Neuroanatomy and Physiology Study Guide

Embryonic Development

  • Surface ectoderm Development:

    • Days of development recognized: 19 days, 20 days, 22 days, 26 days

    • Formation of the neural tube occurs from the infolding of the ectoderm by the end of the first month.

Space Restriction and Brain Development

  • Cranial Regions:

    • Anterior (rostral) and Posterior (caudal) distinguishing features.

    • Major parts of the brain:

    • Metencephalon

    • Mesencephalon (Midbrain)

    • Cerebrum

    • Cerebellum

    • Brain stem (including the pons and medulla oblongata)

    • Diencephalon (including telencephalon and myelencephalon)

  • Flexures in Brain Development:

    • Week 5:

    • Two major flexures form, causing telencephalon and diencephalon to angle toward the brain stem.

    • Week 13:

    • Cerebral hemispheres develop and grow posterolaterally, ultimately enclosing the diencephalon and the rostral brain stem.

    • At Birth:

    • The brain exhibits an adult pattern of structures and convolutions.

Ventricles of the Brain

  • Definition:

    • Hollow chambers present throughout the brain and spinal cord;

    • Filled with cerebrospinal fluid (CSF).

Cerebral Hemispheres

  • Physical Features:

    • Convoluted surface featuring ridges (gyri) and shallow grooves (sulci).

    • Also includes deep grooves known as fissures:

    • Longitudinal fissure

    • Transverse fissure

    • Divided into three basic regions:

    • Cortex

    • White matter

    • Basal nuclei

Cerebral Cortex

  • Composition:

    • Primarily made of gray matter.

    • Functions of the cerebral cortex include:

    • Situated as the location of the “conscious mind.”

    • Engages in sensation, communication, memory, understanding, and voluntary movement.

    • Each hemisphere controls functions of the opposite side of the body.

    • Specialized areas for motor functions and sensory inputs.

Lateralization of Cortical Function

  • Definition:

    • Lateralization is the concept that each hemisphere has distinct abilities not shared by its counterpart.

    • Left Hemisphere:

    • Dominant for language, mathematics, and logical reasoning.

    • Right Hemisphere:

    • Specializes in visual-spatial skills, emotional processing, intuition, and artistic capabilities.

    • This division applies to approximately 90% of people; left-handed individuals tend to show opposite lateralization.

Functional Areas of the Cerebral Cortex

  • Primary Areas:

    • Primary Motor Area: Located in the precentral gyrus.

    • Primary Somatosensory Cortex: Located in the postcentral gyrus.

    • Central Sulcus: Separates the primary motor area from the primary somatosensory cortex.

  • Homunculus Representation:

    • Somatosensory and motor homunculus depict the brain areas dedicated to different body parts and their functions.

Cerebral White Matter

  • Functionality:

    • Forms connections via myelinated fiber tracts including:

    • Commissures: e.g., Corpus callosum

    • Association Fibers

    • Projection Fibers

    • Decussation of Pyramids: Reflects contralateral control of the motor system.

Basal Nuclei

  • Definition and Function:

    • Masses of gray matter located deep within cortical white matter.

    • Responsible for complex motor function controls such as:

    • Starting, stopping, and monitoring intensity of movements.

    • Functions also overlap with the cerebellum and encompass cognition and attention.

Diencephalon – Central Core of the Brain

  • Components:

    • Thalamus: Acts as the “gateway” to the cerebral cortex, filtering information on sensory modalities, motor activities, learning, and memory.

    • Epithalamus: Houses the pineal gland which secretes melatonin, a hormone involved in regulating the sleep-wake cycle.

    • Hypothalamus: Major visceral control center overseeing:

    • Autonomic control

    • Emotional responses

    • Temperature regulation

    • Food intake regulation

    • Water balancing and thirst regulation through osmoreceptors.

    • Regulation of sleep-wake cycles

    • Endocrine control with hormones such as ADH and oxytocin.

Brain Stem – The Base of the Brain

  • Components and Functions:

    • Midbrain: Involves pyramidal tracts.

    • Pons: Serves as a connection between spinal cord and cerebellum.

    • Medulla Oblongata: Centers for cardiovascular and respiratory functions, controlling actions like vomiting, swallowing, coughing, sneezing; also involved in decussation of pyramids.

The Cerebellum

  • Role:

    • Collaborates with basal nuclei, cerebral cortex, and sensory receptors for:

    • Timing and pattern setting of skeletal muscle contractions.

    • Functions subconsciously, also involving language and problem-solving skills; it recognizes and predicts sequences of events.

