CNS mechanisms of motor control

central nervous system (CNS)

includes brain and spinal cord

peripheral nervous system (PNS)

• located throughout body

• sensory and motor division

• both somatic sensory and somatic motor divisions contribute to motor control

sensory division

• includes somatic and visceral subdivisions

• somatic receptors: found in skin, muscles, and joints

• visceral receptors: internal receptors that monitor physiological processes

motor division

• includes somatic and visceral subdivisions

• somatic division: controls skeletal muscle

• autonomic subdivision: regulates smooth muscle and glands

CNS and motor control

• motor control involves planning, initiating, monitoring, and regulating motor skills

Planning

• gathers and processes sensory info and integrates it w prior knowledge to perform action selection and action specification

• action selection: deciding what action (motor skill) to execute

• action specification: formulating how to execute action (motor skill)

Initiation

• transforms motor plans to motor commands used by motor neurons

• motor plans: specify limb and body movements in spatial coordinates

• motor commands: specify muscle activations used to execute movements

monitoring

gathers sensory info related to movement outcomes

regulation

modifies ongoing movements to prevent and correct errors

CNS

brain and spinal cord

brain

• grossly divided into cerebrum, diencephalon, cerebellum, and brainstem

brain regions

area in each division that are anatomically and functionally distinct

brain networks

• groups of brain regions that interact to perform functions

• many networks include regions within all 4 divisions of brain

• networks of regions perform functions that contribute to planning, initiating, monitoring, and regulating motor skills

cerebrum

• includes ext cortex and subcortical basal ganglia

  • cortex divided into 4 lobes that show functional specialization: frontal, parietal, temporal, occipital

  • all regions of cortex contribute to networks that mediate planning, initiation, monitoring, and/or regulation of motor skills

frontal lobe

motor, speech, cognitive functions

parietal lobe

somatosensory and visuospatial functions

temporal lobe

language, auditory, and visual functions

occipital lobe

visual functions

sensorimotor cortex

• includes primary motor and primary somatosensory cortex

• form gross topographic maps of body illustrated by homunculus

primary motor and somatosensory cortex

• form highly interconnected network

• motor cortex receives extensive input from somatosensory cortex

• somatosensory cortex receives extensive info from motor cortex

• illustrates important of networks in processing info

basal ganglia

• subcortical nuclei in cerebrum compose of five nuclei: caudate, putamen, globus pallidus, substantia nigra, and subthalamic nucleus

• nuclei participate in networks involved in planning and initiating motor skills

• highly interconnected with cortex and thalamus (cortex directly projects to BG and BG projects to cortex via thalamus)

Basal ganglia disorders

• commonly affect motor control

• parkinsons, tourettes, huntingtons

diencephalon

• subcortical area that includes thalamus and hypothalamus

thalamus

• filters and relays info to cortex from spinal cord, brainstem, cerebellum and BG

  • participates in networks involved in planning, monitoring, and regulating motor skills

hypothalamus

• contributes to planning and initiation of fight or flight actions

  • part of limbic system which regulates motivation, emotion, and memory

cerebellum

• performs monitoring and regulation of motor skills

• fine tunes intermuscular coordination involved in timing, precision, and coordination of movements

  • uses cortical input and sensory feedback to regulate movements

brainstem

• divided into midbrain, pons, and medulla oblongata

• motor nuclei: neuromuscular control of eye (II, IV, VI), face (VII) and tongue (XII) movements

• several brainstem regions contribute to initiation, monitoring, and regulating subconscious movements (muscle tone, posture, balance)

sensorimotor integration

many brainstem regions integrate sensory input with sensory and motor info from other brain regions

spinal cord

• contributes to initiating, monitoring, and regulating motor skills

  • motor neurons and interneurons

motor neurons

transmit motor commands from spinal cord to muscles

interneurons

mediate multisensory and sensorimotor integration

local sensorimotor integration of spinal cord

integration initiates reflexes involved in posture and balance

global sensorimotor integration of spinal cord

• combines local sensory info w descending info from brain

  • involved in initiating, monitoring, and regulating motor skills

corticospinal tract

• main tract from cortex to spinal cord

  • commonly called pyramidal tract

pyramidal decussation

• found in caudal brainstem

• around 90% of corticospinal axons cross and descend in contralateral spinal cord

• around 10% of corticospinal axons remain uncrossed and descend in ipsilateral spinal cord

  • most corticospinal axons synapse onto spinal interneurons (very few directly synapse onto spinal motor neurons)

decussation

locations where axons crossover to opposite side of brain or spinal cord

dorsal column and spinothalamic tract

two major tracts project from spinal cord to cortex

dorsal column tract

• transmits info related to fine touch and proprioception

• axons ascend in ipsilateral spinal cord and decussate in caudal brainstem

spinothalamic tract

• transmits info related to pain and temp

  • axons immediately decussate and ascend in contralateral spinal cord

somatosensory cortex

• recieves info from dorsal column and spinothalamic tracts

  • processes sensory info obtained from contralateral side of body