Anatomy of the Spinal Cord and Spinal Nerves Flashcards
Where is the spinal cord located?
In the vertebral canal of the vertebral column.
What is the structure of the spinal cord?
Central core of gay matter (neuron cell bodies etc.) and surrounding white matter (axons etc.)
How many pairs of spinal nerves are there and what are they?
31 pairs. 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
What is each spinal nerve formed from?
The union of anterior (central) root and posterior (dorsal) root
What does each spinal nerve divide into?
Anterior ramus and posterior ramus.
Where does the spinal cord begin?
Begins at foramen magnum at base of skull (continuous with medulla of brainstem), travels from vertebral levels C1 to L1/L2 in adults (L3 in infants).
What is conus medullaris?
The tapered inferior end of the spinal cord.
How are spinal nerves names?
named according to their exit point from the spine - intervertebral foramen or anterior and posterior sacral foramen.
Where do cervical spinal nerves exit from?
Exit above corresponding pedicle.
Where do throacic and lumbar spinal nerves exit from?
Below corresponding pedicle.
Where do sacral spinal nerves exit from?
Rami exit via sacral foramina (S1-4) or sacral hiatus
Where are nerve roots located?
In the vertebral canal.
What is the cauda equine?
The nerve roots inferior to cord.
What are the meninges of the spinal cord?
Pia - innermost layer, attached to surface of spinal cord.
Arachnoid - middle layer
Dura - outermost layer, thickest.
Subarachnoid space
Between pia and arachnoid, filled with cerebrospinal fluid (CSF); brain and spinal cord floats in CSF
Subdural space
Between dura and arachnoid, potential space
Epidural space
Between dura and vertebrae, contains fat and blood vessels (but in cranial cavity, a potential space)
Where are the dura, arachnoid and subarachnoid space present?
From foramen magnum to sacral hiatus.
Internal filum terminale
Extension of the pia, anchors conus medullaris of spinal cord to dura inferiorly (at S2).
External filum terminale
Extension of dura, anchors dura (dural sac) at S2 to sacrum/coccyx
Denticulate ligaments
Projections of pia from spinal cord to arachnoid/dura
What are the clinical correlations of the lumbar spine?
Sample CSF
Measure CSF pressure
Deliver drugs or radiological contrast (myelography) from/to subarachnoid space.
Lumbar puncture
Lumbar cistern, with CSF and cauda equine, from L1/2 vertebra (spinal cord termination; L3 in newborn) to S2 vertebra (dural sac termination). Usually accessed between L3 and L4, or L4 and L5 spinous processes of vertebrae.
What is a spinal nerve formed from?
The union of the posterior (dorsal) root (sennsory axons - afferent fibres) and anterior (ventral) root (motor axons - efferent fibres).
Sensor fibres
Afferent fibres. Convey information from the body to the CNS. Axons in spinal nerves, dorsal root and spinal cord.
Where are primary sensory neuron cell bodies located?
In spinal ganglia (dorsal root ganglia, DRG)
Somatic motor (efferent) fibres
Innervate skeletal muscle fibres, causing muscle contraction.
Where are lower motor neuron (LMN) cell bodies found?
in ventral (anterior) horn of spinal cord.
Where are axons of somatic motor fibres found?
Cord, ventral root and spinal nerves.
Visceral motor fibres
Efferent fibres. Control cardiac muscle, smooth muscle, or glands. Are part of the autonomic nervous system.
Visceral motor neuron cell bodies
Located in the lateral horn of spinal cord.
Sympathetic (thoracolumbar) division of ANS: T1-T12 and L1-L2 segments.
Parasympathetic (craniosacral) division of ANS: S2-S4 (others in brainstem in cranial cavity)
Second set of neuron cell bodies in ganglia.
Where are visceral motor neuron axons located?
Ventral roots and spinal nerves.
What are rami?
Rami are mixed nerves: sensory and motor fibres.
What do spinal nerves divide into?
Dorsal (posterior) rami: to muscles and skin of the back.
Ventral (anterior) rami: to muscles and skin of anterolateral trunk and limbs.
What are dermatomes?
Dermatomes are regions of skin supplied by a single spinal cord segment (pair of spinal nerves including dorsal and ventral rami).
What are myotomes?
Myotomes are muscle fibres supplied by a single spinal cord segment.
Lower limb dermatomes
L1-5, S1-3. Adjacent dermatomes overlap.
What is the difference between cutaneous nerves and dermatomes?
Cutaneous nerves are identifiable by dissection, they are peripheral nerves that supply an area of skin. They usually contain axons from more than one spinal nerve and contain sensory fibres and autonomic fibres.
Dermatomes are a region of skin supplied by a single spinal cord segment (pain of spinal nerves) and cannot be identified by dissection.
What are the cutaneous nerves of the thigh?
Lateral cutaneous nerve of the thigh (lateral femoral cutaneous nerve) - separate branch from lumbar plexus.
Anterior cutaneous nerve of the thigh from femoral n.
Posterior cuteneous nerve of the thigh - separate branch from sacral plexus.
Obturator n.
others supply small areas.
Cutaneous nerve of the leg
Sural n (and lateral sural, medial sural)
Saphenous n - from femoral n
Superficial fibular n
Cutaneous nerves of the foot
Superficial fibular n Deep fibular n Medial plantar n Lateral plantar n Sural n Saphenous nn
Anterior rami
Ventral ramus forms a cervical plexus (complex branching of axon fibres)
C1-4: cervical plexus - neck
C5-T1: brachial plexus - upper limbs
T1-L1: intercostal etc. nerves - trunk
L1-S5: lumbar (L1-L4) and sacral plexuses (S4-S5) - lower limbs, pelvis, perineum
What is a plexus?
A mesh or not of nerve fibres
Lumbar and sacral plexuses
Ventral rami of spinal nerves L1-L4 (lumbar plexus) and L4-L5, S1-S4 (sacral plexus)
