segmental motor circuits Flashcards
(30 cards)
1
Q
classes of movement
A
- reflex (stereotyped)
- voluntary (motor cortex)
- cyclical (programmed)
2
Q
motor unit
A
- 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
3
Q
lower motor neurons
A
ventral horn of gray matter of spinal cord
4
Q
3 types of input to a LMN
A
- from local interneurons (neighboring neurons)
- from sensory afferents (pain, temp)
- from higher centers (descending tracts)
5
Q
reflexes can be classified as
A
- monosynaptic (stretch)
- disynaptic (inverse stretch)
- polysynaptic (withdrawal/flexion)
6
Q
monosynaptic (stretch) reflex
A
- afferent and motor neurons
- MOST IMPORTANT
- ex: muscle spindle
7
Q
muscle spindle
A
- intrafusal muscle fibers
- annulospiral fibers that
- sensory fibers go to dorsal root and synapse with motor neuron
8
Q
stretch reflex circuit (spindle)
A
- muscles spindle senses stretch
- spindle activated
- signal to DRG
- signal goes to alpha motor neuron to synapse
- signal to same muscle
- contraction
9
Q
stretch reflex (AKA: myotatic, deep tendon)
A
10
Q
another one
A
11
Q
knee jerk reflex
A
- tendon of quads is hit (stretched)
- causes alpha motor neuron to fire
- quad contracts
- leg kicks
12
Q
why is the reflex so important?
A
- reflexes help muscles contract
- keeps the horse from collapsing
13
Q
stretch reflex functions
A
- holds muscle length constant
- maintenance of erect posture
- responsible for muscle tone
14
Q
what is muscle tone?
A
basal level of contraction of muscle
- only when you are wake
15
Q
gamma motor system
A
- A-gamma motor neurons come out of ventral horn
- smaller motor neurons that go to the spindle
- these can stretch the muscles spindle
16
Q
alpha and gamma co-activation occurs during
A
voluntary movement
17
Q
disynaptic (inverse stretch) reflex
A
- golgi tendon organ
- senses muscle tension
- 2 synapses, 3 neurons
18
Q
golgi tendons measure
A
muscle tension
19
Q
inverse stretch reflex
A
- GTO measure tension
- synapse with inhibitory interneuron
- acts on alpha motor neuron
- cause muscle to relax
20
Q
golgi tendon reflex is a
A
protective reflex
21
Q
polysynaptic (withdrawal flexion reflex)
A
- 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
22
Q
antagonist muscles
A
- 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
23
Q
reciprocal (antagonist) inhibition
A
- muscle spindle reflex
- muscle spindle in extensor muscle branches and connect to inhibitory neurons
- inhibitory neurons acts on the flexor muscle = relax
24
Q
jaw closing reflex
A
- if you stretch masseter by tapping chin = reflex
- under normal circumstances, reflex is ibhibited
- if abnormality of central motor pathway, reflex is apparent
25
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
26
mesencephalic nucleus of V
27
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!!
28
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
29
mastication
- central pattern generator
- stretch reflexes (in jaw closes muscles)
- mandibular rest position (
- periodontal reflexes
- joint reflexes
30
the masticatory system can
exert great forces
