Intro to movt control spinal cord and reflexes Flashcards
What is a reflex?
Stereotyped involuntary response to a stimulus and not subject to conscious control
What mediates autonomic reflexes
autonomic nervous system activating smooth muscle, cardiac muscle and glands
What mediates somatic reflexes
somatic nervous system
What is the function of a monosynaptic reflex
maintains upright posture and controls leg stretch
What are the components of a monosynaptic reflex?
Receptor= muscle spindle Afferent = myelinated, large A alpha afferent axon Interpretation = spinal cord Efferent = alpha motor neuron; large and unmyelinated Effector = muscle fibres
What is endoneurium
surrounds individiual nerves
What is perineurium
surrounds a bundle of nerves
What is epineurium
surrounds entire nerve fibre
What are the components of a post synaptic reflex?
Proprioceptor in skeletal muscle (Golgi tendon in series and spindle fibres in parallel)
Input carried via sensory neurons to CNS
CNS integrates input signal (interneurons)
Somatic motor neurons carry output via alpha motor neurons
Effectors - contract skeletal muscles
What proprioceptors exist in muscle
Golgi tendons in series and spindle fibres in parallel
Why are there both intrafusal and extrafusal fibres in muscle spindles
so spindles move independently to muscle
Why is it important that muscle spindles are sometimes independent to muscles
if it always reflexed and trigger contraction everytime the muscle got stretched then there would be no control of muscle movements
How are automatic reflexes from muscle spindles prevented to allow more control of muscle movement
alpha fibre to extrafusal fibre gives a collateral to the gamma motor neuron (to the intrafusal fibre) preventing a reflex.
Alpha-Gamma coactivation
What is the withdrawal reflex an example of
total flexor pattern
What is reciprocal inhibition
In a total flexor pattern/withdrawal reflex the flexors need to be excited but the extensors need to be inhibited
What are intersegmental reflexes
When total flexor reflex occurs muscles controlled by different segments of the spinal cord need to react together.
Describe the tracts that come down from the brain to inhibit reflexes
Two long tracts: pyramidal and extrapyramidal
What are Renshaw cells
inhibitory neuron
What are the types of pyramidal tracts
corticospinal (cortex to spine)
corticobulbar (cortex to brainstem)
What are the types of extrapyramidal tracts
vestibulospinal = vestibular nerve tectospinal = superior colliculi to midbrain reticulospinal = MRST - pons; LRST - medulla (medial/lateral reticulospinal tracts) Rubrospinal = midbrain
Describe the vestibulospinal tract
works ipsilaterally - controls balance and posture. Innervates flexors in upper limbs and extensors in lower limbs
Describe the tectospinal tract
cervical spine, coordinates head movts. in relation to visual stim. (like responding to waving)
Describe the reticulospinal tract
MRST - increases muscle tone - excitatory to voluntary movt
LRST - decreases muscle tone - inhibitory to voluntary movt
How is the vestibular apparatus a sense organ
it gives an idea of orientation relative to vertical
How are visual reflexes processed
eye - lateral geniculate reflex - midbrain
What are the types of abnormal reflex
absent, distorted, exaggerated, asymmetrical
