The Central Nervous System

The Central Nervous System
Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

Outline Organization Protection Overview of components Cortex
Basal nuclei Thalamus Hypothalamus Limbic system Cerebellum Brain stem Spinal cord

Nervous System Organization
Central nervous system (CNS) Consists of brain and spinal cord Peripheral nervous system (PNS) Afferent division Carries information to the CNS Two branches Sympathetic Parasympathetic

Nervous System Organization

Functional Classes of Neurons
Afferent neurons Inform CNS about conditions in both the external and internal environment Efferent neurons Carry instructions from CNS to effector organs – muscles and glands Interneurons Found entirely within CNS Responsible for Integrating afferent information and formulating an efferent response Higher mental functions associated with the “mind”

Neuroglia Also called glial cells
Physically, metabolically, and functionally support interneurons Four major types of cells Astrocytes Oligodendrocytes Microglia Ependymal cells 90% of CNS cells

Neuroglia Astrocytes Oligodendrogytes
Main “glue” of CNS – holds neurons together Guide neurons during fetal brain development Aid in establishment of blood-brain barrier Important in repair of brain injuries and in neural scar formation Play role in neurotransmitter activity Take up excess K+ from brain ECF Along with other glial cells – enhance synapse formation and modify synaptic transmission Oligodendrogytes Form myelin sheaths around axons in CNS Ependymal cells Line internal, fluid-filled cavities of the CNS In ventricles of brain, help form and circulate cerebrospinal fluid Microglia Immune defense cells of the CNS In resting state release low levels of growth factors that help neurons and other glial cells survive and thrive

Fig. 5-4, p. 135 Figure 5.4: Astrocytes.
Note the starlike shape of these astrocytes, which have been grown in tissue culture. Fig. 5-4, p. 135

Subarachnoid space of brain
Cerebrospinal fluid Lateral ventricle (see next slide) Arachnoid villus Dural sinus Venous blood Cerebrum Vein Choroid plexus of lateral ventricle Choroid plexus of third ventricle Third ventricle Pia mater Arachnoid mater Cranial meninges Dura mater Cerebellum Aperture of fourth ventricle Choroid plexus of fourth ventricle Spinal cord Central canal Pia mater Arachnoid mater Spinal meninges Dura mater Brain stem Fourth ventricle Subarachnoid space of spinal cord Fig. 5-6, p. 137

Protection of CNS Enclosed by hard, bony structures
Wrapped by three protective and nourishing membranes – meninges Dura mater Arachnoid mater Pia mater Floats in cushioning fluid – cerebrospinal fluid (CSF) Surrounds and cushions brain and spinal cord Shock absorbing Formed primarily by choroid plexuses Blood-brain barrier limits access of blood-borne materials into brain tissue

Right lateral ventricle Left lateral ventricle Third ventricle
Central canal of spinal cord Fourth ventricle Fig. 5-5, p. 136

Blood-Brain Barrier (BBB)
Protects brain from chemical fluctuations in blood Minimizes possibility that harmful blood-borne substances might reach central nervous tissue Prevents certain circulating hormones that could also act as neurotransmitters from reaching brain Limits use of drugs for treatment of brain and spinal cord disorders Many drugs cannot penetrate BBB Keeps K+ low and Na+ High Cells joined by tight junctions

Central Nervous System
Enables you to: Subconsciously regulate your internal environment by neural means Experience emotions Voluntarily control your movements Be consciously aware of your own body and your surroundings Engage in other higher cognitive processes such as thought and memory

Brain Anatomy Brain components Brain stem Cerebellum Forebrain
Diencephalon Hypothalamus Thalamus Cerebrum Basal nuclei - dystonia Cerebral cortex

Brain component Cerebral cortex Cerebral cortex Basal nuclei Thalamus
(lateral to thalamus) Basal nuclei Thalamus (medial) Thalamus Hypothalamus Hypothalamus Cerebellum Cerebellum TABLE 5-1: Overview of Structures and Functions of the Major Components of the Brain. Midbrain Brain stem (midbrain, pons, and medulla) Brain stem Pons Medulla Spinal cord Table 5-2 (1), p. 140

Brain Stem Critical connecting link between rest of brain and spinal cord Consists of Medulla Pons Midbrain

Brain Stem Functions Most of cranial nerves arise from brain stem
Neuronal clusters within brain stem control heart and blood vessel function, respiration, and many digestive functions Plays role in regulating muscle reflexes involved in equilibrium and posture Reticular formation within brain stem receives and integrates all incoming sensory synaptic input Centers that govern sleep are in brain stem (evidence suggests center promoting slow-wave sleep lies in hypothalamus)

