Physiology of motor control (unit 1)

what are the 2 forms of signal processing

- hierarchical processing

- parallel distributed processing

- these both occur within the CAP system of movement control

what is hierarchical signaling processing

- within ascending levels of the CNS

- higher brain centers integrate and interpret afferent information = perceptual

- higher brain cents from motor plans and strategies for action = action

what is parallel distributed processing

- when the same information is processed by different brain regions (DCML vs spinocerebellar)

- cerebellum and basal ganglia process information simultaneously before sending information to the cortex for action

spinal cord

- lowest level of perception /action hierarchy

- initial reception and processing of somatosensory (dcml and spinothalamic)

- "final common pathway" ie the last level activated prior to muscle activation

brainstem

- nuceli for postural control and locomotion (vestibular, red nucelus, reticular nuceli)

- ascending and descending tracts sending info to other parts of the CNS

> all descending tracts start here, aside from the corticospinal tract

reticular formation

- arousal and awareness

cerebellum

- receives incoming information from spinal cord provides info to cerebral cortex for planning movements (direct output to brainstem via peduncles)

thalamus

- central processing center for afferent information

- major processing center of brain (dcml and anterolateral ascending tract info goes through thalamus) (receives info from other areas of the brain: basal ganglia and cerebellum)

- lesions in the thalamus will cause severe sensory and motor problems

basal ganglia

- planning motor of motor strategies with input from most areas of cerebral cortex

- sends info to motor cortex via the thalamus

cortex

- highest level of motor control hierarchy

- parietal and premotor areas identify targets in space --> select correct program

- motor cortex --> sends commands to brainstem and spinal cord

what are alpha motor neurons

the neurons that stimulate muscles to contract

what do interneurons make up

the majority of the CNS

what are association, commissural and projection fibers

they carry info in and out and around the CNS

what are sensory receptors

- synapse on interneurons, motor neurons, and ascend to the thalamus or cerebellum

- modulate movement

> stimulate reflexive movement

> movement itself can then stimulate activity of the CPGs/stepping pattern generators (leads to refinement of movement)

> modulation of movement can also originate from central commands (brain)

what is part of intrafusal muscle fibers

- nuclear bag = static, dynamic (nuclei in the center of the noncontractile region)

- nucelar chain = static (single row of nuclei, stretches slowly)

what are group 1a and II afferent neurons

- cell bodies found in the dorsal root ganglion of the spinal cord

- 1a = sensitive to rate of stretch/change and dynamic muscle length

- II are mostly responsive to steady state or static muscle length

- The Ia afferents go to the equatorial region of both the nuclear bag and nuclear chain fibers.

what are gamma motor neurons

maintain sensitivity to stretch

what are golgi tendon organs

- located in the muscle/tendon junction and synapse at the spinal cord with 1b afferents

- sensitive to tension changes resulting from stretch or contraction

what are joint receptors

provide a danger signal about extreme joint motion and facilitate our perception of body in space

what are cutaneous receptors

- mechano, themo, noci, are all lower level receptors in the CNS hierarchy

somatosensation at the SC levels

- Information from the cutaneous, muscle, and joint receptors modifies the output of circuits at the spinal cord level for basic activities, such as locomotion

- Complex movements like locomotion can be generated at the SC without supraspinal influences or inputs from the peripherally

- The addition of accurate sensory information can modulate these movements (refining and improving movements)

ascending pathways

- 2 parallel systems

- dcml

- anterolateral system

- both send different info to the brain, with some overlap

- parallel systems introduce redundancy and enhanced perception due to the multiple modes of processing

DCML

- sends info on cutaneous, muscle, tendon, and joint sensibility up to the somatosensory cortex and other higher brain centers

- includes (proprioception, touch, pressure, discriminative fine touch, vibration)

the anterolateral system consists of:

- spinothalamic

- spinoreticular (synapse in reticular formation so they impact arousal and attention)

- spinomesencephalic (nociceptive -> superior colliculus (eyes/head toward pain))

- carries info on: crude touch and pressure (contribute (minor) to limb proception)

- thermal and nociception (major role)

somatosensory cortex

- major processing area for all the somatosensory modalities (marks the beginning of conscious awareness of somatosensation)

what are the 2 areas of the somatosensory cortex

- primary somatosensory cortex

> broadmans area 1,2, 3a, and 3b

> kinesthetic and touch (contralateral)

- secondary somatosensory cortex

> receives input from SII

> cross modality processing: integration of afferent information

what is the visual system

- identify objects in space to determine required motor action

- improves our knowledge of where we are in space, relation of body parts, motion and oreintation

what is the vestibular system

- two primary senses

> head position in space

> sudden movement of the head

- drastically impacts stabilization of our eyes to facilitate postural stability during standing and walking

what is the motor cortex

- betz cells, or UMN (descending, efferent pathway)

> layer 5 of cortex (cortical spinal tract)

- cortical spinal tract

> contralateral control: roughly 88% decussate prior to the spinal cord

> provide precise movement of distal limbs

> less precise movement of proximal muscles and trunk

SMA and premotor areas project onto?

the motor cortex and spinal cord

SMA

- controls movements that are initiated internally

- activates motor programs for learned sequences

premotor areas

- controls movements activated by external stimuli

- involved in associated learning

higher level association areas

- integrate sensory info (layer 4 of cortex) and select appropriate motor response

- heavy involvement of the prefrontal cortex

- attentional networks (important for our ability to perceive sensory stimuli)

how is the cerebellum important

- important for coordination of movement

- has its own afferent tracts directly to the cerebellum

- receives afferents information from almost every sensory system

what does the cerebellum not directly synapse with

- alpha motor neurons

- impacts movement primarily through associated areas and the basal ganglia

- compares planned action with ongoing action and compensates for "error"

- intended movement vs actual/current movement

- impaired cerebellum usually involved in impaired targeting

what are the non motor functions of the cerebellum

- higher level cognitive processing

- timing production and perception

- long term modification of motor responses

what is the basal ganglia

- set of nuclei at base of cerebral cortex

- striatum (putamen + caudate nucelus)

- lentiform nucleus (globus pallidus (internus, externus) +putamen

- subthalamic nucleus

- substania nigra

- primarily inhibits (primarily uses disinhibition)

- works with cerebellum for coordinated movement

- preperation for and execution of movement

mesencephalon and brainstem

- mediate many aspects of motor control as part of the descending systems

- generate locomotor rhythms

- regulate postural tone

- integrate afferent info for posture and balance

- contribute to anticipatory postural control