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Nervous System: Form, Function, and Cells — Comprehensive Study Notes

Nervous system: form, function, and organization

  • Purpose of the unit

    • Understand the function of the brain and how it changes behavior
    • To understand function we must also understand form (anatomy and development)
    • Central idea: form + function; brain and spinal cord are the focus for anatomy; behavior and processing for function

  • Chapter structure (outline mentioned in lecture)

    • Overview of the nervous system
    • Cells of the nervous system
    • Anatomy of the brain and major divisions (to be covered Monday)
    • Memorization will focus on brain regions and their functions; lobe names are fair game: temporal, parietal, occipital, frontal; cerebellum; spinal cord

  • CNS vs PNS

    • Central nervous system (CNS): brain + spinal cord
    • Peripheral nervous system (PNS): everything outside CNS
    • Easy rule of thumb: CNS = brain + spinal cord; PNS = all other nerves

  • Subdivisions within the PNS

    • Somatic nervous system: direct interaction with the environment; voluntary movements
    • Autonomic nervous system: less direct, regulatory processes beyond conscious awareness
    • Afferent nerves: bring information into the CNS
    • Efferent nerves: send information out from the CNS
    • Reflex example: afferent input from a stimulus goes to the spinal cord, a reflex (via efferent pathways) can cause muscle contraction through acetylcholine at the neuromuscular junction
    • The brain is the main decision-maker; sensory information from the world is processed across brain regions to produce the appropriate output via the efferent system

  • Hierarchical organization and functional focus

    • Decisions are made in the brain across multiple regions; functions are distributed and integrated
    • The course will connect brain regions to behaviors, not just anatomy

  • Brain region identification (exams emphasize function and pictures, not exact locations)

    • You may be shown brain images and given functions; you should identify lobes (temporal, parietal, occipital, frontal) and the cerebellum from images when asked about function
    • The exam will not require memorizing precise anatomical locations for every structure beyond lobes and cerebellum

  • Autonomic nervous system (ANS): sympathetic vs parasympathetic

    • Sympathetic division: fight or flight; mobilizes energy and increases arousal
    • Parasympathetic division: rest and digest; supports digestion and maintenance functions
    • Mnemonic: the sympathetic system “sympathizes” with the situation and prepares you to survive; antagonistic to parasympathetic activity during stress
    • Concept of an on/off switch: sympathetic on during threat → parasympathetic relatively reduced; in non-stressful times, parasympathetic activity dominates

  • Examples of autonomic regulation

    • Sympathetic: dilates bronchial tubes, dilates pupils, redirects blood flow to muscles, increases heart rate, etc.
    • Parasympathetic: promotes digestion and energy storage; conserves energy

  • Central nervous system protection and basic anatomy

    • Protection concepts: skull (cranium) and vertebrae encase the brain and spinal cord to reduce injury
    • Meninges: protective membranes around CNS
    • Dura mater: tough outer layer; anchors and protects
    • Arachnoid mater: spider-like webbing; contains CSF in the subarachnoid space
    • Pia mater: delicate layer closely following the surface of the brain and spinal cord
    • Epidural vs subdural hematomas (clinical cross-section concepts)
    • Epidural hematoma: bleed above the dura mater (epi- = on top of dura)
    • Subdural hematoma: bleed beneath the dura mater (sub- = below dura)
    • Spinal/cranial CSF and ventricles
    • Cerebrospinal fluid (CSF): protective fluid that buoyantly surrounds brain and spinal cord, reducing impact and providing a stable environment
    • Ventricles: four large spaces in the brain filled with CSF; a central canal runs from the brain down into the spinal cord; there are four ventricles (and a central canal) in total
    • Hydrocephalus: condition where excess CSF causes brain swelling; increased intracranial pressure can lead to brain damage or death; treatment often involves draining fluid after traumatic brain injury (TBI) to relieve pressure
    • Bacterial meningitis vs viral meningitis: infection of CSF; bacterial meningitis can be severe, especially in communal living settings like dorms; viral meningitis is more common and typically less severe

  • Neurons and synaptic communication (basic cellular neuroscience)