Functional Brain Systems: Limbic System

  • Structures Involved:

    • Includes olfactory bulbs, thalamic nuclei, hypothalamus, hippocampus, and amygdala.

    • Plays a critical role in linking emotional responses to odor detection (e.g., negative emotion associated with bad smells).

    • Interacts substantially with the cognitive functions of the cerebral cortex, allowing for emotional reactions to conscious events and awareness of emotions.

    • The amygdala is noted as the center for fear responses.

Functional Brain Systems: Reticular Formation

  • Reticular Activating System (RAS):

    • Maintains alertness in the cerebral cortex.

    • Regulates visceral motor functions and filters repetitive or unimportant stimuli.

Higher Mental Functions: Brain Waves

  • Electroencephalogram (EEG):

    • Records electrical activity of the brain which reflects normal function.

    • Findings show brain wave variations due to aging, sensory stimuli, neurological diseases, and body’s chemical state.

    • A flat EEG indicates severe brain inactivity, potentially indicating brain death.

Consciousness

  • Definition:

    • Encompasses perceptions of sensations, voluntary movements, and cognitive capabilities like memory and logic.

    • Associated with simultaneous activities across extensive regions of the cerebral cortex.

    • Levels of Response to Stimuli:

    • Alertness

    • Drowsiness/Lethargy (can lead to sleep)

    • Stupor

    • Coma

Sleep and Sleep Cycles

  • Sleep Definition:

    • A state of partial unconsciousness that allows arousal.

  • Types of Sleep:

    • Non-Rapid Eye Movement (NREM) Sleep: Considered a restorative phase.

    • Rapid Eye Movement (REM) Sleep: Assists in filtering daily information and discarding the unnecessary.

  • Sleep Cycle Composition:

    • Initial 90 minutes consist of NREM stages followed by REM, alternating through the night.

Types and Stages of Sleep

  • NREM Sleep Characteristics:

    • Difficulty in arousal increases, muscles relax, and vital signs approach baseline; dreaming initiates in later stages.

  • REM Sleep Characteristics:

    • Vital signs increase; major muscle atonia occurs, inhibiting all body muscles except ocular and respiratory ones; predominance of dreaming.

Sleep Disorders

  • REM Behavioral Disorder (RBD):

    • Absence of atonia leading to movement during REM sleep; can be caused by various factors, treatable with anticonvulsants.

  • Somnambulism (Sleepwalking):

    • Occurs during NREM stages 3-4; associated with partial unconsciousness and amnesia; stress and psychological factors may contribute.

Additional Sleep Disorders:

  • Narcolepsy:

    • Characterized by sudden onset of REM sleep from wakefulness, lasting around 15 minutes.

  • Insomnia:

    • Represents chronic difficulties with acquiring necessary amounts or quality of sleep, often symptomatic of other underlying issues.

  • Sleep Apnea:

    • Intermittent cessation of breathing during sleep resulting in hypoxia.

    • Obstructive Sleep Apnea: Caused by blockage of the upper airway.

Memory Processing: Stages of Memory

  • Memory Definition:

    • Covering storage and retrieval of information.

  • Short-Term Memory (STM):

    • Continuously records events for a duration from seconds to hours, with an informational cap of 7-8 items.

  • Long-Term Memory (LTM):

    • Features an expansive unlimited capacity; queries remain as to the reasons behind forgetting information.

Transfer from STM to LTM

  • Influencing Factors:

    • Emotional state (impact through shocking events or motivation)

    • Rehearsal of information

    • Making associations

    • Automatic memory occurrences

Categories of Memory: Fact and Skill

  • Fact (Declarative) Memory:

    • Involves explicit information learning tied to conscious thoughts and language capabilities; context in which it was learned is retained.

  • Skill (Non-declarative) Memory:

    • Less conscious engagement, typically relating to procedural, motor, and emotional activities acquired through practice; does not conserve the learning context.

Anatomy of Memory

  • Neuronal Interaction:

    • Large groups of neurons interact to consolidate memories.

    • The hippocampus is crucial for declarative (fact) memory processing, while emotional memory is linked to the amygdala.

    • The basal nuclei and cerebellum correspond to procedural (skill) memory functions.

  • Neuronal Changes:

    • Changes such as livestock increases in synaptic strength may occur with memory formation.

Protection of the Brain

  • Physical Protection:

    • Layers such as bone, meninges, and cerebrospinal fluid (CSF) provide defense against physical trauma.

  • Chemical Protection:

    • The blood-brain barrier helps shield against harmful substances.

