Patho2test 3: Day 1: CNS Overview: Structure and Function
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Questions and Answers

What is the primary function of myelin in the nervous system?

  • To release neurotransmitters into the synaptic cleft
  • To inhibit the transmission of action potentials
  • To break down and recycle neurotransmitters
  • To allow the action potential to rapidly propagate down the axon (correct)

    • What is the role of enzymes in the synaptic cleft?

  • To break apart and recycle excess neurotransmitters (correct)
  • To release neurotransmitters into the synapse
  • To bind to neurotransmitter receptors on the postsynaptic membrane
  • To generate action potentials in the postsynaptic neuron

    • Which of the following neurotransmitters is involved in the regulation of body temperature, sleep, mood, and sexuality?

  • GABA
  • Serotonin (correct)
  • Dopamine
  • Norepinephrine

    • What is the effect of increased levels of dopamine in the brain?

    <p>Increased risk of psychosis, mania, and schizophrenia</p> Signup and view all the answers

    What is the role of acetylcholinesterase in the nervous system?

    <p>To break down acetylcholine in the synapse</p> Signup and view all the answers

    Which of the following neurotransmitters is always the first signal on efferent (motor) pathways in the PNS?

    <p>Acetylcholine</p> Signup and view all the answers

    What is the effect of decreased levels of GABA in the brain?

    <p>All of the above</p> Signup and view all the answers

    What is the role of monoamine oxidase in the nervous system?

    <p>To break down and recycle neurotransmitters</p> Signup and view all the answers

    Which of the following is a characteristic of catecholamines?

    <p>They are synthesized from tyrosine</p> Signup and view all the answers

    What is the effect of decreased levels of serotonin in the brain?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of GABA in the brain?

    <p>To inhibit the creation of an action potential</p> Signup and view all the answers

    What is the effect of increased GABA signaling in the medulla?

    <p>Decrease in respiratory rate</p> Signup and view all the answers

    What is the mechanism by which benzodiazepines affect GABA?

    <p>They are indirect GABA agonists</p> Signup and view all the answers

    What is the primary function of oligodendroglia in the Central Nervous System?

    <p>Depositing myelin within the CNS</p> Signup and view all the answers

    What is the effect of tryptophan-derived neurotransmitter on muscle/motor pathways?

    <p>Excitatory</p> Signup and view all the answers

    Which type of glial cells are responsible for creating and maintaining the myelin sheath in the Peripheral Nervous System?

    <p>Schwann Cells</p> Signup and view all the answers

    What is the role of dopamine in the context of GABA and alcohol?

    <p>It plays an important role in craving and addiction</p> Signup and view all the answers

    What is the characteristic feature of the tryptophan-derived neurotransmitter?

    <p>It is a slow-acting neuromodulator</p> Signup and view all the answers

    What is the primary function of the thalamus in the brain?

    <p>Relay center for sensory information</p> Signup and view all the answers

    Which type of glial cells are responsible for removing debris within the CNS?

    <p>Microglia</p> Signup and view all the answers

    What is the primary function of ependymal cells in the CNS?

    <p>Line CSF filled cavities in the CNS and create CSF</p> Signup and view all the answers

    What is the term for the 'nerve glue' that provides support to the nervous system?

    <p>Neuroglia</p> Signup and view all the answers

    What is the primary function of astrocytes in the CNS?

    <p>Filling spaces between neurons and surrounding blood vessels</p> Signup and view all the answers

    What is the term for the gray matter nuclei deep in the forebrain that control muscle tone and posture?

    <p>Basal Ganglia</p> Signup and view all the answers

    Which of the following is NOT a function of the autonomic nervous system?

    <p>Regulation of voluntary motor control of skeletal muscle</p> Signup and view all the answers

    Which type of neuron is responsible for transmitting impulses from sensory receptors in the periphery to the CNS?

    <p>Sensory neurons</p> Signup and view all the answers

    What is the function of the myelin sheath in myelinated neurons?

    <p>To insulate the axon and speed up transmission</p> Signup and view all the answers

    What is the term for the process of nerve impulse transmission that occurs at the nodes of Ranvier?

    <p>Saltatory conduction</p> Signup and view all the answers

    Which type of neuron is classified by having only one process extending from the cell body?

