The Central Nervous System

1. The Central Nervous System 9

2. Emergent Properties • Emergent properties of neural networks: • Inexplicable properties –the structural components of a neuron cannot explain the complex responses produced during neural processing/integration • Neuron circuits – a single neuron cannot fully perform its function, thus its optimal performance has to be within a circuit • Plasticity- allows the brain to change from circuit to circuit depending on sensory input and past experience

3. Arrangement of Nervous System Pathways

4. Spinal Cord Protection

5. Neural Tissue: Metabolic Needs • Oxygen • Passes freely across blood-brain barrier • Brain receives 15% of blood pumped by heart • Glucose • Brain responsible for about half of body’s glucose consumption • Membrane transporters move glucose from plasma into the brain interstitial fluid • Hypoglycemia leads to confusion, unconsciousness, and death

6. Spinal Cord: Overview Central nervous system, posterior view The spinal cord has two enlargements and ends in the lumbar region. Spinal nerves are part of the PNS and carry both sensory and motor neuron fibers. Figure 9-4a

7. Spinal Cord: Anatomy Specialization in the spinal cord Figure 9-7a

8. Spinal Cord: Anatomy Propriospinal tracts remain within the cord Tracts carry information in only one direction along a specified path of interneuron connections. Figure 9-7b

9. Spinal Cord: Anatomy Figure 9-7c (1 of 2)

10. Spinal Cord: Integrating Center Simple reflexes can be integrated by the spinal cord without input from the brain Figure 9-8

11. Anatomy of the Brain Oldest and most primitive region of the brain. Ascending and descending tracts pass through the brain stem. Figure 9-9d

12. The Brain: The Brain Stem • Divided into three regions- medulla oblongota, pons, and midbrain • Each region contains cranial nerves & nuclei that control autonomic function • Many nuclei are associated with reticular formation- white fibers what interconnect different areas throughout the brain. • Medulla Oblongata- controls involuntary funtions and connects to spinal cord. • Somatosensory (ascending) and corticospinal (descending) tracts in white matter • Pyramids- area where the fibers cross over thus the many functions are controlled by the opposite side of the brain.

13. 2. Reticular formation- These are clusters of neurons (white matter) that run through the core of the brainstem. Involved in maintaining the brain alert, arousal, and sleep. It also control visceral functions like heart rate & vomiting. A motor tract goes down the spinal cord and is involved in movement. Reticular Formation

14. Cranial Nerves • 10 of 12 cranial nerves originate along brain stem. • Create flash cards for the nerves on table 9.1, be able to identify their location, origin & destination, function, type of information each nerve carries

15. Mid-sagittal View of the Brain

16. The Brain: Diencephalon Thalamus is a relay and integrating station Hypothalamus is the homeostasis center and also controls behavior related to homeostasis Two endocrine structures: pineal and pituitary gland. Figure 9-10

17. The Brain: Hypothalamus The hypothalumus contains many nuclei that focus on the specific functions listed here. Make flashcards of the info on this table

18. The Brain: Cerebellum Lateral view of brain The cerebellum coordinates movement- also processes sensory information and motor input from the cerebrum; it smoothes and coordinates movement. Figure 9-9b

19. Cerebral Mid-Sagittal View Corpus Callosum is white matter that connects the two hemispheres Sulci= grooves Gyri= convolutions Figure 9-9c

20. White Matter in the cerebrum contains fibers that connect various brain areas

21. Gray Matter of the Cerebrum Cerebral cortex is 30 layers thick and it’s the site of higher brain function. The level of processing is directly related to the surface area Basal ganglia- neural calculators that control movement Figure 9-11

22. The Brain: The Limbic System • Emotion, memory, learning, and visceral responses • Links higher cognitive functions and primitive emotional responses • Incorporates sensory areas, basal ganglia, and the diencephalon (hypothalamus) relates state of mind to physiological functions Figure 9-13

23. Brain Function: complex processing and responses • The brain may generate information and output signals in the absence of external input • Motor output is influenced by sensory information, cognition, and behavior. Thus cognitive input may influence the motor output sent without sensory input.

24. Brain Function: Functional Areas of the Cerebral Cortex Specialized sensations have separate designated areas on the cortex Figure 9-15

25. Brain Function: Cerebral Cortex • Three specializations – Sensory, Motor, and Association (cognition and behavior). • Sensory areas - stimulus activates sensory receptors, info travels in ascending pathways and stops at the cerebellum or sensory areas of cerebrum • Sensory input translated into perception – brain’s interpretation of various input regions • Motor areas – info travels in descending pathways, cross-over at brainstem or spinal cord, and reaches muscles or glands • Direct skeletal muscle movement – initiated by cognitive system based on input from cerebral motoer ares, cerebellum, & basal ganglia • Association areas - • Integrate information from sensory and motor areas - • Can direct voluntary behaviors – control over conscious actions

26. Specialized Areas of the Cerebral Cortex

27. Body map along the Precentral and Postcental Gyrus

28. Brain Function: Sensory Information • Primary somatic sensory cortex-found on the post-central gyrus (parietal lobe) • Skin, musculoskeletal system, and viscera- components that send information to this region when a stimulus activates a sensory receptor • Somatosensory pathways – carry information of senses in conscious awareness of general somatic sense, damaged in brain area causes reduced sensitivity in opposite side • Touch • Temperature • Pain • Itch • Body position

