Nervous System Notes PDF

 Ganglion Nucleus A group of neurons cell A group of neurons cell bodies outside the CNS bodies within the CNS & have the same function  Nerve Tract A group of nerve fibers A group of nerve fibers (axons...

 Ganglion Nucleus A group of neurons cell A group of neurons cell bodies outside the CNS bodies within the CNS & have the same function  Nerve Tract A group of nerve fibers A group of nerve fibers (axons) outside the CNS (axons) within the CNS Function Neuroglia forms the interstitial supporting tissue of CNS. Neuroglial cells are that protect and provide metabolic and mechanical support for neurons, and assist nerve cells to perform their functions. Their number is 10 times the number of neurons. Neuroglial cells undergo mitosis. They are present in both CNS and PNS. Neuroglial cells in CNS are: Neuroglial cells in PNS are: Astrocytes. Schwann cells. Oligodendrocytes. Satellite cells. Microglia. Ependymal cells.  Astrocytes are the largest neuroglial cells Shape: star-like appearance. It is exist as two distinct types: 1) Protoplasmic astrocytes in the gray matter of the CNS. 2) Fibrous astrocytes present mainly in the white matter of the CNS. It processes are extend between blood capillaries, neurons, nerve fibers and pia matter. They have fewer processes. They are present in both the gray and white matters. These cells are responsible for formation of myelin sheath around the axons of the neurons in CNS. Single oligodendrocyte may form myelin sheath segments on several axons. They are present in both white and grey matters. Microglia are phagocytic cells originate in the bone marrow and are part of mononuclear phagocytic system. They act as antigen-presenting cells and secrete cytokines. They are low columnar or cuboidal epithelial cells. In some regions these cells are ciliated. It is lining the ventricles of the brain and central canal of the spinal cord. Ependymal cells are modified in the ventricles of the brain to form the secretory epithelium of choroid plexus responsible for secreting cerebrospinal fluid (CSF). They are flattened cells that envelope the axons to form the Schwann sheath around them One Schwann cell can envelopes several axons by myelin sheath. In addition; It can wrapping one axon several times. They are small cells that form a thin layer surrounding the nerve cell bodies in the ganglia.  SYNAPSE Synapses are the sites of nerve impulses which transmitted from one neuron to another.  SYNAPSE Depending on the contact region between neurons, synapse, may be: Axodendritic synapse: between an axon and a dendrite. Axosomatic synapse: between an axon and a soma of nerve cell. Axoaxonic synapse: between two axons. Dendrodendritic synapse: between two dendrites.  Synapse Structure 1.Axon terminal: forms a bulbous expansion called terminal button. The cytoplasm of the terminal button contains mitochondria, and many synaptic vesicles filled with neurotransmitters. 2.Presynaptic membrane: It is thick and electron dense. It is the axolemma of the terminal button of stimulating axon. 3.Postsynaptic membrane: It is a thickened part of the plasma membrane of postsynaptic cell. It contains neurotransmitter receptors. 4.Synaptic cleft: It is a thin space (20-30 nm wide) present between presynaptic and postsynaptic membranes. Synapse Structure  Ganglia Are aggregation of neuron cell bodies, located outside CNS. nucleus Are aggregation of neurons cell bodies having the same function inside the CNS  Ganglia are ovoid structures composed of: nerve cell bodies, glial cell & supporting CT.  Types of Ganglia 1. Sensory ganglia 2. Autonomic (Sympathetic or parasympathetic) ganglia..  Sensory Ganglia House cell bodies of sensory neurons. Receive sensory impulses from different parts of the body and transmit it to CNS. Sensory Ganglia which are associated with: 1- cranial nerves (V, VII, IX, and X): are called cranial ganglia Or 2-spinal nerves (dorsal root); are called spinal (dorsal root ) ganglia.  Autonomic Ganglia Autonomic ganglia: (Sympathetic or parasympathetic) are associated with autonomic nervous system, or located within certain organs (wall of digestive system). Nerve cell bodies of autonomic ganglia are motor in function  Autonomic Ganglia Preganglionic fibers (myelinated) synapse with the ganglion cells whose axons leave the ganglia to form the postganglionic fibers (unmyelinated).  