Neurological System

Neuron components

• Cell body

• Dendrites

• Axon

Neuron types

• Sensory (afferent): To CNS

• Motor (efferent): Away from CNS to body

• Interneuron

Additional:

• Supporting cells

Interneuron

Most abundant neuron type, provide connections between neurons and transmit signals between afferent and efferent neurons

Supporting cells

Neuroglia: provide support and nutrition, form myelin and support homeostasis

Membrane potential

Electrical charge difference between inside and outside of the cell

Action potential

A temporary, specific type of change in the broader membrane potential of a cell.

• A rapid, temporary spike and reversal of the membrane potential when a cell is excited and fires a signal

Components of Action potential

1. Resting membrane potential: Na and K channels closed, inside of cell is more negative than outside

2. Depolarization phase: A stimulus hits the threshold, Na channels open and sodium rushes into the cell, making the inside positive

3. Repolarization phase: Na channels close and become inactive, K channels open, making potassium flow out of the cell turning the inside negative again.

Flow of information across a synapse

1. Electrical

2. Chemical

Synapse structures: presynaptic terminal, synaptic cleft, postsynaptic membrane

Processes of Neural Injury

Types:

• Chromatolyosis

• Atrophy

• Neuronophagia

• Intraneuronal inclusions

Chromatolyosis

Neuron swells as a result of an injury

Atrophy

Neurons shrink

Neuronophagia

Dead neuron damages nearby cells, causing phagocytosis and inflammation

Intraneuronal inclusions

Structures formed in the nucleus or cytoplasm

Central nervous system organization

Spinal cord

• Ventral horns

  • Anterior extensions

  • Efferent motor neurons leaving cord

• Dorsal horns

  • Posterior extensions

  • Sensory neurons receiving afferent impulses

Tissue composition

• White matter: Axons and dendrites

• Gray matter: Cell bodies

CNS Pyramidal and Extrapyramidal systems

Pyramidal

• Extends from the sensorimotor areas of the brain to the motor neurons of the ventral horn of the spinal cord

• Controls voluntary movement

Extrapyramidal

• Basal ganglia

• Fine-tunes and stabilizes movement

CNS protection

• Cerebrovascular circulation: can control BP

• Blood-brain barrier

• CSF

Neural injury responses

• Astrogliosis

• Microglial nodules

• Axonal degeneration

• Axonal regeneration

• Neuropathy

• Demyelination

Astrogliosis

In CNS, astrocytes respond to tissue injury by forming a glial scar (examples of injury: contusions, wounds, tumors, hemorrhages)

Microglial nodules

Form when microglia is joined with astrocytes; help fight infection

Axonal degeneration

In PNS, necrosis resulting from injury to neuron cell body or axon. Inflammatory response leads to phagocytosis of cellular debris.

Axonal regeneration

May be possible if cell body and proximal axons are not damaged

Neuronopathy

Damage to cell body causes axonal degeneration

Demyelination

Caused by damage to oligodendrocytes (myelin segments that increase the speed of neuron impulse conduction)

Neuropathy

Nerve degeneration causing delayed nerve conduction and impaired sensory function

PNS organization

Somatic

• Motor and sensory impulses between the CNS and periphery (peripheral nerves)

  • Cranial nerves

  • Spinal nerves

    • Dermatomes

    • Plexus formation

PNS Autonomic components

• Preganglionic neurons

• Autonomic ganglion

• Postganglionic neurons

Activated Autonomic system = Automatic (Fight or Flight)

• Sympathetic

  • Increased heart rate, BP, RR

  • Bronchodilation

  • Vascular smooth muscle constriction

  • Decreased urination and GI function

Activated Parasympathetic (Rest and Digest)

• Heart rate and RR decrease

• BP decreases

• Smooth muscle relaxes to allow for blood flow

• Bronchial constriction

• Relaxation of anal and bladder sphincter

Neural Injury

Cerebral Palsy Pathophysiology

• Group of neuromuscular disorders

• Caused by event during the antenatal or postnatal period that damaged the upper motor neurons

