Neurons = Nerve cells - PowerPoint PPT Presentation

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Neurons = Nerve cells

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Neurons = Nerve cells Neuron anatomy Cell Body = site of protein synthesis Dendrites = receive input from other neurons Axon = conducts signal as electrical impulse ... – PowerPoint PPT presentation

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Title: Neurons = Nerve cells


1
Neurons Nerve cells
2
Neuron anatomy
  • Cell Body site of protein synthesis
  • Dendrites receive input from other neurons
  • Axon conducts signal as electrical impulse
    (action potential)
  • Myelin sheath insulates axon, produced by
    Schwann cells
  • Nerve terminal site of synapses with target
    cell

Signal integration
3
Ligand- or signal-gated Na channel
Voltage-gated Na channel
Voltage-gated K channel
Na/K pump
-70 mV
K Hi
Na Hi
4
Action Potentials
  • Resting potential -70 mV
  • Signal opens some signal-gated Na channels in
    dendrites
  • Some Na rushes in raises potential
    depolarization
  • If raised to -60 mV, no response
  • If raised to -50 mV or higher, opens lots of
    voltage-gated Na channels triggers an action
    potential.
  • -50 mV is the threshold. All-or-none response.

5
Action Potentials II
  • In action potential, depolarizes to 40 mV
  • Extreme depolarization opens voltage-gated K
    channels
  • voltage-gated K channels require voltage to
    open
  • K rushes out down electrochemical gradient
  • Membrane hyperpolarizes (repolarizes) to -80 mV
  • Na/K pump maintains the electrochemical
    potential over long haul

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Action potentials jump between nodes of Ranvier.
Speeds up signal.
saltatory conduction
9
Decision to fire is based on summation of
excitatory and inhibitory inputs
10
Muscle organization
11
Myosin thick filament
M
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13
Neuromuscular junction
Transverse (T) tubule
Sarcoplasmic reticulum
14
Excitation/contraction coupling
  • Nerve impulse releases neurotransmitters
  • Bind to receptors on muscle which generate an
    action potential (AP)
  • AP spreads down T tubule (part of plasma
    membrane)
  • T tubule close proximity to sarcoplasmic
    reticulum opens Ca2 channels in SR
  • Ca2 rushes into cytoplasm

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Muscle cell types
  • Striated skeletal
  • Cardiac (heart) also striated
  • intercalated discs gap junctions between cells
    to directly link them electrically
  • Smooth non-striated, short myosin thick
    filaments throughout
  • Dense bodies Actin filaments contact plasma
    membrane, cell-cell connections
  • Myosin light chain kinase regulation
  • Slow, graded contractions

17
Cumulus layer
Cortical granule
18
Fertilization (mammalian)
  • Sperm forces thru cumulus layer
  • Sperm P.M. binds to zona pellucida
  • Acrosome reaction releases digestive enzymes
  • Sperm P.M. binds oocyte P.M.
  • Membrane fusion of sperm oocyte
  • Cortical granule release causes block to
    polyspermy
  • Pronuclear migration to form diploid nucleus

19
Cleavage rounds to form blastula
blastocoel
blastula
20
Gastrulation
  • Cells on outer top (AP) migrate around. At
    dorsal lip, cells migrate inward into blastocoel.
  • Germ layers established as archenteron forms
  • Future ectoderm migrates to cover whole surface

21
Embryonic germ layers
  • Ectoderm epidermis, epithelial lining of mouth
    rectum, cornea lens, nervous system
  • Endoderm Epithelium of digestive tract
    respiratory system, liver, pancreas, thyroid,
    lining of urethra, bladder, reproductive system
  • Mesoderm Notochord, skeleton, muscles,
    excretory system, circulatory lymphatic
    systems, dermis of skin, reproductive system
    except lining germ cells, lining of body cavity

22
Neurulation
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Determination Differentiation
  • Embryonic precursor or stem cell
  • Determination master control gene is expressed
    determines cell fate
  • Differentiation master control gene turns on
    transcription of cell-type-specific functional
    genes
  • Cell adopts form and function

25
Homeobox (Hox) genes
  • Contain a DNA-binding homeodomain.
  • Act as master control genes to regulate
    transcription of sets of genes during development

26
Soluble signal molecule
IMP signal molecule
27
Different signals bind different receptors to
turn on transcription (Txn) of different genes
Txn. B on
Txn. B on
Txn. A on
28
Apoptosis
  • Programmed cell death
  • Extraneous cells are signaled to commit suicide
    during development
  • Excess neurons
  • Tissue between fingers toes
  • Autoimmune cells
  • Carefully controlled, neat, specific
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