4 CEREBELLAR ANATOMY: INTERNAL FEATURES

Brain Stem and Cerebellum



57



Section in Plane of Superior Cerebellar Peduncle

Decussation of superior cerebellar peduncles



Cerebral peduncle

Medial longitudinal fasciculus



4th ventricle

Superior medullary velum



Superior cerebellar peduncle



Fastigial nucleus

Globose nuclei

Dentate nucleus

Emboliform nucleus



4.4  CEREBELLAR ANATOMY: INTERNAL

�FEATURES

The major internal subdivisions of the cerebellum are shown

in this transverse section. The outer zone, the cerebellar cortex

(three-layered), is infolded to form numerous folia. Deep to the

folia is the white matter, carrying afferent and efferent fibers

associated with the cerebellar cortex. Deep to the white matter are the deep cerebellar nuclei, cell groups that receive most

of the output from the cerebellar cortex via Purkinje cell axon



Lingula

Cerebellar cortex

Vermis



�

projections.

The deep cerebellar nuclei also receive collaterals

from mossy fiber and climbing fiber inputs to the cerebellum.

These direct afferent inputs to the deep nuclei provide a coarse

adjustment for their output to upper motor neurons, whereas

the loop of afferent input through the cerebellar cortex back to

the deep nuclei provides fine � adjustments for their output to

upper motor neurons. The cerebellar peduncles are interior

to the deep nuclei; these massive �fiber bundles interconnect the

cerebellum with the brain stem and the thalamus.



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5



SPINAL CORD



5.1



Spinal Column: Bony Anatomy



5.2



Lumbar Vertebrae: Radiography



5.3



Spinal Cord: Gross Anatomy in Situ



5.4



The Spinal Cord: Its Meninges and Spinal Roots



5.5



Spinal Cord: Cross-Sectional Anatomy in Situ



5.6



Spinal Cord: White and Gray Matter



59



60



Overview of the Nervous System



Anterior View



Left Lateral View



Posterior View



Atlas (C1)



Atlas (C1)



Axis (C2)



Axis (C2)



C7



C7



T1



T1



T12

L1



T12

Intervertebral

disc



Body



L1

Spinous

process

Transverse

process

Lamina

Pedicle

L5



L5



Sacrum

(S1–5)

Sacrum (S1–5)



Coccyx



5.1╇SPINAL COLUMN: BONY ANATOMY

Anterior, lateral, and posterior views of the bony spinal

�column show the relationships of the intervertebral discs with

the vertebral bodies. The discs’ proximity to the intervertebral

foramina provides an anatomical substrate for understanding

the possible impingement of a herniated nucleus pulposus on



Coccyx



spinal roots. Such impingement can cause excruciating, radiating pain if dorsal roots are involved and can cause loss of

motor control of affected muscles if ventral roots are involved.

In the adult, the spinal cord extends caudally only as far as the

L1 vertebral body, leaving the lumbar cistern (the subarachnoid space) accessible for withdrawal of cerebrospinal fluid.



Spinal Cord



Anteroposterior Radiograph



61



Lateral Radiograph

T12



L1

SA



L2



IA



IN



D

SN



T



L3



B



P



P



T



P

I



IA



SA

L4

L



S



S



L



L5



S1

SF



B

IA

L

P

S

SA

SF

T



SF



Body of L3 vertebra

Inferior articular process of L1 vertebra

Lamina of L4 vertebra

Pedicle of L3 vertebra

Spinous process of L4 vertebra

Superior articular process of L1 vertebra

Sacral foramen

Transverse process of L3 vertebra



5.2╇ LUMBAR VERTEBRAE: RADIOGRAPHY

These lumbar radiographs show the lumbar spine in an anteroposterior view and a lateral view. The vertebral bodies,

with their spinous and transverse processes, are visible, and

the spaces occupied by the intervertebral discs are � uniform



S2



D

Intervertebral disc space

I

Intervertebral foramen

IA Inferior articular process of L3 vertebra

IN Inferior vertebral notch of L2 vertebra

P

Pedicle of L3 vertebra

S

Spinous process of L3 vertebra

SA Superior articular process of L4 vertebra

SN Superior vertebral notch of L3 vertebra

Note: The vertebral bodies are numbered



and symmetrical in a normal radiograph. A herniated disc may

show a disruption of that symmetry. However, the �presence

of lumbar radiculopathy and a herniated disc is not always

�accompanied by radiographic abnormalities.



