The somatosensory cortex is the area of the brain that translates and regulates changes on the skin’s surface.
The somatosensory cortex is a part of the sensory nervous system which helps with the localization of the sensations, as well as the perception of pressure on our skin and body – it’s the part of the brain responsible for the fact that we’re able to distinguish between a gentle touch and a hard blow, for instance.
Anatomy and Location of the Somatosensory Cortex
The somatosensory cortex is a complex system responsible for perceiving the sensations of touch, pressure, vibration, limb position, heat, and pain. It receives the sensory information from the skin, the musculoskeletal system, the large organs in the abdominal cavity, as well as the taste buds of the tongue.
From an anatomical point of view, the somatosensory cortex consists of sensory neurons and neural pathways.
Sensory neurons
The sensory neurons detect and carry the external sensory stimuli from the sensory organs to the spinal cord and the brain, i.e. the central nervous system.
After receiving the information at their dendrites, they transform the signals of touch, pain, sense of heat, smell, sight, and auditory signals into an electrical impulse that travels to the corresponding areas of the brain that can process, regulate, and control them.
Neural pathways
They help the sensory signals to be sent from one area of the central nervous system to another. The shorter neural pathways are located in the gray matter of the brain, whereas the longer ones are found in the white matter of the brain.
What Are the Elements of the Somatosensory Cortex?
The somatosensory cortex is further divided into two parts:
- Primary somatosensory cortex (S1) – occupying the postcentral gyrus on the side, and paracentral gyrus on the back of the surface of the cerebral cortex.
- Secondary somatosensory cortex (S2) – occupying the upper area of the lateral sulcus.
These constitutional areas of the somatosensory cortex are further made up of primary, secondary, and tertiary neurons.
First-order neurons
Neurons that carry the sensory impulses from the sensory receptors to the central nervous system.
Second-order neurons
Neurons that transfer the sensory impulses further, from the central nervous system to the thalamus.
Third-order neurons
Neurons that conduct the sensory impulses from the thalamus to the cerebral cortex.
In Which Brain Areas Does Somatosensory Cortex Perform Its Functions?
The somatosensory cortex performs its functions within the following areas of the body: periphery, spinal cord, and the brain. This allows the somatosensory system of the cortex to conduct the sensory information of touch, temperature, position, and balance.
Periphery
In this area of the brain, the thermoreceptors (sensory receptors of temperature) and mechanoreceptors (sensory receptors of mechanical pressure) receive and translate the stimuli from the environment through the sensory organs.
Spinal cord
The sensory information received in the periphery is further transmitted to the other parts of the brain through the spinal cord.
Brain
The somatosensory cortex of the brain contains the Brodmann areas 3a, 3b, 1, and 2 (or S1). These areas are located in the postcentral gyrus on the surface of the brain and are highly responsive only to somatosensory stimuli.
Where Is the Primary Somatosensory Cortex Located and What Is Its Function?
Postcentral Gyrus
The postcentral gyrus and precentral gyrus are the main sensory receptive areas for the sense of touch, i.e. they both constitute the primary somatosensory cortex (S1).
The neurons of the postcentral gyrus (situated in the lateral parietal lobe of the human brain) coordinate and integrate information gathered from different parts of the human body.
The nerve cells from the left side of the body transmit their information to the nerve cells of the right side of the cerebral cortex, and vice versa, thus creating a map on the brain.
There are three different types of neural cells that create the postcentral gyrus. They are labeled as Brodmann areas 1, 2, and 3, and function in correlation with each other. Namely, while the Brodmann areas 3 and 1 help us recognize the texture of objects, Brodmann areas 3 and 2 work together in order to create our perception of the size and shape of the items we touch.
The information gathered by the cells of the Brodmann areas is later sent to the secondary somatosensory cortex in order to process these signals of touch further.
Precentral Gyrus
On the other hand, the precentral gyrus (situated at the back of the frontal lobe of the brain) is the location responsible for the regulation, control, and initiation of voluntary skeletal muscle movement. After receiving the signal from the corresponding sensory organ, the precentral gyrus commands and enables the movements of the skeletal muscles.
Hence, the precentral gyrus creates the motor area of the cortex, where the movements of the body are planned, created, and regulated.
Where Is the Secondary Somatosensory Cortex and What Is Its Function?
The secondary somatosensory cortex (S2) is located above the lateral fissure of the brain, on the parietal lobe. It receives the sensory signals from the primary sensory cortex in order to transmit them further to corresponding parts of the body.
This area of the cortex memorizes the differences between the shapes and textures of the objects detected by our touch, as well as the strength of the touch. It further uses that information in order to help the brain formulate an action or a perception.
Similar to the primary somatosensory cortex, the secondary somatosensory cortex also contains Brodmann areas – BA 40 and 43, that is.
Brodmann area 40 is located in the lower part of the parietal lobe of the human brain. This area is considered to be the center of the brain responsible for the processes of reading, understanding of meaning, as well as comprehension and articulation of sounds and their graphical representations.
