motor 1: pyramidal system

Question 1

1. Anatomy and function of the cerebral motor cortex (= frontal lobe)

Answer 1

• primary motor cortex (M1)
• supplementary motor cortex (SMC) - Premotor cortex (PMC)
• Prefrontal cortex (PFC)

Question 2

Descending motor tracts

Answer 2

that originate from the cerebral motor cortex and target the spinal cord (corticospinal tract) and brainstem

Question 3

somatic motor system: alpha-motor neurons of the spinal cord receive input from three major sources

Answer 3

1. Pyramidal tract (motor neurons of cerebral cortex) & extrapyramidal tracts (brainstem motor nuclei)
2. Muscle sensory (proprioceptive) systems (muscle spindles & Golgi tendon bodies)
3. Spinal interneurons (part of spinal circuitry)
   * alpha-motor neurons convey this information to skeletal muscles to initiate movement

Question 4

upper motoneurons (UMN; 1st order motor neurons)

Answer 4

• 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

Question 5

lower motoneurons (LMN; 2nd order motor neurons)

Answer 5

• 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

Question 6

Body Movements - by skeletal muscles

Answer 6

is achieved by a combination of voluntary & involuntary (reflex) actions
- skeletal muscles are responsible for voluntary movement and are under conscious (= cortical) control

Question 7

CEREBRAL MOTOR CORTEX:

Answer 7

• is the highest center for control of voluntary movements

- controls skeletal muscles through the pyramidal pathways

Question 8

skeletal muscles, other influences

Answer 8

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)

Question 9

Examples of (protective) reflexes at the spinal cord level

Answer 9

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

Question 10

Descending pathways: Pyramidal system

Answer 10

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

Question 11

Descending pathways: Extrapyramidal system

Answer 11

(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

Question 12

Summary of the motor systems of the brain & spinal cord

Answer 12

1. Cerebral motor cortices & descending pathway 1.1 pyramidal tract
2. Brainstem motor nuclei & descending pathway 2.1 extrapyramidal tract
3. Ventral horn of the spinal cord 4. Basal ganglia loop
4. Cerebellar loop

Question 13

Motor cortex and pyramidal tract;

Answer 13

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

Question 14

EXTRAPYRAMIDAL TRACTS - For unconscious movements (supraspinal reflexes)

Answer 14

1. Tectospinal tract
2. Rubrospinal tract
3. Reticulospinal tract
4. Vestibulospinal tract
   re involved in supraspinal reflexes (unconscious = non-cortical) movements

Question 15

Basal gangliacerebellum

Answer 15

• 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

Question 16

cerebellum

Answer 16

prefrontal cortex > pons > cerebellum> thalamus > premotor cortex > primary somatomotor cortex > brainstem then or directly to spinal cord > skeletal muscle

Question 17

The motor cortex – cerebral cortex

Answer 17

§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)

Question 18

Motor areas of the FRONTAL LOBE (medial view)

Answer 18

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

Question 19

Functional fields of cortical areas of the FRONTAL LOBE (lateral view)

Answer 19

§ Premotor cortex: is located just rostral to precentral sulcus; only on LATERAL SURFACE of hemispheres

Question 20

The prefrontal cortex (PFC) anatomy

Answer 20

• 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

Question 21

The prefrontal cortex (PFC) functions

Answer 21

• 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)

Question 22

Supplementary motor cortex (SMC) anatomy

Answer 22

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

Question 23

Supplementary motor cortex (SMC) function

Answer 23

• 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