Somatosensory and Motor Systems Flashcards
What arteries supply blood to the spinal cord?
- paired posterior spinal arteries: dorsal 1/3
- midline anterior spinal artery: ventral 2/3
What are the nuclei of spinal gray matter?
- substantia gelatinosa
- nucleus proprius
- nucleus dorsalis (Clarke’s Nucleus)
- nucleus intermediolateralis
- lower motor neuron pool
What are the fiber tracts of the spinal cord?
- dorsal columns
- spinothalamic tract
- spinocerebellar tract
- corticospinal tract
What is the local (intrinsic) tract of the spinal cord?
- spinospinal (propriospinal system)
What role do spinocerebellar tracts play on the spinal cord, and what sensory information do they carry?
- connect spinal cord with cerebellum
- ipsilateral connections
- convey touch, pressure, and proprioceptive movement for the cerebellum to use
What role do spinospinal tracts play on the spinal cord and what sensory information do they carry?
originate from interneuronal gray
- role in patterns and reflexes
What are the 6 components of the somatosensory system?
- receptors: encode environmental information
- primary afferent neurons: carry info to CNS
- pre thalamic relay nucleus: where first order neurons synapse (primary afferent)
- decussations (crossing): where 2nd order neuron crosses the CNS
- thalamic relay nucleus: where 2nd order neurons synapse
- cerebral cortex: where 3rd order neurons project and terminate
What is topographical organization of the somatosensory system?
has a design and organization to represent and get info from specific region in the body
What is parallel crossing of the somatosensory system?
multiple sensory systems are activated simultaneously (environmental stimuli can activate multiple systems)
What is efferent modulation in the somatosensory system?
each relay structure is subject to regulation by descending fibers from higher centers
What are the two major systems carrying somatic information to the cerebral cortex?
Dorsal Column Medial Lemniscus (DCML)
Spinothalamic Tract (STT)
What are characteristics of the DCML?
- ascending tract
- sends information on fine touch, pressure cutaneous touch discrimination, proprioceptions, and vibration
- highly mylenated (fast)
What is the pathway of the DCML?
- primary afferents enter spinal cord through DR, travel to dorsal column
- ascend towards medulla
- primary afferents synapse with secondary afferents, which decussate across the medulla and form the medial lemniscus
- secondary afferents ascend to the thalamus and synapse with 3rd order neurons (thalamic relay nucleus)
- 3rd order neurons in the thalamus, terminate in the parietal lobe/ primary somatosensory cortex
What kind of receptors are used in the DCML?
mechanoreceptors: respond to deformation
What are the characteristics of the STT?
- ascending
- part of anterolateral system
- pain (nocioception), temperature, and crude touch
- myelinated, not as fast as DCML
What is the pathway of the STT?
- primary afferents enter dorsal root and synapse on cell bodies (nucleus proprius) of 2nd order neuron fibers (substantial gelatinosa) of the dorsal horn
- 2nd order fibers immediately decussate at the same spinal level, ascend in contralateral cord
- synapse in thalamus with 3rd order fibers that project to the parietal lobe (somatosensory cortex)
What is the fasciculus cuneatus?
- from T6 and up, takes DCML from upper extremities
What is the fasciculus gracilis?
- takes DCML from everything below T6 up to higher centers
Where are nucleus cuneatus and nucleus gracilis found in the medulla?
ipsilaterally
What receptors are used in the STT?
thermoreceptors and nocioceptors
How are the DCML and STT similar?
1st order neurons: bring info from periphery to spinal cord
2nd order neurons: cross the midline
3rd order neurons: go from thalamus to primary somatosensory cortex
How are somatic receptors classified?
- structure
- rate of adaption
- source of the stimulus
- type of stimulus energy
What are exteroceptors?
- respond to changes in the immediate external environment
What are interoceptors?
give rise to poorly localized sensation such as visceral pain, thirst, hunger
What are proprioceptors?
respond to stimuli originating within the body itself
What are the mechanoreceptors in the deep tissues?
proprioceptors
- provide info about position of our limbs in space
- sense of static position and of limb movement (kinesthesia)
What do muscle spindles detect?
- length/stretch receptors
- respond to degree and velocity of change
- signal muscle activity (slow adapting) extrafusal fibers
How do muscle spindles work?
when extrafusal muscle fibers lengthen, muscle spindles lengthen
when the fibers shorten, intrafusal fibers keep capability to contract, creating the alpha-gamma co activation
What is the role of Golgi tendon organs?
- located at junction of muscle and tendon
- detect muscle tension
How do GTO work?
When tension increases, collagen fibers press against the GTO and signal the amount of tension present in the muscle
to protect muscle, GTO will signal to stop tension and activate the opposite acting muscle (reflex)
What are the uses and actions of the peripheral receptor info?
- general arousing/alerting/calming effect
- may elicit reflexes
- provide a basses for conscious discrimination of environment
- enables brain to perform coordinated movements
What are cutaneous receptive fields?