Brodmann area 43 is located in the back region of the cerebral cortex. This brain area responds to the stimuli of the eardrums, which can be transmitted by eating and drinking, too. Namely, these two actions change the pressure on the middle ear and the eardrum. This is the main reason why this part of the brain is labeled as a primary gustatory area.
The secondary somatosensory cortex is also divided into several areas which create a map of the surface of the body:
- Parietal ventral (PV) area – located at the entrance of the lateral sulcus
- Secondary somatosensory area – located behind the parietal ventral area
- Ventral somatosensory (VS) area – located deeper in the lateral sulcus, positioned next to the parietal ventral area and the secondary somatosensory area on the side of its outer edge
The parietal ventral area and the secondary somatosensory area contain the neural brain maps of the face, hands, and feet. The neurons which construct this complex mapping network receive sensory information through their receptors from these surfaces of the body in order to create a response.
How Do We Feel Touch Or Pain?
Our sense of touch is controlled by a vast network of nerve endings and receptors of touch located in the skin, i.e. the somatosensory system of the cortex.
Be it hot, cold, tickle, bruising, pain, caress, prickle, or vibration – these sensory receptors transmit their sensory signals to the particular parts of the brain, enriching it with a wealth of information about those external sensations.
The sensory receptors transfer their signals via the spinal cord and lower brain to the somatosensory cortex, or ‘touch center’.
What Are Sensory Receptors?
The specialized neurons and nerve endings that respond to mechanical, temperature, or chemical stimuli received from the environment around us through our sensory organs (skin, eyes, ears, nose, and tongue) are called sensory receptors.
There are five main types of sensory receptors located in the skin:
- Mechanoreceptors – receptors that inform our brain about pressure, vibrations, and texture. The most sensitive mechanoreceptors are located in top layers of the hairless areas of our skin, i.e. palms, lips, tongue, fingertips, eyelids, soles of feet, and the face.
- Thermoreceptors – receptors that inform our brain about temperature as a signal received through our skin. They are able to detect changes of temperature on a vast scale, and are located in the dermis of the skin. The basic division of the thermoreceptors recognizes receptors for cold and hot.
- Pain receptors – (Lat. nociceptor – hurt) – receptors that inform our brain about the possible ‘threat’ received via the skin. These receptors which are of vital importance for the survival of humans are located in the skin, muscles, bones, blood vessels, and some organs of the human body.
When the ‘threat’ signal is received through the skin receptors of pain, it’s translated in the brain as a danger so that the brain can activate its protective systems.
The nociceptors (or the pain receptors) can detect pain caused by mechanical, thermal, or chemical stimuli, such as a sharp knife, hot liquids, or a toxic ingredient.
- Proprioceptors – receptors that inform our brain about the position and movement of our ankles, feet, knees, hips, and neck. They are located in the inner ear, as well as in the tendons, muscles, and joints of our body.
- Photoreceptors/electromagnetic receptors – receptors located in the retina of both of our eyes.
There are two types of photoreceptors: rods and cones. All photoreceptors consist of 4 parts:
- an outer segment
- an inner segment
- a cell body
- a synaptic ending
By converting light, i.e. visible electromagnetic radiation, they inform our brain about the color and brightness of the objects around us.
To Sum Up
The somatosensory cortex is a part of the brain responsible for the recognition, i.e. reception and regulation of the sensory information from all parts of the body.
The postcentral gyrus and precentral gyrus are the main constitutional parts of the main receptive sensory area of touch, pressure, vibration, heat, and pain, as well as limb position. With the help of neurons and the sensory receptors, our brain receives valuable information about our environment, upon which it can base its commands to various parts of our body, as well as regulate and control its actions, reactions, and sensations.
In some ways, the human brain resembles a computer. Performing some of the most complex processes of the human body, the somatosensory cortex is the area which receives the somatosensory information and is responsible for translating the outer sensory information to our brain.
Fun Facts
Did you know?
- Damage to the postcentral gyrus can lead to the loss of our ability to recognize objects by touch.
- The secondary somatosensory area relates to our perception of pain. Its fast transfer of information from the sensory organs to the corresponding parts of the brain can save our life by activating the safety systems of the body.
- The receptors of touch react extremely fast to change. Namely, we can tell whether we’re touching an object or not in a split second.
- The mechanoreceptors in the skin of the fingers inform the brain about the roughness of your skin, while the brain translates this information as a need to reach for a hand lotion.
- The thermoreceptors transmit information about the temperature difference when we go out, which our brain translates as a need for us to wear lighter or warmer clothes.
- The exchange of sensory stimuli and information in the somatosensory cortex of our brain aids our appreciation of hugs and kisses.
- The mechanoreceptors of the skin inform the brain if we stretch our leg a bit more than comfortable, by creating an alert in the form of sharp pain.
- Thermoreceptors are most numerous in our face and ears. This is why our cheeks blush when we feel hot, or we feel cold the most on our nose and ears.
- Merkel’s disks and Meissner’s corpuscles are the mechanoreceptors in the skin that react to a light touch.
- The interactive processes between the sensory organs of sight and the photoreceptors help our brain translate light into color.