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236 Cards in this Set

  • Front
  • Back
What does the spinal cord occupy?
spinal canal of the vertebral column
Where does the spinal cord begin and terminate?
forament magnum and conus medullaris
At what level of vertrebrae is the conus medullaris?
L1-L2
How many spinal cord segments are there?
31
Each has a pair of spinal nerves delineating from it
How are the spinal nerves connected to the cord?
Via the posterior (dorsal) and anterior (ventral) roots
Posterior (dorsal) Root
Area that sensory (afferent) information enters the cord
Ventral (anterior) Root
Area that motor (efferent) activity leaves the cord
Gray matter
The H- or butterfly-shaped central region of the spinal cord
What does gray matter contain?
Nerve cell bodies
Where are the lateral horns (in gray matter) found?
segments T1-T12 and L1-L2
Each segment of the cord has several million neurons in the gray matter, including?
sensory relay neurons,
anterior motor neurons, and
interneurons
Where are anterior motor neurons located?
Anterior (ventral) horns of the gray matter
When axons leave the cord via the anterior (ventral) roots, what do they innervate?
Skeletal muscle fibers
What are the two types of motor neurons?
Alpha motor neurons &
Gamma motor neurons
What gives rise to Large A-alpha nerve axons?
Alpha motor neurons
What do Large A-alpha nerve axons innervate?
Extrafusal skeletal muscle fibers
How much of the total motor neuron pool do alpha motor neurons make up?
2/3
What do gamma motor neurons give rise to?
A-gamma axons
What do A-gamma axons innervate?
Intrafusal muscle fibers in muscle spindles
What makes up about 1/3 of total motorneurons in the anterior horns?
Gamma motor neurons
Are gamma motor neurons smaller or larger than alpha motor neurons?
Smaller
Where does most of the input to the motor neurons come from?
Interneurons
Where are interneurons found?
All areas of the gray matter
What are the most numerous cells in gray matter?
Interneurons
- 30x more than alpha motor neurons
Are interneurons in the gray matter inhibitory or excitatory?
Both
Where is most motor activity descending from the brain directed to first?
Interneurons
Why is white matter white?
Myelination
What does white matter contain?
Numerous bundles (tracts)
What are examples of ascending tracts in white matter?
Lateral spinothalamic &
Posterior spinothalamic tracts
What are lateral spinothalamic tracts for?
Principal pathway for pain and temperature transmission
What is the prinicipal pathway for transmission of tactile and proprioceptive sensations?
Posterior spinothalamic tracts (dorsal columns)
What tract originates in the brain and travels down the cord?
Descending tracts
What motor nerve tract that originates in the motor cortex and terminates primarily on interneurons in the spinal cord gray matter?
corticospinal (pyramidal) tracts
Where do nerve tracts associated with the sympathetic nervous system originate and terminate?
in the brainstem and terminate in spinal segments T1-T12 and L1-L2
What are the three layers of connective tissue that surround the spinal cord?
pia mater
How far do the dura and arachnoid extend to?
level S2
What does the subarachnoid space contain?
CSF
What does the epidural space contain?
fat
Where does the epidural space extend from and go to?
from the foramen magnum to the sacral hiatus
Where does the ligamentum flavum lie?
just posterior to the epidural space
What supplies blood to the spinal cord?
vertebral arteries and thoracic and abdominal aorta
What is the single midline vessel that supplies the anterior 2/3 of the cord?
anterior spinal artery
What paired vessels supply the posterior 1/3 of the cord?
posterior spinal arteries
Where does the anterior spinal artery originate?
from the vertebral arteries at base of skull
Where do the posterior spinal arteries originate from?
posterior cerebellar arteries
What supplies BOTH the anterior and posterior spinal arteries?
radicular arteries
What is a single branch of the aorta
that almost always arises on the left side?
Where is the origin of the artery of adamkiewicz in 60% of individuals?
T9-T12
Where is the artery of adamkiewicz in 25% of individuals?
L1-L2
Where is the artery of adamkiewicz in 15% of individuals?
T5-T8
What does the artery of adamkiewicz supply?
nearly all the blood flow to the lower thoracic and lumbar cord
What may result from injury to the artery of adamkiewicz?
spinal cord ischemia
What can result from spinal cord ischemia?
paraplegia
Give examples of how spinal cord ischemia can happen?
surgical dissection or aortic cross-clamping
What are formed by the joining of the anterior and posterior roots at each of the spinal cord segments?
spinal nerves
Where do spinal nerves exit the vertebral column?
intervertebral foramina
How many pairs of spinal nerves are there?
