RCSI Motor System Presentation PDF

MOTOR SYSTEM Class Year 2, Semester 1 Lecturer DR. VIJAYALAKSHMI S B Department of Anatomy Email id: [email protected] Date 28-10-2024 1 LEARNING OUTCOMES Describe the function and course of corticospinal...

MOTOR SYSTEM Class Year 2, Semester 1 Lecturer DR. VIJAYALAKSHMI S B Department of Anatomy Email id: [email protected] Date 28-10-2024 1 LEARNING OUTCOMES Describe the function and course of corticospinal tracts Describe the structure of the internal capsule Compare and contrast the pyramidal and extrapyramidal motor pathways Compare and contrast the effects and clinical presentations of upper and lower motor neuron lesions Differentiate between upper and lower lesions of the facial nerve  THE SIMPLEST PICTURE…MONOSYNAPTIC NEURONS Dorsal root Respond to a ganglion stimulus Muscle contracts No control e.g., knee jerk (L3,4), biceps reflex (C5,6) Note: motor neurons in the cord (and cranial nerve motor neurons) are Ipsilateral, i.e. they project their axons out to the periphery on the same side  CONTROLLED RESPONSES TO STIMULI SIMPLE PICTURE Afferent (sensory) – Message goes up to a higher centre – 3 neurons Efferent (motor) – Message comes down from the higher centre – 2 neurons  SURFACE NEUROANATOMY Central sulcus Post-central gyrus / Primary Pre-central sensory area gyrus / Primary motor area cerebellum  SURFACE NEUROANATOMY Olives Pyramids Cerebral peduncles Midbrain Pons Medulla  MIDLINE SAGITTAL SECTION Pre-central Central Post-central gyrus sulcus gyrus Thalamus Lateral ventricle Cerebellum midbrain pons medulla  MIDLINE SAGITTAL SECTION Pre-central Central Post-central gyrus sulcus gyrus Thalamus Corpus Cerebellum callosum Lateral ventricle midbrain pons medulla  CORONAL SECTION Lateral ventricle Head of Caudate nucleus a. Putamen b. Globus Internal Pallidus capsule thalamus Lentiform nucleus = a + b  TRANSVERSE SECTION Basal nuclei include: lentiform nucleus + caudate nucleus + substantia nigra Lentiform nucleus = a + b Internal a. Putamen b. Globus Pallidus capsule Thalamus Head of Caudate nucleus  SECTION OF MID-BRAIN Inferior/Superior Posterior Anterior Posterior Colliculius Tectum Midbrain Cerebral aqueduct Pons Substantia nigra Red nuclei 4th ventricle Tegmentum Medulla Spinal Corticospinal & cord Corticobulbar tracts Crus cerebri Anterior Tectum Tegmentum Superior colliculus = reflex movements from Found in all three parts of brainstem visual input Involved in homeostatic and reflexive Inferior colliculus = reflex movements in pathways response to auditory input  PYRAMIDAL AND EXTRAPYRAMIDAL SYSTEMS Pyramidal system upper motor neuron starts in the cerebral cortex (pre-central gyrus). They pass through the pyramids of the medulla. Conscious movement. Extrapyramidal system neurons starts in other brain nuclei (e.g., basal ganglia). They do not pass through the pyramids of the medulla. Fine tune movement Olives Putamen Pyramids Globus Head of Pallidus Caudate nucleus  PYRAMIDAL SYSTEM DEFINITIONS Pyramidal system upper motor neuron starts in the cerebral cortex (pre-central gyrus). They pass through the pyramids of the medulla The pyramidal system is divided based on cranial nerves and spinal nerves. Thus, we define two tracts: – Corticobulbar tracts: group of upper cranial motor nerves that start in cortex and end in brainstem* – Corticospinal tracts: group of upper motor nerves that start in cortex and end in spinal cord *”bulb” is an outdated name for the medulla  PYRAMIDAL SYSTEM DEFINITIONS Pyramidal system upper motor neuron starts in the cerebral cortex (pre-central gyrus). They pass through the pyramids of the medulla There are 2 neurons: Corticobulbar tracts: group of upper cranial Upper motor neuron motor nerves that start in From cerebral cortex cortex and end in – To brainstem (cranial nerve) brainstem* – Or spinal cord (spinal nerve) Lower motor neuron Corticospinal tracts: To muscle group of upper motor nerves that start in cortex – From brainstem cranial nerve motor and end in spinal cord nucleus – Or from cord (anterior horn cell) *”bulb” is an outdated name for the medulla  PYRAMIDAL SYSTEM Pyramidal system upper motor neuron starts in the cerebral cortex (pre-central gyrus). They