Flashcards in Functional Organisation of the spinal cord Deck (20):
What are the functional roles of the spinal cord?
segmental reflexes, intersegmental reflexes, pattern generators, transmission of somatosensory information, relay of descending motor control, relay of descending autonomic commands
At what level would you perform a lumbar puncture?
L3-L4 (below termination of the spinal cord)
Where are the descending motor tracts located in the spinal cord?
Where are the motor neurons for distal muscles located in the spinal cord?
Where are the motor neurons for proximal muscles located in the spinal cord?
What is a motor unit?
group of muscle fibres innervated by a single motor neuron
What is a motor neuron pool?
a group of motor neurons that all innervate a single muscle
What is the function of muscle spindles? where are they located?
to detect muscle stretch (length), they are intrafusal fibres within muscle fibres
What is the function of Golgi tendon organs? where are they located?
to detect muscle force (tension). located in the tendons of skeletal muscles.
Describe the monosynaptic stretch reflex (ie knee-jerk)
tendon hammer produces brief stretch on tendon which is detected by the muscle spindle which sends on AP via the dorsal root to the spinal cord where it makes 2 connections:
1. excitatory connection with the motor neuron innervating the extensor muscle
2. with an inhibitory interneuron which synapses with the motor neuron innervating the antagonistic muscle (ie the flexor)
Describe the Golgi tendon organ reflex (in response to too much force)
want feedback to decrease force -> tendon organ detects an increase in force so signals via in inhibitory interneuron in the spinal cord to decrease contraction of the muscle under tension and an excitatory interneuron to increase contraction of the antagonistic muscle
What is the bilateral/ cross extensor reflex?
an intersegmental reflex ie in response to nociceptive stimuli
Describe the bilateral/cross extensor reflex
when one limb steps on something sharp nociceptors mediate a withdrawal reflex (activate flexors and inhibit extensors) and at the same time there is intersegmental reflexes that work to increase extension on the other leg to maintain posture (involves multiple interneurons - ie NOT monosynaptic)
Lateral propriospinal interneurons are involved in what?
shorter -> for precision/fine movements ie writing
Medial propriospinal interneurons are involved in what?
are longer and involved in action of postural muscles
What is a lower motor neuron?
a neuron that innervates a muscle
What is an upper motor neuron?
function definition -> any neuron that affects the excitation of a lower motor neuron
Are most upper motor interneurons excitatory or inhibitory?
inhibitory -> ie brain is mostly signalling to the spinal cord to do nothing
What happens when you have a lesion in the descending motor pathway?
hyperexcitability or the motor neurons below the lesion (increased muscle tone and exaggerated tendon reflexes) -> lost their inhibitory descending control