Motor Neuron Diseases Lecture Notes 2024/2025 PDF

MOTOR NEURON DISEASES NEUROLOGY LECTURES. GENERAL PATHOLOGY. 3rd YEAR OF MEDICINE Ana Checa-Ros, MD, PhD ACADEMIC YEAR 2024/2025 Lecturer Department of Medicine & Surgery...

MOTOR NEURON DISEASES NEUROLOGY LECTURES. GENERAL PATHOLOGY. 3rd YEAR OF MEDICINE Ana Checa-Ros, MD, PhD ACADEMIC YEAR 2024/2025 Lecturer Department of Medicine & Surgery [email protected] INDEX 1. Neuroanatomy Basis 2. Upper Motor Neuron Syndrome 3. Lower Motor Neuron Syndrome 1. NEUROANATOMY BASIS 1.1. MOTOR FUNCTION The integrity of different structures is required for voluntary and involuntary movements to happen with the appropriate quality: A) Essential structures: they are necessary for the movement to take place B) Auxiliary structures: they are not essential for movement, but control other aspects related to the quality of the movement (coordination, quantity, speeed) UMN MOTOR FUNCTION ESSENTIAL AUXILIARY STRUCTURES STRUCTURES Cerebellum, Upper motor Extrapyramidal proprioception and Praxis System neuron (UMN) system vestibular system Sequence of Lower motor neuron coordination Quantity & speed movements leading (LWN) to a goal Neuromuscular junction LMN Neuromuscular Skeletal muscle Striated junction muscle  pyramidal tract UMN neuromuscular jct squeletal m (voluntary mvmt) = necessary for the mvmt to take place MOTOR FUNCTION ESSENTIAL AUXILIARY STRUCTURES STRUCTURES Cerebellum, Upper motor Extrapyramidal proprioception and Praxis System neuron (UMN) system vestibular system Sequence of Lower motor neuron coordination Quantity & speed movements leading (LWN) to a goal Neuromuscular junction LMN Neuromuscular Striated muscle Striated junction muscle 1.2. ESSENTIAL STRUCTURES 1) Upper motor neuron (UMN) We will see them in this chapter 2) Lower motor neuron (LMN) 3) Neuromuscular junction 4) Skeletal muscle 1.3. PYRAMIDAL TRACT Upper and lower motor neurons are grouped together into the pyramidal tract The pyramidal tract arises from the primary motor cortex and convey efferent signals to either the spinal cord or the brainstem. The pyramidal tract is the primary pathway for voluntary control of muscular movements 1.3. PYRAMIDAL TRACT The pyramidal tract divides into two main tracts: A) The corticospinal tract: from the primary motor cortex to the spinal cord B) The corticonuclear/corticobulbar tract: from the primary motor cortex to the brainstem  UMN + LMN Voluntary PYRAMIDAL movements TRACT Corticospinal Corticobulbar tract tract Trunk Head Limbs Neck 1.3. PYRAMIDAL TRACT A) The corticospinal tract: It is a motor pathway that carries efferent information from the cerebral cortex to the spinal cord It is responsible for the voluntary movements of the limbs and trunk 1.3. PYRAMIDAL TRACT A) The corticospinal tract: UMN: arises from the primary motor cortex and ends in the anterior horn of the spinal cord, where it makes synaptic contact with the LMN LMN: it descends from the anterior horn of the spinal cord to the skeletal muscle  UMN 1.3. PYRAMIDAL TRACT A) The corticospinal tract: Motor Cortex The path starts in the motor cortex (anterior to the central sulcus), where the bodies of UMN lie. 1.3. PYRAMIDAL TRACT UMN A) The corticospinal tract: Axons of UMN converge and descend, passing through the internal capsule (white matter structure, located between the thalamus and the basal ganglia) 1.3. PYRAMIDAL TRACT A) The corticospinal tract: After passing the internal capsule, UMN axons will descend through the midbrain, pons and into the medulla oblongata.  