Exam Notes: Set Three
Exam Notes: Set Three Bio 1144
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This 5 page Class Notes was uploaded by Murry on Tuesday March 8, 2016. The Class Notes belongs to Bio 1144 at Mississippi State University taught by Thomas Holder in Spring 2015. Since its upload, it has received 24 views. For similar materials see Biology II in Biology at Mississippi State University.
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Date Created: 03/08/16
Exam 3 Notes: Set 3 The Nervous System • Closely tied with sensory system • Central Nervous System (CNS) - the brain and the spinal cord • Brain to spinal cord ratio: o Fish: 2:1 o Reptiles: 25:1 o Humans: 55:1 • Peripheral Nervous System (PNS) - all neurons and projections outside of the CNS • Invertebrates have a simple nervous system but the distinction between the CNS and PNS is difficult to distinguish. Some organisms don’t even have a brain. • Neurons – (nerve cells) structural and functional unit of the nervous system o Function: send and receive chemical and electrical signals throughout the body o All members of Kingdom Animalia (except sponges) have neurons; however, the number of neurons varies between size of animal and complexity of nervous system. o Structure: § Soma – the cell body with nucleus and organelles § Dendrites – extensions of plasma membrane that receive incoming signals § Axons – extensions of plasma membrane that send out signals • A coating surrounding the axon called the myelin sheath protects the “wiring” of the axon; signal travels faster & is more contained • Glial Cells – provide support functions for neurons; 1000x more numerous than neurons o Oligodendrocytes (CNS) – produce myelin sheath o Schwann Cells (PNS) – produce myelin sheath o Microglial Cells – remove cellular debris; the “clean up” cells o Astrocytes – involved with metabolic support; associated with nutrition for the neurons; also known as stem cells (can produce glial cells & neurons) o Radial Glial Cells – lay out the pathway for neuron migration during embryotic development; also known as stem cells (can produce glial cells & neurons) • 3 Types of Neurons: o Sensory Neurons – afferent; transmit impulses to the CNS o Motor Neurons – efferent; send signals away from CNS to elicit response; carry message from the CNS o Interneurons – interconnecting cells between other neurons o These 3 types differ in structure of cell body (see figure 41.3 in text) • Reflex Arc o Not a complete circular system o Reflex Arc responsible for involuntary acts o Environmental stimulus picked up by sensory receptors à message carried to CNS à might be little or no interpretation à motor neurons carry response back to effector site à causes a reflex o Examples: touching a hot surface; doctor striking the knee; stepping on a Lego • Electrical Properties of Nervous Tissue 1. Membrane Potential § The membrane is a gatekeeper § Only neurons and muscle cells generate electrical signals § Difference in charge between inside and outside of cells because of the membrane’s restriction of chemical movement § Cells considered to be polarized § Ion concentration differences inside and outside § Ions move through channels in membrane if the channel is open § Resting Membrane Potential – neurons are not sending signals; the “normal” condition (99% of time) • All cells exhibit membrane potential • Selectively permeable to cations and anions • Difference in charge and concentrations inside and outside: inside is more negative and the outside is more positive; causes cells to be polarized • Anions inside drawn to the cations on the outside edge • 3 Factors Contributing to Resting Membrane Potential 1. Sodium-Potassium Pump: ATP expended § 3 Na pumped out for every 2 K pumped in 2. Ion specific channels will allow passive ion movement § Membrane is more permeable to K § K channels most frequently open at resting potential (no energy spent) 3. More negative charged ions inside the cell (Polarity) • Electro-Chemical Gradient: o No net movement; opposing forces of electricity and chemical can cause near equilibrium o Ion movement of cations and anions o Chemical movement of K and Na o Imbalance created between inside and outside of membrane • Neuron Signaling o Involves a change of membrane potential at any given point (changes in degree of polarization) o Depolarization – reducing polarity; membrane becomes less negative to surrounding solution; gated channels for Na open and Na moves in, causing inside to be more positive o Hyperpolarization – increasing polarity; membrane becomes more negative to surrounding solutions; K moves out for the inside to be less positive o Gates open and close in response to voltage or chemical recognition § Voltage-gated – open/close in response to voltage charges § Ligand-gated – open/close in response to chemicals • Nerve Impulse o Frequency – the language of