Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 7

Neurons and Supporting Cells 7-3

Nervous System (NS)  Is divided into:  Central nervous system (CNS)  = brain and spinal cord  Peripheral nervous system (PNS)  = cranial and spinal nerves 7-4

Nervous System (NS) continued  Consists of 2 kinds of cells:  Neurons and supporting cells (= glial cells)  Neurons are functional units of NS  Glial cells maintain homeostasis  Are 5X more common than neurons 7-5

Neurons 7-6

Neurons  Gather and transmit information by:  Responding to stimuli  Producing and sending electrochemical impulses  Releasing chemical messages 7-7

Neurons continued  Have a cell body, dendrites and axon  Cell body contains the nucleus 7-8

Neurons continued  Cell body is the nutritional center and makes macromolecules  Groups of cell bodies in CNS are called nuclei; in PNS are called ganglia 7-9

Neurons continued  Dendrites receive information, convey it to cell body  Axons conduct impulses away from cell body 7-10

Neurons continued  Long axon length necessitates special transport systems:  Axoplasmic flow moves soluble compounds toward nerve endings  Via rhythmic contractions of axon 7-11

Neurons continued  Axonal transport moves large and insoluble compounds bidirectionally along microtubules; very fast  Anterograde transport moves materials away from cell body  Uses the molecular motor kinesin  Retrograde transport moves materials toward cell body  Uses the molecular motor dynein  Viruses and toxins can enter CNS this way 7-12

Functional Classification of Neurons  Sensory/Afferent neurons conduct impulses into CNS  Motor/Efferent neurons carry impulses out of CNS  Association/ Interneurons integrate NS activity  Located entirely inside CNS 7-13

Structural Classification of Neurons  Pseudounipolar:  Cell body sits along side of single process  e.g. sensory neurons  Bipolar:  Dendrite and axon arise from opposite ends of cell body  e.g. retinal neurons  Multipolar:  Have many dendrites and one axon  e.g. motor neurons 7-14

Supporting/Glial Cells 7-15

Supporting/Glial Cells  PNS has Schwann and satellite cells  Schwann cells myelinate PNS axons 7-16

Supporting/Glial Cells continued  CNS has oligodendrocytes, microglia, astrocytes and ependymal cells 7-17

Supporting/Glial Cells continued  Each oligodendrocyte myelinates several CNS axons  Ependymal cells appear to be neural stem cells  Other glial cells are involved in NS maintenance 7-18

Myelination  In PNS each Schwann cell myelinates 1mm of 1 axon by wrapping round and round axon  Electrically insulates axon 7-19

Myelination continued  Uninsulated gap between adjacent Schwann cells is called the node of Ranvier 7-20

Axon Regeneration  Occurs much more readily in PNS than CNS  Oligodendrocytes produce proteins that inhibit regrowth  And form glial scar tissue that blocks regrowth 7-21

Nerve Regeneration continued  When axon in PNS is severed:  Distal part of axon degenerates  Schwann cells survive; form regeneration tube  Tube releases chemicals that attract growing axon  Tube guides regrowing axon to synaptic site 7-22

Astrocytes  Most common glial cell  Involved in:  Buffering K+ levels  Recycling neurotransmitters  Regulating adult neurogenesis  Releasing transmitters that regulate neuronal activity 7-24

Blood-Brain Barrier  Allows only certain compounds to enter brain  Formed by capillary specializations in brain  That appear to be induced by astrocytes  Capillaries are not as leaky as those in body  Gaps between adjacent cells are closed by tight junctions 7-25

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

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 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

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

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

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

 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 Cerebral Lateralization 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

Brain Structures and their Functions 8-41

Diencephalon  Part of the forebrain that contains thalamus, hypothalamus, and part of the pituitary gland  Most of its functions relate directly or indirectly to:  Regulation of visceral activities  Autonomic nervous system

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

Midbrain  Also called mesencephalon  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 8-47

Hindbrain  Contains pons, cerebellum and medulla 8-48

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

 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 Cerebellum 8-50

 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) Medulla 8-51