Fundamentals of Canine Neuroanatomy and Neurophysiology

Etsuro E. Uemura

• Publisher: Wiley-Blackwell
• Year: 2015
• Print ISBN: 9781118771761
• eBook ISBN: 9781118771754
• Edition: 1
• Topic: Medicine
• Subtopic: Veterinary Medicine

Fundamentals of Canine Neuroanatomy and Neurophysiology introduces the fundamentals of veterinary neuroanatomy and neurophysiology, demonstrating structure and function as it relates to clinical applications with a highly visual approach.

• Offers a straightforward yet comprehensive introduction to structure and function of the nervous system
• Demonstrates the relevance of the basic principles to the clinical setting
• Illustrates concepts using line drawings, photographs, micrographs, and MRIs
• Includes access to a companion website with review questions and answers and the figures from the book at www.wiley.com/go/uemura/neuroanatomy

1
Developmental Anatomy

The brain and spinal cord are organized through a series of developmental events. They start as a thickened neural plate and then transform into a simple tubular structure, the neural tube. The cranial end of the tubular structure enlarges to become the brain, whereas the remaining neural tube develops into the spinal cord. As precursor cells of the neural tube proliferate and differentiate into neurons and neuroglia, they migrate to appropriate target locations. This process of proliferation, differentiation, and migration is crucial for further developmental events, including outgrowth of axons and formation of synapses. Any interference with such developmental processes risks congenital malformations, perinatal mortality, and postnatal morbidity.

Formation of the neural tube

1. What embryonic germ layer becomes the nervous tissue?
2. Explain how the neural ectoderm forms the neural tube.

The development of the nervous system, like all other organ systems, starts at fertilization. An oocyte swept from the ovary is transported in the uterine tube to be fertilized. A fertilized ovum undergoes repeated cell division (also called cleavage). The first cleavage of the ovum results in two blastomeres, and successive cell divisions of blastomeres produce a spherical ball of cells. The blastomeres start to rearrange and a fluid-filled cavity, the blastocele, is formed. The wall of the blastocyst is only a single cell in thickness, except the area where a cluster of cells, the inner cell mass, appears. The inner cell mass is destined to be concerned primarily with the formation of the embryonic body. Within the inner cell mass a cavity starts to develop, separating the amnion from the embryo-formative cells, the embryonic disc. The embryonic disc gives rise to the three germ layers (endoderm, mesoderm, ectoderm) that form all the tissue and organs of the embryo.

The dorsomedial area of the ectoderm differentiates to become the neural ectoderm (Fig. 1.1). As the embryo develops, the neural ectoderm separates from the remaining ectoderm. Initially, the neural ectoderm is a flat area made of a single cell layer. There are three developmental stages (neural plate, neural fold, and neural tube) that form a tubular primordium of the central nervous system (CNS) (Fig. 1.2). The neural ectoderm thickens to become the neural plate, which folds into a neural groove. As the neural fold continues to become thicker, the groove becomes narrower and the dorsal edges of the fold fuse and the neural fold becomes the neural tube. The rostral end of the neural tube becomes the brain and the remaining neural tube develops into the spinal cord.

Fig. 1.1 The neural plate develops from the neural ectoderm that occupies the central portion of the ectoderm.

Fig. 1.2 Development of the neural tube and neural crest from the ectoderm. (A) Transverse section of the embryonic disc. The neural plate is the thickened area of the ectoderm. (B) Invagination of the neural plate to form the neural fold. The neural crest appears at the dorsolateral edge of the neural fold. (C) Fusion of the dorsal edges of the neural fold forms the neural tube. (D) The neural crest gives rise to small aggregates of cells that start to migrate ventrally to become ganglia.

Neural plate

The neural ectoderm thickens to form a neural plate (Figs 1.1 and 1.2A). The first step in the formation of the brain and spinal cord is its transformation from a thickened neural plate into a tubular mass of cells.

Neural fold

The neural groove appears as a result of differential growth of the neural plate along the longitudinal axis of the embryo (Fig. 1.2B). The groove deepens and the elevated lateral margins of the neural plate form the neural fold. The neural folds, as they become more elevated, grow toward each other. The neural fold at the rostral end (also referred to as the cephalic end because the rostral neural fold develops into the brain) is much greater in size than it is further caudally. This results in the differentiation of the rostral neural fold into the brain and the remaining caudal portion into the spinal cord. At about the time the neural groove deepens, a cluster of cells appears and forms the neural crest at the area where the neural fold borders on the ectoderm. The neural crest detaches from the ectoderm to become ganglia of the cranial and spinal nerves. A cluster of cells associated with the cephalic end differentiates into the ganglia of the cranial nerves. Those cells associated with the remaining neural fold differentiate into the dorsal root ganglia and ganglia of the autonomic nervous system (ANS).

Neural tube

The neural tube results from fusion of the dorsal edges of the neural fold (Fig. 1.2C and D). Prior to the closure of the neural groove, the neural plate is continuous laterally with the ectoderm. When the two neural folds fuse with each other, the ectoderm also fuses to overlie the newly formed neural tube. The closure of the neural groove begins in the middle of the embryo and proceeds toward the two ends. However, progression of closure is more rapid towards the cephalic end than towards the caudal end (Fig. 1.3). As a result, three stages of neural development (i.e., the neural plate, fold, and tube) coexist simultaneously in different regions of the embryo. The cephalic end of the neural t...

Table of contents

• Cover
• Title Page
• Table of Contents
• Preface
• Abbreviations
• About the Companion Website
• 1 Developmental Anatomy
• 2 Structure and Function of Neurons and Neuroglia
• 3 Anatomy of the Canine Brain
• 4 Meninges and Ventricular System
• 5 Spinal Cord
• 6 Spinal Reflexes
• 7 Somatosensory System
• 8 Viscerosensory System
• 9 Brain Stem
• 10 Midbrain
• 11 Pons
• 12 Medulla Oblongata
• 13 Reticular Formation
• 14 Thalamus
• 15 Cerebrum
• 16 Motor System
• 17 Cerebellum
• 18 Vestibular System
• 19 Auditory System
• 20 Visual System
• 21 Hypothalamus
• 22 Autonomic Nervous System
• Self-Evaluation Answers
• Index
• End User License Agreement