Spinal cord Flashcards
Where does the spinal cord have enlargements - what do these do
Cervical C4T1 & lumbar L1S2
Upper and Lower limbs
Where does the spinal cord end
L1-L2
what is the conus medullaris
Come shaped caudal end of the spinal cord
Often used as a landmark
What is the cauda equina
The dorsal and ventral roots of the lumbar and sacral spinal nerves
Where do most vertebral fractures take place
Cervical bc they’re smaller/more fragile
Where do most vertebral dislocations take place? (Most to least) & why here
C5-6, T12-L1, C1-2
At points of greatest mobility
How many spinal nerve pairs? What’s the ratio of each?
31 :: C=8 T=12 L= 5 S= 5 Coccygeal = 1
What month of fetal development does the vertebrae start not corresponding to the cord length?
3rd
Innervation of a muscle group
Myotome
Skin patches innervated by one particular spinal cord level (I.e a dorsal root)
Dermatome
SCS: back of head
C2-C3
SPS: tip of shoulder
C5
SCS: nipple lolz
T4-5
SCS: xiphoid
T7
SCS: umbilicus
T10
SCS: Pubic region
L1
SCS: big toe/dorsal foot
L5
Lateral door and little toe
S1
Genital anal region
S3-5
Are dermatomes and peripheral nerves the same thing?
No! Dermatomes = one segment
Peripheral nerves = multiple segments (ex: musculocatenous n-C4,C5)
What would a C5 root injury do to the biceps?
What about a peripheral nerve injury?
Root injury = myotome; paresis
Peripheral N = both C5-6 are cut = paralysis
Colors of white and gray matter with myelin stain
White matter = dark blue
Gray matter = light blue
Where is he interomedialateral cell column (lateral horn) located?
T1-L2,3 in the intermediate gray
Dorsal horn does what
Sensory!
Substantia gelatinosa
Interneurons of dorsal horn
Pain and temperature fibers
Lissauers tract
White matter of dorsal horn
Pain axons
Nucleus proprius
Bulk of dorsal horn
Light touch, pain, temperature
Nucleus dorsalis of Clarke levels & what it does
Intermediate gray: C8-L2
Receives afferents from tendons and muscles via spinocerebellar tract
Lateral horn aka the intermedialateral cell column
Intermediate gray: C8/T1-L2,3
Origin if preganglionic axons of the sympathetic nervous system
Ventral horn, what’s it do, what’s it have
Motor - enlargements in cervical and thoracic region
Ventral horn neurons, alpha motor neurons, motoneurons = motor neurons
Lower motor neurons = gammas = muscle spindles
Exteroceptive info
Pain touch temperature vibration pressure
Proprioceptive info
Joint awareness, muscle stretch, Golgi tendon organs
Dorsal root ganglia central process synapses with what
Dorsal horn of spinal gray matter — acts as axon = info from fell body toward synaptic ending in spinal cord
Dorsal root ganglion peripheral
Process goes where
To the periphery
Acts as dendrite - info towards cell body
radiculopathy
=damage to a nerve root; commonly from spondolythesis or intervertebral disc disease
• symptom = shooting pain in dermatomal distribution
Mononeuropathy
Presence of deficits of a peripheral nerve
Common cause is trauma or entrapment/compression syndromes
Loss of proper function of that nerve
Ex: carpal tunnel
Poly neuropathy
Sensory AND motor deficits to multiple peripheral nerves - usually caused by disease
Ex: diabetes
Results in numbness and loss of pain/thermal sensations
Monosynaptic reflex
One synapse
Ex: muscle stretch reflex
Disynaptic reflex
Two synapses
Ex: flexor withdrawal reflex
Multisynaptic reflex
Multisynapses - crossed extensor reflex
What do muscle spindles measure
Length and rate of change of length
Two types of intrafusal fibers
Importance
Nuclear bag fibers
Nuclear chain divers
Units that have contractile ends that can respond to the muscle spindle and change the length of the muscle
-muscle stretch reflex
Two types of sensory fibers that innervate muscle spindles
Muscle spindle reactions
Type Ia primary ending
— wrap around central region of intrafusal fiber (annulospiral ending)
— phasic and tonic response
Secondary type II sensory afferent
—-innervate nuclear chain (flower-spray ending)
—only tonic
Phasic vs tonic response
Muscle spindle reflex
Phasic = during quick stretch of tendon I.e reflex testing
Tonic = long stretch during continued tension
Motor innervation of intrafusal fibers
gamma efferents
Maintain sensitivity if the muscle spindle
What do the central processes of the sensory neurons in the muscle spindle reflex synapse with directly
Alpha motor neurons
This creates the DTR reflex, since alpha motor neurons innervate muscles
If a reflex is hyporeflexive or areflexive (absent) you’re thinking…
Peripheral nerve injury
Bc the peripheral nerve is what causes the overall muscle contraction based on the spindle activity
Hypoflexia indicates lower motor neuron injury
If the reflex is hyperactive you’re thinking ….
