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Clin. Neuro Class 3
| Question | Answer |
|---|---|
| Describe the relationship of white matter and grey matter in the spinal cord? | central grey matter in H shape surrounded by white matter |
| What is located in the grey matter? | cell bodies, dendrites, and termination and projection neurons |
| What is in the grey matter in the dorsal horn? | sensory, contains many interneurons and projection neurons |
| What is the grey matter in the ventral horn consist of? | 1. primarily motor neurons (alpha anterior horn cell) |
| Function of alpha MN | supply skeletal muscle or gamma motor neurons to muscle spindles arranged in groups |
| What can only cause skeletal muscle to contract? | alpha MN by final common pathway |
| What happens with a lesion of an alpha MN? | flaccid type paralysis, no reflexes can be elicited |
| What is in the intermediate area of grey matter? | 1. interneurons and projection neurons 2. autonomic (viscera) motor neurons (at certain levels lateral horn exists) with sympathetic motor neurons |
| What is in white matter? | Axons in tracts ascending and descending spinal cord Propriospinal fibers in Lissauer's tract Anterior, lateral and posterior funiculus |
| What is another name for posterior funiculus? | dorsal columns |
| What is the anterior fissure? | anterior spinal artery runs here |
| What is the posterior lateral sulcus? | posterior spinal arteries run here |
| How many Rexed laminae are there? | ten |
| Where are Lamina I-VI located? | dorsal horn |
| What is in substantial amounts in Lamina II and III? WHy is it important? | gelatinosa, for pain transmission |
| Where is Lamina VII? | intermediate grey (interneurons and autonomic nuclei) |
| Where are Lamina VIII to X located? | Lamina VIII-IX = ventral horn Lamina VIII- includes the interneurons of anterior horn Lamina IX- clusters of gamma and alpha MN Lamina X- grey matter surrounding central canal |
| What are the cross-sectional differences at different levels (grey and whit matter)? | Upper Cerv- greater proportion of white matter Mid-low Cerv- cervical enlargement of UE Thoracic- slender ant horn, intermediolateral cell column in lateral horn Lumbar- lumbar enlargement of LE, grey>white Sacral- sm. dia, least amount of white |
| What are muscle spindles? | stretch receptors in muscle |
| What do muscle spindles respond to? | quick and sustained stretch |
| What information do muscle spindles give to the CNS? | info about static length and the rate of stretch of a muscle |
| Are muscle spindles sensory only, motor only or both? | both |
| What is another name for muscle spindle? | intrafusal fibers |
| What is the size of muscle spindles? | 10 mm long, much shorter than extrafusal fibers (skeletal muscle fibers) |
| What is the structural chara. of muscle spindles? | enclosed in a connective tissue capsule and the central portion is filled with fluid and expands to about 2 mm giving the spindle its characteristic shape |
| What part of the spindle is contractile? | ends not the middle |
| Where is the muscle spindle attached? | the ends of the muscle spindle attaches to extrafusal fibers or have tendinous insertions so whenever extrafusal fibers are stretched, muscle spindles are also stretched |
| What are the two types of intrafusal fibers? | Nuclear bag fibers (nuceli clumped in central region) Nuclear chain fibers- nuclei arranged in single file |
| Primary type of sensory ending? (annulospiral) | wrap around center of every intrafusal fiber, phasic and tonic discharge |
| With a quick stretch how do primary sensory endings discharge? | burst of activity |
| how do primary sensory endings respond to amount of tension? | tonically, increasing or decreasing depending on the amount of tension |
| What fiber type is associated with primary sensory endings? | Ia fiber (axon) type: fast conducting |
| Secondary sensory endings (flower spray) | mainly on nuclear chain fibers off center to the primary endings |
| how do secondary sensory fibers respond? | tonically |
| What type of fibers are they associated with? | Type II (axon) fiber type: (myelinated but little slower than Ia) |
| What are the two types of Motor fibers? | Gamma dynamic axons- innervate end of nuclear bag fibers Gamma static axons- innervate both types of fibers |
| Why is motor innervation of muscle spindle necessary? | when extrafusal fibers contract and shorten, id nothing else happened, the muscle spindle would be put in slack, making the spindle insensitive to stretch |
| How is the sensitivity of the muscle spindle maintained? what is it called? | Gamma Bias:gamma MN cause the contractile ends of the MS to contract in order to maintain stretch on the central portion of the MS, maintaining its sensitivity |
