Nervous system Nervous tissue is highly specialized to employ modifications in membrane electrical potentials to relay signals throughout the body. Neurons form intricate circuits that (1) relay sensory information from the internal and external environments; (2) integrate information among millions of neurons; and (3) transmit effector signals to muscles and glands.

Anatomical subdivisions of nervous tissue _ Central nervous system (CNS) _ Central nervous system (CNS) _ Brain _ Brain _ Spinal cord _ Spinal cord _ Peripheral nervous system (PNS) _ Peripheral nervous system (PNS) _ Nerves _ Nerves _ Ganglia (singular, ganglion) _ Ganglia (singular, ganglion)

Cells of Nervous Tissue ➢ Neurons ➢ Neurons _ Functional units of the nervous system; receive, process, store, and transmit information to and from other neurons, muscle cells, or glands _ Functional units of the nervous system; receive, process, store, and transmit information to and from other neurons, muscle cells, or glands Nervous Tissue Nervous Tissue _ Composed of a cell body, dendrites, axon and its terminal arborization, _ Composed of a cell body, dendrites, axon and its terminal arborization, and synapses and synapses _ Form complex and highly integrated circuits _ Form complex and highly integrated circuits ➢ Supportive cells ➢ Supportive cells _ Provide metabolic and structural support for neurons, insulation(myelin sheath), homeostasis, and phagocytic functions _ Provide metabolic and structural support for neurons, insulation(myelin sheath), homeostasis, and phagocytic functions _ Comprised of astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS; comprised of Schwann cells in the PNS _ Comprised of astrocytes, oligodendrocytes, microglia, and ependymal cells in the CNS; comprised of Schwann cells in the PNS

Structure of a “Typical” Neuron ➢ Cell body (soma, perikaryon) ➢ Cell body (soma, perikaryon) _ Nucleus _ Nucleus _ Large, spherical, usually centrally located in the soma _ Large, spherical, usually centrally located in the soma _ Highly euchromatic with a large, prominent nucleolus _ Highly euchromatic with a large, prominent nucleolus _ Cytoplasm _ Cytoplasm _ Well-developed cytoskeleton _ Well-developed cytoskeleton _ Intermediate filaments (neurofilaments). 8–10 nm in diameter _ Intermediate filaments (neurofilaments). 8–10 nm in diameter _ Microtubules. 18–20 nm in diameter _ Microtubules. 18–20 nm in diameter _ Abundant rough endoplasmic reticulum and polysomes (Nissl _ Abundant rough endoplasmic reticulum and polysomes (Nissl substance) substance) _ Well-developed Golgi apparatus _ Well-developed Golgi apparatus _ Numerous mitochondria _ Numerous mitochondria ➢ Dendrite(s) ➢ Dendrite(s) _ Usually multiple and highly branched at acute angles _ Usually multiple and highly branched at acute angles _ May possess spines to increase surface area for synaptic contact _ May possess spines to increase surface area for synaptic contact _ Collectively, form the majority of the receptive field of a neuron; _ Collectively, form the majority of the receptive field of a neuron; conduct impulses toward the cell body conduct impulses toward the cell body

