Spinal Cord Transmission, Reflexes, Muscle Flashcards
Exam 3
Spinal Cord Transmission
Ascending & Descending Tracts (Gen. Overview)
What information ascends, descends the spinal cord? What is a tract?
-Sensory information ascends the spinal cord, beginning in the periphery of the body and traveling up through the spinal cord, brain stem, cerebellum, and brain.
-There are more sensory pathways than motor pathways, and that’s because we have temperature, vibration, and pain sensors
-Motor information descends the spinal cord and travels to our skeletal muscles
-Tract refers to a bundle of axons within the CNS. A bundle of axons outside the CNS are called nerves.
Motor and Descending Pathways
Pyramidal Tracts: Primary voluntary movement
-Lateral corticospinal tract
-Anterior corticospinal tract
Extrapyramidal Tracts (Accessory tracts): Movement that we do not usually have a knowledge of. Ex: fine-tuning our motor commands
-Rubrospinal tract
-Reticulospinal tract
-Olivospinal tract
-Vestibulospinal tract
Sensory and Ascending Pathways
What are they? (Names)
Dorsal Column Medial Lemniscus: Located in the dorsal part of the cord. These transmit information from pressure sensors in our skin (if we’re holding onto something, or our hands are in the air). Touch sensors
Anterolateral System: Pain signals. Typically follow one of two pathways
-Lateral spinothalamic tract
-Anterior spinothalamic tract
Spinothalamic tract terminology corresponds to the fact that the pain is going into the cord, relayed through the thalamus, and then out to the parietal cortex where it can be sorted out (where is it coming from?)
Rexed’s Laminae- Lamina I
What type of fibers synapse here?
-Numbered starting at the most dorsal portion of the dorsal horn
-Lamina I (Lamina Marginalis): Transmits fast, sharp pain via myelinated nociceptors that fall into the category of A-delta fibers.
Fast pain comes in through the dorsal rootlet, into the dorsal horn, where it has synapses in Lamina I. From there, the sensory information crosses over to the other side of the cord and then ascends the anterolateral pathway
Rexed’s Laminae- Lamina II, III, ~V
-Substantia Gelatinosa
-Synapses for slow pain conduction are located here. Sometimes slow pain signals will also synapse at lamina V
-Slow pain is typically routed through nociceptors that are non-myelinated (C fibers).
Once information is received in the substantia gelatinosa (and sometimes lamina V) it jumps over to the other side of the cord and ascends via the anterolateral pathway
Lamina 1-VI
Mechanoreceptors
-Also have mechanoreceptors that relay information to these areas of the grey matter in the cord.
-Mechanoreceptors are pressure sensors
Rexed’s Laminae-Lamina VII, VIII, IX
-These laminae make up the anterior horn.
-This is where our large motor neuron cell bodies sit, and they can be elicited to send an action potential if the stimulus is strong enough
Lamina X, Anterior White Commisure
Lamina X- An area of the grey matter where signals are relayed to the other side of the cord
AWC- The area of white matter in the spinal cord where information is relayed to the other side
Names & function of the 5 main spinal tracts
Typically the name tells us where the pathway is located or what function it performs
Spinocerebellar Tract: Sensory information that goes up the spinal cord to the cerebellum
Dorsal-Column Medial Lemniscal System (DCML): Major pressure sensory pathway that sits in the dorsal column of the cord. The medial lemniscal portion of the name refers to an area of the brainstem that the information passes through
Spinothalamic Tract/Anterolateral: Pain
Corticospinal Tracts/ Pyramidal tracts: Signal originates in the cerebral cortex (motor cortex) and passes through the spine on the way to the skeletal muscles
Extrapyramidal Tracts: Primarily accessory motor pathways
Dorsal Column Medial Lemniscus
Fibers? Sensory Information? Two routes this info can take
-Major sensory pathway for everything other than pain
-Capable of very fast sigal propagation
-Variety of a-fibers: alpha, beta, delta, gamma
- Fine vibration, fine pressure
- Crosses over at the medulla in the medial lemniscus
The path to getting to the medula follows one of two routes:
Touch sensation coming into the cord-> enters through the posterior rootlets of the doral horn and enters the grey matter of the cord. The information that enters the grey matter of the cord often stays there. This usually involves lateral inhibition or modulation of the activity in the cord
The other route that the sensory information takes is up to the brain through a pathway in the dorsal column (if the information needs to ascend all the way to the brain)
Dorsal Column Pathways: Fasciculus Gracilis
The further up the cord you get, the larger the dorsal column becomes.
