BIO448 - Quiz 9 -Motor unit & Lower motor neurons

lower motor neruons

• cell bodies in ventral horn of spinal cord

• aka alpha-motor neurons

• control skeletal muscles

• send axons directly to muscles via spinal nerves

• activated by motor neurons in the cortex/brainstem

local circuit neurons

upper motor neurons can also synapse on ___, which are interneurons synapsing on alpha-motor neurons

95% of lower motor neurons function via a 3 neurons circuit which include a local interneuron

basal ganglia

located in the motor cortex

responsible for the initiation of voluntary movements

cerebellum

located near the brainstem

deals with postural control and coordination of ongoing movement

Diseases caused by loss of neurons in the basal ganglia

• Huntington’s disease

• Parkinson’s disease

• Multiple system atrophy

motor unit

made of a motor neuron and the multiple muscle fibers that it innervatesmot

motor pools

all the motor neurons (motor units) innervating a single muscle

spatial distribution of motor neurons in the ventral horn of spinal cord

1

each muscle fiber is innervated by __ motor neuron except during development

contractile force

motor units are evenly/widely distributed across the muscle, which will lead to a dispersed/spread out/even ___ force throughout the muscle.

small

muscles used for support or postural control have ___ motor units

large and small

muscles used for dynamic movements requiring significant efforts will have both ___ motor units

more

the smaller the ratio of muscle fibers per motor neurons, the __ precise the control

axial/proximal

___ muscles motor pools are found in the medial white matter of the spinal cord and are used for postural control

distal

___ muscles motor pools are found in lateral white matter of spinal cord and are used for fine/skilled movements

flexor

decrease the angle between 2 bones

motor pools found on the upper part of spinal cord white matter

extensor

___ increases the angle between 2 bones

motor pools found in the lower part of the white matter of the spinal cord

same

all muscle fibers in a motor unit usually have the ___ physiology and the ___ biochemical tybe of fibers

slow muscle fibers

• contract slowly

• red in color because of high concentration of myoglobin aka lots of mitochondria

• very resistant to fatigue

• produce low amount of power

fast fatigue-resistant muscle fibers

• in between category

• red in color due to high amount of myoglobin aka lots of mitochondria

• resistant to fatigue

• contract quickly

• produce moderate amount of power

fast fatigable muscle fibers

• contract quickly

• white in color due to low myoglobin aka less mitochondria

• fatigue very easily

• produce high amount of power

• used in short-term anaerobic activity like sprinting and lifting heavy weight (usually less than a minute)

physiology rule

1 motor neuron = 1 type of muscle fibers = 1 type of motor unit

slow

small motor units are innervated by small neurons and are ___ fibers

fast-fatiguable

large motor units are innervated by large neurons and are ___ fibers

order of recruitment

1. smallest motor unit (slow, fatigue resistant)

2. progressively larger units (fast fatigue-resistant)

3. largest motor units (fast fatigable)