Lecture 2: Introduction to SCI Flashcards
What structures (2) does the CNS include?
brain and spinal cord
Define: meninges
three membrane layers that cover and protect your brain and spinal cord
3 layers of meninges
- Dura mater (compressed of Periosteal and meningeal layer - periosteal is more outer)
- arachnoid mater
- pia mater
Why is the cerebral spinal fluid sometimes sampled?
CSF can be sampled to look for disease markers or to see if an intervention is working or not
Define: the Glimphatic System
An internal plumbing system that rids the brain of toxic wastes. Sleep is when this cleanup ritual occurs.
Describe the functional Segregation of Motor and Sensory Functions in the Brain
The brain is divided by the central sulcus which separates it into the anterior portion and posterior portion.
The anterior portion is associated with motor control and the posterior portion is associated with sensory control.
Anterior to the central sulcus is the precentral gyrus which is the site of the primary motor cortex.
Posterior to the central sulcus is the postcentral gyrus which receives and integrates sensory information relating to touch, pain, temperature, vibration, proprioception and movement; primary sensory cortex
Name the two main descending corticospinal tracts.
Describe their function
Lateral corticospinal tract: controls distal limb muscles
Anterior corticospinal tract: Controls axial trunk muscles (back)
Describe the errors in the schematic drawn in slide 10
Muscles don’t have just efferent nerves; there are also afferent fibres in muscles! Examples: muscle spindles, pain nerve endings, etc.
There are also autonomic motor fibres in the skin. So not just afferent fibres but it is mostly sensory fibres in the skin
Describe the number of spinal cord levels in each spinal cord segment
Cervical: 8
Thoracic: 12
Lumbar: 5
Sacral: 5
Coccyx: 1
Explain the differences of the spinal cord structure at various levels. Why is this difference occurring?
Total cross section of the spinal cord changes at various levels. For example: cross section of C5 and L3 are much larger than C2, T10, and S3. These larger sections have more grey matter. Overall, the amount of grey matter at the thoracic levels are much lower than cervical and lumbar. Additionally, the angle that spinal nerves leave the spinal cord decreases further and further down the cord.
Reason: All the motor neuron cell bodies that project through the arm are at the cervical levels. All the motor neuron cell bodies that project through the legs at the lumbar-sacral levels. This results in a cervical enlargement and a lumbar enlargement. At the thoracic level, a lower number of motor neurons are needed.
Explain the somatotopic organization of dorsal columns.
High cervical spine levels
- Ascending tracts: lower limb projections more medial than trunk and upper limb
^ areas of termination and relay stations for these tracts are: gracile fasciculus, posterior intermediate septum, cuneate fasciculus
Motor and descending (efferent) pathways
- Pyramidal tracts (lateral to dorsal horn): lateral corticospinal tract, anterior corticospinal tract
- Extrapyramidal tracts: Rubrospinal Tract (lateral to dorsal horn), retinculospinal tract (both side of ventral horn), vestibulospinal tract (posterior to ventral horn), Olivospinal tract (posterior to ventral horn)
Sensory and ascending (afferent) pathway
- Dorsal column Medial Lemniscus system (medial to dorsal horn): gracile fasciculus, cuneate fasciculus
- Spinocerebellar tracts (largest, most medial): posterior and anterior spinothalamic tracts
- Anterolateral system: Lateral and anterior spinothalamic tract
Describe the components of one spinal cord segment
1 segment of spinal cord, one set of roots (2 dorsal roots and 2 ventral)
Dorsal roots: sensory
Ventral: motor
The branches of dorsal and ventral roots are caused rootlets. They then become one mixed spinal nerve
Describe: Somatic sensory afferent neurons
- Innervate sensory receptors in skin, skeletal muscles, tendons, joints
- Arrive to the SC through dorsal roots
- Cell bodies are located in the dorsal root ganglia
Describe: proprioceptors
receptors in skeletal muscles, tendons, joints; inform about body position and movement
Describe: exteroreceptors
skin receptors that sense touch, temperature, pressure, pain.
