl substance, dendrites conducting towards the soma, and a single axon conducting away; neurons are multipolar, bipolar or (pseudo)unipolar. The glia outnumber neurons: astrocytes, oligodendrocytes, ependymal cells and microglia in the central nervous system, with Schwann and satellite cells in the peripheral; oligodendrocytes myelinate several central internodes while each Schwann cell wraps a single peripheral internode and permits regeneration.

## What you must remember

- **Perikaryon:** nucleus with prominent nucleolus, coarse Nissl substance (rough endoplasmic reticulum) absent from the axon hillock and axon, neurofibrils, and lipofuscin with age; Nissl disperses peripherally (chromatolysis) after axon injury.
- **Axoplasmic transport:** fast anterograde by kinesin carrying vesicles and transmitters; slow anterograde flow of cytoskeleton; fast retrograde by dynein returning debris — and carrying rabies and herpes viruses to the cell body.
- **Neuron types:** multipolar in brain, cord and autonomic ganglia; bipolar in retina, olfactory epithelium and vestibulocochlear ganglia; unipolar (pseudounipolar) in dorsal root and trigeminal ganglia with a T-shaped junction.
- **Synapse:** presynaptic terminal with vesicles, a cleft and a postsynaptic membrane; mostly chemical and commonly axo-dendritic or axo-somatic.
- **Astrocytes:** the largest glia, protoplasmic in grey and fibrous in white matter; perivascular feet help form the blood-brain barrier, glial fibrillary acidic protein is their marker, and they form the glial scar after injury.
- **Oligodendrocytes:** small, dark nuclei; one cell myelinates internodes of several axons — central myelin is the target in multiple sclerosis.
- **Microglia:** the smallest cells, of mesodermal monocyte origin — the brain's resident macrophages, activated after injury; ependyma lines the ventricles and the choroid plexus epithelium secretes cerebrospinal fluid; satellite cells capsule ganglion neurons.

## Common confusion

Nissl substance is absent from axon and axon hillock, which distinguishes dendrites from axons on a slide. The two myelinating cells are swapped at will: oligodendrocytes serve the central nervous system, many internodes each, with no neurilemma; Schwann cells serve peripheral axons, one internode each, with a neurilemma — the basis of peripheral nerve regeneration and central failure. Microglia alone are mesodermal, not neuroectodermal.

## Exam-focused takeaway

Histology practicals identify neurons, Nissl substance, myelinated fibres with nodes of Ranvier in a teased nerve, and glia on silver-stained sections. Theory questions ask for neuron classification, perikaryon ultrastructure, types and functions of neuroglia, and central versus peripheral myelin. In the viva, explain axoplasmic transport, chromatolysis and Wallerian degeneration.

## Frequently asked questions

### Where is Nissl substance found and where is it absent?

It fills the cell body and dendrites of neurons; it is absent from the axon hillock and axon — the key to telling them apart on a slide.

### Which cell myelinates peripheral axons?

The Schwann cell, one cell per internode, the outer lamella forming the neurilemma; gaps between internodes are the nodes of Ranvier, allowing saltatory conduction.

### What do astrocytes do?

They contribute perivascular feet to the blood-brain barrier, buffer potassium and transmitters, store glycogen and replace dead tissue with a glial scar; their marker is glial fibrillary acidic protein.

### How do microglia differ from other neuroglia?

They arise from mesodermal monocyte precursors rather than neuroectoderm and act as resident macrophages, enlarging and phagocytosing debris after injury.

### What are the types of axoplasmic transport?

Fast anterograde by kinesin, slow anterograde flow of cytoskeletal proteins, and fast retrograde by dynein — the route by which certain viruses reach the cell body.