    • Neuron structure (typical schematic used in class)
    • Soma (cell body): contains nucleus
    • Dendrites: receive input from other neurons
    • Axon hillock: decision point for generating action potentials
    • Axon: conducts electrical impulse away from the soma
    • Myelin sheath: fatty insulation around many axons; increases speed of transmission
    • Nodes of Ranvier: gaps in the myelin sheath that facilitate rapid conduction
    • Terminal boutons (synaptic terminals): release neurotransmitters into the synapse
    • The cell membrane and ion channels
    • Cell membrane: lipid bilayer (phospholipid heads on the outside, tails inside)
    • Selective permeability: ion channels regulate entry/exit of ions, enabling action potentials
    • Synaptic transmission basics
    • Neurotransmitters are stored in vesicles in the presynaptic terminal
    • Action potential triggers release of neurotransmitters into the synapse
    • Neurotransmitters bind to receptors on the postsynaptic membrane
    • Receptor types:
      • Ionotropic (ligand-gated ion channels): direct ion flow when a neurotransmitter binds
      • Metabotropic (seven-pass transmembrane) receptors: activate intracellular signaling cascades; slower but diverse effects
    • Neuron types (illustrative, not exhaustively exhaustive)
    • Unipolar neurons: single projection that splits into two branches (dendritic and axonal processes) and functions as a single unit
    • Bipolar neurons: two poles with dendrites and axon separated by a cell body
    • Classical example shown in lectures as the “test neuron” with a key for exam preparation

  • Glial cells and their roles

    • Oligodendrocytes
    • Location: CNS (brain and spinal cord)
    • Function: myelinate axons in the CNS
    • If myelin is present on CNS axons, it’s produced by oligodendrocytes
    • Schwann cells
    • Location: PNS (peripheral nervous system)
    • Function: myelinate axons in the PNS
    • Important clinically: regeneration after peripheral injuries (e.g., finger reattachment) is possible due to Schwann cell–mediated regeneration
    • Microglia
    • Role: immune-like cells, critical for responding to energy and injury; participate in repair signaling
    • Dynamic states: healthy microglia are “good juju” workers; when activated pathologically, they can morphologically change to a harmful, spiky form and contribute to damage
    • Astrocytes
    • Role: interact with blood vessels and regulate the brain’s microenvironment
    • Astrocytic feet: processes that envelop blood vessels to regulate substance passage
    • Blood-brain barrier (BBB): astrocyte end-feet form tight junctions that limit what passes from the bloodstream into the brain, maintaining CNS homeostasis
    • Comparison to placenta: BBB is a protective barrier akin to placental protection for the baby, tightly regulating entry of substances into the brain

  • Key practical and conceptual takeaways

    • The brain is protected by bones (skull, vertebrae), meninges (dura, arachnoid, pia), and CSF with ventricles
    • The ANS coordinates involuntary functions via two opposing branches (sympathetic and parasympathetic)
    • Neurons communicate through synapses using neurotransmitters that act on receptor proteins (ion channels or metabotropic receptors)
    • Glial cells provide structural support, insulation, immune defense, and regulate the brain’s environment; the BBB is crucial for protecting neural tissue
    • Clinical correlates mentioned in lecture:
    • Epidural and subdural hematomas reflect different tissue layers relative to the dura
    • Hydrocephalus results from CSF imbalance and can lead to dangerous pressure on neural tissue
    • Meningitis represents infection of the CSF, with potential severe outcomes

  • Connections to broader course themes

    • Form (anatomy) ↔ function (behavior and processing) relationship emphasized throughout
    • Foundational principles: CNS protection, synaptic signaling, and glial support underpin all higher-level topics, including behavior, cognition, and clinical pathology
    • Real-world relevance: understanding reflexes, stress responses, and drug effects on autonomic function will be reinforced in later chapters (e.g., drug chapter)

  • Quick reference terms to memorize

    • Dura mater, Arachnoid mater, Pia mater
    • CSF (cerebrospinal fluid); ventricles; central canal
    • Epidural hematoma, Subdural hematoma
    • Afferent vs Efferent; Somatic vs Autonomic
    • Sympathetic vs Parasympathetic
    • Neuron components: soma, dendrites, axon, axon hillock, myelin, nodes of Ranvier, terminal boutons
    • Glial cells: oligodendrocytes (CNS), Schwann cells (PNS), microglia, astrocytes
    • Blood-brain barrier (BBB) by astrocytic end-feet

  • Note about exam-style learning approach (from lecture)

    • You will be given a brain image and a function; you will identify the region based on function, not memorize strict anatomical labels for every structure
    • Emphasis on lobes and major protective structures for initial exam questions

  • Optional reminders and context

    • The instructor mentioned updating the exam dates on Canvas to align with internal planning; check syllabus and announcements for any schedule changes
    • The content covered includes both review for those who have prior biology knowledge and new information for others; use it as a refresher and scaffold for more advanced topics in upcoming weeks