Neuroanatomy Structure AndFunction

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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

Neuroanatomy Structure AndFunction

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