    <p>Unipolar</p> Signup and view all the answers

    What is the term for the receptive portion of a neuron?

    <p>Dendrites</p> Signup and view all the answers

    What is the function of neurofibrils in neurons?

    <p>To provide structural support to the neuron</p> Signup and view all the answers

    Which type of neuron is responsible for transmitting impulses between neurons?

    <p>Interneurons</p> Signup and view all the answers

    What is the term for the process of one neuron receiving many messages from several different cells at the same time?

    <p>Convergence</p> Signup and view all the answers

    What is the term for the group of cell bodies in the peripheral nervous system?

    <p>Ganglia</p> Signup and view all the answers

    What occurs at the proximal end of the injured neuron in the peripheral nervous system?

    <p>Nerve swells, ER/ribosomes move to the injured area</p> Signup and view all the answers

    What is the primary reason for the reduced ability of the CNS to recover from injury?

    <p>Damaged tissue forms a glial scar</p> Signup and view all the answers

    What is the result of Wallerian degeneration in the peripheral nervous system?

    <p>Distal nerve segment has swelling and degeneration</p> Signup and view all the answers

    What is the role of Schwann cells in the peripheral nervous system?

    <p>To create a tunnel to guide regeneration</p> Signup and view all the answers

    What is the outcome of nerve injury in the central nervous system?

    <p>Permanent loss of nerve function</p> Signup and view all the answers

    What is the term for the process of nerve degeneration that occurs in the peripheral nervous system?

    <p>Wallerian degeneration</p> Signup and view all the answers

    What is the primary cause of intracerebral hemorrhage?

    <p>Hypertension</p> Signup and view all the answers

    What is the result of the rupture and seepage of blood into the ventricular system in hemorrhagic stroke?

    <p>Increased mortality rates</p> Signup and view all the answers

    What is the most common cause of spontaneous subarachnoid hemorrhage?

    <p>Trauma</p> Signup and view all the answers

    What is the characteristic of saccular (berry) aneurysms?

    <p>All of the above</p> Signup and view all the answers

    What is the primary mechanism of arteriovenous malformations (AVMs)?

    <p>Direct shunting of arterial blood into venous vasculatures</p> Signup and view all the answers

    What is the most common type of cerebral edema?

    <p>Vasogenic edema</p> Signup and view all the answers

    What is the primary cause of cytotoxic cerebral edema?

    <p>Cerebral ischemia</p> Signup and view all the answers

    What is the result of cytotoxic cerebral edema?

    <p>Na+ accumulates in cells, leading to cell swelling</p> Signup and view all the answers

    What is the characteristic of MCA (middle cerebral artery) stroke?

    <p>Contralateral weakness and sensory loss, visual field abnormalities</p> Signup and view all the answers

    What is the primary function of macrophages and astrocytes in the aftermath of hemorrhage?

    <p>Clearing away blood and debris</p> Signup and view all the answers

    What is the primary mechanism of ischemic strokes?

    <p>Smooth stenotic area degenerates leading to ulcerated area of vessel wall</p> Signup and view all the answers

    What is the term for the zone of borderline ischemic tissue surrounding the central core of irreversible ischemia?

    <p>Penumbra</p> Signup and view all the answers

    What is the most common type of ischemic stroke?

    <p>Thrombotic stroke</p> Signup and view all the answers

    What is the primary cause of atrial fibrillation-related strokes?

    <p>Loss of atrial systole leading to blood pooling in the atria</p> Signup and view all the answers

    What is the term for the process of cell death and tissue disintegration that occurs after infarction?

    <p>Infiltration of macrophages and phagocytosis</p> Signup and view all the answers

    What is the characteristic of lacunar infarcts?

    <p>Caused by perivascular edema/inflammation of arteries that supply small subcortical vessels</p> Signup and view all the answers

    What is the goal of thrombolytic therapy in stroke treatment?

    <p>To restore perfusion to the penumbra</p> Signup and view all the answers

    What is the term for the process of mechanical thrombectomy in stroke treatment?

    <p>Thrombectomy</p> Signup and view all the answers

    What is the term for the 'window of opportunity' for thrombolytic therapy in stroke treatment?

    <p>3 hours</p> Signup and view all the answers

    What is the primary cause of global ischemia?

