Neuro Pathophysiology
Terms
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- Functions of the Nervous System
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Controls skeletal muscle movement
Helps regulate cardiac and visceral smooth muscle activity
Enables reception, integration, and perception of sensory information - Functions of the Nervous System (cont.)
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Provides substratum necessary for intelligence, anticipation, and judgment
Facilitates adjustment to ever-changing external environment - Components of the Nervous System
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CNS
PNS - CNS
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Consists of the brain and spinal cord, which are protected by the skull and vertebral column
Concentration of computational and control functions - PNS
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Found outside structures of CNS
Functions as input-output system for relaying information to CNS and transmitting output messages to control effector organs - Structures of the Brain
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Hindbrain
Midbrain
Forebrain -
Hindbrain
(Brain Stem) -
medulla oblongata
pons
cerebellum - Midbrain
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Include two pairs of dorsal enlargements
- superior coliculi
- inferior colliculi - Forebrain
-
Consists of two hemispheres covered by cerebral cortex
Contains central masses of gray matter, basal ganglia, diencephalon with its derivatives—thalamus and hypothalamus - Lobes of the Brain
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frontal lobe
parietal lobe
temporal lobe
occipital lobe - Frontal lobe
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extends from frontal pole to central sulcus (fissure)
- separated from temporal lobe by lateral sulcus - Parietal lobe
- lies behind central sulcus (postcentral gyrus); above lateral sulcus
- Temporal lobe
- lies below the lateral sulcus and merges with the parietal and occipital lobes
- Occipital lobe
-
- lies posterior to temporal and parietal lobes
- arbitrarily separated from them - Levels of the Spinal Cord
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- spinal cord is shorter than spinal column in adult
Cauda Equina
- collection of spinal nerves that travel down spinal canal below termination of spinal cord - Spinal Nerves
- Each exits at a vertebral level that corresponds to its level in the cord
- Horns of the Spinal Cord
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- extensions of gray matter that form the letter “Hâ€
- White matter of the cord is composed of myelinated axons traveling up cord to the brain (sensory) or down cord from brain (motor).
- dorsal horns
- ventral horns - Dorsal Horns
- Contain neurons that receive afferent impulses through dorsal roots
- Ventral Horns
- Contain neurons and the efferent lower motor neurons that leave the cord through the ventral roots
- Information Flow
-
- cranial and spinal nerves come out from the CNS
BUT
- information flowing through may be coming out (efferent; motor information)
- OR coming in (afferent; sensory information) to the CNS - Afferent Nerve
- - carries information from sensory receptors in skin to brain
- Efferent Nerve
- - carries information from brain to neurons controlling leg muscle, causing response
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Nerves
Cranial or Spinal -
- collections of nerve fibers (individual axons or dendrites of individual neurons)
Individual fibers within nerve may be transmitting motor information out to periphery or sensory information in to CNS - Major Cells of the Nervous System
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- neurons
- glia -
Neurons
(Functioning Cells) -
- Afferent (sensory) neurons carry information to CNS
- Efferent (motor neurons) carry information from CNS to effector organs -
Neurons
(Functioning Cells)
cont. -
- gray matter: nerve cell bodies in CNS
- white matter: myelinated axons forming tracts in CNS - Glia
-
- protect nervous system; supply metabolic support
- astrocytes contribute to blood-brain barrier; also give metabolic support
- oligodendrocytes in brain and Schwann cells in periphery make myelin to insulate nerve fibers
- microglia: immune cells in brain -
Sensory Component of Nervous System
Function - Provides awareness of body sensations (i.e. body position in space, sight, hearing, touch, temperature, limb position, pain)
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Sensory Component of Nervous System
Composition -
- sensory receptors: consist of discrete nerve endings in skin and other body tissues
- dermatomes: areas of skin supplied by discrete levels of spinal nerves - Major Modalities of Sensory Experience
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Discriminative Touch
Temperature Sensation
Body Position
Nociception (Pain sense) - Discriminative Touch
- Location, Sharp, Dull, Soft, Fuzzy, Scratchy
- Temperature Sensation
- Hot, Warm, Cool, Cold
- Body Position
- Flexion, Extension, Position in Space, Balance
- Nociception (Pain sense)
- Sharp, Dull, stabbing, Aching, Burning
- Neurons Found in Sensory Systems
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First-order neurons
Second-order neurons
Third-order neurons - First-Order Neurons
- Transmit sensory information from periphery to spinal cord.
