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ENGL 1010 (7)

Nervous system notes (11).doc

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ENGL 1010
Laura Sterrett

• Nervous system- master controlling and communicating system of the body, uses electrical and chemical signals that cause almost immediate responses • Sensory input- gathered information from external sources • Integration- process by which nervous system processes and interprets sensory input • Motor output- response caused by integration by means of activating effector organs • Ex. Driving, see red light (sensory input), “red light means stop” (integration), and brake with foot (motor output) • Central nervous system- brain and spinal cord in dorsal body cavity, integrating and commands, interpret sensory input and dictate motor responses based on past experience, reflexes, and current conditions • Peripheral nervous system- consists of bundles of axons called nerves that extend from brain and spinal cord • Spinal nerves carry impulses to and from spinal cord • Cranial nerves- carry impulses to and from the brain • Sensory/afferent division of PNS- nerves conveying impulses toward CNS • Somatic afferent fibers- transmit impulses from sin, skeletal muscles, and joints • Visceral afferent fibers- transmit impulses from the visceral organs (in ventral body cavity) • Motor/efferent division of PNS- transmit impulses form the CNS to effector organs (muscles and glands), activate muscles to contract and glands to secrete, effect by bringing about a motor response • Somatic nervous system- motor division part that has somatic motor nerve fibers (axons), called voluntary nervous system, allows us to consciously control muscles • Autonomic nervous system- consists of visceral motor nerve fibers, regulate smooth muscles, cardiac muscles, and glands, involuntary nervous system • Sympathetic division of ANS- mobilizes body systems during activity • Parasympathetic division of ANS- conserves energy, promotes housekeeping functions during rest • Neuroglia/ glial cells- 4 types in CNS and two in PNS, smaller in size and darker nuclei, occur in much higher numbers • Astrocytes- CNS glial cells, (look like sea anemones with radiating arms), most abundant and versatile, support and anchor neurons to blood capillaries which supply nutrients, aid in exchanges between capillaries and neurons, guiding migration of young neurons, synapse formation, and in determining capillary permeability, control chemical environment around neurons by recapturing released neurotransmitters, can release calcium if connected to gap junctions, participate in info processing in the brain • Microglia- CNS glial cells, shaped like ovals with long thorny arms, monitor health of neurons, migrate toward injured neurons, transform into macrophages that kill microorganisms to protect neurons where immune system does not • Ependymal cells- CNS, squamous or columnar, line brain and spinal cord to form permeable barrier between cerebrospinal fluid and tissue fluid, beating cilia helps circulate cerebrospinal fluid cushioning brain and spinal cord • Oligodendrocytes- CNS, line thicker neuron fibers and wrap processes (arm-like extensions) around fibers to form myelin sheaths • Satellite cells- PNS, surround neuron cell bodies in PNS but function is unknown • Schwann cells- PNS, surround and form myelin sheaths around larger nerve fibers in PNS, similar to oligodendrocytes, vital to regeneration of damages peripheral nerve fibers • Neurons/nerve cells- conduct messages by nerve impulse, live long, amitotic (cannot divide after taking a position in body with few exceptions), high metabolic rate and require continuous oxygen and glucose, cell signaling occurs on the plasma membrane • Perikaryon/ soma- cell body of neuron, nucleolus surround by cytoplasm, 5-140 micrometers • Nissl bodies/ chromatophilic substance- protein and membrane making machinery in neuron, consists of clustered free ribosomes and rough ER • Neurofibrils- bundles of intermediate filaments for structure in neuron • Nuclei- cluster of cell bodies in the CNS • Ganglia- clusters of cell bodies that lie along nerves in PNS • Processes-arm like extensions from all neurons (CNS has bodies and processes whereas PNS is mostly just processes) • Tracts- bundles of processes in CNS • Nerves- bundles of processes in PNS • Dendrites- short branching extensions the receive input and channel the input toward the cell body in the form of graded potentials • Axon- single dendrite proceeding from the axon hillock near the cell body that generates and transmits an action potential, can be long, short, or even absent, one per neuron, heavily rely on support from cell body • Nerve fiber- long axon • Axon collaterals- branches of axons • Telodendria- terminal branches of axons, 10,000 or more per axon, have axon terminals at the end • Neurotransmitters- signaling chemicals stored in vesicles at axon terminals, released by action potentials to excite or inhibit neurons • Axolemma- axon plasma membrane • Anterograde movement0 movement toward axon terminals (i.e. membrane components, enzymes, and some neurotransmitters) • Retrograde movement- movement toward cell body, mostly to return things to be degraded or recycled • Myelin sheath- associated only with axons, protects and electrically insulates fibers to increase speed of transmission of nerve impulses, formed by Schwann cells, wraps around axon multiple times • Neurilemma- outer layer of Schwann cell/myelin sheath containing nucleus • Nodes of Ranvier/ neurofibril nodes- gaps between adjacent Schwann cells (1mm) • White matter- dense collections of myelinated fivers in the brain and spinal cord • Gray matter- nerve cell bodies and unmyelinated fivers • Multipolar neurons- 99% of neurons, major type in CNS w/3 or more processes • Bipolar neurons- two processes (axon and dendrite), specialized in retina and nose • Unipolar neurons- one single short process that divides T-like into proximal and distal branches, start as bipolar but the two processes fuse into one, found in ganglia in the PNS where they function as sensory neurons, act as axons • Sensory/ afferent neurons- transmit impulses from sensory receptors in skin/organs towards the CNS, mostly unipolar • Motor/efferent neurons- carry impulses away from the CNS to the effector organs, multipolar, cell bodies in the CNS • Interneurons- shuttle signals through CNS pathways where integration occurs, mostly in CNS, makeup 99% of neurons in body, mostly multipolar • Voltage- measure of potential energy generated by separated charge, volts, measured between two points and is called potential • Current- flow of electrical charge from one point to another • Resistance- hindrance to charge flow due to substances which the current must pass through, high resistance= insulator, low resistance= conductor • Ohm’s law current (I)= voltage (v)/resistance (r) • Chemically-gated / ligand-gated channels- open when appropriate chemical binds • Voltage-gated channels- open and close in response to changes in membrane potential • Mechanically gated channels- open in response to physical deformation of receptor • Leakage/ nongated channels- always open • Electrochemical gradient- ions diffuse passively from area of higher to lower concentration and move toward area of opposite electrical charge • Resting membrane potential- polarized difference between negative charge of cytoplasmic side of membrane relative to positive outside of the membrane • Cell cytosol contains low concentration of Na and high concentration of K than the extracellular fluid - • Extracellular fluid positive charges are balanced by Cl • A sodium potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients for sodium and potassium • Depolarization- reduction in membrane potential, inside of membrane becomes less negative • Hyperpolarization- when membrane potential increases and becomes more negative • Graded potential- short, localized changes in membrane potential, either depolarization or hyperpolarization, stronger stimulus= more voltage= current flows farther, caused by ion channels opening • Action potential- long distance, occur in neuron and muscle cells, depolarization followed by repolarization, don’t decrease in strength with distance unlike graded • Nerve impulse- action potential in a neuron generated in axon • For action potential to occur, sodium ion permeability must increase then impermeab
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