NeuroPT I - Motor Control, Learning and Development

Fundamentals of Motor Control

  • Motor control is the study of posture and movements that are controlled by central commands and spinal reflexes.
  • It involves the ability to regulate or direct the mechanisms essential to movement.
  • The field is directed at studying the nature of movement and how that movement is controlled.
  • It encompasses functions of the mind and body that govern posture and movement.
  • It is defined as the control and organization of processes underlying motor behavior.
  • Motor control processes are measured in units of milliseconds.

Hierarchical Development of the Central Nervous System (CNS)

  • The CNS originates from the Ectoderm and develops into the following structures:
  • PROsencephalon (Forebrain):
    • Telencephalon: Develops into the Cerebral Cortex.
    • Diencephalon: Develops into structures including the Thalamus and Hypothalamus.
  • MEsencephalon (Midbrain).
  • RHOmbencephalon (Hindbrain):
    • Metencephalon: Develops into the Cerebellum and Pons.
    • Myelencephalon: Develops into the Medulla Oblongata.
  • The internal organization of matter differs between the brain and spinal cord:
    • In the spinal cord: Gray matter is on the inside; White matter is on the outside.
    • In the cerebral cortex: Gray matter is on the outside; White matter is on the inside.
    • Gray matter color is derived from the cell bodies of neurons where the nucleus is located.
    • White matter color is derived from dendrites and axons, which are myelinated.

Telencephalon: Cerebral Cortex and Basal Ganglia

  • The Cerebral Cortex is responsible for control and serves as the information processing center of the brain. It is divided into lobes with specific functions:
    • Frontal Lobe: Intelligence, memory, voluntary movement, and emotion.
    • Parietal Lobe: Tactile and proprioceptive sensation.
    • Temporal Lobe: Auditory processing, speech, language, and gestation (taste).
    • Occipital Lobe: Vision.
    • Limbic Lobe (Visceral Brain/Fifth Lobe): Emotions, behavior, and retention of short-term and long-term memory. Dysfunction in this area is associated with dementia.
  • The Basal Ganglia is a collection of motor neurons responsible for fine motor movement and the refinement of movement.
  • Anatomical and Functional Divisions of Basal Ganglia:
    • Striatum: Composed of the Caudate Nucleus and Putamen.
    • Pallidum: Composed of the Globus Pallidus Interna (GPi) and Globus Pallidus Externa (GPe).
    • Neostriatum: Specifically the Caudate Nucleus and Putamen; controls large subconscious movements of skeletal muscles.
    • Paleostriatum: The Globus Pallidus.
    • Lenticular Nucleus: Composed of the Globus Pallidus and Putamen.
    • Corpus Striatum: Composed of the Caudate Nucleus and the Lenticular Nucleus.
    • Amygdaloid Nucleus: Includes all components plus the Claustrum.
  • Clinical Correlations of Basal Ganglia Damage:
    • Parkinson’s Disease: Associated with damage to the Substantia Nigra.
    • Huntington’s Chorea: Associated specifically with damage to the Caudate Nucleus.
    • Chorea (General): Writhing movements resulting from Neostriatum dysfunction.
    • Rigidity: Increased muscle tone associated with Globus Pallidus dysfunction.
    • Ballismus: Violent, large-scale movements associated with Subthalamic Nucleus damage.

Diencephalon and Endocrine Regulation

  • Thalamus: Processes all sensations except for the sense of smell. It contains Reticular nuclei that —cap— the thalamus laterally, appearing as curving translucent structures.
  • Subthalamus: Part of the extrapyramidal system; controls large movements. Damage results in ballismus.
  • Epithalamus: Serves as the connection between the Limbic System and the brain.
  • Hypothalamus: Acts as the site for hormone regulation and the satiety center (feelings of fullness/emptiness). It regulates the Autonomic Nervous System (ANS) and the Endocrine System.
  • Key Glands and Hormonal Controls:
    • Adrenal Glands: Release adrenalin and noradrenalin; increase metabolism, cardiac output, and pulse rate (PR).
    • Pancreas: Releases insulin and glucagon to control blood sugar levels for energy.
    • Pituitary Gland (Master Gland): Regulates the quantity of hormones released by other endocrine glands.
    • Pineal Gland: Involved in the menstrual cycle and the onset of maturation.
    • Thymus Gland: Responsible for the production of White Blood Cells (WBC).
    • Thyroid Gland: Regulates calcium by depositing it into bone and reducing it in the blood.
    • Parathyroid Gland: Removes calcium from bones to increase its concentration in the blood.

Midbrain, Hindbrain, and Cranial Nerve Distribution

  • Midbrain (Mesencephalon):
    • Connects the Pons to the Cerebrum.
    • Contains Cranial Nerves (CN) III and IV.
    • CN IV (Trochlear) is the longest intracranial nerve and controls the superior oblique muscle.
  • Hindbrain (Rhombencephalon):
    • Metencephalon:
    • Cerebellum: Divided into the Archicerebellum (Flocculonodular Lobe) for balance, Paleocerebellum (Anterior Cerebellum) for stereotypical repetitive movement, and Neocerebellum (Posterior Cerebellum) for coordination.
    • Pons: Connects the Midbrain to the Medulla Oblongata. It is the respiratory center (apneustic and pneumotaxic centers) and contains CN V, VI, VII, and VIII.
    • Myelencephalon:
    • Medulla Oblongata: Connects the brainstem to the spinal cord. It acts as the cardiac and vasomotor center (controlling blood flow) and contains CN IX, X, XI, and XII.
  • Summary of CN Distribution:
    • Cerebrum: CN I and CN II.
    • Midbrain: CN III and CN IV.
    • Pons: CN V to CN VIII.
    • Medulla: CN IX to CN XII.