-Lower extremity sensory information is fed into the fasciculus gracilis. As we ascend the cord, more bundles are added to the lateral side of the dorsal column
A tickle on the foot –> information is passed through the dorsal root –> dorsal root ganglia –> into the dorsal column–> ascends the same side of the cord that it entered on–> crosses over at the lower medulla–> medial lemniscus –>relayed to the ventrobasal complex of the thalamus –> internal capsule; a route that the information takes on the way to the parietal lobe
Dorsal Column Pathways: Fasciculus Cuneatus
-Higher up the cord. This is where the sensory information from the upper extremities is fed into the cord
A tickle on the arm –> information is passed through the dorsal root –> dorsal root ganglia –> into the dorsal column–> ascends the same side of the cord that it entered on–> crosses over at the lower medulla (lemniscal decussation)–> medial lemniscus –>relayed to the ventrobasal complex of the thalamus –> internal capsule; a route that the information takes on the way to the parietal lobe
Parietal Lobe layout
Which areas of the parietal lobe receive what information?
-Topographical layout
-Most anterior portion of the parietal lobe receives sensory information from lower extremities
-Immediately posterior (more midline) to that is the trunk sensory area
-Posterior to the trunk sensory area is the upper extremities
-The inferior, lateral borders of the parietal lobe receive sensory information for the face
Creepy Homunculus
The amount of area that you have processing sensory information in the brain is proportional to the number of sensory receptors
We have tons of receptors in our hands. These very sensitive sensors allow us to read braile.
We have a lot of receptors in the face
We have a low density of pressure sensors in trunk
Descending Motor Pathway
Pyramidal Tracts-Primary Pathway
Why are these called pyramidal tracts?
-Two separate tracts, primary and secondary. 80% of motor signals travel through the primary route
-Pass through the pyramids of the medulla
-Primary descending pathway begins in the primary motor cortex –> internal capsule (right outside thalamus) –> upper medulla –> medullary pyramids (anterior brainstem) –> lower medulla –> crosses over at pyramidal decussation –> lateral corticospinal tracts down the cord until at the appropriate level –> activation of motor neurons in anterior horn
Midbrain? Pons? Medulla? Pyramids? Pyramidal Decussation?
-The ridges are the pyramids
-The “cross-hatch” pattern is where the pyramidal decussation lies. These are strands of neurons crossing over, or bridging the gap, between the left and right pyramids
Pyramids? Decussation? Pons?
Anterior Corticospinal Tract
Pyramidal Tracts- Secondary Pathway
What is different about this pathway? How much information gets lost?
-Significantly smalled than the lateral corticospinal tracts.
-Responsible for ~17% of our motor function
2-3% of information does not crossover at all
Crossover happens at the level of the cord where the tract needs to activate a motor neuron
Begins in the primary motor cortex –> internal capsule (right outside thalamus) –> upper medulla –> medullary pyramids (anterior brainstem) –> lower medulla –> pyramidal decussation (information passes through the decussation, does not cross over here)–> continues down the anterior corticospinal tract on the same side of the body in which the signal originated –> crosses over at the level of the motor neuron where the message needs to be communicated
Fast Pain- Gen overview
Which portion of pathway? Runs parallel to? NE? Alt. Name?
-Lateral pathway of the anterolateral pathway
-A delta fibers, heavily mylenated
-Glutamate is always neurotransmitter, acts very quickly
-Runs parallel to the DCML, reaches the parietal lobe allowing for detailed localization of pain
-Also called neospinothalamic tract
Slow Pain- Gen Overview
-Anterior portion of the anterolateral pathway
-Slow, non-myelinated fibers (C fibers)
-Primary NE is substance P, can also use CGRP (Calcitonin G-related peptide) or glutamate (but not fast here)
-“Everything else” other than fast pain. Heat & vibration
-Stimulus travels up to the brainstem, but does not make it past that. Poor localization of pain because it does not reach the parietal lobe. Body has a difficult time pinpointing where the pain is occuring
-Paleospinothalamic Tract
Pain Transmission Pathway
Fast Pain: Anterolateral/Spinothalamic Tracts
Pathway?
