The neural pathways are an important part of the relay of sensory information to the brain. During the process of learning, the chemical or electrical impulse of the sensory stimuli travels along a new brain route. This new path is created by connections between a bundle of axons that project their dendrites to one or more neurons, thus creating the neural pathways of the brain.
The nerve axons in the central nervous system are organized in bundles, called nerve tracts. These neural pathways are located in the brain and the spinal cord. The neuronal cells comprising the nerve tract project their long dendrites that branch out to the neighboring neurons in order to make a synapse.
This enables the electrical or chemical signals to be transmitted to a dedicated area of the brain in order to be further encoded as a feeling, sensation, emotion, etc.
Comprised of neurons that are interconnected by branches of dendrites, the neural pathways are created in the brain by our habits and behaviors. The more we repeat an action or anything we have learned, the more the neural circuits that relay the information are strengthened.
What Is the Structure of the Neuron Pathways and How Do They Function?
The neural pathways can take different forms, so they are divided into
- Converging neural pathways
- Diverging neural pathways
- Reverberating neural pathways
Converging Neural Pathways
These types of neural pathways link up several neurons into one cell of the central nervous system. They increase the sensitivity of the excitatory and inhibitory signals that carry the information from the sensory stimuli.
The converging neural pathway is a typical formation for the neurons of the rods that are located in the retina of an eye.
Diverging Neural Pathways
In this type of pathways, the impulses traveling from one neuron branch out towards several other neuron cells.
As a result, the triggering impulse can stimulate more that one neuron at a time, thus affecting several areas of the brain that control different parts of the body.
Reverberating Neural Pathways
Reverberating neural pathways are neural circuits in which the initially activated nerve impulse later becomes reactivated several times more. This allows the impulse to travel again through the neural pathway.
What Are the Major Types of Neural Pathways in the Brain?
The human brain has numerous neural pathways, each performing the highly significant function of relaying the chemical and electrical impulses that carry the information from the sensory stimuli to a particular brain area.
However, there are several major neural pathways that can be distinguished among the others:
- Spinal Cord Tracts
- Corpus Callosum
- Mesolimbic (Reward) Pathway
- Pain Pathway
- Visual Pathway
- Dorsal Column (Medial Lemniscus Pathway)
- Pyramidal Tracts (corticospinal and corticobulbar tracts)
- Cerebral Peduncles
- Arcuate fasciculus
- Retinohypothalamic tract
Spinal Cord Tracts
The list of spinal cord tracts consists of the following neural circuits:
- Gracile fasciculus – It relays vibration, conscious proprioception, as well as fine touch sensations from the lower body.
- Dorsolateral tract – It controls the muscles of the limbs, shoulders, fingers, and hands.
- Lateral corticospinal tract – It controls the voluntary movement of the extremities on the opposite side of the body.
- Rubrospinal tract – It regulates the movement of large muscles.
- Medullary reticulospinal tract – It controls the muscles of the body, as well as the arms and legs.
- Septomarginal fasciculus – It conveys motor impulses from the nerves.
- Anterior proper fasciculus – It connects the back parts of the temporal, occipital, and frontal lobes of the cerebral cortex.
- Vestibulospinal tract – It supports the coordination between the eyes and the head, balance, upright posture of the body, spatial orientation, and motion.
- Cuneate fasciculus – It’s involved in the transmission of vibration, as well as conscious proprioception.
- Dorsal spinocerebellar tract – It’s responsible for the coordination of movements.
- Anterior spinocerebellar tract – It relays the signals received via the sensory organs of touch, i.e. through the skin.
- Spino-olivary tract – It controls the movement of the body, arms, and legs.
- Spinothalamic tract – This is the most important sensory pathway since it’s responsible for the relay of pain, temperature, and touch.
- Spinoreticular tract – It’s involved in the transmission of the automatic responses of pain.
- Medial longitudinal fasciculus – It coordinates eye movement with the movement of the head and the neck.
- Anterior corticospinal tract – It controls the axial muscles (the muscles of the trunk of the body).
- Anterior Ponto-reticulospinal tract – This tract controls locomotion and posture.
- Tectospinal tract – This is another tract that coordinates the movements of the eyes with the movement of the head.
Corpus Callosum
This neural pathway provides communication between the two brain hemispheres. Namely, different parts of this pathway link similar areas of each hemisphere in order to support the harmony of their functions.
The corpus callosum is mainly involved in the cognitive processes of the brain. It consolidates the motor, sensory, and cognitive functions from the left hemisphere with the right hemisphere of the brain.
Mesolimbic (Reward) Pathway
This neural circuit is responsible for our feelings of pleasure, triggered by a visual image, scent, or sound of something we enjoy. When activated, the brain registers the information as something worth repeating in order to experience the pleasure more often.
Pain Pathway
There are two pain pathways in the brain – the thalamus pathway and the spinothalamic pathway.
