Anatomy - Motor System, Basal Nuclei, and Cerebellum

Corticospinal and Corticobulbar Pathways

Main circuitries that will control the head, trunks, and limbs

Cerebral Cortex

Primary motor that governs movement. Motor association

Cortical Motor Pathways

Produce movements that are more refined and adaptive (adaptive control). These movements are basically voluntary in nature.

Brainstem Motor Pathways

Characterized to have a high degree of automaticity (automatic control). Barely noticeable because they are automatic corrections.

Spinal Level Reflexes

Motor circuitry is simple. Reflex movements. Spinal reflexes are very simple circuitry: Sensory stimulation activates the circuit. The activated circuit will evoke a motor response.

Primitive Reflex

Normal reflexes of the infant. First to appear during the development of a child. But as the infant further develops, these reflexes will disappear. They will disappear because the BRAINSTEM will now take over the spinal motor movement control.

Grasp reflex

SENSORY INPUT : Touching the infant’s palm. MOTOR OUTPUT : Grasping Motion: fingers will flex to grasp the mother’s hand

Sucking (Rooting) Reflex

SENSORY INPUT : Touching the infant’s cheek or corner of the mouth. MOTOR OUTPUT : the baby’s turning of the head towards the origin of the stimulus to suck the finger.

Babinski Reflex

SENSORY INPUT : Touching the plantar’s surface of the infant's foot. MOTOR OUTPUT : Extension and fanning of the toes.

Brainstem Level Reflex

Movements governed by the brain are said to be stereotypic repetitive movements, and they are prelude to movements controlled by the cortical level.

Symmetric Tonic Neck Reflex (STNR)

Complex reflex reaction. When a child reaches the age of 4 to 6 months. Whatever the top half of the body does, the lower does the opposite. Purpose: Precursor for the child to be able to learn creeping. This reflex will help the infant learn to rise up onto the hands and knees.

Asymmetric Tonic Neck Reflex (ATNR)

Appear at around 6 months of age. Purpose: Support the development of asymmetrical, cross lateral motor coordination of the core and limbs. Prepares the child for future transitional movements. Promotes hand and eye coordination.

Cortical Level Reflex

Cerebrum will start to mature, take over, and supersede the lower motor control areas. Movements are no longer reflexive. Movements become highly voluntary, specific, and goal directed. Stage when a child can now control movements on his or her own.

Cruising

With proper muscle control of the upper limb, the child will now learn how to cruise. Will be a precursor for the child to be able to stand and walk independently.

Pathological reflexes

Since the lower centers are now disinhibited, the primitive reflexes will reappear in an adult patient. Since these reflexes are not expected in an adult population, these now become

Brodmann Area 4

Anterior to the central sulcus. Represented by the precentral gyrus; designated as

Touch sensations

Processed behind the central sulcus in the postcentral gyrus known as the primary somatosensory area.

Visual sense

Processed in the occipital lobe.

Hearing and smelling

Processed in the temporal lobe.

Posterior Parietal Lobe

Very important region where all sensory inputs from different areas are integrated. Provides information on the: Distance of an object, Shape of an object, Texture of an object, Temperature etc. Provides a mental picture on how much movement is required based on sensory input

Motor Association Cortex

Where the planning of movement is being done. Receives signals coming from the prefrontal association areas.

Prefrontal Association Areas

Known for its role in learning memory, behavior, and personality. Also plays a vital role in its ability to initiate movements. Area which generates motivation to move.

Motor Association Cortex

Creates a movement blueprint for the primary motor cortex to execute. With its created movement blueprint will now directly influence the output of the primary motor cortex.

Motor Neuron Somatotopy

The point-for-point correspondence of an area of the body to a specific location in the central nervous system.

Cortical Motor Areas

These are the areas of the cerebrum that directly govern the motor movements.

Motor Association Cortex (Area 6)

Subdivided into three (3): Supplementary Motor Area, Premotor Cortex, Cingulate Motor Area. Situated anterior to the PMC is the association motor cortex, some books will call this the secondary motor area.

Motor Association Cortex

Receives information from different association areas of the brain particularly the prefrontal cortex and the posterior parietal cortex, and the limbic system (emotions). Responsible for the movement planning and execution. Axons of the motor association cortex projects to the primary motor cortex readily influencing the descending motor pathway

Premotor Complex

The cerebellum will send its information to the thalamus, specifically in the ventrolateral nucleus of the thalamus and the axons of this thalamic nucleus will project to the premotor cortex.

Supplementary Motor Area

The basal nuclei will synapse to the thalamus via its ventro-anterior nuclei or VA and this thalamic nuclei will synapse with the supplementary motor area. Aside from basal nuclei, the prefrontal complex which generates motivation to move will also send its information via this area.

Cingulate Motor Area

Will receive influence coming from the limbic system. These are motor behaviors or movements evoked by certain responses to emotions or drives.

