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Nervous System • • Only people have the ability to use language, exercise judgment, solve difficult problems, produce creative objects and ideas, and transmit abstract notions from one person to another neurobiologist: biologist who studies the nervous system neurologist: physician who specializes in disorders of the nervous system Central Nervous System • brain: principal organ; adult brains weighs around 3lb; receives messages from sensory organs, blood and other body fluids • spinal cord: thick bundle of nerve fibers located within spinal cavity; merges with brain stem at upper end where nerve fibers continue upward into the brain • 31 spinal nerves: pairs of nerves that branch out from the cord and extend out of spinal cavity; ten pairs continue past end of spinal cord and exit spinal cavity through gaps in lumbar vertebrae and sacrum • 12 cranial nerves: pairs of nerves that branch directly from the brain stem and transmit nerve signals to and from eyes, ears, mouth, face, scalp • spinal cord does not extend all the way down the spine but tapers just below first lumbar vertebra • meninges: layer of protective tissues covering spinal cord and brain; dura mater – arachnoid – pia mater • cerebrospinal fluid circulates through fibers of arachnoid; cushions brain • glial cells: support and insulate nerve tissue • neurons: actual nerve cells; long fibers branch out from cell bodies • cell body: contains nucleus and most of nerve cell's cytoplasm; found only in brain, spinal cord or in a ganglion (mass of cell bodies) • dendrite: branched extension of cell that receives nerve impulses from other neurons and conducts them toward cell body • axon: long extension which relays nerve impulses from the cell body to other neurons; in most sensory neurons dendrites bypass cell body and conduct directly to axon → spinal cord; nerve impulses travel in one direction from dendrites toward cell body to axon • gray matter: consists largely of cell bodies which lack white myelin; white matter composed of axons and glial cells • some ganglia grouped together to form a large nerve called a plexus; brachial plexus at back of neck and shoulder is congregation of nerve cells which help connect median nerve and other arm nerves; • nerve center: group of cell bodies in brain or spinal cord that help control body function • 1) sensory neurons: neurons that transmit information to CNS from senses as well as • • • • • pain signals 2) motor neurons: neurons that relay from CNS to other parts of body 3) interneurons: only in CNS; relay signals between neurons/groups of neurons blood-brain barrier: capillaries of CNS tightly sealed to prevent bacteria from entering brain and spinal cord; brain contains own wbc called microglia meningitis: infection of the meninges; more often affects children b/c blood-brain barrier not fully developed poliomyelitis (polio): virus enters motor neurons of spinal cord and destroys them; connecting skeletal muscles become paralyzed; Peripheral Nervous System • nerves branching from the brain and spinal cord and connecting the CNS to the extremities of the body; can be several feet long - sciatic nerve connects leg extremities with spinal cord in lower back • each of 31 pairs of spinal nerves supplies a particular body part; mixed nerves – contain both sensory and motor fibers • [Fig. 8.8 p.126] sensory nerve fibers located in ganglia outside spinal cord carry impulses from sense-receiving body parts TO brain/spinal cord connect to spinal cord through rear nerve root • motor nerve fibers found in gray matter of spinal cord carry impulses FROM CNS to muscles/organs connect to spinal cord through front nerve root autonomic nervous system: controls involuntary functions (heart, digestive system, glands, etc.) -sympathetic: respond's to body's needs during increased activity, emergency situations by causing heartbeat and breathing rates to increase, supplying more blood to body for quick response -parasympathetic: counteracts sympathetic division by blocking action of sympathetic fibers Nerve Structure • [Fig. 8.10 p.127] • median nerve: bundles of nerve fibers imbedded in connective tissues; axons within bundles imbedded among glial cells protected by myelin sheath; blood, lymph vessels, fatty tissue help nourish and protect nerve fibers • neurons rarely reproduce • Schwann cells: peripheral nerves only; produce layers of myelin sheathing around axons; myelinated axons transmit nerve impulses much faster than non-covered • • • • • • • multiple sclerosis (MS): body's immune system attacks glial cells; myelin sheaths deteriorate and are replaced by scar tissue which slows nerve impulses action potential [Fig 8.11 p.128]: wave of electrical activity in which a brief (+) charge sweeps through neuron and races down axon; propagated by fast-acting, voltagesensing ion gates that quickly open and close, allowing Na and K ions to briefly flow into and out of cell; after action potential passes, cell membrane's ion pumps restore cell's original ion balance to be ready in as little as 1/2000 second synapse: enclosed junction between axon of one neuron and dendrites or cell body of another; when action potential reaches synapse → neurotransmitter released into synapse → sensors in receiving neuron detect neurotransmitter → trigger neuron to fire some substances can inhibit transmission of nerve impulses -Novocaine (anesthetic) blocks nerve impulses in sensory nerves -botulinum B toxin inhibits impulse transmission in motor nerves Parkinson's disease: lack of neurotransmitter dopamine in the motor-control areas of brain caused by damage to a region of the midbrain that produces dopamine; affects patient's control of movement characterized by tremors and limb stiffness reflex action: quick, automatic response; simplest act of the nervous system reflex arc: short circuit allows nerve impulses to bypass brain Homework Section 8.1 (p.126) #1-6 Section 8.2 (p.129) #1-6 (#5 can be written as a flow chart)