Neurons = Nerve cells

1. Neurons = Nerve cells

2. Neuron anatomy Signal integration • 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

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

8. 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

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

16. 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

24. 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