Notes: Brain and Behavior — Sections 2.1, 2.3, 2.4, 2.5 (Seventh Edition)

Plastic Patterns of Neural Organization

  • The brain is “plastic”: neural tissue can adapt to the world by changing how its functions are organized.
  • Neuroplasticity: the nervous system’s potential for physical or chemical change that enhances its adaptability to environmental change and its ability to compensate for injury.
  • Important caveat: we learn the major divisions and regions of the nervous system, but there are species differences based on needs and individual differences within a species due to experience.

The Nervous System: Key Divisions and Functions

  • Peripheral Nervous System (PNS) and Central Nervous System (CNS) definitions are implied by structure:
    • CNS: brain and spinal cord.
    • PNS: nerve fibers radiating from the CNS and neurons outside it.
  • PNS divisions:
    • Somatic nervous system (SNS): carries sensory information to the CNS from muscles, joints, and skin; transmits motor instructions from the CNS to muscles and tissues.
    • Autonomic nervous system (ANS): prepares internal organs for internal states; subdivides into sympathetic and parasympathetic branches.
    • Enteric nervous system (ENS): a mesh of neurons embedded in the lining of the gut; communicates with the CNS via the ANS but largely operates autonomously.
  • Four-part interacting system: CNS, SNS, ANS, ENS.

Direction of Neural Information Flow

  • Afferent information: sensory information entering the CNS (A = arriving at the CNS).
  • Efferent information: information leaving the CNS (E = exiting the CNS).
  • Mnemonic: afferent comes before efferent alphabetically; sensory signals enter the brain before motor responses are triggered.

Orientation and Structure of the Brain: Terms and Planes

  • Brain-body orientation terms:
    • Medial vs lateral: structures toward the brain's midline are medial; toward the sides are lateral.
    • Anterior vs posterior: anterior = front; posterior = back.
    • Dorsal vs ventral: dorsal = top/back (superior); ventral = bottom/belly (inferior).
    • Rostral vs caudal: rostral (beak) = toward the nose; caudal (tail) = toward the tail.
    • Superior vs inferior often used interchangeably with dorsal/ventral in some contexts; these terms refer to location, not importance.
  • Orientation in animals:
    • Spatial orientation (dorsal/ventral) may differ in animals standing on four legs; for humans, dorsal is top, ventral is bottom.
  • Planes of section (anatomical orientation):
    • Coronal section: vertical plane cutting crown-to-neck, yielding a frontal view of internal structures.
    • Horizontal section: view looking down from above (dorsal view).
    • Sagittal section: lengthways from front to back; midsagittal divides brain into symmetrical halves (medial view).
  • Brain structure overview (major components):
    • Hindbrain (part of brainstem): cerebellum, pons, medulla; governs motor coordination, basic life functions.
    • Midbrain (brainstem): tectum (roof) and tegmentum (floor); includes substantia nigra and periaqueductal gray.
    • Diencephalon: thalamus and hypothalamus.
    • Forebrain: cerebral cortex (neocortex), limbic system, basal ganglia, and other subcortical structures.
    • Cortex: outer layer of the brain; folds into gyri and sulci.
    • Corpus callosum: large white-matter tract connecting the two hemispheres.

Brain Structures and Spatial Organization

  • Frontal lobe: motor and executive functions.
  • Parietal lobe: sensory integration.
  • Occipital lobe: vision.
  • Temporal lobe: auditory processing and memory.
  • Cerebral cortex: outer “bark” layer; six layered (laminar) structure; gyri = bumps; sulci = grooves.
  • Gyri and sulci are visual indicators of cortical organization and specialization.

Major Subcortical Structures

  • Corpus callosum: a band of white matter with about 200 million nerve fibers; connects the two hemispheres to allow communication.
  • Limbic system: regulates emotions and memory; includes amygdala, hippocampus, cingulate cortex, and olfactory structures.
  • Basal ganglia: caudate nucleus, putamen, globus pallidus; control voluntary movement and motor patterns; linked to disorders such as Parkinson’s disease and Tourette syndrome.
  • Thalamus: gateway/relay for sensory information to the cortex.
  • Hypothalamus: hormonal regulation via connections to the pituitary; temperature regulation, eating, drinking, sexual behavior.
  • Olfactory system: olfactory bulbs and receptors; pyriform cortex; involved in sense of smell.

The Cerebral Cortex: Neocortex vs Allocortex and Lamination

  • Neocortex: six layered cortex; responsible for most higher-order cognitive functions; characterized by multiple laminae and columns.
  • Allocortex: evolutionarily older, with 3–4 layers; involved in motivational states.
  • Cortical organization: lamina (layers) and columns (vertical functional units) shape functional specialization.

The Four Lobes and Their Primary Functions

  • Frontal lobe: motor control; executive functions; planning and inhibition.
  • Parietal lobe: sensory integration and spatial awareness.
  • Occipital lobe: primary visual processing.
  • Temporal lobe: auditory processing; memory formation and retrieval; language in dominant hemisphere (in many individuals).
  • Frontal view, dorsal view, ventral view, lateral view, and medial view perspectives help map lobes and structures (central sulcus, lateral fissure/cerebral fissure, etc.).

