Week 8 - Motor 1: Overview of Movement & Lower Motor Neurons

What is motor control?

The way the human body controls movement; includes voluntary and reflexive movements

What is a reflex?

Occurs as a reaction to something without conscious thought, typically involving a specific stimulus.

What is a voluntary movement?

A movement that is consciously controlled and intentionally executed by an individual, often involving complex motor planning.

What are the two kinds of voluntary (volitional) movement?

Autonomic and Cortical

What is autonomic voluntary movement?

Movement that occurs automatically, often without conscious awareness, usually for routine or habitual actions; requires little conscious attention

What is cortical voluntary movement?

Movement that is consciously initiated and controlled, requiring higher brain functions, such as planning and decision-making, often involving complex tasks or actions; requires conscious attention

What is required to produce voluntary movements?

Neural structures

What role does the visual system play in motor control?

Vision; eye movement in coordination with the vestibular system

How does the visual system contribute to movement?

Contributes through motor planning; supports postural control, maintaining an upright posture

What is the role that the somatosensory (tactile/proprioception) system plays in motor control?

Helps us understand our environment; gives us sense of joint position; awareness of movement

What does the somatosensory system contribute to movement?

Contributes to motor learning; helps to plan and execute multi-joint movement

What role does the vestibular system play in motor control?

Detects head movement; detects head and body position relative to gravity; eye movement coordinates with the vestibular system

What does the vestibular system contribute to movement?

Maintains posture and equilibrium; contributes to motor planning

What are higher centers of motor control involved in?

Voluntary movements

What are higher centers of motor control?

Long descending tracts that originate from the cortex or brainstem; synapses with lower motor neurons or interneurons

They are parallel pathways with overlapping and complementary functions

What is controlled by a balance of the long descending tracts?

Movement, Posture, Muscle Tone, and Reflexes

Where is the motor cortex located?

Frontal lobe; anterior to precentral gyrus

What are the main areas of the motor cortex?

Premotor Area/Cortex (PMA/PMC)

Supplementary Motor Areas (SMA)

Primary Motor Cortex (M1)

What are the areas that the motor cortices receives information from?

Somatosensory Areas

Other areas of the frontal lobe

Association Areas

Basal ganglia

Cerebellum

Where is the primary motor cortex location (M1)?

Precentral gyrus

What is the primary motor cortex responsible for?

Controls contralateral voluntary movements; specifically controls fine movements of hands and face

How is the primary motor cortex organized?

Somatotopically; homunculus

Where is the premotor area/cortex (PMC, M2) located?

Anterior to M1; located laterally

What are the functions of the premotor area/cortex (PMC, M2)?

Motor planning, selection and planning of actions, processing of actions

Where is the supplementary motor area/cortex (SMA, M2) located?

Anterior to M1; located medially

What are the functions of the supplementary motor area/cortex (SMA, M3)?

Motor planning, planning bimanual and sequential movements

Where do upper motor neurons have their cell bodies?

Cortex, brainstem

Where do upper motor neurons travel through?

Descending pathways

What are the functions of upper motor neurons?

Conveys commands for movement; adjusts motor activity

Where are lower motor neuron cell bodies located?

Spinal cord (ventral horn); brainstem (only CNs)

Where do lower motor neurons travel through?

Nerves

What do lower motor neurons synapse on?

Skeletal muscle fibers.

What are the functions of lower motor neurons?

Convey information to the muscles

What are the two major descending systems?

Dorsolateral System and Ventromedial System

What are the tracts included in the dorsolateral system?

Lateral Corticospinal

Rubrospinal

Corticobulbar (terminates in brainstem)

Reticulospinal

What are the overall functions of the dorsolateral system?

Limb flexion and fine movements

What type of control is involved with the dorsolateral system?

Voluntary control of limbs

Where does the dorsolateral system originate?

2 from the cortex; 1 from the brainstem

Where does the dorsolateral system terminate?

Lateral ventral horn of spinal cord (lateral motor neuron pools)

What tracts are included in the ventromedial system?

Anterior/ventral corticospinal

Reticulospinal

Vestibulospinal

• Medial Vestibulospinal

• Lateral Vestibulospinal

What are the overall functions of the ventromedial system?

Posture and gross limb movements

What does the ventromedial system control?

Automatic (without conscious effort) movement of limbs

Where does the ventromedial system originate?

3 tracts from brainstem; 1 tract from cortex

Where does the ventromedial system terminate?

In the medial ventral horn of the spinal cord (medial motor neuron pools)

What are different terms for a bundle of axons?

Fasciculus, Funiculus

What is fasciculus?

Group of axons which have a similar function

What is funiculus?

Group of axons located in a given area

What are examples of fasciculus that we’ve learned?

Fasciculus gracilis and Fasciculus cuneatus

What are examples funiculus that we’ve learned?