Enters the cord at the level of the painful stimulus (primary ascending) –> synapses in lamina I –> crosses over at the anterior white commisure via the secondary ascending neuron
–> ascends the lateral portion of the anterolateral pathway, passing through the brainstem, ventrobasal complex of thalamus, internal capsule, and finally arriving in the parietal lobe
Pain Transmission Pathway
Slow Pain: Anterolateral/Spinothalamic Pathway
Pathway? Emotional centers? Reticular Formation?
-Enters cord at level of the stimulus (primary ascending)–> synapses in laminas II, III, sometimes V–> crosses over at the AWC (secondary ascending) –> ascends the cord in the anterior portion of this pathway.
The majority of this information terminates in the brainstem at the reticular formation (swaft of tissue) or immediately after leaving the brainstem
-Chronic, slow pain typically affects the emotional centers in the brain. The emotional centers in the brain are located very close to the middle of the brain, or right around where the brainstem connects with the diencephalon
Descending Motor Accessory Pathways
Extrapyramidal Tracts
- Vestibulospinal tract: Maintain balance, focus our eyes
- Olivospinal: Don’t really have anything to say
- Reticulospinal tract: Maintaning a certain level of muscle tone. Muscles aren’t entirely relaxed, all of the time. Underlying activity
- Rubrospinal: Monitoring and adjusting voluntary movements
Descending Pain Suppression System (DIC)
-Inhibitory in nature
-Operates in the background and helps the body deal with pain after the ascending signal has arrived at the brain
-Three neurons in the DIC
-The first order descending neuron originates from either the periaqueductal grey (around the midbrain) or the periventricular nuclei (located in front of 3rd ventricle)
-When excited, the first order descending neuron will release Enkephalins right in the middle of the pons (Raphe magnus nucleus)
-Enkephalins excite the second order descending neuron inside of the RMN. Second order descending neuron releases serotonin (5-HT) in the dorsal horn of the spinal cord. 5-HT is inhibitory in the spinal cord
-5-HT can excite a third order descending neuron (very small) that also excretes enkephalins, but in the cord enkephalins are an inhibitory neurotransmitter
-The enkephalin receptors in the cord are located ON the pain nociceptors of the pain sensing neuron. The pain sensing neuron has dendrites out in the periphery
-Pain signal travels into the dorsal root–> dorsal rootlets –> dorsal part of the cord –> enkephalin is being released and binding to the nociceptors –> inhibits that receptor causing pain to be diminished
-Another neuron that contains enkephalin receptors is the second order neuron in the ascending pathway
-Depending on the type of pain, the synapse will be in laminate I, II, III
Enkephalins, Enkephalin Receptors, and DBS
What is it? Where are they located? Where are they E, I
Endogenous Morphine analog
Opiate receptors = enkephalin receptors
Enkephalin is released in the raphe magnus nucleus (the first synapse in the DIC)- Stimulatory at this point
Enkephalin is also released in the dorsal horn (inhibitory here)
If we were to implant an electrode into the periaquaductal gray or the periventricular nuclei, that would generate an inhibitor pain signal that could reduce the amount of pain we perceive. Why? DIC. If activated strongly enough, it can surpass pain within the body. The presence of this system gives anesthesia a target for their drugs (dulls pain perception)
Enkephalin Receptors
Where are they located? GPCR? Interacts with what kind of channel?
-Enkephalin receptors are within the cord ON nociceptors and 2nd order ascending neurons
These receptors are GPCRs that typically interact with a K+ channel
When opiates hit these receptors–> open our K+ channels –> outward K+ current = hyperpolarization
Other receptor types/drugs that modulate pain response
-Pain synapses usually express A2 receptors, so an A2 agonist can bind and will also interact with a K+ channel (unsure if the same K+ channel as enkephalin receptors or not)
A2 Agonists: Xylazine, Clonidine, Precedex (most specific). Pain suppression, relaxation, without euphoria
-Volatile anesthetics: Increased K+ conductance, suppressing the CNS. Can also interact with inhibitory neurotransmitters
-Cox-2; Expressed in 1st order & 2nd order ascending pain neurons –> produce prostaglandins –> prostanglandinds interact with PGT receptors–> increases sensitivity to painful stimuli because they increase the likelihood of an action potential firing or repetitive action potentials
-INOS:
Odd enzyme. Induceable nitric oxide synthase –> increases sensitivity to painful stimuli
Ascending Pain Pathway & DIC
Overview of both, and how they interact, what gets shut down here?
