Coordination (Chapter 10)

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  • Coordination
    • Neurones
      • Structure of Neurones
        • cell body
          • nucleus
          • large amount of RER
            • proteins
            • neurotransmitters
        • myelin sheath
          • covering of axon made of schwann cells
          • rich in myelin lipid
          • faster impulses
        • Schwann cells
          • surround axon in layers
          • electrical insulation
          • phagocytosis
          • nerve regeneration
        • nodes of Ranvier
          • every 1-3mm
          • gaps between schwann cells
          • 2-3 micrometers long
        • Axon
          • single long fibre
          • impulse away from cell body
        • Dendrons
          • small extentions of cell body
          • branch into dendrites
          • impulse towards cell body
        • Neurone classifications
          • Sensory
            • receptor > relay
            • one dendron
          • Motor
            • relay > effector
            • long axon
            • many short dendrites
          • Relay
            • between neaurones
            • numerous short purposes
    • Coordination
      • Plant Growth Factors
        • plants have no nervous system
        • Respond to
          • Gravity
            • to be firmly anchored into soil
            • Roots
            • Positive geotropism
          • Light
            • stems
            • positive phototropism
            • for photosynthesis
          • Water
            • roots
            • positive hydrotropism
            • for
              • photosynthesis
              • Metabolic processes
              • support
        • Name better than hormones
          • affect growth
          • made by cells throughout organism not organs
          • some affect releasing tissues
        • produced in small quantites
        • e.g. indoleacetic acid (IAA)
      • Chemical Mediators
        • cellular level
        • Mammalian
        • chemicals effecting cells in immediate vicinity
        • typically released by cells that are
          • injured
          • infected
        • cause
          • small arteries and arterioles dilate
          • inflammatory response
            • Swelling
            • Temperature rise
        • e.g.
          • histamine
            • stored in WBCs
            • released
              • injury
              • allergen
            • Causes
              • increased permeability of capillaries
              • dilation of small arteries and arterioles
            • syptoms
              • swelling
              • redness
              • itching
          • prostaglandins
            • in cell membranes
            • causes
              • dilation of small arteries and arterioles
              • increased permeability of capillaries
              • affect blood pressure
              • affect neurotransmitters
              • affect pain sensation
            • released following injury
      • Control of tropisms by IAA
        • Light
          • stems
          • elongation
        • Gravity
          • roots
          • decreases growth
        • Steps
          • 4.greater [IAA] on shaded side
          • 3.light causes it to move to shaded side
          • 5.IAA causes shadey side to elongate
          • 2.transported to all sides initially
          • 6.shoot bends towards light
          • 1.tip produces IAA which travels down shoot
      • Principles of coordination
        • Nervous system
          • nerve cells
          • Electrical impulses
          • Secrete neurotransmitters directly onto target cells
          • Rapid
          • short lived
          • localised
          • e.g.
            • Reflex actions
            • drawing hand away from harmful stimulus
        • Hormonal system
          • chemicals
          • transported in blood plasma
          • slow
          • long-lasting
          • Widespread
          • e.g.
