Chapter 13 Study Guide

Chapter 13: Brain and Cranial Nerves

13.1-13.5 Overview

  • Presenting Doctor: Katy Talerico, MD

Chapter 13: Outline

  • The brain is part of the Central Nervous System (CNS) and is composed of four major divisions:

    • Brainstem: Connects spinal cord to cerebrum, involved in homeostatic functions, houses cranial nerve nuclei

    • Cerebellum: Regulates muscle activity, maintains posture and balance

    • Diencephalon: Connects brainstem to cerebrum, has relay and homeostatic functions

    • Cerebrum: Responsible for perception, thought, memory, emotion, and conscious motor control

TABLE 13.2: Development of the Central Nervous System

Comparison through Embryonic Stages:

  • Early Embryo: Forebrain (Telencephalon, Diencephalon), Midbrain (Mesencephalon), Hindbrain (Metencephalon, Myelencephalon)

  • Late Embryo: Adult Brain Structures such as the weight and cavities of adult brain regions (e.g., lateral ventricles for Telencephalon, third ventricle for Diencephalon).

Functions of Adult Brain Structures

  • Higher brain functions: Telencephalon

  • Relay center, autonomic nerve control, endocrine control: Diencephalon

  • Nerve pathways, reflex centers, muscle coordination: Metencephalon

Divisions of the Brain and Their Functions (TABLE 13.1)

Brainstem

  • Connects spinal cord to cerebrum

  • Subdivided into:

    • Medulla Oblongata: Pathway for ascending and descending nerve tracts; centers several important reflexes (e.g., heart rate, breathing, swallowing).

    • Pons: Contains ascending and descending tracts; relays information between cerebrum and cerebellum; site of reflex centers.

    • Midbrain: Contains tracts, serves as a visual reflex center, part of the auditory pathway.

  • Reticular Formation: Scattered throughout the brainstem; controls many activities including motor control, pain perception, and sleep-wake cycle.

Cerebellum

  • Controls muscle movement and tone; governs balance and regulates the extent of intentional movement; involved in learning motor skills.

Diencephalon

  • Connects the brainstem to the cerebrum; has relay and homeostatic functions:

    • Thalamus: Major sensory relay center affecting mood and movement.

    • Subthalamus: Contains nerve tracts and nuclei.

    • Epithalamus: Includes nuclei for motivation and reward behavior, contains pineal gland.

    • Hypothalamus: Major control center for maintaining homeostasis and regulating endocrine function.

Cerebrum

  • Responsible for perception, thought, memory, emotion, and conscious motor activity.

  • Structures include the Cerebral Cortex, Hippocampus, Amygdala, and Basal Nuclei:

    • Cerebral Cortex: Contains sensory, motor, and association areas.

    • Hippocampus: Involved with learning and memory.

    • Amygdala: Involved with social behavior and emotions.

    • Basal nuclei: Controls muscle activity and posture; inhibits unintentional movement when at rest.

Section 13.2: Brainstem

  • Connects the spinal cord to brain.

  • Major Regions:

    • Medulla Oblongata/Pons/Midbrain.

    • Contains Reticular Formation: vital for autonomic functions necessary for survival.

Medulla Oblongata (1 of 2)

  • Most inferior part of the brain, continuous with spinal cord; has both ascending and descending nerve tracts.

  • Cranial Nerve Nuclei:

    • V, VII, IX - XII: regulates heart rate, blood vessel diameter, respiration, swallowing, vomiting, hiccupping, coughing, and sneezing.

Medulla Oblongata (2 of 2)

  • Anterior surface has descending nerve tracts known as Pyramids, which decussate (cross over), leading each half of the brain to control the opposite half of the body.

  • Olives: help regulate balance, coordination, and modulation of sound from the inner ear.

Pons

  • Located superior to the medulla oblongata, contains fiber tracts for relaying information between the cerebrum and cerebellum.

