Sensory, Motor and Integrative Systems.pptx

physiology notes on sensory motor and intergrative centres.

1. Sensory, Motor and Integrative Systems Lecture outline – Introduction Sensation Sensory modalities The process of sensation Sensory receptors Somatic sensations Somatic sensory pathways Somatic motor pathways Integrative functions of the cerebrum SKM - MedPhysio

2. Introduction The sensory system of the body provide routes for input into the brain and spinal cord. The motor pathways provide output to targeted organs for responses – e.g., muscle contraction. As sensory impulses reach the CNS, they become part of a large pool of sensory input . Each piece of incoming info is combined with other arriving and previously stored info in a process called integration. SKM - MedPhysio

3. Integration occurs at many places along pathways in the CNS; e.g., the spinal cord, brain stem, cerebellum, basal ganglia, and cerebral cortex. SKM - MedPhysio

4. SENSATION S ensation - conscious or subconscious awareness of changes in the external or internal environment . Sensory impulses that reach the spinal cord may serve as input for spinal reflexes. Sensory impulses that reach the lower brain stem elicit more complex reflexes; e.g., changes in heart rate or breathing rate . SKM - MedPhysio

5. When sensory impulses reach the cerebral cortex , the person becomes consciously aware of the sensory stimuli and can precisely locate and identify specific sensations e.g., touch , pain, hearing, or taste . Perception – T he conscious awareness and interpretation of sensations. P rimarily a function of the cerebral cortex . Body has no perception of some sensory info that never reaches the cerebral cortex; e.g. BP. – controlled at the medulla. SKM - MedPhysio

6. Sensory Modalities Modality refers to the type of stimulus or the sensation it produces. Examples of modalities - vision , hearing, and taste. Each unique type of sensation; e.g., touch , pain, vision, or hearing is called a sensory modality. A given sensory neuron carries info for only one sensory modality. SKM - MedPhysio

7. The different sensory modalities can be grouped into 2 classes : G eneral senses. S pecial senses . a) The General Senses – Refer to both somatic senses and visceral senses. i) Somatic senses include tactile sensations (touch, pressure, vibration, itch, and tickle), thermal sensations (warm and cold), pain sensations, and proprioceptive sensations . SKM - MedPhysio

8. Proprioceptive sensations allow perception of both the static (nonmoving) positions of limbs and body parts ( joint and muscle position sense) and movts of the limbs and head. Ii) Visceral senses provide information about conditions within internal organs . b) The Special Senses – I nclude the sensory modalities of smell, taste , vision, hearing, and equilibrium or balance. SKM - MedPhysio

9. The Process of Sensation Begins in a sensory receptor. R eceptor - any structure specialized to detect a stimulus. Some receptors are simple nerve endings. Others receptors are sense organs – i.e., nerve endings combined with connective , epithelial, or muscular tissues that enhance or moderate the response to a stimulus . For a sensation to arise, the following 4 events typically occur:…… SKM - MedPhysio

10. Stimulation of the sensory receptor. Transduction of the stimulus – a sensory receptor transduces (converts ) energy in a stimulus into a graded potential . Generation of nerve impulses - when a graded potential in a sensory neuron reaches threshold, it triggers one or more nerve impulses , which then propagate toward the CNS. Sensory neurons that conduct impulses from the PNS into the CNS are called first-order neurons. SKM - MedPhysio

11. d) Integration of sensory input. A particular region of the CNS receives and integrates the sensory nerve impulses. Conscious sensations or perceptions are integrated in the cerebral cortex. The eyes can see, hear with the ears , and feel pain in an injured part of the body bcoz sensory impulses from each part of the body arrive in a specific region of the cerebral cortex, which interprets the sensation as coming from the stimulated sensory receptors. SKM - MedPhysio

12. Classification of Receptors Receptors can be classified by several overlapping systems: a) By stimulus modality: Chemoreceptors respond to chemicals; e.g., odors, tastes, and body fluid composition. Thermoreceptors respond to heat and cold. Nociceptors are pain receptors; they respond to tissue damage. Mechanoreceptors respond to physical deformation caused by vibration, touch, pressure, stretch, or tension. SKM - MedPhysio

13. Mechanoreceptors include the organs of hearing and balance and many receptors of the skin, viscera, and joints. Photoreceptors, the eyes, respond to light . b) By the origins of the stimuli: Interoceptors detect stimuli in the internal organs and produce feelings of visceral pain, nausea , stretch, and pressure. Proprioceptors sense the position and movts of the body or its parts. They occur in muscles, tendons, and joint capsules. SKM - MedPhysio

