1. Nervous Systems Three Main Functions: 1. Sensory Input 2. Integration
3. Motor Output

2. Figure 48.1 Overview of a vertebrate nervous system

3. Two Main Parts of Nervous Systems
Central nervous system (CNS)
brain and spinal cord
integration
 Peripheral nervous system (PNS)
network of nerves extending into different parts of the body
carries sensory input to the CNS and motor output away from the CNS

4. Two Cell Types in Nervous Systems
Neurons
Cells that conduct the nerve impulses
Supporting Cells - Neuroglia

5. Neuron

6. Figure 48.2x Neurons

7. Three Major Types of Nerve Cells
Sensory neurons
communicate info about the external or internal environment to the CNS
Interneurons
integrate sensory input and motor output
makes synapses only with other neurons
Motor neurons
convey impulses from the CNS to effector cells

9. Supporting Cells - Neuroglia
provide neurons with nutrients, remove wastes
Two important types in vertebrates
Oligodendrocytes – myelin sheath in CNS
Schwann cells -myelin sheath in PNS

10. Myelin Sheath Formation

12. Conduction of the Nerve Impulse
Membrane Potential
Voltage measured across a membrane due to differences in electrical charge
Inside of cell is negative wrt outside
Resting potential of neuron = -70 mV

13. Figure 48.6 Measuring membrane potentials

15. Sodium-Potassium Pump
1. Carrier in membrane binds
intracellular sodium.
2. ATP phosphorylates protein
with bound sodium.
3. Phosphorylation causes
conformational change in
protein, reducing its affinity for
Na+. The Na+ then diffuses out.
4. This conformation has higher
affinity for K+. Extracellular
K+ binds to exposed sites.
5. Binding of potassium causes
dephosphorylation of protein.
Extracellular
Intracellular
ATP
ADP Pi P + K+
Na+
6. Dephosphorylation of protein
triggers change to original
conformation, with low affinity
for K+. K+ diffuses into the cell,
and the cycle repeats.

16. Excitable Cells Neurons & muscle cells
Have gated ion channels that allow cell to change its membrane potential in response to stimuli

18. Gated Ion Channels Some stimuli open K+ channels
K+ leaves cell
Membrane potential more negative
hyperpolarization
Some stimuli open Na+ channels
Na+ enters cell
Membrane potential less negative
depolarization

19. Gated Ion Channels
Strength of stimuli determines how many ion channels open
= graded response

20. Nerve Impulse Transmission

21. Action Potentials Occur once a threshold of depolarization is reached
-50 to –55 mV
All or none response (not graded)
Magnitude of action potential is independent of strength of depolarizing stimuli
Hyperpolarization makes them less likely

22. 3. Top curve 2. Rising Phase 1. Resting Phase 4. Falling Phase
Membrane potential (mV)
2. Rising Phase
Stimulus causes above threshold voltage
+50 1 2 3
–70
Time (ms)
1. Resting Phase
Equilibrium between diffusion of K+ out
of cell and voltage pulling K+ into cell
Voltage-gated
potassium channel
Potassium
channel
sodium channel
Potassium channel
gate closes
Sodium channel
activation gate closes.
Inactivation gate opens.
activation gate opens
3. Top curve
Maximum voltage reached
gate opens
4. Falling Phase
gate open
Undershoot occurs as excess potassium
diffuses out before potassium channel closes
Equilibrium
restored
Na+ channel
inactivation gate
closes K+
Na+
closed

23. Refractory Period
During undershoot the membrane is less likely to depolarize
Keeps the action potential moving in one direction

24. Propagation of Action Potential
Action potential are very localized events
DO NOT travel down membrane
Are generated anew in a sequence along the neuron

25. Cell
membrane
Cytoplasm
resting
repolarized
depolarized
– – – – – – – – –
– –
– – – – – – –
– – – – – – –
– –
– –
– – – – – – –
– – – – – – –
– –
– – –
– – – – – –
– – – – – –
– – –
– –
– – – – – – –
– –
Na+ K+

26. Saltatory Conduction

27. Transfer of Nerve Impulse to Next Cell
Synapse
the gap between the synaptic terminals of an axon and a target cell

28. Transfer of Nerve Impulse to Next Cell
Electrical synapses
Gap junctions allow ion currents to continue
Chemical synapses
More common
Electrical impulses must be changed to a chemical signal that crosses the synapse

29. Synapses

30. Neurotransmitters

31. Summation of postsynaptic potentials

32. Effects of Cocaine

33. Addiction Transporter protein Dopamine Cocaine Receptor
Receptor protein
Drug
molecule
Synapse
1. Reuptake of neuro-
transmitter by transporter
at a normal synapse.
2. Drug molecules block
transporter and cause
overstimulation of the
postsynaptic membrane.
3. Neuron adjusts to
overstimulation by
decreasing the number
of receptors.
4. Decreased number of
receptors make the
synapse less sensitive
when the drug is removed.
Neurotransmitter
Transporter protein

34. Diversity of Nervous Systems
Human
Cerebrum
Cerebellum
Spinal
cord
Cervical
nerves
Thoracic
Lumbar
Femoral
nerve
Sciatic
Tibial
Sacral
Nerve
net
Nerve cords
Associative
neurons
Brain
Giant axon
Mollusk
Echinoderm
Central nervous
system
Peripheral
Ventral
nerve cords
Radial
ribs
Cnidarian
Flatworm
Earthworm
Arthropod

35. Parasympathetic nervous
CNS
Brain and Spinal Cord
Sensory Pathways
Motor Pathways
Sensory neurons
registering external
stimuli
Sensory neurons
registering external
stimuli
PNS
Somatic nervous
system
(voluntary)
Autonomic nervous
system
(involuntary)
Sympathetic nervous
system
"fight or flight"
Parasympathetic nervous
system
"rest and repose"
central nervous system (CNS)
peripheral nervous system (PNS)

36. Parasympathetic Constrict Secrete saliva Dilate Stop secretion
Dilate bronchioles
Speed up heartbeat
Increase secretion
Empty colon
Increase motility
Empty bladder
Slow down heartbeat
Constrict bronchioles
Sympathetic
ganglion
chain
Stomach
Secrete adrenaline
Decrease secretion
Decrease motility
Retain colon contents
Delay emptying
Adrenal gland
Bladder
Small intestine
Large intestine
Spinal cord
Parasympathetic

38. Vertebrate Central Nervous System
Spinal Cord
Receives info from skin & muscles
Sends out motor commands for movement & response
Simple integration -- reflexes
Brain
More complex integration
Homeostasis, perception, movement, emotion, learning

39. Spinal cord Stretch receptor (muscle spindle) Nerve fiber Sensory
Quadriceps
muscle
(effector)
Spinal cord
Dorsal root
ganglion
Gray
matter
White
Monosynaptic
synapse
Sensory
neuro
Nerve fiber
Stretch receptor
(muscle spindle)
Skeletal
Stimulus
Response
Motor neuron

40. The knee-jerk reflex