Structure of a “Typical” Neuron _ Organelles _ Organelles _ Microtubules and neurofilaments _ Microtubules and neurofilaments _ Rough endoplasmic reticulum and polysomes _ Rough endoplasmic reticulum and polysomes _ Smooth endoplasmic reticulum _ Smooth endoplasmic reticulum _ Mitochondria _ Mitochondria ➢ Axon ➢ Axon _ Usually only one per neuron _ Usually only one per neuron _ Generally of smaller caliber and longer than dendrites _ Generally of smaller caliber and longer than dendrites _ Branches at right angles, fewer branches than dendrites _ Branches at right angles, fewer branches than dendrites _ Organelles _ Organelles _ Microtubules and neurofilaments _ Microtubules and neurofilaments _ Lacks rough endoplasmic reticulum and polysomes _ Lacks rough endoplasmic reticulum and polysomes _ Smooth endoplasmic reticulum _ Smooth endoplasmic reticulum _ Mitochondria _ Mitochondria _ Axon hillock. Region of the cell body where axon originates _ Axon hillock. Region of the cell body where axon originates _ Devoid of rough endoplasmic reticulum _ Devoid of rough endoplasmic reticulum _ Continuous with initial segment of the axon that is a highly electrically _ Continuous with initial segment of the axon that is a highly electrically excitable zone for initiation of nervous impulse excitable zone for initiation of nervous impulse _ Usually ensheathed by supporting cells _ Usually ensheathed by supporting cells _ Transmits impulses away from the cell body to _ Transmits impulses away from the cell body to _ Neurons _ Neurons _ Effector structures. Muscle and glands _ Effector structures. Muscle and glands _ Terminates in a swelling, the terminal bouton, which is the presynaptic _ Terminates in a swelling, the terminal bouton, which is the presynaptic element of a synapse element of a synapse

Type of Neurons by Shape and Function ➢ Multipolar neuron. Most numerous and structurally diverse type ➢ Multipolar neuron. Most numerous and structurally diverse type _ Efferent. Motor or integrative function _ Efferent. Motor or integrative function _ Found throughout the CNS and in autonomic ganglia in the PNS _ Found throughout the CNS and in autonomic ganglia in the PNS ➢ Pseudounipolar neuron ➢ Pseudounipolar neuron _ Afferent. Sensory function _ Afferent. Sensory function _ Found in selected areas of the CNS and in sensory ganglia of cranial nerves and spinal nerves (dorsal root ganglia) _ Found in selected areas of the CNS and in sensory ganglia of cranial nerves and spinal nerves (dorsal root ganglia) ➢ Bipolar neuron ➢ Bipolar neuron _ Afferent. Sensory function _ Afferent. Sensory function _ Found associated with organs of special sense (retina of the eye,olfactory epithelium, vestibular and cochlear ganglia of the innerear) _ Found associated with organs of special sense (retina of the eye,olfactory epithelium, vestibular and cochlear ganglia of the innerear)

Supporting cells of the CNS (neuroglial cells); outnumber neurons _ Astrocytes _ Astrocytes _ Stellate morphology _ Stellate morphology _ Types _ Types _ Fibrous astrocytes in white matter _ Fibrous astrocytes in white matter _ Protoplasmic astrocytes in gray matter _ Protoplasmic astrocytes in gray matter _ Functions _ Functions _ Physical support _ Physical support _ Transport nutrients _ Transport nutrients _ Maintain ionic homeostasis _ Maintain ionic homeostasis _ Take up neurotransmitters _ Take up neurotransmitters _ Form glial scars (gliosis) _ Form glial scars (gliosis) _ Oligodendrocytes _ Oligodendrocytes _ Present in white and gray matter _ Present in white and gray matter _ Interfascicular oligodendrocytes are located in the white matter ofthe CNS, where they produce the myelin sheath. _ Interfascicular oligodendrocytes are located in the white matter ofthe CNS, where they produce the myelin sheath. _ Ependymal cells. Line ventricles _ Ependymal cells. Line ventricles _ Microglia _ Microglia _ Not a true neuroglial cell; derived from mesoderm whereas neuroglial _ Not a true neuroglial cell; derived from mesoderm whereas neuroglial cells, as well as neurons, are derived from ectoderm cells, as well as neurons, are derived from ectoderm _ Highly phagocytic cells _ Highly phagocytic cells

