Spinal Cord Anatomy and Blood Supply

Spinal Cord Anatomy

• The spinal cord begins at the foramen magnum and extends down to the level of 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 originating from the lumbar and sacral regions that extend below the conus medullaris.
• The pia mater is the inner layer of meninges that closely adheres to the spinal cord surface.
• Denticulate ligaments attach the spinal cord to the dura mater to stabilize it.

Spinal Cord Blood Supply

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

Reflexes and Reflex Arcs

• The knee-jerk reflex is an example of a monosynaptic reflex involving a single synapse.
• The myotatic reflex helps to resist gravity and maintain posture.
• Reciprocal inhibition involves the simultaneous relaxation of the antagonist muscle while the agonist muscle contracts.
• The Golgi tendon reflex, also known as the inverse myotatic reflex, protects muscles from excessive contraction and injury.

Clinical Conditions Related to the Spinal Cord

• Cauda Equina Syndrome is a medical emergency characterized by urinary retention, bowel dysfunction, and lower extremity weakness.
• Transient Neurologic Syndrome involves mild to severe pain in the legs and buttocks, often resolved with conservative treatment.
• Anterior Spinal Artery Syndrome, also known as Beck's Syndrome, affects the anterior spinal cord causing loss of motor function and pain sensation.
• Damage to the artery of Adamkiewicz can lead to flaccid paralysis.

Functions of the Spinal Cord

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

Intervertebral Discs and Ligaments

• The nucleus pulposus of the intervertebral disc acts as a shock absorber.
• Tendons connect muscles to bones, while ligaments connect bones to bones.
• The ligamentum flavum connects the laminae of adjacent vertebrae and is the strongest ligament in the vertebral column.
• Herniation of the nucleus pulposus typically occurs through the posterior anulus fibrosus.

Somatic Motor Systems

• The somatic motor system controls voluntary muscle movements.
• Upper motor neurons are located in the cerebral cortex and brainstem, while lower motor neurons are located in the spinal cord.
• Alpha motor neurons are another name for lower motor neurons.
• Acetylcholine (ACh) is the neurotransmitter released at neuromuscular junctions.
• Muscle spindles provide feedback about muscle length.

Motor Pathways and Tracts

• The corticospinal tract is part of the pyramidal system and controls voluntary movement.
• The rubrospinal tract originates in the red nucleus and is involved in fine motor control.
• Decussation, or crossing over, of most corticospinal fibers occurs in the medulla.
• Damage to upper motor neurons can lead to hyperreflexia.
• Lesions below the level of the medullary pyramids result in 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) affects both upper and lower motor neurons.
• Anterior Spinal Artery Syndrome is characterized by loss of pain and temperature sensation while sparing vibration.
• Posterior Spinal Artery Syndrome affects the posterior columns, resulting in loss of vibration, proprioception, and touch.

Somatosensory System and Dermatomes

• The dorsal column-medial lemniscus pathway transmits information related to discriminative touch, vibration, and proprioception.
• The C3-C4-C5 spinal nerve roots innervate the diaphragm, essential for breathing.
• Herpes zoster, also known as shingles, can cause painful eruptions in a specific dermatomic area due to reactivation of the varicella-zoster virus.

Pain and Temperature Sensation

• Pain receptors are also called nociceptors.
• Type A delta fibers conduct fast, sharp pain signals.
• Referred pain is often a poorly localized pain sensation that originates from internal organs.
• Phantom limb pain may occur after amputation or congenital limb deficiency.
• Visceral pain originates from internal organs.

Temperature Sensation

• Cold fibers respond to a broad range of temperatures while warm fibers are more specific.
• Pacinian Corpuscles are rapidly adapting mechanoreceptors that detect vibration.
• Cold fibers are primarily involved in detecting changes in skin contact and are crucial for thermoregulation.

Reflex Arcs and Muscle Function

• The brachioradialis reflex is associated with the C5-C6 spinal nerve roots.
• Reciprocal inhibition involves the relaxation of the antagonist muscle during agonist muscle contraction.
• The knee-jerk reflex is a myotatic reflex.
• Golgi tendon organs detect muscle tension and inhibit excessive muscle contraction.
• The ankle reflex is associated with the S1 spinal nerve root.

Neural Pathways for Sensory Processing

• The dorsal column-medial lemniscus pathway decussates at the medulla.
• Damage to the dorsal column-medial lemniscus pathway below the medulla results in ipsilateral loss of proprioception.
• Merkel's disks are slowly adapting mechanoreceptors that detect steady pressure.
• The dorsal column-medial lemniscus pathway is responsible for processing light touch, vibration, and proprioception.
• The spinothalamic tract carries pain and temperature sensation.