pass through the pyramids of the medulla Upper motor neuron From cerebral cortex – To brainstem (cranial nerve) – Or spinal cord (spinal nerve) Lower motor neuron To muscle – From brainstem cranial nerve motor nucleus – Or from cord (anterior horn cell)  PYRAMIDAL MOTOR PATHWAY Motor area Internal capsule – Genu (corticobulbar) – Posterior limb (corticospinal) Midbrain - Cerebral peduncles Pons Medulla – pyramids 85% decussate – lateral corticospinal tracts Note: the anterior corticospinal decussate near termination  PYRAMIDAL MOTOR PATHWAY The body is represented in an inverted manner on the motor (and somatosensory) cortex For your edification, the distorted drawing of a human on the motor cortex is referred to as the “motor homunculus”  Central Lower limb sulcus The primary sensory Abdomen cortex or postcentral Thorax gyrus Upper limb Artefact: a Head saw cut The primary motor cortex or precentral Artefact: a saw cut gyrus Previously you saw the central sulcus, and anterior to it the gyrus representing the primary motor cortex. On both the primary motor and primary sensory gyri the body is mapped, or represented, upside down. Such ‘maps’ are not images like pictures projected onto a screen but are locations of specific electrical or chemical activity within the brain.  PYRAMIDAL MOTOR PATHWAY Motor area Internal capsule Anterior limb – Genu (corticobulbar) – Posterior limb (corticospinal) Midbrain - Cerebral Genu peduncles (Crus cerebri) Posterior limb Pons Medulla – pyramids 85% decussate – lateral corticospinal tracts Note: the anterior corticospinal decussate near termination INTERNAL CAPSULE  The nerve fibres in the corticobulbar and corticospinal tracts pass downwards and backwards through the INTERNAL CAPSULE, between the LENTIFORM NUCLEUS (composed of the putamen and globus pallidus) and the THALAMUS. The corticobulbar tract ends in the brainstem and the corticospinal tract Coronal ends in the Model spinal cord. MB31 section  LENTIFORM NUCLEUS: EXTERNAL CAPSULE PUTAMEN GLOBUS PALLIDUS CAUDATE NUCLEUS THALAMUS INTERNAL CAPSULE: ANTERIOR LIMB Some SENSORY and EXTRAPYRAMIDAL FIBRES INTERNAL CAPSULE: POSTERIOR LIMB CORTICOSPINAL TRACT VISUAL and AUDITORY INTERNAL CAPSULE: fibres GENU (LATIN, = ‘KNEE’, i.e. the bend in the knee) CORTICOBULBAR TRACT Horizontal Model MB31 section  anterior perforated The internal capsule is a common site substance for a STROKE. This is often caused by a haemorrhage from one of the arterial vessels there, but it can also be caused by the blockage of one of the local arteries. The internal capsule is one of the parts of the brain supplied by the ANTERIOR PERFORATING ARTERIES which enter the brain through the ANTERIOR PERFORATED SUBSTANCE. These arteries are branches of the MIDDLE CEREBRAL ARTERY, the larger terminal branch of the INTERNAL CAROTID ARTERY. They are so named because in dissection the arteries can be pulled out of, or ‘unplugged’ from, the brain tissue leaving small tunnels or perforations which can easily be Model seen by the unaided eye. MB33  PYRAMIDAL MOTOR PATHWAY Motor area Internal capsule Cerbral peduncles – Genu (corticobulbar) Midbrain – Posterior limb (corticospinal) Pons Midbrain - Cerebral Medulla peduncles (Crus cerebri) Pons Medulla – pyramids 85% decussate – lateral corticospinal tracts Note: the anterior corticospinal decussate near termination  PYRAMIDAL MOTOR PATHWAY Motor area Internal capsule Olives Pyramids – Genu (corticobulbar) – Posterior limb (corticospinal) Midbrain - Cerebral peduncles (Crus cerebri) Pons Pyramidal Medulla – pyramids decussation 85% decussate – lateral corticospinal tracts Note: the anterior corticospinal decussate near termination  PYRAMIDAL MOTOR PATHWAY Motor area Internal capsule – Genu (corticobulbar) – Posterior limb (corticospinal) Midbrain - Cerebral peduncles (Crus cerebri) Pons Medulla – pyramids 85% decussate – lateral corticospinal tracts Note: the anterior corticospinal decussate near termination  PYRAMIDAL MOTOR PATHWAY Motor area Internal capsule – Genu (corticobulbar) – Posterior limb (corticospinal) Midbrain - Cerebral peduncles (Crus cerebri) Pons Medulla – pyramids 85% decussate – lateral corticospinal tracts Note: the anterior