Nervous System

• The neuron is the functional unit of the nervous system. It consists of a cell body and one or more processes. The long process is an axon, or nerve fiber.
• A nerve is a bundle of nerve fibers outside the central nervous system. A tract is a bundle of nerve fibers within the central nervous system.
• A nucleus is a group of similarly functioning cell bodies inside the central nervous system. Nuclei constitute the gray matter of the brain and cord.
• A ganglion is a group of cell bodies outside the central nervous system. Ganglia are sensory except those of the autonomic nervous system, which are motor.
• Neurotransmitters are amines that transmit nerve impulses across synapses. Neurosecretions are polypeptide hormones secreted by neurosecretory neurons.
• The cell bodies of motor neurons are inside the cord or brain. The one exception is those of postganglionic fibers of the autonomic nervous system, which are in autonomic ganglia.
• The cell bodies of first-order sensory neurons are in sensory ganglia on the pathway of cranial and spinal nerves with three major exceptions: the cell bodies of olfactory nerve fibers are in the olfactory epithelium, those of optic nerve fibers are in the retina, and those of proprioceptive fibers of cranial nerves are in the mesencephalon.
• Sensory ganglia arise chiefly from neural crests. A few in the head arise from ectodermal placodes.
• Olfactory neurons and the rods and cones of the retina are sometimes referred to as neurosensory cells.
• The embryonic neural tube caudal to the forebrain consists of alar and basal plates that are sensory and motor, respectively. The alar plate gives rise to second-order sensory neurons. The basal plate gives rise to motor neurons other than postganglionic.
• Neuroglia, found only in the central nervous system, consists of

  ependyma, oligodendroglia, microglia, and astroglia.
• Schwann cells migrate into the cranial and spinal nerves from the embryonic central nervous system and form a living membrane, or neurilemma, around each peripheral nerve fiber. The membrane secretes myelin of varying thicknesses onto the surface of the axons.
• The cord consists of nuclei surrounding the central canal, and of fiber tracts that ascend, descend, or cross the cord from one side to the other. It is enclosed within one or several meninges.
• A meninx primitiva surrounds the brain and cord of fishes. A dura

  mater and leptomeninx are present in lower tetrapods. The latter differentiates into a pia mater and arachnoid membrane in mammals and some birds.
• The spinal cord exhibits cervical and lumbar enlargements at the level of the paired appendages. When shorter than the column, the cord terminates in a filum terminale accompanied by a cauda equina. Fishes exhibit an unpaired neuroendocrine swelling of the cord, the urophysis at the base of the tail. It houses neurosecretory cells.
• Spinal nerves are metameric in origin and distribution. Most spinal

  nerves exhibit dorsal and ventral rootlets and roots, and dorsal, ventral, and communicating rami. Ventral rami often unite to form simple or complicated plexuses.
• Most spinal nerves exhibit sensory ganglia on their dorsal roots. The following cranial nerves also have sensory ganglia: V, VII, VIII, IX, and X.
• Nervous system is divided into two: anatomical and functional
• anatomical: central nervous system and peripheral nervous system
• Functional: sensation, integration, and response
• Three primary brain vesicles (develops 3-4 weeks): prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
• Prosencephalon develops into secondary vesicles: telencephalon and diencephalon
• The rhombencephalon develops into secondary vesicles: metencephalon and myelencephalon
• The telencephalon develops into the cerebrum
• the diencephalon develops into: thalamus, hypothalamus, and epithalamus
• the mesencephalon develops into midbrain
• the mesencephalon develops into: pons and cerebellum
• myelencephalon develops into medulla oblongata
• cerebrospinal fluid located in the ventricle
• brain ventricular system are open spaces within the hollow center of the neural tube. It is a network of fluid-filled cavities within the central nervous system.
• cerebrospinal fluid provides cushioning, nutrients, and waste removal for the brain, helping maintain a stable environment for optimal neural function.
• Choroid plexus is a region of the blood-brain barrier that produces cerebrospinal fluid along with the ependymal cells, and regulates the brains internal environment
• 4 regions of the brain: cerebrum, cerebellum, diencephalon, and the brainstem
• group of neuron cell bodies (e.g., gray matter) in CNS is called nucleus while ganglion in PNS
• bundle of axons (i.e., white matter) is called tract in CNS and nerve in PNS
• basal nuclei is associated with reward and cognition. Disorder associated is parkinsons disease
• Protective coverings of the brain and spinal cord are the meninges, which are connective tissues that cover & protect the CNS
• Meninges comsists of: dura mater, pia mater, and arachnoid
• dura mater, adjacent to the inner surface of the cranium
• pia mater, adjacent to the surface of the brain