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Nervous System Chapter 45

Nervous System Chapter 45. Neurons, nerve impulses, synapses, CNS, PNS. Except sponges Reponse to stimuli Sensory receptors and motor effectors linked by nervous system Sensory neurons Motor neurons Interneurons. CNS. High degree of cephalization Brain is integrative power

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Nervous System Chapter 45

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  1. Nervous SystemChapter 45 Neurons, nerve impulses, synapses, CNS, PNS

  2. Except sponges • Reponse to stimuli • Sensory receptors and motor effectors linked by nervous system • Sensory neurons • Motor neurons • Interneurons

  3. CNS • High degree of cephalization • Brain is integrative power • Spinal cord integrates simple responses (reflex) and conveys info to brain • Both surrounded by cerbrospinal fluid • Shock absorber • Meninges

  4. PNS -- motor and sensory • Nerves = cablelike collections of axons • Ganglia = nerve aggregates outside CNS • Neurons that run from sensory receptors to CNS and from CNS to effectors • Effectors/motor division • Somatic = stimulate skeletal muscles • Autonomic = involuntary • Sympathetic and parasympathetic

  5. Cell structure • Cell body, dendrite, can have dendritic spines, axon

  6. Neuron support • Supported structurally and functionally • Supporting cells – neuroglia • Supply nutrients, remove waste, immune • Schwann and oligodendrocytes – myelin • Wrap around axon – CNS myelinated – white -- PNS bundled together – nerves Myelination interrrupted by space – nodes of Ranvier

  7. Signals – Membrane Potential • Neurons – generate and spread electrical potentials • Specialized membrane transport proteins • Potential difference – voltage • Extracellular = positive charge • Resting potential -70mV (inside of cell is negative) • Many macromolecules = too large to diffuse = fixed anions • Na+/K+ (two In for every 3 out), K+ leaks easier

  8. Graded Potentials • Impt = sudden temporary disruptions in response to stimuli • Gated ion channels (chemical or ligand) • Depolarization or hyperpolarization • Graded because amplitude depends on strength of stimulus • Summation (occur close and combine) • Threshold – level of depolarization needed to produce an action potential http://www.blackwellpublishing.com/matthews/channel.html

  9. Na+, K+ voltage gated channels open upon depolarization • Na+ in, K+ out, (Cl- in) • All-or-none action potential, up to +30mV • Separate events (Na+ will not reopen immed.) • Action potential is passive • Action potential does NOT travel, but stimulate along axon • http://www.blackwellpublishing.com/matthews/actionp.html

  10. Ending action potential is just as large as beginning • Saltatory conduction • Impulses jump • Velocity – diameter of axon, myelinated • Action potentials only at nodes of Ranvier

  11. Synapses • Junction of axon branches to dendrite • Sends action potential = presynaptic • Receives = postsynaptic • Electrical synapses – direct cytoplasmic connection via gap junction (invertebrates) • Chemical synapse – synaptic cleft – space • Presynaptic has swollen axon with synaptic vessels with neurotransmitters • Ca++ into axon which allows fusion of vessel membrane with plasma membrane, exocytosis • Neurotransmitter binds with ligand gated receptor proteins on postsynaptic

  12. Some neurotransmitters • Acetylcholine – ACh, crosses synapse of motor neuron and muscle fiber • Ligand-gated channels = Na+, K+, depolarize = excitatory postsynaptic potential • Can induce voltage-gated channels for action potential • Need to be removed for relaxation • Acetylcholinesterase – cleave into fragments • Excitatory vs. inhibitory • threshold harder to attain (Cl- in)

  13. Dopamine (body mvmts) • Serotonin • Endorphins (block perception of pain) • Nitric oxide (gas) – produced as needed • Innervate smooth muscles (intestine), Viagra • In brain – learning and memory • Integration – Brain neuron affected by multiple presynaptic neuron (50,000) • IPSP, EPSP

  14. Drug addiction • Constant stimulus = habituation • Receptor proteins may be removed • Drug needed to maintain regular stimulation • Nicotine can bind to ACh receptors • These coordinate signals • Addiction is when constant stimulus causes nervous system to adapt physiologically http://www.pbs.org/wnet/closetohome/animation/coca-anim-main.html

  15. Brain • Sponges • Cnidarians • Platyhelminthes – no associative or interneurons • More interneurons and more tracts • Fishes have three distinct divisions of brain

  16. Hindbrain • Cerebellum, pons, medulla oblangata • Extension of spinal cord devoted to coordinating motor reflexes (sensory and motor) • Cerebellum (little cerebrum) , impt for coordinating mvmt, larger in vertebrates • Processes data on position and mvmt of limbs, muscles, relation of body to outside world

  17. Midbrain • Reception and processing of sensory • Optic lobes – visual • Fish brains continue to grow • Only hippocampus grows in humans

  18. Amphibians and forward • Forebrain – majority of sensory • Thalamus • Incoming sensory to cerebrum • Hypothalamus • Basic drives, emotions, pituitary gland • Autonomic control

  19. Telencephalon • End Brain • Front of forebrain • Associative activity – cerebrum • Mammals have brains relatively large to body mass (1.4 kg) • Enlargement of cerebrum • Correlation, association, learning • Receives sensory data, issues motor commands • CNS – brain and spinal cord • Interneurons and neuroglia • Ascending = to brain • Descending = away

  20. Human Forebrain • Cerebrum “envelops” rest of brain • Right and left cerebral hemispheres • Frontal, parietal, temporal, occipital lobes • Each hemisphere contralateral info • Cerebral cortex • Much of neural activity is gray matter = cerebral cortex • Surface highly convoluted • Each point on surface controls mvmt of different body part • Large parts affiliated with fingers, lips, tongue (dexterity) • White matter is myelinated axons and serves as connector • Majority of cerebral cortex = associative, 95% primates and humans

  21. Basal Ganglia, Thala & Hypo • Deep in cerebrum white matter • Aggregates of gray matter that receive and send motor signals • Thalamus • Primary site of sensory integration, sends to lobes • Hypothalamus • Integrates visceral activities (temperaure, hunger) and emotional states • Limbic system – ancient linked structures • Work with hypothalamus • Hippocampus and amygdala • Memories and emotional responses

  22. Language and etc • Sleep – lack of stimulation of reticular activating system (sleep in dark room) • Not loss of consciousness • Language – • Left hemisphere = dominant in 90% right hand and 66% left handed (most neural processes related to language function) • Nondominant = spatial reasoning, musical ability, recall faces • Memory/Learning – No one part of brain • Short term – removed with electric shock (stored electrically) • Long term – structural changes

  23. Spinal Cord • Cable of neurons, enclosed by vertebral columns & membrane meninges • Inner zone = gray matter • Outer = white matter • Reflexes = involuntary (no higher level processing) • Blinking if insect near • Sensory – motor – muscle

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