The sensorimotor system Flashcards
Types of motor control
Voluntary- running, walking, talking
Goal directed- conscious, explicit, controlled
Habit- unconscious, implicit, automatic
Involuntary- eye movements, facial expressions, tongue, digestion
Control architecture
Pain- spinal corn registers this- makes us escape that situation
Looming threat- sensorimotor midbrain processes sensory information - makes us avoid a bad situation
Learned threat- uses the cortex + limbic system- avoid that situation
Muscles
Antagonistic arrangement- muscles are arranged in ways that oppose each other e.g. triceps and biceps- word in a coordinated fashion to give a precise movement
Recruitment of muscle fibres
Myosin cross-bridge cycle
Myosin head has a neck- attaches to the actin filament and bends it neck and pushes it, then it disconnects and attaches again- this is muscle movement.
Acetylcholine (ATP) is required to break the bond between the myosin head and the actin filament.
Rigor mortis occurs when there is no more ATP is there to break the bond- cant move muscles
Motor unit
A single alpha motor neuron + all the muscle fibres that it innervates
Different motor neurones innervate different numbers of muscle fibres
Fewer fibres means greater movement resolution- those innervating finger tips and tongue
Fast and slow muscle fibres
Slow- muscles used to sit up for hours
Fast fatigue resistant- walking/running- can do for quite a while- takes longer to tire out
Fast fatigueable- short term explosive releases of force
The motor pool
All the lower motor neurone that innervate a single muscle
Sensing in muscles
Muscles can be contracted or relaxed to provide movement, but a good control system (CNS) needs to know two things
- How much tension is on the muscle- Golgi tendon organs
- What is the length (stretch of the muscle)- muscle spindles
Golgi tendon organs
Within the tendon- where the muscles joins to bone
Mostly sends ascending sensory information to the brain via the spinal cord about how much force there is on the muscle
When there is extreme tension it is possible that GTOs act to inhibit muscle fibres to prevent damage
Muscle spindles
Sense the length of muscles- the amount of stretch
When you hit a reflex point (knee cap) you pull the muscle fibres along the muscle and stretch them out- the muscle is contacting as a result of the stretch to return the leg to what it thinks it should be
Intrafusal muscle fibres
Sensory part of the muscle- contains the muscle spindles
Detects when the muscle has been lengthened
Innervated separately to extrafusal fibres- gamma motor neurone
They make sure that the intrafusal fibres are kept at a length that can detect stretch
Reciprocal innervation
Explains why the contraction of one muscle induces the relaxation of the other
Permits the execution of smooth movements
Vestibular righting reflex
Vestibular system detects that the body is not upright, as well as any acceleration due to gravity (falling)
Information from the vestibular system is combines with visual, somatosensory and proprioceptive sensory input in order to specify a pattern of motor activity that will restore ‘uprightness’ and a safe landing
The cerebellum is essential for computing what to do in this situation
Cortical motor areas
Motors command originated in motor cortex pyramidal cells
Pyramidal cells axon can project directly or indirectly to spinal cord and onto lower brain stem motor neurone. These axons form the pyramidal tract
Most cortical projections innervate contra lateral motor units- opposite side of the body
Upper and lower motor neurons
Upper motor neurons start in the cortex and projects down to the spinal cord
Lower motor neurons pick up the signal from the spinal cord and sends it to the muscles and activates the muscle fibres