Classification

• Motor dysfunction type: Spastic, Athetoid/dyskinetic, Ataxic

• Anatomic involvement: Hemiplegia, Diplegia, and Quadriplegia

Cerebral Palsy Clinical Manifestations

Variable severity

• Limited fine motor skills

• Lack of coordination and balance

• Impaired cognitive function

• Speech disorder

• Seizure disorder

Cerebral Palsy Diagnostic Criteria

Diagnosis of exclusion

• History and Physical examination

  • Neurologic exam

    • Testing motor skills and reflexes

  • Developmental milestones

Epilepsy

Seizure disorder; result of impaired chemical and electrical neurotransmission

Seizure types

Partial/Focal: are short lived

• Partial seizures

• Simple partial

• Complex partial

Generalized: affect both sides of brain

• tonic clonic

• absence

• myoclonic

• atonic

• epileptic spasm

Partial seizures

Start local and can spread to other side of the brain

Simple partial

Limited to originating hemisphere and can involve other motor or sensory brain components

Complex partial

involve both hemispheres and result in loss of consciousness and lack of memory

Generalized seizures

Caused by a more generalized electrical transmission

Absence seizures

Brief change in LOC, and eye/mouth movements. Can occur up to 100 times a day

Myoclonic seizures

Involuntary muscle movements of extremities not associated with LOC

Tonic clonic

Convulsive and associated with tonic (continuous muscle contraction) and clonic (alternating muscle contractions and relaxation) LOC and traumatic injury related to fall may result

Seizure Recovery (postictal state)

• Extreme fatigue

• Headache

• Muscle pain and weakness

• Status epilectus: continuous tonic-clonic seizures causing hypoxia

Multiple Sclerosis Pathophysiology

• CNS demyelination also affects PNS

• Etiology

  • Genetics

  • Environmental factors

  • Triggering event

  • Autoimmunity

  • Regional variation

• Inflammatory T and B lymphocytes and IgG and IgM in CSF

MS Manifestation Types

• Related to slowed nerve conduction

• Clinical course variation:

  • Clinically isolated syndrome

  • Relapsing-remitting

  • Primary progressive: slow, chronic deterioration of neurologic function with plateaus

  • Secondary progressive: initially presenting with relapsing-remitting, followed by slow, chronic deterioration

MS Clinical Manifestations

• Unilateral vision loss

• Cognitive loss

• Bowel and bladder dysfunction

• Altered gait and balance

• Spasticity (continuous muscle stiffness)

• Pins and needles (Paresthesias)

• Slurred speech

• Fatigue

• Pain

• Pseudobulbar effect (uncontrollable laughing, crying)

MS Diagnostic Criteria

• Complete medical history

• Neurologic exam

• MRI, CNS response to peripheral stimuli

• Lumbar puncture to evaluate CSF

• Evoked potential testing: time it takes brain to respond to stimuli

Hydrocephalus Pathophysiology

• Increased ventricular accumulation of CSF

  • Ventricular enlargement

  • Increased ICP

• Classifications

  • Noncommunicating

  • Communicating

  • Congenital

  • Acquired

Hydrocephalus causes

• Intraventricular hemorrhage

• Neural tube defect

• Brain tumor

• Meningitis

• Traumatic injury

• CSF flow obstruction

• Impaired CSF absorption

Hydrocephalus Age dependent Clinical Manifestations

• Infant

  • Enlarged head with bulging fontanels

  • Scalp vein distention

  • Difficulty feeding

  • High, shrill cry

• Older children/adults

  • Impaired motor and cognitive function

  • Incontinence

Hydrocephalus Clinical Manifestations

Increased intracranial pressure

• Increased BP

• Altered HR

• Headache

• Vomiting

• Decreased LOC

• Papilledema

Hydrocephalus Diagnostic Criteria

• Head circumference measurement

• Transillumination

• Imaging studies

Hydrocephalus treatment

• Establishment and maintenance of normal CSF volumes and ICP

  • Ventriculoatrial shunt

  • Endoscopic third ventriculostomy

Incomplete Spinal Cord Transection Pathophysiology

Spinal cord injury altering neuronal transmission

Categories

• Complete transection

• Partial transection

  • Central cord syndrome

  • Anterior cord syndrome

  • Brown-Sequard syndrome

Incomplete Spinal Cord Transection Clinical Manifestations

Variable

• Spinal segmental level

• Type of injury

• Degree of cord transection

Central cord syndrome

Anterior cord syndrome

Brown-Sequard syndrome

Incomplete Spinal Cord Transection Diagnostic Criteria

• Physical examination

  • Cognitive function

  • Motor function

  • Sensory function

• Imaging studies

Parkinson Disease Pathophysiology

• Chronic, progressive neurologic condition

• Leads to degeneration of pigmented dopaminergic neurons of the basal ganglia

• Causes impaired transport of dopamine

• Presence of Lewy bodies (protein)

