Spinal Cord Organization Flashcards
CNS originates from ___________
The neural tube
The lumen of the neurotube becomes the ______________and____________filled with cerebral spinal fluid (CSF)
central canal of the cord; ventricles of the CNS
Alar plate = __________(dorsal/ventral)
Dorsal
Basal plate= ___________(dorsal/ventral)
Ventral
Syringomyelia
a rare disorder in which a cyst forms within your spinal cord. As this fluid-filled cyst, or syrinx, expands and lengthens over time, it compresses and damages part of your spinal cord from its center outward.
Metamerism
the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions
*The developing embryo show metamerism
Somites give rise to _______, ___________, and _________.
Sclerotomes, dermatomes, and myotomes
Which nerve fibers play a role in flexing hip during the “ swing phase of walking”?
L2, L3
Which nerve fibers play a role in extending the knee during the “ swing phase of walking”?
L3, L4
Which nerve fibers play a role in extending the ankle during the “ swing phase of walking”?
L4, L5
What type of neurons are found in the spinal cord?
Motor neurons
Interneurons
Projection Neurons
What are the two major functions of interneurons?
Excitatory
Inhibitory
What are the two types of Interneurons?
- intrasegmental interneurons (Renhsaw cell)
- propriospinal interneurons
a. short (3 segments, unilateral)
b. intermediate
c. long (entire length of cord, bilateral)
Cervical enlargement
C5-T1
Surrounding the neural tube you have the __________. This gives rise to________
Neural epithelium gives rise to the alar and basal plates
*Note: Even in a developing neural tube, you see a dorsal-ventral dichotomy separation
What can be found in the lumen of the CNS?
Cerebral spinal fluid
What is the general organization of the spinal cord?
A lumen surrounded by gray matter surrounded by white matter
What is the first structure that forms in the trilaminar embryo? What is it’s importance?
The notochord.
The notochord stimulates formation of the neural tube which comes from the ectoderm.
Lumbosacral enlargement
L1-S4
The intial effect of syringomyelia is on__________ (sensory/motor) function.
Sensory
What is metamerism?
Blocks of cells that begin at cranial region and extend down to the caudal region
During the first 3-4 weeks, what happens with the neuroepithelial of the neural tube?
The cells begin to differientiate forming neurons. These neurons will send out growth codes that inenrvate the dermis cells that will be becoming dermatomes and myotomes.
The dorsal have of spinal cord will innervate the ___________, which the ventral half of the spinal cord will innervate the ___________.
Dermatome; myotome
What’s the difference between the developing neural tube and the adult spinal cord?
In the neural tube, the central canal is large. The central canal is smaller the adult spinal cord
Ventral white commissure
Commissue means axons that are crossing one side of neuron systems to the other. So these commissure neurons are neurons that go from left to right, right to left to allow the 2 parts of the spinal cord to communicate their activities
The __________ matter of the spinal cord comes from the alar and basal plate.
Gray
Which type of neurons are multipolar?
Motoneurons
Which level of the spinal cord has a lateral horn?
Thoracic
If you have a cyst in the central canal, which structure will be affected first?
The ventral white commissure
Lateral horn
- T1-L2
- Found in the thoracic spinal cord
- Related to where the sympathetic nervous system originates.
What are the characteristics of interneurons?
- Axons remain in the spinal cord
- They dont project to peripheral targets or to other structures in the brainstem
- Local circuit neurons
- Connect to different parts of the gray matter
- Make up the bulk of the spinal cord
- Build circuits around which the pattern generator of the spinal cord can function so that we can do basic things like walking and moving stuff.
What are intersegmental interneurons?
- Very short axons that remain in spinal cord segment
- Very powerful inhibitory neurons that have close synaptic connections between the motor neurons
- So motor neurons give off collateral through Renshaw cells, and Renshaw cells go right back to the motor neurons to kind of keep the firing of motor neurons under control
Distinguish between the two types of propriospinal interneurons.
Short
- Span 2/3 spinal cord segments
- Most related to neurons that control upper and lower limbs
- Unilateral
Long
- Some extend the entire length of the spinal cord
- Bilateral
- Axial- musculature and paraspinal muscles
What are projection neurons?
- Send axons to targets in the brainstem or diencephalon
- Project info to high levels of the nervous axis
Through a signle neuron the cervical enlargement is connected to the lumbosacral enlargement. Which neuron does this?
A long propriospinal interneuron
*This makes sense because wjhen you walk, both limbs are moving together in a coordinated fashion
When an axon from a short propriospinal interneuron is jolted with an electrical stimulation, what is produced?
