Which quadrant involves stimulating the senses

Neurons in the posterior parietal cortex are responsive to somatosensory and visual stimuli, have large somatic receptive fields in which responsiveness is based on stimulus context, and are often more responsive to stimulus movement. The perception of a "whole" body is lost and the body parts affected may be considered to belong to someone else.

Visual stimuli on the contralesional side may also be ignored. Pain information is processed in multiple pathways see Table 1 in the chapter on Somatosensory Systems involving multiple thalamic nuclei that project to multiple cortical areas.

In addition to the somatosensory cortex, painful stimuli activate neurons in the rostral cingulate gyrus and the insula. Consequently, all pain sensation is not lost when the primary somatosensory cortex is damaged.

Primary somatosensory cortex neurons that have small receptive fields and are selectively responsive to sharp, cutting painful stimuli are considered to provide the ability to accurately localize the exact point of contact with the painful stimulus. Lesions of the primary somatosensory cortex will affect the quality of pain sensations and the ability to localize the exact location of the painful stimulus. An excellent way to test your knowledge of the material presented thus far is by examining the effects of damage to structures within the somatosensory pathways.

The following section should help you determine how well you can utilize what you have learned thus far about the somatosensory system. Peripheral Nerve Damage: Damage to peripheral nerves often results in sensory and motor symptoms. The sensory losses would include all somatosensory sensations if the peripheral nerve contains all the afferent axons supplying the skin, muscles and joints of a given body part e.

The motor losses may be severe i. The patient reports a loss of all sensation from his left hand. Symptoms: The patient complains of loss of sensation and weakness involving his left hand Figure 5. The physical examination determines that he is insensitive to pain, touch, vibration and finger position in his left hand.

However, touch, vibration, position and pain sensations are normal in the rest of his body and face. Pathway s Affected: You conclude that structures in the following somatosensory pathways Figure 5. A pin prick to the left hand produces no perceived pain sensations; and application of a vibrating tuning fork on the left hand or manipulating the fingers of the left hand produce no vibration or proprioceptive sensations.

Press THUMB to view the course of action potentials generated in response to application of a vibrating tuning fork or a pin prick to the left hand. Vibration and pain sensations are normal in the rest of the body and face.

Press FOOT to view the course of action potentials generated in response to application of a vibrating tuning fork or a pin prick to the left foot. When these nerves are severed, the area normally innervated loses all sensations and motor functions. Damage to peripheral nerves results in a loss of all somatosensory modalities and motor function in a restricted area of the body defined by the nerve distribution. Electrophysiological methods can be used to determine the nerves involved and the degree of nerve damage Refer to the section "Peripheral Somatosensory Axons" in the chapter on Somatosensory Pathways.

The area of the body innervated by a posterior root is called a dermatome Figure 5. Posterior root damage would result in somatosensory losses in the dermatome supplied by the root. All sensations would be lost in the central area of the dermatome. The more peripheral areas of the dermatome will have some sensation, albeit less than normal, as consecutive roots have partially overlapping dermatomes. T4 for the fourth thoracic root. A given dermatome e. T4 posterior root.

The symptoms produced by cranial nerve root damage depend upon the cranial nerve involved. The patient reports a loss of sensation along the lateral aspect of his left arm that extends down to include the thumb of his left hand.

The patient complains of a loss of sensation along the side of his left arm that extends down to include the thumb of his left hand Figure 5. Physical examination determines that there are decreases in the abilities to detect vibration and position involving the left elbow and thumb and loss of touch and pain sensations along the lateral edge of the left arm down to the thumb.

Touch, vibration, position, and pain sensations are normal for the rest of the body and face. A pin prick to the left thumb produces no perceived pain sensations; and a vibrating tuning fork in contact with the left arm or manipulating the left arm and thumb produce no vibration or proprioceptive sensations. Press HAND to view the course of action potentials generated in response to application of a vibrating tuning fork or a pin prick applied to the left thumb.

Vibration and pain sensations are normal for the rest of the body. Press FOOT to view the course of action potentials generated in response to application of a vibrating tuning fork or a pin prick applied the left foot.

Compression of the posterior roots will prevent action potentials generated by somatic stimulation from reaching the spinal cord. Section of a Posterior Root results in the loss of all somatosensory modalities in a restricted area of the body defined by the root dermatome Figure 5.

Consequently, the damaged posterior root can be identified by the dermatomal pattern of sensory loss. Radiographic methods can be used to determine if the roots are being compressed by abnormalities in the vertebra.

Spinal Cord Damage : Although there are numerous tracts in the spinal cord, the tracts considered to be of major clinical importance are limited. There are three major ascending tracts in the spinal cord, the posterior funiculus which includes the gracilis and cuneatus fasciculi, aka posterior columns ; the spinothalamic tract in the anterior and lateral funiculi ; and the posterior spinocerebellar tract in the lateral funiculus.

The patient suffers from loss of discriminative touch and proprioception i. Symptoms: The patient complains of problems with walking, especially at night when there is little light. He also reports a loss of sensation in his right foot. Physical examination determines that there are decreases in vibration and position sensations and poor localization of tactile stimuli involving the right half of his body starting just below the right nipple and extending down to include his right foot Figure 5.

