Primary motor cortex Domina Petric, MD

Upper motor neurons (descending systems): Basal ganglia: gating proper initiation of movement Upper motor neurons (descending systems): Motor cortex (planing, initiating and directing voluntary movements) Brainstem centers (basic movements and postural control) Cerebellum: sensory motor coordination and ongoing movement Local circuit neurons: lower motor neuron integration Motor neuron pools: lower motor neurons Sensory inputs Sceletal muscles

Motor cortex It is concerned with encoding the movement intention. Motor cortex includes precentral gyrus and posterior parts of superior, middle and inferior frontal gyri. Motor cortex is mostly concerned with voluntary movements, but it is also related to behaviors that are concerned with expression of emotions. So, the motor cortex is also concerned with non-verbal communication (facial gestures, body posture). Brainstem motor centers are concerned with adjustment of posture, with setting the gain of segmental reflexes and it is important for expressing the skill.

Somatotopic organisation of the ventral horn www.studyblue.com

Spinal cord Lateral corticospinal tract provides axons that are mostly concerned with governing the control of distal extremity muscles. Axons in the lateral white matter come from motor cortex. Lateral corticospinal tract is associated primarily with skills. Axons in the ventral and medial white matter of the spinal cord come from the brainstem. These ventromedial spinal cord axons terminate in the medial parts of the ventral horn so these axons are concerned with governing the control of the proximal extremity muscles and posture. Ventromedial spinal cord white matter is mainly concerned with posture.

For contralateral limb! Upper motor neurons in brainstem Upper motor neurons in cerebral cortex Input is distributed to both sides of the spinal cord! Cross the midline! For contralateral limb! Anterior and medial white matter of the spinal cord Lateral white matter of spinal cord Lower motor neurons in medial ventral horn Lower motor neurons in lateral ventral horn Axial and proximal limb muscles: posture and balance Distal limb muscles: skilled movements

Volitional movement: descending pyramidal and extrapyramidal projections from motor cortex and brainstem Emotional expression: descending extrapyramidal projections from limbic centers of ventro-medial forebrain and hypothalamus Lateral: fine control of distal muscles of extremities Medial: posture and proximal muscles of extremities Medial: gain setting, rhythmical reflexes Lateral: specific emotional behaviors Corticobulbar pathway Pyramidal pathway Brainstem reticular formation Motor neuron pools Motor neurons of cranial nerve nuclei and ventral horn of the spinal cord Autonomic preganglionic neurons Muscle contraction and movement Activation of smooth muscles and glands

Motor cortex Motor cortex is divided into: Primary motor cortex includes the precentral gyrus and paracentral lobule. Premotor cortex includes posterior parts of the superior, middle and inferior frontal gyri. Thalamic nuclei that send inputs to the motor cortex are VENTRAL ANTERIOR THALAMIC NUCLEUS and VENTRAL LATERAL THALAMIC NUCLEUS (VA-VL COMPLEX OF THE THALAMUS).

Motor cortex Somatosensory cortex also sends inputs to the motor cortex, both primary motor cortex and premotor cortex. ˝Where˝ (magnocellular) visual pathway sends inputs to the premotor cortex.

Primary motor cortex (Brodmann´s area 4) Layer 5 in the primary motor cortex (Betz cells) gives rise to spinal cord and brainstem projections: corticospinal and corticobulbar tract. Primary motor cortex has the lowest treshold for the elicitation of movement and it is concerned with those movements that are primarily concerning our body and the space in front of the body.

Somatotopy of the precentral gyrus is rather fractured! BUT! Somatotopy of the precentral gyrus is rather fractured! Somatotopy http://brainconnection.brainhq.com

Fractured somatotopy There are overlapping representations in the precentral gyrus for flexor and extensor muscles. There are multiple representations of the same body region. There is no internal somatotopy in the region for arm in the precentral gyrus.

Fractured somatotopy Single corticospinal axon supplies multiple columns of lower motor neurons in ventral horn. Single spike in a corticospinal axon activates many different muscles in the forelimb.

Representations of the primary motor cortex movements (not muscles) or movement intentions multiple dimensions of movement (force, direction, amplitude) movements that engage hand, lower face and hand to mouth coordination skilled manual behavior in central personal space lesions impair fractionated (skilled) finger-facial movements

Literature https://www.coursera.org/learn/medical-neuroscience/lecture: Leonard E. White, PhD, Duke University www.studyblue.com http://brainconnection.brainhq.com