  • Organized into Pontine Nuclei for relay and reflex centers.

Midbrain (1 of 3)

  • Also called Mesencephalon; functions as a visual reflex center, housing superior and inferior colliculi.

    • Tectum: Forming Corpora quadrigemina (superior colliculi for vision, inferior for hearing).

Midbrain (2 of 3)

  • Red Nuclei aid in the unconscious regulation and coordination of motor activities.

  • Substantia Nigra: connected with basal nuclei to maintain muscle tone and coordinate movements.

Midbrain (3 of 3)

  • Tegmentum: Ascending tracts such as spinothalamic and medial lemniscus; Cerebral Peduncles: descending tracts from the cerebrum.

Reticular Formation:

  • Role in arousal, awareness, posture, and regulation of various cranial activities like swallowing and breathing.

Section 13.3: Cerebellum (1 of 3)

  • Attached to the brainstem posterior to the pons, consists of outer gray cortex folded in ridges (folia) and deep internal nuclei resembling a tree structure (arbor vitae).

Major Sections:

  • Flocculonodular Lobe: Small and inferior.

  • Vermis: Narrow, central body.

  • Lateral Hemispheres: Divided into anterior and posterior lobes by primary fissures.

Cerebellar Neurons:

  • Contains Purkinje cells (largest in CNS) among other neuron types (basket cells, granule cells).

  • Purkinje cells receive about 200,000 synapses and are inhibitory.

Cerebellar Communication:

  • Communicates via Cerebellar Peduncles:

    • Superior Cerebellar Peduncles: Communicate with midbrain.

    • Middle Cerebellar Peduncles: Communicate with pons.

    • Inferior Cerebellar Peduncles: Communicate with medulla oblongata.

Cerebellar Functions:

  • Control of muscle movement and tone, balance, extent of intentional movement, and learning motor skills.

Section 13.4: Diencephalon

  • Located between the brainstem and cerebrum; components include Thalamus, Subthalamus, Epithalamus, and Hypothalamus.

Thalamus (1 of 2)

  • Major sensory relay center; surrounds the third ventricle and connects through interthalamic adhesion.

  • Functionality:

    • Receives almost all sensory information (except smell) and projects it to cerebrum; specific nuclei for auditory (medial geniculate), visual (lateral geniculate), and other sensory information.

Thalamus (Motor Functions):

  • Ventral anterior and ventral lateral nuclei support motor functions, mood regulation linked to the limbic system, and sensory integration by the lateral posterior and pulvinar nuclei.

Subthalamus:

  • Inferior area to thalamus; part of the basal nuclei controlling motor function, containing ascending and descending tracts.

Epithalamus:

  • Area superior and posterior to thalamus; Habenula links with behaviors involving rewards and addictions; modulates sleep/wake cycles and produces melatonin hormone.

Hypothalamus (1 of 2):

  • Most inferior part of diencephalon; houses mammillary bodies important for olfactory reflexes and emotional responses to odors.

  • Links to the pituitary gland via the infundibulum, coordinating hormonal secretions affecting multiple body functions.

Hypothalamus (2 of 2):

  • Influences mood, sexual behavior, and controls body temperature, hunger, thirst, and the sleep-wake cycle based on sensory inputs from various organs.

Functions of the Hypothalamus (TABLE 13.3):

  1. Autonomic: Controls heart rate, urine release, food movement, and blood vessel diameter.

  2. Endocrine: Regulates pituitary gland secretions affecting metabolism and sexual functions.

  3. Muscle Control: Controls swallowing and stimulates shivering to maintain body temperature.

  4. Emotional Regulation: Directly involved in stress-related illnesses, fear, and rage.

  5. Sleep-Wake Cycle: Coordinates with the rest of the brain, particularly with inputs regarding light-dark cycles.

  6. Sexual Development/Behavior: Stimulates sexual functions and development influenced by hormonal levels.

Section 13.5: Cerebrum (1 of 2)

  • Largest portion of the brain, consisting of right and left hemispheres separated by the longitudinal fissure.