- Second-Order Neurons
- Relay sensory information up spinal cord to thalamus.
- Third-order neurons
- Relay information from the thalamus to the cerebral cortex
- Pathways from Spinal Cord to Thalamic Level of Sensation
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- anterolateral pathways (spinothalamic tracts)
- discriminative pathway (posterior columns) - Anterolateral Pathways (Spinothalamic Tracts)
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- bilateral multisynaptic slow-conducting tracts
- provide for transmission of sensory information that does not require discrete localization of signal source or fine discrimination of intensity - Discriminative Pathway (Posterior Columns)
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- crosses at base of medulla
- relays information to brain for perception, arousal, and motor control - Corticospinal (Pyramidal) Tracts
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-Nerve cell bodies: pyramid-shaped neurons in motor cortex
-myelinated axons pass down through brain in bundle called internal capsule.
- In brain stem, axons cross to opposite side: decussation of pyramids
- axons then course down ventral lateral spinal cord
- individual axons peel off from rest at particular levels; then synapse with primary motor neurons
- important in gross motor movement - Extrapyramidal Tracts
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Additional synapses may be present in midbrain and pons and finally at the lower motor neurons at each level of cord.
Serves to smooth and integrate movement - Requirements of Motor Systems
- Functioning neuromuscular junction that links nervous system activity with muscle contraction
- Motor Systems
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Pyramidal motor system
Extrapyramidal system - Pyramidal Motor System
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Originates in motor cortex
Provides control of delicate muscle movement - Extrapyramidal System
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Originates in basal ganglia
Provides background for more crude, supportive movement patterns - Motor Unit
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Excitatory & inhibitory influences come from higher centers.
Excitatory influences may come from sensory input at same level. - Neuromuscular Junction
- Acetylcholine binds to receptors in the endplate region of the muscle fiber surface to cause muscle contraction
- Mechanisms Controlling Coordinated Movement
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Antagonists
- Oppose movement
Synergists
- Assist agonist muscles by stabilizing a joint or contributing additional force to movement -
Spinal Cord Injury (SCI)
Definition - Damage to neural elements of spinal cord
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Spinal Cord Injury (SCI)
Causes - Motor vehicle crashes, falls, violence and sporting activities
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Spinal Cord Injury (SCI)
Involvement -
Most SCIs involve damage to vertebral column and/or supporting ligaments as well as spinal cord
Commonly involve both sensory and motor function - Types of Injuries to Vertebral Column
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Fractures
Dislocations
Subluxations - Incomplete Spinal Cord Injuries
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Central Cord Syndrome
Brown-Séquard Syndrome
Anterior Cord Syndrome - Types of Paralysis
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Monoplegia
Hemiplegia
Tetraplegia or quadriplegia
Paraplegia - Areas Affected by SCI
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Pain Transmission
Bladder and bowel function
Sexual function - Disorders of Motor Function
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Upper motoneuron lesions
Lower motoneuron lesions - Upper Motoneuron Lesions
- Can involve motor cortex, internal capsule, or other brain structures through which corticospinal or corticobulbar tracts descend, or spinal cord
- Lower Motoneuron Lesions
- Disrupt communication between muscle and all neural input from spinal cord reflexes, including stretch reflex, which maintains muscle tone
- Muscle Spasm
- Sudden violent involuntary contraction of a muscle or group of muscles
- Spasticity
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Certain muscles are continuously contracted leads to
- muscle stiffness/tightness
-may interfere with gait, movement, or speech:
= Damage to the portion of brain or spinal cord that controls voluntary movement usually causes spasticity - Diseases Associated with Spasticity
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Brain damage due to lack of oxygen
Brain trauma
Severe head injury
Metabolic disease (adrenoleukodystrophy - Spastic Contractions
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- often triggered by sensory stimuli that normally elicit motor reflex
- sensory stimulus that evokes contraction much smaller than normal
- contraction evoked much stronger than normal - Spasticity (cont.)
