109844
Description
Flashcards by tanitia.dooley, updated more than 1 year ago
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Created by tanitia.dooley
almost 11 years ago
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| Question | Answer |
| If the stretch reflex is exaggerated what is this indicative of? What if it is supressed or absent? | exagerrated= over activation of gamma motor neurons Supressed= depression of gamma motor neurons |
| What neurotransmitter is involved with renshaw cells? | glycine |
| What is the role of the golgi tendon reflex? | prevents the production of excessive tension in a muscle |
| what is the difference between a motosynaptic and a polysynaptic reflex? | monosynaptic-just sensory and motor neurons no interneuron polysynaptic-sensory, motor and many association neurone |
| Describe the knee jerk reflex | if tap patella tendon- sensory stretch receptor=sensory neuron= alpha motor neuron causes contraction of extensor and opposing muscle (flexor) relaxes then extensor then relaxes because of renshaw inhibitory cells |
| Describe the withdrawal reflex | painful stimuli- sends signal up afferent fibres through dorsal root to spinal cord where synapse with excitatory association neurone which synapse with alpha efferent motor neuros stimulating flexor muscles |
| What is recipricol innervation? | withdrawal reflex- collateral axons synapse with inhibitory association neurone which inhibit the alpha motor neuron of the extensor |
| How do we gain awareness of the withdrawal reflex? | collateral branches from the afferent fibres and synapse with ascending fibres to the brain |
| What is the purpose of the crossed extensor reflex? | Withdraw a limb from a noxious stimulus |
| Describe what happens in the crossed extensor reflex? | noxious stimulus- activate pain sensitive sensory neurone- excite motor neurone to flexors on pain side and extensors on opposite side but also inhibit extensor on pain side and flexor on opp side so leg is withdrawn without falling over |
| How is the extensor on the opposite side to the pain innervated in the crossed extensor reflex? | Association neurons in addition to the stimulating motor neurons- send collateral axons through white commisure to the opposite side of the spinal cord so stimulating motor neurone which innervate extensor muscles in the opposite side of body |
| Describe how gamma motor neurons maintain muscle spindle sensitivity? | 1. skeletal muscle contracts 2.Tension of the muscle spindle is relaxed so muscle spindle fibres are less sensitive 3. APs carried by the GMNs stimulate the ends of the muscle spindle cells 4. Muscle spindle cells shorten with the skeletal muscle- contraction of spindles maintains their sensitivity |
| Why are muscle spindles called intrafusal and non-contractile? | within spindle and lack of myofibrils- centre non contractile but ends contractile |
| What innervates the muscle spindles? | gamma motor neurons |
| What is the role of gamma motor neurones? | Maintain Muscle Spindle Sensitivity, Posture, muscle tension and muscle length |
| Where do gamma motorneurones origionate and what do they control? | originate in the spinal cord and they control the contractions of the ends of the muscle spindle cells. |
| What are the non contractile centres of muscle spinde cells innervated by and what do they do? | afferent neurons. Carry impulses to the spinal cord. Synapse directly with a motor neurones |
| Describe the stretch reflex | muscle spindle is also stretched in the muscle fibre> stretch stimulates afferent neurons> increased freq of APs in the afferent neurons stimulates alpha motor neurons in spinal cord=rapid contraction of stretched muscle. This contraction is in opposition to the stretch re estabilishing a normal posture |
| How does the brain percieve that the muscle has been stretched? | collateral axons from the afferent neurons of the muscle spindles also synapse with ascending nerve tracts enabling the brain to percieve stetch |
| What is the role of descending neurons within the spinal cord? | They synapse with the neurons of the stretch reflex so modulating their activity=maintain posture and coordinate muscular activity |
| What are renshaw cells? | inhibitory- generate IPSPs to modulate muscle activity |
| What are muscle spindles and where are they? | in parallel with muscle, respond to changes in length |
| What are golgi tendon organs and where are they? | In series with muscle, respond to changes in tension |
| What innervated golgi tendon organs? | 1b afferent nerve endings |
| Where are golgi tendon organs located? | within tendons near to muscle tendon junction |
| Describe the structure of golgi tendon organs | -Are encapsulated nerve endings that have numerous terminal branches -Small swellings associated with bundles of collagen fibres in the tendons. |
| When are golgi tendon organs stimulated? | as tendon is stretching during muscle contraction- if force is going to damage muscle= inhibition reflex which causes the muscle to relax |
| What happens when the golgi is distorted during contraction? | open Na+ channels=generator potential=AP, (stronger contraction= more distortion) |
| How long are muscle fibres? | ~10ym |
| What are the two types of muscle spindles? | nuclear BAG and nuclear chain fibres |
| Describe chain fibres | static, respond to muscle length,Four to ten per spindle, Nuclei are formed in a line, Found in the central region of the muscle, Underlying sensory nerve (Ia fastest in the body) |
| Describe bag fibres | respond to rate of change of length, usually 2 per spindle, dynamic response, found in central region underlying the sensory nerve endings |
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