Spinal Region Flashcards
What does the spinal region include?
- spinal cord
- dorsal and ventral roots
- spinal nerves
- meninges
What are rootlets?
small groups of axons sending information to the periphery
The ventral root is the coalescence of what?
ventral rootlets
What does the dorsal root contain?
sensory axons bringing information into the spinal cord
Connections of nerve rootlets to the exterior of the cord indicate what?
segments
What do spinal nerves carry?
all motor and sensory axons of a single spinal segment
In the cervical region, spinals nerves are found ____ the corresponding vertebrae, except for which one?
above
except for the 8th spinal nerve (C8 is in between C6-C7)
In the thoracic and lumbar regions, spinals nerves are found ____ the corresponding vertebrae.
below
Describe the arrangement of white and gray matter in the spinal cord
White matter surrounds gray matter and contains axons that link the cord with the brain.
What does the dorsal horn of the spinal cord process?
sensory information
What does the lateral horn of the spinal cord process?
autonomic information
The lateral horn is present at what spinal levels?
T1-L2
What does the ventral horn of the spinal cord process?
motor information
What is the majority of gray matter composed of?
spinal interneurons
Gray matter is classified into 10 histologic regions, called what?
Rexed’s laminae (I-X)
Functionally, what do Laminae I and II process?
pain information
What are meninges?
layers of connective tissue that surround the spinal cord
What are the 3 meninges from internal to external?
- Pia mater
- Arachnoid
- Dura mater
Do physiologic motions significantly change the vertebral canal space in people with normal vertebral canals?
No
What does extending and/or lateral bending of the neck do to cervical levels?
increases the intervertebral foramen pressure
What is the function of the spinal cord?
- To convey information between the neurons innervating peripheral structures and the brain
- To process and modify information within the cord through synapses
What are interneurons categorized by?
function
By integrating volleys of peripheral, ascending, and descending inputs, spinal circuitry provides what 3 things?
- Modulation of sensory information
- Coordination of movement patterns
- Autonomic regulation
What do interneuronal circuits do?
integrate activity from all sources and adjust the output of lower motor neurons
What do interneurons coordinate?
activity in all the muscles when a limb moves
What determines whether a single alpha motor neuron will fire?
Summation of activity at 20,000 to 50,000 synapses
What are Stepping Pattern Generators?
adaptable neural networks that produce rhythmic output
How do SPGs contribute to stepping?
by activating lower motor neurons, eliciting alternating flexion and extension at the hips and knees
When are SPGs normally activated?
when the person voluntarily sends signals from the brain to the stepping pattern generators (SPGs) in the spinal cord to initiate walking
Describe the basis behind Stepping Pattern Generator function
1) Firing the UMN initiates cycles of activity in the SPG.
2) SPG neuron 1 activates extensor motor neurons that signal extensor muscles to contract.
3) Collaterals from neuron 1 synapse with an inhibitory interneuron (neuron 2), which inhibits neuron 3.
4) When this interneuron fatigues, neuron 3 can begin firing, which activates flexor motor neurons that signal flexor muscles to contract.
5) Collaterals from neuron 3 synapse with an inhibitory interneuron (neuron 4), which inhibits neuron 1.
6) When this interneuron fatigues, neuron 1 resumes firing.
Can patients with a complete SCI elicit stepping-like movements?
Yes, by electrically stimulating the posterior spinal roots
When walking, electrical stimulation to a single point on the foot produces different responses, depending on what?
the phase of the gait cycle
If the electrical stimulus occurs at the onset of swing phase, which muscle activity increases?
tibialis anterior
If the electrical stimulus occurs at the end of swing phase, which muscle activity increases and which decreases?
tibialis anterior activity decreases and antagonist muscle activity increases
All spinal reflexes involve interneurons except for which one?
The monosynaptic phasic stretch reflex
Which reflex demonstrates the capacity of interneuronal circuits to generate complex movements?
Withdrawal reflex
What can elicit a withdrawal reflex?
