Lecture 19 Control Of Movement 1 Flashcards
What are the three classes of movement in normal physiological conditions?
Voluntary (planned movements “picking up something”)
Reflexes
Rhythmic motor patterns (“breathing”, “chewing”)
What are the four elements in a voluntary motor pathway
Lower motor neuron (LMN)
Upper motor neuron (UMN) [brainstem- signal spinal nerve to innervante LMN]
Local circuit neurons [brainstem/spinal cord - regulated & coordinate movement, feedback]
Brain stem inputs [involuntary control of these movements]
Functions of the components involved in movement control
1. Motor cortex (UMN)
2. Brainstem centers (UMN)
3. Cerebellum
4. Basal ganglia
5. Local circuit neurons
- Planning, initiating, directing voluntary movement
- Basic movement & postural control
- Coordinate ongoing movement
- Enable movement initiation
- LMN integration of many muscles groups.
Basic pathway for voluntary movement
Extra: A little more complicated pathway for voluntary control
Descending systems (Motor cortex & brainstem centers) -> Lower motor neuron pool -> skeletal muscle
See slide 444 : basal ganglia, cerebellum, descending systems, lower motor neuron pool, local circuit neurons, skeletal muscles
Only understand
Feedback in the motor pathway
- sensory input
- thalamus
Sensory input (via proprioception & outside world) -> ensure movements controlled & coordinated
Thalamus : main feedback system part
Most parts feedback to one each other to make sure movement movement is coordinated and controlled
Upper motor neurons (UMN)
- arrangement
- location
- Premotor cortex
- betz cells ( 1° motor cortex Area 4 layer 5)
- based on homunculus (map - amount of muscle/control there is/ needed)
- 1° motor cortex
- planning movement , feedback to 1° motor cortex
- large pyramidal cells -> send signal to LMN
Motor Fibre pathways
* understand how they travel down to synapse with different body parts, no need know details*
- pathways (from top)
- how fibres travel
- Corticobulbar tract (control cranial nerves)
- Corticospinal tracts (control rest of body) -> Anterior (axial/proximal muscles) & lateral (distal muscles)
- UMN travel down from homunculus by corticobulbar tract (cerebral peduncle)
- pyramids decussation :~ 85% fibres crossover (LCT), ~ 15% don’t (ACT)
- ACT decussate at spinal cord
- synapse with LMN, innervate skeletal muscles
Lower Motor Neurons (LMN)
- Alpha motor neurons (LMNs)
- Gamma motor neurons
Project out & control muscles
- Innervate striated muscles (contraction)
- Innervate muscle spindles
Brainstem inputs (function of the tracts)
1. Rubrospinal tract
2. Reticulospinal tract
3. Vestibulospinal tract
4. Tectospinal tract
- Upper limbs control
- Lower limbs control
- Balance
- Startle reflex, control moment of head & eyes orient ourselves to be aware of stimuli
Local circuit neurons coordination
1. Commissural axons
2. Long distance local circuit neurons
3. Short distance local circuit neurons
- Crossover to contralateral side, coordinating postural control of both body sides & processes like breathing (lungs move same time)
- Extend many spinal cord levels, movement coordination, posture control
- Control local group of muscles (like fingers) for coordination of fine control (like playing an instrument)
What is the purpose of brainstem centers feeding into local circuit neurons
Posture control like through reticulospinal & vestibule spinal tract
Alpha LMN
Involve in striatal muscle contraction
- innervate extrafusal muscle fibres (muscle contraction & movement)
Gamma LMN
Involve in proprioception
Neuromuscular synapse
1 muscle fibre = 1 synapse
Cholinergic (acetylcholine)
Initiating muscle contraction (Neuromuscular synapse)
- ACh release (axon terminal) -> bind to receptors
- AP reach T tubule
- Sarcoplasmic reticulum release Ca2+
- Active site (actin molecule) exposed & cross-bridge (actin - myosin) formation
- Contraction
Terminating muscle contraction (neuromuscular synapse)
- AchE remove Ach
- Sarcoplasmic reticulum recaptures Ca2+
- Active site covered -> no cross bridge interaction
- Contraction ends
- Fibres relax & return to resting length
Motor unit
- 1 motor neuron + all associated muscle fibres (More than one)
(One muscle fibre is innervates by one motor neuron but one motor neuron can innervate many fibres) - Differnt motor unit muscle fibres intermingled -> force distribution constant even if some contract and some relax
Alpha motor neurons
Size
- small
- large
Types
- S type
- FF type
- stimulate few muscle fibres -> motor units -> small forces
- stimulate larger, more powerful motor units
- slow twitch, Type I
- fast twitch, fast fatigue, Type IIB
FF and S
- Twitch time
- Force
- No. of firing
- Fatigue
- Size
- Power
FF
Short, high, high AP but available for short time, quick, large, powerful (max force) but for short time
S
Long, very low, low AP but present for longer time, none/slow, small, weak
- What is a twitch?
- What results to sustained contraction?
- How can MN increase muscle force production
- A single contraction of all fibres in motor unit caused by motor unit AP
- Increase AP frequency through twitches summation
- Increase AP frequency in individual alpha MNs, recruiting more alpha motor units
S type motor units correlate with slow twitch muscle fibres. Describe how they correlate with each other.
Recruit first (muscle - aerobic, endurance)
Active -> weak contractions (graded - greater precision than strong contraction )
Lower thresholds activation
Tonically active -> sustained effort motor acts (muscle - fatigue slowly, contract -> slower, longer time period)
FF type motor units correlate with fast twitch muscle fibres. Describe how they correlate with each other.
Recruit: relatively high muscle force levels (activity bursts)
Activation threshold: only rapid movements that require greater force
Exercise need -> prevent atrophy
Muscle: anaerobic, contracts & relaxes quickly, fatigues quickly