1st order ascending nociceptor senses pain –> pain travels up the spinal nerve, through the dorsal root, through the dorsal rootlets–> synapses in the dorsal horn–> 2nd order ascending neuron hops over to the other side of the cord via the AWC–> travels up the anterolateral pathway
-Slow pain will terminate in brain stem
-Fast pain will travel through the brain, thalamus, internal capsule, to the parietal lobe
Our descending pain suppression system starts in either the periaquaductal grey or periventricular nuclei –> 1st order descending neuron (enkephalin neuron) –>synapses in the RMN of the pons, releases enkephalins which are excitatory–> 2nd order descending (serotonergic neuron) travels down toward the dorsal horn, releases 5-HT–> stimulates 3rd order descending neuron–> 3rd order descending releases enkephalins in the synapse in the dorsal horn.
Shuts down the presynaptic and post synaptic side of the synapse
Things that cause a nociceptor to depolarize
What causes pain?
Is pain a survival mechanism? Meditation can do what?
Pain is a survival mechanism that tells us when we’re doing something stupid.
Meditation and massive self-control over the mind can do things like deaden our pain completely, or allow us to lift a car off of a kid
-Damage (crush injury, cuts)
-H+ ions (acid)
-Lactic acid build up in the muscle
-Hyperkalemia (causes cells to depolarize) (Dialysis patient example)
-Histamine (inflammation)
-5-HT in the periphery
-Prostaglandins (cannot generate an action potential, but causes more sensitivity to pain)
-Bradykinins
Chronic Pain
What are some drug classes that can help? SSRI, TCA, Wind up
-Serotonin is recycled and reused by the neuron (serotonin reuptake system)
-If serotonin is what stimulates the 3rd order descending neuron to release enkephalins, then inhibiting the serotonin reuptake process should help reduce pain
-Some tricyclic antidepressants (have been around 50-60yrs) also inhibit serotonin reuptake. One main side effect of this class are drugs is drowsiness, which can actually be beneficial in chronic pain management. Because pain is stimulating the brain, it is harder for these people to sleep
Process of windup:
With chronic pain, more AMPA and NMDA receptors are inserted at the synpase. The more these receptors are stimulated, the more that our body places. If you remove the source of pain, the amount of these receptors will decrease over time (months)
Lateral Inhibition
Pressure sensor in the periphery takes the DCML pathway (this is the portion of the information that stays in the grey matter of the cord)–> this runs paralell to the 1st order ascending nociceptor
When neurons are close to together, they are able to talk to each other (mechanism unknown at the moment, probably uses a neurotransmitter & receptor). Neighboring neurons have the ability to shut down neurons nearby.
When there is a pressure sensor running parallel to a nociceptor, the pressure sensor has the ability to shut down some of the pain response.
This is how acupuncture works
Receptors in the pain system- AMPA
- Primary glutamate receptor is the AMPA receptor –> they open in response to glutamate–> causes ion channel next to the glutamate receptor to open and allow Na+ through the cell wall. (This occurs due to an increase in Na+ permeability in the target cell)
Glutamate release & binding process
-Glutamate is the primary fast pain neurotransmitter and is almost always excitatory
-1st order nociceptor releases glutamate in response to Ca++ fluxing into the cell. Ca++ interacts with glutamate storage vesicles, vesicles fuse with the cell wall and dump their contents into the synapse
-The 2nd order ascending neuron will need to have receptors on it in order to receive messages from the nociceptor
Growth and development?
Receptors in pain system- NMDA
Ions that flow through? Slower or Faster? How do these work?