Primary Motor Cortex

Located anteriorly to the central sulcus. Also known as precentral gyrus (PCG). Designated as Brodmann Area 4. It is responsible for generating electrical impulses that will evoke a voluntary motor movement.

Central Sulcus (sulcus of Rolando)

Separates the frontal lobe from the parietal lobe,

Betz cells

The primary motor cortex is highly populated by triangular/pyramidal shaped neurons called?

Primary Motor Cortex

Influenced by the outputs of the association motor cortex, which receive inputs from prefrontal cortex, cerebellum and the basal nuclei via the thalamus.

Red Nucleus

Also known as Nuclear Rubber. Located in the rostral midbrain. Pale pink in color (in actual: red area with pale gray structure at the center). Associated with Cranial Nerve III

Vestibular Nucleus

Embedded inside the pons. Receives fibers from CN VIII (Vestibulocochlear nerve). The nucleus has four subnuclear components, the superior, inferior, medial, and lateral. Both the medial and lateral components are the ones related to motor control

Reticular Formation

The brain stem's central core, known as the reticular formation, contains neurons that control the excitability of other neurons throughout the nervous system, which controls our arousal level.

Deep Superior Colliculus

The term corpora quadrigemina refers to the group of colliculi or swellings seen at the rear of the midbrain. It contains a deeper group of neurons that send fibers down to the spinal cord that can influence movements in relation to eye movements.

Cortical Pathway

Arises from the primary motor cortex. Since this arises from the betz cells, this pathway is also called the pyramidal tract.

Corticospinal tract

Arises from the cortex and descends to the spinal cord. Synapses in the anterior horn cell motor neurons of the spinal cord, making this the second neuronal component of the chain. Anterior horn cell exits at the spinal cord and forms the spinal nerve which reaches the skeletal muscles of the trunk and limbs.

Corticobulbar tract

Terminates on the brain stem where it synapses with the motor cranial nuclei

Motor cranial nuclei

Becomes cranial nerves. 2nd order neuron of the motor chain. Will serve the skeletal muscles of the head and neck region.

Outer Layer of Cerebrum

Made up of gray matter. Populated by cell bodies of neurons

Inner (Central) Core of Cerebrum

Made up of white matter. Location of axons

Corticospinal Tract

Coincide with the motor homunculus somatotopy. This is the region where the trunks and limbs represented

Corticobulbar Tract

Region where the head and neck is represented

Corona Radiata

As motor fibers descend, they organize the ________. A bundle of white matter representing the axons that moves in and out the cerebrum.

Internal Capsule

As the motor fibers descend further, they become more compact and organized in the area known as the?

Genu of Internal Capsule

Junction between Anterior limb and Posterior limb. Corticobulbar tract fibers are positioned

Posterior Limb of Internal Capsule

Corticospinal tract fibers are positioned here

Brainstem

After the Internal Capsule, the motor tracts will continue to descend in the

Crus cerebri

Where both corticospinal and corticobulbar tracts will be arranged.

Medial side

What is the cortical origin of the corticobulbar tract: medial or lateral?

Lateral side

What is the cortical origin of the corticospinal tract: medial or lateral?

Area of midbrain

In this area, some fibers of the corticobulbar tract will leave the Crus Cerebri and blend with the Tegmentum where it will start to supply the motor nuclei bilaterally.

Pons

In this area, the corticobulbar tract is seen interspersed within the basis pontis as bundles of descending motor tracts coming from the Crus Cerebri of the Midbrain.

Pyramidal swelling

Formed by the fibers of the corticospinal tract as it reaches the area of the medulla.

Lateral Column

The crossed 90% of the corticospinal tract will organize itself and will form a column of white matter on the lateral side of the spinal cord. This is called?

Gray matter

The core of the spinal cord surrounded by the white matter on its periphery.

Lateral system fibers

Will synapse with the anterior horn cell that is responsible for moving the limbs.

Ventral Column

Are tasked to supply the muscles of the trunk. Will not only supply the ipsilateral side but other fibers will cross the opposite side to supply the contralateral region.

Rubrospinal tract

Arises from the red nucleus found in the midbrain. As the fibers emerge from the red nucleus it will cross the opposite side and will descend as this tract. Will only reach the area of the upper thoracic segment of the spinal cord. Upper flexor biased

Vestibulospinal Tract

The role of this pathway is to provide an immediate postural correction, maintain an erect posture and balance. Extensor biased

Vestibular nucleus

Located in the Lower Pons and Upper Medulla. Receive information from vestibular canals located in the middle ear. Activated each time we move our head and body

Lateral Vestibulospinal Tract

Span the entire length of the cord. Supplies all extensors of the trunk. Maintain balance. Keep the trunk in erect position by contacting postural back muscles of the spine.

