ANA 305 Histology of the Spinal Cord Flashcards
Discuss the spinal cord
The Spinal cord is a long, thin, tubular structure that is made up nervous tissue.
•It extends from the medulla Oblongata (BS) to the lumbar region of the vertebral column.
•It encloses the central canal of the spinal cord that contains CSF
Location: It is located in the vertebral foramen and is made up of 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
Note: A pair of spinal nerves leave each segment of the cord
The spinal cord is a flattened cylindrical structure that is directly continuous with the brainstem
•It begins superiorly at the foramen magnum in the skull, and it is continuous with the medulla oblongata of the brain
• it terminates inferiorly in the adult at the level of the lower border of the first lumbar vertebra
• In the young child, it is relatively longer and usually ends at the upper border of the third lumbar vertebra
•it is surrounded by the three meninges, the dura mater, the arachnoid mater, and the pia mater
How many spinal nerves are there and types?
It has 31 pairs of spinal nerves
•8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
Length of the spinal cord
The length of the spinal cord is about 45 cm in men and 43 cm in women.
How are the spinal nerves connected to the spinal cord?
by the anterior or motor roots and the posterior or sensory roots.
What is the structure of the spinal cord?
In transverse section, the spinal cord is incompletely divided into symmetrical halves by a dorsal (posterior) median septum and a ventral (anterior) median sulcus.
Parts of spinal cord
•It consists of
i. an outer layer of white matter and
ii. an inner core of gray matter.
•The amount of gray matter reflects the number of neurons present.
it is proportionately largest in the cervical and lumbar enlargements, which contain the neurons that innervate the limbs.
•The absolute amount of white matter is greatest at cervical levels, and decreases progressively at lower levels, because descending tracts shed fibres as they descend and ascending tracts accumulate fibres as they ascend.
Describe the grey matter of the spinal cord
●In transverse section, the gray matter is seen as butterfly-shaped or an H-shaped pillar
●with anterior and posterior gray columns or horns, united by a thin gray commissure containing the small central canal.
●A small lateral gray column or horn is present in the thoracic and upper lumbar segments of the cord.
The gray matter of the spinal cord is a complex mixture of neuronal cell bodies (nerve cells), their processes, synaptic connections, neuroglia and blood vessels.
● The nerve cells in gray matter are multipolar, and the neuroglia forms an intricate network around the nerve cell bodies and their neurites.
•The gray matter that immediately surrounds the central canal and unites the two sides constitutes the dorsal and ventral grey commissures.
Describe the ventral and lateral horn of the grey matter
The ventral horn contains efferent neurons whose axons leave the spinal cord in ventral nerve roots.
• A small intermediate or lateral horn is present at thoracic and upper lumbar levels; it contains the cell bodies of preganglionic sympathetic neurons.
What are Rexed’s laminae?
These laminae are defined on the basis of neuronal size, shape, cytological features and density and are numbered in a dorsoventral sequence.
Describe Lamina I
Lamina I (lamina marginalis or Posteromarginal nu) is a very thin layer with an ill-defined boundary at the dorsolateral tip of the dorsal horn.
Describe lamina III
Lamina III consists of somata which are mostly larger, more variable and less closely packed than those in lamina II.
•It also contains many myelinated fibres.
•The ill-defined nucleus proprius of the dorsal horn corresponds to some of the cell constituents of laminae III and IV.
Describe lamina II
➢The much larger lamina II (Substantia gelatinosa) consists of densely packed small neurons, responsible for its dark appearance in Nissl-stained sections.
➢ With myelin stains, lamina II is characteristically distinguished from adjacent laminae by the almost total lack of myelinated fibres. Lamina II corresponds to the substantia gelatinosa.
Describe lamina IV
Lamina IV is a thick, loosely packed, heterogeneous zone permeated by fibres. Its neuronal somata vary considerably in size and shape, from small and round, through intermediate and triangular, to very large and stellate.
Describe lamina V and VI
Laminae V and VI lie at the base of the dorsal horn.
•They receive most of the terminals of proprioceptive primary afferents, profuse corticospinal projections from the motor and sensory cortex and input from subcortical levels, suggesting their involvement in the regulation of movement.
➢Lamina V is a thick layer, divisible into a lateral third and medial two-thirds (spinothalamic & spinoreticular fibres)
➢Lamina VI is most prominent in the limb enlargements.
Describe lamina VII
Lamina VIII spans most of the ventral horn or the base of the thoracic ventral horn but is restricted to its medial aspect in limb enlargements (Ventromedial nu & Dorsomedial nu.)
Describe lamina IX
Lamina IX is a complex array of cells consisting of α and γ motor neurons and many interneurons in the ventral horn (Ventrolateral, Dorsomedial and retrodorsolateral nu.)
