Motor cortex

Motor cortex
and
Descending pathways
D.A. Asir John Samuel, BSc (Psy), MPT (Neuro Paed),
MAc, DYScEd, C/BLS, FAGE
Lecturer, Alva’s college of Physiotherapy,
Moodbidri

Lobes of cerebral cortex

• Frontal lobe – in front of central sulcus or
fissure of Roland

• Parietal lobe – central sulcus/parieto-occipital
sulcus

• Occipital lobe – behind parieto-occipital cortex

• Temporal lobe – below lateral or sylvian fissure

Frontal lobe
• Broadmann’s Area 4 – precentral gyrus and is
Primary motor Area

• Supplementary motor Area – ant. to Areas 4 & 6

• Premotor Area (Area 6) – ant. to Area 4

• Broca’s Area (Area 44) – motor area for speech,
in post. part of frontal operculum in domi. H

• Frontal eye field (Area 8)

Broadmann’s Area 4
• Primary motor area

• Occupies posterior part of precentral gyrus
and ant.lip and walls of central sulcus

• Highest centre for voluntary movements

• Gives origin to fibres of pyramidal tract and
other descending tract

• Interconnected to Area 6 and sensory area

Broadmann’s Area representation
• Size of cortical area is proportional to
functional importance and activity of region

• Order of representation from medial to lateral
surface is toes, ankle, knee, hip, trunk,
shoulder, arm, elbow, wrist, hand, fingers,
thumb, eyes, face, jaw and tongue

• Motor homonuclus

Supplementary motor area

• Medial surface of hemisphere in front of area
4 and 6, in medial frontal gyrus

• Representation is head to foot anteroposterly

• Provides background for fine complex
movements from motor cortex

Area 6. Premotor area
• Anterior to area 4 and in medial aspect of H

• Planning and rehearsal takes place before
execution

• Gives fibres to pyramidal tract and basal
ganglia concerned with postural control

• Postural background for complex coordinated
movements

Frontal eye field (Area 8)

• Middle frontal gyrus

• Receives association fibres from occipital
cortex (Areas 18, 19)

• Projects of oculomotor nuclei

• Moving head and eyes towards the objects to
be seen

Layers of cerebral cortex

1. Molecular layer (Plexiform layer)

2. External granular layer

3. External pyramidal layer

4. Internal granular layer

5. Ganglionic layer (Internal pyramidal layer)

6. Multiform layer (layer of polymorphic cells)

Descending pathways
• Corticospinal (Pyramidal) and corticobulbar
tracts

• Vestibulospinal

• Reticulospinal

• Tectospinal

• Rubrospinal

• Olivospinal

Corticospinal tract

• Arise from axons of pyramidal cells situated in
5th layer of cerebral cortex

• Primary motor area – 30%

• Premotor area – 30%

• Postcentral gyrus (Parietal lobe) – 40%

Corticospinal tract
Descend in corona radiata and converge in
posterior limb of internal capsule

In midbrain, occupies middle 3/5 of basis
pedunculi (crus cerebri)

In pons, broken up into small no.of bundles

Corticospinal tract

In lower part of Pons, fibres reunite to form
compact bundle

Descends in ventral part of medulla forms

Prominent Pyramids of Medulla

Corticospinal tract
At junction of MO & SC, most fibres cross midline
at decussation of Pyramids

Form Lateral corticalspinal tract

Uncrossed – Anterior corticospinal tract

Terminates in anterior gray column, by internuncial

Corticospinal tract

• Speed and agility to voluntary movements

• Rapid skilled movements

• Upper motor neuron lesion

• Spasticty

Vestibulospinal tract

• Vestibular nuclei are situated in pons and MO
beneath floor of 4th ventricle`
• Neurons of lateral vestibular nucleus give rise
to axons that form VST
• Tract descends uncrossed though medulla and
through length of SC in ant.white column

Vestibulospinal tract

1. Ventral or anterior VST

2. Lateral VST

• Regulate muscle tone and equilibrium

• Facilitates activity of extensor muscles and
inhibit activity of flexor muscles

Reticulospinal tract

• Throughout midbrain, pons and MO, groups of
scattered nerve cells and nerve fibers exist
that are collectively known as reticular
formation

1. Pontine reticulospinal tract

2. Medullary reticulospinal tract


• From pons, neurons send axons, which are
mostly uncrossed, down into SC and form
pontine reticulospinal tract (medial RST)
• From medulla, which are crossed and
uncrossed, to SC and form medullary
reticulospinal tract (lateral RST)


• Reticulospinal fibres from pons descend
through ant.white column
• While from MO descend in lateral white
column
• Both sets enter AGC and may facilitate or
inhibit activity of α and β


• Influence voluntary movements and reflex
activity

• Provide a pathway by which hypothalamus
can control sympathetic outflow and sacral
parasympathetic outflow

Rubrospinal tract
• Arises from posterior 1/3rd or nucleous
magnocellularis of red nucleus in midbrain

• On leaving RN, fibres cross to opposite side in
tegmentum of midbrain as Forel’s decussation

• Descend through reticular formation of pons
and medulla to SC

Rubrospinal tract

• Lies anterior to lateral corticospinal tract

• Prominent upto mid thoracic region

• Receives impulses from cerebral cortex,
cerebellum and corpus striatum

• Part of lateral motor system

• Facilitates flexor muscle and inhibits ext./AG

Tectospinal tract

• Arise in superior colliculus of midbrain

• Cross over to opposite side in tegmentum as
Meynert’s decussation

• Descend through RF of pons and medulla

Tectospinal tract

• Superior colliculus
receives fibres from
retina
• Coordinate retinal
impulses with body
movements and reflex
postural movements

Olivospinal tract

• Arise in inferior olivary nucleus of medulla

• Descend in anterolateral part of white column

• Traced only as far as cervical region

Motor cortex

More Related Content

What's hot

Similar to Motor cortex

More from Asir John Samuel

Recently uploaded

Motor cortex