Back: Spinal Cord Flashcards
Spinal Cord
- Part of the central nervous system
- Located in the vertebral canal
- Spans from the foramen magnum to L2
Cervical Enlargement
- C4-T1 segments of cord
Lumbar Enlargement
- L1-S3 segments of cord
Conus Medullaris
- End of the spinal cord located at L2
Thoracic Spine
- Gives rise to the nerves that innervate the upper extremity
Lumbar Spine
- Nerves that innervate the lower extremities
Embryology
- Differential growth between cord and vertebral column/dura mater
Embryo/Fetus Prior to 8 Weeks
- Cord extends length of vertebral canal
Embryo/Fetus 6 Months Onward
- Tip of cord is at vertebral level S1
Spinal Cord Segment
- Gives rise to rootlets at a particular level
Anterior (Ventral) Rootlets
- Contain efferent (motor) nerve fibers
Posterior (Dorsal) Rootlets
- Contain afferent (sensory) nerve fibers
Dorsal Root Ganglion
- Cell bodies of pseudounipolar sensory neurons
Anterior and Posterior Root
- Unite to form spinal nerve
Spinal Nerve
- Mixed nerve (motor and sensory)
- Representative of spinal cord segment
- Exits out intervertebral foramen
Cauda Equina
- spinal nerve roots from the lumbosacral enlargement and conus medullaris
Posterior and Anterior Rami
- Spinal nerves branch into these
Posterior Ramus
- Facet joints of vertebral column
- Deep back muscles
- Skin over the back
Anterior Ramus
- Supply almost everything else
- Anterior and lateral trunk/abdomen (intercostal nerves)
- Upper and lower extremity (brachial & lumbosacral plexuses)
- Neck (cervical plexus)
Meningeal Branches of Spinal Nerves
- Recurrent meningeal nerve
- Branch off the spinal nerve of anterior ramus
Supplied by Recurrent Meningeal Nerve
- Periosteum of portion of the vertebra
- Outer annulus fibrosis
- Dura mater
- PLL
- Blood vessels
Recurrent Meningeal Nerve
- Loops back/passes through the IVF
Posterior Ramus
- Provides motor to deep back muscles and branches that supply the skin, facet joints, zygapophyseal joints
Anterior Ramus
- Larger component of the spinal nerve that innervates everything else
- Forms a plexus (network of nerves)
- T1 and sometimes T2, the lumbar and sacral region nerves connect with each other to for plexus
PLL
- Supplies dura mater
Cervical Spinal Nerves
- Exit vertebral canal above same number vertebrae
Cervical
- 8 spinal nerves
Thoracic
- 12 spinal nerves
Lumbar
- 5 spinal nerves
Thoracic and Lumbar Spinal Nerves
- Exit vertebral canal below same number vertebrae
Sacral
- 5 spinal nerves
Spinal Nerve S5
- Exits through sacral hiatus
S1-S4
- Anterior/posterior rami exit through anterior/posterior sacral foramina
Coccygeal
- Nerves exit through sacral hiatus
Anterior Rami
- Give rise to the intercostal nerves in the thoracic region
- Form plexuses in the cervical and lumbosacral regions
Plexuses
- Give rise to multi-segmental peripheral nerves
Peripheral Nerve
- Nerves that come together from different regions to form a new name nerve
Somatic Nervous System
- Sensory and motor to everything except viscera, smooth muscle, glands
Somatic Nerve Fibers
- Sensation from the body, typically reaches consciousness
- Pain, temperature, touch, pressure
- Proprioceptive (mostly subconscious)
Afferent
- General sensory
Efferent
- Somatic motor
Somatic Motor (Efferent) Nerves
- Skeletal muscle (voluntary)
- Single neuron from spinal cord to muscle
Dermatome
- Area of skin supplied by a spinal segment and spinal nerve
- Usually there is overlap between them
Peripheral Nerve Distribution
- Area of skin supplied by peripheral nerve
Myotome
- Group of muscles innervated by a spinal nerve
- Most muscle groups of the extremity are innervated by multiple spinal nerves (formed by multiple of these)
- One or two are more strongly associated with each muscle groups
Peripheral Nerve Innervation
- Can innervate one or muscle groups
Visceral Innervation
- Cardiac and smooth muscle, glands
Visceral Sensory
- Normally not perceived, subconscious reflexes
