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Spinal Cord, Reflexes, Meninges
LECOM Yr 1
72
Anatomy
Graduate
08/10/2011

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Cards

Term
how many segments does the spinal cord have?
Definition
31 segments
Term
what are the two enlargements of the spinal cord?
Definition
cervical and lumbar
Term
what does a radiculopathy involve?
Definition
a spinal nerve
Term
around joints, movements can be thought of as having?
Definition
segmental components
Term
the dura is continuous with the ______ past the ganglia.
Definition
epineurium
Term
if you find several neutrophils in the CSF, the patient has?
Definition
meningitis
Term
what do the enlargements of the spinal cord receive and send?
Definition
receive sensory (afferent) information from the limbs and sends motor (efferent) axons to the limb muscles
Term
where does the dural sac (thecal sac) typically end?
Definition
S2, the level which is marked by a line through the posterior superior iliac spines (PSISs)
Term
the spinal cord is attached distally to the coccyx by the _____ ______.
Definition
filum terminale
Term
the internal filum of the filum terminale is formed by what?
Definition
pia mater
Term
the external filum of the filum terminale has a covering of what?
Definition
dura
Term
which root of the spinal cord is associated with motor/efferent?
Definition
anterior root
Term
which region of the spinal cord is associated with sensory/afferent?
Definition
posterior root
Term
the spinal ganglion is derived from what structure?
Definition
the neural crest
Term
what does the spinal ganglion contain?
Definition
sensory neurons
Term
True or false: many muscles contain portions of more than one myotome.
Definition
True
Term
what is a radiculopathy and what does it affect?
Definition
an injury to a spinal nerve and affects the dermatome innervated by the segment from which that nerve arises.
Term
True or false: Because a myotome contributes to more than one muscle, a radiculopathy causes muscle weakness in multiple muscles rather than paralysis of those muscles.
Definition
True
Term
peripheral nerve injuries affect how many dermatomes?
Definition
more than 1
Term
what do peripheral nerve injuries cause?
Definition
affect adjacent dermatomes and cause paralysis of the innervated muscles
Term
what do sensory tracts carry?
Definition
sensory information to the brain
Term
what are motor tracts involved in?
Definition
movement; neurons in the cortex that control movement are called upper motor neurons
Term
what are upper motor neurons?
Definition
neurons in the cortex that control movement
Term
True or false: tracts in the spinal cord white matter are somatotopically organized.
Definition
True
Term
where are lower motor neurons located?
Definition
reside in the anterior horn of the spinal cord
Term
what do lower motor neurons innervate?
Definition
their axons innervate skeletal muscle; form the motor portions of peripheral nerves and are called "the final common pathway" because they receive input from higher brain areas such as the cerebral cortex
Term
where are upper motor neurons generally located?
Definition
in higher centers such as the motor cortex
Term
what do the axons of upper motor neurons do?
Definition
they excite or inhibit lower motor neurons
Term
what is the name of the region where the upper motor neuron crosses over into the lower motor neuron?
Definition
caudal medulla-spinal cord junction (in the brain stem)
Term
where are the lower motor neurons that innervate axial muscles generally located in the anterior horn?
Definition
more medial
Term
where are the lower motor neurons innervating the proximal limb muscles generally located in the anterior horn?
Definition
lateral; lower motor neurons innervating the more distal limb muscles are most lateral
Term
lower motor neurons innervating flexors are more ______ and those innervating extensors are more _____.
Definition
posterior, anterior
Term
what is the afferent component of somatic reflexes?
Definition
Primary afferent (sensory) neurons reside in spinal (dorsal root) ganglia.
Peripheral axon carries information from receptors in skin, muscles, tendons or joints.
Central axons, within the posterior spinal roots (dorsal roots), carry information into the spinal cord.
Term
what is the efferent component of somatic reflexes?
Definition
Spinal efferent (motor) neurons, lower motor neurons, reside in the anterior horn.
Alpha motor neurons form neuromuscular junctions on extrafusal muscle fibers. These fibers generate force.
A single alpha motor neuron and the muscle fibers that it innervates is call a motor unit.
In large muscles (e.g. quadriceps femoris) with course movements, motor units are large.
In small muscles (e.g. extraocular eye muscles) with fine, precise movements, motor units are small.
Gamma motor neurons form junctions on intrafusal muscle fibers. These fibers regulate tension on muscle spindles.
They use acetylcholine as their transmitter
Term
what is a motor unit?
Definition
a single alpha motor neuron and the muscle fibers that it innervates
Term
what does the muscle spindle detect?
Definition
changes in length
Term
what 2 functions do reflexes serve?
Definition
postural and protective functions
Term
what do absent reflexed (areflexia) or diminished reflexes (hyporeflexia)indicate?
Definition
a problem with the particular spinal segment or segments involved in the reflex being tested
Term
what may increased reflexes (hyperreflexia) indicate?
Definition
upper motor neuron problems
Term
list and describe some of the superficial reflexes
Definition
Stroke the skin of the abdomen, underlying muscles will contract.
Upper abdomen: T7-T9
Lower abdomen: T10-T11

Cremasteric reflex involves stroking the skin of the medial thigh. Cremasteric muscle contracts elevating testis.
Tests T12, L1 and L2

Plantar reflex involves stroking bottom of foot from heel to toe. Provokes plantar flexion of toes.
Tests L4, L5, S1 and S2

