1. Nervous System Basics and Nervous System Tissues
Chapter 11:
Nervous System Basics and Nervous System Tissues

2. Santiago Ramon Y. Cajal (1852-1934)
Founding Scientist in the Modern Approach to
Neuroscience. Received Nobel Prize in 1906

3. Figure 11.1: The nervous system’s functions, p. 388.
Sensory input
Integration
Motor output

4. Figure 11.2: Levels of organization in the nervous system, p. 389.
Key:
Brain
Central nervous system (CNS)
Brain and spinal cord
Integrative and
control centers
= Sensory (afferent)
division of PNS
= Motor (efferent)
Key:
= Structure
= Function
Visceral
sensory fiber
Peripheral nervous system (PNS)
Cranial nerves and spinal
nerves
Communication lines
between the CNS and the
rest of the body
Central
nervous
system
(CNS)
Parasympathetic
motor fiber of ANS
Sympathetic
motor fiber of ANS
Visceral organ
Spinal
cord
Skin
Somatic sensory
fiber
Sensory (afferent) division
Somatic and visceral
sensory nerve fibers
Conducts impulses from
receptors to the CNS
Motor (efferent) division
Motor nerve fibers
Conducts impulses from
the CNS to effectors
(muscles and glands)
Motor fiber of
somatic nervous
system
Skeletal
muscle
Sympathetic division
Mobilizes body systems
during activity
Autonomic nervous
system (ANS)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Somatic nervous
System
Somatic motor
(voluntary)
Conducts impulses
from the CNS to
skeletal muscles
Peripheral nervous system
(PNS)
Parasympathetic division
Conserves energy
Promotes housekeeping
functions during rest
(b)
(a)

5. Brain or spinal cord tissue
Figure 11.3: Neuroglia, p. 390.
Capillary
Neuron
(b) Microglial cell
(a) Astrocyte
Nerve fibers
Myelin sheath
Fluid-filled cavity
Process of
oligodendrocyte
(c) Ependymal cells
Brain or spinal cord tissue
Cell body
of neuron
(d) Oligodendrocyte
Schwann cells
(forming myelin sheath)
Satellite cells
Nerve fiber
(e) Sensory neuron with Schwann cells and satellite cells

6. Figure 11.4: Structure of a motor neuron, p. 392.
Dendrites
(receptive
regions)
Cell body
(biosynthetic center
and receptive region)
Neuron cell body
Nucleus
Dendritic
spine
(a)
Axon
(impulse generating
and conducting
region)
Nucleolus
Impulse
direction
Nissl bodies
Node of Ranvier
Axon terminals
(secretory
component)
Axon hillock
Schwann cell
(one inter-
node)
Neurilemma
(sheath of
Schwann)
Terminal branches
(telodendria)
(b)

7. Schwann cell cytoplasm Schwann cell plasma membrane Axon Myelin sheath
Figure 11.5: Relationship of Schwann cells to axons in the PNS, p. 394.
Schwann cell
cytoplasm
Schwann
cell plasma
membrane
Axon
Myelin sheath
Schwann cell
nucleus
(a)
Schwann cell
cytoplasm
Axon
Neurilemma
(b)
(d)
Neurilemma
Myelin
sheath
(c)

8. Figure 11.6: Operation of gated channels, p. 398.
Neurotransmitter
chemical attached
to receptor
Receptor
Na+
Na+
Chemical
binds K+ K+
Closed
Open
(a) Chemically gated ion channel
Na+
Na+
Membrane
voltage
changes
Closed
Open
(b) Voltage-gated ion channel

9. Figure 11.7: Measuring membrane potential in neurons, p. 399.
Voltmeter
Plasma
membrane
Ground electrode
outside cell
Microelectrode
inside cell
Axon
Neuron

10. Figure 11.8: The basis of the resting membrane potential, p. 399.
Cell
exterior
Na+
15 mM
Na+
Cell interior
Na+ K+
150 mM
Na+
ion
Diffusion us
Na+–K+
pump
Diff
-70 mV
Cl–
10 mM
Na+
Na+
150 mM A–
100 mM
Na+ K+
Na+ A–
0.2 mM
Na+
Plasma
membrane K+
5 mM K+
Cl–
120 mM K+
Cell
interior
Cell exterior K+ K+