CNS injury bc descending systems are thought to inhibit descending reflexes
Hypereflexia = upper motor neuron injury
Triceps reflex
Triceps brachii
C6,7,8
Radial N
Biceps reflex
Biceps brachii
C5,6
Musculocutaneus
Knee jerk (patellar) reflex
Quadriceps femoris
L3,4
Femoral n
Ankle jerk (Achilles) reflex
Gastroc, soleus
S1,2
Tibial n
Two major functions of the gamma motor neuron loop
Maintain sensitivity of muscle spindle
Determine muscle tone
*they are responsible for resetting the spindle so it can feel further length -under cortex control
Gamma—intrafusial fiber contraction— incr sensory activity —alpha motor neuron
Muscle toned is maintained by…
Gamma and alpha motor neurons
Descending pathways; inhibitory control
Hypertonicty or spasticity (increased tone) could indicate…
It’s typically seen with injury to the descending control of gamma loop
OR
An upper motor neuron lesion
Hypotonicity or flaccidity (decrease muscle tone) is…
Typically seen with a peripheral nerve injury
OR
A Lower motor neuron lesion
Spasticity
Velocity dependent
Usually results from injury to descending motor systems controlling the muscle stretch reflex
Rigidity
Increased uniform resistance that persists throughout the whole range of motion
Typical of basal ganglia injury
Flexor withdrawal reflex
Disynaptic reflex arc that facilitates flexion with antagonistic extension in response to a painful stimuli
Crossed extension reflex by way of internet ribs
Define dessucate
Cross the midline
Location of 1st order neuron of ascending pathway
2nd
3rd?
Dorsal root ganglia and sensory ganglia of cranial nerves
Nucleus along pathway
Nucleus in thalamus
Define medial lemniscus
Works with what?
Makes up what
Bundle of axons within the brain stem
Dorsal column to carry Info from the body
Dorsal column-medial lemniscal system
Dorsal column medial lemniscal system
Carries what info
Discriminative touch, sterognosis (3d recognition), vibration = cutaneous
Position sense & kinesthesia (awareness of joints)
=proprioception
When you test Discriminative touch Two point discrimination Graphesthesia Vibration, propriception, kinesthesia awareness
You’re testing what?
The dorsal column-medial lemniscus pathway
Look at packet for details on these tests – we did them in exams
What are the dorsal columns subdivided into in the cervical and upper thoracic regions?
What does each do?
Fasciculus gracilis & fasiculus cubeatus
Gracilis = found at all levels; info from lower limb T6 & below
Cuneatus= only in thoracic/cervical; carries upper limb/above T6 info
Define somatotopic mapping
Lower portions of body mapped medially, rostral mapped more laterally in dorsal column
Where do fasiculus gracilis and cuneatus synapse?
What do they do
What do they give rise to
In the dorsal column nuclei= nucleus gracilis and nucleus cuneatus
These relay to higher centers, stimulating peripherals and strengthening the signal
Give rise to medial lemniscus
How is the contra lateral medial lemniscus formed?
Where does it synapse?
