Nervous Tissue- Syllabus (1)

Page 1: Nervous Tissue Learning Objectives

Learning Objectives

  1. Identify the major divisions of the nervous system: motor, sensory, autonomic.

  2. Describe cytological organization of nerve cells.

  3. Describe histological appearance of peripheral nerves and their coverings.

  4. Explain the appearance and function of myelination.

Vocabulary

  • Auerbach’s plexus

  • Myelin

  • Autonomic ganglia

  • Neurokeratin

  • Axon

  • Nissl substance

  • Axon hillock

  • Nodes of Ranvier

  • Dendrite

  • Perineurium

  • Endoneurium

  • Pseudounipolar

  • Enteric ganglia

  • Satellite cells

  • Epineurium

  • Schwann cells

  • Meissner's plexus

  • Sensory ganglia

  • Multipolar

  • Synapse

Textbook Chapters

  • Wheater's Functional Histology: Chapter 7 - Nervous Tissue

  • Junquiera's Basic Histology: Chapter 9 - Nerve Tissue & The Nervous System

Overview of Nervous System

  • Divided into central nervous system (CNS) and peripheral nervous system (PNS).

  • PNS is responsible for sensory and motor innervation, relaying information to CNS for interpretation.

Page 2: Overview of Peripheral Nervous System (PNS)

Structure of PNS

  • Composed of various neurons, supporting cells, and specialized connective tissues.

  • All peripheral nerves are mixed (contain sensory, motor, autonomic axons).

  • Myelin sheath: surrounds sensory and motor axons, facilitating fast conduction; autonomic axons are variably myelinated.

Sensory Nerves

  • Collect sensory data from somatic and visceral sources.

  • Afferent impulses travel toward spinal cord via dorsal roots.

  • Cell bodies located in dorsal root ganglia and are pseudounipolar.

  • No synapses in sensory ganglia, surrounded by satellite cells.

Motor Nerves

  • Control voluntary movements through stimulation of skeletal muscle.

  • Cell bodies in the ventral horn of the spinal cord; send efferent impulses.

  • Myelinated fibers provide fast conduction from spinal cord to target organs.

Page 3: Neuron Structure and Function

Structure of Motor Neurons

  • Large soma with round nucleus and well-developed organelles (Golgi, mitochondria).

  • Cytoplasm is basophilic (Nissl substance, extensive RER), absent in axon hillock.

  • Neurons primarily incapable of division, except olfactory neurons.

  • Dendrites receive impulses; axons transmit them to target organs or other neurons.

Autonomic Nerves

  • Control involuntary muscle and secretory activities (smooth/cardiac muscle).

  • Two-neuron system: preganglionic (myelinated) synapses with postganglionic (unmyelinated).

Page 4: Autonomic Nervous System (ANS)

Divisions of ANS

Sympathetic System

  • Preganglionic neuron in spinal cord with short fibers synapsing in sympathetic ganglia.

  • Long postganglionic fibers innervate smooth/cardiac muscle and sweat glands.

Parasympathetic System

  • Neurons originate from cranial and sacral areas with long preganglionic fibers.

  • Short postganglionic fibers synapse close to or within target organs.

Enteric Nervous System

  • Contains autonomic ganglia in gut walls (controls peristalsis/glandular secretion).

  • Composed of a complex network (100 million neurons).

Ganglia Types

  • Three types of ganglia: sensory, autonomic, and enteric.

Page 5: Sensory Ganglia

Sensory Ganglia Structure

  • Contain cell bodies of sensory neurons (pseudounipolar).

  • No synapses present in sensory ganglia.

  • Surrounded by satellite cells in a complete ring, visible with H&E stain.

Page 6: Autonomic and Enteric Ganglia

Autonomic Ganglia

  • Contain multipolar postganglionic neurons (second neuron chain).

  • Examples: sympathetic ganglia (paravertebral and prevertebral), parasympathetic ganglia associated with cranial nerves.

Enteric Ganglia

  • Specific to gut wall; highly interconnected network (plexus).

  • Includes myenteric plexus (Auerbach’s) and submucosal plexus (Meissner's).

Page 7: Enteric Plexuses

Morphology of Enteric Plexuses

  • Located between smooth muscle layers (circular and longitudinal) in gut wall.

Page 8: Synapses

Types of Synapses

  • Include axodendritic, axoaxonal, axosomatic, neuromuscular junctions, electrical.

Synapse Cycle

  1. Action potential travels to axon terminal.

  2. Depolarization induces neurotransmitter release into synaptic cleft.

  3. Neurotransmitter binds to postsynaptic membrane, causing depolarization.

  4. Remaining transmitter is degraded.

Page 9: Peripheral Nerve Structure

Connective Tissue Layers

  • Epineurium: outermost layer, dense irregular CT.

  • Perineurium: surrounds nerve fascicles.

  • Endoneurium: delicate CT around individual axons, external to myelin sheath.

Page 10: Peripheral Nerve Staining

Identifying Peripheral Nerves

  • Staining techniques reveal structure and arrangement of nerve fibers and connective tissue.

Page 11: Schwann Cells

Function of Schwann Cells

  • Derived from neural crest; wrap around peripheral axons (Schwann sheath).

  • Facilitate rapid conduction of action potentials through myelination.

  • Nodes of Ranvier enable saltatory conduction.

Page 12: Myelination and Regeneration

Myelination Details

  • Interruptions in myelin allow communication between Schwann cell and axon (Schmidt-Lanterman incisures).

  • Wallerian degeneration: nerve regeneration occurs in PNS; CNS develops a glial scar that prevents regeneration.