14. Exteroceptors sense stimuli external to the body; they include the receptors for vision, hearing, taste , smell, touch, and cutaneous pain . c) By the distribution of receptors in the body. There are 2 broad classes of senses : General (somesthetic) senses, with receptors that are widely distributed in the skin, muscles, tendons , joint capsules, and viscera. These include the sense of touch, pressure, stretch etc. Special senses , which are limited to the head and innervated by the cranial nerves. The special senses are vision, hearing, equilibrium, taste, and smell . SKM - MedPhysio

15. Adaptation in Sensory Receptors Adaptation – occurs when the generator potential or receptor potential decreases in amplitude during a maintained, constant stimulus. X ristic of most sensory receptors. Bcoz of adaptation, the perception of a sensation may fade or disappear even though the stimulus persists. SKM - MedPhysio

16. Somatic Sensations Somatic sensations arise from stimulation of sensory receptors embedded in the – S kin or subcutaneous layer. M ucous membranes of the mouth, vagina and anus. Muscles , tendons, and joints. I nner ear . There are four modalities of somatic sensation: tactile, thermal, pain, and proprioceptive . SKM - MedPhysio

17. Tactile Sensations – Include touch, pressure , vibration, itch, and tickle . Tactile receptors in the skin or subcutaneous layer include – Meissner corpuscles H air root plexuses Merkel discs Ruffini corpuscles P acinian corpuscles F ree nerve endings SKM - MedPhysio

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19. Free nerve endings are thought to mediate the tickle sensation. This intriguing sensation typically arises only when someone else touches you, not when you touch yourself . Thermal Sensations – Thermoreceptors are free nerve endings on the skin surface. Temps below 10C and above 48C primarily stimulate pain receptors, rather than thermoreceptors, producing painful sensations. SKM - MedPhysio

20. Pain Sensations – Pain is indispensable for survival. It serves a protective function by signaling the presence of noxious, tissue-damaging conditions. Nociceptors, the receptors for pain, are free nerve endings found in every tissue of the body except the brain. Tissue irritation or injury releases chemicals such as prostaglandins, kinins, and potassium ions (K) that stimulate nociceptors. SKM - MedPhysio

21. Pain that arises from stimulation of receptors in the skin is called superficial somatic pain; stimulation of receptors in skeletal muscles, joints, tendons, and fascia causes deep somatic pain. Visceral pain results from stimulation of nociceptors in visceral organs. If stimulation is diffuse (involves large areas ), visceral pain can be severe . Diffuse stimulation of visceral nociceptors might result from distention or ischemia of an internal organ . SKM - MedPhysio

22. Somatic pain is well localized. The visceral pain is felt in or just deep to the skin that overlies the stimulated organ, or in a surface area far from the stimulated organ. This phenomenon is called referred pain. In general, the visceral organ involved and the area to which the pain is referred are served by the same segment of the spinal cord . E.g., the sensory fibers from the heart, the skin over the heart, and the skin along the medial aspect of the left arm enter spinal cord segments T1 to T5 – Heart Attack pain felt along the l. arm. SKM - MedPhysio

23. Distribution of Referred Pain SKM - MedPhysio

24. Proprioceptive S ensations – Allows people to know where their head and limbs are located. Allows people to know how they are moving even if they are not looking at them. This enables them to walk, type, or dress without using their eyes. Kinesthesia - the perception of body movts. Proprioceptive sensations arise in receptors termed proprioceptors. SKM - MedPhysio

25. Those proprioceptors embedded in muscles ( esp postural muscles) and tendons inform us of the degree to which muscles are contracted, the amount of tension on tendons, and the positions of joints. Hair cells of the inner ear monitor the orientation of the head relative to the ground and head position during movts . The way they provide information for maintaining balance and equilibrium. SKM - MedPhysio

26. Three types of proprioceptors – Muscle spindles (within skeletal muscles). Tendon organs (within tendons). Joint kinesthetic receptors (within synovial joint capsules). Muscle spindles are the proprioceptors in skeletal muscles that monitor changes in the length of skeletal muscles and participate in stretch reflexes. SKM - MedPhysio

