Module 2 Flashcards
Where is Rexed’s laminae IX, and what is its function?
It makes up the majority of the anterior horn of gray matter and gives rise to motor neurons. The medial aspect of the anterior horn contains axons that innervate proximal muscles, while the lateral aspect contains axons that innervate distal muscles.
How many spinal segments are there, and how many vertebrae are in each region? Where does the SC end?
31 spinal segments.
7 cervical (8 cervical nerves), 12 thoracic, 5 lumbar, 5 sacral, 1 coccyx.
The SC ends at L1-L2 vertebrae.
Define the conus medullaris, cauda equina, and filum terminale.
Conus medullaris: the tip of the spinal cord.
Cauda equina: from L2 and below, a bundle of nerves like a ‘horse’s tail’
Filum terminale: a thin continuation of pia mater connecting to the base of the coccyx that holds the SC in place.
Where do cervical nerve roots exit?
Above the associated vertebrae. Since there are 7 cervical vertebrae and 8 cervical nerves, C8 exits below C7 and above T1.
Where do thoracic and lumbar nerve roots exit?
Below the associated vertebrae.
Where is the cervical enlargement?
From C3-T1 segments. It has a larger proportion of white matter, as there is more communication with the brain higher up in the spinal cord.
Where is the lumbosacral enlargement?
From L1-S3 segments. It has a larger proportion of gray matter, as there is more communication with the periphery.
What is a myotome?
All the muscles innervated by a single spinal cord segment.
What are the clinically relevant nerve roots for the arm?
C5: innervates the shoulder muscles.
C5 + C6: innervates elbow flexors.
C6: innervates wrist extensors.
C7: innervates elbow extensors.
What are the clinically relevant nerve roots for the leg?
L4: innervates knee extensors.
L5: innervates ankle dorsiflexors.
S1: innervates ankle plantar flexors.
What are lower motor neurons (LMNs)?
Neurons that project from the spinal cord to the periphery. They are the final common pathway from the CNS to the muscle.
Where are LMNs located?
In the anterior horn of the SC, also in cervical and thoracic regions.
What are the symptoms of LMN lesions?
- Weakness
- Fasciculations
- Atrophy
- Hyporeflexia
- Hypotonia (AKA flaccid paralysis)
What is seen in high steppage gait?
Happens when L5 neurons are damaged (dorsiflexors).
- Excessive knee flexion ipsilateral to the injury to avoid dragging of the foot
- lack of dorsiflexion during the swing phase, so the toe hangs down
- Foot lands toe first and sets down carefully.
What are the causes of LMN lesions?
Injury or disease that affects motor neurons in the anterior horn, ventral nerve roots, or spinal nerves.
What is polio?
A virus that attacks cell bodies in the anterior horn (LMN symptoms). Primarily affects muscles in the lumbar region.
How can spinal cord damage cause LMN damage?
If disc herniations impinge on ventral nerve roots.
If a tumor grows into the anterior horn.
**There will only be LMN symptoms AT the level of the injury.
How do ventral roots and spinal nerves get injured?
Through compression, traction, laceration, or entrapment.
Where are upper motor neurons (UMN) located, and what do they do?
Cell bodies are in the motor regions of the cortex. They synapse onto LMNs.
Where is the primary motor cortex located (PMC)? What is the somatotopic organization?
The precentral gyrus.
Leg areas are most medial, face areas are most lateral. Think of a person lying on their back with their arms out.
What are corticospinal tracts?
Bundles of UMN axons from the motor cortex travelling to the SC.
Recite the path of the corticospinal/corticobulbar tracts from the cortex to the spinal cord.
Corona radiata -> posterior limb of the internal capsule -> basis pedunculi in the midbrain -> medullary pyramids -> cross the midline at the pyramidal decussation -> SC
What is the function of the lateral corticospinal tract, and which side(s) of the body does it control?
Controlling the periphery, primarily fine motor control of distal muscles.
The neurons control contralateral sides of the body.
Where does the lateral corticospinal tract enter, and where does it terminate?
It enters into the lateral column of the SC. It terminates at the spinal enlargements (cervical and lumbosacral).
What are the components of the internal capsule?
Anterior limb, genu, and the posterior limb.
What is the function of the anterior corticospinal tract, and which side(s) of the body does it control?
It primarily controls axial muscles (neck and trunk). It controls bilaterally, as the axon bifurcates at the spinal level it wants to innervate. Not all axons bifurcate, but most do.
How do the anterior corticospinal tract axons cross the midline of the SC?
Via the anterior commissure.
What are corticobulbar tracts?
Tracts that originate in the cortex and go to the brainstem.