NMDA-r; glutamate receptor that is attached to an ion channel. This receptor is large, so allows Na & Ca++ through the cell wall (Ca++ is primary). This receptor is a little slower than the AMPA receptor
-The NMDA-r needs two things in order to open:
1. Glutamate and
2. Prior depolarization. NMDA-r are typically blocked by extracellular Mg++. The negative charge on the inside of the cell draws Mg++ to the NMDA-r. When the cell depolarizes, the Mg++ leaves the area
These are placed in the CNS as a result of development; super important in the growth and development of the CNS
Things that block NMDA-r
5 total in this list
ETOH
Lead
Ketamine- Removes the Ca++ mediated portion of this pathway. Pain signals are still being sent via AMPA, but the CNS does not perceive it. Ketamine typically works on the brain in kids rather than in the cord (because of decreased NMDA-r)
Nitrous
Tramadol (but its terrible): Decent SSRI, but does not do much through the enkephalin receptors. Should not be used as primary pain control after surgery
Basic Overview- Spinal Reflex Pathways
Names, Function
- Stretch Reflex
- Tendon Reflex
-Stretch or tension reflexes; embedded in the muscles in our extremities - Withdrawal Reflex
- Crossed Extensor Reflex
-Responses to pain
Basic Spinal Wiring Schematic- General overview
What types of sensors? Where are they located?
-All of these reflex pathways are going to consists of some sensory component and then a way to elicit the reflex
-Reflexes that are dependent on skeletal muscle contraction or relaxation will need to have a way for the sensory reflex arc to influence motor function
-We have pain sensors out in the periphery. These pain sensors can elicit a reflex
-Tension receptors are located in the skeletal muscle or found within the tendons of skeletal muscle. Can sense the amount of tension within a muscle.
Consider the sensor a “spring,” if you pull apart the muscle, the spring will have increased tension
This gives our CNS a picture of what’s happening in the skeletal muscle
Interneurons
What are they? Function? Bridge between what?
-Sensory information can travel into the dorsal horn via it’s regular pathway. Sometimes sensory information projects directly into the anterior horn to elicit a reflex, other times we need the help of an intermediary neuron referred to as an interneuron
-Considered a bridge between the sensor itself and the motor neuron that needs to be communicated with
-Can be excitatory or inhibitory
-Reflexes can be bilateral and interneurons are utilized for crossover of the sensory information
Stretch Reflex
Goal? Reflex 1, 2. Interneurons? How to test for this clinically?
-Goal: Keep your muscles at a constant length. This reflex is engaged to keep our posture constant
Applicable to weight bearing muscle. Usually involve the leg muscle
Ex: Pushing in your forehead; this causes you quadricep muscles to stretch out. Without this reflex, your body will allow itself to be pushed backward
Reflex 1: With this reflex engaged, the quadricep muscles stretch, contract, then shorten back to their original length, allowing us to keep our posture constant.
Typically one sensory neuron is needed to achieve this reflex. The sensory neuron can synapse directly onto the motor neuron in the anterior horn of the cord without the help of an interneuron
**Reflex 2: **Involves an antagonistic muscle and an inhibitory interneuron. Antagonistic muscle in this case is the hamstring muscle. This muscle relaxes via an inhibitory connection, allowing the leg to straighten
How to test for this clinically?
Goal of this test is to determine if the sensors have a complete circuit with the other portions of the pathway.
To elicit this reflex, tap lightly on the ligament inferior to the patella. Striking that ligament causes contraction (shortening) of the quadricep muscle, and relaxation of the hamstring muscle. Striking the ligament does not directly engage the muscle spindle. Foot will also twitch
Quadriceps= extensor muscle
Stretch Reflex- Complete Circuit
- Stretching stimulates the muscle spindle (stretch receptor)
- Sensory neuron is excited
- Sensory information travels to spinal cord. Some information travels to the brain, some passes over to the anterior horn to activate a motor neuron
- Motor neuron is excited
- Effector muscle (where the original muscle spindle is located) contracts to relieve the stretching, antagonistic muscle relaxes
Tendon Reflex
Goal? Where are the sensors? Reflex 1, 2, bicep example, interneurons?
-Protective in nature. Consists of stretch receptors that are embedded in the tendons of our skeletal muscle capable of sensing large amounts of tension within the tendon
-Golgi tendon sensors detect heavy loads on the muscle by measuring tension.