Supporting cells of the PNS. Schwann cells. Schwann cells _ Satellite Schwann cells surround cell bodies in ganglia _ Satellite Schwann cells surround cell bodies in ganglia _ Ensheathing Schwann cells _ Ensheathing Schwann cells _ Surround unmyelinated axons. Numerous axons indent the Schwann cell cytoplasm and are ensheathed only by a singlewrapping of plasma membrane. _ Surround unmyelinated axons. Numerous axons indent the Schwann cell cytoplasm and are ensheathed only by a singlewrapping of plasma membrane. _ Produce the myelin sheath around axons _ Produce the myelin sheath around axons Myelin Sheath Myelin Sheath ➢ The myelin sheath is formed by the plasma membrane of supporting cells wrapping around the axon. The sheath consists of multilamellar, lipid-rich segments produced by Schwann cells in the PNS and oligodendrocytes in the CNS. ➢ The myelin sheath is formed by the plasma membrane of supporting cells wrapping around the axon. The sheath consists of multilamellar, lipid-rich segments produced by Schwann cells in the PNS and oligodendrocytes in the CNS.

Functions _ Increases speed of conduction (saltatory conduction) _ Increases speed of conduction (saltatory conduction) _ Insulates the axon _ Insulates the axon ➢ Similar structure in CNS and PNS with some differences in protein ➢ Similar structure in CNS and PNS with some differences in protein composition composition ➢ Organization ➢ Organization _ Internode. Single myelin segment _ Internode. Single myelin segment _ Paranode. Ends of each internode where they attach to the axon _ Paranode. Ends of each internode where they attach to the axon _ Node of Ranvier. Specialized region of the axon between myelin _ Node of Ranvier. Specialized region of the axon between myelin internodes where depolarization occurs internodes where depolarization occurs ➢ In the PNS, each Schwann cell associates with only one axon and ➢ In the PNS, each Schwann cell associates with only one axon and forms a single internode of myelin. forms a single internode of myelin. ➢ In the CNS, each oligodendrocyte associates with many (40– 50) axons ➢ In the CNS, each oligodendrocyte associates with many (40– 50) axons (i.e. each oligodendrocyte forms multiple internodes on differentaxons). (i.e. each oligodendrocyte forms multiple internodes on differentaxons). Connective Tissue Investments of Nervous Tissue Connective Tissue Investments of Nervous Tissue

➢ Peripheral nervous system _ Endoneurium. Delicate connective tissue surrounding Schwann _ Endoneurium. Delicate connective tissue surrounding Schwann cells; includes the basal lamina secreted by Schwann cells as well as reticular fibers cells; includes the basal lamina secreted by Schwann cells as well as reticular fibers _ Perineurium. Dense tissue surrounding groups of axons and their surrounding Schwann cells, forming fascicles; forms the bloodnerve barrier _ Perineurium. Dense tissue surrounding groups of axons and their surrounding Schwann cells, forming fascicles; forms the bloodnerve barrier _ Epineurium. Dense connective tissue surrounding fascicles and the entire nerve _ Epineurium. Dense connective tissue surrounding fascicles and the entire nerve Glial cells Glial cells Astrocyte, protoplasmic,Astrocyte, fibrous,Astrocyte nuclei,Astrocytic end feet,Microglial cell nuclei, Myelin sheath,Oligodendrocyte nuclei,Oligodendrocyte, satellite,Oligodendrocyte, interfascicular,Grey matter, Astrocyte, protoplasmic,Astrocyte, fibrous,Astrocyte nuclei,Astrocytic end feet,Microglial cell nuclei, Myelin sheath,Oligodendrocyte nuclei,Oligodendrocyte, satellite,Oligodendrocyte, interfascicular,Grey matter, Meninges,Arachnoid,Dura mater,Pia mater,Subarachnoid space,Subdural space Meninges,Arachnoid,Dura mater,Pia mater,Subarachnoid space,Subdural space

Neuron Types Bipolar neurons,Central axons,Peripheral axons,Cochlear branch of cranial nerve Bipolar neurons,Central axons,Peripheral axons,Cochlear branch of cranial nerve Multipolar neurons,Axon,Axon hillock,Cell body,Dendrite,Nissl substance Multipolar neurons,Axon,Axon hillock,Cell body,Dendrite,Nissl substance Nucleolus,Nucleus Nucleolus,Nucleus