Pain sensation is normal in the right torso, leg and foot. Touch, vibration, position and pain sensations are normal for the rest of the body and face. The Romberg test is positive. Pathway s Affected: You conclude that structures in the following somatosensory pathway may have been affected Figure 5. Consequently, within the spinal cord, discriminative touch and proprioception of the right side of the body is represented in the ipsilateral right posterior funiculus and pain and temperature from the right side of the body is represented in the contralateral left lateral funiculi.

Applying a vibrating tuning fork on the right foot and manipulating right foot produce no vibration or proprioceptive sensations. However, a pin prick to the right foot produces a well-localized sensation of sharp pain. Press FOOT to view the course of action potentials generated in response to the tuning fork on the right foot and pin prick to the right foot.

Vibration and pain sensations are normal in the rest of the body. Press HAND o view the course of action potentials generated in response to application of a vibrating tuning fork to the right and left hands. The afferents pain and temperature sensations from the right and left side of the body were spared as the lateral and anterior columns were not damaged.

When only the posterior column of the spinal cord is damaged, there are losses involving discriminative touch and proprioception, but no loss of pain, temperature or crude touch sensitivity. The deficit is ipsilesional and extends down the body from the level of the lesion.

There is an inability to appreciate vibrating stimuli and the position and movement in the ipsilesional lower body. The remaining tactile sense in the ipsilesional lower body is poorly localized as the spinothalamic tracts are undamaged. The Romberg test is positive as the patient has lost proprioception in a leg and cannot maintain normal posture with eyes closed. The patient suffers from loss of pain and temperature sensations from the left half of the body starting just below the left nipple and extending down to and including his left foot.

Symptoms: The patient presents with a complaint of repeatedly injuring his left foot. Physical examination determines that there are losses of pain and temperature sensations involving the left half of his body starting just below the left nipple and extending down to include his left foot Figure 5.

However, discriminative touch, and position sensations are normal in the left torso, leg and foot. Touch, vibration, position, pain, and temperature sensations are normal for the rest of the body and face.

The result of the Romberg test is negative. Pathway s Affected: You conclude that structures in the following somatosensory pathway Figure 5.

A pin prick to the left foot does not produce a well localized sensation of sharp pain. However, a vibrating tuning fork on the left foot or manipulating the foot produces vibration or proprioceptive sensations, respectively.

Press FOOT to view the course of action potentials generated in response to the tuning fork on, and a pin prick to, the left foot. Pin pricks to the upper body produce well localized sensations of sharp pain. Press HAND to view the course of action potentials generated in response to pin pricks to the left and right hands. Anterolateral cordotomy has been used to relieve intractable pain. When the cut is limited to section of the spinothalamic tract, there is a decrease in pain and temperature sensitivity.

As the posterior funiculus is not involved in the section, discriminative touch and proprioception remain intact. The deficit in pain and temperature sensitivity is contralesional and extends down the length of the body from the site of the lesion.

However, pain sensation often returns, albeit in a different form, following the surgical section of the spinothalamic tract. He also exhibits loss of discriminative touch and proprioception in a corresponding area on the right side of his body. Symptoms: The patient exhibits a loss in voluntary control of the right leg. He also reports loss of sensation in both feet Figure 5. Physical examination determines that there are losses of pain and temperature sensations involving the left half of his body starting just below the left nipple and extending down to include his left foot.

Without the brain, the body would not be able to function. The brain is very delicate and is well protected by the skull. It is surrounded by a fluid called cerebrospinal fluid CSF. The main functions of CSF are to protect the brain it acts as a shock absorber , to carry nutrients to the brain and remove waste from it. The frontal lobe governs our personality, character and behaviour. It is where we control our body movement and how we express ourselves.

This part of the brain allows us to speak. It is also where we solve problems and do most of our learning. It allows us to organise and plan. The occipital lobe receives messages from the eyes and recognises shapes, colours and objects. This bit of the brain allows you to tell the difference between a square and a triangle. It also controls your eye movements. The parietal lobe gives you a sense of 'me'.

It figures out the messages you receive from the five senses of sight, touch, smell, hearing and taste. This part of the brain tells you what is part of the body and what is part of the outside world. You have two temporal lobes, one behind each ear. They receive messages from the ears so that you can recognise sound and messages. This part of the brain also recognises speech and is how you understand what someone says to you.

It also helps your sense of smell. Your short term memory is also kept here. The cerebellum sits at the back of the brain and controls your sense of balance. This allows you to stand up, walk in a straight line, and know if you are standing up or sitting down. The brain stem controls your lungs and heart and blood pressure.

The parasympathetic system slows it down to the resting heart rate of 60—80 bpm. Another example is in the control of pupillary size Figure 4. The afferent branch responds to light hitting the retina. Photoreceptors are activated, and the signal is transferred to the retinal ganglion cells that send an action potential along the optic nerve into the diencephalon.

If light levels are low, the sympathetic system sends a signal out through the upper thoracic spinal cord to the superior cervical ganglion of the sympathetic chain. The postganglionic fiber then projects to the iris, where it releases norepinephrine onto the radial fibers of the iris a smooth muscle. When those fibers contract, the pupil dilates—increasing the amount of light hitting the retina.