Lateral funiculus and posterior funiculus

What type of matter are both fasciculus and funiculus are a part of?

White matter

What is the function of the lateral corticospinal tract (dorsolateral)?

Voluntary control of distal muscles needed for precise movement; fractionation; acts to suppress or inhibit reflex activity

What is fractionation?

Ability to activate individual muscles independently of other muscles

What is the pathway of the lateral corticospinal tract (dorsolateral system)?

Originates in the motor areas of the cortex

Descends through internal capsule

Decussates at pyramids of medulla

Travels through lateral funiculus in the spinal cord

Most fibers terminate by contacting interneurons in the spinal cord; some of the fibers synapse directly with lower motor neurons

Is the lateral corticospinal tract (dorsolateral system) a chain or one long neuron?

One long neuron

What is the function of the ventral/anterior corticospinal tract (ventromedial system)?

Control of neck, shoulder, and trunk muscles

What is the pathway of the ventral/anterior corticospinal tract (ventromedial system)?

Originates in cortical motor areas

Travels through internal capsule

Descends ipsilaterally

Travels through anterior funiculus of the spinal cord

Can have a bilateral projection; decussating at the spinal cord level

What are the main differences between the lateral corticospinal tract and the ventral/anterior corticospinal tract?

Lateral Corticospinal:

Decussates at pyramids of medulla

Contralateral control

Ventral/Anterior:

Have a bilateral projection

Bilateral control

What is the function of the corticobulbar tract (dorsolateral system)?

Analogous to the lateral corticospinal tracts, but to FACE

What is the pathway of the corticobulbar tract (dorsolateral system)?

Originates in motor areas of cortex

Projects to and terminates on cranial nerve nuclei in brainstem

• Some terminates contralaterally

• Some terminates bilaterally (since upper and lower face are controlled differently

How do brainstem nuclei react to stimuli?

Acts reflexively to stimuli in response to descending information from the cortex and cerebellum

What are motor tracts from the brainstem?

• Vestibulospinal tracts (medial & lateral)

• Reticulospinal tracts (medial & lateral)

• Rubrospinal tract

What is the function of vestibulospinal tracts?

Postural control

What is the function of the reticulospinal tracts?

Postural control and gross limb movements

What is the function of the rubrospinal tract?

Works closely with the lateral corticospinal tract; controls distal musculature (mainly upper limb flexors); acts to suppress/inhibit reflex activity

What is the pathway of the rubrospinal tract (dorsolateral system)?

Originates in the red nucleus of midbrain

Immediately decussates

Descends to spinal cord to synapse on lower motor neurons

What are the two types of lower motor neurons?

Alpha and gamma motor neurons

What are alpha motor neurons?

Projects to the extrafusal skeletal musclesthat are responsible for muscle contraction and movement. They are the primary motor neurons that innervate skeletal muscle fibers.

What are gamma motor neurons?

Projects to the intrafusal skeletal muscle fibers within muscle spindles, regulating the sensitivity of these sensory receptors and modulating muscle tone.

What is a motor unit?

A motor unit consists of an alpha motor neuron and all the extrafusal muscle fibers it innervates, functioning together to produce muscle contraction.

What are extrafusal muscle fibers?

Extrafusal muscle fibers are the primary muscle fibers that generate force during muscle contraction and are innervated by alpha motor neurons.

What are intrafusal muscle fibers?

Intrafusal muscle fibers are specialized muscle fibers located within muscle spindles that are responsible for detecting changes in muscle length and stretch, playing a crucial role in the proprioceptive feedback system.

They are innervated by Gamma motor neurons

What can be affected by motor neuron lesions?

Muscle strength

Muscle bulk

Muscle contraction

Muscle tone

Muscle stiffness

Reflexes

What is muscle tone?

Resistance inside the muscle at all durations of time; it reflects the level of muscle tension at rest and contributes to posture and stability.

What are the ranges of muscle tone you can see?

Typical

Hypotonia

Hypertonia

What is hypotonia?

Atypically decreased to passive stretch of the muscles, resulting in reduced resistance and flexibility.

What is hypertonia? And the two types?

Atypically increased resistance to passive stretch of the muscles, resulting in stiffness and reduced flexibility.

Two types: (1) Spastic (velocity dependent), (2) Rigid (velocity independent)

What is spastic hypertonia?

A type of hypertonia characterized by increased muscle tone and resistance that varies with the speed of movement, often resulting in stiffness.

Seen when you move the limb quickly

What is rigid hypotonia?

A type of hypotonia that presents with increased resistance to passive movement, regardless of the speed of stretch. This condition leads to stiffness and decreased flexibility of the affected muscles.

Doesn’t matter if you move limb fast or slow; at all periods of time, it will be rigid