The spinal cord is a vital component of the central nervous system, responsible for transmitting sensory and motor information between the brain and the body. Understanding its anatomy is crucial for comprehending neurological function and the impact of spinal cord injuries.
Spinal Cord Introduction
This is a tubular bundle of nervous tissue and supporting cells that extend from the brainstem to the lumbar vertebrae.
Location: Extends in adults from the foramen magnum to the inferior border of the 1st lumbar vertebrae.
Functions:
- Carries sensory information from the body and part of the head to the CNS via afferent fibers.
- Performs initial processing of this information.
Features
- Shape: Elongated and nearly cylindrical.
- Diameter: Approximate 1cm.
- Length: 45cm in males and 40cm in females.
- Weight: About 30g.
- Has cortical and lumbar enlargements for nerve supply of upper (C5-T1) and lower (L1-S2) extremities.
- Terminates caudally as conus medullaris.
- The spinal nerves bundled at the end of the spinal cord form the cauda equina.
Surfaces:
- Anterior median fissure
- Anterior lateral sulcus
- Posterior median sulcus
- Posterior intermediate sulcus
- Posterior lateral sulcus
Internal structure:
- Central surface
- White matter
- Grey matter
Central surface:
- Cross-section of the spinal cord displays a butterfly-shaped grey matter surrounded by white matter.
White matter:
- Consists of a collection of axons promoting communication, often between layers of cells.
- A tract is a collection of axons and carries specialized information.
- Ascending and descending tracts send and transmit signals from the brain to other nerve cells of the body.
- White matter is divided into right and left halves by the anterior median fissure and posteromedian sulcus.
- This forms the anterior, lateral, and posterior white columns.
- They decussate to form the vertebral white commissure.
Grey matter:
- Consists of 4 projections (horns) which form the area containing neurons and cells of the CNS and the central canal at the center filled with CSF.
- There are 2 ventral and dorsal horns.
- The amount of grey matter found at a particular level correlates to the amount of tissue supplied.
- The ventral horn contains motor neurons that innervate skeletal muscles.
- The dorsal horn receives somatosensory information which is transmitted via ascending pathways to the brain.
Spinal Meninges:
- Three membranes that surround the spinal cord.
- Contain CSF to protect and support the spinal cord.
- Distally they form the filum terminale which attaches to the vertebral bodies of the coccyx.
They include:
- Dura
- Arachnoid
- Pia
Spinal dura mater:
- Most external.
- Extends from the foramen magnum to the filum terminale.
- Separated from the walls of the vertebral canal by the epidural space.
Spinal arachnoid mater:
- Found between the dura and pia mater.
- Separated from pia by the subarachnoid space.
- Distal to the conus medullaris forms the lumbar cistern.
Spinal pia mater:
- The innermost of the meninges.
- Fuses with the filum terminale inferiorly.
Spinal Nerves Introduction
- Consists of 31 pairs of nerves that emerge from the spinal cord.
- Contain both motor and sensory nerve fibers.
- With the exception of C1, spinal nerves exit the vertebral canal via intervertebral foramina.
- C1 passes between the skull and atlas.
- C2 passes through the axis and atlas.
- C1 and the coccygeal nerve have no posterior roots.
Functional Components
- GSA: General Somatic Afferent (Sensory)
- GSE: General Somatic Efferent (Motor)
- GVA: General Visceral Afferent (Sensory)
- GVE: General Visceral Efferent (Motor)
Spinal Nerve Innervation
One spinal nerve innervates the derivatives from one somite that includes the following:
- Dermatome: Cutaneous areas innervated by one spinal nerve.
- Myotome: Muscles innervated by one spinal nerve.
- Sclerotome: Bones and joints innervated by one spinal nerve.
Arterial Supply
- Anterior spinal artery
- Posterior spinal artery
- Anterior and posterior segmental arteries (the largest anterior is the artery of Adamkiewicz)
Venous Drainage
- Anterior and posterior spinal veins
- Radicular veins
Clinical Correlates
Damage to the spinal cord results in paralysis:
- Paraplegia: Paralysis of the lower body.
- Tetraplegia: Paralysis of all four limbs.
Other clinical issues:
- Referred pain: Pain felt in a part of the body other than its actual source.
- Spinal cord infection: Infection affecting the spinal cord or surrounding tissues.
