Transcript Motor Function_2 - bloodhounds Incorporated

Disorders of Motor
Function
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 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)
Homunculus
Basal Ganglia
• A group of deep, interrelated subcortical nuclei
that play an essential role in control of movement
• Receives indirect input from the cerebellum and
from all sensory systems, including vision, and
direct input from the motor cortex
– Functions 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 nucleus
• Putamen
• Globus pallidus in the forebrain
– Substantia Nigra (midbrain)
– Subthalamic nucleus
Structural Components of the Basal
Ganglia
• Caudate + Putamen = Striatum
• Putamen + Globus Pallidus = Lentiform nucleus
• Cortex sends messages to the caudate and
putamen of the basal ganglia
– Acts on the Thalamus
– Then to the
and editing
– Then to the
– Then to the brain stem and spinal cord
• The cerebellum – ensures the desired
movements occur smoothly
for review
Basal Ganglia
• 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
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)
• Basal Ganglia modulates the Thalamic
excitability by an inhibitory loop
• 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
Brain Stem
Midbrain
• Associated with vision,
hearing, motor control,
sleep/wake, arousal
(alertness), and
temperature regulation
Pons
• Nuclei that deal primarily
with sleep, respiration,
swallowing, bladder
control, hearing,
equilibrium, taste, eye
movement, facial
expressions, facial
sensation, and posture
Brain Stem
Medulla
• Contains the cardiac,
respiratory, vomiting
and vasomotor centers
dealing with
autonomic, involuntary
functions
– Breathing, heart rate
and blood pressure
Spinal Cord Structure and Function
– Myelinated axons surrounding gray matter = cell
bodies and their synaptic interconnections
– Collections of motor neurons with related function
in the anterior horns
– Sensory relay neurons in the posterior horn
Dorsal
Ventral
Ascending (Sensory) Pathways
– Carries information from pain, temperature and
crude touch receptors to the thalamus (relay
station of the brain)
– First neuron synapses in the dorsal horn
– Second neuron crosses the cord to the region
ventral to the central canal and travels in the
spinothalamic tract to the thalamus
Ascending Pathways
Ascending (Sensory) Pathways
Dorsal Columns
– Carries information from the skin of the lower and
upper limbs (light touch, vibration, ability to
discriminate between adjacent stimuli, pressure)
– Carries information from shoulder, arm and finger on
position and tension in muscles and tendons,
movement, etc.
– Dorsal root ganglion to the cord, to the dorsal column
of white matter, to a nucleus in the medulla to the
thalamus to the cortex for conscious perception
Descending Pathway
Descending (Motor) Pathways
Descending (Motor) Pathway
– Provides for the support of movements of the
lateral corticospinal tract
• Movements of the trunk, proximal limb muscles,
balance, posture, orienting to sight or sound and
more.
• Originates in the motor • Originates in the basal ganglia
– Includes the substantia nigra,
cortex
caudate, putamen, globus pallidus,
• Controls all of our
thalamus, and subthalamic nucleus.
voluntary movements
• Provides background for the
more crude, supportive
• Consists of upper motor
movement patterns
neurons in the Primary
Motor Cortex and lower
motor neurons in the
anterior horn of the
spinal cord
• Rapidly progressive weakness, muscle atrophy,
spasticity, dysphagia
• Early symptoms: muscle weakness in an arm or
leg, twitching, slurred speech
• Death within 2-3 years due to respiratory
compromise
• Sensory and cognitive function are unaffected
Locations of Motorneurons
Affected by ALS
• The anterior horn cells of the
spinal cord are affected
• Death of LMNs leads to
denervation, with subsequent
shrinkage of musculature and
muscle fiber atrophy.
• The UMNs of the cerebral
cortex are affected later
• Lastly the motor nuclei of the
brain stem, particularly the
hypoglossal nuclei are
affected
Lou Gehrig
Steven Hawking
http://www.youtube.com/
watch?v=-qFSMXEYC3c
Spinal Cord Trauma
• Often leads to paraplegia or quadriplegia
depending on the location and extent of the
injury
• Hyperextension Injury
– When the forehead is struck and driven
posteriorly
• Diving impact in shallow water
• May tear the anterior spinal ligament and spinal cord
may contact the vertebral body
Trauma to the Spinal Cord
• Hyperflexion Injury
– When the head of shoulders are struck
from behind by an object of
considerable weight or from a fall
Spinal Cord Trauma
• Concussion
– Mild injury, transient and reversible
– Contusion
• Severe trauma with hemorrhagic necrosis, edema
and softening of the cord – Myelomalacia,
• or
blood in the cord – Hematomyelia
– Laceration or Tansection
Cervical Contusion
• Characteristics of Disorders of the
Basal Ganglia
– Involuntary movements
– Alterations in muscle tone
– Disturbances in body posture
Characteristics of Disorders of the
Basal Ganglia
• Involuntary movements
• Alterations in muscle tone
• Disturbances in body posture
Types of Involuntary Movement Disorders
• Tremor = Trembling or vibrating
• Tics = A habitual spasmodic contraction of the
muscles, most often in the face
• 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
• Characteristics
– 0.3% of the general population has Parkinson Disease =
80,000 people
– Usually begins after 50 years of age
– Affects men twice as often as women
– Course of the disease is 10-20 years
• Clinical syndrome
– Parkinsonism
• James Parkinson, 1817 = ‘shaky palsy’
Parkinson Disease
• Degeneration of pigmented neurons (containing
dopamine) in the substantia nigra
• Cause unknown: May be environmental/genetic
• Early symptoms: tremor, rigidity, slow
movement
• Later: cognitive problems, dementia, dyskinesia
• Gross: atrophy of substantia nigra
• Microscopic: Lewy bodies (inclusions in
neurons)
Parkinson Disease
• Cogwheel-type motion
– Ratchet-like movements
• Bradykinesia
– Slowness initiating and performing movements
• Difficulty walking
• Neuropsychiatric disorders
Parkinson disease (R) : atrophy of substantia nigra
Parkinson disease: Lewy body
Michael J. Fox and Muhammad Ali
• http://www.youtube.com/watch?
