Nervous Tissue and Neurons

Nervous Tissue

• Dendrites contain Nissl bodies.
• Synapses transmit nerve impulses between neurons.
• Nissl bodies, present in the perikaryon and dendrites, are composed of ribosomes and rough endoplasmic reticulum.
• Nervous tissue is vascularised.
• Ganglia are clusters of neuron cell bodies outside the CNS.
• Motor neurons send impulses to effector organs.
• Sensory neurons conduct impulses to the CNS.

Glial Cells

• Protoplasmic astrocytes are found in gray matter of CNS.
• Schwann cells form myelin sheaths around axons in PNS.
• Glial cells provide metabolic and mechanical support to neurons.
• Ependymal cells line the ventricles of brain and central canal of spinal cord.
• Microglial cells are macrophages of CNS.
• Astrocytes regulate neuronal activity and metabolism.
• Astrocytes form pedicels (vascular feet).

Neurons

• Nissl bodies are located in the perikaryon and dendrites.
• Neurons are metabolically active cells.
• Most neurons have one axon and multiple dendrites.
• Multiple axons exist in multipolar neurons.

Ganglia

• Ganglia are comprised of neuron cell bodies and nerve fibers.
• Sensory ganglia are surrounded by a capsule.
• Multipolar neurons are found in autonomic ganglia.
• Pseudounipolar neurons are in sensory ganglia.

Unmyelinated Axons

• Schwann cells envelop multiple unmyelinated axons in PNS.
• Myelin sheaths don't wrap each axon in unmyelinated axons.
• Nodes of Ranvier are not present along unmyelinated nerve fibers.
• Schwann cells envelop just one axon in unmyelinated axons.

Epineurium

• Surrounds the entire nerve.
• Composed of dense irregular connective tissue.
• Contains blood vessels.

Neuroglia

• Satellite cells are located in ganglia.
• Oligodendrocytes are myelin-forming cells in the CNS.
• Ependymal cells line the central canal of spinal cord.
• Microglia are macrophages of CNS.
• Astrocytes are myelin-forming cells in the CNS.
• Astrocytes form pedicels (vascular feet).

Interneurons

• Can connect motor and sensory neurons.
• Are association neurons.
• Create the majority of neurons in the human CNS.
• Their axons are not always myelinated.

Neural Crest

• Molecules such as ephrin B1 and chondroitin sulfate proteoglycans are permissive for neural crest cell migration.
• Neural crest originates from mesenchyme.

Blood and Bone Marrow

• Plasma contains fibrinogen.
• Serum doesn't contain fibrinogen.
• Reticulocytes are immature red blood cells.
• Lymphocytes constitute 4–8% of circulating leukocytes.
• The biconcave shape of erythrocytes facilitates gas exchange.
• Leukocytes are the predominant cells of blood.
• Red blood cells can leave blood vessels by diapedesis.
• Megakaryocytes are large cells with polyploid nuclei.
• Megakaryocytes are part of mononuclear phagocyte system.

Hematopoietic Stem Cells

• All blood cells are derived from one hematopoietic stem cell.
• Stem cells have high potential for self-renewal.

Erythropoiesis

• Red blood cells develop from myeloid cells.
• Erythrocytes transport oxygen and carbon dioxide.
• Erythrocytes lack a nucleus.
• Erythrocytes have a biconcave shape.

Leukocytes

• Monocytes differentiate into macrophages.
• Monocytes constitute about 25-35% of leukocytes.
• Neutrophils are least numerous granulocytes.

Bone Marrow

• Yellow bone marrow is not found in adults.
• Red bone marrow is located in flat bones and vertebrae.

Lymphatic System

• The lymphatic system includes lymph nodes (with capsule), spleen (with capsule), and tonsils (without capsule).
• Lymph nodes are located in lymphatic vessels, filtering lymph.
• Some lymphatic organs are not encapsulated.

Thymus

• Belongs to central lymphoid organs.
• Doesn't produce immunoglobulins.

Lymph Nodes

• Lymph nodes are distributed along lymphatic vessels.
• They filter lymph, containing immune cells.
• Outer cortex contains lymph nodules.

Skin

• Epidermis is ectodermal in origin.
• Dermis is not of ectodermal origin.
• Keratinocytes are the primary cells in epidermis.
• Melanocytes produce melanin.
• Langerhans cells are antigen-presenting cells.
• Melanocytes reside in stratum basale of epidermis.
• Langerhans cells are found in stratum spinosum.

Respiratory System

• Trachea wall is comprised of mucosa, submucosa, and adventitia.
• Tracheal cartilage is C-shaped.
• Alveoli are lined with simple squamous epithelium.
• Type I pneumocytes make up most of the alveolar surface.
• Type II pneumocytes produce surfactant.

Trachea

• Trachea wall is composed of mucosa, submucosa, and adventitia.
• Tracheal cartilage is C-shaped.
• The open end of the cartilage rings is on its posterior part.
• The lamina propria contains elements of MALT.

Nasal Cavities

• The internal part of the nasal cavities are called nasal fossae.
• External portion of nasal cavities is called vestibule.
• Superior conchae are covered by olfactory epithelium.
• The nasal fossae communicate with paranasal sinuses.
• Mucous membrane of vestibule has vibrissae.

Alveolar Septa

• Alveolar septa have a dense network of capillaries.
• Alveolar septa contain elastic fibers and fibroblasts.

Clara Cells

• Located in bronchioles.
• Stem cells of bronchiolar exocrine cells.

Bronchus

• Contain cartilage plates in bronchial tree.
• Segmental bronchi are in number: 10 in R, 8 in L.
• Columnar cells with microvilli are called enterocytes or absorptive cells.

Ventilation Process

• The contraction of the diaphragm and intercostal muscles is a part of the ventilation process.
• Cilia movement of respiratory epithelium is also part of the process.

Lung Development

• Lung development begins in the 4th week of prenatal life. -The respiratory diverticulum is separated from the foregut by tracheoesophageal septum.