An antidronic spike, which basically allows it to go in the opposite direction
The long propriospinal interneurons are involved in what pathway? What function does this pathway play a role in?
- Medial motor pathway
- Plays a role in axial movements
- Plays a role in gait, balance, and posture
The short propriospinal interneurons are involved in what pathway? What function does this pathway play a role in?
Lateral motor pathway
- Controls movement of contralateral limbs
- Plays a role in movement and possibly recovery of lost motor functioning
What two neuronal types are found in the ventral horn?
Alpha motor neurons
Gamma motor neurons
In three dimensions, motor nuclei form cell __________
columns
Motoneurons to each muscle form islands of cells called _______ surrounded by a sea of ___________.
Nuclei; Interneurons
NOTE: Motor neurons extend 2, maybe 3, spinal cord segments. This is good becuase it provides for some redundancy. If you have damage to the ventral root at one level, you’ll still have control over the muscle becuase the spinal cord segment beleow would still provide some innervation
Would you have the lateral group innervating the more distal parts of the limbs? Would you find them at every spinal cord level?
You would find the lateral expansion where you have limbs but the core muscles going to the trunk with be at all levels.
In a topographic organization of the motor nuclei of the ventral horn, _________ are found more dorsally, while __________ are found more ventrally.
Flexors; extensors
In a topographic organization of the motor nuclei of the ventral horn, the _________ is found more proximal, while __________ is found more distal.
Trunk; Hand
Which lamina would be related to the ventral horn?
8,9, and 10
What is lamina 1?
Marginal nucleus of spinal cord
- Located at the most dorsal aspect of the dorsal horn of the spinal cord.
- Neurons located here receive input primarily from Lissauer’s tract and relay information related to pain and temperature sensation.
What is lamina 2?
Substantia gelatinosa of Rolando
- one point where first order neurons of the spinothalamic tract synapse.
-
C fibers terminate at this layer.
- conveying slowly conducting, poorly localized pain sensation
What is lamina 3 and 4?
Nucleus proprius
- adjacent to the substantia gelatinosa.
- can be found in the gray matter in all levels of the spinal cord
- involved in sensing pain and temperature.
- Cells in this nucleus project to deeper laminae of the spinal cord
What is lamina 5?
Neck of the dorsal horn
- Mainly involved in processing sensory afferent stimuli from cutaneous, muscle and joint mechanical nociceptors as well as visceral nociceptors.
- Plays a role in pain referral.
What is lamina 6?
Base of the dorsal horn
- Receives input from large diameter fibres innervating muscles and joints and from muscle spindles
- Feedforward this information to the cerebellum where it can modulate muscle tone accordingly.
What is lamina 7 and 10?
Lateral grey column: VII and X
- Lamina VII (Reflex activity)
- intermediomedial nucleus
- intermediolateral nucleus
- mediates the entire sympathetic innervation of the body
- Gives rise to lateral horn
- posterior thoracic nucleus (Clarke’s column) in the thoracic and upper lumbar region
- important structure for unconscious proprioception
- Lamina X
- an area of grey matter surrounding the central canal
What is Lamina 8 and 9?
Anterior (ventral) grey column: VIII-IX
- Lamina VIII
- Motor interneurons
- Commissural nucleus
- Modulates gamma motor neuron activity
- Modulates muscle tone and movement
- Lamina IX
- lateral (in limb regions) and medial motor neurons
The rexed lamina 9 consist of two distinct groups of motor neurons. What are they?
Medial group-axial musculature
- Long propriospinal interneurons are most closely related to this type of musculature
Lateral group- appendiculare musculature
- The short propriospinal interneurons are most closely related to this type of musculature
What is the function of gamma motor neurons?
Responsible for contributing to setting sensitivity of muscle spindle
When you get into regions where you have the lumbosacral enlargment, you will see an exapansion of lamina _____, which we call the intermediate zone.
7
*It becomes larger where you have limbs because you need a lot of interneurons to coordinate reflex activity.
What are the four nuclear groups of the dorsal horn?
Dorsolateral zone (of Lissauer)
- Not a nucleus, its a system of fibers
- Short propriospinal interneurons
Marginal zone (lamina 1)
Substantia gelantinosa (Lamina 2)
Nucleus proprius (Lamina 3 and 4)
Intermediate zone (lamina 7)
- Found between the dorsal and ventral horn
What is the white matter in the CNS?