- Not sensitive to touch, vibration
- Sensitive to chemical irritation, ischemia
- Large amounts of distension, contraction
- Referred pain
Visceral Motor
- Autonomic nervous system
Visceral Motor (Autonomic Nervous System)
- Involuntary muscle (cardiac and smooth muscles)
- Glandular tissue
Autonomic Nervous System
- Efferent to cardiac and smooth muscle, glands
Autonomic Nervous System
- Sympathetic (thoracolumbar) division
- Parasympathetic (craniosacral) division
Autonomic Nervous System
- 2 neuron chain
- Presynaptic and postsynaptic neuron
- Pre-synaptic neuron synapses on the postsynaptic in an autonomic ganglia
Presynaptic Neurons (Sympathetic ANS)
- Originate in the intermediolateral cell columns (IML)
- Lateral horn of T1-L2(3) gray matter
- Leave through the ventral root
- Enter sympathetic trunk via white rami communicantes
White Rami
- Enter sympathetic trunk via these communicantes
- Only found at T1-L2(3) spinal cord segments
Upon Entering Sympathetic Trunk
- Synapse at same level
- Ascend or descend to synapse in paravertebral ganglia at another level (above T1 or below L3)
- Pass through w/o synapsing
Gray Rami Communicantes
- 1 & 2 exit sympathetic trunk exit through this
Postsynaptic Neurons
- Reach destination via spinal/peripheral nerves and periarterial plexus
Parasympathetic Division of ANS (Craniosacral)
- Innervates head, viscera, erectile tissue
- Not found in the limbs or body wall
Presynaptic Fibers Originate
- Brainstem
- Follows cranial nerves III, VII, IX, X
- S2-4 segments of spinal cord
- Pelvic splanchnic nerves
Parasympathetic Ganglia
- 4 associated with the head (later)
GI Tract and Heart
- Have their own network of neural tissue that governs their function
- Modulated by sympathetic and parasympathetic
Spinal Meninges
- Connective tissue membranes
- Support the cord and nerve roots
- Contain the CSF
Dura Mater
- Tough outermost fibrous sheath
- Continuous with cranial dura
Arachnoid Mater
- Deep to dura (stays in contact with dura)
- ** trabeculae connect with pia mater
- Encloses CSF filled subarachnoid space
- Ends at S2
- Forms spinal dural sac (dural sheath)
Dural Sac
- Ends at S2
Pia Mater
- Covers spinal cord and nerve roots
- Thin and delicate
Leptomeninges
- Arachnoid & pia
Filum Terminale
- End of the conus medullaris
Filum Terminale Internum
- Pia mater (L2 – S2)
Filum Terminale Externum
- Coccygeal ligament: pia and dura
- Attaches to coccyx (S2-coccyx)
Denticulate Ligaments
- 20 – 22 pairs of sawtooth fibrous extensions of pia mater - Attach to inner dural sac
- Pass between dorsal and ventral roots
Epidural Space
- Between bony wall of vertebral canal and dura mater
- Fat
- Internal vertebral venous plexus
- Spinal nerves
- Blood vessels
Dural Root Sleeve
- Extension of dural sheath around roots and dorsal root ganglia
Subarachnoid Space
- Between arachnoid and pia mater
- Continuous with cranial **
Content of Subarachnoid Space
- CSF
- Arteries and veins
- Arachnoid trabeculae
- Cauda equina
- Filum terminale
Vertebral Column From Outside Inward
- Bone
- Epidural space (extradural space)
- Dura mater
- Subdural space (potential space)
- Arachnoid mater
- Subarachnoid space
- Pia mater
- Spinal cord
Lumbar Cistern
- Enlargement of subarachnoid space in the dural sac
- Caudal to conus medullaris (L2 – S2)
- Site of lumbar puncture
Lumbar Puncture
- Performed midline between L3/4 or L4/5
- Patient position in a flexed position
- Gain access to subarachnoid space (anesthesia or CSF sample)
Lumbar Puncture Entry Order
- Skin
- Superficial fascia
- Supraspinous ligament
- Interspinous ligament
- Ligamentum flavum
- Epidural space
- Dura mater
- Arachnoid mater
- Subarachnoid space
Spinal Anesthesia
- Anesthesia introduced into subarachnoid space
Epidural Anesthesia (Blocks)
- Similar to lumbar puncture
- Between lamina or through sacral hiatus (caudal)
Spina Bifida
- Developmental neural tube defect that is the result in nonunion of the neural arches.
