Spinal Cord Anatomy and Physiology

Spinal Cord Anatomy

• The spinal cord begins at the foramen magnum and typically ends at the L2 vertebra in adults.
• The conus medullaris is the tapered end of the spinal cord.
• The cauda equina is a bundle of nerve roots that extends from the conus medullaris.

Spinal Cord Blood Supply

• The anterior spinal artery supplies the anterior two-thirds of the spinal cord.
• The artery of Adamkiewicz, a major radicular artery, typically originates in the T8-12 region.
• Occlusion of the artery of Adamkiewicz can lead to paralysis.
• The thoracolumbar region of the spinal cord is most vulnerable to ischemia due to single blood supply.
• The normal autoregulatory range for mean arterial pressure in the spinal cord is 50-150 mm Hg.

Spinal Cord Coverings

• The pia mater is the innermost layer of meninges and adheres to the spinal cord surface.
• Denticulate ligaments connect the spinal cord to the dura mater.
• The dura mater is the tough outer sheath of the meninges.

Reflexes and Reflex Arcs

• The knee-jerk reflex is a monosynaptic reflex.
• The myotatic reflex, also known as the stretch reflex, helps resist gravity.
• Reciprocal inhibition involves the relaxation of the antagonist muscle during agonist muscle contraction.
• The inverse myotatic reflex, also known as the Golgi tendon reflex, protects muscles from injury during extreme contraction.

Clinical Conditions Related to the Spinal Cord

• Cauda Equina Syndrome is a medical emergency characterized by urinary retention, among other symptoms.
• Transient Neurologic Syndrome is associated with mild to severe pain in the legs and buttocks and is often treated with NSAIDs and trigger point injections.
• Lidocaine, a local anesthetic, has been linked to both Cauda Equina Syndrome and Transient Neurologic Syndrome.
• Anterior Spinal Artery Syndrome (Beck's syndrome) causes paralysis and loss of pain and temperature sensation; vibration sense remains preserved.
• Damage to the Artery of Adamkiewicz can cause flaccid paralysis.

Functions of the Spinal Cord

• The posterior portion of the spinal cord is primarily responsible for sensory information.
• The spinal cord serves as a center for reflex coordination.
• The anterior portion of the spinal cord is associated with motor information.

Intervertebral Discs and Ligaments

• The nucleus pulposus of an intervertebral disc acts as a shock absorber.
• Tendons connect muscle to bone; ligaments connect bone to bone.
• The ligamentum flavum is the strongest ligament in the vertebral column.
• Herniation of the nucleus pulposus typically occurs through the posterior anulus fibrosus.
• Intervertebral discs contribute to the length of the spinal column.

Somatic Motor Systems

• The somatic motor system controls voluntary muscle movements.
• Upper motor neurons are located in the cerebral cortex and brainstem.
• Alpha motor neurons, also known as lower motor neurons, are located in the spinal cord.
• Acetylcholine (ACh) is released at the neuromuscular junction by motor neurons.
• Muscle spindles relay feedback about muscle length to the spinal cord.

Motor Pathways and Tracts

• The corticospinal tract, part of the pyramidal system, is responsible for fine motor control.
• The rubrospinal tract, originating in the red nucleus, is responsible for fine motor control.
• Decussation of most corticospinal tract fibers occurs at the medulla.
• Damage to upper motor neurons can lead to hyperreflexia.
• Lesions below the level of the medullary pyramids produce ipsilateral weakness.

Spinal Cord Disorders and Syndromes

• Lower motor neuron lesions typically result in flaccid paralysis.
• Poliomyelitis is a pure lower motor neuron disease.
• Amyotrophic lateral sclerosis (ALS) involves both upper and lower motor neurons.
• Anterior spinal artery syndrome (Beck's syndrome) causes loss of pain and temperature sensation while preserving proprioception and vibration.

Somatosensory System and Dermatomes

• The dorsal column-medial lemniscus pathway does not transmit pain sensation.
• The C3-4-5 nerve roots keep the diaphragm functioning.
• Herpes zoster can cause painful eruptions in a specific dermatomic area due to nerve infection.

Pain and Temperature Sensation

• Nociceptors are pain receptors in the body.
• Type A delta fibers carry fast, sharp pain signals.
• Referred pain, often described as burning or aching, is poorly localized.
• Phantom limb pain can occur after amputation or congenital limb deficiency.
• Visceral pain is associated with internal organ discomfort.

Temperature Sensation

• Cold fibers respond to a broad range of temperatures.
• Warm fibers respond to narrower temperature ranges than cold fibers.
• Pacinian corpuscles detect vibration and are rapidly adapting.
• Cold fibers are involved in detecting skin contact changes.

Reflex Arcs and Muscle Function

• The brachioradialis reflex is associated with the C5-C6 nerve roots.
• Reciprocal inhibition involves the relaxation of the antagonist muscle.
• The myotatic reflex, also known as the knee-jerk reflex, is a monosynaptic reflex.
• Golgi tendon organs inhibit excessive muscle contraction.
• The ankle reflex is associated with the S1 nerve root.

Neural Pathways for Sensory Processing

• The dorsal column-medial lemniscus pathway decussates at the medulla.
• Damage below the medulla results in ipsilateral loss of proprioception.
• Merkel's disks detect steady pressure.
• The dorsal column-medial lemniscus pathway is primarily involved in light touch, vibration, and proprioception.
• An injury to the spinothalamic tract affects pain and temperature sensation.

Disorders Affecting the Dorsal Column-Medial Lemniscus Pathway

• A positive Romberg sign may indicate a problem with the dorsal column-medial lemniscus pathway.
• Tabes dorsalis, a condition affecting the dorsal columns, is often associated with syphilis.
• Vitamin B12 deficiency can lead to neuropathy affecting the dorsal columns.
• Tabes dorsalis typically results in loss of touch and proprioception.
• Loss of proprioception can cause an ataxic, wide-based gait.

Additional Clinical Considerations

• The C5 nerve root is associated with shoulder abduction and external rotation.
• Spinal cord injuries in the thoracolumbar region are most likely to affect lower limb movement.
• Injury to the posterior spinal artery would affect vibration and proprioception.
• Scoliosis results in lateral curvature of the spine.
• The psoas major muscle is primarily responsible for thigh flexion.

This quiz covers essential topics in spinal cord anatomy, including its structure, blood supply, and protective coverings. Test your knowledge on the conus medullaris, cauda equina, and the meninges. Perfect for students studying neuroanatomy.