Chapter 12 Nervous system organization and nervous tissue

1
Chapter 12 Nervous system organization and
nervous tissue

• Nervous system functions
• Sensory input
• Sensory receptors detect stimuli
• Integration
• NS processes information (Information Technology)
• Motor output
• Activates muscles or glands

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Divisions of the NS

• CNS Central Nervous System
• Brain spinal cord

(12.2)
3
Divisions of the NS

• PNS Peripheral Nervous System
• Cranial nerves
• Spinal nerves

(12.2)
4
Sensory / Afferent (Functional) Division

• Somatic nerves
• General somatic (touch, pain, pressure,
  vibration)
• Proprioceptive sense (skin, body wall,
  limbs-muscles joints)
• Special somatic senses (hearing, equilibrium,
  vision, smell)

5
Sensory / Afferent Division

• Visceral nerves
• General visceral stretch, pain, temperature,
  chemical changes, irritation in viscera, nausea,
  hunger
• Special visceral taste

6
Motor / Efferent Division

• Somatic Motor
• Skeletal muscle
• branchial motor

7
Motor / Efferent Division

• Visceral motor (ANS)
• Smooth muscle
• Cardiac muscle
• Glands

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Nervous tissue

• Neurons
• Supporting cells
• Special neuronal characteristics
• Convey APs (excitable)
• Longevity
• Do not divide
• High metabolic rate

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Neuronal cell body

• Soma, perikaryon
• Variable size
• 5-140 µm diameter
• Spherical nucleus
• Nucleolus
• Chromatophilic (Nissl) bodies
• rER free ribosomes
• Neurofibrils
• Intermediate neurofilaments
• Ganglia clusters of soma in PNS (usually)

(12.4)
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Dendrites

• Usually numerous
• Branched
• Contain rER
• Contain receptors to neurotransmitters
• Sends signals to soma

(12.4)
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Axons

• 1 per soma
• Initial segment from axon hillock
• Transmits AP away from soma
• No Nissl bodies (no prot. synth)
• Neurofilaments
• MT
• Axonal transport
• Axon collaterals
• Terminal branches
• Axon terminals

(12.4)
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Neurohistology

• Neuronal cell body
• Nucleus
• Nissl bodies
• Dendrite
• Axon

(12.5)
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Synapses

• Presynaptic neuron
• Postsynaptic neuron

(12.6)
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Synapses

• Axodendritic synapses
• Axosomatic synapses
• Axoaxonic synapses

(12.7)
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Synapse structure

• Presynaptic element
• Axon terminal
• Synaptic vesicles
• Neurotransmitters
• Mitochondria
• Synaptic cleft
• Postsynaptic elements
• NT receptors
• May generate AP

(12.8b)
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Neuron classification by shape

• Multipolar
• gt2 processes
• gt99 of neurons

(12.10a)
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Neuron classification by shape

• Bipolar neurons
• 2 processes
• Rare

(12.10b)
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Neuron classification by shape

• Unipolar neurons
• 1 process
• Quickly forms 2 processes
• Sensory neurons located mainly in dorsal root
  ganglia

(12.10c)
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Neuron classifications by function

• Sensory / afferent neurons
• Sensory receptors in PNS
• Send AP to CNS
• Unipolar soma
• Located in ganglia in PNS

(12.11)
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Neuron classifications by function

• Motor / efferent neurons
• Multipolar
• Soma in CNS
• Except ANS
• Send AP to muscle or gland

(12.11)
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Interneurons / association neurons

• Located in CNS
• gt99 of all neurons
• all multipolar
• Integration of information

(12.11)
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Supporting cells in CNS

• Neuroglia / glial cells
• 101 ratio glianeurons
• Smaller than neurons
• Can divide

12.5
23
CNS Neuroglia

• Astrocytes
• Control ion
• Microglia
• Phagocytic
• Ependymal cells
• Line ventricles
• Oligodendrocytes
• Form myelin sheath

(12.12a)
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Supporting cells in the PNS

• Satellite cells
• Located around nerve cell bodies in ganglia
• Schwann cells / neurolemmocytes
• Form myelin around axons in PNS

(12.13)
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Myelin sheaths

• Wrapping of PM around axon
• Phospholipid bilayers form insulation

(12.15)
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Myelin sheaths

• Allow faster propagation of AP
• Saltatory conduction

(12.14a)
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Myelin in PNS

• Schwann cells wrap around axon
• Gaps between Schwann cells are nodes of Ranvier

12.14a
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Nerve

• Bundle of axons in the PNS
• Endoneurium around each axon
• Loose CT
• Perineurium CT around a bundle of axons
• Epineurium CT around a nerve

(12.16a)
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Reflex arcs

• Reflex rapid motor response to a stimulus
• Unlearned
• Unpremeditated
• Involuntary
• Can involve all muscle types and/or glands

(12.18a)
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Knee-jerk stretch reflex

• Monosynaptic reflex arc
• Tap patellar tendon
• Stretch quadriceps femoris
• Stimulate stretch receptor
• AP to motor neuron
• Contract quadriceps femoris
• Knee extends

12.18a
31
Withdrawal reflex

• Polysynaptic

(12.18b)
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Disorders of NS

• MS multiple sclerosis
• Progressive disease
• Destroys patches of myelin in CNS
• President Bartlet on West Wing
• Autoimmune disease
• AP conduction abnormal
• No known cause
• No cure

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