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BSC 215 Week of 3/7

by: Regan Dougherty

BSC 215 Week of 3/7 BSC 215

Regan Dougherty
GPA 4.0

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Notes for the week of 3/7
Human Anatomy & Physiology 1
Jason Pienaar
Class Notes
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This 9 page Class Notes was uploaded by Regan Dougherty on Tuesday March 8, 2016. The Class Notes belongs to BSC 215 at University of Alabama - Tuscaloosa taught by Jason Pienaar in Spring 2016. Since its upload, it has received 24 views. For similar materials see Human Anatomy & Physiology 1 in Biology at University of Alabama - Tuscaloosa.


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Date Created: 03/08/16
Tuesday, March 8, 2016 BSC 215 Nervous Tissue - Nervous System Organs • Brain • Spinal cord • Nerves - Nerve - bundle of axons + blood vessels + surrounded by connective tissue • Anatomical Subdivisions - CNS (central nervous system) • brain and spinal cord - PNS (peripheral nervous system) • nerves outside of the CNS - Cranial nerves - originate in the brain • 12 pairs - Spinal nerves - branch out of the spinal cord • 31 pairs • Functional Subdivisions - function of CNS: filter and integrate sensory input and coordinate the appropriate responses - PNS • Sensory division - signals are sent to brain; afferent signals (going towards control center) - Somatic sensory division - carries signals from skin, bone, muscle, joints, and special sense organs (eyes, nose, ears, etc.) - Visceral sensory division - carries sensory signals from internal organs 1 Tuesday, March 8, 2016 • Motor division - signals are sent to skeletal muscles; efferent signals (going away from control center) - Somatic motor division - carries signals generated in the CNS to skeletal muscle cells - ANS (autonomic nervous system) - carries signals generated in the CNS to smooth and cardiac muscles and glands; you do not have conscious control over this • Sympathetic - prepares body for action • Parasympathetic - relaxes body; “rest and digest” - Practice: • Somatic sensory division sends an afferent signal to the CNS via spinal nerves. • CNS filters and integrates signals and coordinates appropriate response. An efferent signal is sent to effector organs via the somatic motor division. • - Nervous Tissue • Cells - Cell are responsible for the functions of nervous tissue. - 80% of nervous tissue is cells. • 10% of cells are neurons. - Neurons are broken down into: • dendrites (receive signals and send toward cell body) • cell body (houses nucleus and organelles) • axon (sends signal away from cell body) • 90% of cells are neuroglia (support cells). • ECM - 20% of nervous tissue is ground substance and glycoproteins. - Neuron Structure • There is only one axon, but axons can branch. 2 Tuesday, March 8, 2016 • Most neurons are amitotic (they do not divide). • Neurons = excitable cells • Cell Body - contains nucleus and maintains cytoplasm - produces proteins • Nissl bodies - dark staining areas of ribosomes and rough ER - numerous mitochondria - golgi apparatus - no centrioles (because most are amitotic) - Neurofibrils - intermediate filament cytoskeleton • Dendrites - numerous short, highly-branched processes - large surface area for receiving signals - generate local potentials, but not action potentials • Local potentials are a result of stimulation from other neurons or sensory receptors. • Axons - Only one axon leaves the cell body. - processes that can generate and conduct action potentials - Action potentials are turned into chemical signals and synaptic knobs. - Axolemma - axon plasma membrane - Axoplasm - cytoplasm of axon - Axons are often wrapped in myelin sheath (provides insulation that speeds up action potential). - Axon hillock - place where the axon meets the cell body • high concentration of sodium-gated ion channels 3 Tuesday, March 8, 2016 - This is the reason action potential is generated in axons and not dendrites. - Axon collateral - branch of an axon - Telodendria - lots of branching at the end of an axon • Synaptic knobs are found at the end of the telodendria. - Axonal Transport • Slow axonal transport - anterograde only - rate: 1-3 mm/day - What is transported? cytoskeletal and other proteins - It is slow because it is “stop and go.” • It stops, drops off stuff, continues, stops again, etc. • Fast axonal transport - anterograde and retrograde - rate: 200-400 mm/day - What is transported? vesicles containing substances (ex. neurotransmitters) and membrane bound organelles 4 Thursday, March 10, 2016 BSC 215 Lecture 16 Nervous Tissue - Neuron Classification • Multipolar - one axon with multiple dendrites - motor neurons, interneurons - most neurons in the CNS, motor neurons in the PNS • Bipolar - one axon and one dendrite - sensory neurons - special sense organs in