Neurological System Practice Flashcards

Overview of the Nervous System

• Definition: The neurologic, or nervous, system is the body’s communication network that works to coordinate and organize the functions of all other body systems.

• Structure: This network is made of complex structures that transmit electrical and chemical signals between the body’s organs, tissues, and brain.

• Main Divisions:

  • The Central Nervous System (CNS): Made up of the brain and spinal cord; it acts as the body’s control center.

  • The Peripheral Nervous System (PNS): Composed of cranial and spinal nerves that carry impulses toward the CNS (afferent) and away from the CNS (efferent) to target organs or skeletal muscle.

The Neuron: The Fundamental Unit

• The Neuron (Nerve Cell): The fundamental unit of the nervous system. It is a highly specialized conductor cell that receives and transmits electrochemical nerve impulses.

• Structural Components:

  • Cell Body: The central part of the neuron from which nerve fibers extend.

  • Axons: Nerve fibers that carry impulses away from the cell body. Most neurons have only one axon.

  • Dendrites: Nerve fibers that carry impulses to the cell body. Most neurons have multiple dendrites.

• Neuroglial Cells: These cells outnumber neurons and provide support, nourishment, and protection for them.

• System Function: This intricate network of interlocking receptors and transmitters, along with the brain and spinal cord, forms a living computer that controls and regulates every mental and physical function from birth to death.

The Cerebrum and Cerebral Cortex

• Cerebrum: The largest part of the brain. It houses the nerve center that controls sensory and motor activities as well as intelligence.

• Hemispheres: The cerebrum is divided into the right and left hemispheres.

  • Contralateral Control: Because motor impulses descending from the brain cross in the medulla, the right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body.

• Layered Structure:

  • Cerebral Cortex (Outer Layer): Consists of neuron cell bodies, known as gray matter.

  • Inner Layer: Consists of axons (white matter) plus the basal ganglia, which control motor coordination and steadiness.

• Lobes and Fissures: Several fissures divide the cerebrum into lobes, each with a specific function.

Divisions of the Nervous System (Somatic and Autonomic)

• Somatic Nervous System:

  • Consists of motor and sensory pathways regulating voluntary motor control of skeletal muscle.

  • Composed of somatic nerve fibers that conduct impulses from the CNS to skeletal muscles.

• Autonomic Nervous System (ANS):

  • Consists of motor and sensory involuntary control of organ systems.

  • Regulates the body’s internal environment and controls involuntary body functions such as digestion, respirations, and cardiovascular function.

• Myelin Sheath: A sheath around selected axons that forms insulation, allowing for quicker nerve impulse conduction.

Embryonic Brain Development and Adult Components

• Forebrain (Prosencephalon):

  • Telencephalon: Becomes the Cerebrum in adults.

    • Function: Motor area controls voluntary muscle movements; sensory cortex is the center of conscious perception of touch, pressure, vibration, pain, temperature, and taste; association areas integrate and process sensory data.

  • Diencephalon: Becomes the Thalamus and Hypothalamus in adults.

    • Thalamus Function: Part of the limbic system; integrates sensory information arriving at the thalamus and projects it to the cerebral frontal lobes.

    • Hypothalamus Function: Controls autonomic functions; sets appetitive drives (thirst, hunger, sexual desire) and reproductive behavior; participates in emotional responses; secretes ADH and oxytocin; secretes releasing hormones for anterior pituitary regulation.

• Midbrain (Mesencephalon):

  • Early/Late Embryo: Mesencephalon.

  • Adult Components: Optic lobes (tectum) and midbrain nuclei.

  • Function: Integrates visual information with other sensory inputs; relays auditory information.

• Hindbrain (Rhombencephalon):

  • Metencephalon: Becomes the Cerebellum and Pons in adults.

    • Cerebellum Function: Involuntary coordination and control of outgoing movements for equilibrium, muscle tone, and posture.

    • Pons Function: Links cerebellum with other brain centers and with the medulla and spinal cord; modifies output of respiratory centers in the medulla.

  • Myelencephalon: Becomes the Medulla Oblongata in adults.

    • Function: Regulates heart rate and force of contraction; vasomotor control; sets rate of respiration; relays information to the cerebellum.

• Spinal Cord: Maintains the same general structure from embryo to adult; provides involuntary control of muscle tone and processing of incoming sensations and outgoing motor commands.

The Forebrain, Midbrain, and Brainstem Functions

• The Forebrain: Comprises the two cerebral hemispheres (telencephalon) and includes the cerebral cortex and basal ganglia. Associated with conscious perception of stimuli, cognition, memory, and voluntary control of skeletal muscles.

• The Midbrain: Connects the forebrain and hindbrain. It is a relay center for motor and sensory tracts and a center for auditory/visual reflexes, temperature control, sleep-wake cycles, arousal, and attention.

• The Medulla: Controls activities including heart rate, blood pressure, and reflex activities such as swallowing, coughing, and vomiting.

• Reticular Formation: Maintains wakefulness and attention.

The Limbic System

• Definition: The area of the brain involved with emotion and memory.

