77/78. spinal cord

What is the typical length of the spinal cord in adults?

The spinal cord is approximately 45 cm long in adults.

From where to where does the spinal cord extend in the vertebral canal?

It extends from the Foramen Magnum, an opening at the base of the skull, inferiorly to the level of the L1-L2 intervertebral disk, which is between the first and second lumbar vertebrae.

What is the tapered, cone-shaped inferior end of the spinal cord called?

The Conus Medullaris, which is the official anatomical term for the caudal termination of the spinal cord.

What is the thin, fibrous thread that extends from the apex of the conus medullaris?

The Filum Terminale, a non-nervous fibrous extension of the pia mater.

What is the functional significance of the spinal cord occupying only about two-thirds of the vertebral canal?

This arrangement provides crucial space around the spinal cord, allowing it to move freely within the vertebral canal and preventing injury from friction or compression during body movements.

What are the two major enlargements found along the length of the spinal cord?

The two enlargements are the Cervical Enlargement and the Lumbosacral (or Lumbar) Enlargement. These regions are wider due to increased amounts of grey matter and nerve roots that supply the upper and lower limbs.

What spinal cord segments are associated with the cervical enlargement?

The cervical enlargement corresponds to spinal cord segments C4-T1. These segments give rise to the nerves that form the brachial plexus, innervating the upper limbs.

What spinal cord segments are associated with the lumbosacral enlargement?

The lumbosacral enlargement corresponds to spinal cord segments L2-S3. These segments give rise to the nerves that form the lumbar and sacral plexuses, innervating the lower limbs.

Describe the internal organization of the spinal cord in terms of its grey and white matter.

Internally, the spinal cord consists of an inner core of grey matter, which primarily contains neuron cell bodies, dendrites, and unmyelinated axons, surrounded by an outer covering of white matter, which is composed of myelinated axons organized into tracts.

How does the grey matter typically appear in a cross-section of the spinal cord?

In a cross-section, the grey matter is characteristically H-shaped, featuring anterior (ventral) horns, posterior (dorsal) horns, and in some regions, lateral horns.

What structure connects the ventral and dorsal grey horns in the spinal cord?

The ventral and dorsal grey horns on each side are connected by a thin central grey commissure, which surrounds a small, cerebrospinal fluid-filled central canal.

What type of specialized cells line the central canal of the spinal cord?

The central canal is lined by Ependymal cells, which are a type of glial cell responsible for producing and circulating cerebrospinal fluid (CSF).

How many spinal nerve segments are recognized in the human spinal cord?

There are 31 spinal nerve segments, categorized as: 8 cervical (C1-C8), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral (S1-S5), and 1 coccygeal (Co1).

How are the spinal nerves formed?

Spinal nerves are formed by the union of two roots: the ventral (anterior) root, which carries motor (efferent) nerve fibers away from the spinal cord, and the dorsal (posterior) root, which carries sensory (afferent) nerve fibers towards the spinal cord.

What are the primary longitudinal arteries that supply the spinal cord with blood?

The spinal cord is supplied by 3 main longitudinal arteries: an anterior spinal artery, which runs along the ventral midline, and a pair of posterior spinal arteries, which run along the dorsolateral sulci.

What is the significance of the Artery of Adamkiewicz?

The Artery of Adamkiewicz (also known as the great anterior radicular artery) is a major blood vessel that typically arises from a lower intercostal or lumbar artery and supplies the inferior \frac{2}{3} of the spinal cord, making it crucial for circulation to this region.

What is the primary function of the filum terminale?

The filum terminale primarily functions as an anchor. It securely attaches the conus medullaris (the tapered end of the spinal cord) and its meningeal coverings to the posterior surface of the coccyx, preventing excessive superior movement of the spinal cord within the vertebral canal.

How does venous blood drain from the spinal cord?

Blood drains from the spinal cord predominantly via anterior and posterior spinal veins. These veins ultimately communicate and empty into the internal vertebral venous plexus, which is a network of valveless veins located within the epidural space, connecting to other major venous systems.

Define the subarachnoid space in the context of the spinal meninges.