Gracile and cuneate nuclei axons move towards midline, turn into internal arcuate fibers then decussate in the lower medulla (????)
Where does the medial lemniscus synapse in the thalamus?
Where do they go next?
The nucleus ventralis posterior-lateralis (VPL)
Ascend via posterior limb of internal capsule to the postcentral gyrus = primary somatosensory area
Golgi tendon organ reflex
Located in junction between muscle fiber and tendon
Provides info about tension of muscle
Too much tension –> relaxation of muscle
Maybe be involved in work load efficiency of muscles
What is tabes dorsalis?
Specific dorsal column lesion
Late manifestation of neurosyphilis
Signs of a dorsal column injury
Loss of: Proprioception Stereognosis Two point discrimination Vibration sense
Shuffling, uncoordinated gait due to impaired sensory = sensory ataxia
R
Which way will a patient with dorsal column lesion fall during Romberg?
Toward the side of the lesion
Don’t have the sensory to reposition self
What does the spinothalamic tract send?
What type of fibers
Pain - mechanical, chemical and thermal
temperature
Crude Non discriminative touch
Free nerve fibers - C & alpha delta
What can disruption of the spinothalamic tract cause?
Hypesthesia - reduced sensation
Paresthesia - numbness/tingling
Anesthesia - complete loss
Tests for spinothalamic tract
Sharp/dull - for pain perception
Temperature
Where do alpha delta and C fibers synapse in the dorsal horn?
Importance?
The substantial gelatinosa in the dorsal gray matter
Help with spinal reflexes such as flexor withdrawal reflex
Where do alpha Delta and C fibers bifurcate into ascending and descending branches?
Part of the spinothalamic tract
They bifurcate at lissauer’s tract
Do pain temp fibers attach to substantia gelatinosa at the level they attached to lissauer’s tract?
No way! They ascend a few levels first.
Pain and temp loss due to a lesion will begin one or two segments below injured site
What do the interneurons of the substantia gelatinosa and nuclei a proprius do with their axons?
With what
What does this form
They send them across the midline
Via the anterior white commissure
Forms the contralateral spinothalamic tract
Pain and temp decussates!!
Where do the fibers of the contralateral spinothalamic tract synapse?
Then what?
Thalamus & brainstem reticular formation
Then they carry on to the VPL of the thalamus which goes to the post central gyrus aka somatosensory cortex
What is springomyelia
Proximity of the ventral white commissure to the central canal to the central canal
Clinically important
Brown Sequard syndrome
= unilateral lesion
Touch, vibration, proprioception deficit on the side of the lesion
Pain and temp on the contralateral side
How does voluntary movement work?
Your pyramidal system (or corticospinal tract) takes your idea from the premotor cortex to the lower motor neurons to perform the task
Function of the cerebellum in movement
Coordinates the movement and influences the premotor cortex via thalamus nuclei
Basal ganglia function In movement
Allows desired voluntary movements and necessary postural adjustments via thalamic nuclei
What are the four Brainstem motor centers
Tectum
Vestibular nuclei
Red nucleus
Reticular nuclei
All give rise to extrapyramidal motor tracts
what is the major distinction between the pyramidal motor system & extrapyramidal motor system
it is a clinical difference
lesion to the pyramidal system = paralysis
lesion to the extrapyramidal system = paresis/alternate changes
what does the pyramidal motor system consist of
descending pathway
corticospinal tract, corticopontine, corticobulbar tract
Extrapyramidal system contains
Rubiospinal, retuculospinal, vestibulospinal, and tectospinal tracts
= controls muscles that are important for balance and posture
Main purpose of pyramidal motor system
Voluntary control of movement
Lower Motor neurons are…
Nerve cells that synapse directly with skeletal muscle
Ventral horn motorneurons & cranial nerves
Upper motor neurons are…
Neurons of the descending pathway that descend from the cerebral cortex or brainstem and synapse with ventral horn motorneurons or cranial nerve nuclei
I.e upper motor neurons synapse with lower motor neurons
Where do cell bodies of the pyramidal system lie?