v=xuVY7wS25rc&feature=related
Huntington Disease
• Degeneration of basal ganglia and cerebral
cortex
• Early symptoms: lack of coordination, unsteady
gait
• Later: chorea (involuntary writhing), psychiatric
symptoms, dementia
• Autosomal dominant mutation on chromosome
4
• Begins in 30s-40s; slow progression over 10-20
years
Read this story about Katharine and her family:
http://www.nytimes.com/2007/03/18/health/18huntington.html
Multiple Sclerosis (MS)
• A Demyelinating Disease of the CNS
– Most common non-traumatic cause of
neurologic disability among young and middleaged 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.
http://www.youtube.com/watch?v
=-BGBSsKBrbI&feature=related
http://www.youtube.com/watch?v
=qgySDmRRzxY
Multiple Sclerosis
•
•
•
•
•
Most common demyelinating disorder
Etiology unknown; related to autoimmunity
Variety of motor and sensory symptoms
Relapsing-remitting course
Plaques (areas of demyelination) in brain,
cord
Multiple sclerosis
Multiple sclerosis plaques around ventricles
Segmental Demyelination
• http://www.youtube.com/watch?v=c-8ia81XPMw
• 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.
Guillain-Barre Syndrome
• Acute peripheral neuropathy
• Progressive, ascending weakness
• Usually self-limited (but may involve
respiratory muscles, requiring respiratory
intensive care)
• Autoimmune attack on peripheral nerve
resulting in demyelination and conduction
block
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 full and spontaneous recover in 6
to 12 months
Alzheimer Disease
• Most common cause of dementia in the elderly
• Symptoms:
– Early on: forgetfulness, memory disturbances
– Language deficits, loss of learned motor skills,
alterations in mood/behavior, disorientation
– Finally: patient becomes profoundly disabled, mute,
immobile
• Gross: Cortical atrophy, neuronal loss
• Microscopic: neurofibrillary tangles, neurotic
plaques
Alzheimer Disease
• http://www.youtube.com/watch?v=y3g4emL
Q1Ic
• Neurofibrillary tangles
– Cytoplasmic bundles of filaments encircling the
nucleus of pyramidal cells
– Tau protein
• Amyloid beta protein
– Produced instead of an integral protein
– Triggers an inflammatory response
Alzheimer disease: brain atrophy
Alzheimer disease: brain atrophy
Alzheimer disease: brain atrophy
Alzheimer disease: progression
Alzheimer disease: plaques and tangles
Alzheimer disease: plaques (L) and tangles (R)
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
– Neuron cell bodies grouped together in the PNS
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
• http://www.youtube.com/watch?v=KA8W5Uf
E4ts
Duchenne Muscular Dystrophy
• 1:3500 male births
– Inherited recessive singlegene 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 retardation, 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
Tests
•
•
•
•
Electromyography (EMG)
Genetic tests
Muscle biopsy
Serum CPK
Treatments
• There is no known cure for Duchenne
muscular dystrophy.
• Treatment aims to control symptoms to
maximize quality of life.
– Gene therapy may become available in the
future.
Becker Muscular Dystrophy
• Very similar to Duchenne 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
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 antibodymediated 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
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
• Intravenous immunoglobulin
– Unknown how it works
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
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
THE END
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
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
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•
•
•
Central cord syndrome
Anterior cord syndrome
Brown-Séquard syndrome
Conus medullaris syndrome
Areas Affected by SCI
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•
•
Spinal reflexes
Ventilation and communication
Autonomic nervous system
Temperature regulation
Edema and deep vein thrombosis
Sensorimotor function
Areas Affected by SCI (cont.)
•
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•
•
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
(and Schwann cells in the peripheral nervous
system) 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
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 naked eye
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
Spinal Cord
Spinal Cord
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.
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.