1 : the action of crossing (as of nerve fibers) especially in the form of an X. 2 : a crossed tract of nerve fibers passing between centers on opposite sides of the nervous system.

What is the purpose of decussation?

Objective: In the chordate and vertebrate central nervous system, sensory and motor nerve tracts cross from one side to the other as they connect the brain with sensory receptors and motor neurons. These "decussations," crossings in the form of an X, relate each side of the brain to the opposite side of the body.

What is a decussation in anatomy?

A decussation is an intersection of pathways in the form of an X. Most nerve pathways between our brain and spinal cord cross over at some point. This accounts for why each side of our brain (two cerebral hemispheres) has control over the opposite side of our body.

Where does decussation happen?

The pyramidal decussation marks the border between the spinal cord and the medulla oblongata.

What is decussation and where does it occur in the brain?

This crossover, or decussation, occurs just before the junction between the medulla oblongata and the spinal cord. ... The sensory impulses from your arm or leg cannot reach your spinal cord, and the motor impulses from your brain cannot reach your muscles.

What does decussation mean?

41 related questions found

Why do brain Fibres cross over?

Most sensory and motor pathways in the central nervous system cross the midline. Comparing between different neuronal pathways in different species suggest that, fibers crossing is most probably a response to the development of separated parts for the body during the process of evolution.

What is the level of decussation?

Decussation of the fibers (i.e., the crossing of fibers to the opposite side of the body) occurs at the level of the lower medulla, where 85 to 90% of the fibers cross to form the lateral corticospinal tract (LCST).

How many reticular formations are there in the brain?

Function. The reticular formation consists of more than 100 small neural networks, with varied functions including the following: Somatic motor control – Some motor neurons send their axons to the reticular formation nuclei, giving rise to the reticulospinal tracts of the spinal cord.

What does it mean when a nerve tract Decussates?

1 : the action of crossing (as of nerve fibers) especially in the form of an X. 2 : a crossed tract of nerve fibers passing between centers on opposite sides of the nervous system.

What does white matter do in the brain?

In the most general sense, the gray matter of the brain facilitates information processing, and the white matter facilitates information transfer; both are critical for efficient operation of the neural networks responsible for a specific mental domain.

How does decussation relate to the pyramids of the medulla?

Decussation. The two pyramids contain the motor fibers that pass from the brain to the medulla oblongata and spinal cord. These are the corticobulbar and corticospinal fibers that make up the pyramidal tracts. ... The pyramidal decussation marks the border between the spinal cord and the medulla oblongata.

What is decussation of the pyramids?

Medical Definition of pyramidal decussation

: the crossing of the fibers of the corticospinal tracts from one side of the central nervous system to the other near the junction of the medulla and the spinal cord. — called also decussation of the pyramids.

How many pairs of spinal nerves are there?

There are 31 pairs of spinal nerves and roots. Eight pairs of cervical nerves exit the cervical cord at each vertebral level.

What crosses in the anterior white commissure?

The anterior or ventral white commissure is a collection of nerve fibers that cross the midline of the spinal cord and transmit information from or to the contralateral side of the brain. It is present throughout the length of the spinal cord and lies behind the anterior median fissure.

Do any of the cranial nerves decussate?

The trochlear nerve (cranial nerve IV) is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye. ... Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target.

Is there Decussation of cranial nerves?

Their axons start in either the left or right cerebral hemisphere, and decussate, or simply put, cross the midline, typically at the same level of their cranial nerve nuclei prior to synapsing, By decussating, these nerves can then go on to eventually innervate some structure on the contralateral side of the head.

Where in the brain do most motor tracts decussate?

Peripheral motor nerves carry the motor impulses from the spinal cord to the voluntary muscles. The large majority (90%) of motor neurons cross (decussate) to the contralateral side of the brain at the level of the brainstem.

Is the red nucleus part of the reticular formation?

RETICULOSPINAL TRACTS

The reticular formation is a phylogenetically primitive network of small neurons extending throughout the brainstem and into the spinal cord. It has a diverse input; its descending connexions are mostly from the cerebral cortex, cerebellum and red nuclei.

Does reticular formation control arousal?

The reticular formation may be best known for its role in promoting arousal and consciousness. ... These pathways are predominantly associated with the neurotransmitters acetylcholine and norepinephrine, both of which are thought to play important roles in regulating arousal and wakefulness.

What is the forebrain?

By far the largest region of your brain is the forebrain (derived from the developmental prosencephalon), which contains the entire cerebrum and several structures directly nestled within it - the thalamus, hypothalamus, the pineal gland and the limbic system.

What arouses the cerebrum?

Sensory axons, found in visual, auditory, and sensory impulses, activate RAS neurons in the brain stem. These neurons then relay information to the thalamus and cerebrum. Continuous stimulation of the RAS neurons causes the cerebrum to stay in an aroused state; this gives the feeling of alertness.

What are pyramidal symptoms?

Pyramidal signs include spasticity and weakness of both upper and lower extremities with a greater involvement of the lower extremities (Table II).

Where are upper motor neurons located?

The upper motor neurons originate in the cerebral cortex and travel down to the brain stem or spinal cord, while the lower motor neurons begin in the spinal cord and go on to innervate muscles and glands throughout the body.