THE HUMAN CNS - SPINAL CORD

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Brain lateral view

THE HUMAN CNS

• The human CNS is an over-blown tube.

• During development the simple tubular structure expands.

• Differential growth at rostral and caudal ends.

NEURAL TUBE DEFECTS

• Failure of the neural tube to close may cause spina bifidia

• Or anencephaly

• Folic acid prevents most NTD’s

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Spina bifidia and anencephaly

PRIMARY BRAIN VESICLES

• Vesicles are fluid-filled

swellings at the rostral

end of the neural tube.

• Early vesicles expand and

grow differentially.

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Lateral view

SECONDARY BRAIN VESICLES

• Flexions and

outpocketings

continue

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Lateral view

THE SPINAL CORD

• Retains tubular nature

• Transverse section shows

– White and gray matter (process /

neuronal cell bodies) around a central

canal

• Encased in bony vertebrae

THE SPINAL CORD• From the spinal cord extend

sets of nerve roots

• Dorsal roots and ventral roots

• Dorsal root carries sensory

input in

• Ventral root carries motor

commands out

THE SPINAL CORD INTERNEURONS

• Interneurons may connect between sensory and motor

neurons

• Important in reflexes

SPINAL CORD COLUMNS

• Many pathways run up / down spinal cord

• Ascending and descending pathways

SPINAL CORD COLUMNS• Pathways may have multiple connections (orders,

upper and lower) and many cross over.

THE MENINGES OF THE SPINAL CORD

• Cord is protected by

layers of membrane

– Pia mater

– Arachnoid

– Dura mater

• Continuous with those of

the brain

THE MENINGES OF THE BRAIN

• Dura splits

into two

CEREBROSPINAL FLUID• CSF flows in the central canal, brain ventricles and

subarachnoid space

• CSF floats and cushions the CNS

SAMPLING CSF• CSF composition gives important information on

the state of the CNS

• CSF can be sampled by lumbar puncture

• Needle inserted between 3rd and 4th lumbar

vertebrae

DISORDERS OF CSF FLUID FLOW• Disturbances in fluid flow may evoke hydrocephalus

• External

• Internal

• Increase in intracranial pressure causes cell

death

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Human hydrocephalus - infant

BLOOD-BRAIN BARRIER

• Physiological barrier

• Capillary endothelial cells

• Tight junctions

• Astrocytes

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BBB composition

KEY POINTS

• What’s the neural tube? What if it doesn’t form?

• What are the vesicles? What do they form into?

• Remember the cells, structures and connections of the

spinal cord

• What are the meninges?

• Where is CSF formed? What happens if it doesn’t flow?

• What’s the blood brain barrier?