Spinal Cord Somatosensory – Dorsal column-medial lemniscus tract Touch/proprioception/vibration sensory pathway – Anterolateral system Pain/temperature sensory pathway Motor – Corticospinal tract Motor pathway for upper motor neuronal signals coming from cerebral cortex and brainstem motor nuclei
The cerebellum receives continuous information about the sequence of muscle contractions from the brain Receives sensory information from the peripheral parts of the body – Proprioception sequential changes in the status of each body part
The Cerebellum Coordination of motor movement – proprioception Cerebellum-associated movement disorders – Causes Congenital defect, vascular accident, or growing tumor – Types Vestibulocerebellar ataxia – Not smooth movement Decomposition of movement Cerebellar tremor – Rhythmic back-and-forth movement of a finger or toe – Cannot maintain a fix on the body part
Thalamus It relays to the cerebral cortex information received from other regions of the brain and spinal cord. Sends information down spinal cord to the body – a brain “switching station”
Thalamus The cerebral cortex is interconnected with the Thalamus – Excitatory circuit If unmodulated would cause hyperactivity = stiffness and rigidity with a continuous tremor (tremor at rest)
Structural Components of the Basal Ganglia Caudate nucleus Putamen Globus pallidus in the forebrain – Substantia Nigra (midbrain) – Subthalamic nucleus
Basal Ganglia A group of deep, interrelated subcortical nuclei that play an essential role in control of movement Receive indirect input from the cerebellum and from all sensory systems, including vision, and direct input from the motor cortex – Function in the organization of inherited and highly learned and rather automatic movement programs – Also involved in cognitive and perception functions
Structural Components of the Basal Ganglia Caudate + Putamen = Striatum Putamen + Globus Pallidus = Lentiform nucleus
Basal Ganglia Basal Ganglia modulates the Thalamic excitability by inhibitory loop Basal Ganglia monitors sensory information coming into the brain – sends it to the right place to be stored as a memory
Four Functional Pathways Involving Basal Ganglia 1.A dopamine pathway from the substantia nigra to the striatum 2.A γ-aminobutyric acid (GABA) pathway from the striatum to the globus pallidus and substantia nigra 3.Acetylcholine-secreting neurons, which are important in networks within the neostriatum 4.Multiple general pathways from the brain stem that secrete norepinephrine, serotonin, enkephalin, and several other neurotransmitters in the basal ganglia and the cerebral cortex
Characteristics of Disorders of the Basal Ganglia Involuntary movements Alterations in muscle tone Disturbances in body posture
Motor Cortex Highest level of motor function – Precise, skillful, intentional movements Speech, flexor muscles of limbs, etc. – Controlled by the primary, premotor and supplementary motor cortices in the frontal lobe Receives information from the Thalamus, cerebellum and basal ganglia
Motor Cortex Primary motor cortex Responsible for execution of a movement. Adjacent to central sulcus Motor Humunculus Premotor cortex (areas 6 and 8) Generates intricate plan of movement. Throwing a ball or picking up a fork
Motor Cortex Supplementary motor cortex Involved in the performance of complex, skillful movements – (areas 6 and 8)
Pyramidal motor system Originates in the motor cortex Controls all of our voluntary movements Consists of upper motor neurons in the Primary Motor Cortex and lower motor neurons in the anterior horn of the spinal cord – The Ventral Corticospinal tract Damage to LMN's causes flaccid paralysis Extrapyramidal motor system Originates in the basal ganglia Provides background for the more crude, supportive movement patterns Includes the substantia nigra, caudate, putamen, globus pallidus, thalamus, and subthalamic nucleus. All of these nuclei are synaptically connected to one another, the brainstem, cerebellum and the pyramidal system.