11. Depolarizing stimulus Hyperpolarizing stimulus
Figure 11.9: Depolarization and hyperpolarization of the membrane, p. 400.
Depolarizing stimulus
Hyperpolarizing stimulus
+50
+50
Inside
positive
Inside
negative
Membrane potential (voltage, mV)
Depolarization
Membrane potential (voltage, mV)
–50
–50
Resting
potential
–70
–70
Resting
potential
Hyper-
polarization
–100
–100 1 2 3 4 5 6 7 1 2 3 4 5 6 7
Time (ms)
Time (ms)
(a)
(b)

12. Figure 11.10: The mechanism of a graded potential, p. 401.
Depolarized region
Stimulus
Plasma
membrane
(a)
Depolarization
(b)
Spread of depolarization

13. Membrane potential (mV)
Figure 11.11: Changes in membrane potential produced by a depolarizing graded potential, p. 402.
Active area
(site of initial
depolarization)
Membrane potential (mV) – 70
Resting potential
Distance (a few mm)

14. Figure 11.12: Phases of the action potential and the role of voltage-gated ion channels, p. 403.
Outside
cell
Na+
Outside
cell
Na+
Inside
cell
Inside
cell K+ K+
Depolarizing phase: Na+
channels open
Repolarizing phase: Na+
channels inactivating, K+
channels open 2
Action potential
+30 3
Relative membrane
permeability 2
Membrane potential (mV)
PNa PK
Threshold
–55 1 1 4
–70 1 2 3 4
Time (ms)
Outside cell
Sodium
channel
Potassium
channel
Outside
cell
Na+
Na+
Inside
cell
Activation
gates K+
Inside
cell K+
Inactivation gate 4
Hyperpolarization: K+
channels remain open;
Na+ channels resetting 1
Resting state: All gated Na+
and K+ channels closed
(Na+ activation gates closed;
inactivation gates open)

15. Figure 11.13: Propagation of an action potential (AP), p. 405.
Voltage
at 2 ms
+30
Membrane potential (mV))
Voltage
at 0 ms
Voltage
at 4 ms
–70
(a) Time = 0 ms
(b) Time = 2 ms
(c) Time = 4 ms
Resting potential
Peak of action potential
Hyperpolarization

16. Membrane potential (mV)
Figure 11.14: Relationship between stimulus strength and action potential frequency, p. 406.
Action
potentials
+30
Membrane potential (mV) – 70
Stimulus
amplitude
Threshold
Voltage
Time (ms)

17. Figure 11.15: Refractory periods in an AP, p. 406.
Absolute refractory
period
Relative refractory
period
Depolarization
(Na+ enters)
+30
Repolarization
(K+ leaves)
Membrane potential (mV)
After-hyperpolarization
–70
Stimulus 1 2 3 4 5
Time (ms)

18. Figure 11.16: Saltatory conduction in a myelinated axon, p. 407.
Node of Ranvier
Cell body
Myelin
sheath
Distal
axon

19. Cell body Dendrites Axodendritic Axosomatic synapses synapses
Figure 11.17: Synapses, p. 409.
Cell body
Dendrites
Axodendritic
synapses
Axosomatic
synapses
Axoaxonic
synapses
Axon
(a)
Axon
Axosomatic
synapses
Soma of
postsynaptic
neuron
(b)

20. Figure 11.18: Events at a chemical synapse in response to depolarization, p. 410.
Neurotransmitter
Ca2+
Na+
Axon terminal of
presynaptic neuron
Action Potential
Receptor 1
Postsynaptic
membrane
Mitochondrion
Postsynaptic
membrane
Axon of
presynaptic
neuron
Ion channel open
Synaptic vesicles
containing
neurotransmitter
molecules 5
Degraded
neurotransmitter
Na+ 2
Synaptic
cleft 3 4
Ion channel closed
Ion channel
(closed)
Ion channel (open)

21. Figure 11.19: Postsynaptic potentials, p. 412.
+30
+30
Membrane potential (mV)
Threshold
Membrane potential (mV)
Threshold
–55
–55
–70
–70 10 20
Time (ms) 10 20
Time (ms)
(a) Excitatory postsynaptic potential (EPSP)
(b) Inhibitory postsynaptic potential (IPSP)

22. Figure 11.24: Types of circuits in neuronal pools, p. 422.
Input
Input
Input
Input 1
Input 2
Input 3
Output
Output
Output
Output
(a) Divergence in same pathway
(b) Divergence to multiple
pathways
(c) Convergence,
multiple sources
(d) Convergence,
single source
Input
Input
Output
Output
(e) Reverberating circuit
(f) Parallel after-discharge circuit

23. Figure 11.25: A simple reflex arc, p. 423.
Integration
center
Sensory neuron
Stimulus
Receptor
Interneuron
Response
Effector
Motor neuron
Spinal cord (CNS)