This pathway comprises of 3 orders of neurons that are responsible for the relay of the sensory signal of pain:
- First-order neurons
- Second-order neurons
- Third-order neurons
The pain receptors found in the pain pathways are called nociceptors. Nociceptors are first-order neurons in the pain pathway, located at the free nerve ending of the primary neuron. They can be found in the skin, muscle, joints, bones, and organs of the body.
Visual Pathway
We see the world that surrounds us in shapes, colors, textures, and sizes. But, this is actually the image our brain creates in the visual cortex from the light received through the retina of the eyes.
The visual pathway follows the route of the electrical signals created in the retina of the eye to the brain. The retina is the thin tissue at the back part of the eye, consisting of light-sensitive (or photo-sensitive) cells. According to their shape, these light-sensitive cells are labeled as rods and cones.
Rods and cones transform the visual signals into electrical impulses. They are further transmitted via neurons in order to be translated and processed in the visual cortex of the brain.
Dorsal Column (Medial Lemniscus Pathway)
The medial lemniscus pathway, or the dorsal column, is involved in the transmission of the sensory signals informing on a soft touch, proprioception, as well as vibration.
It carries the signals up to the medulla of the brain, continuing to the brain stem, and the thalamus.
Pyramidal Tracts
The pyramidal tracts stem from the cerebral cortex. These tracts start in the motor cortex, pass through the medullary pyramids, and synapse onto the lower motor neurons in the brainstem.
Since the motor fibers stem from them, the pyramidal tracts are also involved in the voluntary control of both face and body muscles.
This tract comprises of two major neural pathways:
- Corticospinal tract – It controls the primary motor activity of the body from the neck to the feet.
- Corticobulbar tract – This neural tract is responsible for the control of the head, neck, and face muscles.
The axons that stem from the tract create synapses directly with the lower motor neurons on the opposite side of the cranial nerves V, VII, XI, and XII.
Cerebral Peduncles
The cerebral peduncles are nerve tracts through which the cerebellum communicates with the other structures of the central nervous system. They relay the impulses from the brainstem and the cortex of the brain to the parts of the central nervous system.
The function of the cerebral peduncles is to refine our movements.
Arcuate fasciculus
The arcuate fasciculus is a bundle of neuron fibers that comprise a neural pathway responsible for the process of repetition. It also provides connections to the Broca’s Area and Wernicke’s area.
Broca’s Area
Broca’s area is the center for the regulation of motor speech and it also supports the movements which are required for the physical production of speech. Hence, it regulates the motor movement of the tongue, lips, larynx, and pharynx.
Wernicke’s area
Wernicke’s area is an area in the back parts of the cerebral cortex which is specialized in the control of language, as well as the comprehension of spoken words. The cognitive efforts we make during conversation are processed and translated in Wernicke’s area, which in turn gives us fluency in speech.
This area functions in relation to the right part of the brain (or the dominant part of the individual) and is responsible for the non-verbal processing of sounds. The gyri which constitute Wernicke’s area contribute to linking the words into meaningful and logical sentences.
Retinohypothalamic tract
This neural pathway plays a role in the circadian rhythms. It supports the regulation of various vitally important biological processes, such as the sleep-wake cycle, menstrual cycle in women, body temperature, blood pressure, thirst, hunger, important aspects of parenting and attachment behaviors, fatigue, etc.
The main neurotransmitter of the impulses relayed by the neurons in this neuron circuit is the glutamate.
Glutamate is a neurotransmitter found in both the brain and the spinal cord. This powerful neurotransmitter supports the transmission of signals between two neuron cells.
It also plays a vital function in the early development of the brain, the cognitive processes (especially the learning), perception, as well as memory.
What Happens if a Neural Pathway Is Dysfunctional?
The dysfunction of neural pathways is a very common medical condition. Neurological diseases and syndromes, such as multiple sclerosis, Parkinson’s disease, or cerebral palsy, often cause disruption of the neural pathways.
The impairments are usually the result of brain lesions, stroke, or injury to the spinal cord.
Fun Facts
Did you know?
- Around 100 billion neurons comprise the human brain, which equals to 100 trillion neural connections.
- The mono-synaptic reflex pathway is the simplest neural pathway in the brain.
- New neural pathways can be created by our behaviors and habits. Brain training is a classic example of the creation of new neural pathways in the human brain. This, in turn, increases our intelligence.
- It takes at least 21 days to make a good habit or break a bad one. On the other hand, it takes approximately 66-90 days to make a habit your permanent mode of behavior.
- The pain is one of the most vital somatic and emotional sensations for our survival.
- Depending on its origin, pain can be somatic, visceral, thalamic, neuropathic, psychosomatic, referred, or illusionary.
- When we flex our bicep in the mirror, our brain and brainstem send a motor signal through the spinal cord to the muscles in the body.
- Without proper functioning of the cerebral peduncle, we’d be clumsy.
- The image that is perceived by the retina is actually upside down, not the way we see it after the visual information is translated and processed in the visual cortex of the brain.
- There are more than 200 distinctive neurotransmitters identified in the human brain.