- Caused by disruption of neurulation in the embryo
Spinal Bifida Occulta
- Neural tissue IS NOT involved
Spina Bifida Manifesta (Cystica)
- Neural tissue and/or meninges ARE involved
Meningocele (SB Manifesta)
- Meninges protrude through the defect
Meningomyelocele (SB Manifesta)
- Meninges and cord/nerve roots protrude through the defect
Blood Supply of Vertebral Column and Spinal Cord
- Anterior and Posterior Spinal Arteries
Spinal Branches that Pass through the IVF
- Vertebral
- Ascending cervical
- Segmental arteries
- Posterior Intercostal
- Subcostal
- Lumbar
- Lateral sacral
Anterior Spinal Artery
- Branch of vertebral artery
- Runs in anterior median sulcus
- Gives off sulcal arteries
- Supply anterior 2/3 cross-sectional area
Posterior Spinal Arteries
- Branch of posterior inferior cerebellar (most common) or vertebral artery
A/P Radicular Arteries
- Supply the nerve roots
A/P Segmental Medullary Arteries
- Supplement blood supply to spinal cord
- Not present at every level
Great Anterior Segmental Medullary Artery
- Artery of Adamkiewicz
Artery of Adamkiewicz
- Largest segmental medullary artery
- Origin varies: usually left side from lower intercostal or upper lumbar artery
- Blockage can result in caudal cord ischemia
Bastons plexus (Venous Drainage)
- Network of paraspinal veins
Vertebral Column
- Internal/external vertebral venous plexus (epidural venous plexus)
- Basivertebral veins
- Intervertebral vein
Internal/External Vertebral Venous Plexus (Epidural Venous Plexus)
- Communicate with each other through IVF
Basivertebral Veins
- Drain the vertebral bodies
- Communicates with internal & external plexuses
Intervertebral Vein
- Drain cord & column drain into segmental veins
Ant/Post Spinal Veins
- Communicate with internal and external venous plexuses
Vertebal Veinous Plexuses
- Communicate with the dural venous sinuses and deep pelvic veins
- Route of metastasis
- Valveless
Content/Boundaries of IVF
- Spinal nerve
- DRG
- Recurrent meningeal nerve
- Spinal branches of segmental arteries
- Intervertebral veins
- Adipose
Flexion
- Increases IVF size
Extension
- Decreases IVF size
L5
- Has the thickest spinal nerve but smallest IVF (of the lumbar region)
Anatomical Sources of Lower Back Pain
- IVD
- Spinal nerve
- Zygapophyseal joints
- Subchondral bone
- Ligaments
- Muscles
- Viscera (kidneys)
- Sacroiliac joint
Viscera (Kidneys)
- Refer pain to the lower back
Spondylosis
- More generic, broad term that refers to any type of degenerative changes to the spine
Narrowing of IVF
- Osteophytes (bone spurs) on the facet joint
- Osteophytes on uncovertebral processes in the cervical spine
Herniation
- Can decrease the size of the IVF
Herniated Discs
- Can also compress cauda equina and impinge on nerves
Narrowing of Vertebral Canal Causes
- Ligament hypertrophy
- Osteophyte formation
- Disc herniation
- Congenital
Ligament Hypertrophy
- Repeated injuring and healing with additional scar tissue to the point where they become larger
- Can result in narrowing of vertebral canal
Laminectomy
- Removes the lamina of vertebrae (both sides is complete and one side is partial/hemi)
Laminotomy
- Does not remove the lamina, but burrows an opening and removes a portion that is encroaching on cauda equina, nerve roots, etc.
Foraminotomy
- Opens up IVF if it gets narrowed
Discectomy
- Removes pieces if IVF gets narrowed
Herniated Nucleus Pulposus
- Can cause spinal and foraminal stenosis
- Can put pressure on the nerve roots and/or spinal cord
Posterolateral Herniation
- L4/5 and L5/S1 are the most common in lumbar spine
- Typically affects the nerve root below the level of the herniated disc
L4/5 Disc Herniation
- Affects L5 nerve
L5/S1 Disc Herniation
- Affects S1 nerve
Radiculopathy
- Abnormal nerve root sensation depending on what is compressed