29. Brain Function: Sensory Information • Special senses have devoted regions - • Visual cortex –Occipital lobe (Visual Assosiaction area and Visual cortex) • Auditory cortex – Temporal lobe (Auditory association area and Audiotory Cortex • Olfactory cortex- Temporal lobe (uncus) • Gustatory cortex – Frontal lobe • Processed into perception – allows the stimulus to be translated into a different aspect (photons=colors) and “fills-in”missing information. Perception is the brains interpretation of sensory input and it is not directly dictated by the input

30. Brain Function: Motor Output • Three major types • Skeletal muscle movement • Somatic motor division, involves voluntary actions processed at cerebrum or reflexes processed at the spinal cord • Neuroendocrine signals • Hypothalamus and adrenal medulla- secrete neurohormones that influence motor output • Visceral responses • Autonomic division- brains stem and diecephalon stimulate involuntary muscle and glands to maintain involuntary actions needed for function of internal organs and homeostasis • Voluntary movement • Primary motor cortex and motor association- contralateral control, also influence by behavioral and cognitive system

31. Brain Function: Cerebral Lateralization Each lobe has special functions- these are not equally shared by the opposite lobe. Right handed people tend to have left hemisphere dominance. Figure 9-16

32. Brain Function Influenced by Behavioral State • Modulator of sensory and cognitive processes – incorporates the reticular formation, hypothalamus, limbic system, and regions of the cerebral cortex • Neurons known asdiffuse modulatory systems-regulate brain function by affecting attention, motivation, wakefulness, memory, motor control, mood, and metabolic homeostasis • In reticular formation in brain stem- most originate at brain stem and innervate areas of the cerebrum and diencephalon, classified by neurotransmitters used • Four modulatory systems • Adrenergic – secretes norepinephrine, originate at pons, modulate: attention, arousal, sleep-wake cycles, learning, memory, anxiety, pain, and mood. • Serotonergic – secretes serotonin, originate at brain stem midline, modulate pain, movement, sleep-wake cycles, mood, emotion • Dopaminergic – secretes domamine, originate at midbrain, modulate motor control and addictive behaviors • Cholinergic – secrete acetylcholine, originate at cerebrum and brain stem, modulate sensory information pathways through thalamus, arousal, sleep-wake cycles, learning, memory

33. Reticular Formation Pathways for Behavior Systems and Corresponding Neurotransmitters • See table 9-3 for information on neurotransmitter function

34. Behavioral State System: Arousal and Sleep-Wake Cycles • Consciousness- a state of arousal in which the brain is aware of self and environment • Reticular formation- actively interacting through ascending tracts • Anesthetics- block signals from reaching the reticular formation • Electroencephalograms (EGG) • Dectect level of activity of cerebral cortex neurons used electrodes • Awake State- various stage of awareness • Uncoordinate firing of cortical neurons due to ascending signals in reticular formation results in low-amplitude high-frequency waves • As awareness declines signals the frequency of waves declines and amplitute increases • Sleep- major rest period for the body, no external interaction, easily reversible, brain is as active as when awake, sleep inducing factors also boost immunity

35. Behavioral State System: States of Arousal Electroencephalograms (EEGs) and the sleep cycle Wave frequency lessens and amplitude increaes as arousal diminshes During sleep the brain cycles multiple types between all stages Delta waves are high amplitude, low frequency Figure 9-20a

36. Behavioral State System: States of Arousal • Four stages with two major phases • Slow-wave sleep – delta waves, • Adjust body without conscious commands • REM sleep • Brain activity inhibits motor neurons to skeletal muscle, paralyzing them –also reducing homeostasis responses • Dreaming takes place • Circadian rhythm • Suprachiasmatic nucleus- location of neurons that signal light-dark cycle phases and responses

37. Behavioral State System: Emotion and Motivation The link between emotions and physiological functions The amygdala is the center of emotion in the brain Stimulus to Cerebrum- creates perception, limbic creates emotion, cerebrum becomes aware of emotion while hypothalus stimulates multiple responses Figure 9-21

38. Behavioral/Cognitive State : Motivation • Defined as internal signals that shape voluntary behavior (related to survival or emotions) • Some states known as drives create increased arousal, goal-oriented behavior, and disparate behavior to achieve the goal. • Works with autonomic and endocrine responses to maintain homeostasis • Motivated behaviors stop • Satiety Pleasure is related to addictive behaviors which can be changed if given a different motivation.

39. Behavioral State System: Moods • Similar to emotions but longer-lasting- related to sense of being, not purely psychological, related to sense of well-being and proper neurotransmitter function • Mood disorders • Fourth leading cause of illness worldwide today • Depression • Sleep and appetite disturbances • Alteration of mood and libido • Antidepressant drugs alter synaptic transmission – allow a neurotransmitter to remain at the synapse longer, change the receptor, or the amount of NT released.

40. Cognitive State: Learning and Memory • Learning has two broad types • Associative – links two stimuli or a stimulus to a behavior • Nonassociative-change behavior due to repeated exposure • Habituation – do not respond to an irritant stimulus, filters out insignificant stimulus • Sensitization- enhanced response to irritant stimulus, helps avoid harmful stimuli • Memory has several types • Short-term and long-term-combined by working memory, consolidation turns short-term into long term. Changes in synaptic connections are required • Reflexive and declarative-requires unconscious (procedural) or conscious recall (infer, compare, evaluate). Declarative can become reflexive

41. Brain Function: Memory Processing Memory is stored as memory traces Figure 9-22

42. Brain Function: Language Cerebral processing of spoken and visual language Damage to Wernicke’s causes receptive aphasia- unable to understand spoken or visual information Damage to Broca’s area causes expressive aphasia- can understand information but cannot speak or write in proper order, are aware of mistakes Figure 9-23a