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Anatomy & Physiology: Nervous System and Nervous Tissue

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  • What are the two main divisions of the nervous system?
    Central Nervous System (CNS) includes the brain and spinal cord. Peripheral Nervous System (PNS) includes all nervous tissue outside the CNS such as cranial nerves, spinal nerves, and ganglia.
  • What are the three main functions of the nervous system?
    Sensory function: gathers information from internal and external environment. Integrative function: processes and interprets sensory input. Motor function: activates effectors like muscles and glands to respond.
  • What are the two functional divisions of the peripheral nervous system (PNS)?
    Sensory (afferent) division: carries sensory information to the CNS. Motor (efferent) division: carries motor commands from CNS to muscles and glands.
  • What are the subdivisions of the motor (efferent) division of the PNS?
    Somatic nervous system (SNS): voluntary control of skeletal muscles. Autonomic nervous system (ANS): involuntary control of smooth muscle, cardiac muscle, and glands; subdivided into sympathetic and parasympathetic divisions.
  • What is the difference between a neuron and a neuroglial cell?
    Neuron: excitable cells that transmit electrical signals. Neuroglial cells: supporting cells that protect, nourish, and support neurons.
  • Name the six types of neuroglial cells and their locations.
    CNS: Astrocytes, Microglia, Ependymal cells, Oligodendrocytes. PNS: Satellite cells, Schwann cells.
  • What is the function of astrocytes?
    Support and brace neurons, regulate chemical environment, assist in exchanges between capillaries and neurons, and participate in information processing in the brain.
  • What role do microglial cells play in the CNS?
    They act as specialized macrophages that engulf debris, waste, and microorganisms, providing immune defense in the CNS.
  • What is the function of ependymal cells?
    Line brain ventricles and spinal cord central canal, produce and circulate cerebrospinal fluid (CSF) with their cilia.
  • What is the role of oligodendrocytes?
    Form the myelin sheath around CNS axons, which insulates and increases the speed of electrical signal transmission.
  • What do Schwann cells and satellite cells do in the PNS?
    Schwann cells form myelin sheath around PNS axons and aid in nerve regeneration. Satellite cells surround neuron cell bodies and regulate the environment.
  • What are the main parts of a neuron and their functions?
    Dendrites: receive input and convey graded potentials. Cell body: biosynthetic center. Axon: conducts action potentials to other cells.
  • What is the function of the myelin sheath?
    Protects and insulates axons, increases speed of action potential propagation by enabling saltatory conduction.
  • Describe the structural classification of neurons.
    Multipolar: many dendrites, one axon (most common). Bipolar: one dendrite, one axon (special senses). Unipolar: single process that splits into peripheral and central branches (mostly sensory neurons).
  • Describe the functional classification of neurons.
    Sensory neurons: carry impulses to CNS. Motor neurons: carry impulses from CNS to effectors. Interneurons: connect sensory and motor neurons within CNS.
  • What is resting membrane potential and its typical value in neurons?
    The electrical potential difference across the membrane of a resting neuron, typically about \(-70\,mV\), with the inside negative relative to outside.
  • What ions are primarily responsible for resting membrane potential?
    High concentration of K+ inside the cell and Na+ outside. Membrane is more permeable to K+, which leaks out, creating a negative inside charge.
  • What are the four types of ion channels in neurons?
    Leak channels: always open. Ligand-gated channels: open in response to chemicals. Voltage-gated channels: open in response to changes in membrane potential. Mechanically-gated channels: open in response to mechanical stimuli.
  • What is the difference between graded potentials and action potentials?
    Graded potentials are localized, vary in magnitude, and decrease with distance. Action potentials are all-or-none, propagate without decreasing, and travel long distances.
  • Explain the phases of an action potential.
    1. Depolarization: Na+ channels open, Na+ enters cell. 2. Repolarization: Na+ channels close, K+ channels open, K+ leaves cell. 3. Hyperpolarization: K+ channels close slowly, membrane potential temporarily more negative than resting.
  • What is the refractory period?
    Time during which a neuron cannot fire another action potential. Absolute refractory period: no stimulus can trigger AP. Relative refractory period: stronger stimulus needed to trigger AP.
  • Compare continuous and saltatory conduction.
    Continuous conduction occurs in unmyelinated axons with step-by-step depolarization. Saltatory conduction occurs in myelinated axons, with AP jumping between Nodes of Ranvier, increasing speed.
  • What is a synapse?
    A functional junction between a neuron and another cell where signals are transmitted chemically or electrically.
  • Difference between electrical and chemical synapses?
    Electrical synapses have direct cell contact via gap junctions allowing fast ion flow. Chemical synapses use neurotransmitters to transmit signals across a synaptic cleft.
  • Outline the steps of chemical synaptic transmission.
    1. AP reaches presynaptic terminal. 2. Voltage-gated Ca2+ channels open, Ca2+ enters. 3. Neurotransmitter released by exocytosis. 4. Neurotransmitter binds postsynaptic receptors. 5. Ion channels open, causing graded potential. 6. Neurotransmitter removed.
  • How are neurotransmitters removed from the synaptic cleft?
    By diffusion away from the cleft, enzymatic breakdown (e.g., acetylcholinesterase), or reuptake into presynaptic neuron.
  • What are excitatory and inhibitory neurotransmitters?
    Excitatory neurotransmitters depolarize postsynaptic membrane, increasing AP likelihood. Inhibitory neurotransmitters hyperpolarize membrane, decreasing AP likelihood.
  • How does axon diameter affect action potential speed?
    Larger diameter axons have less resistance to current flow and conduct action potentials faster.