Chapters 11-14: Integration of Nervous System Functions

1. Chapters11-14: Integration of Nervous System Functions

2. Sensation • Sensation (perception): conscious awareness of stimuli received by sensory receptors • Steps to Sensation: • Sensory receptors detect the stimulus • Send action potential by nerves to CNS

3. Steps to sensation : Within the CNS, nerve tracts convey action potentials to the cerebral cortex and to other areas of the CNS In CNS, AP are translated so the person can be aware of the stimulus Sensation

4. Sensory Receptors • Three ways to classify Sensory receptors: • Type of stimuli detected • By location • Structural Complexity

5. Mechanoreceptors: respond to touch, pressure, vibration, stretch, and itch, hearing and balance Chemoreceptors: respond to chemicals (e.g. smell, taste) Thermoreceptors: respond to changes in temperature Photoreceptors: respond to light: vision Nociceptors: respond to pain-causing stimuli Classification by Stimulus Type

6. Classification by Location • Exteroceptors: • Respond to stimuli arising outside the body • Found near the body surface • Contains touch, pressure, pain, and temperature receptors in skin • And receptors of special sense organs (vision, hearing, taste, smell)

7. Visceroreceptors: Respond to stimuli arising within the body Found in viscera organs and blood vessels Sensitive to chemical changes, stretch, and temperature changes Proprioceptors: Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Respond to degree of stretch of the organs they occupy Classification by Location

8. Receptors are structurally classified as: Simple receptors Complex receptors Simple Receptors: Are distributed throughout the body and associated with general senses Divided into two groups: -- Somatic senses (provides sensory information about the body and environment): touch, pressure, temperature, proprioception, pain Visceral senses (information about internal organs): pain and pressure Classification by Structural Complexity

9. Complex Receptors: Receptors are present in specific organs and associated with special senses Special senses are smell, taste, sight, hearing, balance Classification by Structural Complexity

10. Free nerve endings Merkel (tactile) discs Hair follicle receptors Pacinian corpuscles (lamellated corpuscles) Meissner’s corpuscles (tactile corpuscles) Ruffini’s end organs Muscle spindles Golgi tendon organs Simple Receptors

11. Free Nerve Endings • Simplest, most common sensory receptor • In all body tissues (esp. epithelium) • Detect pain, temp., and pressure

12. Merkel (Tactile) Disks • Free nerve with disc shaped endings • Found in deep epidermis • Detect light touch and superficial pressure

13. Hair follicle Receptors • Respond to slight bending of hair as occurs in light touch • Pacinian Corpuscles • In hypodermis of skin, periostea, ligaments, joint capsules, fingers, soles of feet, external genitalia and nipples • Deep pressure and stretching • Respond only when pressure first applied

14. Meissner's (Tactile) Corpuscles • Numerous in dermal papillae of hairless skin (lips, nipples, fingertips) • Ability to detect simultaneous stimulations at two points on the skin (Two-point discrimination)

15. Ruffini End Organ • Primarily in dermis of fingers • Respond to continuous touch or pressure

16. Muscle Spindles • 3-10 specialized skeletal muscle cells • Provide information about length of muscles • Involved in stretch reflex

17. Golgi Tendon Organ • Proprioceptors associated with tendons • Respond to increased tension on tendon

18. Sensory receptor generates Graded potential or Receptor potential when interacts with stimulus Primary receptors: axons conduct action potentials in response to graded potential eg. Simple sensory receptors Responses of Sensory Receptors

19. Responses of Sensory Receptors • Secondary receptors: Have no axons or have short axon like projections • Causes release of neurotransmitters that bind to receptors on a neuron causing a receptor potential eg. Smell, taste, hearing, balance

20. Sensory Nerve Tracts : Ascending Pathways • SC and brain stem contains no. of sensory pathway • They transmit action potentials from periphery to various parts of brain • Each pathway involved with specific modality (type of information transmitted) • Names of ascending pathway or tracts in CNS indicate their origin & termination • First half of word indicates origin, second half indicates termination

