Topic 8.7 Flashcards
Where are grey and white matter in the SP?
White matter : superficial
Grey matter : inside
How is the organization of motor neurons in the grey matter?
Musculotopic organization
What are somatic motor neurons?
Neurons that project to skeletal muscle
What are autonomic motor neurons?
Neurons that project to smooth muscle
2 main lasses of somatic motor neurons
alpha and gamma
What is a motor unit?
motor neuron + all the sk muscle fibers it supplies
What does the main alpha motor neuron axon synapse with?
With extrafusal muscle fibers
What is the size principle of motor innervation?
As more force is needed, a greater number of motor units are recruited, in an order according to the magnitude of their force output
Which type of muscles have more / less alpha motor neuron innervation?
More : limb muscles
Less : muscles for manipulation
What do gamma motor neurons synapse with?
with intrafusal muscle fibers
What are the 3 types of inhibitory interneurons?
- Ia
- Ib
- Renshaw cell
What is the role of the Ia interneuron?
inhibitor of antagonist muscles in reflex arch
What is the role of the Ib interneuron?
Found in a reflex arch, where it is activated by a golgi tendon organ
What do Renshaw cells do?
They can modulate the strength of firing rate of a motor neuron via recurrent inhibition
3 examples of proprioceptive receptors
- muscle spindle
- gto
- joint receptors
Where are muscle spindles especially abundant?
In muscles for fine movement (like extraocular muscles)
2 types of intrafusal fibers
- nuclear chain fibre
- nuclear bag fibre
Sensory innervation of muscle spindles
- Group Ia fibers (for both)
- Group II fibers (for nuclear chain fiber)
What do sensory Ia fibers in muscle spindles?
Detect velocity of length change
What do sensory II fibers in muscle spindles?
detect change of length of the muscle fiber
Motor innervation of nuclear bag and nuclear chain fibre
Dynamic and static gamma motor neuron
What does GTO sense?
Tension when we contract the muscles (stretch receptor)
What type of afferent fibers innervate GTO?
type Ib afferent nerves
What is a reflex?
an involuntary instantaneous response to an eliciting stimulus
3 parts of the reflex arc?
- afferent limb
- central component
- efferent limb
4 reflexes
- Stretch (myotatic) reflex
- GT reflex (inverse myotatic)
- Flexor withdrawal
- Baby reflexes
Types of synapses of group Ia afferent fibers (2)
- monosynaptic
- bisynaptic
What maneuver allows better testing of myotatic reflex?
Jendrassik maneuver
What type of reflex is the GTO reflex?
polysynaptic reflex
Which muscle is relaxed in the GTO reflex?
The agonist / homonymous muscle (by inhibitory interneuron)
Which fiber types can carry the noxious stimulus?
Type III, IV fibers - a delta axons
What is the stimulus of the flexor withdrawal reflex?
pain (noxious stimulus)
What is the portion of the reflex that crosses to the other side of SP called?
crossed-extension reflex
4 baby reflexes
- positive support reflex
- babinski reflex
- palmar grasp reflex
- labyrinthine head righting reflex
What is babinski reflex?
big toe of baby’s foot moves upward after the sole is stroked
What is a spinal cord transection?
a tear within the sp as a result of a traumatic injury
2 types of sp cord transection syndromes
- upper motor neuron syndrome
- lower motor neuron syndrome
Symptoms of UMN (3)
- muscle weakness
- hyperreflexia
- tight muscles (hypertonia)
Symptoms of LMN (3)
- weeakened reflexes
- flaccid muscles (hypo / atonia)
- muscle atrophy
What is quadriplegia?
lesion at T1 or above
When do we require mechanical ventilation?
if lesion above C4
What is paraplegia?
Below the level of T1
What is spinal shock?
loss of reflex, motor and sensory function below the level of a spinal cord injury
