motor 1: pyramidal system Flashcards
- Anatomy and function of the cerebral motor cortex (= frontal lobe)
- primary motor cortex (M1)
- supplementary motor cortex (SMC) - Premotor cortex (PMC)
- Prefrontal cortex (PFC)
Descending motor tracts
that originate from the cerebral motor cortex and target the spinal cord (corticospinal tract) and brainstem
somatic motor system: alpha-motor neurons of the spinal cord receive input from three major sources
- Pyramidal tract (motor neurons of cerebral cortex) & extrapyramidal tracts (brainstem motor nuclei)
- Muscle sensory (proprioceptive) systems (muscle spindles & Golgi tendon bodies)
- Spinal interneurons (part of spinal circuitry)
* alpha-motor neurons convey this information to skeletal muscles to initiate movement
upper motoneurons (UMN; 1st order motor neurons)
- cortical motoneurons of the motor cortex (pyramidal tract)
- motoneurons of the brainstem nuclei (red nucleus, tectum, reticular formation and vestibular nuclei)
- upper motor neurons always remain within the CNS and Don’t enter PNS
lower motoneurons (LMN; 2nd order motor neurons)
- alpha and gm-motoneurons of the spinal anterior horn
- motor neurons of cranial nerves in the brainstem
- cell bodies of lower motor neurons LMNs are located in the CNS, whereas their axons are located in the PNS to target skeletal muscles that they innervate
Body Movements - by skeletal muscles
is achieved by a combination of voluntary & involuntary (reflex) actions
- skeletal muscles are responsible for voluntary movement and are under conscious (= cortical) control
CEREBRAL MOTOR CORTEX:
- is the highest center for control of voluntary movements
- controls skeletal muscles through the pyramidal pathways
skeletal muscles, other influences
however, are also directly influenced by “unconscious” CNS centers, i.e. motor neurons of the spinal cord & brainstem:
- this leads to involuntary contraction or movement of skeletal muscles (= Reflex movement) - reflexes induced by motor neurons of the:
1. spinal cord are called spinal reflexes
2. brainstem are called supraspinal reflexes (extrapyramidal tracts)
Examples of (protective) reflexes at the spinal cord level
stretch - monosynaptic
withdrawel - polysynaptic
§The spinal cord is involved in spinal reflex actions, both somatic and visceral
§Spinal reflexes are fastest movement responses to external or internal stimuli
§Spinal reflexes are unlearned (innate) & produce predictable [stereotyped, simple patterned] movements
Descending pathways: Pyramidal system
from cerebral cortex: - corticospinal tract
- cortico[bulbar]nuclear tract (from cortex)
For conscious (voluntary) movements!
Descending motor tract that travels through the medullary pyramids is called the pyramidal tract
Descending pathways: Extrapyramidal system
(from brainstem):
- tectospinal tract (originates from tectum)
- rubrospinal tract (originates from red nucleus)
- reticulospinal tract (originates from reticular formation) - vestibulospinal tract (originates from vestibular nuclei)
For supraspinal reflex (unconscious ) movements
* Descending motor tract don’t that travels through the medullary pyramids is called the pyramidal tract
Summary of the motor systems of the brain & spinal cord
- Cerebral motor cortices & descending pathway 1.1 pyramidal tract
- Brainstem motor nuclei & descending pathway 2.1 extrapyramidal tract
- Ventral horn of the spinal cord 4. Basal ganglia loop
- Cerebellar loop
Motor cortex and pyramidal tract;
Prefrontal cortex (highest order association cortex) > SMC - Supplementary Motor Cortex /PMC=PreMotor Cortex > Primary somatomotor cortex (M1) > pyramidal pathway (for conscious movement)
> SPINAL CORD (via coticospinal tract) > Somatomotor output/skeletal muscles of body
or to brainstem via coticonuclear tract > skeletal muscle 2 head
EXTRAPYRAMIDAL TRACTS - For unconscious movements (supraspinal reflexes)
- Tectospinal tract
- Rubrospinal tract
- Reticulospinal tract
- Vestibulospinal tract
re involved in supraspinal reflexes (unconscious = non-cortical) movements
Basal gangliacerebellum
- nuclei do not have direct connections with the spinal cord (input or output)
- Basal ganglia indirectly modulate the information contained in pyramidal & extrapyramidal pathways
prefrontal cortex > basal ganglia > thalamus > supplementary motor cortex > primary somatomotor cortex > brainstem then or directly to spinal cord
cerebellum
prefrontal cortex > pons > cerebellum> thalamus > premotor cortex > primary somatomotor cortex > brainstem then or directly to spinal cord > skeletal muscle
The motor cortex – cerebral cortex
§is the highest center for voluntary (conscious) movement
§is located in the frontal lobe
§can be divided into:
1. Prefrontal cortex (HIGHEST ORDER motor cortex = for strategy)
2. Premotor cortex (area) &
3. Supplementary motor cortex (area)
4. primary motor cortex (LOWEST ORDER motor cortex = for execution)
Motor areas of the FRONTAL LOBE (medial view)
Primary motor cortex (area): is located in the precentral gyrus, which is the most caudal part of the frontal lobe, just rostral to the central sulcus
§ Supplementary motor cortex (area): is located just rostral to the precentral sulcus, but mostly on MEDIAL ASPECT of the hemispheres
§ Prefrontal cortex (area): is located in frontal pole and most rostral part of the frontal lobe; makes up more than half of the frontal lobe
Functional fields of cortical areas of the FRONTAL LOBE (lateral view)
§ Premotor cortex: is located just rostral to precentral sulcus; only on LATERAL SURFACE of hemispheres
The prefrontal cortex (PFC) anatomy
- Is located in the frontal pole and encompasses most of the rostral cortical part of the frontal lobe
- most cortical part of the frontal lobe is occupied by prefrontal cortex (humans have the biggest)
- towards posterior, it has no clear anatomical boundaries with premotor & supplementary cortices
- is the highest order association cortex of the frontal lobe & the highest level of all cerebral cortices - maintains contact with all sensory cortices, other cortical areas, and subcortical structures
The prefrontal cortex (PFC) functions
- Lateral PFC: rational thinking, plans and solves problems
- Orbital PFC: controls emotional behavior (anticipates behavioural response when planning an action) - Medial PFC: helps to sustain attention, detects errors in own social misconduct (social self-awareness)
Supplementary motor cortex (SMC) anatomy
prefrontal cortex > supplementary motor cortex > primary motor cortex
- is located anterior to precentral sulcus, mostly on MEDIAL SURFACE of the hemispheres
- dorsolaterally, it is located on the superior frontal lobe, just superior (dorsal) to premotor cortex - is a middle-order association cortex (similar to premotor cortex)
- contributes to pyramidal pathway
Supplementary motor cortex (SMC) function
- contributes to learning sequence of movements, and bilateral coordination (especially upper limbs)
- stores skilled (know-how) memory; contributes to mental rehearsal of movement
- Initiates movements specified by internal cues (self-generated) rather than by externally delivered cues - works more closely with the basal ganglia