If light levels are too high, the parasympathetic system sends a signal out from the Eddinger—Westphal nucleus through the oculomotor nerve. This fiber synapses in the ciliary ganglion in the posterior orbit.

The postganglionic fiber then projects to the iris, where it releases ACh onto the circular fibers of the iris—another smooth muscle. When those fibers contract, the pupil constricts to limit the amount of light hitting the retina. Figure 4. Autonomic Control of Pupillary Size. Activation of the pupillary reflex comes from the amount of light activating the retinal ganglion cells, as sent along the optic nerve.

The output of the sympathetic system projects through the superior cervical ganglion, whereas the parasympathetic system originates out of the midbrain and projects through the oculomotor nerve to the ciliary ganglion, which then projects to the iris. The postganglionic fibers of either division release neurotransmitters onto the smooth muscles of the iris to cause changes in the pupillary size.

Norepinephrine results in dilation and ACh results in constriction. In this example, the autonomic system is controlling how much light hits the retina.

It is a homeostatic reflex mechanism that keeps the activation of photoreceptors within certain limits. In the context of avoiding a threat like the lioness on the savannah, the sympathetic response for fight or flight will increase pupillary diameter so that more light hits the retina and more visual information is available for running away. Likewise, the parasympathetic response of rest reduces the amount of light reaching the retina, allowing the photoreceptors to cycle through bleaching and be regenerated for further visual perception; this is what the homeostatic process is attempting to maintain.

The pupillary light reflex involves sensory input through the optic nerve and motor response through the oculomotor nerve to the ciliary ganglion, which projects to the circular fibers of the iris. As shown in this short animation, pupils will constrict to limit the amount of light falling on the retina under bright lighting conditions. What constitutes the afferent and efferent branches of the competing reflex dilation? Organ systems are balanced between the input from the sympathetic and parasympathetic divisions.

When something upsets that balance, the homeostatic mechanisms strive to return it to its regular state. For each organ system, there may be more of a sympathetic or parasympathetic tendency to the resting state, which is known as the autonomic tone of the system. For example, the heart rate was described above. Because the resting heart rate is the result of the parasympathetic system slowing the heart down from its intrinsic rate of bpm, the heart can be said to be in parasympathetic tone.

In a similar fashion, another aspect of the cardiovascular system is primarily under sympathetic control. Blood pressure is partially determined by the contraction of smooth muscle in the walls of blood vessels.

These tissues have adrenergic receptors that respond to the release of norepinephrine from postganglionic sympathetic fibers by constricting and increasing blood pressure. The hormones released from the adrenal medulla—epinephrine and norepinephrine—will also bind to these receptors.

Those hormones travel through the bloodstream where they can easily interact with the receptors in the vessel walls.

The parasympathetic system has no significant input to the systemic blood vessels, so the sympathetic system determines their tone. There are a limited number of blood vessels that respond to sympathetic input in a different fashion. Blood vessels in skeletal muscle, particularly those in the lower limbs, are more likely to dilate.

It does not have an overall effect on blood pressure to alter the tone of the vessels, but rather allows for blood flow to increase for those skeletal muscles that will be active in the fight-or-flight response. The blood vessels that have a parasympathetic projection are limited to those in the erectile tissue of the reproductive organs.

Acetylcholine released by these postganglionic parasympathetic fibers cause the vessels to dilate, leading to the engorgement of the erectile tissue.

Have you ever stood up quickly and felt dizzy for a moment? This is because, for one reason or another, blood is not getting to your brain so it is briefly deprived of oxygen.

When you change position from sitting or lying down to standing, your cardiovascular system has to adjust for a new challenge, keeping blood pumping up into the head while gravity is pulling more and more blood down into the legs. The reason for this is a sympathetic reflex that maintains the output of the heart in response to postural change. When a person stands up, proprioceptors indicate that the body is changing position.

A signal goes to the CNS, which then sends a signal to the upper thoracic spinal cord neurons of the sympathetic division. The sympathetic system then causes the heart to beat faster and the blood vessels to constrict. Both changes will make it possible for the cardiovascular system to maintain the rate of blood delivery to the brain. Blood is being pumped superiorly through the internal branch of the carotid arteries into the brain, against the force of gravity. Gravity is not increasing while standing, but blood is more likely to flow down into the legs as they are extended for standing.

This sympathetic reflex keeps the brain well oxygenated so that cognitive and other neural processes are not interrupted. Sometimes this does not work properly. If the sympathetic system cannot increase cardiac output, then blood pressure into the brain will decrease, and a brief neurological loss can be felt. The name for this is orthostatic hypotension, which means that blood pressure goes below the homeostatic set point when standing. There are two basic reasons that orthostatic hypotension can occur.

First, blood volume is too low and the sympathetic reflex is not effective. This hypovolemia may be the result of dehydration or medications that affect fluid balance, such as diuretics or vasodilators. Both of these medications are meant to lower blood pressure, which may be necessary in the case of systemic hypertension, and regulation of the medications may alleviate the problem.