1. Nerves & signaling
Ch 37

2. I. Nerves =
A. Cells called neurons bundled together in a sheath of connective tissue

3. II. Neurons:(fits form to function)
A. cells that transmit impulses
B. Neuron structure
1. Dendrites : fine branches that receive signals
2. Cell body : nucleus & organelles
3. Axon : transmits signal
4. Synaptic terminal : passes signal to next cell

4. III. Synapse / synaptic cleft
A) Interstitial space between synaptic terminal and next cell
B) signaling neuron is the presynaptic cell
C) receiving cell is the Postsynaptic cell

5. IV. Neurotransmitters
A. signaling molecules (chemical messengers)
B. Carry signal from synaptic terminal to receptors on postsynaptic cell

7. V. Glia
Cells that
support neurons
Nourish
Regulate surrounding interstitial fluid
Schwann cells – make myelin in PNS
(peripheral nervous system)

8. VI. Information Processing : three stages
1. sensory input
2. integration
3. motor output

9. A. Sensory neurons: 1. External a. mechanoreceptors b. chemoreceptors
c. photoreceptors
2. Internal
a. baroreceptors (pressure)
b. pain receptors

10. B. Divisions of Nervous system
1. CNS = central nervous system…spinal cord and brain
2. PNS = peripheral nervous system.. All other nerves

11. C. Integrators
1.Found in CNS : central nervous system
2. called interneurons :connect neurons in brain & longitudinal nerve cord
3. process info sent in by
sensory neurons

12. D. Motor output
1. motor neurons transmit signal from CNS to effector cells
a. muscle cells
b. endocrine cells

13. VII. Movement Across Cell Membrane
A. Simple diffusion
1. very small, not charged
B. facilitated diffusion (protein channel)
C. active transport –against conc. Grad
1. protein pump or co-transporter

14. VIII. Resting Potential
A. Sodium potassium pump
1. active transport
a. 3Na+ out and 2K+ into cell
b. creates concentration gradients
1. high Na+ outside High K+ inside
B. K+ channels leak ions back out
1. electrical gradient slightly positive outside cell
mV potential energy…voltage

15. 2 K+ in for every 3 Na+ out more K+ leaks out than Na+ leaks in

16. C. Equilibrium Potential = magnitude of voltage across membrane
1. EK =-90 mV
2. ENa = +62 mV
3. Resting potential ≈ -70 mV bcs
more K+ leaking
4. Hyper polarization = inside even
more negative…increase K diffusing out
5. Depolarization = inside becomes less negative…open Na channels

17. 6. Graded potentials..
different levels of depolarization
a. different neuron responses
b. no response or action potential
c. depolarization signals are summative

18. Graded potential: High grade: intense or long lasting
Low grade: small stimulus, depolarization does not reach trigger zone with high enough energy = no action potential sent down axon
High grade: intense or long lasting
Signal reaches trigger zone at or above threshold level
Action potential send down axon

19. IX. Action Potential: massive depolarization
A. Sum of depolarization signals causes
depolarization level to reach threshold
B. voltage-gated Na channels open
C. positive feed back opens more
D. Na flow brings voltage closer to 0mV then above 0mV to be positive
E. voltage gated K channels open
F. restore negative cytoplasm
G. undershoot = too much negative charge inside
H. resting potential restored by NaK pumps

20. Action potential initiation
urons_intro.php

22. X.Action potential:quick reversal of polarity
A.Action potential is all or nothing
B.Na+ flow in as fast as possible for .5ms
C.Then Na+ gates shut and K+ gates open

23. XI. Propagation of action potential
swf_action_potenti.swf
A. One patch of membrane activates the Na+ gates next to it by becoming positive inside…..causes more Na+ gates to open
B. Propagation is 1 way due to gate inactivation.
1. refractory period = Na gated channels are inactivated

24. C. Saltatory conduction (leap)
1. Myelin = insulator.
2. space btwn schwann cells =nodes of Ranvier.
Nerve impulse
jumps between
Nodes
=faster
transmission

25. XII. Transduction of Action Potential
A. Electrical synapse: direct transmission
of electric charge via gap junctions
=rapid unvarying response (brain)
B. Chemical Synapse
1. Depolarization opens Ca+ channels
2. Ca+ causes synaptic vesicles to release neurotransmitters by exocytosis
3. Neurotransmitters diffuse to postsynaptic cell & bind to receptors

27. C. Neurotransmitters – 2 categories
1. excitatory : causes depolarization
(encourages signal transmission)
2. inhibitory : causes hyperpolarization
(discourages signal transmission)
3. Ach = acetylcholine (muscle) both excitatory and inhibitory
4. serotonin = mood/ memory/sleep
5. epinephrine/norepinephrine
(called adrenalin & noradrenalin in endocrine function)

28. D. Receptors
1. Most = ligand-gated ion channels
a. neurotransmitter = the ligand
b. binding of ligand opens the gate
c. some let K+ & Na+ pass to depolarize
(excitatory)
d. some let in Cl- to hyperpolarize
(inhibitory)

30. 2) some activate 2nd messenger
a) slower longer lastingresponse
b) binding n.t. activates G protein
c) G protein activates enzyme to make
ATP into cAMP
d) cAMPs activate protein kinase As
e) Kinase As phosphorolate many channels = open them
f) many kinase As = amplified signal

32. E. Transduction = response
1. EPSP=excitatory postsynaptic potential encourages ps cell response
2. IPSP=inhibitory pulls the cell back from threshold (restores resting polarization)
3. integration = summation of EPSP & IPSP determines response of cell
a. spatial summation : multiple synapses of same cell receive signal
b. Temporal summation : rapidly repeated signal

33. F. Clearing of synaptic cleft
1. Neurotransmitters cleared by…
a. diffusion
b. re-uptake into pre-synaptic cell
c. enzyme mediated breakdown

34. IX