UMN 1.3. PYRAMIDAL TRACT Cortex A) The corticospinal tract: In the lower medulla oblongata, Midbrain the fibres decussate and cross to the opposite side Pons Medulla Decussation in the lower medulla MedullaExtracted from: www.osmosis.org Oblongata 1.3. PYRAMIDAL TRACT LMN A) The corticospinal tract: The UMNs descend to the spinal cord and synapse with LMNs located in the anterior horn at each level of the spinal cord The impulses now conveyed by the LMN travel through the anterior root of the spinal nerves, through the peripheral nerve plexuses and along individual peripheral nerves on their way to the skeletal muscles of the limbs and trunk  PYRAMIDAL TRACT Corticonuclear/corticobulbar tract Corticospinal tract UMN: UMN: motor motor cortex cortex Decussation at the Decussation at the medulla braistem LMN: LMN: Spinal Brainstem cord Face, head and Limbs and trunk neck 1.3. PYRAMIDAL TRACT B) The corticonuclear/corticobulbar tract: The path starts in the motor cortex (anterior to the central sulcus), where the bodies of UMN lie UMN Motor Cortex  UMN 1.3. PYRAMIDAL TRACT B) The corticonuclear/corticobulbar Corticospinal / tract: Corticobulbar Tract Axons of UMN converge and descend, passing through the internal capsule (white matter structure, located between the thalamus and the basal ganglia) 1.3. PYRAMIDAL TRACT LMN B) The corticonuclear/corticobulbar tract: After passing the internal capsule, UMN axons will descend to the brainstem, where they will synapse with the LMN of the different cranial nerves, located along the brainstem (midbrain, pons and medulla oblongata). The LMNs will directly carry efferent signals to the muscles of the face, head and neck  UMN Motor Cortex Midbrain LMN Pons Medulla Oblongata 1.3. PYRAMIDAL TRACT B) The corticonuclear/corticobulbar tract: In the midbrain, LMNs carry signals to the oculomotor, trochlear and abducens nerves In the pons, LMNs carry signals dedicated to the trigeminal and facial nerves In the medulla oblongata, LMNs carry signals to the glossopharyngeal and accessory nerves  1.4. CRANIAL NERVES Mnemonic rule Mnemonic rule for the cranial nerves  I-Olfactory II-Optic Smell Sight Cranial Nerves III-Oculomotor IV-Trochlear Eye movements and Eye movements pupillary light reflex Corticonuclear/ VI-Abducens V-Trigeminal corticobulbar tract Facial sensations Eye movements and chewing VII-Facial VIII-Vestibulocochlear Facial movements Balance and sound and taste IX-Glossopharyngeal X-Vague Taste and swallowing Movement, feeling and abdominal organs XI-Accessory XII-Hypoglossal Cervical movements Tongue movements  One important remark in relation to the facial nerve... The axons from the UMN travel along the corticonuclear tract and decussate at the pons, synapsing with the LMN: Facial motor nuclei (LMN) in the pons are divided into two subnuclei: superior and inferior The superior subnucleus innervates the ipsilateral upper quadrant of the face and receives corticonuclear input from both hemispheres The inferior subnucleus innervates the ipsilateral lower quadrant of the face and receives only corticonuclear input from the opposite hemisphere  UMN Motor cortex Facial innervation Superior subnucleus Pons Superior subnucleus Inferior subnucleus Inferior subnucleus LMN Face  There are two types of facial palsy 1) Central facial palsy (UMN lesion): Paralysis of the contralateral (above the facial motor nuclei in the pons) lower quadrant of the face (mouth deviation) Generally secondary to stroke  There are two types of facial palsy 2) Peripheral facial palsy (LMN lesion): Paralysis of the ipsilateral (at or below the facial motor nuclei in the pons) half of the face (mouth deviation, forehead and eyelid paralysis) Causes: neoplasia, infection, idiopathic (Bell’s palsy) Central and peripheral facial palsy  1.5. STRETCH REFLEX/DEEP TENDON REFLEX It is the contraction of a muscle that occurs in response to stretch It is not controlled by the brain It is a monosynaptic circuit that is transmitted to the spinal cord