Types
These types of cells originate in the spinal cord & brainstem to innervate/control the skeletal muscles of the head and body
Lower Motor Neurons
This area is located within the precentral gyrus, is topographically organized (homunculus), and initiates most voluntary movements.
Primary Motor Cortex (M1)
The primary motor cortex (Brodmann area 4) is a brain region that in humans is located in the dorsal portion of the frontal lobe.
Of the three motor cortex areas, stimulation of the primary motor cortex requires the least amount of electrical current to elicit a movement.
These are specialized receptors that act as stretch detectors, i.e. they sense how much and how fast a muscle is lengthened or shortened (Stretch Reflex - Myotatic Response)
Muscle spindles
These motor units are capable of sustained movements and do not generate much force (e.g., muscles responsible for posture).
Slow (S) Motor Units
These motor units are resistant to fatigue
Both slow and fast fatigue-resistant :D
This area is important for suppressing and preparing for voluntary motor movements
These types of neurons innervate intrafusal muscle fibers to detect stretch.
𝞬-motor neurons (gamma) plays a critical role in the maintaining muscle tone by manipulating the length of intrafusal muscles
This descending motor pathway is made up of 2 different tracts, it is named as such because these tracts (usually) decussate at the medullary pyramids
Pyramidal Tract
These types of cells originate in the brainstem and/or cortex and synapse onto local circuit neurons
Upper motor neurons
Neurons that innervate the distal muscles have cell bodies that are more __________ in the ventral horn of the spinal cord compared to proximal muscles
Lateral
Golgi tendon organs respond to ______ and not stretch
tension
"“In short, the muscle spindle system is a feedback system that monitors and maintains muscle length, and the Golgi tendon system is a feedback system that monitors and maintains muscle force.”
This theory states that The orderly recruitment of motor neurons by size to increase contractile strength of the muscle
Size principle
These neurons are critical for coordination of complex movements through activating appropriate lower motor neurons at the right time.
Local Circuit Neurons are cells that receive sensory information from the body and descending information/instructions from the cortex (i.e. interneurons).
These are a microcircuit of spinal cord neurons that can excite/inhibit motor neurons to limbs to generate rhythmic behaviors (e.g., walking, coughing, sucking, chewing, swallowing).
Central Pattern Generators
This reflex helps us to prevent muscles from generating excessive and dangerous levels of tension (which could cause muscle damage).
Inverse Myotatic Reflex
What are the symptoms of lower motor neuron disease?
atrophy, flaccidity, hyporeflexia, fasciculation