In the white matter ther are fiber tracts
What is the difference between a fiber tract and a peripheral nerve?
In the PNS, you have collagen fibers surrounding the myelin sheaths and nerves (like perinerium). In CNS, you don’t.
The white matter of the spinal cord is organized into 3 funiculi. What are they and where are they found?
Posterior funiculus (Found btween posterior lateral sulcus; between the dorsal horns)
Lateral funiculus
- Dorsolateral funiculus
- Ventrolateral funiculus
Anterior Funiculus
If the axon potentials are going up towards the cortex, we call it an __________ tract. If the axon potentials are going down, away from the cortex or brainstem, we call it ____________ tracts.
Ascending; descending
*You don’t have a mixture of tracts like you do nerves, it’s either motor or sensory
What are the three long tracts and what are their functions?
(Lateral) Spinothalamic tract
- Pain, temperature, crude touch
- Ventrolateral funiculus
Dorsal columns
- Fine touch, proprioception
- Dorsal funiculus
Corticospinal tract
- Voluntary movements
- Dorsolateral funiculus
Which two levels of the spinal cord have large ventral horns?
Cervical and lumbar, due to enlargements
Are axons in the dorsal root of uniformed diameter?
No
Are fiber diameter and spike duration directly or indirectly proportional?
Indirectly
What are the nerve fiber types in mammalian nerve? List their function and whether or not they are myelinated.
A (Myelinated)
- alpha (a.k.a 1a, 1b)
- Function: proproception; somatic motor
- Innevate some part of the muscle spindle and Golgi tendon
- beta (a.ka. II)
- Function: Touch, pressure
- gamma
- Function: Motor to muscle spindles
- delta (a.k.a III)
- Function: Pain, cold, touch
- Pain (mechanical and thermal)
B (Myelinated)
- Preganglonic autonomic
C (Unmyelinated)- A.K.A. IV
- Dorsal root
- Pain, temperature, some mechanoreception, reflex response
- Sympathetic
- Preganglionic sympathetics
Are fiber diameter and conduction velocity directly or indirectly proportional?
Directly
Which nerve fibers are proprioceptors?
A-alpha or Ia, Ib
Which nerve fibers are mechanoreceptors?
A-beta or II
Which nerve fibers are nocioceptors?
A-delta or III
C or IV
Axons entering the dorsal root divide into two division according to axon diameters. What are they and what fibers are found ineach division?
- Medial division
- A-alpha (proprioceptor) and A-beta (mechanorecptors)
- Axons ascend through dorsal column but give off collaterals to different lamina in the dorsal and ventral horn to subserve reflexes and to provide sensory feedback
- Lateral division
- A-delta and C (nocioceptors)
- Terminates in the dorsal horn
Axons from the periphery come back to the spinal cord via the ____________.
Dorsal root ganglion
Pain infor terminates where?
In the upper two lamina
*As you move down the lamina, you start to get more of mechanoreceptor info to determine if that painful stimulus requires you to withdraw your hand or if it not so painful maybe you want to hold it in a particular position.
Dorsolateral Zone is also known as_________
Zone of Lissauer
Characteristics of Dorsolateral Zone
- Lateral part of the dorsal root “entry zone”
- Nociceptive (small diameter) axons branch
- Descend and ascend to terminate at several other spinal cord levels
*Contain spinothalamic tract (second order sensory neuron)
Afferents enter the ________, ascend and descend giving off collaterals that synapse at several spinal cord levels.
Zone of lissauer
Largest, fastest conducting fibers for sensory info
Ia and Ib fibers
Inhibitory interneurons are also known as
Renshaw cells
The posterior spinal arteries supply ________
Dorsal funiculus
The anterior spinal arteries supply_________
Anterior funiculus
Lateral funiculus
Ventral horn
The spinal arteries begin as branches of the __________
Vertebral artery
*NOTE: The initial branching in the vertebral are not large enough to supply blood all the way down to the lower sacrum and coccyx part of the spinal cord. So these spinal arteries have to be reinforced by arteries that are coming off at different levels.
The spinal arteries are reinforced by __________ arteries from different spinal levels of the aorta.
Medullary (radicular)
What artery supplies the lumbosacral enlargement?
The greater anterior segmental medullary artery of Adamkiewicz
The aorta gives branches to each area of the somite. At the thoracic level, they are called __________ arteries. At the lumbar level, these arteries are called ________ arteries.
Intercostal; Lumbar
*lumbar arteries give off segmental branches that go to the intervertebral foramen and some of which reach the spinal cord