What do their axons become
In the primary motor cortex
Axons going to spinal cord = corticospinal tract
To brainstem = cortiobulbar tract
Where is the origin of corticospinal tract neurons?
Precentral gyrus = brodmann area 4
Premotor cortex = brodmann area 6
Postcentral gyrus = areas 3,1,2
What is the corticospinal tract path
Axons in primary motor center -> through the corona radiate into the posterior limb of the internal capsule
Through midbrain (cerebral peduncle & crus crebri) through pins where it separates into bundles
To medulla! Where it decussates and creates the medullary pyramids
Axons of the corticonuclear tract do what
Synapse with cranial nerves to control eyes, facial expression, etc. III, IV, V, VI, IX, X, XII
What does the corticospinal tract continue as after it’s decussation?
What about the fibers that didn’t?
The lateral corticospinal tract
Injuries to this area = upper motor neuron injury
Fibers that didn’t continue as: ventral corticospinal tract =axial muscles
The corticospinal tract synapses withd
Ventral horn motor neurons
Dorsal horn nucleus proprius
Plays a role in sensory input –> usually inhibitory
Medial and lateral reticulospinal pathways
From the brainstem (extrapyramidal pathway)
Medial = activate extensor musculator of limbs Lateral = facilitate or inhibit extensors of limbs
Maintenance of posture and modulation of tone
Lateral and medial Vestibulospinal tracts
Part of the extrapyramidal pathway
Lateral = antigravity muscles (extensors for posture)
Medial = controls neck and head posture
Both = terminate on gamma motor neurons and alpha motor neurons -> vestibular labyrinth and cerebellum
Tectospinal tract function
Turn head in response to light stimulus
Coordinate head movement with visual tracking
Lateral brainstem (extrapyramidal) pathway aka, rubiosoinal tract
Originates in the red nucleus of midbrain; descends best the lateral corticospinal tract
Cervical cord levels only!
Proximal limb flexors of upper limb - correct errors in movement
May be important in acquiring new skills
If there is damage to the CST in the medulla, does that mean the brainstem pathways are messed up too (since they go through the medulla)?
No! They’re far enough away that it’s not forsure that they’d be hit
Two types of Iower motor neurons
Ventral horn motor neurons
Cranial nerve motor nuclei
6 parts of neurological exam
Observe Inspect Palpate Muscle tone testing (PROM) Functional testing (check for drift) Strength testing - MMT
Signs of an upper motor neuron lesion/damage
All muscle groups affected /signs at SCI and below:::
Muscles weak/flaccid
Spastic paralysis = Hypertonicity (increased tone) + paralysis
Hyper reflexia
Babinski sign (stroke foot, toes extend)
Pronator drift
Signs of lower motor neuron injury
Damage of Lower motor neuron/peripheral nerve:::
Flaccid paralysis or paresis =Hypotonia
+ paralysis
Muscle atrophy
Fasciculations -abnormal muscle twitches
Rigidity
Two types
Increased muscle tone not reliant on speed / felt in both agonist and antagonist muscles
Lead pipe = increase tone throughout whole range
Cogwheel = leadpipe + tremor jerky resistance to passive movement
Spasticity
Increased tone that is speed dependent
Asymmetrical about joint (can be greater in flexors than extensors etc)
Exaggerated reflexes and clonus are other symptoms
What is poliomyelitis
Viral disease of ventral horn cells results in long term lower motor neuron damage
Tabes dorsalis
Form of neurosyphilis that causes dorsal root/column issues
Proprioception and vibratory sensation and DRR (bc of afferent) affected
Subacute combined degeneration
Bilateral demyleination and loss of nerve fibers in dorsal column and dorsolateral funiculus due to B12 deficiency
Loss of sense of position discrimitive touch vibration & ataxic gait
Springomyelia
Shawl like anesthesia for pain and temp over shoulders/upper limbs
Type of dissociated sensory loss
Amyotrophic lateral sclerosis
Degenerative disease of the ventral horn and lateral corticospinal tract bilaterally
Combo of upper and lower motor signs