and back to the muscle It is an automatic response of the human body triggered by passive stretch of the muscle (eg. by a tendon hammer) It is also responsible for muscle tone  When the muscle is stretched, they send an impulse via the sensory neurons to the relevant spinal cord segment The neuron synapses with a second neuron within the spinal cord, which is the lower motor neuron (LMN) The efferent impulse travels through the LMN back to the muscle in milliseconds  1.6. CORTICORETICULOSPINAL TRACT It arises from the motor cortex, the fibres synapse with the neurons from the reticular formation in the brainstem before arriving in the spinal cord Closely related to the corticospinal tract: so when there is lesion of the UMN of the corticospinal tract, there is always lesion of the corticoreticulospinal tract  1.6. CORTICORETICULOSPINAL TRACT Functions: Production of plantar reflex Regulatory actions over the monosynaptic circuit responsible for muscle tone and stretch reflex  1.6. CORTICORETICULOSPINAL TRACT Plantar reflex: Normal: A reflex characterised by flexion of the big toe and adduction and flexion of the rest of the toes when the sole of the foot is stroked It appears above 2 years of age  1.6. CORTICORETICULOSPINAL TRACT Plantar reflex: Abnormal (Babinski reflex): Characterised by extension of the big toe, accompanied by extension and abduction of the other toes when the sole of the foot is stroked It is physiological until 2 years of age 2. UPPER MOTOR NEURON SYNDROME 2.1. ETIOLOGY Ischaemic or haemorraghic cerebrovascular disease (stroke) 2.2. CLINICAL PRESENTATION 1) PARESIS (incomplete paralysis) OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY *We will only analyse the motor symptoms derived from the upper motor neuron syndrome; other symptoms (sensory, language...) will be described in further chapters and during neurology lectures 2.2. CLINICAL PRESENTATION 1) PARESIS OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY (loss of muscle use) 1) PARESIS OR PARALYSIS We distinguish different grades: Paralysis of one Paralysis of the lower Paralysis of all four Paralysis of one limb side of the body sides of the body limbs Monoplegia Haemiplegia Paraplegia Tetra/Quadriplegia 1) PARESIS OR PARALYSIS The clinical presentation will vary depending on the level of affection: 1A) Motor cortex 1B) Internal capsule 1C) Brainstem 1D) Spinal cord 1) PARESIS OR PARALYSIS 1A) Motor cortex: Affection of the corticospinal tract leads to: Monoplegia (small affection) or haemiplegia (larger) as motor symptoms Motor symptoms will be contralateral (UMN lesion before decussation) 1) PARESIS OR PARALYSIS 1A) Motor cortex: Affection of the corticobulbar tract may lead to: Central facial palsy (UMN lesion before decussation) 1) PARESIS OR PARALYSIS 1B) Internal capsule: Axons of UMN along the corticospinal tract converge before reaching the internal capsule, leading to: Haemiplegia as the motor symptom The hemiplegia will be contralateral (UMN lesion before decussation) 1) PARESIS OR PARALYSIS 1B) Internal capsule: Affection of the corticobulbar tract may lead to: Central facial palsy (UMN lesion before decussation) 1) PARESIS OR PARALYSIS 1C) Brainstem: Midbrain: Contralateral haemiplegia (corticospinal tract lesion before decussation) Central facial palsy (UMN lesion before decussation) 1) PARESIS OR PARALYSIS 1C) Brainstem: Pons: Contralateral haemiplegia (corticospinal tract lesion before decussation) Peripheral facial palsy (LMN lesion after decussation)  Medulla Oblongata 1) PARESIS OR PARALYSIS 1C) Brainstem: Medulla oblongata: Haemiplegia (corticospinal tract lesion), dysphagia and dysarthria (lesion of IX, X, XI and XII cranial nerves) The haemiplegia may be ipsilateral (lateral corticospinal tract after