Afferent information from skin, muscles, and/or joints
The specificity of the movement pattern associated with the withdrawal reflex is referred to as what?
a local sign, which indicates that the response depends on the site of the stimulation
What reflex is activated if a person is standing when a lower limb is abruptly withdrawn, another interneuronal circuit quickly adjusts the muscle activity in the stance limb to prevent the person from falling?
Crossed extension reflex
What do interneurons in inhibitory circuits contribute to?
spinal cord motor coordination
What 2 things do inhibitory interneurons provide?
- Reciprocal inhibition
- Recurrent inhibition
What does reciprocal inhibition do?
Decreases activity in antagonist when an agonist is active, allowing the agonist to act unopposed. This prevents unwanted activity of the antagonists.
_____ inhibition separates muscles into agonists and antagonists.
Reciprocal
Recurrent inhibition _____ agonists and synergists, and _____ antagonists.
inhibits
disinhibits/facilitates
What type of interneuron cells produce recurrent inhibition?
Renshaw cells
What stimulates Renshaw cells?
a recurrent collateral branch from the alpha motor neuron
What do Renshaw cells inhibit and facilitate?
They inhibit agonists and synergists and facilitate agonists
How do Renshaw cells isolate desired motor activity from gross activation?
By focusing motor activity
What does a loss of descending influence on Renshaw cell activity cause?
difficulty in achieving fine-motor control
A lesion in the spinal region may interfere with what 3 things?
- Segmental function
- Vertical tract function
- Both segmental and vertical tract function
What do segmental lesions interfere with?
neural function only at the level of the lesion
What do segmental signs of dysfunction include?
abnormal or lost sensation in a dermatomal distribution and/or LMN signs in a myotomal distribution
What do lesions interrupting vertical tracts result in?
a loss of function below the level of the lesion
Ascending tract lesions result in what?
problems with the regulation of blood pressure, sweating, and bladder and bowel control.
Descending tract lesions result in what?
- paralysis
- spasticity
- muscle hypertonia
- Babinski’s sign present
All signs of damage to vertical tracts occur ____ the level of the lesion.
below
What 3 things do peripheral nerve lesions cause?
- Altered or lost sensation in a peripheral nerve distribution
- Decrease or loss of muscle power in a peripheral nerve distribution
- No vertical tract signs
What 3 things do segmental spinal region lesions cause?
- Altered or lost sensation in a dermatome
- Decreased or lost muscle power in a myotome
- Decreased or lost phasic stretch reflex
What 3 things do vertical spinal region lesions cause?
- Altered or lost sensation below the level of the lesion
- Altered or lost descending control of BP, pelvic viscera, and thermoregulation
- UMN signs
What are the 4 characteristics of an UMN lesion?
- Decrease or loss of muscle power
- Spasticity
- Muscle hypertonia
- Positive Babinski’s sign and clonus
What is a syndrome?
a collection of signs and symptoms that do not indicate a specific cause
What are examples of syndromes resulting from tumors or trauma in the spinal region?
- Anterior cord syndrome
- Central cord syndrome
- Brown-Séquard syndrome
- Cauda equina syndrome
- Tethered cord syndrome
What does anterior cord syndrome interfere with?
pain and temperature sensation and motor control
What does central cord syndrome result in? (small lesion)
loss of pain and temperature at the level of the lesion
What does central cord syndrome result in? (large lesion)
Impairment of upper limb motor function
What does Brown-Séquard syndrome result in?
- Ipsilateral loss of voluntary motor control, conscious proprioception, and discriminative touch below the level of the lesion
- Contralateral loss of pain and temperature sensation below the level of the lesion
What does Cauda equina syndrome cause?
sensory impairment and flaccid paresis or paralysis of lower limb muscles, bladder, and bowels
What does Tethered cord syndrome cause?
- low back and lower limb pain
- difficulty walking
- excessive lordosis
- scoliosis
- problems with bowel and/or bladder control
- foot deformities