Disorders Affecting the Dorsal Column-Medial Lemniscus Pathway

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

Additional Clinical Considerations

• C5 spinal nerve roots are involved in shoulder abduction and external rotation.
• Thoracolumbar spinal cord injuries typically affect lower limb movement.
• Injury to the posterior spinal artery causes loss of vibration and proprioception.
• Scoliosis is characterized by a lateral curvature of the spine.
• The psoas major muscle is the primary muscle responsible for thigh flexion.

Anatomy of the Spinal Cord

• The spinal cord begins at the foramen magnum and ends at the L2 vertebral level in adults.
• The conus medullaris is the tapered end of the spinal cord.
• The cauda equina is a bundle of nerve roots extending 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 blood supply to the spinal cord, typically arises from the T8-12 vertebral level.
• Occlusion of the artery of Adamkiewicz can lead to paralysis.
• The thoracolumbar region of the spinal cord is most vulnerable to ischemia due to its single blood supply.
• Spinal cord autoregulation maintains mean arterial pressure between 50-150 mm Hg.

Spinal Cord Coverings

• The pia mater is the innermost meningeal layer, closely adhering 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 an example of a monosynaptic reflex.
• The myotatic reflex helps resist gravity.
• Reciprocal inhibition involves the relaxation of antagonist muscles during agonist muscle contraction.
• The inverse myotatic reflex, also known as the Golgi tendon reflex, protects muscles from over-contraction.

Clinical Conditions Related to the Spinal Cord

• Cauda equina syndrome is a medical emergency characterized by urinary retention and other neurological deficits.
• Transient neurologic syndrome causes mild to severe leg and buttock pain, typically resolved with conservative treatments.
• Lidocaine is a local anesthetic associated with both Cauda equina syndrome and Transient Neurologic Syndrome.
• Anterior Spinal Artery Syndrome (Beck's Syndrome) causes paralysis and sensory loss except for vibration sense.
• Damage to the artery of Adamkiewicz can lead to flaccid paralysis.

Functions of the Spinal Cord

• The posterior part of the spinal cord primarily processes 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 within an intervertebral disc acts as a shock absorber.
• Tendons connect muscle to bone, while 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 (lower motor neurons) release acetylcholine at the neuromuscular junction.
• Muscle spindles are proprioceptors that provide feedback about muscle length.

Motor Pathways and Tracts

• The corticospinal tract is part of the pyramidal system involved in fine motor control.
• The rubrospinal tract originates in the red nucleus and is responsible for fine motor control.
• Decussation of most corticospinal tract fibers occurs at the medulla.
• Damage to upper motor neurons leads to hyperreflexia and spasticity.
• Lesions below the medullary pyramids cause ipsilateral weakness.

Spinal Cord Disorders and Syndromes

• Lower motor neuron lesion typically results 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 causes loss of pain and temperature sensation while preserving proprioception and vibration.

Somatosensory System and Dermatomes

• The dorsal column-medial lemniscus pathway transmits discriminative touch, vibration, and proprioception.
• The C3-4-5 spinal nerve roots innervate the diaphragm.
• Herpes zoster can cause painful eruptions in a specific dermatomic area due to nerve infection.

Pain and Temperature Sensation

• Nociceptors are pain receptors.
• Type A delta fibers carry fast, sharp pain signals.
• Referred pain is poorly localized and often burning or aching.
• 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 a narrower range of temperatures, detecting high temperatures.
• Pacinian corpuscles detect vibration and are rapidly adapting.
• Cold fibers are primarily involved in recognizing skin contact changes.

Reflex Arcs and Muscle Function

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

Neural Pathways for Sensory Processing

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

Disorders Affecting the Dorsal Column-Medial Lemniscus Pathway

• A positive Romberg sign indicates a problem with the dorsal column-medial lemniscus pathway.
• Tabes dorsalis, a condition associated with syphilis, affects the dorsal columns causing loss of touch and proprioception.
• Vitamin B12 deficiency can lead to dorsal column neuropathy.
• Tabes dorsalis typically causes loss of touch and proprioception.
• Loss of proprioception can cause an ataxic, wide-based gait.

Additional Clinical Considerations

• The C5 spinal nerve root is essential for shoulder abduction and external rotation.
• Thoracolumbar spinal cord injuries primarily affect lower limb movement.
• Injury to the posterior spinal artery affects vibration and proprioception.
• Scoliosis is a lateral curvature of the spine.
• The psoas major muscle is primarily responsible for thigh flexion.

This quiz covers the essential anatomy of the spinal cord and its blood supply, including the conus medullaris, cauda equina, and major arteries. It also discusses the implications of blood supply occlusions and the stabilization of the spinal cord. Test your knowledge on these crucial topics in neurology.