Untitled Quiz

Nervous Tissue Overview

• Nervous tissue comprises two main cell types: neurons and neuroglia.
• Neurons are the functional units of the nervous system, responsible for transmitting signals.
• Neuroglia (glial cells) provide support and protection to neurons.

Neuron Structure

• The neuron's structure involves a cell body (soma/perikaryon) and cell processes (neurites).
• The cell body contains the nucleus and cytoplasm, with specialized components like Nissl granules, neurofibrils, and specific pigments such as lipofuscin and melanin.
• Neurites include dendrites, receiving impulses, and axons, carrying impulses away from the cell body.

Neuron Classification

• Neurons are classified according to the number of processes extending from the cell body.
• Unipolar neurons have a single process that divides into two branches.
• Bipolar neurons have one axon and one dendrite.
• Multipolar neurons have one axon and many dendrites.
• Anaxonic neurons have numerous dendrites but lack a distinct axon.

Synapse

• Synapses are specialized junctions connecting neurons.
• Chemical synapses involve neurotransmitter release, creating a delay in signal transmission.
• Electrical synapses do not involve neurotransmitters, allowing rapid signal transmission through direct ion channels.

Chemical Synapse Structure

• Chemical synapses consist of a presynaptic side (neuron), a postsynaptic side (neuron or effector cell), and a synaptic cleft, the gap between the two sides.
• The presynaptic side contains synaptic vesicles with neurotransmitters.
• The postsynaptic side has receptors for neurotransmitters.

Synapse Classification

• Axodendritic: axon to dendrite
• Axosomatic: axon to cell body
• Axoaxonic: axon to axon

Peripheral Nervous System (PNS)

• The PNS comprises nerves, ganglia, and nerve endings.
• Ganglia are ovoid structures containing neuronal cell bodies and surrounding glial cells, encased in a connective tissue capsule.
• Spinal ganglia, and sympathetic ganglia are examples.

Peripheral Nerve Structure

• Peripheral nerves are bundles of nerve fibers held together by connective tissue.
• Fascicles, groups of fibers, are enveloped by perineurium.
• Individual nerve fibers are enclosed in endoneurium.
• The entire nerve is surrounded by epineurium.

Myelinated and Unmyelinated Nerve Fibers

• Myelinated axons are surrounded by a myelin sheath, a fatty insulating layer that speeds up signal transmission.
• Schwann cells in the PNS and oligodendrocytes in the CNS form the myelin sheath.
• Nodes of Ranvier are gaps in the myelin sheath, where signal transmission "jumps" between them, a process called saltatory conduction.

Myelin Sheath Formation

• Myelin sheath is formed through invagination of the axon into Schwann cell / oligodendrocyte.
• The subsequent rotation of the cell around the axon forms multiple layers of the myelin sheath.
• Each Schwann cell provides the myelin sheath for a short segment of the axon.

Ganglia: Types and Features

• Ganglia come in different types, each categorized by features like shape, size, arrangement of cells, presence of satellite cells, and the presence of a capsule.
• Typical features include CT capsules, blood vessels, cells, shaped and arranged differently, and numbers of satellite cells.