SR

exam study guide 1

Chapter 1: Structure & Function of the Nervous System

  • Functional descriptions of neuron parts

    • Dendrites
    • Receptive surfaces that receive synaptic inputs from other neurons.
    • Produce graded potentials that contribute to the neuron's decision to fire an action potential.
    • Often numerous and highly branched to maximize input integration.
    • Soma (cell body)
    • Metabolic center of the neuron; contains nucleus and most organelles.
    • Integrates inputs from dendrites and initiates action potentials if threshold is reached.
    • Axon
    • Conducts electrical impulses away from the soma toward synapses.
    • Axon hillock: trigger zone where summated inputs determine action potential initiation.
    • Axon terminals end in synaptic boutons that release neurotransmitters.
    • Myelination (oligodendrocytes in CNS; Schwann cells in PNS) increases conduction velocity; saltatory conduction occurs at nodes of Ranvier.
    • Synaptic terminals and synapse
    • Presynaptic terminal contains neurotransmitter-filled vesicles and release machinery (e.g., SNARE proteins).
    • Synaptic cleft: extracellular gap between pre- and postsynaptic neurons.
    • Postsynaptic membrane with receptors, signaling cascades, and postsynaptic density.
    • Key numerical/functional note
    • Resting membrane potential of most neurons is about V_{rest} \approx -70 \,\mathrm{mV}, established by ion gradients and selective permeability, plus the Na⁺/K⁺-ATPase pump.
    • Significance
    • Structure underpins how neurons receive, integrate, and transmit information across networks.

  • Different classifications of glia cells based on function

    • Astrocytes
    • Support neurons metabolically, maintain extracellular ion balance, and contribute to the blood–brain barrier; clear neurotransmitters from synapses.
    • Oligodendrocytes (CNS) and Schwann cells (PNS)
    • Create myelin sheaths around axons, accelerating conduction velocity via saltatory conduction.
    • Microglia
    • Immune defense of CNS; prune synapses and respond to injury.
    • Ependymal cells
    • Line ventricles and contribute to CSF production and circulation.
    • Satellite cells (PNS)
    • Provide support around neuronal somata in peripheral ganglia.
    • Significance
    • Glia actively shape signaling, metabolic support, and protection, not just passive scaffolding.

  • Different classifications of neurons based on structure & function

    • By structure
    • Multipolar: many dendrites; most CNS neurons (e.g., motor, interneurons).
    • Bipolar: two processes; often retinal or olfactory neurons.
    • Unipolar/Pseudounipolar: single process from soma; typical of many peripheral sensory neurons.
    • By function
    • Sensory (afferent): convey information from periphery to CNS.
    • Motor (efferent): convey commands from CNS to effectors (muscle/gland).
    • Interneurons (association neurons): integrate information within CNS; often local circuits.
    • Examples and significance
    • Pyramidal neurons (often pyramidal-shaped, excitatory, glutamatergic) in cortex are typically multipolar.
    • Interneurons in cortex can be GABAergic and regulate network activity.

  • Description of key components of a synapse

    • Presynaptic terminal
    • Houses synaptic vesicles with neurotransmitters; voltage-gated Ca²⁺ channels trigger release.
    • Synaptic cleft
    • Narrow gap where neurotransmitters diffuse to postsynaptic receptors.
    • Postsynaptic membrane
    • Receptors (ligand-gated ion channels and G-protein-coupled receptors) that transduce the signal.
    • Synaptic vesicle release machinery
    • SNARE complex drives vesicle fusion with the presynaptic membrane.
    • Types of synapses
    • Excitatory (e.g., glutamatergic) typically produce EPSPs.
    • Inhibitory (e.g., GABAergic) typically produce IPSPs.
    • Autoreceptors
    • Receptors on the presynaptic terminal that regulate transmitter release.
    • Functional significance
    • Synapses determine the strength and timing of neural communication; they are sites of plasticity and learning.

  • Divisions of the Nervous System

    • Central Nervous System (CNS)
    • Brain and spinal cord.
    • Peripheral Nervous System (PNS)
    • Cranial nerves, spinal nerves, and autonomic/sensory/motor components.
    • Subdivisions by function
    • Somatic: voluntary control of body movements; sensory and motor pathways.
    • Autonomic: involuntary regulation of internal organs; includes sympathetic and parasympathetic divisions (and sometimes enteric system).
    • Directional and projection terminology
    • Afferent (toward CNS) vs Efferent (away from CNS).
    • Ipsilateral vs Contralateral; Ascending vs Descending tracts.
    • Significance
    • Provides framework for locating function and understanding disease pathways.

  • Different Cranial Nerves and Function

    • 12 pairs with mixed modalities (sensory, motor, autonomic).
    • Functions (high-level):
    • I Olfactory: smell; II Optic: vision; III Oculomotor: eye movements, pupil constriction; IV Trochlear: eye movements (superior oblique);
      V Trigeminal: facial sensation and mastication; VI Abducens: lateral eye movement; VII Facial: facial expression, taste anterior 2/3; VIII Vestibulocochlear: hearing and balance; IX Glossopharyngeal: taste posterior 1/3, swallowing; X Vagus: parasympathetic innervation; XI Accessory: head/neck movement; XII Hypoglossal: tongue movement.
    • Significance
    • Core for autonomic and somatic control of head and neck, with diffuse CNS connections.