Medial Vestibulospinal Tract

Appreciated up to the cervical region of the spinal cord. Only supplies the cervical muscles. Keep head in midline position.

Vestibular apparatus

Each time we move out of our balance zone, this structure of the ear is being activated, sending signals to the vestibular nucleus through the vestibulospinal tract, providing us with an automatic correction of our posture.

Reticulospinal Tract

Originates from the reticular formation. Nuclei are embedded in the brain stem, responsible for maintaining state of arousal and wakefulness. Also contributes to the movement of the reticulospinal tract.

Reticulospinal Tract

Will descend on the ipsilateral side of the cord and will blend with the ventral white column, together with the vestibulospinal and the ventral corticospinal tracts. The tract will span the entire length of the cord, thereby affecting the muscles of the trunk and limbs. Like the vestibulospinal, this is extensor bias.

Tectospinal Tract

This tract arises from the tectum. Role is to control the movement of the neck in relation to visual stimulus

Decorticate Posturing

Usually seen in patients with affection of the motor cortex. Therefore, the corticospinal tract is the one primarily involved. Upper limb flexion, lower limb extension

Decerebrate Posturing (Rigidity)

Associated with direct damage to both the red nucleus and the cerebrospinal tract. Damage to the midbrain. Patient denotes a more severe form of neurological insult. Extension of both upper and lower limb

15

What is the highest GCS score?

3

What is the lowest GCS score?

Best eye response (E), Best verbal response (V), Motor response (M)

What are the 3 testing parameters for the Glasgow Coma Scale (GCS)?

Cerebellum

Latin for “Little Brain”. Located posterior to the pons and medulla. Separated from the Cerebral Cortex by Tentorium Cerebelli

Primary, Posterolateral

What are the two cerebellar fissures?

Anterior, Posterior, Flocculonodular

What are the cerebellar lobes?

Deep Cerebellar Nuclei

Paired nuclei embedded within the white matter. Cerebellar Output. 4 Types (Medial → Lateral): Fastigial, Globose, Emboliform, Dentate. Interposed Nuclei- Globose + Emboliform

Spinocerebellum

Important in controlling the posture and movement of the trunk and limbs. Comprises the Input: Vermis, Intermediate Hemisphere, Output: Fastigial and Interposed Nuclei. Somatotopic Organizations: Vermis– Axial and Proximal Muscles, Intermediate– Limb Muscles

Cerebrocerebellum

Involved in the planning of movement and is interconnected with diverse region of the cerebral cortex. Comprises the Lateral Hemisphere and Dentate Nucleus. Input: Contralateral Cerebral Cortex. Output: Dentate Nucleus

Basal Ganglia

Comprises multiple subcortical nuclei involved in motor and non-motor functions. Strongly interconnected with the cerebral cortex, thalamus, and brainstem

Corpus Striatum

Caudate + Putamen + Globus Pallidus

Neostriatum (Striatum)

Caudate + Putamen

Paleostriatum

Globus Pallidus

Lentiform Nucleus

Putamen + Globus Pallidus

Input Nuclei (Striatum)

Receive afferent connections from cerebral cortex. Includes the Caudate Nucleus, Putamen, and Nucleus Accumbens

Caudate Nucleus

Eye movement control and cognition. Located near the center of the brain sitting astride the thalamus. Resemble a C-shape structure with a wider head tapering into the body and the tail. Head and Body forms the floor of the Anterior Horn of the lateral ventricle

Putamen

Control of limbs and trunk movements. Rounded structure located at the base of the forebrain. Separated from the caudate nucleus by the Internal Capsule

Nucleus Accumbens

Participates in emotion

Intrinsic Nuclei

Consist of other nuclei of the Basal Ganglia. Contributes to the formation of the Indirect Pathway (which inhibits the production of movement). Includes the Globus Pallidus Externus, Subthalamic Nucleus, Substantia Nigra Pars Compacta

Subthalamic Nucleus

Located in the Diencephalon. Located ventral to the Thalamus. Lesion: Contralateral Hemiballismus

Output Nuclei

Efferent Nuclei of the Basal Ganglia projecting to the Thalamus. Includes the Globus Pallidus Internus, Substantia Nigra Pars Reticulata

Globus Pallidus

Latin for “pale globe”. Occupies the medial surface of the Putamen, lateral to the internal capsule. Has 2 segments: Externus, Internus

Substantia Nigra

Located in the Midbrain. Latin for “black substance”. Separates the Crus Cerebri from Tegmentum. Lesion: Parkinson’s Disease. 2 parts: Reticulata, Compacta

Direct Pathway

Promote movements. Lesion: HYPOkinetic movements. Parkinson’s, Akinesia, Bradykinesia, Rigidity

Indirect Pathway

Inhibit movements. Lesion: HYPERkinetic movements. Ataxia, Athetosis, Chorea, Hemiballismus, Tics, Tremors Blepharospasm