How many cranial nuclei are there? What do they give rise to?
- They give rise to the 12 cranial nerves.
Which cranial nerve is considered the ‘facial nerve’?
Cranial nerve VII.
Where do facial nuclei originate?
In the pons.
Which side(s) of the body does the facial nerve control? How does this change between the upper and lower face?
The facial nerve controls ipsilateral muscles.
For muscles above the eyes, the UMN input is bilateral to the facial nerve.
For muscles below the eyes, UMN input is contralateral to the facial nerve.
Where is the injury located if there is weakness on the entire side of the face?
There is damage to the facial nuclei on the side ipsilateral to the weakness. There will be LMN symptoms.
Where is the injury located if there is weakness just on the lower side of the face?
There is an injury to the UMNs contralateral to the weakness.
There is some preserved function in the upper face, as there is bilateral input to the upper face, and the other UMNs are still intact.
What is Bell’s Palsy?
A condition with an unknown cause that attacks the facial nerve. Damage is to the entire ipsilateral side of the face. Symptoms subside after 2-3 wks, but it takes 3-6 months to fully recover.
How does the somatotopic organization of the CS and CB tracts change as they descend to the SC?
- In the cortex, the head areas are most lateral, and the legs are most medial.
- When the tracts reach the internal capsule, they rotate so the face becomes most anterior, and the legs become most posterior.
- At the midbrain, they have fully rotated so the face is most medial and the legs are most lateral.
- The tracts get off in order. Face at the pons, arms at the cervical region, trunk at the thoracic region, and legs at the lumbar region.
What is the function of the rubrospinal tract, and where does it travel?
It travels from the red nucleus in the midbrain to the lateral column of the spinal cord, and it terminates at the cervical level.
It has contralateral arm control, facilitates flexor muscle tone of the arms, and inhibits extensor tone of the arms.
What is the function of the vestibulospinal tract, and where does it travel?
It travels from the vestibular nuclei in the pons and medulla and down through the anterior column of the SC.
It is important for arm and leg tone, and neck + balance reflexes.
What is the function of the lateral vestibulospinal tract, and where does it travel?
It travels from the lateral vestibular nucleus in the pons, and goes ipsilaterally down to all levels of the SC.
It facilitates extensor muscles tone of arms and legs, and inhibition of flexor muscle tone of arms and legs.
What is the function of the medial vestibulospinal tract, and where does it travel?
It splits immediately from the medial vestibular nuclei, and runs bilaterally down to the cervical and thoracic levels of the SC.
It controls the tone of neck and axial muscles.
What is the function of the reticulospinal tract, and where does it travel?
It travels from the reticular formation (central brainstem) and ipsilaterally down through the anterior column of the SC to all levels.
It modulates general muscle tone and reflexes (i.e. the startle reflex).
What are UMN lesions?
Injury or disease affecting upper motor nuclei in the motor cortex, or axons descending through the brain, brainstem, or SC.
Depending on where the injury is, where will you see symptoms?
Lateral CST lesions: symptoms in distal muscles.
Cortical lesions: symptoms will be seen contralateral to the injury.
Lesions past the cervicomedullary junction: symptoms will be ipsilateral to the injury.
What are the symptoms of UMN lesions?
- Weakness
- Hyperreflexia
- Hypertonia
- Positive Babinski’s sign
What is decorticate posture?
It happens when the lesion is above the midbrain. It involves the rubrospinal tract, so there a net flexion effect.
You will see upper body flexion and lower body extension.
If the damage is on one side, the symptoms will be contralateral to the lesion.
What is decerebrate posture?
It happens when the lesion is below the midbrain. It involves the vestibulospinal tract, so there a net extension effect.
You will see upper body extension and lower body extension.
If the damage is on one side, the symptoms will be contralateral to the lesion.
What is hemiplegic gait?
When someone is walking with decorticate posture. One arm is in flexion and there is circumduction of the extended leg.
What are the causes of UMN lesions?
- Injury to the motor cortex where the cell bodies are
- Damage to the internal capsule or cerebral peduncles
- SC lesion or compression
- Diseases attacking UMNs
What is PLS?
A disease with an unknown origin that attacks UMNs specifically. It primarily affects cells in the motor cortex. It is progressive, but non-fatal, and there is not cure.
What is ALS?
AKA Lou Gehrig’s disease.
It involves the degeneration of UMNs and LMNs. The origin is potentially genetic, but otherwise unknown. It results in problems with breathing, swallowing, and speaking. It is fatal in 2-4 years.
LMN symptoms:
1. Atrophy
2. Fasciculations
UMN symptoms:
1. Hypertonia
2. Hyperreflexia