• Components in the Diencephalon:

  • Anterior group of thalamic nuclei.

  • Hypothalamus.

• Components in the Cerebrum:

  • Cingulate gyrus.

  • Parahippocampal gyrus.

  • Hippocampus.

  • Amygdaloid body.

• Other structures: Fornix, Mamillary body, and Pineal gland (located near the corpus callosum).

The Blood–Brain Barrier (BBB)

• Definition: A highly selective semipermeable border of endothelial cells.

• Function: Prevents solutes in the circulating blood from non-selectively crossing into the extracellular fluid of the CNS where neurons reside. It prevents harmful substances from entering the brain.

• Composition: Endothelial cells in brain capillaries and associated supporting cells.

Spinal Cord Structure and CNS/PNS Communication

• Information Relay: The PNS relays information from the CNS to muscles and effector organs via cranial and spinal nerve tracts arranged in fascicles.

• Gray Matter: Contained within the spinal cord and divided into "horns." These consist mostly of neuron cell bodies and relay sensations needed for voluntary or reflex motor activity.

• White Matter: Surrounds the gray matter horns. It consists of myelinated nerve fibers grouped in vertical columns called "tracts."

  • Sensory (Ascending) Tracts: Carry sensory impulses up the spinal cord to the brain.

  • Motor (Descending) Tracts: Carry motor impulses down the spinal cord.

• Upper Motor Neurons: Also called cranial motor neurons. They conduct impulses from the brain to the spinal cord to reach the descending tracts of the PNS.

Specialized Motor Systems

• Pyramidal System (Corticospinal Tract): Responsible for fine, skilled movements of the skeletal muscle.

• Extrapyramidal System (Extracorticospinal Tract): Responsible for the control of gross motor movements.

  • Extrapyramidal Motor Syndromes: Include basal ganglia and cerebellar motor syndromes.

  • Drug-Induced Movements: Extrapyramidal symptoms (EPS) are side effects caused by certain antipsychotic and other drugs. These include tremors, muscle contractions, and involuntary/uncontrollable movements.

The Peripheral Nervous System (PNS)

• Origin: Composed of $31$ pairs of spinal nerves arranged in segments and attached to the spinal cord.

• Function: Messages transmitted through the spinal cord reach outlying areas via the PNS.

• Subdivisions: Divided into the somatic nervous system (voluntary) and the autonomic nervous system (involuntary).

Autonomic Antagonism and Homeostasis

• The ANS is divided into two antagonistic systems to balance homeostasis:

  • Sympathetic Nervous System: Responds to stress by mobilizing energy stores and preparing the body to defend itself ("fight or flight"). It releases the adrenergic catecholamine norepinephrine.

  • Parasympathetic Nervous System: Conserves energy and the body's resources. It releases the cholinergic neurohormone acetylcholine.

Sensory Regulation: Thermoregulation and Proprioception

• Temperature Regulation:

  • Mediated by the hypothalamus.

  • Peripheral Thermoreceptors: Located in the skin.

  • Central Thermoreceptors: Located in the hypothalamus, spinal cord, and abdominal organs.

• Proprioception:

  • The perception of the position and location of the body and its parts.

  • Proprioceptors: Located in the inner ear, joints, and ligaments.

  • Necessity: Essential for balance, coordinated movement, and grading of muscular contraction.

Sleep Disorders and Parasomnias

• Common Parasomnias: Arousal disorders, sleep-wake transition disorder, and disorders associated with REM sleep.

• REM-Associated Parasomnias:

  • Nightmares: Frightening dreams or disturbing mental experiences that usually awaken the sleeper from REM sleep.

  • Hypnagogic and Hypnopompic Hallucinations: Vivid perceptual experiences occurring at sleep onset (hypnagogic) or upon awakening (hypnopompic). Result from the intrusion of REM processes into the waking state. Hallucinations can be visual (shadows to complex images), auditory, tactile, or cenesthopathic (abnormal sensations).

  • REM-Sleep Behavior Disorder (RBD): Characterized by limb/body jerking, punching, kicking, talking, shouting, swearing, leaping from bed, running into furniture, and striking or choking a bed partner.

Auditory Disorders

• Sensorineural Hearing Loss: Develops with impairment of the organ of Corti or its central connection. Can be caused by cumulative exposure to traffic sounds, construction, noisy offices, and loud music.

• Presbycusis: Age-related hearing loss; the most common form of sensorineural hearing loss. It is commonly caused by gradual changes in the inner ear.

• Conductive Hearing Loss: Occurs when sound waves cannot be conducted through the middle ear.

• Acute Otitis Media: An infection of the middle ear.

  • Clinical Manifestations: Ear pain, fever, an inflamed tympanic membrane, and fluid in the middle ear.

Brainstem Function and Clinical Indicators

• Pupillary Changes: Reflect levels of brainstem function, drug action, and response to hypoxia and ischemia.

  • Hypoxia/Severe Ischemia: Usually produces dilated, fixed pupils.

  • Hypothermia: May cause fixed pupils.

  • Opiates: Cause pinpoint pupils.

