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Neuroanatomy:Structure & Function
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The Nervous System
Consists of:
Brain
Spinal Cord
Cranial nerves and branches
Spinal nerves and branches
Ganglia
Enteric Plexuses
Sensory receptors
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The Nervous System
3 Functions1. Sensory function
Detection of stimuli (internal and external)
Sensory neurons
2. Integrative function
Process sensory input and make decisions about responses
to stimuli
Interneurons
3. Motor function
Respond to sensory input and carry message to effectors
Motor neurons
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The Nervous System
The Nervous System has 2 subsystems:
Central Nervous System
Brain
Spinal Cord
Peripheral Nervous System
Nerves
Ganglia Receptors
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Peripheral Nervous System
Peripheral Nervous System- 2 subdivisions
1. Somatic Nervous System
Sensory neurons deliver to CNS
Motor neurons from CNS deliver messages to skeletal
muscle only
Motor aspect is consciously controlled- Voluntary
2. Autonomic Nervous System
Innervation of Viscera and GI tract
Motor neurons deliver messages to cardiac muscle, glands,smooth muscle in GI tract
Motor aspect not consciously controlled- Involuntary
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The Nervous System
2 cell types in Nervous System:
1. Neurons
specialised nerve cells
2. Neuroglia
Provide support, nourishment, protection to neurons
i.e. Schwann cell
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Structure of Neuron
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Neuroglia
Schwann Cell
Outer layer called neurolemma* (sheath of
Schwann)
Secretes lipid and protein inner layer called myelin
sheath
Electrically insulates axon and increases speed of
nerve conduction
*Aids in regeneration if axon damaged
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Schwann Cell
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The Spinal Cord
Located within the vertebral canal formed byvertebral foramina
Extends from medulla oblongata in the brainto inferior border of L1
Followed by cauda equina- nerve roots below2ndlumbar vertebrae
Filum terminale- anchors spinal cord to coccyx
Protected by Vertebrae
Meninges (3 layers)
Cerebrospinal fluid (CSF)
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The Spinal Cord
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The Spinal Cord
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The Spinal Cord
Grey matter
Contains cell bodies of neurons, dendrites
of interneurons and motor neurons
Receives input from sensory neurons,
integrates information and provides output
via motor neurons
Nervous tissue with little or no myelin
appears grey
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Grey Matter
Grey matter is shaped like the letter H Divided into regions called horns
Dorsal (posterior) gray horn contains
sensory cell bodies Ventral (anterior) gray horn contains motor
cell bodies
Lateral gray horn contain cell bodies of theautonomic motor neurons that regulate
smooth muscle, cardiac muscle and glands
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The Spinal Cord
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The Spinal Cord
White matter Contains bundles of myelinated and unmyelinated
axons of sensory neurons, interneurons and motor
neurons
Nervous tissue (axons) that are myelinated appear
white
It is divided into 3 columns
Ventral (anterior)
Dorsal (posterior)
Lateral
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White Matter
Each column of white matter contains bundlesof axons called tracts that carry information
up and down the spinal cord
Sensory (ascending) tracts
Motor (descending) tracts
Sensory tracts contain axons that carry nerve
impulses towards the brain; motor tracts carry
nerve impulses down the spinal cord away
from the brain
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The Spinal Cord
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Voluntary Movement
Nerve impulses for precise voluntary
movements propagate from the cortex in the
brain to somatic motor neurons that innervate
skeletal muscles via the direct pathway
The simplest of these pathways consists of
sets of two neurons;
Upper motor neurons
Lower motor neurons
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Upper Motor Neurons
Cell bodies located in the cortex of thecerebrum
Axons descend through the pons and
decussate (cross over) to the opposite side The motor cortex of the right side of the brain
controls muscles on the left side of the body
and vice versa
The axons descend through the lateral
corticospinal (descending) tracts and
terminate in the anterior gray horn
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Lower Motor Neurons
Cell body located in the anterior gray horn at
each spinal cord segment
Axon emerges from spinal cord via the ventral
(anterior) root
Dorsal and ventral roots unite to form a spinal
nerve at the intervertebral foramen where it
exits the vertebral canal
Axons terminate as motor end plates in
skeletal muscle
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The Spinal Cord
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Upper & Lower Motor Neurons
A few upper motor neurons synapse directly
with lower motor neurons
The majority of upper motor neurons synapse
with an interneuron which in turn synapses
with a lower motor neuron
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UMN & LMN Lesions
Upper Motor Neurone Lesions Spastic paralysis of muscles on the opposite side
of the body
Hyper-reflexive (& pathological reflexes) Clonus
Lower Motor Neurone Lesions
Flaccid paralysis of muscles on the same side ofthe body
No voluntary or reflex activity of innervated
muscle fibres
Muscle tone decreased or lost
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References
Tortora, G., Derrickson, B., 2008. Principles of
Anatomy and Physiology. 12thEdition. John Wiley &
Sons
Waugh, A., Grant, A, 2006. Ross and Wilson:Anatomy and Physiology in Health and Illness. 10th
Edition. Churchill Livingstone
OBrien, M., 2010.Aids to the examination of the
peripheral nervous system. 5thEdition. Elsevier
Saunders
Nolte, J., 2008. The Human Brain: An introduction to
its functional anatomy 6th
Edition Mosby Inc