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118 Cards in this Set
- Front
- Back
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What does the spinal cord occupy?
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Spinal canal of the vertebral column
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Where does the spinal cord begin and terminate?
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Foramen magnum and conus medullaris
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At what level of vertrebrae is the conus medullaris?
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L1-L2
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How many spinal cord segments are there?
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31
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How are the spinal nerves connected to the cord?
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Via the posterior (dorsal) and anterior (ventral) roots
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Posterior (dorsal) Root
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Area where sensory (afferent) information enters the cord
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Ventral (anterior) Root
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Area that motor (efferent) activity leaves the cord
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Gray matter
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The H- or butterfly-shaped central region of the spinal cord
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What does gray matter contain?
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Nerve cell bodies
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Where are the lateral horns (in gray matter) found?
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segments T1-T12 and L1-L2
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Each segment of the cord has several million neurons in the gray matter including?
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Sensory relay neurons,
Anterior motor neurons, and Interneurons |
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Where are anterior motor neurons located?
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Anterior (ventral) horns of the gray matter
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When axons leave the cord via the anterior (ventral) roots, what do they innervate?
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Skeletal muscle fibers
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What are the two types of motor neurons?
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Alpha motor neurons &
Gamma motor neurons |
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What gives rise to Large A-alpha nerve axons?
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Alpha motor neurons
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What do Large A-alpha nerve axons innervate?
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Extrafusal skeletal muscle fibers
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How much of the total motor neuron pool do alpha motor neurons make up?
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2/3
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What do gamma motor neurons give rise to?
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A-gamma axons
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What do A-gamma axons innervate?
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Intrafusal muscle fibers in muscle spindles
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What makes up about 1/3 of total motorneurons in the anterior horns?
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Gamma motor neurons
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Are gamma motor neurons smaller or larger than alpha motor neurons?
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Smaller
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Where does most of the input to the motor neurons come from?
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Interneurons
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Where are interneurons found?
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All areas of the gray matter
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What are the most numerous cells in gray matter?
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Interneurons
- 30x more than alpha motor neurons |
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Are interneurons in the gray matter inhibitory or excitatory?
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Both
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Where is most motor activity descending from the brain directed to first?
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Interneurons
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Why is white matter white?
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Myelination
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What does white matter contain?
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Numerous bundles (tracts)
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What are examples of ascending tracts in white matter?
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Lateral spinothalamic &
Posterior spinothalamic tracts -project to thalamus |
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What are lateral spinothalamic tracts for?
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Principal pathway for pain and temperature transmission
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What is the prinicipal pathway for transmission of tactile and proprioceptive sensations?
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Posterior spinothalamic tracts (dorsal columns)
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Descending tracts
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Originate in the brain and travel down the cord
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Corticospinal (pyramidal) tracts
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Motor nerve tract that originates in the motor cortex and terminates primarily on interneurons in the spinal cord gray matter
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Where do nerve tracts associated with the sympathetic nervous system originate and terminate?
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Originate in the brainstem and terminate in spinal segments T1-T12 and L1-L2
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What are the three layers of connective tissue that surround the spinal cord?
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- Pia mater
- Arachnoid mater - Dura mater |
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How far do the dura and arachnoid extend?
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Level S2
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What does the subarachnoid space contain?
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CSF
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What does the epidural space contain?
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- Fat
- Connective tissue - Venous plexuses |
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Where does the epidural space extend from and go to?
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Foramen magnum to the sacral hiatus
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Ligaments
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- Ligamentum flavum
- Interspinous ligament - Supraspinous ligament |
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Where does the ligamentum flavum lie?
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Just posterior to the epidural space
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What supplies blood to the spinal cord?
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Vertebral arteries and thoracic and abdominal aorta
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What is the single midline vessel that supplies the anterior 2/3 of the cord?
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Anterior spinal artery
- originates from the vertebral arteries |
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What paired vessels supply the posterior 1/3 of the cord?
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Posterior spinal arteries
- arise from the posterior cerebellar arteries |
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Where does the anterior spinal artery originate?
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Vertebral arteries at base of skull
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Where do the posterior spinal arteries originate from?
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Posterior cerebellar arteries
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What supplies BOTH the anterior and posterior spinal arteries?
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Radicular arteries
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What is the single branch of the aorta that almost always arises on the left side?
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Artery of Adamkiewicz
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Where is the artery of adamkiewicz in 15% of individuals?
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T5-T8
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Where is the origin of the artery of adamkiewicz in 60% of individuals?
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T9-T12
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Where is the artery of adamkiewicz in 25% of individuals?
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L1-L2
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What does the artery of adamkiewicz supply?
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Nearly all the blood flow to the lower thoracic and lumbar cord
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What may result from injury to the artery of adamkiewicz?
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Spinal cord ischemia
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What can result from spinal cord ischemia?
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Paraplegia
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Give examples of how spinal cord ischemia can happen?
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Surgical dissection or aortic cross-clamping
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Spinal nerves
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Formed by the joining of the anterior and posterior roots at each spinal cord segment
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Where do spinal nerves exit the vertebral column?
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Intervertebral foramina, between the vertebrae
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How many pairs of spinal nerves are there?
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31
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How many cervical spinal nerves?
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8
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How many thoracic spinal nerves?
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12
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How many lumbar spinal nerves?
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5
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How many sacral spinal nerves?
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5
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How many coccygeal spinal nerves?
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1
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Where do the lower lumbar and sacral nerves descend before they exit the vertebral column?
