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Nervous System. Structures of the Nervous System. The structures that make up the nervous system include: Brain. Spinal cord. Cranial nerves and their branches. Spinal nerves and their branches. G anglia, enteric plexuses, and sensory receptors. Organization of the Nervous System.
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Structures of the Nervous System The structures that make up the nervous system include: • Brain. • Spinal cord. • Cranial nerves and their branches. • Spinal nerves and their branches. • Ganglia, enteric plexuses, and sensory receptors.
Organization of the Nervous System • Anatomical Organization: • CENTRAL NERVOUS SYSTEM: • The brain is enclosed and protected by the skull in the cranial cavity. • The spinal cord is enclosed and protected by the bones of the vertebral column in the vertebral canal. Function: The CNS processes many different kinds of incoming sensory information. It is also the source of thoughts , emotions, and memories. Most nerve impulses that stimulate muscles to contract and glands to secrete originate in the CNS.
Organization of the Nervous System 2. PERIPHERAL NERVOUS SYSTEM: composed of all the nervous structures outside the CNS, such as: • cranial nerves and their branches : Twelve pairs (right and left) of cranial nerves, numbered I through XII. • spinal nerves and their branches : Thirty-one pairs of spinal nerves emerge from the spinal cord, each serving a specific region on the right or left side of the body. • ganglia: are small masses of nervous tissue, consisting primarily of neuron cell bodies, that are located outside the brain and spinal cord. • enteric plexuses: extensive networks of neurons In the walls of organs of the gastrointestinal tract. • sensory receptors: are structures that monitor changes in the internal and external environment
HISTOLOGY OFNERVOUS TISSUE • nervous tissue is comprised of two types of cells neurons and neuroglia. • Neurons (nerve cells):cells possess the ability to respond to a stimulus and convert it into a nerve impulse. • Parts of a Neuron: • Cell Body: contains a nucleus surrounded by cytoplasm. Its cytoplasm includes typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex. Neuronal cell bodies also contain prominent clusters of rough endoplasmic reticulum, termed Nisslbodies. • Nerve Fibers: • Dendrites : are the receiving portions of a neuron. They usually are short, tapering, and highly branched. • Axon: isalong, thin, cylindrical projection that carries nerve impulses toward another neuron, a muscle fiber, or a gland cell. An axon is often joins the cell body at a cone-shaped elevation called the axon hillock. The cytoplasm of an axon, called axoplasm , is surrounded by a plasma membrane known as the axolemma.
HISTOLOGY OFNERVOUS TISSUE 2. Neuroglia: neuroglia are smaller than neurons, they are much more numerous. In contrast to neurons, glia do not generate or propagate nerve impulses, and they have the ability to multiply and divide in the mature nervous system. • astrocytes, oligodendrocytes, microglia, and ependymal cells—are found only in the CNS. • Schwann cells and satellite cells—are present in the PNS.
HISTOLOGY OFNERVOUS TISSUE • Structural classification of neurons: • Multipolar neurons usually have several dendrites and one axon. • Bipolar neurons have one main dendrite and one axon. • Unipolar or pseudounipolarneurons have a single process that divides into two branches a short distance from the cell body. Both branches have the characteristic structure and function of an axon.
Gray and White Matter • The white matter is aggregations of myelinated and unmyelinatedaxons of many neurons. • The gray matter of the nervous system contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. • In the spinal cord, the white matter surrounds an inner core of gray matter shaped like a butterfly or the letter H. • in the brain, a thin shell of gray matter covers the surface of the largest portions of the brain, the cerebrum and cerebellum.
SPINAL CORD • Protective Structures: • Vertebral Column. • Meninges: are three protective, connective tissue coverings that encircle the spinal cord and brain. From superficial to deep they are: • duramater; (2) arachnoid mater; and (3) pia mater. • Between the arachnoid mater and piamater is a space, the subarachnoid space, which contains the shock-absorbing cerebrospinal fluid.
SPINAL CORD External Anatomy of the Spinal Cord: • In adults, it extends from the medulla oblongata (the most inferior part of the brain) to the superior border of the second lumbar vertebra. • In newborn infants, the spinal cord extends to the third or fourth lumbar vertebra. • two enlargements can be seen. The superior enlargement, the cervical enlargement, extends from the fourth cervical vertebra (C4) to the first thoracic vertebra (T1). Nerves to and from the upper limbs arise from the cervical enlargement. The inferior enlargement, called the lumbar enlargement, extends from the ninth to the twelfth thoracic vertebra (T9–T12). Nerves to and from the lower limbs arise from the lumbar enlargement. • The spinal cord terminates as a tapering, conical structure called the conusmedullaris. The conusmedullaris ends at the level of the intervertebral disc between the first and second lumbar vertebrae (L1–L2) in adults. • Arising from the conusmedullaris is the filumterminale, an extension of the pia mater that extends inferiorly and fuses with the arachnoid mater and dura mater to anchor the spinal cord to the coccyx. • nerves that arise from the lumbar, sacral, and coccygeal regions of the spinal cord do not leave the vertebral column at the same level they exit the cord. The roots of these lower spinal nerves angle inferiorly alongside the filumterminalein the vertebral canal like wisps of hair. The roots of these nerves are collectively named the caudaequina
SPINAL CORD • Internal Anatomy of the Spinal Cord: • A transverse section of the spinal cord is characterized by a central letter H or butterfly-shaped gray matter region that is surrounded by whit matter. • The anterior median fissure is a wide groove on the anterior (ventral) side. • The posterior median sulcus is a narrow groove on the posterior (dorsal) side. • The gray commissure forms the crossbar of the H. • In the center of the gray commissure is a small space called the central canal; it extends the entire length of the spinal cord and contains cerebrospinal fluid. • Anterior to the gray commissure is the anterior (ventral) white commissure, which connects the white matter of the right and left sides of the spinal cord. • The gray matter on each side of the spinal cord is subdivided into regions called horn (dorsal and ventral). • Between the anterior and posterior gray horns are the lateral gray horns, which are present only in the thoracic, upper lumbar, and sacral segments of the spinal cord.Thelateral horns contain the cell bodies of autonomic motor nuclei that regulate activity of smooth muscle, cardiac muscle, and glands. • The white matter, like the gray matter, is organized into regions. The anterior and posterior gray horns divide the white matter on each side into three broad areas called columns: (1) anterior (ventral) white columns, (2) posterior (dorsal) white columns, and (3) lateral white columns.