= Motor fibers = Sensory fibers Lateral rectus
1. Olfactory nerve = Sensory fibers Retina Mucosa of nasal cavity 3. Oculomotor nerve 5. Trochlear nerve 2. Optic nerve Termination of fibers of olfactory nerve 6. Abducens nerve Motor— muscles of mastication 4. Trigeminal nerve Olfactory bulb Lateral rectus Sensory—face and head Motor—muscles of face and scalp; salivary and tear glands Sensory— taste buds on anterior tongue mnemonic On olfactory Old optic Olympus oculomotor Towering trochlear Top trigeminal A abducens Famous facial Vocal vestibulocochlear German glossopharyngeal Viewed vagus Some spinal accessory Hops hypoglossal 7. Facial nerve Fig. 5-21, p. 165

8. Vestibulocochelar nerve 9. Glossopharyngeal nerve 12. Hypoglossal
Motor—muscles of pharynx; parotid gland Sensory—taste buds on posterior tongue; receptors in pharynx and carotid sinus = Motor fibers = Sensory fibers Vestibular branch 8. Vestibulocochelar nerve Cochlear branch Cochlea, vestibule, and semicircular canals of inner ear 9. Glossopharyngeal nerve 12. Hypoglossal nerve 10. Vagus nerve 11. Accessory nerve Motor—muscles of pharynx and larynx; thoracic and abdominal organs Tongue muscles Muscles of larynx, pharynx, soft palate, shoulder, and neck Sensory—taste buds on tongue and pharynx; thoracic and abdominal organs Fig. 5-21, p. 165

Cerebellum Important in balance and in planning and executing voluntary movement Three different parts Vestibulocerebellum Important in maintaining balance and controls eye movements Spinocerebellum Enhances muscle tone and coordinates skilled, voluntary movements Cerebrocerebellum Plays role in planning and initiating voluntary activity by providing input to cortical motor areas Stores procedural memories

Cerebellum Attached at top rear portion of brain stem
Maintains proper position of the body in space Subconscious coordination of motor activity (movement) Plays key role in learning skilled motor tasks

Fig. 5-20, p. 163 Figure 5.20: Cerebellum.
(a) Gross structure of the cerebellum. (b) Unfolded cerebellum, revealing its three functionally distinct parts. (c) Internal structure of the cerebellum. Fig. 5-20, p. 163

Diencephalon Houses two brain components Hypothalamus Thalamus
Controls many homeostatic functions important in maintaining stability of internal environment Thalamus Performs some primitive sensory processing

Basal Nuclei Act by modifying ongoing activity in motor pathways
Primary functions Inhibiting muscle tone throughout the body Selecting and maintaining purposeful motor activity while suppressing useless or unwanted patterns of movement Helping monitor and coordinate slow, sustained contractions, especially those related to posture and support negative

Thalamus Part of diencephalon
Serves as “relay station” and synaptic integrating center for processing sensory input on its way to cerebral cortex Along with brain stem and cortical association areas, important in ability to direct attention to stimuli of interest Capable of crude awareness of various types of sensation but cannot distinguish their location or intensity Positive, screener

Hypothalamus Brain area most involved in directly regulating internal environment Functions Controls body temperature Controls thirst and urine output Controls food intake Controls anterior pituitary hormone secretion Produces posterior pituitary hormones Controls uterine contractions and milk ejection Serves as a major ANS coordinating center Plays role in emotional and behavioral patterns Participates in sleep-wake cycle

Limbic System Includes portions of the hypothalamus and other forebrain structures that encircle brain stem Responsible for Emotion Basic, inborn behavioral patterns related to survival and perpetuation of the species Plays important role in motivation and learning

Frontal lobe Cingulate gyrus Fornix Thalamus Hippocampus Temporal lobe
Amygdala Hypothalamus Olfactory bulb Fig. 5-17, p. 153

Cerebrum Highly developed
Makes up about 80% of total brain weight (largest portion of brain) Inner core houses basal nuclei Outer surface is highly convoluted cerebral cortex Highest, most complex integrating area of the brain Plays key role in most sophisticated neural functions

Cerebral Cortex Organized into six well-defined layers
Layers are organized into functional vertical columns Each half of cortex divided into four major lobes Occipital Temporal Parietal Frontal

Central sulcus Frontal lobe Parietal lobe Parietooccipital notch
Lateral fissure Preoccipital notch Temporal lobe Brain stem Cerebellum Fig. 5-8, p. 143

Cerebral cortex Occipital lobe Temporal lobe Parietal lobe
Carries out initial processing of visual input Temporal lobe Initial reception of sound sensation Parietal lobe Somatosensory processing Frontal lobe Responsible for Voluntary motor activity Speaking ability Elaboration of thought

Cerebral Cortex Primary motor cortex Located in frontal lobe
Confers voluntary control over movement produced by skeletal muscles Primarily controls muscles on the opposite side of the body Motor homunculus Depicts location and relative amount of motor cortex devoted to output to muscles of each body part

Figure 5.11: Somatotopic map of the primary motor cortex.
(a) Top view of cerebral hemispheres. (b) Motor homunculus showing the distribution of motor output from the primary motor cortex to different parts of the body. The distorted graphic representation of the body parts indicates the relative proportion of the primary motor cortex devoted to controlling skeletal muscles in each area. Fig. 5-11, p. 145