Usually involves both reflexes and an inhibitory and excitatory interneuron
Reflex 1: Ceases contraction (relaxation) under a heavy load in order to prevent tendon tears or ripping the muscle out of their insertion point in the bone
Reflex 2: Contracts antagonistic muscles in order to speed up retraction from the heavy load.
There are ways to get around this reflex, but not totally sure of the mechanism. Ex: lifting a 5000lb car off of a child
Biceps/triceps Ex:
Reflex 1: Inhibits bicep with inhibitory neuron
Reflex 2: Excite triceps with excitatory neuron
Tendon Reflex- Complete Circuit
- Increased tension stimulates the golgi tendon sensor
- Sensory neuron is excited, travels through the dorsal horn
- Interacts with both and inhibitory and excitatory interneuron.
-Inhibtory interneuron is responsible for inhibiting the motor neuron that attaches to the muscle under the heavy load
- The excitatory interneuron causes reflex activation of the antagonistic muscle group
Flexor/Withdrawal Reflex
Goal? Muscle type used? Interneurons? Where are the cell bodies?
Goal: Withdraw from painful stimuli to avoid injury. This is usually done with the flexor muscles
-This reflex involves only one side of the cord. We have ascending and descending interneurons, and an interneuron that facilitates communication with the dorsal and anterior side of the horn
-Involves multiple levels of the cord, ~ two levels above and two levels below, via ascending and descending interneurons. The cell bodies of these interneurons reside in the lateral dorsal area of the white matter “ Tract of Lissaur”
Ex; Stub your toe–> reflex is to pull your limb away from whats doing the injury–> this activates the flexor muscle (hamstring in this case) and also relaxes the antagonistic muscle/extensors (quadriceps) to speed up the process of withdrawing
Flexor Reflex- Complete Circuit
- Painful stimuli
- Sensory neuron excited–> info travels to the cord
- Ascending and descending interneuron transmit information two levels above and two levels below stimuli
- Motor neuron excited–> flexor muscles contract to pull away from painful stimuli
- Antagonistic muscle relaxes
Crossed Extensor Reflex
-Involves withdrawing from pain, but also stabilizing with the other side of the body if there our weight is shifting. Allows us to withdraw from pain, but not fall over
-We have ascending and descending interneurons that run through the tract of lissaur, and interneurons that allow communication to the other side of the cord
Ex: Stub right toe or run into furniture –> we will need to plant our left leg to stabilize –> extensor muscles in the left leg contract, flexor muscles in this leg relax, straightening the leg, and giving us a stable base.
The affected limb will contract the flexor muscle group, and we will see relaxation in the antagonistic muscle group (extensor muscles)
Crossed Extensor Reflex- Complete Circuit
- Painful stimuli on one side of the body
- Sensory information sent to multiple levels of the cord via ascending and descending interneurons
- Motor information leaves the spinal cord
4a. Extensor muscles contract, flexor muscles relax allowing for us to stabilize
4b. Flexor muscles of affected limb contract, extensor muscles relax allowing us to withdraw the limb
nACh-r Variants
Low conductance, Fetal, how does succhinylcholine effect?
-Young/fetal, low conductance channels
-These are not restricted to the NMJ. These can be placed on the periphery of the muscle
-Have five domains;
Alpha & Alpha 1
Beta, Delta, and Gamma in place of Epsilon
-While open, the ion conductance is much slower than the mature version. The channels also stay open longer because their response to ACh is extended
When succhinylcholine is given, these nACh-r channels stay open for much longer. This can obvi
nACh-r Variants
High conductance, Adult
-Mature/Adult, High-Conductance channels are the version of nACh-r found at the NMJ in healthy adults.
-Restricted to the NMJ
-Have five domains;
Alpha & Alpha 1: two neurotransmitter binding domains
Beta, Delta, and Epsilon
Called high conductance because when the channel is open, the speed at which ions move through the channel is incredibly fast. These channels are only open for a very brief period of time
nACh-r Variants
Neuronal
Alpha 7 Neuronal nACh-r
Located in the CNS and ANS
Have five domains, all alpha 7
2nd order ascending neuron is usually…
Myelinated, even if it is a slow pain neuron
Kainate Receptor
3rd type of glutamate receptor in the pain pathway
This receptor mediates GABA activity in the brain
We don’t deal with this much in our class
Neuromuscular Junction Terminology
Junctional Area: In the NMJ
Perijunctional area: Lateral, out at the borders of the NMJ
Postjunctional: Further down the length of the muscle (not usually affected by paralytics)
What branches off the aorta? Which structures do we have at every lvl?
