Reflexes Flashcards
What are reflexes and what types of reflexes are there
Involuntary response to stimulus
Autonomic reflexes: mediated by ANS, SM, stimulaation of Cardiac muscle, glands
Somatic reflexes: Somatic nervous system, stimulation of skeletal muscles
What are the 5 elements of a reflex
receptor, sensory neurone (afferent pathway to CNS), interpretation centre (one or more synapses in CNS)), motor neuorne (efferent pathway from CNS), effector
Where are propriocepetors located
skeletal muscle, tendons, joint capsules, ligaments
What is reciprocal inhibition
excitation of one group of muscle->inhibition of its antagonist caused by contraction of agonist
What is recurrent inhibition
the inhibition of motor neurone which usually causes excitation under certain stimuli by inhibitory interneurone=Renshaw cell
What is a cross cord reflex, how does it work
If stimulus is on one limb, other limb also affected but in opposite ways.
Ipsilateral limb: +flexor -inhibitor (e.g. removing pin from leg)
Contralateral limb: -flexor +inhibitor (shifting weight to this leg)
What are central pattern generators and what does it allow
rhythmically active network of nerve cells. . Control rhythmic motor patterns such as walking, breathing without sensory or descending inputs instructing specific timings.
What are motor patterns
Programmed sequences of muscle activity
what allows descending control and what does descending control involve
Pyramidal and extra pyramidal tracts change motor neurone pool excitability
What tracts are in pyramidal and extrapyramidal and where are they located
ref. notes
Pyramidal-corticospinal, corticobulbar
Extrapyramidal-vestibulospinal, tectospinal (superior colliculus of mid brain), reticulosspinal (MRST pons, LRST medullaa), rubrospinal (mid brain)
What do the tracts of the extrapyramidal do
Vestibulospinal-Lateral VS=ipsilateral, control balance+posture, innervate antigravity muscle
Medial VS=bilateral, neck and shoulder
Tectospinal-cervical spine, coordinates head movement in relation to visual stimulation
Reticulosspinal-MRST=increases muscle tone->excite vol movement
LRST=inhibits musscle tone, inhibits vol. movement
Rubrosspina-contralateral, fine movements
What does the vestibular reflex do
lean off balance->stimulate semicircular canals->motor response in neck and limbs->maintain upright posture
The lateral vestibulospinal tract to all spinal cord. Excites ipsilateral extensor motor neurones and inhibits flexor motor neurones via interneurone.
Medial vestibulospinal tract to mid thorax excites neck muscle
The vestibular reflex requirers info orientation to vertical so needs vetibular apparatus
What do the following things do: visual reflex, pressure receptors, cerebellar reflexes
visual reflex-powerful input posture control
pressure receptor-important receptors for maintaining posture. e.g. when standning, sole of feet monitor weight distribution
cerebellar reflex–integrates sensory information, position of the body, coordinates complex movement, maintain pressure
how are reflexes clinically relevant and how can reflex abnormalities be spotted
reflexes lost before weakness in muscle
Signs: absent, distorted, exaggerated, symmetry, degeneration, demyelination
If reflexes are weak/absent, what disease can one have and what do these diseases involve
peripheral neuropathy-damage to the nerves outside the spinal cord
motor neurone disease-damage to the motorr neurone
myasthenia gravis-neuromuscular junction
myopathy-muscle dissease
What are excessive and asymmetric response caused by
Excessive=spinal cord damage above the level controlling hyperactive response, higher CNS damage
Asymmetric response-early onset progressive disease, localised nerve damage e.g. trauma
How to test for spinal cord injury and closed head injury
spinal cord=motor neurones above area of injury unaffected but below affected
Closed head injury=if bleed in/around brain, increase pressure in cranium so pressure on CR III. eye reflex response may be changed
What does the babinski reflex imply in neonates, young infants and adults
neonates+young infants
When standing, the flexor reflex in lower limb controlled by dorsal reticulospinal tract
When walking, flexor synergy for walking patterns
Adults
if babinski reappears, loss of upper motor neurone control
Why does the survival pattern of response have to be inhibited
to allow mature pattern response and postural reflexes to develop. to regulate higher movement control centres
what is the clinical consequence of disinhibited survival pattern of response
Cerebral palsy
Movement random and uncontrolled, failed development of higher control (spectra of disorders, retain primitive reflexes which affect sensory perception of movement
