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Anatomy & Physiology: Nervous and Muscle Tissue Fundamentals

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  • Three overlapping functions of the nervous system
    Sensory input: gathering information about changes; Integration: processing and interpreting sensory input; Motor output: activating effectors to produce a response.
  • Two principal parts of the nervous system
    Central nervous system (CNS): brain and spinal cord; Peripheral nervous system (PNS): nerves outside CNS including spinal and cranial nerves.
  • Functional divisions of the Peripheral Nervous System (PNS)
    Sensory (afferent) division: transmits impulses to CNS; Motor (efferent) division: transmits impulses from CNS to muscles and glands.
  • Two subdivisions of the motor (efferent) division
    Somatic nervous system: voluntary control of skeletal muscles; Autonomic nervous system (ANS): involuntary control of smooth muscle, cardiac muscle, and glands.
  • Four main types of neuroglia in the CNS
    Astrocytes, Microglial cells, Ependymal cells, and Oligodendrocytes.
  • Functions of astrocytes
    Support neurons, regulate chemical environment, guide neuron migration, recycle neurotransmitters, and maintain blood-brain barrier.
  • Role of Schwann cells in the PNS
    Surround peripheral nerve fibers, form myelin sheaths, and aid regeneration of damaged nerves.
  • Structure of a neuron
    Consists of a cell body (soma), dendrites (input), and an axon (conducting region) ending in axon terminals.
  • Difference between nuclei and ganglia
    Nuclei: clusters of neuron cell bodies in CNS; Ganglia: clusters of neuron cell bodies in PNS.
  • Function of myelin sheath
    Protects and electrically insulates axons, increasing speed of nerve impulse transmission.
  • Types of neurons by function
    Sensory (afferent): transmit impulses to CNS; Motor (efferent): carry impulses from CNS; Interneurons: connect sensory and motor neurons within CNS.
  • Resting membrane potential of neurons
    Approximately −70 mV; inside of cell is negative relative to outside; membrane is polarized.
  • Types of ion channels in neuron membranes
    Leakage (nongated): always open; Gated channels: open/close in response to stimuli (chemical, voltage, mechanical).
  • Events causing an action potential in muscle fibers
    1. End plate potential from ACh binding; 2. Depolarization via voltage-gated Na+ channels; 3. Repolarization via voltage-gated K+ channels.
  • Sliding filament model of muscle contraction
    Thin filaments slide past thick filaments, increasing overlap; sarcomeres shorten without filaments changing length.
  • Four steps of the cross bridge cycle
    1. Cross bridge formation; 2. Power stroke; 3. Cross bridge detachment; 4. Cocking of myosin head using ATP.
  • Cause of rigor mortis
    Lack of ATP after death prevents detachment of myosin heads from actin, causing muscle stiffness.
  • Motor unit definition
    One motor neuron and all the muscle fibers it innervates; smaller units allow finer control.
  • Phases of a muscle twitch
    Latent period (excitation-contraction coupling), contraction period (cross bridge formation), relaxation period (Ca2+ reentry into SR).
  • Graded muscle contractions
    Varying strength of contraction by changing stimulus frequency (temporal summation) and stimulus strength (recruitment).
  • Isotonic vs. isometric contractions
    Isotonic: muscle shortens and moves load; Isometric: muscle tension increases but length does not change.
  • Three pathways for ATP regeneration in muscle
    1. Direct phosphorylation by creatine phosphate; 2. Anaerobic glycolysis; 3. Aerobic respiration in mitochondria.
  • Causes of muscle fatigue
    Ionic imbalances, increased inorganic phosphate, decreased ATP, and decreased glycogen.
  • Characteristics of smooth muscle fibers
    Thin, spindle-shaped, uninucleate, no striations, less developed SR, no T tubules, connected by gap junctions.
  • Mechanism of smooth muscle contraction
    Ca2+ binds calmodulin, activating myosin kinase which phosphorylates myosin heads to form cross bridges.
  • Differences between smooth and skeletal muscle contraction
    Smooth muscle uses calmodulin instead of troponin, slower contraction, and can maintain tone with less energy.
  • Functions of muscle tissue
    Produce movement, maintain posture, stabilize joints, and generate heat.
  • Four main characteristics of muscle tissue
    Excitability, contractility, extensibility, and elasticity.