Biol 3324 1nd Edition Lecture 5 Outline of Last LectureI. System reflex II. HormonesIII. Pituitary glandIV. HypothalamicOutline of Current Lecture II. Endocrine PathologiesIII. NeuronsIV. ionV. Graded potentialsCurrent LectureEndocrine PathologiesImbalance of hormonoes leads to endocrine pathologies.Three basic patterns: hormone excess,hormone deficiency,abnormal responsiveness---Hormone excess(hypersecretion) resulting from abnormal secretion(e.g.tumors or exogenous stimulus) or lack of upstream regulation– Hormone deficiency(hyposecretion) resulting from gland atrophy or abnormal tropic hormone secretion (tumor)– Abnormal responsiveness• Down-regulation – excessive hormone levels cause down-regulation of the receptor to diminish responsiveness• Abnormalities in the signal transduction pathway or in ligand-receptor mechanicsThese notes represent a detailed interpretation of the professor’s lecture. Grade Buddy is best Used as a supplement to your own notes, not as a substitute.The Nervous System• Network of billions+ nerve cells linked in a highly organized manner to from the control system of the body.• Nerve cells (neurons) carry electrical signals rapidly (and often over long distances) to relay messages from one side of the cell to the other– Most neurons release chemical signals (neurotransmitters) into ECF to signal between cells– Other use gap junctions to allow electrical signals to travel between cells• Glial cells provide support to the neurons – Do not participate in the direct transmission of electrical impulses– Outnumber neurons >10 to 1Organization of the Nervous system• Two major systems– Central Nervous System (CNS): Brain and spinal cord– Peripheral Nervous System (PNS): Nerve fibers carry information between the CNS & the rest of the body• Afferent division – info carried to the CNS• Efferent division – info sent from the CNS– Somatic nervous system: motor neurons that innervate skeletal muscles– Autonomic nervous system: neurons that innervate glands, smooth muscle, & cardiac muscle» Sympathetic» Parasympathetic• All of the divisions & subdivisions are ways to classify and distinguish between location, structure and function– The nervous system is an integrated systemThe Neuron: three “regions”• Cell body – contains the organelles• Dendrites – collect signals from the surrounding cells– Graded signals are produced in response to triggering events– Sparse Na+ gated channels• Axon – conducts the action potential away from the cell– Axon Hillock: where the axon leaves the cell• Concentration of Na+ gated channels• Site where AP are initiated by graded potentials (if of sufficient magnitude)– Axon terminal: release chemical messengers in response to AP to influence other cellsThree functional classes of neurons:• Afferent neurons– Receptor at the “receiving” end to generate an AP in response to a stimulus– Cell body is devoid of dendrites (located near the spinal cord)– Possesses a long peripheral axon (afferent fiber) that extends from the receptor to the cell body– Possesses a short central axon that extends from the cell body to the spinal cord– Lie primarily in the PNS• Interneurons– Lie within the CNS– 99% of neurons (~1 x 1011)– Two roles:• Lie between afferent & efferent neurons serving to integrate peripheral response to peripheral information• Least understood: responsible for the abstract phenomena associated with the mind• Efferent neurons– Lie primarily in the PNS– Cell bodies originate in the CNS– Axon extends from the cell body to the effector organGlial Cells• General functions– Do not conduct nerve impulses– Communicate to nerves & other glial cells via chemical messengers– Serve as connective tissue– Maintain the extracellular environment• Four types found in CNS– Astrocytes – physical and chemical support; forms BBB; acts a neural scar tissue– Oligodendrocytes – form myelin sheaths– Microglia – immune defense cell– Ependymal cells – lines central cavities of the CNS; produces ECF; neural stem cell• Two types found in PNS– Schwann cells – form myelin sheaths– Satellite cells – physical supportIon movements across a membrane creates electrical signals• Recall that all cells have a resting membrane potential– Determined primarily by K+ concentration gradient and cell’s resting permeability to K+, Na+, & Cl-• Changes in membrane permeability to these ions results in a change in the membrane potential– Net inward flow of positive ions (Na+) results in depolarization (less negative)– Net outward flow of positive ions (K+) results in hyperpolarization (more negative)• Very few molecules need to enter/exit the cell to create a 100 mV change in potential Ion permeability is dependent on gated channels states• Gated channels can be opened or closed in response to a particular stimulus• Types of gates:– Voltage-gated – Change in response to membrane potentials– Chemically-gated – Change in response to a chemical messenger with a membrane receptor closely associated– Mechanically-gated – Respond to stretching or other mechanical deformation• Different gated channels have different threshold levels (minimal activation stimulus)– Some channels that we call leak channels are actually voltage-gated channels that open in the range of the resting membrane potential• Different gated channels open and close and different speeds– In neurons, Na+ channels open fast, K+ channels open slowly but are stimulated atthe same voltage. Results in Na+ into the cell then K+ out of the cell• Closing a gated channel can result from repolarization of the membrane or an inactivation event (needs to be reset)Changes in membrane potential result in electrical signals• The flow of ions is dependent on the electrochemical gradient of the ion– K+ generally moves out of the cell– Na+, Cl-, Ca2+ generally moves into the cell• Two kinds of potential change– Graded potentials• Variable strength signals• Serve as short-distance signals• Signals diminish in strength as they travel through the cell• Can initiate an action potential in the integration region of the neuron– Action potentials• Very brief, large depolarizations• Serve as long-distance signals• Do not diminish in strength• Function as a rapid signal over long distancesGraded potentials• Local changes in