Spinal Cord: Structure and Rex Lamination

  • The spinal cord consists of White Matter (tracts) and Gray Matter (laminae).
  • Rexed Laminae (Rex Lamination):
    • Lamina I: Lissauer’s Tract.
    • Lamina II: Substantia Gelatinosa.
    • Laminae III and IV: Nucleus Proprius.
    • Laminae V and VI: Clarke’s Column, Nucleus Dorsalis.
    • Lamina IX: Anterior Horn Cells (AHC).
    • Lamina X: Central Gray Commissure.

Ascending (Afferent) Sensory Tracts

  • Located in the white matter, these tracts send sensory input from effector organs toward the brain.
  • Spinothalamic Tract (STT):
    • Anterior STT: Processes light touch, crude touch, and pressure. Responsible for "closing the gate."
    • Lateral STT: Processes pain and temperature. Responsible for "opening the gate."
    • Decussation: Crosses to the opposite side 2—32 — 3 segments above or below the point of entry.
  • Dorsal Column / Medial Lemniscal Pathway:
    • Fasciculus Cuneatus: Sensation from the Upper Extremities (UE).
    • Fasciculus Gracilis: Sensation from the Lower Extremities (LE).
    • Functions: Discriminative touch, two-point discrimination, vibration, and pressure.
    • Decussation: Takes place in the lower medulla.
  • Spinocerebellar Tract: Conveys unconscious proprioception from the spinal cord to the cerebellum; does not cross to the opposite side.
  • Spinotectal Tract: Involved in the spinovisual reflex and vertical eye alignment.
  • Spinoreticular Tract: Influences the level of consciousness.

Descending (Efferent) Motor Tracts

  • These tracts carry impulses from the brain to effector organs.
  • Corticospinal Tract (CST) / Pyramidal Tract: Controls voluntary movement.
    • Lateral CST (90%90\% of fibers): Decussates in the lower medulla. Controls fine motor movement and distal muscles.
    • Anterior (Ventral) CST (10%10\% of fibers): Controls proximal and axial muscles, posture, and gross motor movement.
  • Extrapyramidal Tracts:
    • Vestibulospinal Tract: Postural reflexes and extensor muscles of the UE.
    • Rubrospinal Tract: Flexor muscles of the UE.
    • Reticulospinal Tract: Inhibits or stimulates the body; controls extensor muscles of the LE.
    • Tectospinal Tract: Visuospinal reflex; facilitates reflex head turning in response to moving stimuli.

Brodmann’s Area (BA) Classifications

  • Frontal Area:
    • BA 4: Primary Motor Area.
    • BA 6: Premotor Area.
    • BA 8: Frontal Gaze / Frontal Eye Field.
    • BA 44: Broca’s Area.
  • Temporal Area:
    • BA 41: Primary Auditory Area.
    • BA 42: Auditory Association Area.
    • BA 22: Wernicke’s Area.
  • Parietal Area:
    • BA 3, 1, 2: Primary Sensory Area.
    • BA 5, 7: Sensory Association Area.
    • BA 5, 7, 39, 49: Gnostic Area (memory, pleasure, affection, sexual, fear, and survival).
    • BA 39: Dysfunction results in agraphia and acalculia.
  • Occipital Area:
    • BA 17: Primary Visual Area.
    • BA 18, 19: Visual Association Area.

Autonomic Nervous System (ANS)

  • Sympathetic Nervous System (SNS):
    • Function: Fight or Flight (Ergotropic/Catabolic).
    • Outflow: Thoracolumbar (T2—L3T2 — L3).
    • Neurotransmitters: Epinephrine and Norepinephrine (Adrenergic).
    • Effects: Increased BP, PR, and RR; Bronchodilation; Decreased urine output and peristalsis; Ejaculation.
  • Parasympathetic Nervous System (PNS):
    • Function: Rest and Digest (Trophotropic/Anabolic).
    • Outflow: Craniosacral (CN IX, X, VII and Sacral segments).
    • Neurotransmitter: Acetylcholine (Cholinergic).
    • Effects: Decreased BP, PR, and RR; Bronchoconstriction; Increased urine output, peristalsis, and salivation; Erection.