decussation) or contralateral (anterior corticospinal tract before decussation) 1) PARESIS OR PARALYSIS 1D) Spinal cord: If the lesion affects one side: haemiplegia or monoplegia (depending on the level of the lesion) If the lesion affects both sides: tetraplegia or paraplegia (depending on the level of the lesion) Motor symptoms will be ipsilateral (LMN lesion) 2.2. CLINICAL PRESENTATION 1) PARESIS OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY 2) MUSCLE TONE DISORDER Alterations of muscle tone disorder arise from lesions of descending pathways closely related to the corticospinal tract, such as the corticoreticulospinal tract In physiological conditions, the corticoreticulospinal tract exerts an inhibitory effect on muscle tone and the stretch reflex 2) MUSCLE TONE DISORDER Lesions of the corticoreticulospinal tract in upper motor neuron syndrome lead to: Hypertonia Spasticity Hemiparetic gait 2) MUSCLE TONE DISORDER Spasticity: It is a velocity-dependent increase in a muscle resistance to passive movement Clasp-knife response: brisk movements of muscles will cause an abrupt increase in tone followed by a decrease in muscle resistance with continued movement Clasp-knife response 2) MUSCLE TONE DISORDER Hemiparetic gait: It results from the combination of muscle weakness and spasticity It is characterised by hip extension and adduction, knee extension and ankle inversion Hemiparetic gait 2.2. CLINICAL PRESENTATION 1) PARESIS OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY 3) REFLEX DISORDER It results from lesion of descending inhibitory pathways, such as the corticoreticulospinal tract: Hyperreflexia Babinski sign Clonus 3) REFLEX DISORDER Hyperreflexia of deep tendon reflexes: abnormally brisk stretch reflex 3) REFLEX DISORDER Babinski sign: 3) REFLEX DISORDER Clonus: Sequence of rhythmic, involuntary muscle contractions in response to abruptly applied stretch stimuli Most easily elicited at the knee and ankle Ankle Clonus Patellar Clonus 3. LOWER MOTOR NEURON SYNDROME 3.1. ETIOLOGY Spinal cord compression by trauma Spinal cord ischaemia or haemorraghe Spinal cord tumour 3.2. CLINICAL PRESENTATION 1) PARESIS (incomplete paralysis) OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY *We will only analyse the motor symptoms derived from the lower motor neuron syndrome; other symptoms (sensory) will be described in further chapters and during neurology lectures 3.2. CLINICAL PRESENTATION 1) PARESIS (incomplete paralysis) OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY 1) PARESIS OR PARALYSIS Depending on the level of the lesion: Ventral root or plexus: homolateral myotome Spinal/cranial peripheral nerve: individual muscles (homolateral) 3.2. CLINICAL PRESENTATION 1) PARESIS (incomplete paralysis) OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY 2) MUSCLE TONE DISORDER The efferent signal of the stretch reflex (LMN) is damaged, so there will be hypotonia 3.2. CLINICAL PRESENTATION 1) PARESIS (incomplete paralysis) OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY 3) REFLEX DISORDER The efferent signal of the stretch reflex is damaged, so there will be hyporeflexia 3.2. CLINICAL PRESENTATION 1) PARESIS (incomplete paralysis) OR PARALYSIS 2) MUSCLE TONE DISORDER 3) REFLEX DISORDER 4) MUSCLE ATROPHY 4) MUSCLE ATROPHY Intense atrophy Fasciculations (muscle twitches): they occur in chronic damage to LMN, indicating sporadic discharges of motor units Fasciculations TO RECAP...  UMN Syndrome LMN Syndrome Paresis/Paralysis Monoplegia Myotome Haemiplegia Individual muscles Paraplegia Tetra/Quadriplegia Muscle tone Hypertonia Hypotonia Spasticity Clasp-knife response Hemiparetic gait Reflexes Hyperreflexia Hyporeflexia Babinski sign Clonus Atrophy Muscle atrophy Muscle atrophy Fasciculations