Chapter 8 Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 8 outline Structural organization of the brain Cerebrum Diencephalon Midbrain and hindbrain Spinal cord tracts Cranial and spinal nerves 8-2

Structural Organization of the Brain 8-3

Structure Organization of the Brain Consists of brain and spinal cord Receives input from sensory neurons Directs activity of motor neurons Association neurons integrate sensory and motor activity Perform learning and memory 8-4

CNS continued CNS composed of gray and white matter Gray matter consists of neuron bodies and dendrites White matter (myelin) consists of axon tracts Adult brain weighs 1.5kg Contains 100 billion neurons Receives 20% of blood flow to body 8-5

Embryonic Development 8-6

Embryonic Development Neural tube forms from groove in ectoderm by 20th day Becomes the CNS Neural crest cells develop where tube fuses Become ganglia of PNS 8-7

Embryonic Development continued During 4th week, 3 swellings form on neural tube These will become forebrain, midbrain and hindbrain 8-8

Embryonic Development continued During 5th week: Forebrain elaborates into telencephalon and diencephalon Midbrain does not subdivide Hindbrain forms metencephalon and myelencephalon 8-9

Embryonic Development continued Telencephalon grows disproportionately forming hemispheres of cerebrum Ventricles and central canal are remnants of hollow part of neural tube Contain cerebral spinal fluid (CSF) 8-10

Cerebrum 8-11

Cerebrum Is largest part of brain (80% of mass) Is responsible for higher mental functions 8-12

Cerebrum continued Its right and left hemispheres are interconnected by tract of the corpus callosum 8-13

Cerebral Cortex Is highly convoluted An elevated fold is called a gyrus A depressed groove is called a sulcus 8-14

Cerebral Cortex continued Each hemisphere has 5 lobes: frontal, parietal, temporal, occipital and insula 8-15

Cerebral Cortex continued Frontal lobe is separated from parietal by central sulcus Precentral gyrus of frontal lobe is involved in motor control Postcentral gyrus of parietal lobe receives sensory info from areas controlled by precentral gyrus 8-16

Cerebral Cortex continued 8-17

Cerebral Cortex continued Temporal lobe contains auditory centers; receives sensory info from cochlea Also links and processes auditory and visual info 8-18

Cerebral Cortex continued Occipital lobe is responsible for vision and coordination of eye movements 8-19

Cerebral Cortex continued Insula plays role in memory encoding Integrates sensory info with visceral responses Assesses bodily states that accompany emotions 8-20

Visualizing the Brain 8-21

Visualizing the Brain X-ray computed tomography (CT) visualizes soft tissues Positron-emission tomography (PET) is used to examine brain metabolism and blood flow, drug distribution 8-22

Visualizing the Brain continued Magnetic resonance imaging (MRI) shows brain function in the image below Functional MRI (fMRI) shows areas with increased neural activity by tracking blood flow 8-23

Electroencephalogram (EEG) Measures electrical activity of cerebral cortex Used to diagnose epilepsy and brain death 8-24

EEG Waves Alpha waves are recorded from parietal and occipital lobes with person awake, relaxed, eyes closed Beta waves are strongest from frontal lobes; evoked by visual stimuli and mental activity 8-25

EEG Waves continued Theta waves come from temporal and occipital lobes Common in newborns In adults indicates severe emotional stress Delta waves are from cerebral cortex Common during adult sleep and in awake infants In awake adult indicates brain damage 8-26

Sleep 2 types of sleep are recognized REM - rapid eye movement EEGs are similar to awake ones Type when dreaming occurs Non-REM has delta waves Appears to be crucial for consolidation of short- into long-term memory 8-27

Functional Specializations of the Brain 8-28

Cerebral Nuclei Are distinct masses of cell bodies located deep inside cerebrum Function in control of voluntary movement 8-29

Cerebral Nuclei continued Have reciprocal excitatory connections with the cerebral cortex that create a motor circuit 8-30

Cerebral Lateralization Refers to specialization of each hemisphere for certain functions Each cerebral hemisphere controls movement on opposite side of body And receives sensory info from opposite side of body Hemispheres communicate thru the corpus callosum (Fig 8.1) which contains about 200 million fibers 8-31

Cerebral Lateralization continued Left hemisphere possesses language and analytical abilities Right hemisphere is best at visuospatial tasks 8-32

Language Language areas of brain are known mostly from aphasias = speech and language disorders due to brain damage Broca’s area is necessary for speech Wernicke’s area is involved in language comprehension 8-33

Limbic System and Emotion The hypothalamus and limbic system (shown in green) are crucial for emotions Including aggression, fear, feeding, sex and goal-directed behaviors 8-34

Learning and Memory 8-35

Memory Includes short- and long-term memory Involves a number of regions in brain There are two types of long-term memory Non-declarative (explicit) includes memories of simple skills and conditioning Declarative (implicit) includes verbal memories Amnesiacs have impaired declarative memory 8-36

Memory continued Hippocampus is critical for acquiring new memories And consolidating short- into long-term memory Amygdala is crucial for fear memories Storage of memory is in cerebral hemispheres Higher order processing and planning occur in prefrontal cortex 8-37