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Cauda equina
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Why are spinal nerves called mixed nerves?
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They contain somatic (sensory and motor) and autonomic nerve fibers
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What does each spinal segment supply?
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A specific region of skin (dermatome) and skeletal muscle
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What are the two major branches of spinal nerves?
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Anterior and posterior ramus
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What supplies long muscles of the back and tissue overlying them?
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Posterior primary division (posterior ramus)
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What is the main portion of the spinal nerve called?
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Anterior primary division (anterior ramus)
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Plexus
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An intermingling collection of nerves that emanate from different cord segments
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What joins to form the cervical plexus in the neck?
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Anterior rami of spinal nerves C1-C4
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What do peripheral nerves emerging from the cervical plexus supply?
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Skin and muscles of the neck and posterior scalp
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What emerges to innervate the diaphragm?
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Phrenic nerve, C3-C5
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What joins to form the brachial plexus?
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Anterior rami of spinal nerves C5-C8 and T1
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Peripheral nerves from the brachial plexus innervate what?
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Upper limbs
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What joins to form the lumbosacral plexus?
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Anterior rami of spinal nerves L1-L5 and S1-S4
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Peripheral nerve emerge from the lumbosarcral plexus to innervate what?
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The lower limbs and pelvis
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What provides continuous feedback information to the CNS with respect to muscle length and tension and the rate of change of muscle length and tension during movement?
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Muscle receptors (proprioceptors)
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Where is feedback information for muscle receptors directed to?
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- Spinal cord
- Cerebellum - Motor cortex |
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What are the two types of muscle receptors?
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Muscle spindles &
Golgi tendon organs |
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What do muscle spindles function as?
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Stretch receptors and they detect changes in muscle length
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What are muscle spindles made up of?
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Intrafusal muscle fibers
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What are the muscle spindles attached to?
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Glycocalyx of surrounding extrafusal fibers
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The central region of the spindle is innervated by what types of sensory nerves?
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Types Ia & II
- the central region is extremely sensitive to stretch |
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The end portions of the intrafusal fibers contain actin and myosin and are innervated by?
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A-gamma motor fibers from the brain stem
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Golgi tendon organs
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Sensory receptors located in the muscle tendons near the point of attachment of the tendons to the skeletal muscle fibers
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What are golgi tendon organ receptors sensitive to?
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Tension developed within the muscle
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What sensory nerves transmit information from the golgi tendon organs to the CNS?
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Type Ib
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Where are Type Ib signals directed to?
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- Spinal cord
- Cerebellum - Cerebral cortex |
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What is unique to the monosynaptic reflex?
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Very little delay
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What do the knee-jerk reflex and other muscle jerk reflexes test?
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Excitability of motor neurons
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What is elicited most often by a painful stimulus?
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Flexor (withdrawal) reflex
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Flexion of one limb is accompanied by extension of the opposite limb is called?
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Crossed extension
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What acts over long distances of the spinal cord to control reciprocal limb movements during locomotion?
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Crossed extension
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What does crossed extension prevent?
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Disturbance of equilibrium
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What represents a reflex response to irritations of muscle?
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Muscle spasm
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What can cause contraction (spasm) of abdominal mucsles?
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Peritonitis
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What can cause local muscle spasms or cramps?
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Ischemia
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Lesion to the spinal cord can result from a variety of insults:
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- Trauma
- MS - ALS - Tumors - Infections - Ischemia |
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What happens during spinal cord transection during the initial period of spinal shock?
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Both somatic and autonomic reflexes below the lesion are temporarily interrupted - decrease in blood pressure
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Spinal neurons below the lesion (in spinal transection) regain excitability and some reflex activity, but what is still lost?
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Sensation and voluntary movement below the transection
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What is overactivity of the sympathetic nervous system?
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Autonomic hyperreflexia
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With whom is autonomic hyperreflexia commonly seen?
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Patients with cord transections at T5 or above (but unusual with lesions below T10)
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What can trigger strong autonomic responses below the level of transection?
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Cutaneous (incision) or visceral (distended bladder) stimulation
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What does sympathetic discharge below the lesion cause?
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Intense vasoconstriction (increase BP)
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What does sympathetic discharge above the lesion cause?
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Reflex bradycardia and vasodilation, resulting in hypertension
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Spinal block
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Local anesthetics are injected into the subarachnoid space of the spinal cord
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Where is a spinal block injection usually performed?
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Below the end of the spinal cord (L3-L4 or L4-L5)
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Where is the uptake of local anesthetics into?
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- Spinal nerve roots
- Dorsal root ganglia - Spinal cord |
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What does not affect distribution of local anesthetic in CSF?
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CSF circulation
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What are the two complications associated with spinal blocks?
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Hypotension &
Postspinal headache |
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What occurs as a result of CSF leakage from puncture site?
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Postspinal headache
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What is caused by a reduction of CSF pressure in the subarachnoid space that causes tension in the meninges?
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Post-spinal headache
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What is the result of venous pooling and decreased venous return caused by sympathetic nervous system blockade?
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Hypotension
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What is placement of local anesthetics into the epidural space of the spinal cord?
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Epidural block
Typically at the lumbar level |
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Where is the major site of action for epidural blocks?
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Spinal nerve roots
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Is onset of epidural block faster or slower than spinal block?
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Slower
No free-moving fluid |
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What nerves are blocked during epidurals?
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- Sympathetic
- Sensory - Motor |