• Results in neuronal injury from oxidative damage being suspected

Parkinson Disease Clinical Manifestations

• Tremor

• Rigidity

  • Jerky movements

  • Flat affect

• Bradykinesia (slowed movement)

  • Shuffling gait and stooped posture

• Postural instability

Parkinson Disease Diagnostic Criteria

• History and Physical exam

• Hoehn and Yahr scale

  • Stage 1: mild, unliateral

  • Stage 2: bilateral, posture and gait affected

  • Stage 3: slowed movements, impaired balance

  • Stage 4: severe, limited walking, rigidity

  • Stage 5: cachectic, total disability

Stroke Pathophysiology

• Any clinical event that leads to the impairment of cerebral circulation

• Thrombotic, embolic, or hemorrhagic

• Inflammation, ischemia, death of neurons

• CVA or TIA

Stroke Clinical Manifestations

• Focal brain injury

• Dizziness, diplopia

• Abrupt onset of hemiparesis

• Ataxia, aphasia

• Vision loss or field deficits

• Sudden decreased in LOC

Stroke Diagnostic Criteria

• History and Physical examination

• Lab studies

• CT scan

Alzheimer Disease Pathophysiology

• Neurodegenerative disorder

  • Neurofibrillary tangles

    • Tau protein

  • Senile plaques

    • B amylod protein

  • Inflammation

• Neuronal atrophy

• Genetic and environmental factors

Alzheimer Disease Clinical Manifestations

7 stages

• General

  • Global cognitive decline

  • Behavior changes

  • Eventual loss of function

• Severity based on stage and progression

• Initial symptoms

  • Memory loss

  • Confusion

  • Restlessness

  • Mood swings

  • Difficulty interpreting visual information

Alzeheimer Disease Diagnosis

• History and physical exam

• Neurologic evaluation

  • Mental status

  • Communication ability

  • Memory

  • Math ability

  • Balance

• Imaging studies to rule out other conditions

  • Brain scan

  • MRI

  • CT scan

• Definitive diagnosis at autopsy

Migraine Headache Pathophysiology

• Recurrent headaches with aura

  • Moderate to severe intensity

  • Duration of 1-2 days

• Cause: likely initiated by neurologic and biochemical events

Migraine Headache Clinical Manifestations

• Pain

  • Unilateral

  • Pulsing and throbbing

• Aura

  • Visual disturbances preceding headache may be associated

• Prodromal symptoms

  • Mood changes

  • Food cravings

  • Constipation

Migraine Headaches Diagnostic Criteria

• History and Physical examination

• Imaging for acute, sudden onset

  • MRI

  • CT scan

Brain Cancer Pathophysiology

• Metastasis much more common to brain than primary tumors

• Primary tumors

  • Gliomas (in cerebrum)

  • Meningiomas

  • Pituitary adenomas

  • Acoustic schwannoma

Brain Cancer Clinical Manifestations

• Loss of motor/sensory function

• Cognitive or behavioral changes

• Headache

• Vomiting

• Seizures

Brain Cancer Diagnostic Criteria

• History and Physical examination

• Imaging studies

Huntington Disease Pathophysiology

• Progressive degenerative neurologic disorder with an autosomal dominant inheritance pattern

  • Defect on chromosome 4

• Degeneration of the basal ganglia and cortical regions of the brain

  • Movement

  • Emotional

  • Cognitive impairments

Huntington Disease Clinical Manifestations

Present in all with inherited defective gene

• Involuntary movements

  • Dyskinesia

  • Chorea (involuntary, rapid jerky movements)

• Cognitive impairment

• Emotional disturbance

Huntington Disease Diagnostic Criteria

• Family and personal medical history

• Genetic testing

• Physical exam

• Blood testing

• Mental, cognitive, and emotional evaluation

• CT, MRI, PET scans

Bacterial Meningitis

• Inflammation of the meninges of the brain and spinal cord

• Commonly caused by N. meningitidis

• Respiratory droplet transmission; mechanism for entry into CNS unknown

• Bacteria proliferate in CNS

• Exudate damages and obstructs CNS structures, leading to reduced oxygen to the brain

Bacterial Meningitis Clinical Manifestations

• Rapid and sever onset

• Severe headache

• Photophobia

• Nuchal rigidity

• Decreased alertness

• Loss of consciousness

• Changes in mental status

• Vomiting

• Seizures

• Fever

• Leukocytosis

• Anorexia

Bacterial Meningitis Diagnostic Criteria

• History and Physical examination

  • Kernig sign

  • Brudzinski sign

• Blood cultures

• CSF analysis and cultures

Meningitis types