Motor System Flashcards
What is motor control?
Motor control involves a dynamically changing mix of conscious and unconscious regulation of muscle force, informed by continuous and complex sensory feedback, operating in a framework sculpted by evolutionary pressures
What are the 4 types of muscle control?
Voluntary
Goal-directed
Habit
Involuntary
Give examples of voluntary motor control
Running
Walking
Talking
Playing guitar etc
What is goal-directed motor control?
Conscious
Explicit
Controlled
What is ‘habit’ motor control?
Unconscious
Implicit
Automatic
Give examples of involuntary motor control
Eye movements
Facial expressions
Jaw
Tongue
Postural muscles throughout trunk
Hand and fingers
Diaphragm
Cardiac
Intercostals (around lungs)
Digestive tract
What is motor control governed by?
Upper and lower motor neurones
Where does the lower motor neurone begin?
Brainstem or spinal cord
Where do upper motor neurones originate?
Higher centres
What do lower motor neurones project to?
Muscles
Where do upper motor neurones project to?
Project down to meet the lower motor neurones
What type of manner do individual muscles fibres act in?
‘All-or-none’ manner
What does control of muscle force depend on?
The way in which lower motor neurones activate different types of muscle fibre
What % of body weight do muscles make up?
40%
What are the 3 types of muscle?
Cardiac
Smooth
Skeletal
What is the smallest muscle in the body?
Stapedius, found in the inner ear
What is the largest muscle in the body?
Gluteus maximus, found in the hip/buttock
What is the strongest muscle in the body?
Masseter, found in the jaw
What is antagonistic arrangement?
Combined co-ordinated action
What is muscle size/strength about?
Cross sectional area of individual fibres and different proportions of the different types of fibre
What attaches a skeletal muscle to bone?
Tendon
What is skeletal muscle comprised of?
Several muscle fasciculi (group of muscle fibres)
What is muscle fasciculus comprised of?
Several muscle fibres (= muscle cells)
What is muscle fibre constituted of?
Several myofibrils
What do myofibrils contain?
Actin and Myosin myofilaments
What happens in rigor mortis?
After death the body is no longer able to produce ATP by oxidative metabolism.
So muscles remain stiff and contracted as no ATP is present to break the bond between the myosin head and actin filament.
What does a motor unit consist of?
Single alpha motor neurone + all the muscle fibres it innervates
What do fewer muscle fibres mean?
Greater movement resolution
What is the final common pathway for motor control?
Motor unit
Average number of muscle fibres innervated by a motor unit varies according to 2 functional requirements, what are these?
Level of control
Strength
What is the size principle?
Units are recruited in order of size (smallest first)
Fine control typically required at lower forces
What represents the ‘unit of control’ of muscle force?
Alpha motor neuron and the muscle fibres it connects to
What is the motor pool?
All the lower motor neurones that innervate single muscle
What does the motor pool contain?
Alpha and gamma motor neurones
What are motor pools often arranged in?
Rod like shape within the ventral horn of the spinal column
Where do alpha motor neurones originate in?
Spinal Cord
What are cell bodies in the ventral horn activated by?
Sensory information from muscle
Descending information from brain
What does a good control system need to know?
How much tension is on the muscle;
What is the length (stretch) of the muscle
Where are golgi tendon organs located?
Within the tendon
What is the main function of golgi tendon organs?
Sends ascending sensory information to the brain via the spinal cord about how much force there is in the muscle
What are golgi tendon organs critical for?
Proprioception
How do golgi tendon organs act under conditions of extreme tension?
Act to inhibit muscle fibres (via a circuit in the spinal cord) to prevent damage
What do muscle spindles sense?
The length of muscles, i.e. the amount of stretch
What are reflexes critical for?
The avoidance of injury and effective motor control
What would happen if intrafusal muscle fibre was controlled by the same motor neurones as extrafusal muscle fibre?
When muscle is slack (or taught), the system won’t be sensitive to slight changes
What are intrafusal fibres innervated by?
Gamma motor neurons
What is the function of gamma motor neurones?
Keep the intrafusal fibres set at a length that optimises muscle stretch detection
What is reciprocal innervation of antagonistic muscle?
Explains why the contraction of one muscle induces the relaxation of the other
What is the basal ganglia?
A group of structures beneath the cortex that act as a ‘gate-keeper’ for control of the motor system (muscles)
What are the 5 principle nuclei that make up the basal ganglia?
Substantia nigra
Caudate
Putamen
Globus Pallidus
Subthalamic nucleus