- area of cutaneous skin that when activated by an adequate stimulus will activate a primary afferent neuron
- smallest in areas of highest innervation density
What is two point discrimination and where do we have the best sensation of this?
- when two points can be discriminated on cutaneous skin
- best in areas of high innervation density (fingertips, face, tongue)
Do primary afferents need to be myelinated?
no, conduction speed depends on the degree of myelination and diameter of fiber
How do you test for nociceptors and which tract is related?
stimulate skin with alternating sharp or dull end of safety pin, STT (anterolateral)
How do you test for temperature and which tract is associated?
tubes of hot and cold water placed on skin , STT (anterolateral)
How do you test light touch and which tract is associated?
stroke skin with wisp of cotton
STT and DCML
How do you test for point localization and which tract is associated?
touch on body of the patient, have patient place index finger on point stimulated
DCML
How do you test for two-point discrimination and which tract is associated?
distance between two points stimulated on skin
STT and DCML
Between which tract, which is more localized?
STT: poorly localized
DCML: localized discriminate touch
How do you test for position sense and which tract is associated?
patient eyes closed, you move body segment into flexion/extension, have to tell you what position
DCML
How do you test for kinesthesia and which tract is associated?
patient eyes closed, you move extremity in space, patient mimics movement
DCML
How do you test for graphesthesia and which tract is associated?
patient eyes closed, draw symbol, number, or letter on skin
DCML
How do you test for stereognosis and which tract is associated?
patient identifies object in hands without use of vision
DCML
How do you test for vibratory sense and which tract is associated?
vibrate tuning fork over bony prominence
DCML
What is the somatic motor system?
all structures of CNS and PNS that contribute to motor activity
What are the somatic motor system components?
- originate from upper motor neuron
- decussation
- synapse on lower motor neuron
- efferent fibers of lower motor neuron
5 neuromuscular junction - circuitry to plan, program, coordinate, and modulate the descending motor pathways
What are upper motor neurons? (UMN)
- projections that descend to converge on lower motor neurons
- originate from areas in higher centers
- motor areas of cerebral cortex (responsible for voluntary movement)
- brainstem nuclei (responsible for influencing voluntary movement, posture, tone, and regulation of reflexes)
What is the pyramidal tract?
UMN fibers originating in cerebral cortex, descending longitudinally through pyramids of the medulla, terminating on LMNs in the spinal cord
What do fibers do in the pyramidal system?
twist as they descend toward internal capsule
Where does the pyramidal tract originate?
- primary motor cortex (Brodmann’s area 4
- premotor and supplementary motor cortex (brodmann’s area 6)
- postcentral gyrus (brodmann’s area 3,1,2)
What is the other name of the pyramidal tract and what is its LMNs equivalent?
- corticospinal tract
- corticobulbar tract
What is the lateral corticospinal tract?
- 75-90% of cortiocospinal tract fibers
- cross midline at pyramidal decussation
- descends in contralateral lateral funiculus
What is the anterior corticospinal tract?
- smaller contingent of uncrossed fibers
- descends in ventral funiculus
What do lesions above the decussation of the motor system cause?
- result in contralateral symptoms
What do lesions below the decussation of the motor system cause?
- result in ipsilateral symptoms
What are lower motor neurons? (LMNs)
- alpha motor neurons (final common pathway)
- cell bodies are in anterior horn or in CN nuclei of brainstem
- axons leave to striated muscle
excitatory at NMJ - part CNS and PNS
What are the consequences of summation at the LMN?
- when only excitatory inputs are active, LMN generates many AP, strong contraction
- inhibitory input is added to excitatory input, net excitation but less forceful contraction
- only inhibitory input LMN does not have discharge, muscle relaxes
What structures provide modulation of the UMN systems?
thalamus, basal ganglia, and cerebellum
What described the coordination of the motor system?
coordination of movement utilizes reciprocal innervation of agonist and antagonist
purposeful movement involves variety of synergists
How does the motor system reduce the complexity of signals required for movement?
central pattern generators
What is tonus (muscle tone)?
- background muscle activity
What is muscle reflex?
- simple, stereotyped overt movements set into motion by a peripheral stimulus
What is voluntary movement?
- decision to act, learned, exploits hard wired subroutines
What is indicated by the positive sign of UMN?
- release phenomena due to loss of inhibition
- excess neural activity
- hyperflexia, hypertonicity, babinksi reflex
- presence of what wasn’t there before
What is indicated by the negative sign of UMN?
- motor deficits due to loss of function of damaged neural structures
- weakness, loss of speed, loss of dexterity
- loss of what was there before
What is a motor unit?
- single alpha motor neuron and the group of muscle fibers it innervates
What are the three muscle fiber types?
- red: slow twitch (highly vascularized)
- white: fast twitch (less vascularized)
- intermediate: fast twitch, fatigue resistant
What is the order of muscle fiber recruitment?
slow > fast twitch fatigue resistant > fast twitch
What is the neuromuscular junction?
chemical synapse between axon terminal of alpha motor neuron and sarcolemma
ACh release
What is LMN syndrome?