31
Where do the lower lumbar and sacral nerve descend before they exit the vertebral column?
cauda equina
How many cervical spinal nerves?
8
How many thoracic spinal nerves?
12
How many lumbar spinal nerves?
5
How many sacral spinal nerves?
5
how many coccygeal spinal nerves?
1
Why are spinal nerves called mixed nerves?
they contain somatic (sensory and motor) and autonomic nerve fibers
What does each spinal segment supply?
specific region of skin (dermatone) and skeletal muscle
What are the two major branches of spinal nerves?
anterior and posterior ramus
What supplies long muscles of the back and tissue overlying them?
posterior primary division (posterior ramus)
What is the main portion of the spinal nerve called?
anterior primary division (anterior ramus)
What is a intermingling collection of nerves that emanate from different cord segments?
plexus
What joins to form the cervical plexus in the neck?
anterior rami of spinal nerves C1-C4
What emerges to innervate the diaphragm?
phrenic nerve
What do peripheral nerves emerging from the cervical plexus supply?
skin and muscles of the neck and posterior scalp
What joins to form the brachial plexus?
anterior rami of spinal nerves C5-C8 and T1
Peripheral nerves from the brachial plexus innervate what?
upper limbs
What joins to form the lumbosacral plexus?
anterior rami of spinal nerves L1-L5 and S1-S4
Peripheral nerve emerge from the lumbosarcral plexus to innervate what?
the lower limbs and pelvis
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?
muscle receptors (proprioceptors)
Where is feedback information for muscle receptors directed to?
spinal cord
What are the two types of muscle receptors?
muscle spindles and golgi tendon organs
What do muscle spindles function as?
stretch receptors and detect changes in muscle length
What are muscle spindles made up of?
intrafusal muscle fibers
What are the muscle spindles attached to?
glycocalyx of surrounding extrafusal fibers
The central region of the spindle is innervated by sensory nerves
what type?
The end portions of the intrafusal fibers contain actin and myosin and are innervated by?
A-gamma motor fibers
What are sensory receptors located in the muscle tendons near the point of attachment of the tendons to the skeletal muscle fibers?
golgi tendon organs
What are golgi tendon organ receptors sensitive to?
tension developed within the muscle
What sensory nerves transmit information from the golgi tendon organs to the CNS?
Type Ib
Where are Type Ib signals directed to?
spinal cord
What is unique of the monosynaptic reflex?
very little delay
What do the knee-jerk reflex and other muscle jerk reflexes test?
excitability of motor neurons
What is elicited most often by a painful stimulus?
flexor (withdrawal) reflex
Flexion of one limb is accompanied by extension of the opposite limb is called?
crossed extension
What also acts over long distances of the spinal cord to control reciprocal limb movements during locomotion?
crossed extension
What does crossed extension prevent?
disturbance of equilibrium
What represents a reflex response to irritations of muscle?
muscle spasm
What can cause contraction (spasm) of abdominal mucsles?
peritonitis
What can can local muscle spasms or cramps?
ischemia
Lesion to the spinal cord can result from a variety of insults
name them?
What happens during spinal cord transection during the initial period of spinal shock?
both somatic and autonomic reflexes below the lesion are temporarily interrupted - decrease in blood pressure
Spinal neurons below the lesion (in spinal transection) regain excitability and some reflex activity
but what is still lost?
What is overactivity of the sympathetic nervous system?
autonomic hyperreflexia
With whom is autonomic hyperreflexia commonly seen?
patients with cord transections at T5 or above (unusual with lesions below T10)
What can trigger strong autonomic responses below the level of transection?
cutaneous (incision) or visceral (distended bladder) stimulation
What does sympathetic discharge below the lesion cause?
intense vasoconstriction (increase BP)
What does sympathetic discharge above the lesion cause?
reflex bradycardia and vasodilation
What is Brown-Sequard syndrome?
hemisection of spinal cord
State characteristics of brown-sequard syndrome?
1) loss of sensation/hypotonic paralysis @ level of injury (same side)
2) below lesion - same side = loses tactile
sensory capacity
3) below lesion - opposite side = loss of pain/temp sensation
no loss of motor function
What is it called when local anesthetics are injected into the subarachnoid space of the spinal cord?
Spinal block
Where is a spinal block injection usually performed?
below the end of the spinal cord (L3-L4 or L4-L5)
Where is the uptake of local anesthetics into?
spinal nerve roots
What does not alter local anesthetic in CSF?