Nerve Endings  Peripheral nerve terminals. Nerve Endings Receptors Effectors  Nerve Endings  Receptors: Terminals of dendrites (sensory endings), which receive stimuli or impulse from outside the body or from tissues and transmit it to CNS.  Effectors: Terminals of axons (motor endings), which transmit impulse from CNS. To skeletal or smooth muscles and glands.  Receptors Classification according to Site of Receptors for stimulation special sense Type of Histological stimulation structure  According to the site of stimulation:  Exteroceptors: for pain, touch and temperature.  Receptors for deep sensation (Proprioceptors): Sense of pressure, vibration sense and tactile localization.  Receptors for the viscera (Visceroceptors): They transmit autonomic sensation from the viscera to the C.N.S. According to the type of stimulation:  Mechanoreceptors: respond to touch stretch, vibrations & pressure  Thermoreceptors: respond to change in temperature.  Nociceptors: respond to pain. Receptors for special sense. According to the Histological Structure 1- Non-capsulated Mechanoreceptors 2- capsulated Mechanoreceptors  Non-Capsulated Mechanoreceptors Peritrichial Free nerve Nerve ending ending Merckl Disc  Non-Capsulated Mechanoreceptors 1- Free nerve endings  Sites: Epidermis of skin and cornea.  Structure: They are unmyelinated, lack Schwann cells, and are not covered by a connective tissue capsule. Free nerve endings  Non-Capsulated Mechanoreceptors 2- Peritrichial nerve endings (receptors around hair follicle):  Sites: They surround the bases and shafts of hair follicles.  Structure: They are unmyelinated, lack Schwann cells, and are not covered by a connective tissue capsule.  Non-Capsulated Mechanoreceptors 3- Merkel’s disks:  Sites: Epidermis of skin of the soles, palms and tips of fingers (Non-hairy skin)  Structure: these receptors are composed of an expanded unmyelinated nerve terminal associated with Merkel cells, these cells are specialized epithelial cells in the stratum basale of the skin epidermis. expanded unmyelinated nerve terminal Merkel’s disks  Capsulated Mechanoreceptors Pacinian Krause Golgi Corpuscle End Bulb Tendon Organs Messiner,s Ruffini Muscle Corpuscle Corpuscle Spindle Capsulated Mechanoreceptors 3- Ruffini corpuscles:  Sites: They are found in the dermis of the skin.  Structure: These large receptors are composed of branched, unmyelinated terminals interspersed with collagen fibers and surrounded by four to five layers of modified fibroblasts. The connective tissue capsule surrounding ` each of these receptors is anchored at ` each end, increasing their sensibility to ` stretching and pressure. ` ` ` ` `  Nerve Endings Nerve Endings Receptors Effectors  Effectors Effectors Visceral (cardiac & smooth M. + glands) Autonomic motor ending Secretary Ending Somatic (skeletal muscle) Motor End Plate  Effectors 1- Motor end plates: They are the ends of axons of anterior horn cells of spinal cord. They transmit motor impulses causing contraction of skeletal muscle fibers.  Effectors 2- Autonomic motor endings: These are the ends of autonomic motor fibers which cause contraction of smooth muscles.  Effectors 3-Secretory endings: They are the terminals of autonomic nerve fibers that causing secretion of the glands.  The cell bodies of first neurons (Preganglionic fibers) are located in the C.N.S nuclei and their axon terminals synapse with the cell bodies of the second neurons in the autonomic ganglia.  The cell bodies of second neuron (postganglionic fibers) are located in the autonomic ganglia that lie outside the C.N.S. and their axons leave the ganglia to reach the effectors organs. 2nd neuron 1st neuron 1- Sympathetic The origin of sympathetic system is in the thoracic and upper lumber segments of spinal cord (T1 to L2), so it is called thoraco-lumber division. 2- Parasympathetic  The origin of this system lies in the brain and sacral regions of spinal cord, so it is called cranio-sacral division.  The preganglionic fibers leave C.N.S. through four cranial nerves (3rd, 7th, 9th and 10th ) and 2nd, 3rd & 4th sacral spinal nerves.