corticospinal decussate near termination  PYRAMIDAL TRACT PROBLEM Upper motor neuron lesion (e.g., stroke) If unilateral damage in cerebral hemisphere – then contralateral If in spinal cord, then…ipsilateral Initial weakness/ paralysis Later hypertonicity – Increased resistance to passive stretching of muscles Spasticity – clasp knife initial resistance to muscular stretching followed by relaxation Hyperreflexia Clonus - a rhythmic series of muscle contractions induced by stretching the tendon. It most commonly occurs at the ankle, typically elicited by suddenly dorsiflexing the patient's foot and maintaining light upward pressure on the sole. Babinski’s sign (extensor response) by kind permission of Dr Charlie Goldberg & the Regents of the University of California A positive Babinski sign indicates an upper motor neuron lesion, but it is also normally present in infants up to the age of 6 months to 2 years, while the corticospinal tract is being Babinski’s sign myelinated.  PYRAMIDAL TRACT PROBLEM Lower motor neuron lesion (e.g., polio) Ipsilateral Weakness – Paresis/paralysis of individual muscles (-plegia) Wasting of muscles Fasciculations – (visible spontaneous contraction of muscles) Hypotonicity – reduced resistance to passive stretching Hyporeflexia MNEMONIC  MOTOR CRANIAL NERVES III – mixed - motor + parasympathetic IV – motor BILATERAL Vc - mixed - motor + sensory CONTRALATERAL ONLY MIXTURE VI - motor VII - mixed – motor + sensory +parasympathetic (below eyes contralateral only) IX – mixed - motor + sensory + parasympathetic X – mixed - motor + sensory + parasympathetic XI - motor XII - motor  CORTICOBULBAR TRACTS Left motor cortex Right motor cortex All lower motor neurons in their nuclei in the mid- and hind-brain receive bilateral innervation: UMN 1. they receive axons from the opposite side (black line) 2. Receive axons from the same side (red line). LMN All motor cranial nuclei in the brainstem (except CNVII & XII) receive bilateral innervation MOTOR CRANIAL NERVES: FACIAL NUCLEUS (VII) Left Hemisphere Right Hemisphere UMN LMN  MOTOR CRANIAL NERVES 1. UMN injury to facial nerve – Wrinkling of forehead is spared (bilateral innervation) – Face droops below the eye 2. LMN injury to facial nerve – Facial muscles damaged above and below eyes  Upper Motor Neuron Lesions CORTICOBULBAR TRACT & SITE OF UPPER MOTOR NEURON LESION of the Facial Nerve The corticobulbar tract carries impulses from the motor cortex to the facial nucleus in the pons. This pathway can be damaged by a number of conditions including stroke, multiple sclerosis and motor neuron disease. The fibres from the motor cortex concerned with the lower facial muscles cross the FACIAL NUCLEUS midline and supply the facial nucleus of the opposite side. Those concerned with the upper facial muscles (frontalis and orbicularis oculi) are distributed bilaterally. Consequently, the upper facial muscles are spared in an upper FACIAL NERVE & SITE OF LOWER motor neuron lesion of the MOTOR NEURON facial nerve. LESION  Lower Motor Neuron Lesions of the Facial Nerve BELL’S PALSY is the most common type of ACUTE FACIAL NERVE PARALYSIS. It is thought to be caused by a viral infection affecting the nerve in its course through the facial canal (which ends at the stylomastoid foramen). It typically presents with unilateral weakness of the facial muscles and pain around the ear on the affected side. The muscle weakness is variable. In mild cases some motor function is retained. In severe cases complete paralysis can occur with the patient being unable to close the eye on that side. After some weeks the majority of patients experience full recovery. The stapedius muscle normally to contracts to reduce the efficiency of sound transmission in the middle ear as a protective response to loud noises. If it is paralysed the patient will experience HYPERACUSIS (very sensitive hearing) on the affected side. There may be taste disturbance and reduced lacrimation if the sensory root is also involved. Other causes of a lower motor neuron lesion in the facial nerve include trauma, neoplasms, and parotid surgery. left-sided upper motor neuron lesion right-sided lower motor neuron lesion of the facial nerve, resulting