Long-Term Potentiation (LTP) Glutamate activates AMPA and NMDA postsynaptic receptors in hippocampus Promotes an inc. in Ca2+ concent. in cytoplasm needed for LTP to be induced 8-38

Long-Term Potentiation (LTP) continued Post-synaptic neuron also receive input from other presynpatic neurons (release GABA) GABA’s inihibiton lessened by another retrograde messenger prod. by post-synaptic neuron endocannabinoid as retrograde messenger stim. by depolarization (by glutamate) effect termed—depolariztion-induced suppression of inhibition may also effect LTP 8-39

Neurogenesis in Hippocampus Appears to be crucial for learning and memory Hippocampus contains neural stem cells that continually produce new neurons (neurogenesis) Stress or depression impede learning and cause hippocampus to shrink Stress reduction and antidepressants return size to normal 8-40

Brain Structures and their Functions 8-41

Thalamus and Epithalamus Are located at base of cerebral hemispheres Thalamus is a relay center thru which all sensory info (except olfactory) passes to cerebrum And plays role in level of arousal Epithalamus contains the choroid plexus which secretes CSF Also contains pineal gland which secretes melatonin Involved in sleep cycle and seasonal reproduction 8-42

Hypothalamus Is most important structure for homeostasis Contains neural centers for hunger, thirst, body temperature Regulates sleep, emotions, sexual arousal, anger, fear, pain and pleasure Controls hormone release from anterior pituitary Produces ADH and oxytocin Coordinates sympathetic and parasympathetic actions 8-43

Pituitary Gland Is divided into anterior and posterior lobes Posterior pituitary stores and releases ADH (vasopressin) and oxytocin Both made in hypothalamus and transported to pituitary Hypothalamus produces releasing and inhibiting hormones that control anterior pituitary hormones 8-44

Circadian Rhythms Are body's daily rhythms Regulated by SCN (suprachiasmatic nucleus) of hypothalamus SCN is the master clock Adjusted daily by light from eyes Controls pineal gland secretion of melatonin which regulates circadian rhythms 8-45

Midbrain Contains: Superior colliculi -- involved in visual reflexes Inferior colliculi -- relay auditory information Red nucleus and substantia nigra -- involved in motor coordination S. nigra dopamine neurons degenerate in Parkinson’s 8-46

Midbrain continued Mesolimbic dopamine neurons are involved in reward and addiction Abused drugs cause dopamine release from the nucleus accumbens 8-47

Hindbrain Contains pons, cerebellum and medulla 8-48

Respiratory Control Centers in Brain Stem Contains several nuclei of cranial nerves And 3 important respiratory control centers Apneustic and pneumotaxic centers in pons Rhythmicity center in medulla oblongata 8-49

Cerebellum 2nd largest structure in brain containing 50 billion neurons Receives input from proprioceptors (joint, tendon and muscle receptors) Involved in coordinating movements along with cerebral nuclei and motor areas of cortex 8-50

Medulla Contains all tracts that pass between brain and spinal cord nuclei of cranial nerves And several crucial centers for breathing and cardiovascular systems (vital centers) 8-51

Reticular Activating System (RAS) Is an ascending arousal system that originates in groups of neurons in the pons, midbrain reticular formation, hypothalamus and basal forebrain These project to the cerebral cortex and control its level of arousal Activation of the RAS promotes wakefulness; inhibition promotes sleep 8-52

Spinal Cord 8-53

Spinal Cord Tracts Sensory info from body travels to brain in ascending spinal tracts Motor activity from brains travels to body in descending tracts 8-54

Ascending Spinal Tracts Ascending sensory tracts decussate (cross) so that brain hemispheres receive info from opposite side of body Same for most descending motor tracts from brain 8-55

Descending Spinal Tracts Are divided into 2 major groups: Pyramidal (or corticospinal) tracts descend from cerebral cortex to spinal cord without synapsing Originate in motor cortex Function in control of fine movements 8-56

Descending Spinal Tracts continued Extrapyramidal (or Reticulospinal) tracts descend with many synapses Influence movement indirectly 8-57

Descending Spinal Tracts continued 8-58

Peripheral Nervous System 8-59

Peripheral Nervous System (PNS) Consists of nerves that exit from CNS and spinal cord, and their ganglia (= collection of cell bodies outside CNS) 8-60

Cranial Nerves Consists of 12 pairs of nerves 2 pairs arise from neurons in forebrain 10 pairs arise from midbrain and hindbrain neurons Most are mixed nerves containing both sensory and motor fibers Table 8.7 Summary of Cranial Nerves 8-61

Spinal Nerves Are mixed nerves that separate next to spinal cord into dorsal and ventral roots Dorsal root composed of sensory fibers Ventral root composed of motor fibers 8-62

Spinal Nerves continued There are 31 pairs: 8 cervical pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs, 1 coccygeal pair 8-63

Reflex Arc Is a simple sensory input, motor output circuit involving only peripheral nerves and spinal cord Sometimes arc has an association neuron between sensory and motor neuron 8-64