segmental motor circuits Flashcards
classes of movement
- reflex (stereotyped)
- voluntary (motor cortex)
- cyclical (programmed)
motor unit
- basic lowest level
- alpha motor neuron
- in ventral horn
- sends axon out into periphery
- connects to skeletal muscle fibers
- decides whether muscle will contract or not
lower motor neurons
ventral horn of gray matter of spinal cord
3 types of input to a LMN
- from local interneurons (neighboring neurons)
- from sensory afferents (pain, temp)
- from higher centers (descending tracts)
reflexes can be classified as
- monosynaptic (stretch)
- disynaptic (inverse stretch)
- polysynaptic (withdrawal/flexion)
monosynaptic (stretch) reflex
- afferent and motor neurons
- MOST IMPORTANT
- ex: muscle spindle
muscle spindle
- intrafusal muscle fibers
- annulospiral fibers that
- sensory fibers go to dorsal root and synapse with motor neuron
stretch reflex circuit (spindle)
- muscles spindle senses stretch
- spindle activated
- signal to DRG
- signal goes to alpha motor neuron to synapse
- signal to same muscle
- contraction
stretch reflex (AKA: myotatic, deep tendon)
another one
knee jerk reflex
- tendon of quads is hit (stretched)
- causes alpha motor neuron to fire
- quad contracts
- leg kicks
why is the reflex so important?
- reflexes help muscles contract
- keeps the horse from collapsing
stretch reflex functions
- holds muscle length constant
- maintenance of erect posture
- responsible for muscle tone
what is muscle tone?
basal level of contraction of muscle
- only when you are wake
gamma motor system
- A-gamma motor neurons come out of ventral horn
- smaller motor neurons that go to the spindle
- these can stretch the muscles spindle
alpha and gamma co-activation occurs during
voluntary movement
disynaptic (inverse stretch) reflex
- golgi tendon organ
- senses muscle tension
- 2 synapses, 3 neurons
golgi tendons measure
muscle tension
inverse stretch reflex
- GTO measure tension
- synapse with inhibitory interneuron
- acts on alpha motor neuron
- cause muscle to relax
golgi tendon reflex is a
protective reflex
polysynaptic (withdrawal flexion reflex)
- response to painful stimuli
- free nerve ending synapse in substantia gelatinosa
- polysynaptic connection of interneurons to alpha motor neurons
- ascending spinothalamic tract
- synapse with interneurons which converge on alpha motor neuron
- ex: touching hot stove
antagonist muscles
- with any movement there is an opposite movement
- ex: contract bicep = relax tricep
- both muscles in pair cannot contract at same time
- one contracts, the other relaxes
reciprocal (antagonist) inhibition
- muscle spindle reflex
- muscle spindle in extensor muscle branches and connect to inhibitory neurons
- inhibitory neurons acts on the flexor muscle = relax
jaw closing reflex
- if you stretch masseter by tapping chin = reflex
- under normal circumstances, reflex is ibhibited
- if abnormality of central motor pathway, reflex is apparent
jaw jerk reflex
- spindle in masseter afferents to mesencephalic nucleus (pseudounipolar neuron)
- spindle fiber synapses with alpha motor neuron in motor nucleus of V
- masseter contracts and closes the jaw
mesencephalic nucleus of V
corneal reflex
touch cornea = blinking reflex
- unencapsulated receptors in cornea go thru V1
- synapse in brainstem @ chief nucleus of V
- interneuron goes to motor nucleus of V
- contract eye muscles
- blink!!
central pattern generators
neuronal networks in spinal cord or brain stem that generate rhythmic alternative activity like
- walking
- swimming
- chewing
- breathing
- eye movements
- sneezing and coughing
mastication
- central pattern generator
- stretch reflexes (in jaw closes muscles)
- mandibular rest position (
- periodontal reflexes
- joint reflexes
the masticatory system can
exert great forces
