College Anatomy & Physiology: Chapter 11 – The Nervous System Part 1
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What does the CNS consist of?
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-Brain -Spinal cord
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What does the PNS consist of?
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-Nerves that connect the CNS to the rest of the body -Afferent sensory nerves -Efferent motor nerves
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What are the efferent parts of the PNS?
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-Autonomic nervous system (ANS) -Somatic Nervous System
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What are the 2 parts of the ANS?
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-Sympathetic nervous system -Parasympathetic nervous system
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What do the sympathetic and parasympathetic nervous system do?
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Maintain unconscious homeostasis
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What are the 2 types of nerve cells?
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-Neurons -Neuroglial cells
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What are neurons?
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-Basic functional unit of the nervous system -Excitable -React to change -Transmit messages
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What are neuroglial cells?
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-Accessory cells -Have a varity of support functions -Have no impulse transmission
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What are the cells of the CNS?
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-Neurons -Neuroglial cells: -Astrocytes -Oligodendrocytes -Microglia -Ependymal cells
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What is an astrocyte?
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-Star shaped CNS cell -Supports the neuron -Exchanges with blood capillaries for the neuron -Helps form the blood brain barrier -Used for synapse formation
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What is an oligodendrocyte?
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CNS cell that makes the myelin sheath in the CNS only
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What are microglia?
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-Phagocyte of the CNS -Assists injured neurons
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What are ependymal cells?
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-Cells that line the ventricles of the brain -Help circulate cerebrospinal fliud
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What are the cells of the PNS?
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-Neuron -Neuroglial cells: -Satellite cells -Schwann cells
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What are Schwann cells?
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-Cells that make the myelin sheath for the PNS only -Cells that are used in the regeneration of axons
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What are the anatomical types of neurons?
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-Multipolar -Bipolar -Unipolar
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What are multipolar cells?
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-Neurons that have many cytoplasmic extensions from the cell body (3 or more) -Most common kind of neuron (99%) -Major type of neuron in the CNS -They're used for motor or association messages
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What are bipolar cells?
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-Neurons that have 2 extensions from the cell body -They're used for special sensory messages for the eyes/olfactory
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What are unipolar cells?
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-Neurons that have 1 extension from the cell body -They're used for sensory messages (ganglia)
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What are the functional types of neurons?
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-Sensory -Association -Motor
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What are sensory neurons?
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-Their sensory receptors send messages through the PNS to the CNS via afferent nerves -Mostly unipolar
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What are visceral afferent neurons?
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Sensory neurons from organs
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What are association neurons?
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-Via interneurons -Located in the CNS -Transmit messages from 1 part of the CNS to another part of the CNS -Mostly multipolar
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What are motor neurons?
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-Efferent nerves -Send messages from the CNS to the PNS -Carry messages to the effectors (muscles and glands) -Contain somatic nerves -Contain autonomic nerves
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What are somatic nerves?
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Nerves that send messages from the nervous system to skeletal muscles
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What are autonomic nerves?
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Nerves that send messages from the nervous system to smooth muscles, cardiac muscles, and glands
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What are the characteristics of neurons?
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-Amitotic -Have extreme longevity -Have a high metabolic
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What are some characteristics of neurons in the PNS and CNS?
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-Have a cell body with neuroplasm and organelles -Have no centrioles -Golgi are well developed -Have NISSL BODIES instead of the endoplasmic reticulum -Their nucleus don't reproduce after maturity -Have pigment inclusions -Have 2 cytoplasmic extensions
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What are the pigment inclusions of the neuron?
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-They're held in the vacuole sac -The lipofuchsin pigment is a sign of aging
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What are the 2 cytoplasmic extensions of the neuron?
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-Dendrite -Axon
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What are clusters of cell bodies in the CNS called?
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Nuclei
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What are clusters of cell bodies in the PNS called?
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Ganglia
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What are bundles of cell processes in the CNS called?
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Tracts
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What are bundles of cell processes in the PNS called?
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Nerves
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What some characteristics of a dendrite?
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-Short and highly branched -Have an enormous surface area for receiving signals from other neurons -Their receptor for messages are graded potential and are conducted into the cell body
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What are some characteristics of an axon?
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-Long and singular -Each cell has 1 axon -Arise from axon hillock near the cell body -Generate and conduct messages away from the cell body -Has fine branching at its end -Have a pre-synpatic terminal with synaptic knobs containing neurotransmitter that can diffuse into the ECF when released -Has all the organelles of a cell body, dendrites, except Nissl bodies, and golgi. -Deteriorates if cut -Uses microtubules to aid in movement of molecules in long axon in either direction
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What is the pre-synaptic terminal?
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-Contain vesicles with neurotransmitter -Releases neurotransmitter to diffuse across synapse to the next dendrite on the 2nd neuron (synaptic transmission)
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What is a myelin sheath?
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White lipid-protein membrane of a Schwann cell wrapped around an axon
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What is the neurilemmal sheath?
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A sheath external of the myelin sheath
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What does the neurilemmal sheath do?
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-Increase impulse conduction -Allow regeneration
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What does myelin do?
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Increase the speed of transmission
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What is a node of ranvier?
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A naked spot on an axon
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What is saltatory conduction?
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Where the transmission can jump from node to node
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What is white matter?
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Regions of the brain and spinal cord with dense myelination
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What is gray matter?
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Cell bodies and unmyelinated fibers
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What happens when an axon is severed in the PNS?
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-Everything except the myelin sheath distal to the cut is decomposed -The proximal axon sprouts to the cytoplasm and seeks the tube of the myelin sheath for a path to the muscle -If the sprout enters the sheath, then the axon can re-grow -Then, the myelin sheath shows a path to the growing axon until it finds a muscle or gland
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What happens during regeneration in the CNS?
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-There's no neurilemmal sheaths in the CNS -There's no axon regeneration -Adult neurons do not divide *If there's a cut through a cell body in either the PNS or CNS, it results in cell death -There's limited growth with fetal tissue implants