in the of the facial nerve, resulting in the characteristic paralysis of the lower characteristic paralysis of the entire right side of the face right side of the face  PYRAMIDAL AND EXTRAPYRAMIDAL SYSTEMS Pyramidal system upper motor neuron starts in the cerebral cortex (pre-central gyrus). They pass through the pyramids of the medulla. Conscious movement. Extrapyramidal system neurons starts in other brain nuclei (e.g., basal ganglia). They do not pass through the pyramids of the medulla. Fine tune movement Olives Putamen Pyramids Globus Head of Pallidus Caudate nucleus  EXTRAPYRAMIDAL: BASAL GANGLIA Basal Ganglia include: lentiform nucleus + caudate nucles + substantia nigra Lentiform nucleus = a + b b. Globus Internal a. Putamen Pallidus capsule Thalamus Head of Caudate nucleus  EXTRAPYRAMIDAL: RUBROSPINAL PATHWAY Red nucleus in midbrain – Receives inputs from cerebellum & cerebral cortex – Projects to interneurons in cord – Controls tone of flexor muscles in limbs Red nucleus  OTHER EXTRAPYRAMIDAL TRACTS Tectospinal tract – From superior colliculi to cervical cord – Reflex movements in response to visual stimuli Vestibulospinal tract – From vestibular nuclei (in medulla & pons) – Medial and Lateral Nuclei – Fibres descend ipsilaterally in the spinal cord Superior colliculus – Synapse on anterior horn cells – control tone of extensor muscles – Maintain posture (antigravity)  NOTE: TECTUM VS. TEGMENTUM Tectum – Midbrain region posterior to aqueduct of sylvius – Superior colliculus = reflex movements from visual input – Inferior colliculus = reflex movements in response to auditory input Tegmentum – Found in all three parts of brainstem – Anterior to aqueduct of sylvius in Superior midbrain colliculus – Involved in homeostatic and reflexive pathways Infererior colliculus  NOTE: TECTUM VS. TEGMENTUM Inferior/Superior Posterior Anterior Posterior Colliculius Tectum Midbrain Cerebral aqueduct Pons Substantia nigra Red nuclei 4th ventricle Tegmentum Medulla Spinal Corticospinal & cord Corticobulbar tracts Crus cerebri Anterior Tectum Tegmentum Superior colliculus = reflex movements from Found in all three parts of brainstem visual input Involved in homeostatic and reflexive Inferior colliculus = reflex movements in pathways response to auditory input  OTHER EXTRAPYRAMIDAL TRACTS Reticulospinal tract Midbrain – From two nuclei (in pons and medulla). – medial (or pontine) and lateral (or medullary) Pons reticulospinal tracts – Medial fibres descend ipsilaterally in the cord Medial – Lateral fibres descend bilaterally in the cord Lateral – Involved in locomotion and postural control Medulla Vestibulospinal and reticulospinal tracts of called the Medial System – involved in the control of balance and posture SPINAL CORD  NEUROLOGICAL EXAM Spinal reflexes (as well as tests of muscle tone) test integrity of sensory, CNS and motor reflex arc Patella tendon tap can be used to assess (others include ankle jerk, biceps, triceps etc. ) The tap causes a brief stretch of the quad muscle spindle which increases firing of the 1a sensory afferent– this monosynaptically activates the motor nerve supplying that muscle. A second branch of the afferent activated an inhibitory interneuron in the spinal cord which inhibits the motor nerve supplying the antagonist muscle (semitendinosus) A diminished response (hypo-reflexia) would be possible in someone with a lower motor neuron lesion whereas hyper-reflexia is more likely if it is an upper motor neuron lesion.  NOMENCLATURE & CLINICAL DEFINITIONS Stroke – UMN presentation Polio – virus that typically affects anterior horn cells causing LMN injury presentation in spinal nerves Multiple Sclerosis – affects the myelin coating on neurons (UMN and LMN), which damages the conduction of signals along nerves Motor Neuron Disease – group of diseases that affect motor neurons: UMN, LMN or both Palsy – paralysis Paralysis – loss/ impairment of motor function Paresis – as paralysis but not as severe Paraplegia – paralysis of lower limbs Hemiplegia – paralysis of one side of body Monoplegia – paralysis restricted to one limb or region  PRACTICE REFERENCES QUESTIONS ACKNOWLEDGMENT Prof. Robin O’ Sullivan Prof Clive Lee Dr Adrian Dervan