Physiology 2.3: Motor systems part 1

what are the 3 classes of motor movements

• reflexes

• voluntary

• rhythmic motor patterns

describe reflexes

• simple

• involuntary

• rapid

• ex: sneezing, knee-jerk, flexor withdrawal

describe voluntary movements

• goal-directed and purposeful

• initiated based on response to external stimuli or will

• learned and improved with practice

• ex: playing piano, writing, etc

describe rhythmic motor patterns

• starting and stopping is voluntary

• sequence of stereotype, repetitive movements formed in reflex manner

• ex: walking, running

what does it mean for motor behaviors existing on the voluntary ←→ involuntary continuum

• almost all motor behaviors have voluntary and involuntary components

  • reflexes can be consciously modified or overridden

  • learning can be previously consciously directed behaviors automatic (almost reflexive)

what are the basic tasks of the motor system

• muscle contraction and relaxation

• precision and timing

  • timed commands to several different muscles and joints

• postural adjustments

  • preparation of movement

• dynamic feedback

  • continuously modify motor commands during active movement for real-time changes

what are the two core features that allow for the motor system to perform

• continuous sensory feedback

  • sensory information on body and surrounding environment

• hierarchical organization

  • motor system is structured as clear hierarchy with different responsibilities

    • sensory integration

    • lower levels (reflexes)

      • autonomic movement

    • higher levels (strategy)

      • dynamic voluntary movement

describe this

• motor control hierarchy

describe the higher levels of the motor hierarchy

• creates general intention to move

• includes areas involved in memory and emotion/motivation

• communicates with middle level of hierarchy with command neurons

describe the middle level of motor hierarchy

• specifies posture and movements to execute intended action

  • sensory information and command signals from higher order generates motor programs to achieve movement

what is the motor program generated by middle level

• sequence of muscle contractions needed to achieve the movement

what are the components of the middle level of motor hierarchy

• consists of

  • sensorimotor cortex

  • cerebellum

  • subcortical and brainstem nuclei

describe interneurons in the motor program transmission pathway

• synapses on interneurons can be inhibitory or excitatory

  • higher centers can use interneurons to turn movement on or off

• allows override of spinal reflexes

what percent of spinal cord neurons are interneurons

• 90%

what are the final pathways in motor functions

• motor neurons

describe motor neurons

• innervate skeletal muscles

• action potential leads to muscle contraction

what is a motor nucleus

• a group of motor neurons that innervate a particular group of muscles

where are the cell bodies of somatic motor neurons

• ventral horn of spinal cord

what is this

medial motor nucleus

what is this

lateral motor nucleus

describe the medial motor nuclei

controls axial muscles concerned with posture and balance

describe the lateral motor nuclei

• found in only cervical and lumbar enlargements

  • control muscles of arms and legs

describe the reflex arc

• sensory neuron in PNS → interneuron in CNS → motor neuron in PNS affecting target cell

describe the muscle spindle

• specialized sensory receptors inside skeletal muscles that detect changes in muscle length

  • encapsulated

  • parallel to regular muscle cells

how do muscle spindles work in myotatic reflex

• when stretched

  • afferent neuron fires more action potentials to contract

    • prevent overstretching (injury)

• when contracted

  • afferent neurons fires less action potentials to prevent over-contraction (injury)

what are the two muscle pairings

• agonist

  • opens joints

    • extensor

• antagonist

  • closes joints

    • flexor

what is reciprocal innervation

• coordination of opposing muscles so that when one contracts, the other relaxes

breakdown how the stretch reflex works for postural adjustment

• automatically corrects body’s posture for balance

• path A

  • when muscle stretches, stretch receptor activated and afferent neuron branch fires more rapidly

  • motor neuron excited

    • contraction of agonist

• path B

  • another afferent branch activates inhibitory interneuron that inhibits of motor neurons that go to antagonist

    • relaxation of antagonist

describe how the patellar reflex is an example of the stretch reflex

• physician stretches the patellar ligament

  • quadriceps muscles are stretched

    • path A

      • afferent neuron fires AP in agonist quadricep muscle to contract it

    • path B

      • afferent neuron inhibits AP in antagonist hamstring muscle to relax it

what are the 3rd and 4th branches of the myotatic reflex arc

• 3rd branch

  • activates synergistic muscles to assist agonist muscle

• 4th branch

  • up to brain to carry information about adjustment

what is the golgi tendon reflex

• specialized sensory receptor inside tendons to detect muscle force

  • prevents muscles from tearing under tension

    • adjusts muscle contraction

describe the mechanism of the golgi tendon organ

• if contraction too high

  • sensory neurons on GTO fires frequent signals

    • SC tells muscle to relax to prevent injury

• if too relaxed

  • sensory neurons fires less signals

what is the inverse stretch reflex

• over-contraction of the muscle and the correction of it via golgi tendon organs

what is the stretch reflex

• over-relaxation of the muscle and the correction of it via muscle spindles

differentiate which protective mechanisms are used in over-stretching and over-contraction

• overstretching

  • muscle spindles: detect muscle length

    • contract agonist

    • relax antagonist

• over contraction

  • golgi tendon organ: detect muscle force

    • relax muscle to prevent excessive force

describe path A and B of golgi tendon organ (inverse myotatic reflex)

• muscle is over-contracted

  • sensory receptors in golgi tendon organfire rapidly

    • inhibition of motor neuron to contracted agonist muscle

      • relaxation

    • excitation of motor neuron antagonist muscle

      • contract

describe flexor withdrawl reflect

• contact with painful stimuli causes…

  • flexor muscles to contract (pull away

  • inhibit extensor muscles

describe crossed extensor reflex

• injured

  • contraction of flexor muscles

• uninjured leg

  • contraction of extensor muscles

Briefly explain the importance of the spinal and supraspinal postural reflexes to voluntary movement.

Spinal and supraspinal postural reflexes provide the stable foundation and background muscle tone necessary for voluntary movements to occur smoothly and accurately.

• coordinated actions and balance