27. Tendon organs are located at the junction of a tendon and a muscle. By initiating tendon reflexes tendon organs protect tendons and their associated muscles from damage due to excessive tension . Several types of joint kinesthetic receptors are present within and around the articular capsules of synovial joints. Free nerve endings and Ruffini corpuscles in the capsules of joints respond to pressure changes. SKM - MedPhysio

28. SOMATIC SENSORY PATHWAYS Relay info from the somatic sensory receptors to the primary somatosensory area in the cerebral cortex and to the cerebellum . The pathways to the cerebral cortex consist of thousands of sets of 3 neurons : A first-order neuron. A second-order neuron . A third order neuron . SKM - MedPhysio

29. First-order neurons – C onduct impulses from somatic receptors into the brain stem or spinal cord. From the face, mouth, teeth , and eyes, somatic sensory impulses propagate along cranial nerves into the brain stem. From the neck, trunk, limbs, and posterior aspect of the head, somatic sensory impulses propagate along spinal nerves into the spinal cord. SKM - MedPhysio

30. Second-order neurons – C onduct impulses from the brain stem and spinal cord to the thalamus. Axons of second-order neurons decussate in the brain stem or spinal cord b4 ascending to the ventral posterior nucleus of the thalamus. Thus , all somatic sensory info from one side of the body reaches the thalamus on the opposite side. SKM - MedPhysio

31. Third-order neurons – C onduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side . Relay stations – R efers to regions within the CNS where neurons synapse with other neurons that are a part of a particular sensory or motor pathway. They are known as relay stations bcoz neural signals are being relayed from one region of the CNS to another . Thalamus, brainstem and SC act as relay stations. SKM - MedPhysio

32. Somatic sensory impulses ascend to the cerebral cortex via 3 general pathways: T he posterior column - medial lemniscus pathway T he anterolateral (spinothalamic) pathway. T he trigeminothalamic pathway. Somatic sensory impulses reach the cerebellum via the spinocerebellar tracts. SKM - MedPhysio

33. The Posterior Column - Medial lemniscus Pathway The name of the pathway comes from the names of 2 white-matter tracts that convey the impulses: T he posterior column of the spinal cord. T he medial lemniscus of the brain stem . Nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex along this pathway. SKM - MedPhysio

34. First-order neurons extend from sensory receptors in the limbs , trunk, neck, and posterior head into the spinal cord and ascend to the medulla oblongata on the same side of the body. The cell bodies of these neurons are in the posterior (dorsal ) root ganglia of spinal nerves . In the spinal cord, their axons form the posterior (dorsal) columns, which consist of 2 parts: T he gracile fasciculus. T he cuneate fasciculus . SKM - MedPhysio

35. The axon terminals synapse with second-order neurons whose cell bodies are located in the gracile nucleus or cuneate nucleus of the medulla . Nerve impulses for touch, pressure, vibration, and conscious proprioception from the upper limbs, upper trunk, neck, and posterior head propagate along axons in the cuneate fasciculus and arrive at the cuneate nucleus. SKM - MedPhysio

36. Nerve impulses for touch, pressure, vibration, and stereognosis from the lower limbs and lower trunk propagate along axons in the gracile fasciculus and arrive at the gracile nucleus . The axons of the second-order neurons cross to the opposite side of the medulla and enter the medial lemniscus , a thin ribbon-like projection tract that extends from the medulla to the ventral posterior nucleus of the thalamus. SKM - MedPhysio

37. In the thalamus, the axon terminals of second-order neurons synapse with third-order neurons, which project their axons to the primary somatosensory area of the cerebral cortex. SKM - MedPhysio

38. Anterolateral Pathway to the Cortex Also called the spinothalamic pathway. Nerve impulses for pain, temp, itch, and tickle from the limbs , trunk, neck, and posterior head ascend to the cerebral cortex along the anterolateral or spinothalamic pathway. The first-order neurons connect a receptor of the limbs , trunk, neck, or posterior head with the spinal cord. The cell bodies of the first-order neurons are in the posterior root ganglion . SKM - MedPhysio

39. The axon terminals of the first-order neurons synapse with second-order neurons, whose cell bodies are located in the posterior gray horn of the spinal cord. The axons of the second order neurons cross to the opposite side of the spinal cord. Then, they pass upward to the brain stem as the spinothalamic tract . The axons of the second-order neurons end in the ventral posterior nucleus of the thalamus, where they synapse with the third order neurons . SKM - MedPhysio

40. The axons of the third-order neurons project to the primary somatosensory area on the same side of the cerebral cortex as the thalamus. SKM - MedPhysio