    <p>Cardiac arrest leading to inadequate blood supply to the brain</p> Signup and view all the answers

    Study Notes

    CNS Overview: Structure and Function

    • Central Nervous System (CNS) = brain and spinal cord
    • Peripheral Nervous System (PNS) = cranial nerves and spinal nerves
    • PNS pathways divided into:
      • Ascending (afferent) pathways: carry sensory information towards CNS
      • Descending (efferent) pathways: carry motor information away from CNS to innervate effector organs
    • Descending (efferent) division further divided into:
      • Somatic nervous system: regulates voluntary motor control of skeletal muscle
      • Autonomic nervous system: regulates involuntary control of organ systems/internal viscera, divided into sympathetic and parasympathetic systems

    Cells of the Nervous System

    • Neurons:
      • Electrically excitable cells that transmit electrical or chemical information between other neurons to an effector organ
      • Three main components: cell body, dendrites, and axons
    • Neuroglia (support cells):
      • Provide structural support, nutrition, protection for neurons, and facilitate neurotransmission
      • Types: astrocytes, microglia, oligodendrocytes (CNS), Schwann cells, satellite cells (PNS)

    Neuron Structure

    • Cell Body:
      • Located mainly in CNS
      • Components: microtubules, neurofibrils, Nissl substances (granules made of rough ER, responsible for protein synthesis)
    • Dendrites:
      • Receptive portion of neuron, receives signals from other neurons and sends impulses to cell body
    • Axons:
      • Long projection from cell body that carries nerve impulses away from cell body
      • Myelinated neurons have a myelin sheath wrapped around the axon, insulating layer that speeds up transmission
      • Nodes of Ranvier: interruptions of myelin sheath that allow saltatory conduction (faster transmission)

    Neuron Communication Principles

    • Axon Convergence:
      • Axon branches allow one neuron to receive many messages from several different cells at the same time
    • Axon Divergence:
      • Axon branching allows one neuron to influence/send messages to many different neurons simultaneously

    Neuron Classification

    • Structural Classification:
      • Unipolar, pseudounipolar, bipolar, multipolar (most common)
    • Functional Classification:
      • Sensory neurons: transmit impulses from sensory receptors in periphery to CNS
      • Motor neurons: transmit impulses from CNS to an effector organ
      • Interneurons (associational neurons): transmit impulses between neurons

    Neuroglia (Glial Cells)

    • Central Nervous System:
      • Oligodendrocytes: deposit myelin within CNS
      • Astrocytes: fill spaces between neurons and surround blood vessels in CNS
      • Microglia: remove debris within CNS (brain macrophages)
      • Ependymal cells: line CSF-filled cavities in CNS and create CSF
    • Peripheral Nervous System:
      • Schwann cells: wrap around and cover axons in PNS, forming and maintaining myelin sheath

    Anatomy Review

    • White matter: myelinated axons, organized into tracts
    • Gray matter: unmyelinated cell bodies, on the cortical surface and subcortical regions
    • Basal ganglia: group of gray matter nuclei deep in the forebrain, connected with cortex, thalami, and brain stem, controlling muscle tone, posture, and large muscle movements
    • Thalamus: relay center for sensory information, associating sensory input with emotions, memory, and motor planning

    Neurotransmitters & Synapses

    • Review: Action Potentials
      • When a stimulus depolarizes the cellular membrane, it triggers an action potential
      • Action potential must meet the threshold to be propagated down the axon
    • Chemical Synapses
      • Presynaptic and postsynaptic cells separated by a thin synaptic cleft
      • Signaling from one cell to the next occurs through release of neurotransmitters from the terminal of the presynaptic neuron
    • Neurotransmitters:
      • Acetylcholine, norepinephrine, dopamine, serotonin, GABA
      • Two possible effects on the postsynaptic neuron: excitation (depolarization) or inhibition (hyperpolarization)
      • Summation of EPSPs and IPSPs determines whether an action potential will occur

    Neurotransmitters

    • Excitatory:
      • Acetylcholine
      • Dopamine
      • Norepinephrine
      • Epinephrine
      • Serotonin
    • Inhibitory:
      • GABA
      • Serotonin