- when chronic can result in contractures
- Basal Ganglia
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function in inherited & highly learned & rather automatic
- involved in cognitive and perception functions - Dopamine pathway & effects
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Mesocortical - Cognition
Mesolimbic - Emotions
Nigrastriatal - Extra-pyramidal system that modulate movement -
Cholinergic pathway & effects
Cortex and Limbic System -
-Learning and memory;
-Wakefulness and attention -
Cholinergic pathway & effects
PNS -
Useful throughout the body
- Regulation of Parasympathetic Nervous System
- Excitatory transmission at neuromuscular junction -
Disorders of the Basal Ganglia
Characteristics -
Involuntary movements
Alterations in muscle tone
Disturbances in body posture - Involuntary Movement Disorders Types
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Tremor
Tics
Chorea
Athetosis
Ballismus
Dystonia
Dyskinesias -
Parkinson Disease
Definition - degenerative disorder of basal ganglia function that results in variable combinations of tremor, rigidity, and bradykinesia
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Parkinson Disease
Characteristics -
- progressive destruction of nigrostriatal pathway
- subsequent reduction in striatal concentrations of dopamine - Multiple Sclerosis (MS)
- - most common non-traumatic cause of neurologic disability among young & middle-aged adults
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Multiple Sclerosis (MS)
Characteristics -
- exacerbations and remissions over many years in several different sites in CNS
- starts with normal or near-normal neurologic function between exacerbations
- during progression, less improvement between exacerbations, neurologic dysfunction increases - Brain Injury Causes
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Trauma
Tumors
Stroke
Metabolic derangements
Degenerative disorders - Brain Injury Manifestations
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Alterations in sensory and motor function
Changes in the level of consciousness - Levels of Consciousness
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Confusion
Delirium
Obtundation
Stupor
Coma - Signs of Decreased LOC
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Earliest
- Inattention, mild confusion, disorientation, and blunted responsiveness
Later
- marked inattention; variable lethargic or agitated
- may progress to obtunded; may respond only to vigorous or painful stimuli - Common Pathways of Brain Damage
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Effects of ischemia
Excitatory amino acid injury
Cerebral edema
Injury due to increased intracranial pressure (ICP) - Hypoxia
- deprivation of oxygen with maintained blood flow
- Ischemia
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- greatly reduced or interrupted blood flow
- interferes with O2 and glucose delivery, and metabolic waste removal -
Injury From Excitatory Amino Acids
Definition - Injury to neurons caused by overstimulation of receptors for specific amino acids that act as excitatory neurotransmitters
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Injury From Excitatory Amino Acids
Causes -
Stroke
Hypoglycemic injury
Trauma
Chronic degenerative disorders (Huntington’s disease,Alzheimer’s dementia) - Cerebral Edema
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Vasogenic Edema
Cytotoxic Edema - Vasogenic Edema
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- occurs with conditions that impair the function of blood-brain barrier
- allows transfer of water and protein from vascular into interstitial space - Cytotoxic Edema
- - increase in intracellular fluid
- Brain Injury Types
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Primary or Direct
Secondary Injuries - Primary or Direct Brain Injuries
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Damage is caused by impact
Include diffuse axonal injury and focal lesions of laceration, contusion, and hemorrhage - Secondary Brain Injuries
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Damage results from subsequent brain swelling, infection, cerebral hypoxia
Often diffuse or multi-focal, including concussion, infection, and hypoxic brain injury - Epidural Hematoma
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- Usually caused by head injury with skull fracture