62



Overview of the Nervous System



C1

1st cervical nerve

Cervical enlargement

C7

8th cervical nerve

T1

1st thoracic nerve

Spinal dura mater

Filaments of nerve root



T12

Lumbosacral enlargement

12th thoracic nerve

L1

1st lumbar nerve

Conus medullaris

Cauda equina

L5

5th lumbar nerve

S1

1st sacral nerve

Filum terminale

5th sacral nerve

Coccygeal nerve

Coccyx



5.3╇ SPINAL CORD: GROSS ANATOMY IN SITU

The posterior portions of the vertebrae have been removed to

show the posterior (dorsal) surface of the spinal cord. Cervical

and lumbosacral enlargements of the spinal cord reflect innervation of the limbs. The spinal cord extends rostrally through

the foramen magnum, continuous with the medulla. The conus medullaris is located under the L1 vertebral body. The

longitudinal growth of the spinal column exceeds that of the

spinal cord, causing the spinal cord to end considerably more

rostrally in the adult than in the newborn. The associated

nerve roots traverse a considerable distance through the subarachnoid space, particularly more caudally in the lumbar cistern, to reach the appropriate intervertebral foramina of exit.

In the lumbar cistern, this collection of nerve roots is called

the cauda equina (horse’s tail). The lumbar cistern is a large

reservoir from which cerebrospinal fluid can be � withdrawn.



The filum terminale helps to anchor the spinal cord caudally

to the coccyx.

CLINICAL POINT

In the adult, the spinal cord ends at the level of the L1 vertebral body,

and the roots extend caudally in the cauda equine to exit in the appropriate intervertebral foramina. As a consequence, a large lumbar cistern is filled with cerebrospinal fluid (CSF); from this cistern, samples

can be drawn in a spinal tap with little risk for neurological damage by

the needle. Analysis of CSF is a vitally important part of neurological

assessment in many conditions, such as infections, bleeds, inflammatory conditions, some degenerative conditions, and other disorders.

The CSF is commonly analyzed for color and appearance, viscosity,

cytology, and the presence of red and white blood cells, protein, and

glucose. It should be noted that in some conditions in which intracranial pressure is elevated, withdrawal of CSF from the lumbar cistern

may encourage brain stem herniation through the foramen magnum.



Spinal Cord



63



Posterior View

Rami communicantes

Dura mater

Dorsal root

Dorsal root (spinal) ganglion

Arachnoid

Mesothelial septum in posterior median sulcus

Subarachnoid space

Pia mater (overlying spinal cord)

Filaments of dorsal root

Denticulate ligament



Anterior View

Gray matter

Lateral funiculus



Filaments of dorsal root

White matter

Dorsal root

Dorsal root (spinal) ganglion

Spinal nerve

Ventral root

Filaments of ventral root

Anterior median fissure

Anterior funiculus



5.4╇THE SPINAL CORD: ITS MENINGES

AND SPINAL ROOTS

The upper illustration is a posterior (dorsal) view of the �spinal

cord showing both intact and reflected meninges. The pia �adheres

to every contour of the spinal cord surface. The arachnoid

�extends over these contours and adheres to the overlying dura, a

very tough, fibrous, and protective membrane. These meninges

extend outward to the nerve roots. The denticulate �ligaments are

fibrous structures that help to anchor the spinal cord in place.

The posterior spinal arteries supply the dorsal spinal cord with

blood and run just medial to the dorsal root entry zone. The

lower illustration shows an anterior (ventral) view of the spinal

cord with the meninges stripped away. Both the dorsal and the

ventral roots consist of a convergence of rootlets that provide a

continuous dorsal and ventral array of rootlets along the entire

longitudinal extent of the spinal cord.



CLINICAL POINT

Groups of contiguous dorsal and ventral spinal rootlets converge to

form the major dorsal and ventral roots associated with each level of the

spinal cord. Herniation of an intervertebral disc, usually resulting from a

Â�flexion injury, may cause the nucleus pulposus to extrude in a posterolateral direction and impinge on a dorsal root. The L5–S1 and L4–L5 discs

are most commonly involved in the lower extremities, and the C6–C7,

C5–C6, and C4–C5 in the upper extremities. Sharp, radiating pain in

the territory of the nerve root is the most common symptom. In some

disc herniations, a specific muscle-stretch reflex may be absent or diminished. When there is compression of a dorsal root, there will not be a

corresponding nerve root territory in which anesthesia is present, unlike

in a branch lesion of the trigeminal nerve; the dorsal roots send sensory

axons to at least three dermatomal segments and have sufficient overlap

that an isolated root lesion is unlikely to produce complete anesthesia in

that territory. Compression of a ventral root because of disc herniation

is less common than that of a dorsal root; it may be accompanied by

significant weakness in the muscles supplied by that ventral root.