1. Nerve Signal Transmission
Raise your right hand.
Easy, right?
You don’t even have to think twice and your right arm is moving….
But what makes it happen???
How does your brain tell your body what to do?

2. The Nervous System Central nervous system (CNS)
brain and spinal cord
Peripheral nervous system (PNS)
sensory and motor neurons
Nerves
bundles of neurons wrapped in connective tissue

3. Simple Nerve Circuit
Reflex: simple response-- sensory to motor neurons
Involuntary; not analyzed or interpreted by brain
Ganglion (ganglia): cluster of nerve cell bodies in the PNS
Glia: cell that provides support, insulation, and protection
astrocytes, radial glia, oligodendrocytes, Schwann cells

4. Information Processing
External stimuli detected
sight, sound, touch, smell, taste, etc.
Information sent to the CNS
analysis and interpretation
Motor output is relayed to the effector cells
muscle/ endocrine cells

5. Neuron Structure Cell body~ nucleus and organelles
Dendrites~ receiving signals
Axons~ transmitting signals
Hillock~ connects axon to cell body; generates signal
Synaptic terminals~ communicates w/ another cell (releases neurotransmitters)
Synapse~ neuron junction (site of cell communication)

6. Neuron Diversity Sensory neuron: convey information to spinal cord
Interneurons: information integration
Motor neurons: convey signals to effector cell (muscle or gland)

7. Schwann Cells and Myelin
PNS support cells
Wraps around axon, creating layers of myelin
Myelin sheath
supporting, insulating layers
Nodes of Ranvier
Gaps between Schwann cells

8. Membrane Potential
Intracellular/extracellular ionic concentration difference
K+ diffuses out/Na+ in; large anions cannot follow (selective permeability of the plasma membrane)
Voltage difference between -60 and -80 mV

9. It has potential….
Resting potential~ membrane potential of a neuron that is not transmitting
Equilibrium potential~ magnitude of membrane voltage at equilibrium
Nernst equation- Eion = 62mV (log [ion]outside / [ion]inside

10. Gated Ion Channels Open/ Close in response to stimuli… Photoreceptors
Changes in light intensity
Vibrations in air
sound receptors
Chemical
neurotransmitters
Voltage
membrane potential changes

11. Graded Potentials Depend on strength of stimulus
Threshold potential must be reached for reaction to occur
Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more negative
Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less negative

12. Threshold potential: if stimulus reaches a certain voltage (-50 to -55 mV)…. The action potential is triggered….
1. Resting state
Both Na+ and K+ voltage-gated channels are closed
2. Threshold
a stimulus opens some Na+ channels
3. Depolarization
action potential generated
Na+ channels open
cell becomes positive (K+ channels closed)
4. Repolarization
Na+ channels close, K+ channels open; K+ leaves
cell becomes negative
5. Undershoot
both gates close, but K+ channel is slow; resting state restored
Refractory period~ insensitive to depolarization due to closing of Na+ gates

13. Conduction of Action Potential
Movement of the action potential is self-propagating
Depolarization of one part of axon triggers the action potential in the next part
Regeneration of “new” action potentials only after refractory period
This keeps signal moving in the forward direction only

14. Action Potential Speed
Axon diameter (larger = faster; 100m/sec)
Nodes of Ranvier (concentration of ion channels)
saltatory conduction- transmission “jumps” from one node to the next
150m/sec

15. Synaptic communication
Depolarization of the membrane (from a.p.) causes Ca+ influx (voltage gated channel)
Ca+ causes vesicles to fuse with the presynaptic membrane and release neurotransmitters
Neurotransmitters bind w/ ligand-gated ion channels on postsynaptic membrane
Neurotransmitter releases from the receptor and the channels close

16. Postsynaptic Potential
EPSPs- excitatory postsynaptic potentials
IPSPs- inhibitory postsynaptic potentials

17. Indirect Transmission
Neurotransmitters bind with specific receptors instead of ion channels
Much slower reaction time but last longer
Different neurotransmitters produce diverse effects
Psychological drugs interact at the location of these receptors

19. Moving Muscles

20. Muscles contract
Muscles move by shortening, or contracting… they cannot extend on their own
Each muscle has an antagonistic muscle that contracts to move in the opposite direction

21. What’s in a Muscle? Muscles are a bundle of muscle fibers.
Muscle fibers: single cell w/ many nuclei composed of myofibrils
Myofibrils: longitudinal bundles composed of myofilaments
Myofilaments:
Thin~ 2 strands of actin protein and a regulatory protein
Thick~ myosin protein
Sarcomere: repeating unit of muscle tissue within a myofibril

22. Sarcomere Structure Z lines~ sarcomere border I band~ only actin
A band~ actin and myosin overlap
H zone~ central sarcomere; only myosin

23. Sliding-filament model
Theory of muscle contraction
Sarcomere length reduced
Z line length becomes shorter
Actin and myosin slide past each other (overlap increases)

24. Actin-myosin interaction
Myosin head hydrolyzes ATP to ADP and inorganic phosphate (Pi)-- “high energy configuration”
Myosin head binds to actin; forming a “cross bridge”
Releasing ADP and P, myosin relaxes sliding actin; “low energy configuration”
Binding of new ATP releases myosin head
Creatine phosphate~ supplier of phosphate to ADP

25. Contraction Regulation
Relaxation:
tropomyosin blocks myosin binding sites on actin
Contraction:
calcium binds to toponin complex
tropomyosin changes shape, exposing myosin binding sites

26. ACTION! Acetylcholine released from synaptic terminal of motor neuron
Acetylcholine binds w/ receptors and causes an action potential in the muscle fiber
A.P travels down the T (transverse) tubules and triggers release of Ca+ from the sarcoplasmic reticulum
Modified endoplasmic reticulum
Contraction begins when Ca+ reaches the sarcomere and binds to troponin