Subcortical White Matter and Neuroglia

  • White Matter Fibers:
    • Transverse Fibers: Connect right and left hemispheres (e.g., Corpus Callosum).
    • Projection Fibers: Connect the brain to lower structures.
    • Association Fibers: Connect different parts of the same hemisphere.
  • Meninges:
    • Pia Mater (Leptomeninx).
    • Arachnoid Mater (Pachymeninx).
    • Dura Mater (Pachymeninx).
  • Neuroglia of the CNS:
    • Astrocytes: Fibrous (white matter) and Protoplasmic (gray matter); act as electrical insulators and the blood-brain barrier.
    • Oligodendrocytes: Form myelin sheaths in the CNS.
    • Microglia: Perform phagocytic functions.
  • Ependyma (Ventricular Linings):
    • Ependymocytes: Line ventricles and the central canal; assist in CSF absorption and circulation.
    • Tanycytes: Line the floor of the 3rd ventricle; transport CSF to the hypophyseal portal system.
    • Choroidal Epithelial Cells: Cover the choroid plexus; produce and secrete CSF.

Cerebrospinal Fluid (CSF) Dynamics

  • CSF Flow Sequence:
    1. Choroid Plexus
    2. Lateral Ventricles
    3. Foramen of Monro
    4. Third Ventricle
    5. Sylvian Aqueduct
    6. Fourth Ventricle
    7. Foramen of Magendie
    8. Foramen of Luschka

Motor Neurons and Nerve Fiber Electrophysiology

  • Alpha Motor Neurons:
    • Largest neurons; stimulated by I−alphaI-alpha and IIII fibers of muscles.
    • Direct motor activity; known as the final common pathway.
    • Damage results in a flaccid state of the muscle.
  • Gamma Motor Neurons:
    • Part of the loop of the fusimotor system; innervate intrafusal fibers.
    • Responsible for adjusting muscle length during contraction to maintain a constant state of readiness.
  • Nerve Fiber Types (General Classification by Diameter and Myelination):
    • Group A Fibers: Large diameter, heavily myelinated. Velocity: 150 m/s150\,m/s (∼300 miles/hr∼ 300\,miles/hr).
    • Group B Fibers: Intermediate diameter, lightly myelinated. Velocity: 15 m/s15\,m/s.
    • Group C Fibers: Smallest diameter, unmyelinated. Velocity: 1 m/s1\,m/s. Least sensitive to anesthesia.
  • Specific Nerve Fiber Properties:
    • α\alpha: Proprioception and somatomotor; size 12—20 μ12 — 20\,μ; speed 100 m/s100\,m/s. Most sensitive to anesthesia.
    • β\beta: Touch and pressure; size 5—12 μ5 — 12\,μ; speed 30—70 m/s30 — 70\,m/s.
    • γ\gamma: Muscle spindle fibers.
    • δ\delta: Sharp/localized pain, temperature, and touch; size 2—5 μ2 — 5\,μ; speed 12—30 m/s12 — 30\,m/s.
    • C: Thermal pain, mechanoreception, and diffuse/deep pain.

Sensory Fiber Classifications

  • IA: Annulospiral fibers.
  • IB: Golgi Tendon Organ (GTO) control.
  • II: Flower Spray Ending; handles muscle tension and discriminative touch.
  • III: Fast pain (superficial/prickling), temperature, and crude touch.
  • IV: Slow pain (deep/aching), temperature, and crude touch.
  • Speed Equivalencies: IA=IB=A−αIA = IB = A-\alpha (Fastest); II≈A−β and A−γII ≈ A-\beta \text{ and } A-\gamma; III≈A−δIII ≈ A-\delta; IV≈CIV ≈ C (Slowest).

Somatosensory Receptors and Reflex Arc

  • Reflex Arc Components: Receptor → Afferent nerve fiber → Synapse at the brain/cord → Efferent nerve fiber → Effector organ.
  • Interoceptors: Monitor events within the body (respiratory, cardiovascular, GI, and GU systems).
    • Carotid Sinus: Baroreceptors located in the carotid artery (parasympathetic).
    • Destrusor Muscle (Bladder Wall): Involved in the micturition reflex.
    • Inversion Technique: Affects chemical proportions of the brain, increasing consciousness, sports performance, and blood flow; promotes drainage of venous, lymphatic, and respiratory systems.
  • Exteroceptors: Located under the skin or in special sense organs.
    • Free Nerve Endings: Encapsulated and unmyelinated. Non-specific for pain, crude touch, and temperature. Used in counter-irritation to relieve pain (Lateral STT).
    • Hair-end Organs: Wrapped around hair follicles. Light touch/stroking results in relaxation and goosebumps (Anterior STT).
    • Meissner’s Corpuscles: Encapsulated; found in hairless/glabrous skin (fingertips, tongue). Responsible for fine tactile discrimination (stereognosis) and Braille reading (Dorsal Column).
    • Pacinian Corpuscles: Largest encapsulated receptors; found in deep skin and ligaments. Fastest adapting. Respond to deep pressure and vibration. Stimulation results in muscle relaxation or calming effects (Dorsal Column).
    • Merkel’s Tactile Disk: Non-encapsulated; found in deepest layer of hairless skin. Very sensitive to slow movement and tickle/pleasure (Pressure receptor).
  • Proprioceptors: Monitor awareness of space, posture, and equilibrium.
    • Conscious: Joint position and kinesiology.
    • Subconscious: Muscle spindle and GTO input directed to the cerebellum, vestibular apparatus, and cerebral cortex.