    Acetylcholine

    • Made when acetyl CoA attaches to choline molecule
    • Always the first signal on efferent (motor) pathways in PNS
    • Released, binds to receptors on postsynaptic membrane, triggers opening of ion channels, and depolarizes the neuron
    • Acetylcholinesterase breaks down acetylcholine within the synapse
    • Clinical correlation: Myasthenia gravis, acetylcholinesterase inhibitors are used as treatment

    Catecholamines (Dopamine, Epi, Norepi)

    • Made from amino acid tyrosine
    • Norepinephrine and epinephrine are crucial in the sympathetic nervous system
    • Dopamine is involved in pleasure, reward centers, movement, and learning
    • Clinical correlation: MAO inhibitors (antidepressants) work by inhibiting the action of MAO

    Serotonin

    • Made from amino acid tryptophan
    • Slower than other neurotransmitters, more of a "neuromodulator"
    • Can be both excitatory and inhibitory
    • Clinical correlation: GABA, benzodiazepines, anticonvulsants, and muscle relaxants affect GABA signaling

    Cerebrovascular Disease

    • Refers to a group of conditions that affect blood flow and blood vessels in the brain
    • Most common type is stroke/CVA, which can be ischemic or hemorrhagic

    Stroke/CVA

    • Abrupt onset of focal or global neurologic impairment lasting > 24 hours
    • Ischemic stroke (87%) and hemorrhagic stroke (13%) are two main types
    • Ischemic stroke can be further divided into:
      • Focal (territorial) ischemia: due to occlusion of a particular blood vessel, causes infarct within territory of occluded vessel
      • Global (generalized) ischemia: due to cardiac arrest, shock, or increased ICP, causes widespread ischemia and necrosis

    Types of Ischemic Strokes

    • Transient ischemic attack (TIA): episode of neurologic dysfunction lasting < 1 hour, due to transient focal cerebral ischemia
    • Thrombotic stroke: arterial occlusion caused by thrombus formation in large or small arteries
    • Embolic stroke: fragments break off from thrombus formed outside the brain, commonly in the heart, aorta, or carotid arteries
    • Lacunar stroke: also called "small vessel disease", caused by perivascular edema/inflammation of arteries that supply small subcortical vessels
    • Hypoperfusion stroke: systemic hypoperfusion due to cardiac arrest, leading to inadequate blood supply to the brain

    Transient Ischemic Attack (TIA)

    • Clinical manifestations depend on the location of the blockage
    • Symptoms include:
      • Weakness/numbness
      • Confusion
      • Loss of balance
      • Loss of vision
      • Sudden severe headache
    • Causes of TIA include:
      • Embolic TIA
      • Lacunar TIA
      • Large artery, low flow TIA

    Thrombotic Stroke

    • Smooth stenotic area degenerates, leading to ulcerated area of vessel wall, platelets/fibrin adhere to damaged wall, forming clots
    • Thrombus formation in large or small arteries, most often due to atherosclerosis and inflammatory diseases

    Embolic Strokes

    • Fragments break off from thrombus formed outside the brain, commonly in the heart, aorta, or carotid arteries
    • Risk factors include:
      • Atrial fibrillation
      • LV aneurysm/thrombus
      • Valvular disease/endocarditis
    • Clinical correlation: Afib and stroke, due to loss of atrial systole, blood pools in the atria, and especially in the left atrial appendage, forming a blood clot

    Lacunar Infarcts

    • Perivascular edema/inflammation of arterial walls, leading to small vessels, predominantly occur in basal ganglia, internal capsules, and pons
    • Risk factors include:
      • Hyperlipidemia
      • Tobacco use
      • HTN
      • Diabetes
    • Make up ~ 25% of all ischemic strokes

    Pathophysiology of Infarction

    • Infarction occurs when occlusion leads to loss of blood supply and ischemia, causing cell death
    • Infarction leads to necrosis and swelling (cerebral edema) in 48-72 hours
    • Ultimately causes disintegration of tissue (infiltration of macrophages/phagocytosis)
    • After ~ 2 weeks, left with a cavity surrounded by glial scarring

    Ischemic Core vs Penumbra

    • Central core of irreversible ischemia/necrosis
    • Surrounded by zone of borderline ischemic tissue called the penumbra
    • Penumbra is area of salvageable damage
    • Restoration of perfusion to the penumbra can prevent necrosis and loss of function
    • Window of opportunity is ~ 3 hours

