ANATOMY OF THE NERVOUS SYSTEM�

Functions of the nervous system

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• 1. Initiate and/or regulate movement of body parts

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• 2. Regulate secretions from glands

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• 3. Gather information about the external environment and the internal environment of the body
• using senses (sight, hearing, touch, balance, taste) and mechanisms to detect pain, temperature, pressure, and certain chemicals, such as carbon dioxide, hydrogen, and oxygen
• 4. Maintain an appropriate state of consciousness

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• 5. Stimulate thirst, hunger, fear, rage, and sexual behaviors appropriate for survival

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• The entire nervous system can be divided into two parts:

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1. Central nervous system (CNS)

• includes the brain and spinal cord

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2. Peripheral nervous system (PNS), which consists of:

• Cranial nerves
• Spinal nerves

1. Sensory (Afferent) Nerves
• gather information about the external and internal environments and relay this information to the CNS.
• The specialized organs or cells that detect specific stimuli are sensory receptors.
1. CNS interprets information arriving via the PNS, integrates that information, and initiate
• appropriate movement of body parts
• glandular secretion
• behavior response.

2- Motor Efferent Nerve

• Communication between the CNS and muscles and accomplished via nerves of the PNS

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In the PNS:

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• the which integrates activity of visceral structures
• smooth muscle
• cardiac muscle
• glands

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• The ANS has elements in both the central and peripheral nervous systems, and have both sensory and motor components.

Autonomic nervous system (ANS)

Microscopic Neuroanatomy

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• The individual nerve cell is called a neuron.

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• Each neuronal cell body gives rise to one or more nerve processes and cytoplasmic extensions of the cell.

Microscopic Neuroanatomy

• Dendrites if they nerve processes transmit electrical signals toward the cell bodies

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• axons conduct electrical signals away from the cell bodies.

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• The junction between the axon of one neuron with another neuron or target cell is the synapse.

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• The neuron belonging to the axon is the presynaptic neuron,
• The one receiving information from the axon is the postsynaptic neuron.

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• A synapse may be between the axon of one neuron and the cell body, dendrites, and/or axon of the postsynaptic neuron.

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• Neurons may be classified morphologically according to their number of nerve processes:
• Unipolar neurons have one process
• Bipolar neurons have one dendrite and one axon
• Multipolar neurons have a number of dendrites in addition to their single axon.

• Nervous tissue consists not only of neurons but also of supportive cells.
• In the CNS, these supportive cells are the neuroglia, comprising a variety of glial cells
• while most of the supporting tissue of the PNS is ordinary white fibrous connective tissue.

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• Groups of nerve cell bodies within the CNS are generally called nuclei, while groups of nerve cell bodies in the PNS are called ganglia.
• In general terms:
• Aggregates of neuronal cell bodies form the gray matter of the CNS
• Regions characterized primarily by tracts are white matter.

Development of CNS�

• Shortly after gastrulation, ectodermal cells on the dorsum just cranial to the primitive streak begin to proliferate and differentiate into a neural plate.

• The neural plate proliferates faster along its lateral margins than on the midline, creating the neural groove

Development of CNS�

• The edges of which (the neural folds) ultimately meet dorsally to form the neural tube.

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• The entire CNS is formed from the cells of the neural tube.

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• The lumen of the neural tube persists in the adult as the central canal of the spinal cord and as the ventricles of the brain.

• Development of the spinal cord continues by an increase in the thickness of the wall of the neural tube.

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• As cells divide and differentiate, three concentric layers of the neural tube emerge:
• an inner (ventricular zone)
• a middle (intermediate zone)
• a superficial (marginal zone)

• The thin ventricular zone of cells (also called ependymal zone) surrounds the lumen of the neural tube and is the site of mitosis of neuronal and glial precursors in the developing nervous system.

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• It will ultimately form the ependyma of the central canal of the spinal cord and of the ventricles of the brain.

• As cells are born in the germinal layer, they migrate outward to form the intermediate zone (also called mantle zone).
• The intermediate zone comprises neurons and neuroglia and becomes the gray matter near the center of the cord.

