Spinal Cord and Nerves Overview

Spinal Cord and Spinal Nerves

• The spinal cord is 45 cm (18 inches) long and extends from the brain to L1-L2.
• It passes through the foramen magnum.
• It's made up of cervical, thoracic, lumbar, sacral, and coccygeal regions.
• It has cervical and lumbosacral enlargements.
• The spinal cord ends at the conus medullaris, continuing as the filum terminale, which is part of the coccygeal ligament.
• Dentate ligaments anchor the spinal cord within the vertebral canal.

Spinal Cord Features

• It integrates and processes information.
• It can function independently of the brain or in conjunction with the brain.
• It's a pathway for sensory and motor signals.
• Spinal reflexes are the body's fastest responses to stimuli.

Spinal Cord Meninges

• Spinal meninges protect, stabilize, and absorb shocks.
• They're continuous with the cranial meninges and contain three layers.
  • Dura mater: tough, fibrous outer layer
  • Arachnoid mater: middle layer
  • Pia mater: innermost layer
• Denticulate ligaments anchor the spinal cord in position.

Spinal Nerves

• 31 pairs of spinal nerves connect the spinal cord to different parts of the body.
• 8 cervical nerves
• 12 thoracic nerves
• 5 lumbar nerves
• 5 sacral nerves
• 1 coccygeal nerve

Spinal Nerve Structure

• Each spinal nerve has a sensory (dorsal) and a motor (ventral) root.

• Sensory and motor nerves transmit impulses to and from the spinal cord.

  • Sensory nerves are afferent nerves and carry impulses towards the spinal cord
  • Motor nerves are efferent nerves and transmit impulses away from the spinal cord

• The spinal nerve structure consists of several layers:

  • Epineurium: outer layer that surrounds the whole nerve
  • Perineurium: layers surrounding fascicles (bundles of axons)
  • Endoneurium: layer surrounding individual axons

Spinal Cord Pathways

• Sensory Pathways: relay information from receptors to the brain

  • Ascending pathways carry sensory information up the spinal cord to the brain
  • Composed of primary, secondary, and tertiary neurons.

• Motor Pathways: transmit signals from the brain to muscles or glands

  • Descending pathways carry motor instructions down the spinal cord to muscles
  • Composed of upper and lower motor neurons.

Spinal Cord Gray Matter Organization

• Gray matter contains cell bodies, dendrites, and axons.
• Nuclei: groupings of cell bodies that control specific functions
  • Sensory nuclei
  • Motor nuclei
• Posterior gray horns: somatic sensory and visceral sensory nuclei
• Lateral gray horns: visceral motor nuclei
• Anterior gray horns: somatic motor nuclei

Spinal cord White Matter

• White matter is composed of myelinated axons that form tracts.
• These tracts carry specific types of information and are organized into funiculi (posterior, lateral, anterior).
• Different tracts carry sensory and motor signals to brain or from brain.

Spinal Cord Injury

• SCI (spinal cord injury) can result in varying degrees of paralysis depending on the level and type of injury.

Pyramidal Tracts

• Descend directly from the cerebral cortex.
• 80% cross over in the medulla, some cross lower in the spinal cord
• Responsible for voluntary movement, especially fine motor skills.

Extrapyramidal Tracts

• Originate in the brainstem.
• Control posture and involuntary movements.
• Do not rely on the cerebral cortex for control
• Include rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts.

This quiz explores the structure and functions of the spinal cord and spinal nerves. It covers aspects such as the length, regions, meninges, and features that allow for reflex actions and information processing. Test your knowledge on the anatomy and functionality of this vital part of the nervous system.