Disorders of Motor Function Upper motoneuron (UMN’s) Originate in the motor region of the cerebral cortex or brain stem – Carries motor information down spinal cord to stimulate target muscle Lesions can involve the motor cortex, the internal capsule, or other brain structures through which the corticospinal or corticobulbar tracts descend, or the spinal cord
1. Paralysis or weakness of movements of the affected side but gross movements may be produced. – No muscle atrophy is seen initially 2. Babinski sign is present: 3. Loss of performance of fine-skilled voluntary movements especially at the distal end of the limbs 4. Superficial abdominal reflexes and cremasteric reflex are absent. 5. Spasticity or hypertonicity of the muscles. 6. Clasp-knife reaction: initial higher resistance to movement is followed by a lesser resistance 7. Exaggerated deep tendon reflexes and clonus may be
Disorders of Motor Function Lower motoneurons (LMN’s) Connects the brainstem and spinal cord to muscle cells – Brings nerve impulses from upper motor neuron to the muscles Lesions disrupt communication between the muscle and all neural input from spinal cord reflexes, including the stretch reflex, which maintains muscle tone
Signs of Lower Motor Neuron Lesions (LMNL) 1. Flaccid paralysis of muscles supplied. 2. Atrophy of muscles supplied. 3. Loss of reflexes of muscles supplied. 4. Muscles fasciculation (contraction of a group of fibers) due to irritation of the motor neurons – seen with nakedeye
Disorders of Skeletal Muscle Groups Muscular atrophy – If a normally innervated muscle is not used for long periods, the muscle cells shrink in diameter, lose much of their contractile protein, and weaken. Muscular dystrophy – Genetic disorders that produce progressive deterioration of skeletal muscles because of mixed muscle cell hypertrophy, atrophy, and necrosis
Muscular Dystrophy Involves the motor neuron – Probably do not involve the nervous system Slow progressive onset of muscle weakness
Duchenne Muscular Dystrophy 1:3500 male births – Inherited recessive single- gene defect On short arm of X chromosome – Gene codes for dystrophin Connects Z-lines to connective tissue surrounding muscle – Break down of sarcolemma = necrosis of muscle fibers
Duchenne Muscular Dystrophy Symptoms usually appear before age 6 and may appear as early as infancy. They may include: Fatigue, mental retardtion, muscle weakness (begins in legs and pelvis), difficulty with motor skills (running, jumping hopping), frequent falls May be confined to wheelchair by age of 12
Signs and Tests A complete nervous system (neurological), heart, lung, and muscle exam may show: Abnormal heart muscle Congestive heart failure Arrhythmia Scoliosis Respiratory disorders Muscle wasting
Treatments There is no known cure for Duchenne muscular dystrophy. There is no known cure for Duchenne muscular dystrophy. Treatment aims to control symptoms to maximize quality of life. Treatment aims to control symptoms to maximize quality of life. – Gene therapy may become available in the future. Gene therapy may become available in the future.
Becker Muscular Dystrophy Very similar to Duchenne muscular dystrophyDuchenne muscular dystrophy – Becker muscular dystrophy gets worse much more slowly 3 - 6 out of every 100,000 males X-linked – Manifests later in childhood of adolescence
Question Which motor system is responsible for crude muscle movements? a.Pyramidal motor system b.Extrapyramidal motor system
Answer b. Extrapyramidal motor system: This system originates in the basal ganglia and provides background for the more crude, supportive movement patterns.
Neuromuscular Junction Serves as a synapse between a motor neuron and a skeletal muscle fiber Consists of the axon terminals of a motor neuron and a specialized region of the muscle membrane called the endplate The transmission of impulses is mediated by the release of the neurotransmitter acetylcholine from the axon terminals. Acetylcholine binds to receptors in the endplate region of the muscle fiber surface to cause muscle contraction.