21. Anterolateral System: Spinothalamic Tract • Located in the anterior and lateral white columns of spinal cord • Convey sensory information such as pain, temp, light touch, pressure, tickle, and itch • Consist of three Neuron system: • Primary neuron: Relay sensory input from periphery to posterior horn of SC • And synapse with interneurons • Interneurons synapse with sec. neuron • Secondary neuron : cross to opposite side of SC & enter spinothalamic tract, ascend to thalamus • Tertiary neuron: thalamus to somatic sensory cortex

22. Dorsal-Column/Medial-Lemniscal System • Carries sensations of two-point discrimination, proprioception, pressure, vibration to cerebrum, and cerebellum • Primary neurons: Located in dorsalroot ganglion • Axons enter spinal cord and ascend to the medulla oblongata where they synapse with secondary neurons • Secondary neurons: axons travel contralaterally and ascend to thalamus • Tertiary neurons: thalamus to somatic sensory cortex

23. Trigeminothalamic Tract • Fibers of Trigeminothalamic tract join the spinothalamic tract in the brainstem • Made up of afferent (sensory) fibers from Cranial nerve V • Carries similar information to that of the spinothalamic and dorsal-column/medial-lemniscal system, but from the face, nasal cavity and oral cavity

24. Spinocerebellar System • Carries proprioceptive information to cerebellum • Information concerning actual movements is monitored • Two spinocerebellar tracts extend through spinal cord: • Posterior spinocerebellar tract : • Carries information from thoracic and upper lumbar regions to cerebellum • Anterior spinocerebellar tract: • Carries information from lower trunk and lower limbs to cerebellum

25. Sensory and Association Areas of the Cerebral Cortex • Sensory Areas: • Primary somatic sensory cortex (general sensory area): posterior to the central sulcus, Post central gyrus area • General sensory input for pain, pressure, temperature • Taste area: located at inferior end of post central gyrus • Olfactory cortex: at inferior surface of frontal lobe • Primary auditory cortex: superior part of temporal lobe • Visual cortex: occipital lobe

26. Sensory and Association Areas of the Cerebral Cortex • Association areas: Involved in process of recognition • Somatic sensory Association Area: • posterior to primary somatic sensory cortex • Visual Association area: • anterior to visual cortex: • Where present visual • information is comparedto past • visual experience

27. Control of Skeletal Muscles • Motor system of brain and SC: maintains posture and balance; moves limbs, trunk, head, eyes; facial expression, speech • Voluntary movements: consciously activated to achieve a specific goal, eg. walking • Voluntary movements depend on two neurons: • Upper motor neurons: directly or through interneurons connect to lower motor neurons • Lower motor neurons: Have axons that leave the CNS, and supply to skeletal muscles

28. Three Steps to Voluntary Movements • Initiation of voluntary movement begins in the premotor areas of the cerebral cortex and results in the stimulation of upper motor neurons • The axons of the upper motor neurons form the descending nerve tracts. They stimulate lower motor neurons which stimulate skeletal muscles to contract • The cerebral cortex interacts with the basal nuclei and cerebellum in the planning, coordination and execution of movements

29. Motor Areas of the Cerebral Cortex • Precentral gyrus (primary motor cortex, primary motor area): 30% of upper motor neurons. Another 30% in premotor area, rest in somatic sensory cortex • Premotor area: ant. to primary motor cortex. Motor functions organized here & initiation takes place in motor cortex area • Prefrontal area: motivation, foresight to plan and initiate movements takes place • Also involved in emotional behavior, mood

30. Motor Nerve Tracts : Descending pathways • Axons carry AP from cerebrum or cerebellum to brain stem or SC • Descending motor fibers are divided into two groups: • Direct pathways (pyramidal system): Involved in maintenance of muscle tone, controlling speed and precision of skilled movements • Indirect pathways (extrapyramidal system): Involved in less precise movements, such as posture

31. Direct Pathways • Control muscle tone and conscious fine, skilled movements in the face and distal limbs • Direct synapse of upper motor neurons of cerebral cortex with lower motor neurons in brainstem or spinal cord • Tracts • Corticospinal: direct control of movements below the head • Corticobulbar: direct control of movements in head and neck

32. Corticospinal Tracts • Axons of upper motor neurons descend through internal capsules and cerebral peduncles to pyramids of medulla oblongata • 75-85% decussate and descend in the lateral Corticospinal tracts. Supply all levels of body • Remaining fibers descend uncrossed in anterior Corticospinal tracts but decussate near level of synapse with lower neurons. Supply neck; upper limbs

