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Neurons Structure and Conduction of a Nerve Impulse

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Neurons Structure and Conduction of a Nerve Impulse Two coordinating systems which respond to environmental stimuli Nervous System & Endocrine (hormone) System Begin ... – PowerPoint PPT presentation

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Title: Neurons Structure and Conduction of a Nerve Impulse


1
NeuronsStructure and Conduction of a Nerve
Impulse
2
Two coordinating systems which respond to
environmental stimuli
  • Nervous System Endocrine (hormone) System
  •  
  • Begin with Nervous System (data processing
    system)
  • 3 interconnected functions ? input / integration
    / output

3
Basic Organization
sensory receptor (sensory input) ? integration ?
(motor output) ? effector
  • Sensory Input triggered by stimuli
  • conduction of signals to processing center
  • Integration
  • interpretation of sensory signals within
    processing centers
  • Motor output
  • conduction of signals to effector cells (i.e.
    muscles, gland cells)

4
Neuron
  • Dendrite - conducts signal toward the cell body
    -- input zone
  • often short, numerous highly branched
  • signal comes from sensory cell or neighboring
    neuron
  • Axon - usually a single fiber -- conducting
    zone
  • conducts signal away from cell body to another
    neuron or effector cell
  • Axon Ending
  • a cluster of branches (100s to 1000s)
  • each with a bulblike synaptic knob
  • relays signal to next neuron / effector cell

5
Generation - Conduction of Neural Impulses
  • Dependent on concentration gradients of Na K
  • Na 14x greater outside
  • K 28x greater inside
  • Membrane permeability
  • lipid bilayer bars passage of K Na ions
  • protein channels and pumps regulate passage of
    K Na
  • at rest more K move out than Na move in
  • K ions diffuse out leave behind excess negative
    charge
  • Sodium-potassium pump
  • Na out - K in (more Na out than K in
  • contributes to loss of ()

6
Overview of Neural Impulse
7
  • Maintenance of negative charge within neuron
  • resting membrane potential about -70 millivolts
  • 5 voltage of AA battery
  • Dissolved organic molecules negative charge
    kept inside
  • Na - K balance

8
  • Stimulus causes opening of Na gates closing
    of K gates -
  • Threshold 30 mV
  • all - or - nothing response
  • Action potential localized electrical event
  • Changes permeability of region immediately ahead
  • changes in K Na gates
  • domino effect
  • propagation of signal
  • Intensity of stimuli (i.e. pinch vs. punch)
    number of neurons firing
  • Speed on impulse based on diameter of axon
    amount of myelination wire for internet

9
(No Transcript)
10
Myelin Sheath
  • Resembles chain of beads
  • Prevents ions from flowing through membranes
  • Na channels highly concentrated at nodes
  • Allows signal to travel faster because impulse
    jumps from node of Ranvier to node of Ranvier
    (with myelin sheath (225 mph / without 11 mph)
  • MS ? destruction of mylin sheath by own immune
    system (progressive loss of signal conduction,
    muscle control brain function)

11
Neurons Communicate at Synapses
  • Electrical no synapse
  • common in heart digestive tract - maintains
    steady, rhythmic contraction
  • All cells in effector contain receptor proteins
    for neurotransmitters
  • Chemical - skeletal muscles CNS
  • presence of gap (SYNAPTIC CLEFT) which prevents
    action potential from moving directly to
    receiving neuron
  • ACTION POTENTIAL (electrical) converted to
    CHEMICAL SIGNAL at synapse (molecules of
    neurotransmitter) then generate ACTION POTENTIAL
    (electrical) in receiving neuron

12
Overview of Transmission of Nerve Impulse
  • Action potential
  • ? synaptic knob
  • ? opening of Ca channels
  • neurotransmitter vesicles fuse with membrane
  • release of neurotransmitter into synaptic cleft
  • binding of neurotransmitter to protein receptor
    molecules on receiving neuron membrane
  • opening of ion channels
  • triggering of new action potential
  • Neurotransmitter is broken down by enzymes ion
    channels close -- effect brief and precise

13
Nerve Impulse
  • Presynaptic neuron
  • Vesicles
  • Calcium channels
  • Synaptic cleft
  • Postsynaptic neuron
  • Neurotransmitter receptor

14
Nerve Impulse
  • Action potential
  • ? synaptic knob
  • ? opening of Ca channels
  • neurotransmitter vesicles fuse with membrane
  • release of neurotransmitter into synaptic cleft

Ca2
15
Nerve Impulse
  • Action potential
  • neurotransmitter vesicles fuse with membrane
  • release of neurotransmitter into synaptic cleft

16
  • Action potential
  • binding of neurotransmitter to protein receptor
    molecules on receiving neuron membrane
  • opening of sodium channels
  • triggering of new action potential

17
Neurotransmitters
  • Catecholamine Neurotransmitters
  • Derived from amino acid tyrosine
  • Dopamine Parkinsons, norepinephrine,
    epinephrine
  • Amine Neurotransmitters
  • acetylcholine, histamine, serotonin
  • Amino Acids
  • aspartic acid, GABA, glutamic acid, glycine
  • Polypeptides
  • Include many which also function as hormones
  • endorphins

18
  • Transmission of signals based on MULTIPLE STIMULI
  • combined excitatory inhibitory neurons
  • Inhibition in Pre-synaptic neuron
  • Ca channels blocked
  • stops release of neurotransmitter
  • Inhibition in Post-synaptic neuron
  • opens Cl- channels
  • makes interior more -
  • increase permeability of K ions
  • makes interior more -
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