| Explain alpha-gamma co-activation | in almost eveyr muscle contraction, the gamma MN is activated by collateral from higher centers of the CNS that will also activate the alpha MN, assures that gamma bias will happen as muscle contracts and sensitivity of MS is maintained |
| What are golgi tendon organs? | stretch receptor in the tendon near musculotendonous border, with encapsulated nerve ending woven among collage fibers |
| What is the sensitivity of GTOs | very small changes in tension (<1g) |
| What do GTOs respond to? | active muscle contraction and passive stretch |
| What fibers are GTOs associated with? | Type Ib Fibers (only slightly slower than Ia but faster than II) |
| What are joint receptors? | detect stretch of joint capsule and ligmanets |
| What do joint receptors respond to? | extremes of ROM and some to non extremes of ROM |
| How do joint receptors respond? | phasically or tonically |
| What do free nerve ending receptors transmit? | pain associated with tissue damage and inflammation |
| What do joint receptors contribute to? | proprioception (position) and kinesthesia (sense of movement) |
| What are cutaneous receptors? | detect pressure, sharp, dull temperature and vibration; involved in reflexes |
| Can cut. receptors contrib to kinesthesia and proprioception? | yes |
| What is required to get a reflex? | stimulus, receptor, afferent fiber, efferent fiber, effector, and response |
| What is a Monosynaptic Stretch reflex? | quick stretch of muscle |
| What sensory ending is activated with MSR? | primary |
| What fibers send msg. to Spinal cord? | Ia afferent |
| from Ia afferent to the ________? | dorsal horn |
| Then there is a _________ synapse to what? | direct, to alpha motor neuron |
| WHat isthe result of MSR? | activation of alpha MN and contraction of stretched muscle (homonymous muscle) |
| What inhibitory response results? | inhibits heteronymous muscle (opposing) called reciprocal inhibition |
| What is recurrent inhibition? | the inhibition of the homonymous alpha MN bia a collateral which excites and ihibitory interneuron called a Renshaw cell. (limits the duration of the alpha MN) |
| Clinically the monsynaptic reflex is measured by what? | DTR |
| LMN lesion always results in ___________ | hyporefelxia |
| UMN lesion usually presents with | hyperreflexia |
| Define upper motor neuron | referes to all MN originating above the spinal cord that have influence over the activity of the alpha motor neuron |
| Define lower motor neuron | refers to the alpha motor neuron aka final common pathway (also includes gamma MN) |
| Why is there hyperreflexia with UMN lesion? | Partly because when higher center control of the alpha motor neuron is removed, the MS assumes much more influence over the alpha MN. And partly because local inhibitory circuits are affected so inhibition is reduced |
| What does DTR assess? | screening test for muscle spindle, afferent Ia fibers, dorsal root, spinal cord segment needed for reflex (myotome related) alpha motor neuron, neuromuscular junction and muscle |
| With EMG what produces the M wave? | stimulation of Tibial n. in popliteal fossa-->orthodromic muscle contraction of gastrocsoleus group |
| What produces the H wave? | sensory axons in nerve are also stimulated, (Ia fibers), monosynaptic excitation of alpha MN, and muscle contraction of gastrocsoleus group |
| What determines if a stimulus will cause action potentials in alpha MN and muscle contraction? or just facilitation of the alpha MN without reaching the level of an AP and muscle contraction? | Related to EPSPs generated from quick stretch and the other influences on the alpha MN at the time. (additional excitatory infl, or inhibitory infl. that need to be overcome |
| How is a sustained slow stretch inhibited? | inhibited by higher center's influence on iinhibitory interneurons in the spinal cord (only in UMN lesions |
| How long does the response to sustained slow stretch last? | as long as the stimulus is maintained |
| what sensory endings are activated with a sustained slow stretch | both primary and secondary |
| What fiber types are afferent axons? | Ia and II |
| The synapse on the excitatory interneuron activates what neuron? | alpha MN in homonymous muscle |
| excitation of homonymous muscle causes recipricol inhibition of what? | heteronymous msucle |
| Withdrawal reflex from what | noxious stimulus (heat, sharp, etc) |
| describe process of withdrawal | 1. stimulus 2. withdraw limb 3. more than one spinal cord level (by collaterals via Lissauer's track) |
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