- damage to LMN cell body or axon
- hypoflexia
- hypotonia
- paralysis
- atrophy
- denervation (fasciculations and fibrillations)
What is fasciculations?
involuntary twitching of whole muscle
What is fibrillations?
involuntary muscle fiber twitch
What are the diseases of the motor unit?
neurogenic: affecting cell body or axons
myopathic: affecting the junction or striated muscle
What is polio?
- viral infection
- attacks cell bodies of LMN
- weakness/paralysis, atrophy, decreased reflexes
What are the pathologic changes of the peripheral nerves?
- segmental degeneration (myelin sheath)
- axonal degeneration
- wallerian degeneration (axon and myelin distal to injury)
What is myasthenia gravis?
- autoimmune disorder of neuromuscular transmission resulting in weakness
- muscle of mastication, expression, swallowing
What is a myopathy?
- progressive hereditary diseases of skeletal muscle
What is Duchenne muscular dystrophy?
- defective gene that codes for protein dystrophin
- sarcolemma vulnerable
- weakness, tearing, and loss of muscle fibers
- shortens life expectancy
What is amyotrophic lateral sclerosis?
Lou Gehrig’s disease
- most common but rare motor neuron disease
- weakness, denervation, atrophy
- role of DPT: ADs, educate, exercise
What are spinal cord reflexes?
involuntary, short latency and stereotyped response set into motion by environmental stimulus
What are the components of spinal cord reflexes?
- receptor
- afferent fiber
- reflex center in CNS
- efferent fiber
- effector organ
What is the stretch (myotatic) reflex?
- simplest
- elicited by tapping tendon of the muscle with reflex hammer
- brief contraction of stretched muscle
- mediated by muscle spindle
What are the commonly tested structures for stretch reflex?
- achilles, patellar, bicep, and tricep tendon
- reciprocal inhibition via interneurons to antagonist
What is inverse myotatic reflex?
- mediated by GTO
- autogenic inhibition: results in relation of agonist and contraction of antagonist
What is the flexion reflex?
- response to suddenly applied noxious stimulus
- withdrawal of limb
- reciprocal inhibition of antagonists of ipsilateral limb
What is the crossed extension reflex?
- flexion of ipsilateral limb and extension of contralateral limb
- mediated by inter nouns that cross midline of spinal cord
Can you suppress a reflex reaction?
through the tonic descending inhibitory pathway (TDIP)
What are the suprasegmental structures that exert control over reflexes?
- reticular formation
- cerebellum
- cerebral cortex
What is the consequences of TDIP in paraplegic patients?
overly active flexion reflex responses and may develop a chronic posture of flexion
How do you evaluate reflexes?
- is it present?
- is status altered?
- are pathological reflexes present?
What is spasticity?
- motor disorder characterized by velocity dependent increase in tonic stretch reflexes and exaggerated tendon jerks
- develops with UMN damage like stroke, MS, and spinal cord injury
What is spinal shock?
- following complete spinal cord transaction or compression, the initial response is transient hypotonia and hypoflexia
- all sensation below lesion lost
- all voluntary movement below lost
- reflex activity below lost
What does spinal shock also lead to?
fecal and urinnary incontinence
What is the triple flexion reflex?
- single foot prick, elicits withdrawal of whole extremity causing ankle, knee, and hip flexion
What can be said about the emergence of spasticity?
eventually and gradually, extensor tone also increases
- due to suprasegmental influences
What is the result of LMN damage?
- flaccid paralysis of individual muscles or group of muscles
- ipsilateral to lesion
What is the result of UMN damage?
- spastic paresis of synergistic muscle groups
- contralateral to lesion if damage is rostral to decussation
- ipsilateral to lesion if damage is caudal to decussation
What are the pathological reflexes (UMN signs)?
- babinski
- flexion
- clasp knife
- clonus
What is the babinski reflex?
- when elicited beyond infancy, reliable sign of corticospinal tract damage
- stroking the foot
- abnormal response of dorsiflexion of great toe and abduction of other toes
What is the flexion reflex of UMN pathology?
- following UM. damage, flexion response may be seen with innocuous stimuli
- due to disruption of suprasegmental inhibition
What is the clasp-knife phenomena?
- sudden collapse of the resistance to limb extension
- elicited with passive limb movement
What is clonus?
- sign of clinical spasticity
- elicited with abrupt and sustained ankle dorsiflexion
- series of rhythmic involuntary muscle contraction
UMN injury can lead to what?
lack of descending control, can lead to:
- spasticity
- clonus
- hyper reflexia
- hypertonia
- return to primitive reflexes
- synergies
- WEAKNESS
What is Brown-Sequard Syndrome?
paralysis on one side of the body, and loss of sensation on the other side of the body due to spinal cord injury
