BIO 2401 NERVOUS SYSTEM HISTOLOGY page 1 FUNDAMENTALS OF NERVOUS SYSTEM NERVOUS TISSUE FUNCTIONS Master control and communication center of the body 1 sensory input millions of sensory receptors monitor changes occurring inside and outside of the body 2 integration processes and interprets sensory input and decides what to do about it 3 motor output activates effector organs muscles glands to cause a response to the sensory input ORGANIZATION according to structure and function 1 central nervous system CNS brain and spinal cord integrating and command center interprets sensory input and dictates motor output 2 peripheral nervous system PNS outside CNS nerves that extend from the brain and cord has two divisions somatic and visceral A sensory or afferent division nerve fibers that convey impulses to CNS those conveying impulses from the skin skeletal muscles and joints are somatic afferent fibers those conveying impulses from visceral organs are visceral afferent fibers B motor or efferent division transmits impulses from the CNS to effector organs to activate a response also two divisions somatic and visceral 1 somatic nervous system somatic motor nerve fibers that conduct impulses from CNS to skeletal muscles voluntary system 2 autonomic nervous system visceral motor neurons regulate activity of smooth muscle glands cardiac muscle visceral sensory system input from glands blood vessels organs etc a sympathetic division mobilizes body systems to respond to fight or flight situations increase heart rate breathing shut off digestive processes shunt blood to the skeletal muscles b parasympathetic division conserves energy promotes vegetative functions like digestion slows breathing and heart HISTOLOGY Two types of nervous tissue 1 neuroglial cells supporting cells called glial cells 6 types 4 found in CNS 2 in PNS most have branching processes and a central cell body outnumber neurons CNS astrocytes microglia ependymal cells and oligodendrites PNS satellite cells and Schwann cells BIO 2401 NERVOUS SYSTEM HISTOLOGY page 2 2 neurons structural units of the nervous system large complex cells dendrites extend from cell body single axon emanating from axon hillock plasma membrane neurolemma is site of electrical activity GLIAL CELLS neuroglial A astrocytes star cells most abundant and versatile glial cell numerous radiating processes cover capillaries and cling to neurons to anchor them to the nutrient source control chemical environment by soaking up leaked potassium ions and recycling neurotransmitters guide growth of neural cells as well as migration B microglia small ovoid cells with thorny like processes may touch neurons to determine their health migrate toward injured neurons can transform into macrophages phagocytize invading microorganisms or neuronal debris C ependymal range in shape from squamous to columnar and can be ciliated line central cavity of brain and spinal cord to form a semi permeable barrier between the cerebrospinal fluid and tissue fluid cilia help circulate cerebrospinal fluid D oligodendrocytes fewer branches than astrocytes line up along thick neron fibers in CNS wrap cytoplasmic extensions tightly around fibers produce myelin sheaths in CNS E Schwann cells neurolemmocytes wrap themselves around nerve fibers to form myelin sheath gaps between cells called nodes of Ranvier F satellite cells surround neuron cell bodies within ganglia function unknown NEURONS 1 characteristics extreme longevity life time of individual 100 years 2 amitotic loses the ability to divide only a few exceptions 3 have high metabolic rate need large amounts of oxygen and glucose 4 substances can move from cell body to axon terminal since the axon lacks Golgi bodies 5 materials can return to cell bodies for degradation and recycling BIO 2401 NERVOUS SYSTEM HISTOLOGY page 3 cell body soma cell body has transparent spherical nucleus with chromosomes lacks centrioles amitotic best developed ER of all cell types called Nissl bodies most are located in CNS if clustered called nuclei in CNS if clustered in PNS called ganglia but there are exceptions to this naming rule processes or fibers arm like extensions mostly in PNS but also found in CNS neurons called tracts in CNS called nerves in PNS 2 types dendrites and axons differs in structure and function of plasma membrane dendrites differ in sensory and motor neurons in motor neurons they are short and profusely branched close to cell body in sensory neurons are thorny appendages of bulbous ends called dendritic spines these neurons convey messages toward the cell body and are not impulses but graded potentials that decay with time and distance depending upon stimulus intensity axons 1 per neuron near soma is cone shaped axon hillock otherwise is narrow short long or absent conducting area has organelles collaterals rare branches that extend from axon at right angles emerge at nodes of Ranvier axon terminals multiple knob like endings with vesicles neurotransmitters neurotransmitters chemicals in vesicles are released into synaptic cleft MyeIin whitish fatty segmented sheath protects and electrically insulates fibers from each other increases speed of transmission 1 in the PNS Schwann cells wrap around axons in concentric layers have few carrier proteins so are good insulators neurilemma exposed part of Schwann cell plasma membrane includes nucleus and cytoplasm nodes of Ranvier gaps in sheath occurring at regular intervals occur between adjacent Schwann cells 2 in the CNS oligodendrocytes multiple flat processes that coil around 60 different axons at same time widely spaced nodes of Ranvier lack neurilemmas GRAY MATTER AND WHITE MATTER A gray matter nerve cell bodies and unmyelinated fibers nucleus clusters of cell bodies in CNS ganglion clusters of cell bodies in PNS lie along nerves BIO 2401 NERVOUS SYSTEM HISTOLOGY page 4 B white matter myelinated fibers that are bundled together are deep to gray matter responsible for communication among cerebral areas cortex and lower CNS centers tract bundles of nerve fibers in CNS nerve bundles of nerve fibers in PNS PROPERTIES of Neurons A irritability responsive to stimuli B conductivity electrical impulse generation and transmission is ALL or NONE CLASSIFICATION Of NEURONS 1 structural classification multipolar 3 or more processes numerous dendrites 1 axon most common type bipolar 2 processes axon and dendrite rare only in specialized sense organs unipolar 1 process that emerges from cell body and