Alterations of Neuromuscular Function Drugs and Toxins can alter neuromuscular function by changing the release, inactivation, or receptor binding of acetylcholine. – Curare acts on the post-junctional membrane of the motor endplate to prevent the depolarizing effect of the neurotransmitter. Used during many types of surgical procedures – Clostridium botulinum blocks acetylcholine release and results in paralysis Botox – Organophosphates block acetylcholinesterase Nerve gases and pesticides
Myasthenia Gravis Definition – Disorder of transmission at the neuromuscular junction that affects communication between the motoneuron and the innervated muscle cell Cause – Autoimmune disease caused by antibody- mediated loss of acetylcholine receptors in the neuromuscular junction Sensitized Helper T Cells – Antibody directed attack on receptors
Myasthenia Gravis Muscle weakness and fatigability with sustained effort – Ptosis due to eyelid weakness – Diplopia – Progresses to generalized weakness Myasthenic crisis – Compromised ventilation – Usually during a period of stress
Diagnosis Tensilon or Edrophonium test – Acetylcholinesterase inhibitor Patient feels little to no weakness for a short period of time MUSK antibodies http://www.youtube.com/watch?v=k7YX9kuWr xA http://www.youtube.com/watch?v=k7YX9kuWr xA
Treatment Pyridostigmine and neostigmine are the drugs of choice – Drug used to inhibit acetylcholinesterase Plasmapheresis – Removes antibodies from circulation – http://www.youtube.com/watch?v=AwAs7uUZJVE http://www.youtube.com/watch?v=AwAs7uUZJVE Intravenous immunoglobulin – Unknown how it works
Components of the Peripheral Nervous System Motor and sensory branches of the cranial and spinal nerves The peripheral parts of the autonomic nervous system Peripheral ganglia
Peripheral Nerve Regeneration Damage to a peripheral nerve axon due to injury or neuropathy – Results in degenerative changes, followed by breakdown of the myelin sheath and Schwann cells Regeneration factors – Proximity to soma – Crushing vs. cutting
Peripheral Neuropathy Definition – Any primary disorder of the peripheral nerves Results – Muscle weakness, with or without atrophy and sensory changes Involvement – Can involve a single nerve (mononeuropathy) or multiple nerves (polyneuropathy)
Mononeuropathies Caused by localized conditions such as trauma, compression, or infections that affect a single spinal nerve, plexus, or peripheral nerve trunk – Fractured bones may lacerate or compress nerves. – Excessively tight tourniquets may injure nerves directly or produce ischemic injury. – Infections such as herpes zoster may affect a single segmental afferent nerve distribution.
Mononeuropathies Carpal Tunnel Syndrome – Compression-type mononeuropathy Median nerve compression – Tinsel Sign Development of a tingling sensation in palm by light percussion on median nerve at the wrist
Polyneuropathy Involves demyelination or axonal degeneration of multiple peripheral nerves that leads to symmetric sensory, motor, or mixed sensorimotor deficits Typically, the longest axons are involved first, with symptoms beginning in the distal part of the extremities.
Causes of Polyneuropathies Immune mechanisms (Guillain-Barré syndrome, rheumatoid arthitis, lupus, hypothyroid) Toxic agents (arsenic polyneuropathy, lead polyneuropathy, alcoholic polyneuropathy) Metabolic diseases (diabetes mellitus, uremia, chronic kidney disease) Low levels of vitamin B12 or other problems with your diet Poor blood flow to the area
Segmental Demyelination Disorder of the Schwann cells – Guillain-Barré Syndrome Autoimmune disorder – Linked to CMV, Campylobacter jejuni, and Epstein-Barr Virus Common in people of both sexes between ages 30 and 50 Can replace the Schwann cells New myelin sheath is thin and subject to injury A serious disorder that occurs when the body's defense (immune) system mistakenly attacks part of the nervous system. This leads to nerve inflammation that causes muscle weakness.muscle weakness.