Describe: Somatic motor efferent neurons
- where are their cell bodies
- where do they exit the SC
- what are their target fibers
- Motor neurons with cell bodies in the gray matter
- Exit the SC through ventral roots
- Conduct impulses to their target skeletal muscle fibers
Describe: Alpha motor neurons
innervate extrafusal muscle fibers
Describe: gamma motor neurons
innervate intrafusal muscle fibers
note: We cannot replace function of gamma motor neurons in practice
List the two major sensory (somatic) pathways
Anterolateral system (aka spinothalamic pathway)
Dorsal column - medial lemniscal system (proprioceptive pathway)
What is the function of the anterolateral system (aka spinothalamic pathway)
Function: nociception, temperature, coarse touch
What is the function of the dorsal column - medial lemniscal system (proprioceptive pathway)
Function: Fine touch, proprioception, vibration
Describe the anterolateral system (aka spinothalamic pathway)
Primary sensory neuron enters the dorsal horn and synapses onto a secondary sensory neuron (aka second order neuron). This neuron becomes the spinothalamic axon. The spinothalamic axon crosses at the spinal cord segment right away and then ascends toward the brain and synapses onto the thalamus. From here, information regarding the stimulus is sent from the thalamus via the third order neuron (tertiary neuron), to the primary somatosensory cortex
Describe the dorsal column - medial lemniscal system (proprioceptive pathway)
Primary sensory neuron enters the dorsal horn and ascends ipsilaterally to synapse onto medulla. Information regarding the stimulus crosses to the opposite side at the medulla and synapses onto the thalamus via a secondary sensory neuron (aka second order neuron). From here, information regarding the stimulus is sent from the thalamus via the third order neuron (tertiary neuron), to the primary somatosensory cortex
Describe the functions of the peripheral nervous system
- transmits motor output signals from the CNS to target muscles
- transmits sensory information from peripheral receptors to the CNS
Describe the components of the peripheral nervous system
includes all parts of the nervous system outside of the dura matter
includes peripheral portions of spinal and cranial nerves (also from the autonomic NS) and sensory ganglia
What does the femoral nerve supply
anterior thigh
What does the sciatic nerve supply
hamstring, back of leg, everything under knee
What does the sural nerve supply
skin of lower leg; note: sacrificial lamb for some surgeries. 50cm long.
What does the axillary nerve supply
upper arm
What does the intercostal nerve supply
low belly and thorax
What do the medial, ulnar, and radial nerves supply
forearm and hand
Why are injuries to the brachial plexus quite serious
Difficult to repair injuries due to intricate crossovers
How do nerve fibers know where to go?
Decided by timing
Earliest fibers to grow find their targets first
Define: dermatome
Area of skin that is supplied by afferent nerve fibres from a single dorsal spinal root
How can neurologists easily assess which dorsal root is injured?
Neurologists probe the skin to assess sensation. Abnormal or loss of sensation can indicate which dorsal root is affected
How do spinal nerve roots and cutaneous nerves differ in innervation? [ Fix card ]
A patch of skin is innervated by a singular cutaneous nerve. If that cutaneous nerve is damaged, an entire area of skin is denervated
If you lose one dorsal root, there is only a partial loss of sensation due to dermatomal overlap.
Define: visceral sensory afferent neurons
innervate receptors in smooth muscle and cardiac muscle (enteroceptors). They enter the SC through dorsal roots, with cell bodies located in dorsal root ganglia
Define: visceral motor efferent neurons
conduct impulses to smooth muscle, cardiac muscle and glands.
How does the autonomic peripheral system match and differ from the somatic peripheral system as per discussed in lecture?
Both have afferents that travel through dorsal root ganglion and meet target neuron within the dorsal horn. The afferents synapse onto an interneuron.
Somatic interneuron synapses onto a somatic efferent which project directly to muscle.
Visceral efferents projections involve two neurons.
The interneuron synapses with the preganglionic neuron which synapses with the postganglionic neurons at an autonomic ganglion.
Visceral interneuron synapses onto an upper motoneuron which projects onto a ganglion which synapses with a visceral efferent that supplies the smooth muscle.
Describe the difference between preganglionic neurons and post ganglionic neurons
Preganglionic neurons have their cell bodies in the SC gray matter and leave the SC through ventral roots of spinal nerves, then leave the spinal nerve as a white ramus that ends in an autonomic ganglion (either sympathetic or parasympathetic). In the ganglion, preganglionic neurons synapse with postganglionic neurons.
Postganglionic neurons have their cell body in a sympathetic ganglion and may exit the ganglion through a gray ramus, then proceed to visceral structures (smooth muscle, cardiac muscle, or gland).
Describe the splanchnic nerves
paired visceral nerves that contribute to the innervation of the internal organs, carrying fibers of the autonomic nervous system (visceral efferent fibers) as well as sensory fibers from the organs (visceral afferent fibers).
