Lecture notes

Nervous system
3 Basic functions of the nervous system
1-Sensory
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!
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2-Integration
!
!
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3-Motor
I. Central Nervous System
(CNS)!
!
•
Brain!
!
!
!
!
•
Spinal Cord
I. Peripheral Nervous System (PNS)!
2) Afferent “towards”!
afferent sensory neurons!
!
3) Efferent “away”!
efferent motor neurons
efferent (con’t)!
ii) Somatic nervous system!
!
!
Skeletal!
voluntary
efferent (con’t)!
ii) Autonomic
nervous system!
Smooth muscles!
Cardiac muscle!
Glands (endo/exocrine)!
Involuntary
2 subdivisions of the
ANS!
b) Sympathetic!
c) Parasympathetic
Histology!
Neuroglial cells!
!
!
!
!
Astrocytes!
!
!
!
!
!
!
Oligodendrocytes
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Histology!
Neuroglial cells!
Microglia!
!
!
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Ependymocytes!
!
!
!
!
!
gliomas
!
!
Example: anaplastic astrocytoma,
glioblastoma multiforme
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Neurons!
Cell body, soma, perikaryon!
!
Nissl bodies!
Neurofibrils!
Dendrites
Neurons!
Axon!
Structure!
Axon hillock!
Axoplasm!
Axolemma
Neurons!
Axon collaterals!
!
!
Axon terminals!
(telodendria)
telodendria
Neurons!
Synaptic end bulbs!
!
Synaptic vesicles
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Axoplasmic flow!
!
!
!
Axonal transport
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Nerve fiber!
!
!
!
!
Myelin sheath
Multiple sclerosis!
!
!
Nodes of Ranvier !
(neurofibril nodes)
Neurolemmocytes/ Schwann cells!
In PNS!
Neurolemma!
!
Regeneration
Oligodendrocytes!
!
No regeneration
Generation of an Action potential (nerve impulse)
At the resting state…
1) The different concentrations of Na+ and K+ across the plasma
membrane are maintained by the Na+/K+ ATPase with the
expenditure of energy in the form of ATP. Membrane potential
difference (PD)=-70mv, inside negative. The membrane is
polarized
At the resting state…
2) Activation gate (called this because when the gate is stimulated it activates or
opens the channel) on the voltage-sensitive Na+ channel is closed.!
3) The inactivation gate is open at present.!
4) No Na+ flow in or out of the cell.!
5) The voltage-sensitive K+ channel is slightly open, so there is a small K+ leak
out of the cell.
1)! A stimulus opens the activation gate of the voltage-sensitive Na channel.!
2)! The channel is now open and Na+ flows inward, down its [Na+] and electrical
gradient.!
3)! As more Na+ enters the cell, the inside of the cell becomes positive. The PD
passes 0 mV, then approaches +30 mV. The membrane becomes depolarized.
1)! The stimulus also causes the inactivation gate (called that because it
inactivates the channel when it is stimulated) to close. This happens slowly,
after the channel has been open for several microseconds.!
2)! The flow of Na+ into the cell stops.!
3)! The membrane PD does not go beyond +30 mV.
1) The voltage-gated K+ channels opens slowly, at the same time that the
inactivation gate of the Na+ channel closes.!
2) K+ flows out of the cell, down the [K+] and electrical gradient: !
!
Remember- the inside of the cell in now more positive than the outside.
3) K+ movements carries positive charges out of the cell and the inside becomes
more negative. The cell becomes repolarized.!
4) When PD= -70 mV the gates return to their resting state.!
5) The Na+-K+ ATPase returns the concentrations of the Na+ and K+ ions to the
resting state levels.
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Refractory period!
!
Absolute!
!
!
Relative
Nerve AP vs. Muscle AP
nerve
muscle
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Saltatory conduction!
!
Nodes of Ranvier!
!
Increase speed of conduction!
!
Decrease in energy use
Nerve fiber types
Fiber types
A
B
C
Size
4-20µm
2-4µm
<2µm
Myelination
Yes
Yes
No
Speed
140m/sec
18m/sec
1m/sec
Example
Some sensory
and skeletal
Temp. pain,
smooth muscles
Neuroeffector junction!
!
Neuromuscular junction (motor endplate)!
!
Neuroglandular junction
Temp. pain,
smooth muscles
Synapse!
Junction between neurons!
!
Structure!
Synaptic cleft
Synaptic end bulbs!
!
Axodendritic!
Axosomatic!
Axoaxonic
One-way impulse conduction!
!
Synaptic vesicles!
Neurotransmitter
Excitatory transmissions!
!
Excitatory transmitter-receptor interaction
Two mechanisms!
1-Receptors open Na+ channels!
!
!
2-Adenylate cyclase cAMP-kinases
Caffine!
Phosphodiesterase inhibitor!
!
!
!
Excitatory post-synaptic potential, EPSP
Facilitation!
!
Summation!
Spatial!
!
!
Temporal
Inhibitory transmissions!
Inhibitory transmitter-receptor interaction or ITRI!
Inhibitory post-synaptic potential IPSP!
!
Integrator post-synaptic neuron
Neurotransmitters!
Acetlycholine (ACh)!
Peripheral mostly!
Acetlycholine esterase!
Acetate and choline
Neural networks!
!
Simple!
Diverging!
Converging!
Reverberating
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