mossy fibers

(noun)

One of the major inputs to the cerebellum from sources such as the cerebral cortex.

Related Terms

Examples of mossy fibers in the following topics:

  • Functions of the Cerebellum in Integrating Movements

    • In the human cerebellum, information from 200 million mossy fiber inputs is expanded to 40 billion granule cells, whose parallel fiber outputs then converge onto 15 million Purkinje cells.
    • Different modules share input from mossy fibers and parallel fibers, but in other respects they appear to function independently.
    • The synapses between parallel fibers and Purkinje cells, and the synapses between mossy fibers and deep nuclear cells, are both susceptible to modification of their strength.
    • In a single cerebellar module, input from as many as a billion parallel fibers converge onto a group of less than 50 deep nuclear cells, and the influence of each parallel fiber on those nuclear cells is adjustable.
    • As the illustration on the right shows, Purkinje cell dendritic trees are flattened in a way that aligns with the microzone length, and parallel fibers cross the microzones at right angles.

  • Functions of the Cerebellum

    • Divergence and convergence: In the human cerebellum, information from 200 million mossy fiber inputs is expanded to 40 billion granule cells.
    • This neural divergence is followed by parallel fiber outputs that converge onto 15 million Purkinje cells.
    • Due to their longitudinal alignment, the approximately 1000 Purkinje cells belonging to a microzone may receive input via neural convergence from as many as 100 million parallel fibers.
    • Plasticity: The synapses between parallel fibers and Purkinje cells and between mossy fibers and deep nuclear cells are both susceptible to modification of their strength.
    • In a single cerebellar module, input from as many as a billion parallel fibers converge onto a group of less than 50 deep nuclear cells, and the influence of each parallel fiber on those nuclear cells is adjustable.

  • Modulation of Movement by the Cerebellum

    • It receives input from thousands of parallel fibers, each individually very weak.
    • However, each cerebellar Purkinje cell also gets input from one single climbing fiber, which is so strong that a single climbing fiber action potential will reliably cause a target Purkinje cell to fire a burst of action potentials.
    • The basic concept of the Marr-Albus theory is that the climbing fiber serves as a teaching signal, which induces a long-lasting change in the strength of synchronously activated parallel fiber inputs.
    • Plasticity: The synapses between parallel fibers and Purkinje cells, and the synapses between mossy fibers and deep nuclear cells, are both susceptible to modification of their strength.
    • The influence of each parallel fiber on nuclear cells is adjustable.

  • Dietary Fiber

    • Lignin, a major dietary insoluble fiber source, may alter the fate and metabolism of soluble fibers.
    • The term "fiber" is something of a misnomer since many types of so-called dietary fiber are not actually fibrous.
    • Dietary fiber is found in plants.
    • Fiber-rich plants can be eaten directly.
    • The plum's skin is a source of insoluble fiber while soluble fiber is in the pulp.

  • Characteristics of Connective Tissue

    • Connective tissue fibers provide support.
    • Three types of fibers are found in connective tissue:
    • Elastic fibers are long, thin fibers that form branching network in the extracellular matrix.
    • Reticular fibers are short, fine collagenous fibers that can branch extensively to form a delicate network.
    • Collagen fibers are the strongest and most abundant of all the connective tissue fibers.

  • Overview of Motor Integration

    • When a motor unit is activated, all of its fibers contract.
    • The number of muscle fibers within each unit can vary.
    • Motor units are generally recruited in order of smallest to largest (from fewest fibers to most fibers) as contraction increases.
    • These small motor units may contain only 10 fibers per motor unit.
    • These muscles may have as many as a thousand fibers in each motor unit.

  • Slow-Twitch and Fast-Twitch Muscle Fibers

    • Most muscles are made up of combinations of these fibers, although the relative number substantially varies.
    • Unlike slow-twitch fibers, fast twitch-fibers rely on anaerobic respiration (glycolysis alone) to produce two molecules of ATP per molecule of glucose.
    • As fast-twitch fibers generally do not require oxygenation, they contain fewer blood vessels and mitochondria than slow-twitch fibers and less myoglobin, resulting in a paler colour.
    • Muscles controlling eye movements contain high numbers of fast-twitch fibers (~85% fast-twitch).
    • Describe the different types of skeletal muscle fibers and their respective functions

  • Classification of Nerves

    • These classifications apply to both sensory and motor fibers.
    • The A group is further subdivided into four types (A-alpha, A-beta, A-delta, and A-gamma fibers) based on the information carried by the fibers and the tissues they innervate.
    • The primary role of B fibers is to transmit autonomic information.
    • C fiber axons are grouped together into what is known as Remak bundles.
    • A-delta and C fibers both contribute to the detection of diverse painful stimuli.

  • Parasympathetic (Craniosacral) Division

    • The motor root carries presynaptic parasympathetic nerve fibers (general visceral efferent fibers) that terminate in the ganglion by creating a synapse for the postsynaptic fibers traveling to target organs.
    • The sympathetic root carries postsynaptic sympathetic fibers (general visceral efferent fibers) that traverse the ganglion without creating a synapse.
    • The sensory root carries general sensory fibers (general somatic afferent fibers) that also do not create a synapse in the ganglion.
    • Some ganglia also carry special sensory fibers (special visceral afferent) for taste sensation.
    • Pre- and post-ganglionic fibers and targets are depicted.

  • Preganglionic Neurons

    • In the autonomic nervous system (ANS), nerve fibers that connect the central nervous system to ganglia are known as preganglionic fibers.
    • In the autonomic nervous system (ANS), fibers from the central nervous system to the ganglion are known as preganglionic fibers.
    • Sympathetic preganglionic fibers tend to be shorter than parasympathetic preganglionic fibers because sympathetic ganglia are often closer to the spinal cord while parasympathetic preganglionic fibers tend to project to and synapse with the postganglionic fiber close to the target organ.
    • Another major difference between the two ANS systems is divergence, or the number of postsynaptic fibers a single preganglionic fiber creates a synapse with.
    • Pre- and post-ganglionic fibers and targets are depicted.