41. The Trigeminothalamic Pathway to the Cortex Nerve impulses for most somatic sensations (tactile, thermal, and pain) from the face, nasal cavity, oral cavity, and teeth ascend to the cerebral cortex along the trigeminothalamic pathway. First-order neurons extend from somatic sensory receptors in the face, nasal cavity, oral cavity , and teeth into the pons thro’ the trigeminal (V) nerves. SKM - MedPhysio

42. The cell bodies of these first-order neurons are in the trigeminal ganglion . The axon terminals of some first-order neurons synapse with second-order neurons in the pons. The axons of other first-order neurons descend into the medulla to synapse with second-order neurons. The axons of the second-order neurons cross to the opposite side of the pons and medulla and then ascend as the trigeminothalamic tract to the ventral posterior nucleus of the thalamus. SKM - MedPhysio

43. In the thalamus, the axon terminals of the second-order neurons synapse with third-order neurons, which project their axons to the primary somatosensory area on the same side of the cerebral cortex as the thalamus. SKM - MedPhysio

44. Mapping the Primary Somatosensory Area Specific areas of the cerebral cortex receive somatic sensory input from particular parts of the body . Other areas of the cerebral cortex provide output in the form of instructions for movt of particular parts of the body. The somatic sensory map and the somatic motor map relate body parts to these cortical areas . SKM - MedPhysio

45. Precise localization of somatic sensations occurs when nerve impulses arrive at the primary somatosensory area which occupies the postcentral gyri of the parietal lobes of the cerebral cortex. SKM - MedPhysio

46. Somatic Sensory Pathways to the Cerebellum Two tracts in the spinal cord – T he posterior spinocerebellar tract. T he anterior spinocerebellar tract. They are the major routes proprioceptive impulses take to reach the cerebellum. Although they are not consciously perceived, sensory impulses conveyed to the cerebellum along these two pathways are critical for posture, balance, and coordination of skilled movements. SKM - MedPhysio

47. SOMATIC MOTOR PATHWAYS Neural circuits in the brain and SC orchestrate all voluntary and involuntary movts. All excitatory and inhibitory signals that control movt converge on the motor neurons that extend out of the brain stem and SC to innervate skeletal muscles in the body. Lower motor neurons (LMNs) – refers to the above neurons whose cell bodies are located in the brain stem and SC. SKM - MedPhysio

48. From the brain stem, axons of LMNs extend thro’ cranial nerves to innervate skeletal muscles of the face and head. From the SC, axons of LMNs extend thro’ spinal nerves to innervate skeletal muscles of the limbs and trunk. LMNs provide output from the CNS to skeletal muscle fibers. For this reason, they are also called the final common pathway. SKM - MedPhysio

49. Neurons in 4 distinct but highly interactive neural circuits, collectively termed the somatic motor pathways, participate in control of movt by providing input to LMNs in specific muscle groups; e.g., alternating flexion and extension of the lower limbs during walking. 1) Local circuit neurons – Input arrives at LMNs from nearby interneurons called local circuit neurons. These neurons are located close to the LMN cell bodies in the brain stem and SC. SKM - MedPhysio

50. Local circuit neurons receive input from somatic sensory receptors, e.g., nociceptors and muscle spindles, as well as from higher centers in the brain. They help coordinate rhythmic activity in specific muscle groups, such as alternating flexion and extension of the lower limbs during walking. 2) Upper motor neurons – Originate from the cerebral cortex and other motor centers of the brain stem: the red nucleus, the vestibular nucleus, the superior colliculus, and the reticular formation. SKM - MedPhysio

51. Most upper motor neurons synapse with local circuit neurons, which in turn synapse with LMNs. UMNs from the brain stem regulate muscle tone, control postural muscles, and help maintain balance and orientation of the head and body. Both the basal ganglia and cerebellum exert influence on upper motor neurons. SKM - MedPhysio

52. 3) Basal ganglia neurons – Assist movt by providing input to UMNs. Neural circuits interconnect the basal ganglia with motor areas of the cerebral cortex (via the thalamus) and the brain stem. These circuits help initiate and terminate movts, suppress unwanted movts, and establish a normal level of muscle tone. SKM - MedPhysio

