Control of movement- lipski 1 and 2 Flashcards
What are the three types of movement
Voluntary
Reflexes (somatic e.g. withdrawal reflex)
Rhythmic motor patterns (e.g. breathing)
What part of the brain controls voluntary movements
The forebrain
What parts control reflex movements and rhythmic motor patterns
The spinal cord and brainstem
What are the three parts of the brainstem
Midbrain, pons, medulla
Where are motor neurons located
Nuclei in the brainstem and in the anterior horn of the spinal cord
How do motor neurone that have their cell bodies in the brainstem communicate with the muscles
The motor neurons that have their cells bodies in the brain stem connect to their muscles through cranial nerves e.g. the vagus nerve, and oculomotor nerve.
What are the types of motoneurons
Alpha and gamma
What are the main kind of fibres in our skeletal muscle
Extrafusal muscle. These fibres generate tension (force) by contracting.
What kind of motoneurons innervate extrafusal muscle fibers
Alpha motorneurons
What do gamma motorneurons innervate
Intrafusal muscle fibres
What are intrafusal muscle fibres
Muscle fibres that lie within muscle spindles. There are multiple spindles within muscles and they sense changes in the length etc of the muscle.
What is the role of gamma motoneurons
They innervate intrafusal muscle fibres. When the neuron is activated the muscles spindles have an increased response to stretch. Increasing contraction of muscle
What is the motor unit
The anatomical and functional unit of the muscle system (neuron plus all the muscle fibres it innervates)
How many muscle fibers can one MN innervate
5-2000
What are the two classifications of motor units
Type 1 / S type (slow)
Type 2b/ FF type (fast, fatigable)
Type 2a is intermediate (mix of two types)
What are the 4 most important differences in S and FF type motor units and how do S types better
Metabolism- S oxidative, FF glycolytic
Twitch time S- long, FF-short
Size- S- small, FF large
Power S weak, FF powerful
But there are many S types and they don’t fatigue or fatigue slowly.
How does recruitment of the different motor units occur
Using the size principle. S type are recruited first- i.e. the are recruited during relatively weak contractions. FF type units are recruited only at relatively high force
What do we need to do to prevent FF type atophy
Exercise!
What are the two mechanisms that control force in muscle contraction
The frequency of AP, recruitment of additional motor units
What are the main receptors which control movement
Muscle spindles (monitor muscle length and speed of length change) Golgi tendon organs (monitor muscle tension) Pain receptors in the skin Joint receptors (monitor position and if hyperextension or flexion is occurring)
What are the five elements of a spinal reflex
Receptors Afferent (sensory) fibers Central synaptic relay Efferent (motor) fibers Effectors (skeletal muscles)
What are the fastest conducting nerve fibres in our body
Type 1a afferents
Describe the pathway of the stretch reflex
Receptors located in the muscle spindle detect changes in length of muscle and the speed of length change, transmit via type 1a afferents whose cell body lies in the dorsal root ganglion, synapses with alpha motoneuron in the ventral horn of the spinal cord, transmits via axon of alpha motoneuron to effectors, extrafusal muscle fibres.
Where are cell bodies of sensory (afferent) nerve cells found
In the dorsal root ganglion.
Describe the second pathway or additional synaptic relay in stretch reflexes
1a afferent fiber transmits to an interneuron (as well as excitatory alpha mn) which inhibits other motoneurons from innervating the antagonist muscle. E.g. prevents triceps from firing if you are trying to activate a biceps reflex.
What fibers are involved in the inverse myototic reflex and what is it
The golgi tendon organ reflex. Stop muscles from being overstretched. Fibres are 1b afferents which synapse with 1b interneurons who synapse with alpha motoneurons.
What fibres are involved in reciprocal inhibition
1a sensory afferents have slips to 1a inhibitory interneurons which inhibit alpha motoneurons that supply the muscle that has the opposite action to the one required in the stretch reflex.
What fibres are involved in the stretch reflex
1a afferents that are in muscle spindles synapse with alpha motoneurons in the ventral horn of the spinal cord the alpha motoneurons innervate extrafusal muscle fibres
What fibres are involved in the withdrawal reflex
Type III and IV afferent fibers relay nociceptive stimuli to excitatory interneurons that synapse with alpha motoneurons that innervate extrafusal fibres that are in flexor muscles in the flexor or withdrawl reflex.
Where are cell bodies of afferent nerve fibres found
In the dorsal root ganglion