an impulse o The higher the frequency, the greater the excitation o In Resting Potential: § Imbalance between K and Na inside and outside cells § Charge imbalance (gradient) inside and outside cells § At rest, membrane selectively permeable to K; Na and Cl channels are closed until there is an impulse § 10x more Na outside than inside § 5x more Cl outside than inside § 30x more K inside than outside 2. Action Potential – rapid/brief change of nerve fiber; “electric potential” of impulse § Self-propagating – one it starts, it is continuous in one direction only § After passing, membrane returns to resting potential § At a given point, Na channels open and Na diffuses in § K diffuses out due to electrical gradient changes 3. Sodium Potassium Pump § A complex of proteins in membrane § Pump out Na and carries in K at ATP expenditure § 3Na : 2K § Impulse conduction rate: how fast is the impulse? § Conduction rate variable depending on organism and how complex the nervous system is • Sea anemones: 0.1m/s • Mammals: 120m/s • Invertebrates: speed directly related to diameter of axon • Vertebrates: speed related directly between axon diameter and layers of myelin sheath § Nodes of Ranvier – sections of myelin sheath § Saltatorial Conduction – every time a signal hits a junction, its speed picks up § Synapses – a gap between end of neuron to the next; gaps or junctions between neurons or effector site § Axon – myelin sheath has gaps; as impulse travels down the axon, it jumps these gaps § Types of Synapses • Electrical – ionic currents flows across the gap; FAST • Chemical – neurotransmitters (acetylcholine) carry “packages” § Pre synaptic neuron vs. Post synaptic neuron § Acetylcholine released (carrying impulse) across cleft to open channels § Binding of neurotransmitters changes the membrane potential and changes chemical concentration • Evolution of the Nervous System in Animals o Phylum Cnidaria (jellyfish) § Very simple neural organization § Have protoneurons which are simple, primitive cells § Nerve Net – impulses are not one way § Simplest nervous system of all animals o Phylum Platyhelminthes (flatworms) § 2 anterior ganglia – each has a network branching off of it § Weakly developed CNS and PNS; don’t have a brain or spinal cord § Mostly 1 way impulses o Phylum Annelida (segmented worms) § Motor and sensory neurons § Brain § Ventral nerve cord § Primitive CNS (impulses go in only 1 direction) o Phylum Mollusca (squids, clams, snails, etc.) § Squids and octopi have been studied a lot for being highly complex organism; have nervous system similar to fish; might have most advanced system of all non-chordata invertebrates § Everything else similar to segmented worms o Phylum Arthropoda (insects, crustaceans) § Similar to segmented worms and Mollusca (except squids & octopi) § Social insects (bees, ants, wasps, etc.) have well developed parts of the brain & elaborate communication system § Social behavior, learning, communication, division of labor indicates perhaps most complex system of non-chordata invertebrates • Vertebrate Nervous System o Brain + Spinal Cord = CNS (dorsal, hollow) o Spinal Cord – dorsal, hollow; protected within the vertebral column § Meninges – layers that surround and protect the spinal cord and brain • Dura mater – outer • Arachnoid – middle • Pia mater – inner § Cerebrospinal fluid – between each layer and in the hollow canal for more protection o Brain § Increased in size and complexity with vertebrate evolution § Changes in embryonic development (cerebrum) § Entire nervous system develops from Neural Fold in embryo § Changes in sections of the brain § 3 divisions of Vertebrate’s Brain • Hindbrain • Midbrain • Forebrain (most significant changes occur here) o Mammals have largest forebrain of any other group § Spinal cord supports the brain; surrounded by vertebral column § Medulla oblongata – continuation of spinal cord; associated with heart rate, breathing, & all metabolic activities; damage can be severe if not fatal § Midbrain – the top portion of brain stem; a relay and analysis center for senses like vision, hearing, and olfaction § Cerebellum – dorsal to midbrain; involved with movement, equilibrium, and balance; largest in birds and mammals § Thalamus – the middle relay station between the hindbrain and the forebrain § Pituitary gland – hormonal gland § Hypothalamus – below the thalamus; a small part that is the “housekeeping center” for everything having to do with homeostasis § Corpus callosum – thick band of nerve fibers connecting the left and right sides of the cerebrum; the thicker the band, the faster the messages can be sent back and forth; found only in mammals § Cerebrum – highest and largest portion of the brain; associated with thought process, problem solving, language, artistic and musical abilities, emotions, & mating behaviors
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