CSF circulation
What are the two complications associated with spinal blocks?
hypotension and postspinal headache
What occurs as a result of CSF leakage from puncture site?
postspinal headache
What is caused by a reduction of CSF pressure in the subarachnoid space that causes tension in the meninges?
post-spinal headache
what happens when the sympathetic nervous system blockade can cause venous pooling of blood and decreased venous return and cardiac output?
hypotension
What is placement of local anesthetics into the epidural space of the spinal cord?
epidural block
Where is the major site of action for epidural blocks?
spinal nerve roots
Is onset of epidural block faster or slower than spinal block?
slower
What nerves are blocked during epidurals?
sympathetic
Sensory receptors are usually what?
nerve endings
Receptors act as transducers to what?
convert the natural form of the stiumulus into electrical impluses - action potentials
What are necessary for the nervous system to process a sensory event?
electrical impulses (action potentials)
What is the magnitude of the receptor potential determined by?
stimulus strength
The stimulus causes a change in membrane permeability of the receptor and then?
DEPOLARIZATION
What happens if receptor potentials reach threshold?
action potentials are generated
What is the receptor potential analogous to?
the excitatory postsynaptic potentials in the CNS
what is the frequency of action potentials produced by the receptor proportional to?
magnitude of receptor potential
All sensory receptors have receptor fields
which are?
all sensory receptors show some degree of what?
adaptation to a stimulus
What are the 5 types of sensory receptors?
mechanoreceptors
What do mechanoreceptors detect?
mechanical deformation of tissue
What do thermoreceptors detect?
detect changes in tissue temperature both cold and warmth
Nociceptors detect?
tissue injury (pain)
electromagnetic receptors detect?
light waves
chemoreceptors detect?
changes in the chemical composition of the local environment (PO2
sensory nerves transmit action potentials from _______ to _____?
sensory receptors
What are the two types of sensory nerves?
type A and Type C fibers
Which spinal nerves are myelinated?
Type A fibers
What are the subgroups of Type A fibers?
alpha
What are small diameter
non-myelinated fibers?
What comprises more than 50% of peripheral somatic sensory nerve fibers?
Type C Fibers
What are the "special" senses?
vision
What arises from the body surface as well as from deep tissues such as viscera
muscles
What are 5 somatic sensations?
tactile sensations
What are tactile sensations?
touch
What are proprioceptive sensations?
limb position and joint angle
What is kinesthesis?
body and limb movement
What are found extensively in the skin and detect touch and pressure?
free nerve endings
Most tactile sensory receptors transmit sensory signals to the CNS via?
Large
free nerve endings transmit signals via?
smaller A-delta fibers and unmyelinated type C fibers (itch
sensory information enters the spinal cord via the dorsal roots and is directed to the brain via?
dorsal columns
ascending fibers synapse in the dorsal column nuclei in the medulla and cross-over and pass upward to the thalamus via?
medical lemniscus pathway
fibers in the medial lemniscus synapse with?
specific sensory relay nuclei in the thalamus
3rd order fibers project from Sensory relay nuclei in the thalamus to the?
somatic sensory cortex
where is the body "map" preserved?
dorsal column lemniscal system and thalamus
a signal originating in a peripheral sensory nerve is transmitted where?
cerebral cortex (where intensity of signal is preserved)
Where is the somatic sensory cortex?
anterior portions of the parietal lobes
What are the two areas that are involved in the ssc?
SS area I and SS area II
Where is the somatic sensory area I located?
postcentral gyrus
How are the areas of the body represented within SS I?
according to the density of their sensory receptors (sensory homunculus)
What is highly represented in the sensory homunculus?
lips
Injury to SS I can cause what?
1) loss of discrete tactile sense
What is located in the parietal lobe behind SS I?
somatic association cortex
Where does the somatic association cortex receive input from?
SS I
What plays an important role in the INTERPRETATION of sensory information?
somatic association cortex
What can damage to the somatic association cortex cause?
astereogeneis (inability to identify an object by touch without visual input)
What is it called when one forgets that one side of the body exists?
amorphosynthesis
Position sense and kinesthesis are what kind of sensations?
proprioceptive
Where are proprioceptive receptors located?
joint capsules and ligaments
Give examples of joint capsule and ligament receptors?
ruffini end-organs and golgi tendon organs
Where is transmission of proprioceptive information?
dorsal column - lemniscal system
What is an unpleasant sensory and emotional experience associated with actual or potential tissue damage?
pain
Why is pain just not a physiological process?
it is an experience that is affected by past events
What are the two types of pain?
fast (first) pain and slow (second) pain
What is fast pain AKA?
acute
What arises primarily in skin
not felt in deeper tissues and is well-localized?
