뒤로Fundamentals of the Nervous System - Anatomy & Physiology
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Sensory input gathers information about internal and external changes,
integration processes and interprets sensory input
motor output activates effector organs to produce a response.
The Central Nervous System (CNS) consists of the brain and spinal cord, and the Peripheral Nervous System (PNS) consists of nerves extending from the CNS.
The PNS has a sensory (afferent) division that conveys impulses to the CNS, and a motor (efferent) division that transmits impulses from the CNS to effectors.
The somatic nervous system controls voluntary skeletal muscles, and the autonomic nervous system regulates involuntary smooth muscle, cardiac muscle, and glands.
The sympathetic division mobilizes body systems during activity, and the parasympathetic division conserves energy and promotes housekeeping functions during rest.
Neuroglia are small cells that support and protect neurons, and neurons are excitable cells that transmit electrical signals.
Astrocytes, microglial cells, ependymal cells, oligodendrocytes are in the CNS; satellite cells and Schwann cells are in the PNS.
They support neurons, regulate the chemical environment, guide neuron migration, respond to nerve impulses, and participate in brain information processing.
Microglial cells monitor neurons, migrate to injured neurons, and can transform to phagocytize microorganisms and debris.
Ependymal cells line brain and spinal cord cavities, may be ciliated to circulate cerebrospinal fluid, and form a permeable barrier between CSF and tissue fluid.
Oligodendrocytes wrap CNS nerve fibers with myelin sheaths, insulating axons and increasing impulse transmission speed.
Satellite cells surround neuron cell bodies and support them; Schwann cells form myelin sheaths around peripheral nerve fibers and aid regeneration.
Neurons are long-lived, amitotic, have high metabolic rates, and consist of a cell body and one or more processes.
The cell body is the biosynthetic center, synthesizing proteins and membranes, and contains the nucleus and organelles.
Dendrites receive signals and convey them to the cell body; axons generate and transmit impulses away from the cell body.
Dendrites are short, branched processes that receive input and convey graded potentials toward the cell body.
The axon hillock is the cone-shaped region where the axon arises from the cell body; it is the trigger zone for nerve impulses.
Schwann cells wrap around axons in a jelly-roll fashion, forming concentric layers of plasma membrane that create the myelin sheath.
Myelin protects and electrically insulates axons, increasing the speed of nerve impulse transmission.
In the CNS, oligodendrocytes form myelin sheaths with multiple flat processes; in the PNS, Schwann cells wrap entire segments of axons.
Multipolar neurons have many dendrites and one axon, bipolar neurons have one dendrite and one axon, and unipolar neurons have a single short process that splits into two branches.
Multipolar neurons are most common in the CNS, bipolar neurons are found in special sensory organs, and unipolar neurons are mainly in the PNS sensory ganglia.
Sensory (afferent) neurons transmit impulses to the CNS, motor (efferent) neurons carry impulses from the CNS to effectors, and interneurons connect sensory and motor neurons within the CNS.
Most sensory neurons are unipolar, with cell bodies located in ganglia outside the CNS.
Motor neurons are multipolar, with most cell bodies located within the CNS.
Interneurons lie entirely within the CNS and shuttle signals between sensory and motor neurons, making up 99% of neurons.