- between inner table of bones of skull and dura - Subdural Hematoma
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- Usually result of tear in small bridging veins that connect veins on surface of cortex to dural sinuses
- Develops in area between dura and arachnoid (subdural space) - Blood Supply to Brain
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Anterior
- two internal carotid arteries
Posterior
- vertebral arteries -
Cerebral Blood Flow
Metabolic Factors -
Carbon dioxide
Hydrogen ion
Oxygen concentration - Ischemic Strokes
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- interruption of blood flow in cerebral vessel
- most common type of stroke (70%-80%) - Hemorraghic Strokes
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- bleeding into brain tissue
- blood vessel rupture
-- HTN, aneurysms, AVM, head injury, blood dyscrasias - Stroke Risk Factors
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Age, sex, race
Family history
Hypertension
Smoking
Diabetes mellitus
Asymptomatic carotid stenosis
Sickle cell disease
Hyperlipidemia
Atrial fibrillation - Stroke Related Deficits
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Motor deficits
Dysarthria and Aphasia
Cognitive and Other Deficits - Seizure
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- uncontrolled, chaotic activity in brain
- produces muscular activity
-- tonus (muscle contraction)
-- clonus (alternate contraction and relaxation
-- complete relaxation/ paralysis - Seizure Risk Factors
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Lifetime risk - 10%
Epilepsy at some point: 3-4%
Epilepsy at any given time: 0.5-1%
Acute reaction seizure: 3-4%
Single unprovoked seizure: 1%
Active epilepsy >55 yrs: 0.9% -
Seizure Activity Risk Factors
Specific Populations -
Acute stroke – ~ 25%
Brain tumor – 30% as first symptom
-- 18% with brain metastasis
Infection
-- Bacterial meningitis – 25%
-- Herpes encephalitis – 50%
Dialysis encephalopthy – 50%
Alzheimer's – 16% - Seizure Classification
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Partial
Generalized - Partial Seizures
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Simple - no impairment of consciousness
Complex - impairment of consciousness
Partial seizures evolving to secondarily generalized seizures - Generalized Seizures
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Absence seizures (typical or atypical)
Atonic seizures
Myotonic seizures
Clonic seizures
Tonic seizures
Tonic-clonic seizures - Status Epilepticus
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Definition
- Rapid succession of epileptic seizures
Sudden withdrawal of AEDs may precipitate seizures or status epilepticus
First drug of choice
- IV diazepam (benzodiazepine) -
Status Epilepticus
(cont.) -
- possible intubation, ventilation
- after IV benzo, give loading dose of phenytoin (long-acting anticonvulsant)
- Possible complications: lactic acidosis, hyperthermia - Bacterial Meningitis
-
“Meningococcal meningitis†= Neisseria meningitides.
“Pneumococcal meningitis†= Streptococcus pneumonae.
Other bacterial causes:
- Haemophilus influenza
- Mycobacterium tuberculosis. -
Bacterial Meningitis
(cont.) -
- after infecting meninges, rapidly destroy capillary structure and invade brain
- can be rapidly fatal (hours)
- prophylactic abx w/exposure - Viral Meningitis
-
- caused by various viruses
- usually mild
Immunosuppressed patients (HIV, chemotherapy) can get fulminant, fatal viral meningitis caused by
- Epstein Barr virus
- herpes simplex virus
- West Nile virus - Alzheimer's Disease Stages
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- progressive, unrelenting
- NO KNOWN CURE
- few therapeutic options
- > 4 million Americans
- by 2010, Medicare/Medicaid costs will be >$79 billion
- other costs include informal caregiving (can cost businesses $61 billion/yr in lost work days - Clinical Hallmarks/Major Symptoms Of Alzheimer’s Disease
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Progressive cognitive impairment, particularly memory loss.
Impaired judgment and decision-making ability.
Difficulty orienting to physical surroundings.
Language problems - Neuropathological Hallmarks of Alzheimer’s Disease
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Neuron Death
Neurofibrillary Tangles
Amyloid Plaques