Spinal Cord Structure and Function Quiz

Spinal Cord Structure and Function

• The spinal cord extends from the medulla to L1/L2.
• It is located within the vertebral canal of the vertebral column.
• In adults, the spinal cord only occupies the upper two-thirds of the vertebral column.
• It is protected by the vertebral column, meninges and cerebrospinal fluid.

Intended Learning Outcomes

• Describe the gross anatomy and internal structure of the spinal cord.
• Identify the locations of the ascending and descending tracts within the spinal cord.
• Differentiate between upper and lower motor neurons.
• Describe the mechanism of spinal reflexes and their significance.

Gross Anatomy

• The spinal cord has two swollen regions: cervical and lumbar.
• The spinal cord ends between L1 and L2.
• The spinal cord is considerably shorter than the vertebral column.

Gross Anatomy - Details

• Conus Medullaris: Tapered end of the spinal cord (L1/L2).
• Filum Terminale: Delicate strand of fibrous tissue extending downwards from the conus medullaris.
• Cauda Equina: Lumbosacral nerve roots surrounding the filum terminale, resembling a horse's tail.

Meninges of the Spinal Cord

• Dura Mater: Outermost meninx.
• Arachnoid: Middle meninx.
• Pia Mater: Innermost meninx.

Clinical Connection - Spinal Tap

• A spinal tap (lumbar puncture) involves inserting a needle into the subarachnoid space to withdraw cerebrospinal fluid (CSF).
• This procedure is used for diagnostics, introducing medications and measuring CSF pressure.
• Access to the subarachnoid space during a spinal tap is facilitated by the space between vertebrae L3 and L4 or L4 and L5. Flexion of the spine further increases this space.

Spinal Nerves

• Spinal nerves connect the spinal cord to the rest of the body.
• They are composed of two bundles of axons (roots): posterior roots and anterior roots.
• Spinal nerves exit through intervertebral foramina.
• Spinal nerves from different levels combine to form peripheral nerves.

Spinal Segmentation

• There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
• Cervical nerves exit above their corresponding vertebral body (C8 is an exception).
• All other spinal nerves exit through the intervertebral foramen below their corresponding vertebra.
• Lumbar and sacral nerves extend some distance before exiting their intervertebral foramina.

Dermatome

• A dermatome is an area of skin innervated by a single spinal nerve root.

Myotome

• A myotome is a group of muscles innervated by a single spinal nerve root.
• Used to assess muscle activity, particularly in cases of suspected nervous system damage.
• These contractions are performed isometrically, in mid-range.

Internal Structure of the Spinal Cord

• The spinal cord contains gray and white matter.
• Gray matter houses cell bodies of neurons and interneurons.
• White matter consists of myelinated axons.

White Matter Tracts

• Anterior Column
• Lateral Column
• Posterior Column

Descending Tracts

• Lateral corticospinal
• Rubrospinal
• Reticulospinal
• Vestibulospinal
• Anterior corticospinal
• Tectespinal

Ascending Tracts

• Posterior spinocerebellar
• Lateral spinothalamic
• Anterior spinocerebellar
• Spinotectal
• Anterior spinothalamic
• Fasciculus cuneatus
• Fasciculus gracilis

Types of Neurons in the Spinal Cord

• Sensory neurons
• Upper motor neurons
• Alpha (skeletomotor) neurons
• Gamma (fusimotor) neurons
• Interneurons

Motor Neuron

• Upper motor neuron: Entirely within the central nervous system (CNS).
• Lower motor neuron: Cell body in the CNS sending axons to innervate muscles.

Spinal Reflex

• A reflex is a fast, involuntary action in response to a stimulus.
• A reflex arc is the pathway of neural impulses involved in a reflex.

Classification of Reflexes

• Monosynaptic/polysynaptic
• Ipsilateral/contralateral
• Intra-segmental/inter-segmental

Spinal Reflexes - Examples

• Stretch reflex
• Flexor withdrawal reflex
• Crossed extension reflex
• Plantar reflex/Babinski sign

What does the spinal cord do?

• Motor control
• Sensory information transmission
• Autonomic regulation
• Central pattern generators (coordinating rhythmic movements like stepping).