            • control of blood glucose
    • The Nerve Impulse
      • Action Potential
        • Process
          • 4.+40mV
            • Na+ channels close
            • K+ channels open
          • 3.More Na+ channels open
            • due to changed voltage
            • greater influx
          • 5.Repolarisation
            • electrical gradient reversed
            • more K+ channels open so more diffuse out
          • 2.Stimulus triggers depolarisation
            • some Na+ voltage gated channels open
            • Na+ in due to electrochemical gradient
          • 6. hyper polarisation
            • temporary overshoot
            • K+ channels close
            • Sodium-Potassium pump reastablish -65mV
          • 1.Resting potential
            • K+ channels open
            • Na+ channels closed
        • temporary reversal
          • depolarisation
          • -65mV > +40mV
        • due to voltage gated channels
      • Resting Potential
        • Movement of ions controlled
          • Ptorein channels
            • intrinsic proteins
            • some gated
              • allow ions through some times
              • types
                • Ligand
                • voltage
            • some open all the time
            • diffusion
          • Phospholipid bilayer
            • of axon
            • no ion diffusion accross it
          • sodium-potassium pump
            • intrinsic proteins
            • active transport
            • potasssium ions in
            • Sodium ions out
        • Established due to
          • Naturally diffuse down gradient
          • chemical gradient
            • although both positive
            • More Na+ in tissue fluid
            • more K+ in cytoplasm
          • gates
            • K+ open
            • Na+ closed
          • 3 Na+ out for 2 K+ in
          • potential difference increased
            • K+ diffuse out faster than Na+ diffuse in
            • 100x more permeable to K+
          • K+ in by sodium-potassium pump
          • Electrical gradient
            • tissue fluid more positive
            • K+ held inside of axon due to repelling and attractive forces
          • Na+ out by sodium-potassium pump
          • Equillibrium
            • no net ion movement
        • Polarised
        • inside more negative than outside
        • ~65mV
    • Passage of an Action Potential
      • Along an unmyelinated axon
        • Mexican wave analogy
          • wave moves around stadium
          • Individuals stay still
        • Process
          • 3.Localised circuit means depolarisation occurs a little further along
          • 2.Stimulus causes depolarisation
          • 4.depolarisation continues along axon, hyper polarisation occurs
          • 1.Resting Potential
          • 5.Resting potential re established
      • Along a Myelinated axon
        • Action potentials cannot form over myelin
        • Saltatory conduction
        • Faster than unmyelinated
        • Localised circuit longer
        • action potential jumps between nodes of ranvier
    • Speed of the Nerve Impulse
      • Refractory Period
        • impossible for new action potential
        • Na+ gates closed
        • Na+ cannot enter axon
        • Purpose
          • One direction only
            • active region > resting region
            • no propogation in refractory region
            • would otherwise spread out in both directions
          • discrete impulses
            • seperated
            • cannot be formed immediately behind eachother
          • limits number of action potentials
            • seperated
            • limits number in given time
      • Factors effecting Speed of impulse
        • Myelin sheath
          • electrical insulator
          • saltatory conduction
          • action potential only at nodes of ranvier
          • 30ms-1 unmyelinated > 90ms-1 myelinated
        • axon diameter
          • larger diameter = faster
          • less leakage of ions
        • Temperature
          • higher = faster
          • increases rate of diffusion
          • energy for active transport comes from repiration
            • enzyme controlled
            • faster up till certain point
            • enymes denature after certain point
          • Important factor for response time of ectotherms
      • All-or-nothing principle
        • Above threshold = impulse
        • Below stimulus = no impulse
        • how size of stimulus percieved
          • more frequent = larger
          • different neurones with different thresholds
    • Structure and Function of Synapses
      • Functions
        • Junctions
          • single > many
            • single stimulus
            • simultaneousresponses
          • many > single
            • stimuli from many receptors
            • one reponse
        • neurotransmitter made only in pre
        • neurotransmitter released due to action potential
        • neurotransmitter diffused across cleft
        • neurotransmitter binds to receptor and starts new action potential
      • Features
        • Summation
          • Two types
          • Low frequency action potentials do not produce new action potential in post synaptic neurone
          • Untitled
        • Uni directionality
          • pre > post
          • act like valves
        • Inhibition
          • post synaptic membrane
          • ligand gated Cl- channels open
          • more negative than resting potential
            • hyper polarisation
            • as Cl- in
          • action potential less likely
      • Structure
        • Synaptic cleft
          • gap seperating neurones
          • 20-30nm
        • neurotransmitter
          • diffuse across
        • presynaptic neurone
          • axon ends in synaptic knob
          • many mitochondria and RER
          • synaptic vesicles
            • Store neurotransmitter
            • fuse with membranse to release
        • postsynaptic neurone
          • receptors
    • Transmission Across a Synapse

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