Ch 11 - Fundamentals of Nervous System (1)

  1. What is the nervous system?
    • Nervous system and endocrine system coordinate organ system activities in response to changing environmental conditions
    • nervous system controls fast but brief responses (body position, eye movement)
    • endocrine controls slow lasting processes (energy use)
    • master controlling and communicating system of body
    • cells communicate via electrical and chemical signals (rapid and specific; usually almost immediate responses)
    • Nervous system controls endocrine also
  2. 3 overlapping functions of nervous system
    • 1) Sensory input
    • information gathered by sensory receptors about internal and external environment
    • 2) Integration
    • processing and interpretation of sensory input
    • 3) Motor output
    • coordinates voluntary and involuntary responses of many organ systems
    • nervous system activates effector organs to cause response
  3. Divisions of nervous system: 2 parts
    • 1) Central nervous system (CNS)
    • brain and spinal cord of dorsal body cavity
    • higher functions (intelligence, memory, emotions)
    • integration and control center (interprets sensory input and dictates motor output)
    • 2) Peripheral nervous system (PNS)
    • the portion of the nervous system outside CNS
    • all peripheral nerves to and from the spinal cord (spinal nerves) and brain (cranial nerves)
    • serves as communication lines that link all parts of body to the CNS
  4. Peripheral nervous system (PNS): 2 functional divisions
    • 1) Afferent - "carrying toward" (sensory)
    • carry info from the periphery to the CNS
    • keeps CNS informed of events in&out of body
    • 2) Efferent - "carrying away" (motor)
    • carry info from the CNS to the target organ
    • impulses activate muscles to contract and glands to secrete
  5. PNS - Afferent system
    • (af - to, fere- to carry; sensory)
    • ~10 million sensory neurons in body

    • 2 main groups:
    • Somatic sensory fibers - convey impulses from skin, skeletal muscles and joints to CNS
    • Visceral sensory fibers - convey impulses from visceral organs to CNS
  6. PNS - Efferent system
    • (ef- from; motor)
    • ~ 1/2 million motor neurons
    • transmits impulses from CNS effector organs

    • 2 divisions:
    • Somatic nervous system - voluntary muscle control
    • Autonomic nervous system - involuntary control, smooth muscle, heart, glandular secretions
  7. motor division of PNS: Autonomic nervous system
    • visceral motor nerve fibers
    • regulates smooth muscle, cardiac muscle, and glands
    • involuntary nervous system

    • 2 functional divisions (work in opposition):
    • Sympathetic
    • Parasymphathetic
  8. Histology of nervous tissue
    highly cellular with little extracellular space

    • 2 main cell types:
    • Glia - regulate neuronal environment; form supporting frame; immune cells
    • Neurons (nerve cells) - basic "unit" of the nervous system; excitable cells that transmit electrical signals
  9. histology of nervous tissue:  Glia
    4 cells in CNS; 2 in PNS

    • In CNS:
    • Astrocytes
    • Microglial cells
    • Oligodendrocytes
    • Ependymal cells
    • In PNS:
    • Satellite cells
    • Schwann cells
  10. Astrocytes
    • CNS - glia
    • largest, most abundant, and highly branched glial cells
    • cling to neurons, synaptic endings, and capillaries
    • shaped like sea anemones

    • Functions:
    • control chemical environment
    • structural framework of the brain
    • **maintain blood-brain barrier** (most essential)
    • repair neuronal tissue
  11. Microglial cells
    • CNS - glia
    • smallest, rarest glial type
    • small, ovoid cells with thorny processes that touch and monitor neurons
    • "white blood cells" of the CNS
    • phagocytize microorganisms and neuronal debris
    • only cells that move under the microscope
  12. Oligodendrocytes
    • CNS - glia
    • branched cells with fewer processes than astrocytes
    • cytoplasmic extensions wrap around axons, forming myelin sheath
    • myelin sheath electrially isolates individual axons
  13. Ependymal cells
    • CNS - glia
    • range in shape from squamous to columnar
    • line the central cavities of the spinal cord and brain -- only found there
    • produce cerebrospinal fluid (CSF)
    • may be ciliated
  14. Satellite cells
    • PNS - glia
    • surround neuron cell bodies in PNS
    • function similar to astrocytes of CNS
  15. Schwann cells (neurolemmocytes)
    • PNS - glia
    • surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers
    • similar function as oligodendrocytes
    • vital to regeneration of damaged peripheral nerve fibers
  16. neurons - "nerve cells"
    • structural units of nervous system
    • large, highly specialized cells that conduct electrical impulses
    • extreme longevity -- 100+ years
    • amitotic - with few exceptions (does not divide)
    • highly metabolic rate - requires continuous supply of oxygen, glucose, and nourishment
    • all have cell body and one or more processes
  17. neuronal cell body (perikaryon or soma)
    • biosynthetic center of neuron (synthesizes proteins, membranes, and other chemicals; Rough ER -- chromatophilic (color loving) substance or nissl bodies -- most active and best developed in body)
    • in most neurons the plasma membrane of the soma is part of the receptive region
    • most neuron cell bodies in CNS (nuclei - clusters of neuron cell bodies in CNS)
    • Ganglia - lie along nerves in PNS
  18. neuron processes
    • 2 types of processes:
    • dendrites - receive input, numerous
    • axon - output, only one