Central nervous system _ Meninges _ Meninges _ Pia mater _ Pia mater _ Thin membrane lying directly on the surface of the brain andspinal cord _ Thin membrane lying directly on the surface of the brain andspinal cord _ Accompanies larger blood vessels into the brain and spinalcord _ Accompanies larger blood vessels into the brain and spinalcord _ Arachnoid membrane _ Arachnoid membrane _ Separated from pia mater by connective tissue trabeculae _ Separated from pia mater by connective tissue trabeculae _ Encloses the subarachnoid space, which contains blood vessels and the cerebrospinal fluid (CSF) produced by the cells of thechoroid plexus _ Encloses the subarachnoid space, which contains blood vessels and the cerebrospinal fluid (CSF) produced by the cells of thechoroid plexus _ Together with pia mater, constitute the leptomeninges; inflammation _ Together with pia mater, constitute the leptomeninges; inflammation of these membranes produces meningitis of these membranes produces meningitis

_ Dura mater _ Outermost of the meninges _ Outermost of the meninges _ Dense connective tissue that includes the periosteum of theskullStructures Identified in This SectionAutonomic ganglionPurkinje cell (neuron),Purkinje cell body,Purkinje cell dendrites,Dendritic spines,Pyramidal neuron,Apical endrites,Pseudounipolar neuronsAxons,Dorsal root ganglion,Myelin,Satellite Schwann cells,Peripheral nerveAdipose tissue,Axon,Basal lamina,Blood vessels,Connective tissue,Duct of sweat glands,Endoneurium,Epineurium,Microtubules,Muscle tissue,Myelin lamella,Myelin sheath,Nerve fascicle,Neurofilaments,Node of RanvierParanodal loops,Paranodal region,Perineurium,Schwann cell nucleusSchwann cell process,Unmyelinated axons,Receptors,Axon,Meissner’s corpuscle,Muscle spindle,Skeletal muscle fibers,Modified skeletal muscle fibers,Capsule,Sensory axon,Pacinian corpuscle,Perineurial cells,Spinal cord,Spinal nerve roots,Synapses,Motor end plate,Skeletal muscle,AxonsCNS synapse,Terminal bouton,Synaptic vesicles (Neurotransmitter,vesicles),Mitochondria, Synaptic cleft,Postsynaptic cell,Postsynaptic density,Dendrite Dendritic spine. _ Dense connective tissue that includes the periosteum of theskullStructures Identified in This SectionAutonomic ganglionPurkinje cell (neuron),Purkinje cell body,Purkinje cell dendrites,Dendritic spines,Pyramidal neuron,Apical endrites,Pseudounipolar neuronsAxons,Dorsal root ganglion,Myelin,Satellite Schwann cells,Peripheral nerveAdipose tissue,Axon,Basal lamina,Blood vessels,Connective tissue,Duct of sweat glands,Endoneurium,Epineurium,Microtubules,Muscle tissue,Myelin lamella,Myelin sheath,Nerve fascicle,Neurofilaments,Node of RanvierParanodal loops,Paranodal region,Perineurium,Schwann cell nucleusSchwann cell process,Unmyelinated axons,Receptors,Axon,Meissner’s corpuscle,Muscle spindle,Skeletal muscle fibers,Modified skeletal muscle fibers,Capsule,Sensory axon,Pacinian corpuscle,Perineurial cells,Spinal cord,Spinal nerve roots,Synapses,Motor end plate,Skeletal muscle,AxonsCNS synapse,Terminal bouton,Synaptic vesicles (Neurotransmitter,vesicles),Mitochondria, Synaptic cleft,Postsynaptic cell,Postsynaptic density,Dendrite Dendritic spine.