“Anal Wink” involves stimulus of perianal region. Anal sphincter contracts.
Tests S2-S4
Term
how are deep tendon reflexes graded?
Definition
on a 0 to +4 scale
0 – no response – called areflexia
+2 – normal
+4 – referred to as hyperreflexia
Term
what is the main spinal root involved in the ankle reflex?
Definition
S1
Term
what is the main spinal root involved in the knee reflex?
Definition
L4
Term
what is the main spinal root involved in the brachioradialis reflex?
Definition
C6
Term
what is the main spinal root involved in the triceps reflex?
Definition
C7
Term
describe the mechanism of deep tendon reflexed
Definition
Muscle spindles detect muscle length and stretch.
When a muscle is stretch by tapping its tendon with a reflex hammer, that information is carried to the spinal cord by a 1a afferent axon.
The 1a fiber is a proprioceptive afferent, i.e. carries information about deep somatic structures.
The 1a fibers synapse directly on alpha motor neurons that innervate the muscle (monosynaptic).
The alpha motor neurons fires and the muscle contracts.
Alpha motor neurons innervating the antagonist muscle are inhibited.
Term
what is the flexor withdrawal crossed extensor reflex?
Definition
This is a polysynaptic reflex.
A painful or noxious stimulus to the foot causes a flexor withdrawal reflex.
To maintain balance and posture, extensor motor neurons on the opposite (contralateral) side are activated.
Term
where does the lateral corticospinal tract arise from?
Definition
upper motor neurons in the motor cortex
Term
what does the lateral corticospinal tract innervate?
Definition
lower motor neurons which innervate limb muscles
Term
what percent of axons cross in the pyramidal decussation?
Definition
85-90%
Term
what is the postcentral gyrus, Brodmann's areas 3,1,2?
Definition
the primary sensory cortex
Term
list and describe the 2 major sensory pathways in a somatosensory system.
Definition
Dorsal columns (lemniscal system)
discriminative touch, proprioception, and vibratory sense
Crosses in the medulla

Anterolateral (spinothalamic) system
crude touch, pain and temperature
Crosses in the spinal cord
Term
which ascending sensory pathway carries crude touch, pain and temperature sense while crossing in the spinal cord?
Definition
anterolateral pathway
Term
which ascending sensory pathway carries discriminative touch, vibration sense and proprioception while crossing in the medulla?
Definition
dorsal column system
Term
what damage does upper motor neuron injury cause?
Definition
Injury of corticospinal system (pyramidal tract) anywhere above the pyramidal decussation causes contralateral paralysis paresis of the limbs.

Injury below the pyramidal decussation will cause ipsilateral paralysis or paresis below the lesion.
Term
injury to the ____ ____ will cause loss of pain and temperature sense on the contralateral side below the lesion.
Definition
spinal cord; Such an injury will cause ipsilateral loss of fine (discriminative) touch, proprioception and vibration below the lesion.
Term
what does the pia mater form?
Definition
denticulate ligaments and internal filum terminale
Term
what is the dura mater derived from?
Definition
the mesenchyme
Term
what is the dura mater composed of?
Definition
dense connective tissue with longitudinal collagen fibers with circular elastic fibers
Term
what is a leptomeninx?
Definition
Arachnoid and pia mater
Believed derived from neural crest
Arachnoid and pia contain blood vessels
Term
describe the dural or thecal sac
Definition
The dura encloses the dural or thecal sac
The thecal sac ends at S2
Below S2 the dura continues as the external filum terminale which ends at the coccyx
The dura and extends laterally into the intervetebral foraminae to enclose the spinal ganglia
Term
Can one enter the subdural space with a needle in a living patient?
Definition
No, it is a potential space
Term
what does the subarachnoid space function as?
Definition
a cushion for the spinal cord; contains CSF
Term
what is a spinal tap used for?
Definition
sampling CSF or measuring intrathecal pressure
Term
where is the needle inserted in a spinal tap?
Definition
through the ligamentum flavum between L# and L4 or between L4 and L5; caudal to the spinal cord; the roots are not damaged, they are pushed aside within the CSF like spaghetti is a bag od water reference
Term
what does an epidural allow for?
Definition
allows for selective blockage of roots without affecting the cord
Term
where is the anesthetic infused during an epidural?
Definition
around the outside of the dural sac
Term
where is the anesthetic place in spinal anesthesia?
Definition
put in the subarachnoid space
Term
what are the 2 components of the vertical arterial supply?
Definition
Single Anterior Artery
Arises intracranially from the vertebral arteries

Two Posterior Arteries
Typically arise intracranially from the vertebral arteries, but may arise from the posterior inferior cerebellar arteries
Term
what are the components of the horizontal arterial supply to the spinal cord?
Definition
Segmental medullary arteries supplement anterior and posterior arteries

Lower 2/3 of cord dependent on a medullary segmental artery that is usually larger than the others, the arteria radicularis magna or great radicular artery of Adamkiewicz which typically (65% of people) arises on the left at T12 or L1
Term
does the epidural plexus which drains the spinal cord and meninges have any valves?
Definition
no
Term
what effect can increased intra-abdominal pressure have on blood?
Definition
Increased intra-abdominal pressure can cause a reflux of blood into the plexus and thereby carry metastatic cells, such as prostate CA and infections, such as pelvic infections, along the spinal column to more cranial levels.
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