PBL1 Flashcards
What are reflexes
Reflexes are involuntary motor actions triggered by sensory input
what are the types of reflexes
Monosynaptic or polysynaptic
what can reflexes be controlled by
Controlled by descending cortical input
what are the neurones that are involved in reflexes
Sensory Neuron
- From the body to the spinal cord (dorsal horn)
- Utilises various different receptors
Motor Neuron
- Upper – brain to spinal cord (ventral horn)
- Lower – spinal cord (ventral horn) to muscle
Interneuron – connect sensory/motor neurons
what are the exteroreceptors
- free endings
- meissners
- merkels
- pacinian
- Ruffini
what do the exteroreceptros do
Free endings – mechano/chemo/thermos/nociception Meissner’s – light touch Merkel – texture (i.e. Braille) Pacinian – vibration Ruffini – deep touch
what are the proprioceptors do
Golgi Tendon – senses tendon stretch
Muscle Spindle – senses muscle length
describe how a muscle spindle works
Modified muscle fibres sensing muscle stretching
- Activation (stretching) = motor nerve activation
- i.e. tendon reflexes (patellar, biceps, etc…)
Mediates sensitivity of tendon reflex
- Controlled by gamma fibres to muscle spindle
describe how a Golgi tendon organ works
Located in tendons of muscles sensing muscle tension
Senses muscle tension
Prevents muscle damage from excess muscle contraction via inhibitory signalling to motor neuron
what is the reflex pathway
Sensory Nerve → Dorsal Horn → Motor Nerve → Ventral Horn → Muscle
Polysynaptic has interneuron between s/m nerves
which receptor is being testes by
- two point discrimination
- joint position sense
- vibrations sensation
- meissners
- spindle
- pacinian corpuscles
describe the biceps reflex
Biceps tendon stretch = biceps contraction
Controlled by C5/6 (musculocutaneous)
describe the supinator reflex
Brachioradialis tendon stretch = brachioradialis contraction
Controlled by C6/7 (radial nerve)
describe the triceps reflex
Triceps tendon stretch = triceps contraction
Controlled by C7/8 (radial nerve)
describe the achilles reflex
Stretch of Achilles = plantarflexor contraction
Controlled by S1/S2 Roots (tibial of sciatic nerve)
describe the patellar reflex
Stretch of Patellar tendon = quadriceps contraction
Controlled by L3/L4 Roots (femoral nerve)
what is reciprocal inhibition
Afferent neuron synapses with inhibitory interneuron connected to antagonising muscle
i.e. patellar reflex inhibits hamstrings
what is an crossed extensor reflex
Flexor reflex causes extension of opposite leg
Sensory neuron innervates stimulates efferent fibres of contralateral side via interneuron
what is the difference between extensor and flexor reflexes
Extensor reflexes tend to be faster
Due to extensors preventing falls
what does electromyography do
it tests nerve function
describe how electromyography works
Can derive compound motor action potentials
- Summation of multiple muscle fibres’ activity
Reduced CMAP indicates motor nerve issues
what causes weak or absent reflexes
Issues in the Sensory Nerve
- i.e. GTO issues = NO REFLEX
Issues in the Motor Nerve
- i.e. femoral nerve issues = reduced quadriceps response
Issues in the Spinal Cord
- i.e. transection of spinal cord (i.e. Spinal shock in PBL2
what does the lack of biceps and supinator reflexes indicate in the context of normal sensory nerve function
Sensory nerve is not problematic
Motor nerve issues – abnormal EMG
what nerve roots are affected
Affects roots C5/C6/C7
what could the patient be effected by
Cervical Spondylosis – radiculopathy in C-spine?
Name and describe two of the three parameters that can be measured with electrophysiological tests for sensory or motor nerve function
- Action potential latency: Interval between stimulus onset & response onset
- Action potential duration: Time from action potential onset to termination; duration measures the dispersion of all components.
- Action potential amplitude: Proportional to the number & size of nerve fibres that are activated in SNAP. In CMAP shows how many motor units are recruited simultaneously.