Subcortical Pathways and White/Gray Matter

  • White matter: rich in myelinated axons; facilitates long-range communication between brain regions.
  • Gray matter: regions dominated by neuron cell bodies and blood vessels; sites of synaptic connections.
  • The cerebral cortex’s surface features include gyri (ridges) and sulci (furrows).

White Matter Connectivity: The Corpus Callosum

  • The corpus callosum connects the left and right hemispheres and contains about 200 million nerve fibers for interhemispheric communication.

Cerebral Circulation, Blood Vessels, and Stroke

  • Stroke: sudden onset of neurological symptoms due to severe interruption of blood flow.
  • Cerebral connections are crossed; a stroke in the left hemisphere often affects the right side of the body.
  • Three major arteries feed blood to the cerebral hemispheres; these arteries branch extensively to supply the shaded regions.

Blood-Brain Barrier (BBB) and Cerebrospinal Fluid (CSF)

  • BBB function:
    • Keeps out viruses, bacteria, and many chemicals; restricts amino acids, vitamins, and hormones unless actively transported.
    • Allows through small uncharged molecules, fat-soluble molecules, and glucose (energy).
    • Some viruses can still enter; barrier is not absolute.
  • CSF and ventricles:
    • Four ventricles: two lateral ventricles, third ventricle, fourth ventricle.
    • CSF circulates in the ventricles and subarachnoid space, providing cushioning and nutrient transport.

Neurons vs Glial Cells

  • Neuron: cell body (soma) with dendrites and axon; primary signaling unit.
  • Glial cells (e.g., astrocytes): supportive roles; maintain homeostasis, form myelin, provide support and modulate transmission.

Key Terminology: Tract, Nerve, Nucleus, Ganglion

  • Tract: a set of axons within the CNS (projection from one structure to another).
  • Nerve: a bundle of axons in the PNS, connecting CNS to muscles/glands or sensory organs to CNS.
  • Nucleus: a cluster of neuron cell bodies within the CNS.
  • Ganglion: a cluster of neuron cell bodies outside the CNS (e.g., in the sympathetic nervous system).
  • Note: When axons extend from cell bodies in one structure to synapse onto another, they are said to project.

Spinal Cord and Spinal Nerves

  • The spine contains 31 vertebrae, organized into 5 segments (cervical, thoracic, lumbar, sacral, coccygeal).
  • Spinal cord segments are interconnected, enabling coordinated movements across adjacent segments.
  • Dermatome: area of skin supplied by afferent nerve fibers from a single spinal cord dorsal root.
  • Bell–Magendie law: sensory information enters the spinal cord via the posterior (dorsal) roots; motor information exits via the anterior (ventral) roots.
  • Spinal nerves have dorsal (afferent) and ventral (efferent) roots; gray matter contains neuron cell bodies; white matter contains myelinated axons; dorsal root ganglion houses sensory neuron cell bodies.

Autonomic and Enteric Nervous Systems (Visceral Relations)

  • Autonomic Nervous System (ANS): balances internal functions; involuntary control of internal organs.
    • Sympathetic division: arouses the body for action (fight or flight); general effects include increased heart rate, pupil dilation, redirection of blood flow, and energy mobilization.
    • Parasympathetic division: promotes rest and digest; counteracts sympathetic effects; conserves energy and facilitates digestion and calm states.
  • Sympathetic division overview (highlights):
    • Dilates pupil, inhibits salivation, relaxes airways, stimulates heart rate, constricts blood vessels, inhibits digestion, stimulates glucose release, stimulates adrenal gland activity, etc.
    • Neural pathways include preganglionic neurons exiting the spinal cord (thoracic and lumbar regions) and synapsing in sympathetic chain ganglia or prevertebral ganglia.
  • Parasympathetic division overview (highlights):
    • Slows heart rate, stimulates digestion, constricts pupils, constricts airways, stimulates saliva production, etc.
    • Pathways include cranial nerves (e.g., vagus) and sacral outflow to pelvic organs.
  • Enteric Nervous System (ENS): network of neurons in the GI tract lining; regulates bowel motility, secretion, and blood flow to support absorption and waste elimination.
    • Brain–ENS connections occur via the ANS, especially through the vagus nerve.
    • Emerging evidence links ENS to certain behavioral disorders; stress and anxiety can modify gut function.
    • Psychobiotics: live microorganisms used to treat behavioral disorders.

The Forebrain: Cerebral Cortex, Limbic, and Basal Ganglia

  • Cerebral Cortex:
    • Neocortex: six-layered structure responsible for higher cognitive functions; executes perceptual processing and planning.
    • Allocortex: includes older cortical areas with fewer than six layers; part of limbic and related structures.
    • Cortex has laminae (layers) and columns (functional units).
  • Limbic System: regulation of emotions and memory; includes:
    • Amygdala: emotions (especially fear).
    • Hippocampus: memory and mood.
    • Cingulate cortex: emotion formation, processing, learning, memory, motivation linkage.
    • Olfactory system: olfactory bulbs and receptors, piriform olfactory cortex, vomeronasal organ (VNO).
  • Basal Ganglia: caudate nucleus, putamen, globus pallidus; control of voluntary movement and coordination of movement patterns; implicated in Parkinson’s disease and Tourette syndrome.
  • Forebrain: overall functional divisions include the cerebral cortex, limbic system, basal ganglia, and other subcortical structures.