Meninges

  • Purpose:

    • Serve to cover and safeguard the CNS.

    • Protect blood vessels and contain venous sinuses; encloses cerebrospinal fluid (CSF) and contributes to forming partitions within the skull.

Meninges and Bone Protection

  • Layered Structure:

    • Dura Mater: Features two layers (periosteal and meningeal).

    • Arachnoid Mater

    • Pia Mater

    • Specific spaces: Subdural and subarachnoid spaces, scalp skin, periosteum, and various layers of meninges.

Cerebrospinal Fluid (CSF)

  • Characteristics:

    • A watery solution resembling blood plasma composition.

    • Functions as a protective liquid cushion, offering buoyancy for CNS organs.

    • Prevents brain crushing due to its weight and protects against blows or trauma.

    • Nourishes the brain and conveys chemical signals.

Blood-Brain Barrier

  • Definition:

    • A protective mechanism ensuring a stable environment for the brain.

    • Operates as a selective barrier, permitting free passage of nutrients while blocking hormones and certain substances that are not essential.

    • Diffusible substances such as oxygen, carbon dioxide, lipids, alcohol, nicotine, and anesthetics can cross it, while it's absent in certain regions allowing monitoring of blood chemistry (e.g., hypothalamus).

Homeostatic Imbalances: Traumatic Injury

  • Concussion:

    • A mild brain injury leading to dizziness and temporary loss of consciousness.

  • Contusion:

    • Impacts causing brain bruising and significant contusions leading to long-term unconsciousness (coma).

  • Subdural or Subarachnoid Hemorrhage:

    • Bleeding resulting in elevated intracranial pressure.

  • Cerebral Edema:

    • Associated with swelling of the brain contributing to increased intracranial pressure.

Cerebrovascular Accidents (Strokes)

  • Definition:

    • Occurs due to interrupted blood circulation to the brain, causing tissue death (ischemia).

    • Most common cause is blockage of a cerebral artery; can also occur from compression due to hemorrhage or edema, or from atherosclerosis.

Degenerative Brain Disorders

  • Alzheimer’s Disease:

    • A progressive degenerative brain disease leading to forms of dementia, with a particular association with the hippocampus.

  • Parkinson’s Disease:

    • Degeneration of dopamine-releasing neurons results in overstimulation of the basal nuclei; difficulty in initiating movement is a primary symptom.

  • Huntington’s Disease:

    • A fatal hereditary disorder inducing degeneration in basal nuclei, characterized by lost control over inhibitory functions resulting in chorea (exaggerated movements).

Spinal Cord

  • Functionality:

    • Central nervous system tissue enclosed within the vertebral column, featuring 31 pairs of spinal nerves; serves as a two-way communication channel to/from the brain and major reflex center.

  • Protection:

    • Protected by bones, meninges, and cerebrospinal fluid (CSF).

Spinal Cord Anatomy

  • End Location:

    • The spinal cord terminates at the level of L1-L2, leading into conus medullaris and cauda equina areas.

  • Parts of the Spinal Cord:

    • Cervical enlargement, thoracic spinal nerves, lumbar spinal nerves.

Gray Matter, White Matter, and Spinal Roots

  • Gray Matter Structure:

    • Dorsal horn, ventral horn, lateral horn, gray commissure, and central canal.

  • White Matter Structure:

    • Dorsal, ventral, and lateral funiculus, along with spinal nerves.

  • Neuronal Pathways:

    • Includes sensory and motor neuron functionality, linking dorsal roots (sensory) and ventral roots (motor).

Spinal Cord Trauma

  • Paralysis:

    • Defined as loss of motor function.

    • Transection Effects:

    • Leads to total motor and sensory loss in regions below the cut.

    • Paraplegia:

    • Resultant from transection between T1 and L1, leading to loss of movement in legs.

    • Quadriplegia:

    • Results from transection in the cervical region, leading to loss of function in both arms and legs.

Homeostatic Imbalances of the Spinal Cord

  • Amyotrophic Lateral Sclerosis (ALS):

    • A progressive destruction of motor neurons with intact sensory and intellectual functions; results in muscle atrophy and loss of various functions including speech and breathing.

  • Shingles (Herpes Zoster):

    • Reactivates from chicken pox virus remaining in dorsal root ganglia, potentially affecting those with weakened immune systems, commonly after the age of 50.

  • Spina Bifida:

    • Formation defect in vertebra leading to potential protruding cyst; adequate folic acid intake during pregnancy may lessen the occurrence.