Fast pain signals are transmitted to the CNS via?
type A-delta sensory nerve fibers
What is slow pain aka?
throbbing
What is the onset of slow pain?
slower than fast pain (obviously) usually 1 second or more
What can arise from skin and deeper tissues and if often poorly localized?
slow pain
Slow pain signals are transmitted to the CNS via?
type C nerve fibers (non-myelinated)
What are the majority of free nerve endings called?
pain receptors (nociceptors)
What do pain receptors respond to?
mechanical
Where are nociceptors located?
somatic (skin
What can persistent stimulation of pain receptors cause?
increase in sensitivity (hyperalgesia)
Where do type A-delta axons synapes with second-order neurons?
laminae I (in gray matter)
Where do type C axons primarily synapse with interneurons?
Laminae II (substantia gelatinosa) and III
(type C)After synapses with interneurons in laminae II and III where do they project signals?
second-order neurons in Lamina V
What kind of second-order neurons are most abundant in laminae V?
wide dynamic range
Axons of second-order neurons immediately do what?
cross over to opposite side of cord
After second order neurons cross over to the opposite side of cord where do they ascend?
lateral spinothalamic tracts
Where is fast pain primarily directed to?
ventrobasal nuclei of the thalamus --> third-order neurons to the somatic sensory cortex
Where is slow pain primarily directed to?
midbrain reticular formation
What does slow pain do when transmitted to limbic system?
causes emotional arousal and activation of descending inhibitory pathways
What is the periaqueductal gray area?
gray matter that surrounds the acqueducts of sylvius (which connects the 3rd and 4th ventricle)
What is another name for a chemical mediator of pain?
alogen
What is released from injured tissue to directly stimulate free nerve endings?
bradykinin and prostaglandin E2
What other alogens are released from injured cells?
K+ and H+
What alogen is released from tissue mast cells?
histamine
What is primary hyperalgesia mediated by?
alogens such as histamine and serotonin
Local collateral axons terminals of pain afferent nerves release ________ which stimulates mast cells and platelets to release alogens
substance P
Another name for when afferent nerves release substance P?
antidromic release
What is manifested by enhanced pain response to stimuli outside area of injury?
secondary hyperalgesia
In the dorsal horn
what do afferent pain fibers release?
What does glutamate activate in the post-synaptic membrane?
AMPA and NMDA receptors
What does substance P activate in the post-synaptic membrane?
Nk-1 receptors
What is a common mechanism of central sensitization?
increased intracellular calcium
What does glutamate binding to the NMDA receptors cause?
removal of Mg+2 block and increased calcium permeability
What does central sensitization greatly enhance?
pain signal transmission and pain perception
When central sensitization is established what happens?
very difficult to interrupt
The periaqueductal gray area receives ascending slow pain activity which activates what?
descending adrenergic tracts to the spinal cord and descending enkephalin-secreting tracts to the raphe magnus nucleus
Activation of the raphe magnus nucleus causes?
activation of descending serotoninergic tracts to spinal cord
What do descending adrenergic axons in the dorsal horn release?
norepinephrine
What happens after release of norepinephrine in adrenergic axons?
activations of pre-synaptic and post-synaptic alpha-2 receptors
What happens when alpha-2 receptors are activated?
inhibition of pain neurotransmission
descending serotoninergic axons stimulate interneurons to release?
enkephalins
Enkephalins bind to presynaptic opiod receptors on pain afferents and inhibit release of what?
substance P
What happens with release of endorphins in the periaqueductal gray area and limbic system?
interference with pain transmission and modulation of pain perception
Where are beta-endorphin and dynorphin released in?
periaqueductal gray area and limbic system in response to pain
What acts in the spinal cord to inhibit pain transmission?
met-enkephalin and leu-enkephalin
What pain is percieved in a part of the body that is removed from the actual site of painful stimulus?
referred pain
Pain originated in the viscera is referred where?
to the body surface
What doesn't the viscera contain?
somatic sensory receptors except for pain receptors
pain receptors are sparsely distributed where?
in the viscera
highly localized tissue damage can cause what?
very little visceral pain
visceral pain typically involves diffuse activation of pain receptors due to?
ischemia
visceral pain is transmitted to the CNS via?
autonomic type C sensory fibers
Give examples of visceral pain?
cardiac ischemia
What causes parietal pain?
injury or disease to a visceral organ which may affect the parietal wall
parietal pain is transmitted to the spinal cord via?
somatic sensory nerves
example of parietal pain?
appendicitis
what receptors play a critical role in central sensitization?
NMDA
What is a noncompetitive NMDA antagonist?
ketamine
What does pre-emptive acetaminophen do?
indirect inhibitor of NMDA receptor