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You are watching: Important synapse site for afferent fibers traveling to the sensory cortex

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The nervous mechanism subdivides into the main nervous system and also the peripheral concerned system. The central nervous device is the brain and spinal cord, if the peripheral concerned system consists of everything else. The main nervous system"s responsibilities incorporate receiving, processing, and responding to sensory information.  

The mind is an body organ of nervous organization that is responsible because that responses, sensation, movement, emotions, communication, thought processing, and also memory. Protection for the human brain comes native the skull, meninges, and cerebrospinal fluids. The nervous organization is very delicate and can suffer damage by the smallest amount that force. In addition, it has actually a blood-brain barrier staying clear of the brain from any harmful problem that might be floating in the blood.

The spinal cord is a vital aspect the the CNS uncovered within the vertebral column. The purpose of the spinal cord is to send motor commands from the mind to the peripheral body and to relay sensory information from the sensory organs to the brain. Spinal cord security is through bone, meninges, and cerebrospinal fluids.


Structure and also Function

The mind is damaged up right into two hemispheres, the left, and the right. While they room in consistent communication, the left and also right hemisphere are responsible for various behaviors, recognized as brain lateralization. The left hemisphere is much more dominant v language, logic, and math abilities. The best hemisphere is an ext creative, being leading in artistic and also musical situations, and also intuition. 

Cerebral cortex: The cerebral cortex is the outermost layer that surrounds the brain. That is written of gray matter and also filled with billions that neurons offered to command high-level executive, management functions. The cortex divides into 4 lobes; frontal, parietal, occipital, and also temporal by different sulci.<1> The frontal lobe, situated anteriorly to the central sulcus, is responsible because that voluntary motor function, problem-solving, attention, memory, and also language. Situated in the frontal lobe space the motor cortex and also the Broca area. The engine cortex allows for the precise voluntary motions of our skeletal muscles, if the Broca area controls motor attributes responsible for producing language. The parietal lobe is separated indigenous the occipital lobe through the parieto-occipital sulcus and is behind the main sulcus. The is responsible for handling sensory information and contains the somatosensory cortex. Neurons in the parietal lobe receive info from sensory and also proprioceptors throughout the body, procedure the can, and type an understanding about what is gift touched based on previous knowledge. The occipital lobe, recognized as the visual handling center, consists of the intuitive cortex. Comparable to the parietal lobe, the occipital lobe receives information from the retina and also then provides past visual experiences to interpret and also recognize the stimuli. Lastly, the temporal lobe processes auditory stimuli v the hear cortex. Mechanoreceptors situated in the hair cells lining the cochlea space activated by sound energy, which consequently sends impulses come the listening cortex. The advertise is processed and stored based on previous experiences. The Wernicke area is in the temporal lobe and functions in speech comprehension. 

Basal nuclei: The basal nuclei, additionally known as basal ganglia, is located deep within the cerebral white matter and is written of the caudate nucleus, putamen, and globus pallidus. This structures form the pallidum and also striatum. The basal ganglia space responsible for muscle movements and coordination.<2>

Thalamus: The thalamus is the relay center of the brain. It receives afferent impulses native sensory receptors located throughout the body and also processes the details for circulation to the proper cortical area. It is additionally responsible because that regulating consciousness and sleep.

Hypothalamus: While the hypothalamus is among the smallest components of the brain, that is an essential to keeping homeostasis. The hypothalamus associate the central nervous device to the endocrine system. That is responsible because that heart rate, blood pressure, appetite, thirst, temperature, and the release of various hormones. The hypothalamus additionally communicates through the pituitary gland to relax or inhibit antidiuretic hormone, corticotropin-releasing hormone, gonadotropin-releasing hormone, expansion hormone-releasing hormone, prolactin inhibiting hormone, thyroid releasing hormone, and also oxytocin.<3>

Pons: found in the brainstem, the pons connects the medulla oblongata and also the thalamus. That is created of tracts responsible for relaying impulses from the engine cortex to the cerebellum, medulla, and thalamus.

Medulla oblongata: The medulla oblongata is in ~ the bottom that the mind stem, where the spinal cord meets the foramen magnum that the skull. The is responsible for autonomic functions, several of which are an essential for survival. The medulla oblongata monitors the body respiratory device using chemoreceptors. This receptors are able to detect alters in blood chemistry. For example, if the blood is also acidic, the medulla oblongata will increase the respiratory tract rate enabling for much more oxygen to reach the blood.<4> that is likewise a cardiovascular and vasomotor center. The medulla oblongata can regulate the body"s blood pressure, pulse, and also cardiac contractions based upon the body’s needs. Lastly, it controls reflexes choose vomiting, swallowing, coughing, and also sneezing.

