Paramedian pontine reticular formation
Encyclopedia
The paramedian pontine reticular formation, or PPRF, is part of the pontine reticular formation
, a brain
region without clearly defined borders in the center of the pons
. It is involved in the coordination of eye movements, particularly horizontal gaze and saccade
s.
and lateral to the medial longitudinal fasciculus
(MLF). It receives input from the superior colliculus
via the predorsal bundle and from the frontal eye fields
via frontopontine fibers
. The rostral PPRF probably coordinates vertical saccades; the caudal PPRF may be the generator of horizontal saccades. In particular, activity of the excitatory burst neuron
s (EBNs) in the PPRF generates the "pulse" movement that initiates a saccade. In the case of horizontal saccades the "pulse" information is conveyed via axon
al fibers to the abducens nucleus
, initiating lateral eye movements. The angular velocity
of the eye during horizontal saccade ranges from 100 to 700 degree
s per second. Larger saccades have faster pulses; the PPRF is involved in this determination.
s of the PPRF produce characteristic findings:
Reticular formation
The reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli...
, a brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
region without clearly defined borders in the center of the pons
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
. It is involved in the coordination of eye movements, particularly horizontal gaze and saccade
Saccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...
s.
Input, Output, and Function
The PPRF is located anteriorAnatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
and lateral to the medial longitudinal fasciculus
Medial longitudinal fasciculus
The medial longitudinal fasciculus is a pair of crossed fiber tracts , one on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem and are composed of both ascending and descending fibers that arise from a number of sources and terminate in different...
(MLF). It receives input from the superior colliculus
Superior colliculus
The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a...
via the predorsal bundle and from the frontal eye fields
Brodmann area 8
Brodmann area 8 is one of Brodmann's cytologically defined regions of the brain. It is involved in planning complex movements.-Human:Brodmann area 8, or BA8, is part of the frontal cortex in the human brain...
via frontopontine fibers
Frontopontine fibers
The frontopontine fibers are situated in the medial fifth of the base of the cerebral peduncles; they arise from the cells of the frontal lobe and end in the nuclei of the pons....
. The rostral PPRF probably coordinates vertical saccades; the caudal PPRF may be the generator of horizontal saccades. In particular, activity of the excitatory burst neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s (EBNs) in the PPRF generates the "pulse" movement that initiates a saccade. In the case of horizontal saccades the "pulse" information is conveyed via axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
al fibers to the abducens nucleus
Abducens nucleus
The abducens nucleus is the originating nucleus from which the abducens nerve emerges - a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the caudal portion of the pons, medial to the sulcus limitans....
, initiating lateral eye movements. The angular velocity
Angular velocity
In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...
of the eye during horizontal saccade ranges from 100 to 700 degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
s per second. Larger saccades have faster pulses; the PPRF is involved in this determination.
Lesions
Unilateral lesionLesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s of the PPRF produce characteristic findings:
- Loss of horizontal saccades directed towards the side of the lesion, no matter the current position of gaze
- Contralateral gaze deviation (acute lesions, such as early strokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
, only) - Gaze-evoked lateral nystagmus on looking away from the side of the lesion
- Bilateral lesions produce horizontal gaze palsyOphthalmoparesisOphthalmoparesis or ophthalmoplegia refers to paralysis of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic illnesses.-Classification:...
and slowing of vertical saccades
See also
- Internuclear ophthalmoplegiaInternuclear ophthalmoplegiaInternuclear ophthalmoplegia is a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction. When an attempt is made to gaze contralaterally , the affected eye adducts minimally, if at all. The contralateral eye abducts, however with nystagmus...
- Multiple sclerosisMultiple sclerosisMultiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
- One and a half syndromeOne and a half syndromeThe one and a half syndrome is a rare ophthalmoparetic syndrome characterized by "a conjugate horizontal gaze palsy in one direction and an internuclear ophthalmoplegia in the other". The most common manifestation of this unusual syndrome is limitation of horizontal eye movement to adduction of...
- OphthalmoparesisOphthalmoparesisOphthalmoparesis or ophthalmoplegia refers to paralysis of one or more extraocular muscles which are responsible for eye movements. It is a physical finding in certain neurologic illnesses.-Classification:...
- Reticular formationReticular formationThe reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli...
- StrokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
- Paramedian reticular nucleusParamedian reticular nucleusThe paramedian reticular nucleus sends its connections to the spinal cord in a mostly ipsilateral manner, although there is some decussation....
- OpsoclonusOpsoclonusOpsoclonus refers to uncontrolled eye movement. Opsoclonus consists of rapid, involuntary, multivectorial , unpredictable, conjugate fast eye movements without intersaccadic intervals. It is also referred to as saccadomania or reflexive saccade...
- SaccadeSaccadeA saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...