Specific Features:

  • Gyri: Folds;

  • Sulci: Depressions.

  • Notable features: central sulcus (between frontal and parietal lobes), lateral fissure (between temporal and other lobes).

Cerebral Cortex:

  • Composed of layers of gray matter with various neuron types including fusiform, stellate, and pyramidal cells.

Lobes of the Cerebrum (1 of 2):

  • Frontal Lobe: Responsible for voluntary motor functions, motivation, aggression, decision making and personality traits.

  • Parietal Lobe: Involved in the reception and evaluation of sensory information (excluding smell, hearing, and vision).

  • Occipital Lobe: Evaluates and integrates visual input.

Lobes of the Cerebrum (2 of 2):

  • Temporal Lobe: Involved in smell and hearing reception, along with memory and judgment capabilities.

  • Insula: Located within the lateral fissure; evaluates taste information.

Cerebral Medulla:

  • Structurally between the cortex and nuclei; includes:

  1. Association Fibers: Connections within the same hemisphere.

  2. Commissural Fibers: Connects both hemispheres (e.g., corpus callosum).

  3. Projection Fibers: Connects the cerebrum with other parts of the brain and spinal cord.

Basal Nuclei:

  • Found in cerebrum, diencephalon, and midbrain; primarily involved in motor control.

Compositions:

  • Corpus Striatum:

    • Caudate Nucleus

    • Lentiform Nucleus (consisting of putamen and globus pallidus).

  • Includes external nuclei such as subthalamic nucleus and substantia nigra present in midbrain.

Limbic System (1 of 2):

  • Composed of cerebrum and diencephalon, plays roles in motivation, emotion, learning, and memory; impacts both endocrine and autonomic systems.

  • Connective areas:

    • Cingulate gyrus

    • Parahippocampal gyrus

    • Hippocampus

  • Other nuclei involved include anterior nuclei of thalamus, amygdala, and mammillary body.

Limbic System (2 of 2):

  • Overall coordination via tracts such as the fornix; involved in emotional regulation and motivational behaviors.

TABLE 13.6: Diseases and Disorders of the Brain

CNS Disorders:

  • Cerebral Aneurysm: Artery dilation or ballooning leading to potential hemorrhage.

  • Stroke: Loss of blood flow due to bleeding or a blockage, leading to potential brain damage.

  • Concussion: Temporary loss of function due to a blow to the head, potentially leading to postconcussion syndrome.

  • Cerebral Compression: Increased intracranial pressure from hematomas, tumors, edema, or injury.

Cerebrovascular Accidents (1 of 2):

  • Referred to as strokes; caused by either blockage (thrombotic or embolic) or breakage of a blood vessel (hemorrhagic).

  • Symptoms include hemiplegia, balance issues, visual problems, among others.

Interactions of a Stroke with Other Body Systems:

  • Integumentary: Bedsores from immobility.

  • Urinary: Possible loss of bladder control; urinary tract infections may occur.

  • Digestive, Muscular: Dysphagia may occur as well as muscle atrophy from lack of movement.

  • Cardiovascular: Increased risks of phlebothrombosis; damage to brain centers could affect blood pressure.

Cerebrovascular Accident Symptoms and Treatment:

  • Treatments vary; effective if attended to swiftly within the ‘FAST’ framework (Face, Arms, Speech, Time).

Traumatic Brain Injury (TBI):

  • Concussion: Temporary functional change.

  • Contusion: Permanent brain damage.

  • Risks of subdural hemorrhage and cerebral edema.

Cranial Nerve Disorders:

  • Trigeminal Neuralgia: Sharp pain related to the trigeminal nerve.

  • Migraine: Severe headaches linked to the trigeminal nerve.

  • Facial Palsy: Unilateral paralysis, often linked to stroke or viral infections such as Herpes simplex.