    • tracts - bundles of neuron processes in CNS
    • nerves - bundles of neuron processes in PNS

    CNS contain both neuron cell bodies and their processes; PNS contain only neuron processes
  19. structural classification of neurons: 3 types
    grouped by number of processes extending from cell body

    • 1) Multipolar - 3 or more processes
    • 1 axon, others dendrites
    • most common; major neuron in CNS
    • 2) Bipolar - 2 processes
    • 1 axon and 1 dendrite
    • rare; ex- retina and olfactory mucosa
    • 3) Unipolar - 1 short process
  20. functional classification of neurons: 3 types
    grouped by direction in which nerve impulse travels relative to CNS

    • 3 types:
    • - sensory (afferent)
    • - motor (efferent)
    • - interneurons (connect neurons to each other; lie between neurons; ex- brain)
  21. Axon: structure
    • one axon per cell arising from axon hillock (triangular region)
    • in some axon- short or absent; in others- as long as 1 meter
    • long axons called nerve fibers
    • occasional branches are called axon collaterals
    • branches profusely at target organ (up to 10,000 terminal branches)
    • distal endings called axon terminals or terminal boutons
  22. Axon: functional characteristics
    • conducting region of neuron
    • generates nerve impulses at axon hillock
    • transmits them along axolemma (nerve cell membrane) to axon terminal -- secretory region; neurotransmitters released into extracellular space
    • lacks rough ER and Golgi apparatus -- does not make protein
    • cytoplasmic extension
  23. myelin sheath
    • composed of myelin - a white, protein-lipoid substance
    • segmented sheath around most long or large-diameter axons (myelinated fibers)
    • Function of myelin:  protects and electrically insulates myelin; increases speed of nerve impulse transmission
    • nonmyelinated fibers conduct impulses more slowly
  24. myelination in the PNS
    • plasma membranes of myelinating cells have less membrane protein -- no channels or carriers; good electrical insulators; interlocking proteins bind adjacent myelin membranes; formed by Schwann cells
    • Nodes of ranvier - -myelin sheath gaps b/w adjacent Schwann cells
    • nonmyelinated fibers -- thin fibers not wrapped in myelin; single Schwann cell may surround as many as 15 different fibers
  25. nervous system
    fast acting control system that triggers muscle contraction or gland secretion
  26. nonmyelinated fibers
    axons lacking a myelin sheath and therefore conducting impulses quite slowly
  27. Nodes of ranvier
    myelin sheath gaps between adjacent Schwann cells
  28. myelin sheaths in the CNS
    white matter -- regions of brain and spinal cord with dense collections of myelinated fibers - usually fiber tracts; white color comes from myelin

    gray matter -- mostly neuron cell bodies and nonmyelinated fibers
  29. what is the difference between a somatic reflex and an autonomic (visceral) reflex?
    contraction of a skeletal muscle is a part of the somatic reflex.  Impulse conduction over somatic reflex arcs produces somatic reflexes. 

    Autonomic (visceral) reflexes consist of smooth or cardiac muscle or secretion by glands.  They are mediated by impulse conduction over autonomic reflex arcs.
  30. describe the components and responsibilities of the central nervous system (CNS)
    the CNS comprises both the brain and spinal cord.  It is the principal integrator of sensory input and motor output.  Thus the CNS is capable of evaluating incoming information and formulating responses to changes that threaten out homeostatic balance.
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Ch 11 - Fundamentals of Nervous System (1)
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