The Cerebral Cortex: Lobes, Orientation, and Major Gyri/Sulci

  • Four cerebral lobes (overview): Frontal, Parietal, Occipital, Temporal.
  • Frontal lobe: motor control and executive functions.
  • Parietal lobe: sensory integration and perception.
  • Occipital lobe: visual processing.
  • Temporal lobe: auditory processing and memory.
  • Surface orientation views (A–D in figures):
    • Dorsal view, Ventral view, Lateral view, Medial view.
  • Central sulcus and longitudinal fissure (between hemispheres) as key landmarks; lateral fissure (Sylvian fissure) separates frontal/temporal from parietal lobes.

Neocortical Layers and Functional Specialization

  • Neocortex consists of six layers with different cell types and densities; layer-specific connectivity underlies distinct functions.
  • Laminae and columns contribute to cortical processing and integration across regions.

Meninges, Protection, and CSF

  • Meninges: three protective layers surrounding the CNS:
    • Dura mater: hard outer layer; tough fibrous tissue.
    • Arachnoid layer: web-like, delicate connective tissue.
    • Pia mater: soft inner layer that clings to the brain’s surface.
  • Functions: protection and stabilization of the CNS; spinal meninges are continuous with cranial meninges.
  • CSF resides in the subarachnoid space; CSF cushions the brain and supports nutrient/waste exchange.

Review: Summary of Major Structures and Concepts

  • Central nervous system (CNS): brain and spinal cord.
  • Peripheral nervous system (PNS): all neural elements outside the CNS.
  • Somatic nervous system (SNS): sensory input from body to CNS; motor output from CNS to muscles.
  • Autonomic nervous system (ANS): involuntary control of internal organs; includes sympathetic and parasympathetic divisions.
  • Enteric nervous system (ENS): gut-brain network; largely autonomous.
  • Brain orientation terms: anterior, posterior, medial, lateral, dorsal, ventral, rostral, caudal, superior, inferior.
  • Planes of section: coronal, horizontal, sagittal (including midsagittal).
  • Major brain divisions: hindbrain (cerebellum, pons, medulla), midbrain (tectum, tegmentum, substantia nigra), diencephalon (thalamus, hypothalamus), forebrain (cerebral cortex, limbic system, basal ganglia).
  • Cerebral cortex and lobes: six-layer neocortex; four lobes with distinct functions; gyri and sulci.
  • Subcortical structures: corpus callosum, thalamus, hypothalamus, limbic system, basal ganglia.
  • Cerebral circulation and BBB: cerebral arteries; BBB characteristics and transport; glucose and energy transport; CSF production and circulation.
  • Neurons vs glia: cell bodies vs support cells; roles in signaling and homeostasis.
  • Spinal cord organization: vertebral segments, dermatomes, Bell–Magendie law (sensory dorsal, motor ventral).
  • Autonomic and enteric systems: sympathetic vs parasympathetic function and pathways; ENS roles; psychobiotics.
  • Key cranial nerves: listing from Olfactory (CN I) to Hypoglossal (CN XII) with primary functions; mnemonic provided in slides for recall.

Quick Reference: Cranial Nerves (Names and Basic Functions)

  • CN I: Olfactory – Smell
  • CN II: Optic – Vision
  • CN III: Oculomotor – Eye movement
  • CN IV: Trochlear – Eye movement
  • CN V: Trigeminal – Masticatory movements and facial sensation
  • CN VI: Abducens – Eye movement
  • CN VII: Facial – Facial movement and sensation
  • CN VIII: Vestibulocochlear – Hearing and balance
  • CN IX: Glossopharyngeal – Tongue and pharynx movement and sensation
  • CN X: Vagus – Heart, blood vessels, viscera, movement of larynx and pharynx
  • CN XI: Spinal accessory – Neck movement
  • CN XII: Hypoglossal – Tongue movement

Mnemonic (as presented in the slides)

  • Oh 1 Olfactory – Sensory
  • Say 2 Optic – Visual
  • Oh 3 Oculomotor – Motor
  • Marry 4 Trochlear – Motor
  • But 5 Trigeminal – Both sensory and motor
  • Money 6 Abducens – Motor
  • Touch 7 Facial – Both
  • Says 8 Vestibulocochlear – Sensory
  • Big 9 Glossopharyngeal – Both
  • Vegas 10 Vagus – Both
  • Brains 11 Spinal accessory – Motor
  • Slot 12 Hypoglossal – Motor

End of Notes on Section 2.x (Brain and Behavior)

  • For exam readiness, focus on definitions, hierarchical organization, key structures and their primary functions, and the relationships between systems (CNS vs PNS, SNS vs ANS vs ENS).