3 - sensorimotor system Flashcards
what are different types of motor control?
voluntary: walking, talking
goal-directed: conscious, explicit
habit: unconscious
involuntary: eye movements, diaphragm
what is the evolutionary perspective of hierarchical control architecture?
pain - spinal cord - motor activity - defence-related output (escape)
looming threat - sensorimotor midbrain - avoidance
learned threat - cortex + limbic system - avoidance
overview of the sensorimotor system/
- muscles are under the influence of motor units and circuits
- that’s under the influence of brainstem motor systems and them cortical motor systems
- basal ganglia: what to do
- cerebellum: how to do it
how are neurons organised in the sensorimotor system?
governed by lower and upper motor neurons
- lower motor neuron begins in brainstem or spinal cord and projects to muscle
- upper motor neuron originates in higher centres and projects to meet lower motor neurons
how do muscle fibres act?
- ‘all-or-none’ principle
- can only contract or relax
- control of muscle force depends on how different types of muscle fibres are activated
what are the different types of muscle?
skeletal
cardiac
muscle
how are muscle fibres arranged?
antagonistic arrangement - combined co-ordinated action (oppose each other)
how can muscles change over time?
number of muscle fibres changes very little (genetically determined)
cross sectional area of muscle fibres changes and different proportions of the different types of fibre
how do muscles contract?
actin and myosin filaments lock in a slide against each other
when muscle is contracted there is more overlap of actin and myosin
release of acetylcholine leads to release of calcium for inside muscle cell
causes myosin head to bind with actin filament
ATP required to break bond between myosin head and actin filament
what is a motor unit?
a group of muscle fibres and the single motor (alpha) neuron that innervates them
(all-or-nothing)
what determines size of motor unit?
functional requirements for muscle:
- level of control
- strength
what is the size principle?
motor units are recruited to muscles in order of size, smallest first
fine control typically required at lower forces
what are the different types of muscle fibres?
slow twitch - efficient for endurance and low-intensity activities
fast fatigue-resistant - combining endurance and strength capabilities
fast fatiguable - high force output but fatigue quickly, for short, intense bursts of activity
what is a motor pool?
all the lower motor neurons that innervate a single muscle (both alpha and gamma motor neurons)
where do alpha motor neurons originate?
spinal cord
how does the spinal cord receive and send signals
sensory input - dorsal root
motor output - ventral root
what senses tension in the muscle?
Golgi tendon organs
positioned where the muscle attaches to the bond
what senses stretch in the muscle?
muscle spindles
how do Golgi tendon organs work?
sends sensory information to the brain via spinal cord about amount of force in a muscle
critical for proprioception
inhibits muscle fibres under extreme tension
what is the stretch reflex? (monosynaptic)
corrects stretching of muscle to maintain muscle in its state, important for maintaining posture
what system detects stretch regardless of muscle length?
gamma motor neurons which innervate intrafusal fibres (spindle fibres)
they keep intrafusal fibres set at a length that optimises muscle stretch detection
what is the withdrawal reflex?
reciprocal innervation of antagonistic muscles explains why the contraction of one muscle induces the relaxation of the other
permits the execution of smooth movements
supports and maintains balance during withdrawal response
what is the process of the stretch reflex?
- intrafusal muscle fibres detects lengthening and sends signals to spinal cord
- causes alpha motor neurons to fire AP which contract muscle back into position
(monosynaptic)
where are muscle spindles located?
embedded within muscle fibres