The subarachnoid space is the interval located between two of the spinal meninges: the arachnoid mater (the middle layer) and the pia mater (the innermost layer that adheres directly to the spinal cord surface). This space is filled with cerebrospinal fluid (CSF).

What specialized ligaments attach to the dura mater and help suspend the spinal cord within the vertebral canal?

Denticulate ligaments. These are flat, triangular projections of pia mater that extend laterally from the spinal cord, piercing the arachnoid mater and attaching to the inner surface of the dura mater, thereby laterally stabilizing the spinal cord.

weight, length and end

30g

45 cm long from the foramen magnum to L1/2 L3 in newborns

the end is called conus medullaris which extends to a thin thread called the filum terminale

enlargements

• cervical enlargement C5-T1

• lumbar enlargement L1-S2

located

in the vertebral canal of the vertebral column

how many spinal nerves?

31 pairs

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

internal structure

• grey matter is in a H shape composed of neuronal cell bodies, show ventral and dorsal grey horns connected by thin commissure containing a small central canal

• white matter surrounds the grey made up of axons which connect the brain to the PNS

• small intermediate grey horn present from T1-L2 and S2-S4

• central canal lined by ependymal cells surrounded by glial cells filled with CSF connected to the 4th ventricle

meninges

spinal cord and nerve root wrapped in 3 meninges

epidural space between dura and vertebra

dura mater thickest

subdural space

arachnoid mater

subarachnoid space containing CSF

pia mater

blood supply

• vertebral artery give rise to ant. and post, spinal arteries

• segmental arteries are deep cervical, ascending cervical and posterior intercostal which give rise to 31 pairs of radicular arterial branches supplying the roots of spinal nerves

• the segmental arteries pass through the intervertebral foramen and divide into anterior and posterior radicular aa.

• 1 anterior spinal artery supply 2/3 of SC

• 2 posterior spinal arteries supply posterior 1/3 of SC

• artery of Adamkiewicz is a dominant segmental artery and damage to this can cause paralysis from spinal cord infarction

• anterior and posterior spinal veins drain into radicular veins which empty into vertebral venous plexus which empty into vertebral and segmental veins

• veins of spinal cord and vertebral column are valveless

white matter

• divided into 3 columns/funicili

• anterior, lateral, and posterior, containing myelinated axons that facilitate communication between the spinal cord and the brain

• in CNS nerve cell bodies are organised into functional clusters called nuclei

• axons in CNS are grouped into tracts

spinal cord nerve segments

ventral (anterior) is motor and dorsal (posterior) is sensory they combine to form spinal nerves on each side of the spinal cord

ascending tract

carry sensory information from the PNS to the brain

pain, temperature, pressure, touch

descending tract

relaying motor commands from the brain to the muscles

intersegmental tracts

part of white matter consist of axons that connect different segments of the spinal cord with each other and brain

what are the nerve cell groups in the posterior horn

• zona spongiosa

• substantia gelatinosa

• nucleus proprius

• nucleus dorsalis

depressions on surface of spinal cord

The spinal cord is marked by two depressions on its surface. The anterior median fissure is a deep groove extending the length of the anterior surface of the spinal cord. On the posterior aspect there is a slightly shallower depression – the posterior median sulcus.

arterial supply

The arterial supply to the spinal cord is via three longitudinal arteries – the anterior spinal artery and the paired posterior spinal arteries.

• Anterior spinal artery – formed from branches of the vertebral arteries. They travel in the anterior median fissure.

• Posterior spinal arteries – originate from the vertebral artery or the posteroinferior cerebellar artery. They anastamose with one another in the pia mater.

Additional arterial supply is via the anterior and posterior segmental medullary arteries – small vessels which enter via the nerve roots. The largest anterior segmental medullary artery is the artery of Adamkiewicz. It arises from the inferior intercostal or upper lumbar arteries, and supplies the inferior 2/3 of the spinal cord.

dorsal funiculus

The ascending gracile and cuneate fasciculi occupying the dorsal column, and sometimes are named the dorsal funiculus.

fibers carry information related to tactile, two point discrimination of simultaneously applied pressure, vibration, position, and movement sense and conscious proprioception.