Pelvic splanchnic fibres (s2-4) contain only parasympathetic fibres
Describe the vagus nerve (CNX)
responsible for parasympathetic control of every organ (heart, larynx, trachea, esophagus)
Describe the importance of the chain of sympathetic ganglia. At what SCI level would result in loss of function? What would this be called?
Responsible for sympathetic control.
You may lose all sympathetic control if you have a spinal cord injury at a level above T6 (autonomic dysreflexia)
How does the parasympathetic system affect the following:
- Eye
- Saliva glands
- Heart beat
- Lungs
- GI tract
- Liver
- Bladder
- ?
- stimulates flow of saliva
- slows heartbeat
- constricts bronchi
- stimulates peristalsis and secretion
- stimulates release of bile
- constricts bladder
How does the sympathetic system affect the following:
- Eye
- Saliva glands
- Heart beat
- Lungs
- GI tract
- Liver
- Bladder
- dilates pupil
- inhibits flow of saliva
- accelerates heartbeat
- dilates bronchi
- inhibits peristalsis and secretion
- conversion of glycogen to glucose
- secretion of adrenaline and noradrenaline
- inhibits bladder contraction
Describe where parasympathetic supply normally originates from and where it differs
- normally comes from brainstem via cranial nerves (CNIII, CNVII, CNIX, CNX)
- parasympathetic supply for part of the distal intestine, uterus, bladder, and external genitalia come from the spinal cord (sacral levels 2,3,4) and not the vagus nerve
Describe 4 ways an SCI can arise
Neck flexion
- often from being rear ended; ruptures posterior ligaments and results in forward dislocation of the neck
Neck hyperextension
- can be from hitting table with chin; or punch in the face
- ruptures anterior ligament
- compressed posterior ligaments
Compression fracture
- diving injury; direct superior blunt trauma
- fractured vertebrae
Flexion rotation injury
- combination of head flexion (bending the head forward) and rotation (twisting) movements
- displacement of vertebrae
What are the two leading causes of SCI?
MVA then falls
What are the causes of SCI by age
- 0-15
- 16-30 –> 60
- 61 - 98
- 0-15: Vehicular, Violence, Sports, Falls
- 16-30 –> 60: Vehicular, Violence, Falls, Sport
- 61 - 98: Falls, Vehicular, Violence, Sports
List a few countries (6) where sport accounts for over 13% of SCI
Highest to lowest: Russia, Fiji, New Zealand, Iceland, France and Canada
What individual sports with high risk for SCI
Diving, skiing, rugby, and horseback riding
For hockey, skiing, diving and American football, what is the most common level of SCI?
almost entirely cervical for hockey, skiing, diving and American football
For horseback riding and snowboarding what is the most common level of SCI?
Half of horseback riding and snowboarding injuries are thoracic or lumbosacral
What is the most common site of SCI?
cervical; 47% occur at C4-C7
How come SCIs can affect breathing?
Cervical level injuries can cause
paralysis of the diaphragm
because the phrenic nerves
originate from C3-C5. This affects respiratory drive
Note that each phrenic nerve supplies only half the diaphragm
List some causes of diaphragm paralysis
- brain or brainstem stroke, ALS
- Spinal cord injury, syringomyelia, polio
- Autoimmune (MS, Guillain-Barré)
- Phrenic nerve trauma from surgery, radiation, tumor
- Phrenic neuropathy, viral or bacterial infections, unknown etiology (idiopathic)
Describe the difference between ventilator dependent and ventilator independent SCI subjects
Ventilator independent individuals are more likely to survive the next 3 years post injury
Describe how an SCI can cause cardiac dysfunction
Reduced sympathetic activity below the level of injury and unopposed parasympathetic outflow through the intact vagal nerve: results in cardiac dysrhythmias, bradycardia and hypotension
In the acute phase following SCI, there is a transitory suspension of function and reflexes below the level of the injury (spinal shock), severe bradycardia and hypotension.
Autonomic dysreflexia appears during the chronic phase after spinal shock resolution. This is a life–threatening syndrome of massive imbalanced reflex sympathetic discharge that occurs in patients with SCI above the splanchnic sympathetic outflow (T5–T6).
