Motor System 1

somatic motor system

- skeletal muscles and the parts of the nervous system that control neural structures

- voluntary movement

motor pathways include 2 principal neurons, ______ and _______

- upper motor neurons (UMN)

- lower motor neurons (LMN)

where do upper motor neurons reside

- CNS, they do NOT leave here

- housed in the brain and spinal cord

upper motor neurons

- run from cortex to brainstem

- synapse with lower motor neurons (LMNs) in the brainstem (cranial nerves) and spinal cord (spinal nerves)

where do lower motor neurons reside

- consists of cranial nerves and spinal nerves

- part of PNS

LMN: cranial nerves innervate ______ and exit out of ______

- face/neck

- brainstem

LMN: spinal nerves innervate ______ and exit out of ______

- leg/arm muscles

- spinal cord

where do the UMNs synapse with LMNs in the lateral corticospinal tract

- ventral horn

caudal medulla

- where contralateral innervation (decussation) happens for the lateral corticospinal tract

- right side of brain controls left side of body

what does the lateral corticospinal tract innervate?

- arms and legs

majority of the ______ is decussation (90%)

- lateral corticospinal tract

the other 10% of decussation is in the _____

- anterior corticospinal tract

anterior corticospinal tract

- small part of the corticospinal tract

- tract stays on the same side until they are ready to synapse with LMN

characteristics of UMN damage

- weakness

- hypERactive reflexes

- increased tone

- NO atrophy

- NO fasciculations

- spasticity present

characteristics of LMN damage

- weakness

- hyPOactive reflexes

- decreased tone

- atrophy present

- fasciculations present

- flaccidity present

spasticity

- hyperactive reflexes + increased tone

- muscles are stiff

flaccidity

- hypoactive reflexes + decreased tone

- muscles are very limp

fasciculations

- flickering-like, involuntary twitches of muscles

atrophy

- very weak muscles

hypertonia

- increased muscle tone

hypotonia

- decreased muscle tone

motor control hierarchy

- just know that every part of this is equally important and essential

lower motor neurons

- only this DIRECTLY command and innervate muscles

- last part of journey of all motor signals

- the final common pathway

where do LMNs receive sources of input

- UMNs

- spinal interneurons

- spindles

***sensory input in order to initiate movement!

spindles

- within the muscles cells

- ex. tells you that you are sore from a workout

how are lower motor neurons classified?

- based on the type of muscle fiber they innervate

LMNs: alpha motor neurons

- innervate extrafusal muscle fibers (muscle contraction)

- extrafusal = muscle contraction

- involved with generating muscle force (ex. pushing things away, kicking a ball, etc.)

LMNs: gamma motor neurons

- innervate intrafusal muscle fibers (sensory)

intrafusal muscle fibers and sensory afferents compose ____

- muscle spindles

propiroception

- awareness of how muscles feel / monitor amount of muscle stretch

- ex. trying a new exercise and feeling like you are not doing it right

intrafusal fibers

- involved in a SMALL part of muscle contraction

dorsal horn

- where sensory neurons go to after exiting spinal cord

ventral horn

- where motor neurons (efferent fibers) exit

motor unit

- consists of 1 motor neuron and all the muscles fibers it innervates

why are motor units important?

- our body is made up of small and large motor units

motor neuron pool

- all motor neurons innervate the same single muscle

- reside and live in the same place (pool)

small motor units

- innervate and have a lesser amount of number of muscle fibers

- involved in precise and fine motor movements (ex. writing, texting, typing, and SPEECH!)

larger motor units

- innervates a large amount of muscle fibers

- can innervate muscle fibers at the same time

- generates bigger motor movements and in charge of our lower extremities (ex. jump, dance, walk)

size of motor units are determined by...

- the number of muscle fibers

neuromuscular junction

- acetylcholine (ACh) is released here in order to innervate muscles

acetylcholine receptors

- release of this causes an action potential in the sarcolemma

- multiple steps involved in this

cross bridge cycle

- the actual muscle contraction