53. 4) Cerebellar neurons – Aid movt by controlling the activity of UMNs. Neural circuits interconnect the cerebellum with motor areas of the cerebral cortex (via the thalamus) and the brain stem. Cerebellum monitors differences between intended movts and movts actually performed. Then, it issues commands to UMNs to reduce errors in movt. The cerebellum thus coordinates body movts and helps maintain normal posture and balance. SKM - MedPhysio

54. Organization of Upper Motor Neuron Pathways The axons of UMNs extend from the brain to LMNs via 2 types of somatic motor pathways - direct and indirect. Direct motor pathways – Provide input to LMNs via axons that extend directly from the cerebral cortex. Indirect motor pathways – Provide input to LMNs from motor centers in the brain stem. SKM - MedPhysio

55. Direct and indirect pathways both govern generation of nerve impulses in the LMN, the neurons that stimulate contraction of skeletal muscles. SKM - MedPhysio

56. Mapping the Motor Areas Control of body movts occurs via neural circuits in several regions of the brain. The primary motor area is located in the precentral gyrus of the frontal lobe of the cerebral cortex. Precentral gyrus is a major control region for the execution of voluntary movts. Different muscles are represented unequally in the primary motor area. SKM - MedPhysio

57. More cortical area is devoted to those muscles involved in skilled, complex, or delicate movements. Muscles in the thumb, fingers, lips, tongue, and vocal cords have large representations; the trunk has a much smaller representation. SKM - MedPhysio

58. Direct Motor Pathways Nerve impulses for voluntary movts propagate from the cerebral cortex to LMNs via the direct motor pathways. The direct motor pathways are also known as the pyramidal pathways . They consist of axons that descend from pyramidal cells. Pyramidal cells are UMNs with pyramid-shaped cell bodies located in the primary motor area and the premotor area of the cerebral cortex. Direct motor pathways consist of the corticospinal pathways and the corticobulbar pathway. SKM - MedPhysio

59. Corticospinal Pathways Conduct impulses for the control of muscles of the limbs and trunk. Axons of UMNs in the cerebral cortex form the corticospinal tracts which descend thro’ the internal capsule of the cerebrum and the cerebral peduncle of the midbrain. In the medulla oblongata, the axon bundles of the corticospinal tracts form the ventral bulges known as the pyramids. SKM - MedPhysio

60. About 90% of the corticospinal axons decussate (cross over) to the contralateral (opposite) side in the medulla oblongata. They then descend into the spinal cord where they synapse with a local circuit neuron or a LMN. 10% that remain on the ipsilateral (same) side eventually decussate at the spinal cord levels where they synapse with a local circuit neuron or LMN. SKM - MedPhysio

61. Thus – The right cerebral cortex controls muscles on the left side of the body. The left cerebral cortex controls muscles on the right side of the body. There are 2 types of corticospinal tracts: Lateral corticospinal tract. Anterior corticospinal tract. SKM - MedPhysio

62. Lateral Corticospinal Tract Conveys nerve impulses from the motor cortex to skeletal muscles on opposite side of body for precise, voluntary movts of the distal parts of the limbs. Axons of UMNs descend from the precentral gyrus into the medulla. Here 90% decussate and then enter the contralateral side of the SC to form this tract. At their level of termination, these UMNs end in the anterior gray horn on the same side. They provide input to lower motor neurons, which innervate skeletal muscles. SKM - MedPhysio

63. Anterior Corticospinal Tract Conveys nerve impulses from the motor cortex to skeletal muscles on opposite side of body for movts of the trunk and proximal parts of the limbs. Axons of UMNs descend from the cortex into the medulla. Here the 10% that do not decussate enter the spinal cord and form this tract. At their level of termination, these UMNs decussate and end in the anterior gray horn on the opposite side of the body. They provide input to lower motor neurons, which innervate skeletal muscles. SKM - MedPhysio

64. Corticobulbar Pathway Conducts impulses for the control of skeletal muscles in the head. Axons of UMNs from the cerebral cortex form the corticobulbar tract. This pathway descends along with the corticospinal tracts thro’ the internal capsule of the cerebrum and cerebral peduncle of the midbrain. Some of the axons of the corticobulbar tract decussate; others do not. The axons terminate in the motor nuclei of nine pairs of cranial nerves in the brain stem:………….. SKM - MedPhysio

65. The oculomotor (III) The trochlear (IV) The trigeminal (V) The abducens (VI) The facial (VII) The glossopharyngeal (IX) The vagus (X) The accessory (XI) The hypoglossal (XII) The LMNs of these cranial nerves convey impulses that control precise, voluntary movts of the eyes, tongue, and neck, plus chewing, facial expression, and speech. SKM - MedPhysio