33. Corticobulbar Tracts • Innervate the head • Upper neurons enter the cranial nerve nuclei after forming the reticular formation • Lower motor neurons control eye and tongue movement, mastication, facial expression, palatine, pharyngeal, and laryngeal movements

34. Indirect Pathways • Control conscious and unconscious muscle movements in trunk and proximal limbs • Synapse in some intermediate nucleus rather than directly with lower motor neurons • Tracts • Rubrospinal: upper neurons synapse in red nucleus • Regulates fine motor control of muscles in distal part of upper limb • Vestibulospinal: Originate in vestibular nuclei and synapse in SC • influence neurons innervating extensor muscles in trunk and proximal portion of lower limbs; help maintain upright posture • Reticulospinal: Present in reticular formation of pons and medulla and synapse in SC • maintenance of posture

35. Basal Nuclei • Important in planning, organizing, coordinating movements and posture • Complex neural circuits between basal nuclei, thalamus, and cerebral cortex • Stimulatory circuit : facilitate muscle activity like rising from a chair • Inhibitory circuit : inhibit activity in antagonistic muscles

36. Cerebellum • Helps maintain muscle tone in postural muscles, helps control balance during movement, and coordinate eye movements • Cerebellum compares the intended movement with the actual movement • e.g. Touching the nose

37. Brainstem Functions • All ascending and descending pathways pass through the brainstem • Nuclei of cranial nerves II-XII located here • Many reflexes important to survival located here: heart rate, blood pressure, respiration, sleep, swallowing, vomiting, coughing, and sneezing • Reticular activating system (RAS)- controls sleep/wake cycle • RAS receives input from cranial nerves II (optic), V (trigeminal), VIII (Vestibulocochlear), ascending tactile sensory pathways and descending neurons from the cerebral cortex

38. Speech • Speech Area normally is in left cerebral cortex • Wernicke's area: sensory speech area- Understanding written and spoken language • Broca's area: motor speech area - sending messages to the appropriate muscles to actually make the sounds • Aphasia: absent or defective speech or language comprehension. Caused by lesion in the language area of the cortex

39. Right and Left Cerebral Cortex • Right: controls muscular activity in and receives sensory information from left side of body • Left: controls muscular activity in and receives sensory information from right side of body • Sensory information of both hemispheres shared through commissures: corpus callosum • Language, and possibly other functions like artistic activities, not shared equally • Left: mathematics and speech • Right: three-dimensional or spatial perception, recognition of faces, musical ability

40. Brain Waves and Sleep • Electroencephalogram (EEG): record of brain’s electrical activity Summation of all of the action potentials occurring at a particular moment sensed by electrodes placed on the scalp • Brain wave patterns • Alpha: Resting state with eyes closed • Beta: During intense mental activity • Theta: Occur in children but also in adults experiencing frustration or brain disorders • Delta: Occur in deep sleep, infancy, and severe brain disorders

41. There are two major types of sleep: Non-rapid eye movement (NREM) Rapid eye movement (REM) One passes through four stages of NREM during the first 30-45 minutes of sleep REM sleep occurs after the fourth NREM stage has been achieved Types of Sleep

42. Memory • Sensory: very short-term retention of sensory input received by brain • Short-term: information retained for few seconds to minutes • Long-term: Two types • Explicit or declarative memory: • Retention of facts, such as names, dates • Accessed by hippocampus, part of temporal lobe (actual memory) • and amygdaloid nucleus – emotional, such as like or dislike • Implicit (procedural; reflexive) memory: development of skills such as riding a bicycle, playing a piano

43. Limbic System • Influences emotions, visceral responses to emotions, motivation, mood, sensations of pain and pleasure • Limbic system is associated with Basic survival instincts: acquisition of food and water; reproduction • Major source of sensory input in Limbic System is Olfactory nerve • Pheromones: molecules released by one organism that have an effect on another organism; e.g., females release pheromones that affect menstrual cycle of other women • Cingulate gyrus: satisfaction center

44. Effects of Aging on the Nervous System • Gradual decline in sensory and motor function • Reflexes slow • Size and weight of brain decrease • Decreased short-term memory in most people • Long-term memory unaffected or improved • Changes in sleep patterns