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• The dorsal parts of the intermediate zone develop into the dorsal horns.

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- The ventral intermediate zone becomes the ventral horns

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• The marginal zone, which is most superficial, consists of nerve processes that make up the white matter of the spinal cord.

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• The spinal cord white matter is divided into dorsal, lateral, and ventral funiculi, which are delimited by the dorsal and ventral horns of gray matter.

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• Development of the brain:

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• The first gross subdivisions of the brain create the three-vesicle stage.

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• These subdivisions, which consist of three dilations of the presumptive brain, are
• prosencephalon (forebrain)
• mesencephalon (midbrain)
• rhombencephalon (hindbrain)

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• In the five-vesicle stage of development
• the prosencephalon further subdivides to form the telencephalon (future cerebrum) and the diencephalons

• the rhombencephalons divides into the Metencephalon (future pons and cerebellum) and the myelencephalon (future medulla oblongata).

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• The mesencephalon does not subdivide.

�Brain �

• The gross subdivisions of the adult brain includes:
• cerebrum
• cerebellum
• brainstem.
• The cerebrum develops from the embryonic Telencephalon.
• The components of the brainstem are include:
• diencephalon
• midbrain
• pons
• medulla oblongata

• Cerebrum
• Comprises of two cerebral hemispheres, including the cerebral cortex, the basal nuclei

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• The surface area of the cerebrum in domestic mammals is increased by numerous foldings to form convex ridges, called gyri (singular gyrus), which are separated by furrows called fissures or sulci.

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• Cerebrum

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• A particularly prominent fissure, the longitudinal fissure, lies on the median plane and separates the cerebrum into its right and left hemispheres.

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• Deep to the cerebral cortex are aggregates of subcortical gray matter called the basal nuclei

Diencephalon

• Is a derivative of the prosencephalon.
• thalamus
• epithalamus
• hypothalamus
• the third ventricle is included in the diencephalon.
• The thalamus is an important relay center for nerve fibers connecting the cerebral hemispheres to the brainstem and spinal cord.

Diencephalon

• Epithalamus, dorsal to the thalamus, includes a number of structures, the pineal gland, which is an endocrine organ in mammals.
• Hypothalamus, ventral to the thalamus, surrounds the ventral part of the third ventricle and comprises many nuclei that function in autonomic activities and behavior.
• Attached to the ventral part of the hypothalamus is the hypophysis, or pituitary gland

Mesencephalon

• The mesencephalon (midbrain)
• lies between the diencephalon rostrally and the pons caudally.
• The two cerebral peduncles
• four colliculi are the most prominent features of the midbrain.

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Mesencephalon

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• The cerebral peduncles, also called crura cerebrii, are large bundles of nerve fibers connecting the spinal cord and brainstem to the cerebral hemispheres.
• These peduncles consist of both sensory and motor fiber tracts.

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• The colliculi are four small bumps (colliculus is Latin for little hill) on the dorsal side of the midbrain.
• They consist of right and left rostral colliculi and right and left caudal colliculi.
• The rostral colliculi coordinate certain visual reflexes,
• The caudal colliculi are relay nuclei for audition (hearing).

Metencephalon.

• The metencephalon includes
• the cerebellum dorsally and the pons ventrally.

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• The cerebellum features two lateral hemispheres and a median ridge called the vermis.

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• The surface of the cerebellum consists of many laminae called folia. In the cerebellum, like the cerebrum, the white matter is central, and the gray matter is peripheral in the cerebellar cortex.

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Metencephalon.

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• The cerebellum is critical to the accurate timing and execution of movements; it acts to smooth and coordinate muscle activity.

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• The pons is ventral to the cerebellum, and its surface possesses visible transverse fibers that form a bridge from one hemisphere of the cerebellum to the other.

Myelencephalon

• The myelencephalon becomes the medulla oblongata in the adult.

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• It is the cranial continuation of the spinal cord

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• The medulla oblongata (often simply called the medulla) contains a number of important autonomic centers and nuclei for cranial nerves.