Symptoms of autonomic dysreflexia: bradycardia (can lead to fainting, severe hypertension, excessive sweating
Types of injuries to neurons (3)
Cell death - irreplacable
Axon damage - severed
Myelin damage
Describe 3 types of SCI
- complete transection: disconnection – can be caused by mechanical fracture, ischaemia or disease
Acute phase: Initially spinal shock – flaccid paralysis of all muscles below the injury, areflexia (no reflexes) and loss of all sensation
Chronic phase: Followed weeks later by hyperreflexia (stronger than normal reflexes), clonus (severe tremors), spasticity (severe tremor)
- Partial transection: Anatomically incomplete disconnection, with some remaining motor and sensory connectivity
- Similar sequelae as in complete transection however prognosis for at least some recovery of function is generally favorable - Hemisection (Brown-Sequard syndrome) - paralysis in only one part of the body
- Ipsilateral signs of a corticospinal tract lesion
- Ipsilateral signs of a posterior column lesion- Contralateral loss of pain and temperature perception
- Loss or impairment of autonomic function
Describe: multiple sclerosis
nontraumatic disorder, auto- immune, progressive, episodic. Signs can include proprioceptive sensory loss, nystagmus, signs of upper motor neuron injury, many small lesions throughout the spinal cord, dysarthria.
Describe: syringomyelia
cysts formed within the spinal cord (central syndrome); causes compression neuropathy
Describe: subacute combined degeneration
Usually a consequence of vitamin B12 deficiency (macrocytic anemia) resulting in gait disorder, sensory ataxia, peripheral neuropathies.
Direct Impact: Subacute combined degeneration primarily affects the dorsal columns and the lateral corticospinal tracts. The spinothalamic tract may not be directly damaged by the degeneration itself, so pain and temperature sensations might remain intact in the early stages of the disease.
Secondary Effects: Over time, however, as the disease progresses and the damage to the spinal cord becomes more extensive, there could be secondary effects on the spinothalamic tract. For instance, significant degeneration or damage to surrounding structures might impact the spinothalamic tract’s function, leading to altered pain and temperature sensations.
Describe: Friedrich’s ataxia
a genetic condition, with distribution of spinal cord lesions similar to that of combined system disease. Spinocerebellar tracts are affected. Ataxia in walking, spastic weakness, loss of proprioception. Ankle and knee
jerks are lost (loss of reflex). Babinski signs are present (an extension of the big toe with fanning of the other toes in response to the stimulus
- Also affects cerebellum
- progressive and leads todeath
- inherited
- presents at teen
Fill in the blank: The ______ of descending spinal cord pathways causes immediate _____ of motor neurons below the level of injury and _____
transection
silencing
flaccid muscle paralysis
Describe the patellar reflex
- a hammer tap stretches the tendon in the knee, stretching receptors in the quadricep
- stretch receptor fire action potentials which travel up the spinal nerve
- sensory neuron synapses with a motor neuron in the spinal cord
- the motor neuron conducts action potentials to the quadricep, causing contraction
- simultaneously a spinal interneuron inhibits firing in the motor neuron for the antagonistic muscle
Describe spinal reflexes
provide fast, first
responses to certain sensory inputs and occur largely independently from supraspinal participation
How can spinal cord injuries cause abnormal reflexes?
Excitatory and inhibitory modulation components originate from brainstem nuclei and act on spinal interneurons
For example, in the case of the patellar reflex, it can reduce the excitability of the interneuron and make it less likely to inhibit the antagonist muscle, resulting in clonus
Describe generalities of the acute and chronic phase of an incomplete SCI
Why do they differ?
1 day after SCI
- paralysis, hyporeflexia, spinal shock, possible paresis
- Loss of total drive to lower motor neuron due to loss of afferent input.
2 months after SCI
- Paresis and hyperreflexia, clonus, spasticity
- Slight increase in efferent and afferent branches. Vacated synaptic sites (due to loss) now are free to be taken over by collaterals from surviving fibers
- key note: movement is feeble (paresis) but reflexes are changed! hyperreflexia is due to super strong input as stretch reflexes have much higher gain
List some consequences of spinal injuries
- Leg bones don’t grow as fast; become thin and weak; can break easily
- Sudden high blood pressure with pounding headache (autonomic dysreflexia) due to irritation (ex: cutaneous input) in non-feeling parts (quadriplegics only); can also cause fainting
- Depression, anger, difficulty accepting disability
- Child suffers greatly in hot weather because body loses ability to control its temperature
- Increased risk of pneumonia in quadriplegics due to weak breathing muscles
- Burns where body cannot feel
- Pressure sore from long leg brace (incomplete SCI)
- Contractures
- Spasticity causes legs to straighten and pull together and feet to tiptoe stiffly (equinovarus)
- Rash or sores between legs due to loss of urine and bowel control
- Pressure sores where body has lost feeling (butt)
- Curving or hunching in spine
- Urinary infections may involve kidneys and cause death