    Clinical Correlation: Thrombolytics

    • Goal in stroke treatment is to intervene early enough to restore perfusion to the penumbra
    • Tenecteplase (TNK) is now the standard of care, rather than Alteplase (tPA)
    • Patients who present < 4.5 hours from onset of symptoms

    Clinical Correlation: Thrombectomy

    • Patients who are "out of the window" for thrombolytics, not a candidate due to bleeding risk, or who have significant symptoms and a "large vessel occlusion (LVO)" on imaging, can undergo mechanical thrombectomy
    • Specially trained radiologist will access the cerebral vessel and physically remove the thrombus

    Hemorrhagic Strokes

    • Presenting with headache and vomiting
    • Intracerebral: most commonly due to HTN, vascular changes in HTN can evolve over several years, leading to necrosis and vessel rupture
    • Subarachnoid: associated with ruptured aneurysms, AV malformations, or head trauma
    • Subdural: most often due to trauma

    Infarction due to Hemorrhage

    • Mass of blood is formed as bleeding occurs, surrounding brain tissue is compressed and displaced, leading to ischemia, edema, and necrosis
    • Rupture and seepage of blood can occur into the ventricular system, often associated with higher mortality rates
    • In massive ICH (> 150 mL), cerebral perfusion falls to zero, leading to death

    Aftermath of Hemorrhage

    • In the absence of massive cerebral edema, most patients survive a hemispheric stroke
    • Cerebral hemorrhage is reabsorbed, macrophages and astrocytes clear away blood
    • Cavity forms surrounded by dense scarring

    Subarachnoid Hemorrhage (SAH)

    • Most common cause of spontaneous SAH is trauma
    • Aneurysmal: weak bulging areas of arterial wall, due to atherosclerosis, HTN, congenital abnormalities, drug use, or inflammation
    • May be single, but more than one is present in 20-25% of patients
    • Peak incidence for aneurysmal rupture occurs in people 50-59

    Saccular (Berry) Aneurysms

    • Arises at forks of arteries in the base of the brain
    • 85% in anterior circulation and 15% posterior
    • Occur in ~ 2% of the population, but rupture is rare
    • Due to a combination of factors, including congenital abnormalities of tunica media, loss of smooth muscle cells/inflammation, thrombus formation, and degenerative changes

    Arteriovenous Malformation (AVM)

    • Tangle of abnormal arteries and veins with no intervening capillary bed
    • Developmental abnormality due to a persistence of embryonic patterns of blood vessels
    • Direct shunting of arterial blood into venous vasculatures without time to "slow down" and decrease pressure in the capillary leads to a risk for ruptures
    • Can lead to hemorrhagic stroke, seizures, chronic headaches, or focal neurologic deficits due to shunting of blood flow from nearby structures

    Stroke Syndromes

    • MCA (middle cerebral artery) stroke: largest artery and most commonly affected, contralateral weakness and sensory loss, visual field abnormalities, language disturbance or spatial perception problems
    • Posterior circulation (Vertebrobasilar) stroke: double vision, clouding/blurring or loss of vision, vertigo, unilateral or bilateral weakness or numbness, dysarthria or difficulty swallowing, lack of coordination, gait instability

    Cerebral Edema

    • Three types:
      • Vasogenic edema: most common, increased permeability of capillaries that make up blood-brain barrier, causes include tumors, infection, and inflammatory/autoimmune diseases
      • Cytotoxic (metabolic) edema: most common cause is cerebral ischemia, ischemia leads to damage of Na+/K+ membrane pumps, Na+ accumulates in cell, pulling in water
      • Interstitial edema: most often seen with noncommunicating hydrocephalus, increased pressure in ventricles leads to CSF migration out of ventricles into interstitial space

    Nerve Cell Injury and Repair

    • Can nerve cells repair themselves? It depends...
    • Nerve repair in CNS: mature neurons that become injured lead to permanent loss, common clinical example is with acute ischemic stroke
    • Nerve repair in PNS: peripheral nerves can repair, Wallerian degeneration (anterograde) occurs distal to the injury, and retrograde changes occur at the proximal end of the injured neuron

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