  • Atropine and Scopolamine: Large doses fully dilate and fix pupils.

  • Sedatives (e.g., Glutethimide): Doses sufficient to produce coma cause midposition or moderately dilated, unequal pupils, commonly fixed to light.

  • Barbiturates: Severe intoxication may produce fixed pupils.

Alzheimer’s Disease (AD)

• Definition: The most common chronic, irreversible dementia.

• Pathophysiology: Characterized by accumulations of amyloid and tau protein neurofibrillary tangles.

• Distinguishing Brain Tissue Features:

  1. Neurofibrillary tangles: Formed out of fibrous proteins in the neurons.

  2. Beta-amyloid plaques: Deposits of protein-like substances. Large numbers of plaques correlate with more severe dementia; they exert neurotoxic effects and lead to neuronal death.

  3. Granulovacuolar degeneration of neurons.

• Neurotransmitter Deficit: Severity of dementia is directly related to a reduction in acetylcholine. Autopsies show levels as low as $10\%$ of the normal amount.

• Complications: Injury from wandering, malnutrition, dehydration, pneumonia (from lack of exercise), and aspiration.

• Drug Therapy:

  • Cholinesterase Inhibitors: Donepezil (Aricept), Rivastigmine (Exelon), Galantamine (Razadyne). These keep acetylcholine levels high by preventing its breakdown.

  • NMDA Receptor Antagonist: Memantine (Namenda), an uncompetitive low-to-moderate affinity N-methyl-d-aspartate antagonist, regulates glutamate activity involved in information processing.

  • Supplements: Vitamin E is commonly prescribed to defend the brain against damage.

Seizure Disorders

• Definition: Abnormal, excessive hypersynchronous discharges of cerebral neurons with transient alterations in brain function.

• Categories: Genetic, Structural, Metabolic, Immune, Infectious, and Unknown.

• Seizure Types:

  • Generalized Onset Seizures: Affect both sides of the brain (or groups of cells on both sides) simultaneously. Includes tonic-clonic, absence, and atonic types.

  • Focal Onset Seizures: Begin in one area or group of cells on one side of the brain (replaces the term "partial").

  • Focal Onset Aware: Person is awake and aware (formerly "simple partial").

  • Focal Onset Impaired Awareness: Person is confused or awareness is affected (formerly "complex partial").

Movement and Motor Neuron Disorders

• Parkinson’s Disease (PD): Degenerative disorder of the basal ganglia (corpus striatum) involving the dopamine-secreting nigrostriatal pathway.

  • Triad of Symptoms: Tremor, Rigidity, and Bradykinesia.

  • Other features: Emotional lability (limbic system involvement) and progressive dementia in advanced stages.

• Amyotrophic Lateral Sclerosis (ALS): A motor neuron disease involving degeneration of upper and lower motor neurons, as well as nonmotor neurons in the cortices and spinal cord.

  • Clinical Manifestations: Muscle weakness (may start in one group), slurred speech, and difficulty swallowing.

  • Syndrome: Characterized by flaccid paresis progressing to paralysis (lower motor neuron syndrome).

Schizophrenia and Psychopharmacology

• Antipsychotic Generations:

  • First Generation: Blocks the dopamine $D_2$ receptor.

  • Second Generation (Atypical): Blocks $D_2$ receptors as well as serotonin and other neurotransmitter receptors.

• Negative Symptoms of Schizophrenia:

  • Lack of interest in the world and social withdrawal.

  • Anhedonia (inability to feel pleasure).

  • Avolition (lack of motivation) and decreased sense of purpose.

  • Inability to act spontaneously and poverty of speech (not talking much).

• Therapy: Talk therapies are used to increase drug compliance and coping strategies, as medication is not always effective for severe negative symptoms.

Mood and Anxiety Disorders

• Depression: Linked to uncontrollable stress, which elevates cortisol and proinflammatory cytokines. Thyroid hormone abnormalities are also common.

• Bipolar and Manic Disorders: Treated with lithium or mood stabilizers.

• Pharmacotherapy (Depression): Includes MAOIs, TCAs, SSRIs, and atypical antidepressants.

• Generalized Anxiety Disorder (GAD): Characterized by persistent worries about life events. Symptoms include motor disturbances, irritability, and fatigue; often manifests with symptoms of depression.

• Obsessive Compulsive Disorder (OCD): A time-consuming illness impairing function. Involves obsessions (e.g., preoccupation with doubting, religious/sexual themes, or fear of negative outcomes if acts are not performed).

Cerebral Palsy and Brain Tumors

• Cerebral Palsy (CP): A group of nonprogressive syndromes caused by prenatal cerebral hypoxia or perinatal/postnatal trauma.

  • Associated Symptoms: Intellectual disability, seizure disorders, or developmental disabilities.

  • Types: Can be extrapyramidal/nonspastic or pyramidal/spastic.

• Brain Tumors:

  • General Symptoms: Most common is increased Intracranial Pressure (ICP), manifesting as headache, irritability, vomiting, somnolence, and bulging fontanels in infants.