Neurons = Nerve cells

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Neurons Nerve cells
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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
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Ligand- or signal-gated Na channel
Voltage-gated Na channel
Voltage-gated K channel
Na/K pump
-70 mV
K Hi
Na Hi
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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.

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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
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Decision to fire is based on summation of
excitatory and inhibitory inputs
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Muscle organization
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Myosin thick filament
M
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Neuromuscular junction
Transverse (T) tubule
Sarcoplasmic reticulum
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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

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Cumulus layer
Cortical granule
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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

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Cleavage rounds to form blastula
blastocoel
blastula
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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

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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

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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

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Homeobox (Hox) genes

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

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Soluble signal molecule
IMP signal molecule
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Different signals bind different receptors to
turn on transcription (Txn) of different genes
Txn. B on
Txn. B on
Txn. A on
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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