Introduction to Nervous Tissue - JU Medicine · 2018-08-11 · Introduction to Nervous Tissue ....
Transcript of Introduction to Nervous Tissue - JU Medicine · 2018-08-11 · Introduction to Nervous Tissue ....
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Introduction to Nervous Tissue
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Nervous Tissue
▪ Controls and integrates all body activities within limits that maintain life
▪ Three basic functions
1. sensing changes with sensory receptors
2. interpreting and remembering those changes
3. reacting to those changes with effectors (motor function) 2
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The PNS is divided into :
1- a somatic nervous system
(SNS)
2- an autonomic nervous system
(ANS)
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Sensory (Afferent) vs. Motor (Efferent)
e.g., skin
e.g., muscle
Gray’s Anatomy 38 1999
sensory (afferent) nerve
motor (efferent) nerve
(pseudo-) unipolar neurons conducting impulses
from sensory organs to the CNS
multipolar neurons conducting impulses
from the CNS to effector organs (muscles & glands)
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Organization
6
Integration MotorSensory
SNS
(Sensory)
ANS
(Sensory)
Brain
Spinal
cord
SNS
(Motor)
ANS
(Motor)
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Neuron has three parts:
(1) a cell body: perikaryon or soma
(2) dendrites
(3) an axon
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Neurons
cell
body
dendrites
axon with
myelin sheath
synapses
Schwann
cell
Moore’s COA5 2006
• Dendrites: carry nerve impulses toward cell body
• Axon: carries impulses away from cell body
• Synapses: site of communication between neurons using chemical
neurotransmitters
• Myelin & myelin sheath: lipoprotein covering produced by glial cells that
increases axonal conduction velocity
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Notice that action potential propagation is unidirectional
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Neurons
1. Cell body
a) Nissl bodies
b) Golgi apparatus
c) Neurofilaments (IFs)
d) Microtubules
e) Lipofuscin pigment clumps
2. Cell processes
a) Dendrites
b) Axons
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Structure of neurons
▪ Axoplasm: cytoplasm of axon
▪ Axolemma: cell membrane of axon
▪ Axon hillock: where axon originates from soma
▪ Synaptic boutons: swelling of axon terminal
▪ Synapse: junction axon makes with cell acting upon
▪ Synaptic vesicles
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Axon
▪ Nearly constant diameter
▪ Much Longer
▪ Branches less profusely
▪ Distal end forms terminal arborization and
terminal boutons
▪ Mostly myelinated, could be unmyelinated
▪ Axoplasm contains mitochondria,
microtubules, neurofilaments and SER but
not RER and ribosomes
▪ Bidirectional transport along the axon
Dendrite
▪ Becomes much thinner (tapering)
▪ short
▪ Branches profusely
▪ The cytoplasm of its base is similar to cell
body
▪ Dendtric spines (points of synapse with
other neurons)
▪ Typically unmyelinated
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presynaptic neuron
postsynaptic neuron
Synaptic vesicles
contain the neurotransmitter
synaptic cleft
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Axonal transport
Anterograde: movement away from soma
Retrograde: movement up toward soma
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Neuroglia :
➢Support, nourish, and protect neurons
➢Divide
➢Smaller cells but they greatly outnumber neurons
Neurons:
➢ Sensing, thinking, remembering, controlling muscle activity, and regulating glandular
secretions
➢Do not divide (no centriols!!!)
➢Long lived
➢High metabolic activity
➢Electrically excitable
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Parts of a Neuron
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Nucleus with
Nucleolus
Axon or
Dendrites
Cell body
Neuroglial cells
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1. Multipolar neurons
➢ usually have several dendrites and one axon
➢ motor neurons
2. Bipolar neurons
➢ have one main dendrite and one axon
➢ the retina of the eye
3. Unipolar neurons (pseudounipolar neurons)
➢ sensory neurons
Structural classification
of neurons
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Copyright © McGraw-Hill CompaniesFigure 9-4
4- Anaxonic neuron:
-CNS
-Lack true axon
-Don’t produce action potential
-Regulatory function
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1. Tissues: neurons vs. glia
2. Position: CNS vs. PNS
3. Function 1: sensory vs. motor
4. Function 2: somatic vs. visceral
Gray’s Anatomy 38 1999
neuron
glial cell
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Continuous versus Saltatory Conduction
1. Continuous
conduction
(unmyelinated fibers)
2. Saltatory conduction
(myelinated fibers)
A.P.Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
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Saltatory Conduction
▪ Nerve impulse conduction
in which the impulse jumps
(Salta) from node to node
A.P.Na
Na
Na
Na
Na
Local anesthetics!!!!!!
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Types of synapses
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1. a ganglion (plural is ganglia) a cluster of
neuronal cell bodies located in the PNS.
2. a nucleus: a cluster of neuronal cell bodies
located in the CNS.
Clusters of Neuronal Cell Bodies
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• A nerve: is a bundle of axons that is located in the PNS.
➢Cranial nerves connect the brain to the periphery
➢ spinal nerves connect the spinal cord to the periphery
• A tract: is a bundle of axons located in the CNS.
➢ Tracts interconnect neurons in the spinal cord and brain.
Bundles of Axons
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Copyright © McGraw-Hill CompaniesFigure 9-26
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Copyright © McGraw-Hill CompaniesFigure 9-26
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Peripheral Nerve