MOTOR FUNCTIONS

PRESETED BY

SRILOY MOHANTY

B.N.Y.S

MOTOR CORTEX

• Primary motor cortex ( M1)

• Premotor area (PMA)

• Supplementary motor area (SMA)

Note: All the three projects directly to the spinal cord via

corticospinal tract.

• Premotor and supplementary motor cortex also project to

primary motor cortex and is involved in coordinating &

planning complex sequences of movement (motor learning).

PRIMARY MOTOR CORTEX (M-I)

Location :-

Immediately anterior to the central sulcus and

extends to the medial surface of hemisphere

also known as Broadmann’s area 4 is a

motor homunculus.

Description: Body is represented as up side

down and stretched on the medial surface

where pelvic and leg muscles are

represented.

Hand and mouth has a greater area of

representation and is large because of

- It controls the musculature of the opposite side of the body.

-Face area is bilaterally represented.

Functions:-

Is used in execution of skilled movements also in codes the direction, force and velocity of movements.

Lesions:-

Pure M-I lesions are rare. May have contra lateral weakness in distal muscle (fingers).

Ability to control fine movements is gone.

Ablation of M-I alone cause hypotonia not Spasticity.

SUPPLEMENTARY MOTOR AREA (M-II)

Location: Found on both in lateral and medial aspect of the frontal

lobe. It extends from cingulate sulcus on the medial side to reach premotor cortex on the lateral surface of the brain.

Function:It works together with premotor cortex.Involved in programming of motor sequences. Lesions:

Produces awkwardness in performing complex activity like bimanual coordinated activity.

It function in mental rehearsal of movements before

performing a complex motor functions.

With premotor cortex it translates the desire to

perform a motor task into a series of motor

command that will do the task.

PREMOTOR CORTEX (PMC)

Location:

Broadmann’s area 6. It lies immediately anterior to primary

motor cortex. It is more extensive than primary motor

cortex (about 6 times)

Functions:

It works with the help of basal ganglia, thalamus, primary

motor cortex, posterior parietal cortex. It plays role in

planning and anticipation of a specific motor act.

Premotor cortex – Two-hand Coordination

THE MONKEY HAS LEARNED THE TASK

PUSH THE OBJECT THROUGH THE HOLE AND CATCH IT WITH THE OTHER HAND; With

damage to premotor cortex, cannot coordinate two hands to do the task

Lesion:

It results in re-emergence of suckling and grasp

reflex in adults.

Its lesion do not case paralysis but only slowing of

the complex limb movement.

Lesion may result in loss of short-term or working

memory.

When damaged with supplementary cortex it may

result in APRAXIA.

VOLUNTARY MOVEMENT: INSTRUCTIONS FROM CEREBRAL CORTEX

•Dorsolateral Prefrontal Cortex: directs movement of our limbs (as in reaching) and movements of our fingers.

•Actual signal for movement must go through pre-motor cortex, then motor cortex.

• From motor cortex, signal travels down spinal cord eventually reaching the alpha motor neuron.

• BUT, the instructions for this movement ultimately comes from our Parietal lobe, which receives sensory input.

CEREBELLUM• Vermis

• Intermediate zone

• Lateral zone

• Within are deep cerebellar nuclei:

• Fastigial nucleus

• Interpositus nucleus

• Dentate nucleus

VERMIS

Kinesthetic and

somatosensory inputs

from the spinal cord

projections to fastigial

nucleus

• Damage interrupts

posture and walking

• In monkeys, unilateral

lesions of the fastigial

nucleus cause the

monkeys to fall

(ipsilateral side)

INTERMEDIATE ZONE

• Inputs from red nucleus (brain stem & motor cortex) and somatosensory info from the spinal cord

• Projects to interpositus nucleus red nucleus (loop)

• Damage produces rigidity and difficulty in moving limbs

• Action tremor or intention tremor – a tremor causing movement to occur in a staggered manner during motor act.

LATERAL ZONE

• Inputs from motor and association cortices (through pons)

• Projections to dentate nucleus primary motor and premotor cortex

1. Balistic movement –movement that occurs so quickly that it can not be modified by feedback

• E.g., swinging of a batter trying to hit a ball moving 140 km/h

LATERAL ZONE

2. Multijoint movements

3. Learning of new movements

4. Timing of motor movements (and

cognitive functions)

BASAL GANGLIA• Unlike the cerebellum, which

plays a role in rapid balistic movements, the basal ganglia are more important for the accomplishment of movements that may take some time to initiate or stop

• Important for internal guiding (rather then external) of movement

• Dopamine – nigrostriatal pathway

BASAL GANGLIADamage to the basal ganglia:

• Produces either too much activation (hyperkinetic) responses= twitches, movements bursts, jarring, etc.

• Huntington’s Chorea-dominant gene based, increases glutamate in striatum which destroys GABA neurons in BG and loss of inhibition

• No cure

• Tourette’s

OR

• Produces too little force (hypokinetic)=rigidity

• Parkinson’s disease

Pink=inhibitionBlue=excitation

BRAIN STEM MOTOR CENTERS

• Pontine reticular nuclei – excite antigravity

muscles (muscles of the vertebral column and

limb extensor muscles) – pontine reticulospinal

tract.

•Medullary reticular nuclei – inhibit antigravity

muscles – medullary reticulospinal tract.

Pontine & medullary systems balance each other.

• Vestibular nuclei – supplement the excitatory

function of the pontine system by integrating

vestibular information – lateral and medial

vestibulospinal tracts.

Summary of the

major descending

spinal tracts and

their points of

origin corticospinal tract

rubrospinal

tract

reticulospinal tracts

tectospinal,

vestibulospinal

tracts

Corticospinal Tract

Origin – Sensory cortex, primary Motor Cortex, premotor & supplementary cortex

(40%) (30%) (30%)

Internal Capsule

Pons

Cerebral Peduncle (midbarain)

Medullary Pyramid

Pyramidal Decussation

Lat.Cross & Vent. Uncross White matter in spinal cord

Ant. Horn of spinal cord through a interconnection

α motor neuron of opposite side

MOTOR UNIT…

•Every striated muscle has encapsulated muscle fibers scattered throughout the muscle called muscle spindles.

•Extrafusal and intrafusalfibers

organization of motor subsystems

Overview - organization of

motor systemsMotor Cortex

Brain Stem

Spinal Cord

Skeletal muscle

-motor

neuron

Final common

pathway

Steps in Motor Action

THANK YOU…