66. Indirect Motor Pathways Also called the extrapyramidal pathways. Include all somatic motor tracts other than the corticospinal and corticobulbar tracts. Axons of UMNs that give rise to the indirect motor pathways descend from various nuclei of the brain stem into 5 major tracts of the spinal cord. They terminate on local circuit neurons or LMNs. These tracts are the – Rubrospinal tract Tectospinal tract Vestibulospinal tract SKM - MedPhysio

67. Lateral reticulospinal tract Medial reticulospinal tract Rubrospinal tract: Conveys nerve impulses from the red nucleus (which receives input from the cerebral cortex and cerebellum) to contralateral skeletal muscles that govern precise, voluntary movts of the distal parts of the upper limbs. Tectospinal tract: Conveys nerve impulses from the superior colliculus to contralateral skeletal muscles that reflexively move the head, eyes, and trunk in response to visual or auditory stimuli. SKM - MedPhysio

68. Vestibulospinal tract: Conveys nerve impulses from the vestibular nucleus (which receives input about head movts from the inner ear) to ipsilateral skeletal muscles of the trunk and proximal parts of the limbs for maintaining posture and balance in response to head movts. Medial and lateral reticulospinal tracts: Conveys nerve impulses from the reticular formation to ipsilateral skeletal muscles of the trunk and proximal parts of the limbs for maintaining posture and regulating muscle tone in response to ongoing body movts. SKM - MedPhysio

69. Functions of the Basal Ganglia The basal ganglia and cerebellum influence movt thro’ their effects on UMNs. Roles of Basal Ganglia – a) Initiation and termination of movts – Two parts of the basal ganglia, the caudate nucleus and the putamen, receive input from sensory, association, and motor areas of the cerebral cortex and from the substantia nigra. Output from the basal ganglia comes from the globus pallidus and substantia nigra, which send feedback signals to the upper motor cortex by way of the thalamus. SKM - MedPhysio

70. This circuit - from cortex to basal ganglia to thalamus to cortex - appears to function in initiating and terminating movts. b) Suppressing unwanted movts – Basal ganglia has inhibitory effects on the thalamus and superior colliculus. c) Influences on muscle tone – The globus pallidus sends impulses into the reticular formation that reduce muscle tone. Damage or destruction of some basal ganglia connections causes a generalized increase in muscle tone. SKM - MedPhysio

71. d) Influences cortical function – The basal ganglia influences cortical functions including sensory, limbic, cognitive, and linguistic functions. E.g., the basal ganglia help initiate and terminate some cognitive processes, such as attention, memory, and planning. In addition, the basal ganglia may act with the limbic system to regulate emotional behaviors. SKM - MedPhysio

72. The integrative Functions of the Cerebrum Integration - the processing of sensory info by analyzing and storing it and making decisions for various responses. Integrative functions include cerebral activities e.g.: Sleep and wakefulness Learning and memory Emotional responses SKM - MedPhysio

73. Wakefulness and Sleep Human beings sleep and awaken in a 24-hr cycle called a circadian rhythm that is established by the suprachiasmatic nucleus of the hypothalamus. EEG recordings show that the cerebral cortex is very active during wakefulness. Fewer impulses arise during most stages of sleep. SKM - MedPhysio

74. The Reticular Activating System and Awakening Bcoz stimulation of some of its parts increases activity of the cerebral cortex, a portion of the reticular formation is known as the reticular activating system (RAS). When RAS is active, many nerve impulses are transmitted to widespread areas of the cerebral cortex, both directly and via the thalamus. The effect is a generalized increase in cortical activity. SKM - MedPhysio

75. Arousal, or awakening from sleep involves increased activity in the RAS. Many sensory stimuli can activate the RAS: Painful stimuli detected by nociceptors Touch and pressure on the skin Movt of the limbs Bright light The buzz of an alarm clock Once the RAS is activated, the cerebral cortex is also activated, and arousal occurs. The result is a state of wakefulness called consciousness. SKM - MedPhysio

76. NOTE: The RAS receives no input from olfactory receptors. Thus, even strong odors may fail to cause arousal. People who die in house fires usually succumb to smoke inhalation without awakening. For this reason, all sleeping areas should have a nearby smoke detector that emits a loud alarm. A vibrating pillow or flashing light can serve the same purpose for those who are hearing impaired. SKM - MedPhysio