the PNS • Pseudounipolar - one axon that branches into two axons, no dendrites - sensory neurons - sensory neurons in the PNS associated with pain, touch, and vibration sensations - Neuron Functional Grouping • The cell bodies of neurons in common signaling pathways tend to group together. - CNS: nuclei - PNS: ganglia • The axons of neurons in common signaling pathways tend to group together. - CNS: tracts - PNS: nerves - Neuroglia Functions: • - hold neurons together - maintain extracellular fluid - assist neural function 1 Thursday, March 10, 2016 - repair damaged tissue • 6 different types (4 types in CNS and 2 types in PNS) - CNS • astrocytes - anchor neurons and blood vessels in place, maintain extracellular environment, assist in blood-brain barrier formation, repair damaged tissue - various processes • oligodendrocytes - flattened end processes form myelin sheaths around some CNS axons • microglial cells - macrophage-like activity • ependymal cells - line brain ventricles, produce cerebrospinal fluid, circulate cerebra spinal fluid with cilia - PNS • Schwann cells - form myelin sheath • satellite cells - surround and support cell bodies - Myelin Sheaths - electrical insulators (multiple layers of phospholipid bilayers) • CNS - Oligodendrocytes reach out with numerous extensions that wrap around multiple axons. • The cells wrap from the outside in. • There is no neurolemma; the nucleus and organelles are in a centralized location outside of the wrapping. • Myelination begins after birth. • PNS - Schwann cells wrap around part of the axon. • The cells wrap from the inside out. • The outer layer forms a neurolemma, containing the nucleus and organelles. • Myelination begins in the early fetal period. 2 Thursday, March 10, 2016 • In some cases, one Schwann cell will surround multiple axons (the axons are bundled together). - This formation is somewhere between typical Schwann cell formation and the activity of oligodendrocytes. - This is very rare. - Nervous Tissue Regeneration • CNS - Astrocytes form scar tissue (this is not the same as tissue replacement). - Damaged neurons cannot be replaced. • PNS - Axon regeneration is possible as long as the cell body and part of the myelinated axon is present. - Neurons cannot undergo mitosis (they do not have centrioles). - How do you regenerate an axon? • 1. Wallerian degeneration - phagocytes digest components distal to the severance point • 2. Growth processes form. - Several proximal cell extensions sprout from the axon that is connected to the cell body. • 3. Regeneration tube forms. - Schwann cells and basal lamina form a regeneration tube. • 4. Regeneration tube directs growth. - The tube is stimulated to continue growing. • 5. Connection with the target cell is reestablished. - Schwann cells form myelin sheaths; muscle atrophy is halted. - When a pathologist performs an autopsy on a person who died of a brain injury, why does he or she usually observe a number of microglia? 3 Thursday, March 10, 2016 • Because there is a bunch of damaged tissue, so the microglia need to clean up that damaged nerve tissue - If someone suffers severe damage to a number of vertebral ganglia, are they likely to regain the functions the neurons involved used to serve? No, because the ganglia are the cell bodies in the PNS and the cell bodies cannot • regenerate. - Neural Electrophysiology • Ion channels - Leak Channels - you cannot control what goes through leak channels (always open) - Gated Channels • Ligand-gated - specific ligand causes the cannel to open Voltage-gated - change in voltage across the membrane opens the channel • • Mechanically-gated - mechanical deformation opens the channel • Resting Membrane Potential - Na+/K+ pump - 3 Na+ move out, 2 K+ move in; requires ATP • More positive ions move out than in; this contributes to the resting membrane potential (outside of the cell is more positive). - Leak channels • There are Na+ and K+ leak channels. - There are more K+ leak channels. K+ diffuses out of the cell, contributing to the greater positive charge on the outside of the cell. • Local Potential - Graded depolarization - gradual depolarization over time • Neurotransmitters open ligand-gated Na+ channels (Na+ enter the cell). • There is not a high concentration of ligand-gated Na+ channels (gradual). - Graded hyper-polarization - makes it harder to turn local potential to an action potential 4 Thursday, March 10, 2016 • Cl- enter the cell • You need to open more Na+ channels to counteract this (you need more neurotransmitters that will act as ligands). - Local potentials are caused by ligand-gated ion channels in dendrites and the cell body. • useful for short-distance signaling, not for long distance signaling • Nerve signaling is all about converting local potentials to action potentials. 5


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