Cerebellum: The cerebellum, also known as the tiny brain, is responsible because that smooth, coordinated voluntary movements. That subdivides right into three lobes: the anterior, posterior, and also flocculonodular lobes. The cerebellum has a cerebellar circuit, making use of Purkinje cells and also cerebellar peduncles to connect to other parts that the brain. The exceptional cerebellar peduncle is composed of white matter that connects the cerebellum to the midbrain and enables for coordination in the arms and legs. The inferior cerebellar peduncle connect the medulla and also cerebellum using proprioceptors to maintain balance and also posture. Lastly, the middle cerebellar peduncle is supplied as a one-way communication method from the pons come the cerebellum. The is largely composed that afferent fibers that alert the cerebellum about voluntary motor actions. The cerebellum is in consistent communication through the cerebral cortex, taking higher-level instructions around the brain’s intentions, processing them v the cerebellar cortex, then sending out messages come the cerebral engine cortex to do voluntary muscle contractions. These contractions room calculated to identify the force, direction, and also momentum crucial to ensure every contraction is smooth and coordinated.

Limbic System: The limbic mechanism is written of the piriform cortex, hippocampus, septal nuclei, amygdala, cell nucleus accumbens, hypothalamus, and anterior nuclei the the thalamus.<5> The fornix and also fiber tracts affix the limbic system parts enabling them to manage emotion, memory, and motivation. The piriform cortex is part of the olfactory system and is in the cortical area of the limbic system. The hypothalamus receives many of the limbic output, which explains psychosomatic illnesses, where emotional stressors reason somatic symptoms. For example, a patient that is at this time having gaue won struggles can present come his primary care physician through hypertension and tachycardia. The septal nuclei, amygdala, and nucleus accumbens are found in the subcortical areas and also are responsible because that pleasure, emotional processing, and addiction, respectively.

Reticular formation: Reticular formation is considerable network that pathways include neurons that begins in the brainstem and also travels from the top of the midbrain to the medulla oblongata. These pathways have projecting reticular neurons that affect the cerebral cortex, cerebellum, thalamus, hypothalamus, and also spinal cord. The reticular formation controls the body"s level the consciousness with the reticular activation system, additionally known together RAS. Sensory axons, discovered in visual, auditory, and sensory impulses, activate RAS neurons in the mind stem. This neurons then relay details to the thalamus and also cerebrum. Consistent stimulation the the RAS neurons causes the cerebrum to stay in an aroused state; this offers the emotion of alertness. However, RAS can filter out repetitive, weak stimuli; this avoids the brain from responding come unimportant information, as well as being sensory overloaded.

Spinal cord: The spinal cord ideal extends native the foramen magnum the the skull to the an initial or 2nd lumbar vertebrae. It creates a two-way pathway between the mind and the body and also divides into 4 regions -  cervical, thoracic, lumbar, and also sacral. These regions are then broken down right into 31 segments with 31 bag of spinal nerves. There are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and also 1 coccygeal nerve. Each nerve exit the vertebral pillar passing through the intervertebral foramina and to that is designated ar in the body.

Due to cervical and also lumbar enlargements, the spinal cord differs in width throughout the structure. The cervical enlargement occurs at C3 to T1, and also the lumbar enlargement is at L1 to S2. The white matter is present on the exterior of the spinal cord, with gray matter situated in its core and cerebrospinal fluid in the main canal. The gray commissure, the dorsal, lateral, and also ventral horns space all written of gray matter. The gray commissure surrounds the central canal. The dorsal horns room made of interneurons, when the ventral horns space somatic motor neurons. Afferent neurons in the dorsal roots carry impulses indigenous the body’s sensory receptor to the spinal cord, where the information begins to it is in processed. The ventral horns save on computer efferent motor neurons, which manage the body"s periphery. The axons of motor neurons are found in the body"s skeletal and smooth muscle to regulate both involuntary and also voluntary reflexes.   

The spinal cord end in a cone-shaped structure referred to as conus medullaris and also is supported to the end of the coccyx through the filum terminale. Ligaments are uncovered throughout the spinal column, securing the spinal cord from peak to bottom.

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Ascending pathway come the brain: Sensory information travels from the body to the spinal cord prior to reaching the brain. This info ascends upwards using first, second, and also third-order neurons. First-order neurons receive impulses indigenous skin and also proprioceptors and also send them come the spinal cord. They climate synapse v second-order neurons. Second-order neurons live in the dorsal horn and also send impulses come the thalamus and also cerebellum. Lastly, third-order neurons choose up this impulses in the thalamus and relay it to the somatosensory section of the cerebrum. Somatosensory sensations are pressure, pain, temperature, and also the body"s senses. 

Descending pathway: Descending tracts send motor signals indigenous the brain to reduced motor neurons. This efferents neurons then produce muscle movement.<6>