-Intercostal arteries branching from the aorta
- The intercostal arteries connect to the dorsal branch –> connects to the spinal branch which sits on top of the doral root ganglia (We will have this setup at every level of the cord). Whether or not this branch will continue all the way to supply the cord at the posterior or anterior portion will vary at each level.
- This image shows us all of the possible paths these arteries can take. We will not have all four feeding into the spinal cord at one level
-The majority of the blood flow branches around the rib cage, but there are smaller vessels that work their way in to support the underlying tissues
Pattern of intercostal arteries, renal & mesenteric aorta
-Notice the pattern of the intercostal arteries; primarily responsible for keeping the rib cage perfused
-Where do the renal aorta arteries branch off?
-Abdominal aorta?
-The mesenteric artery?
C-Spine
Anterior spinal artery
Posterior spinal artery
Anterior radicular artery
Posterior radicular artery
Vertebral arteries
GRA, range & absolute range. GRA provides the spinl cord with what?
What % of blood does the anterior spinal artery provide? The posterior?
-The anterior spinal artery supplies the cord with about 75% of it’s neccessary blood supply
-The posterior spinal arteries supply the cord with about 25%
-Great radicular artery/ Radicular artery of Adamkiewicz; this artery provides the anterior cord with 2/3rds of it’s blood supply (especially to the lower parts of the cord)
-GRA will enter on the left side of the patient in the vast majority of people. Closer to the aorta
Spinal level that is most associated with the GRA connecting to the anterior spinal artery: T10
Typical range: T9-T12 (~75% of people)
Absolute range where it could be found: T5-L5
Spinecerebellar Tracts; Anterior & Posterior pathways
-Spinocerebellar Tracts; cerebellum helps us coordinate complex movements
Two tracts: Will have one of each at each level of the cord
- Anterior/ventral spinocerebellar tract
-Ascends information up to the cerebellum regarding the amount of activity taking place in the anterior horn.
-Travels to the cerebellum via the ventral spinocerebellar tract into the superior cerebellar peduncle - Posterior/dorsal spinocerebellar tract
-Sends golgi tendon (can actually shut down the entire muscle if it needs to) and muscle spindle information to the cerebellum
-Ascends the dorsal spinocerebellar tract into the inferior cerebellar peduncle –> fans out throughout the inferior cerebellum
Why is heart pain referred to the left side?
The heart: The reason pain is typically referred to the left side here is because the right side of the heart is much less prone to ischemia due to the pressures being lower
Stomach: Felt higher than the umbilicus. Can be mistaken for an MI
Kidneys: Lower back
Limbic System. What does it consist of?
-Emotional center of the brain; sits right on top of the brain stem
-Slow pain feeds into the limbic system
- Amygdala
- Hypothalamus
- Cingulate gyrus
Cingulate gyrus; part of the cerebral cortex
Located just out of the corpus callosum
Buried deep in the brain
What is the sarcolemna?
-Cell wall of the skeletal muscle is called the sarcolemna
-Muscle fibers have specialized ERs called the sarcoplasmic reticulum
-Transverse tubules run perpendicular to the length of the muscle, allowing for the action potential to enter deep into the muscle
-Myofibrils (100s-1000s) make up the skeletal muscle fiber
-Borders of the sarcomere can be seen in this image
Sarcomere anatomy. What makes up the sarcomere?
Z disc, I band, A band, H band, Titan
-Myosin and actin filaments are contained within the sarcomere
-Contraction of the muscle depends on shortening of the sarcomeres
-The border of the sarcomere, where the thin filaments all connect, is called a Z disc. There is a Z disc at each end of the sarcomere
-The I band is an area within the sarcomere where there are only thin filaments located
-Area of the sarcomere where there are only thick myosin filaments is called the H band
-Where thick filament overlaps thin filament (small area) is called the A band
-Stretchy connective tissue that holds everything togethr- Titan
Cross section. Z disc, myosin, I band, mitochondria, T tubule
The green line is active tension
Blue line is passive tension
Red line is total tension