Guillain-Barré Syndrome Symptoms – Rapidly progressing limb weakness and loss of tendon reflexes – Flaccid paralysis – Pain – May lead to death due to ventilatory failure and autonomic disturbances Treatment – Plasmapheresis – Intravenous Immunoglobulin therapy – 80-90% achieve a gull and spontaneous recover in 6 to 12 months
Nerve Root Injuries Herniated or Ruptured intervertebral disk – Sensory deficits Spinal nerve root compression Paresthesias and numbness – Particularly of the leg and foot – Knee and ankle reflexes also may be diminished or absent – Motor weakness and Pain
Question Lead toxicity would result in which of the following conditions? a.Mononeuropathies b.Polyneuropathies c.Upper motor lesion d.Myasthenia gravis
Answer a.Mononeuropathies b.Polyneuropathies: Polyneuropathies would result from systemic exposure to lead. c.Upper motor lesion d.Myasthenia gravis
Types of Involuntary Movement Disorders Tremor Tics Chorea = Irregular writhing movements Athetosis = Wormlike twisting of limb Ballismus = Violent flinging motion of limbs Dystonia = Abnormal posture Dyskinesias = Bizarre wriggling movements – Tardive Dyskinesia Develops due to use of antipsychotic medications
Parkinson Disease Definition – A degenerative disorder of basal ganglia function that results in variable combinations of tremor, rigidity, and bradykinesia Characteristics – 0.3% of the general population has Parkinson Disease – Usually begins after 50 years of age – Progressive destruction of the nigrostriatal pathway, with subsequent reduction in striatal concentrations of dopamine – Caused by environmental and genetic factors Clinical syndrome – Parkinsonism James Parkinson, 1817 = ‘shaky palsy’ Drug induced parkinsonism due to antipsychotics in high doses
Amyotrophic Lateral Sclerosis (ALS) Definition – A devastating neurologic disorder that selectively affects motor function – The disease typically follows a progressive course, with a mean survival period of 2–5 years from the onset of symptoms.
Locations of Motoneurons Affected by ALS The anterior horn cells of the spinal cord The motor nuclei of the brain stem, particularly the hypoglossal nuclei The UMNS of the cerebral cortex Death of LMNs leads to denervation, with subsequent shrinkage of musculature and muscle fiber atrophy.
Multiple Sclerosis (MS) A demyelinating disease of the CNS Most common nontraumatic cause of neurologic disability among young and middle-aged adults Characterized by exacerbations and remissions over many years in several different sites in the CNS – Initially, there is normal or near-normal neurologic function between exacerbations. – As the disease progresses, there is less improvement between exacerbations and increasing neurologic dysfunction.
Spinal Cord Injury (SCI) Definition – Damage to the neural elements of the spinal cord Causes – Motor vehicle crashes, falls, violence, and sporting activities Involvement – Most SCIs involve damage to the vertebral column and/or supporting ligaments as well as the spinal cord. – Commonly involve both sensory and motor function
Types of Injuries to the Vertebral Column Fractures Dislocations Subluxations
Types of Incomplete Spinal Cord Injuries Central cord syndrome Anterior cord syndrome Brown-Séquard syndrome Conus medullaris syndrome
Areas Affected by SCI Spinal reflexes Ventilation and communication Autonomic nervous system Temperature regulation Edema and deep vein thrombosis Sensorimotor function
Areas Affected by SCI (cont.) Skin integrity Pain reception Bladder and bowel function Sexual function
Question Demyelination is the causative factor in which disease? a.Parkinson disease b.ALS c.Multiple sclerosis
Answer a.Parkinson’s disease b.ALS c.Multiple sclerosis: MS is caused by an autoimmune attack on the oligodendrocytes of the CNS.
Classifications of Muscles Extensors – Muscles that increase the angle of a joint Flexors – Muscles that decrease the angle of a joint
Components of the Neuromuscular System Neuromuscular unit containing motor neurons Myoneural junction Muscle fibers – Actin and Myosin Spinal cord Efferent pathways from the brain stem circuits
Requirements of Motor Systems Upper motoneurons project from the motor cortex to the brain stem or spinal cord. – Directly or indirectly innervate the lower motoneurons or contracting muscles – Motor unit is a motor neuron and all the muscle fibers it innervates Sensory feedback from the involved muscles – Continuously relayed to the cerebellum basal ganglia and sensory cortex Functioning neuromuscular junction that links nervous system activity with muscle contraction
Mechanisms Controlling Coordinated Movement Agonists – Promote movement Antagonists – Oppose movement Synergists – Assist the agonist muscles by stabilizing a joint or contributing additional force to the movement
Motor Unit The motor neuron and the muscle fibers it innervates – A single motor neuron may innervate a few thousand muscle fibers Upper motor neurons Lower motor neurons