Figure 5.10: Somatotopic map of the somatosensory cortex.
(a) Top view of cerebral hemispheres. (b) Sensory homunculus showing the distribution of sensory input to the somatosensory cortex from different parts of the body. The distorted graphic representation of the body parts indicates the relative proportion of the somatosensory cortex devoted to reception of sensory input from each area. Fig. 5-10, p. 145

Cerebral Cortex Supplementary motor area Premotor cortex
Plays preparatory role in programming complex sequences of movement Premotor cortex Important in orienting the body and arms toward a specific target Posterior parietal cortex

Cerebral Cortex Primary areas of cortical specialization for language
Broca’s area Governs speaking ability Wernicke’s area Concerned with language comprehension Responsible for formulating coherent patterns of speech Language disorders Aphasias Speech impediments Dyslexia

Supplementary motor area
Primary motor cortex Somatosensory cortex Central sulcus Premotor cortex Posterior parietal cortex Parietal lobe Prefrontal association cortex Wernicke’s area Frontal lobe Parietal-temporal-occipital association cortex Broca’s area Primary auditory cortex Cerebellum Occipital lobe Limbic association cortex Temporal lobe Primary visual cortex Brain stem Spinal cord Fig. 5-9, p. 144

Fig. 5-9b, p. 144 Figure 5.9: Functional areas of the cerebral cortex.
(b) Different areas of the brain “light up” on positron-emission tomography (PET) scans as a person performs different tasks. PET scans detect the magnitude of blood flow in various regions of the brain. Because more blood flows into a particular region of the brain when it is more active, neuroscientists can use PET scans to “take pictures” of the brain at work on various tasks. Fig. 5-9b, p. 144

Cerebral Hemispheres Left cerebral Right cerebral hemisphere
Excels in logical, analytic, sequential, and verbal tasks Math, language forms, philosophy Excels in nonlanguage skills Spatial perception and artistic and musical talents Figure 5.7: Brain of human cadaver. (a) Dorsal view looking down on the top of the brain. Note that the deep longitudinal fissure divides the cerebrum into the right and left cerebral hemispheres. (b) Sagittal view of the right half of the brain. All major brain regions are visible from this midline interior view. The corpus callosum serves as a neural bridge between the two cerebral hemispheres. Longitudinal fissure Fig. 5-7, p. 142

Cerebral Cortex Schematic Linking of Various Regions of the Cortex
Flow of signals

Outline part 2 EEG memory Spinal nerves Reflex arcs

Electroencephalogram (EEG)
Record of postsynaptic activity in cortical neurons “Brain waves” Three major uses Clinical tool in diagnosis of cerebral dysfunction Used in legal determination of brain death Used to distinguish various stages of sleep

Electroencephalogram (EEG)

Memory Storage of acquired knowledge for later recall Memory trace
Neural change responsible for retention or storage of knowledge Short-term memory Lasts for seconds to hours Long-term memory Retained for days to years Consolidation Process of transferring and fixing short-term memory traces into long-term memory stores Working memory Temporarily holds and interrelates various pieces of information relevant to a current mental task

Comparison of Long-Term and Short-Term Memory

Decreased response to continued stimuli Increased response
Habituation (in Aplysia) Sensitization (in Aplysia) Repetitious indifferent stimulus Strong or noxious stimulus Release of serotonin from facilitating interneuron Decreased response to continued stimuli Increased response to continued stimuli Cyclic AMP in presynaptic neuron Blockage of K+ channels in presynaptic neuron Prolongation of action potential in presynaptic neuron Closing of Ca2+ channels in presynaptic neuron Ca2+ channels in presynaptic neuron kept open longer Ca2+ influx Ca2+ influx Output of transmitter from presynaptic neuron Output of transmitter from presynaptic neuron Postsynaptic potential in efferent neuron Postsynaptic potential in efferent neuron Reduced behavioral response to indifferent stimuli Enhanced behavioral response to mild stimuli Fig. 5-18, p. 160

Long Term Potentiation
Figure 5.19: Possible pathways for long-term potentiation. Prolonged increase in the strength of existing synaptic Connections in activated pathways following brief periods of repeated stimulation Fig. 5-19, p. 162

Presynaptic neuron Nitric oxide Glutamate release release Ca2+ NMDA
receptor AMPA receptor Ca2+ entry (increases availability of AMPA receptor) Ca2+-dependent second messenger system Excitatory postsynaptic potentials (brings about nitric oxide release) Postsynaptic neuron Fig (1), p. 162

Sleep Function of sleep is unclear Sleep-wake cycle
Normal cyclic variation in awareness of surroundings Active process consisting of two types of sleep characterized by different EEG patterns and different behaviors Slow-wave sleep Paradoxical, or REM sleep

Comparison of Slow-Wave and Paradoxical Sleep

EEG Patterns During Different Types of Sleep

Spinal Cord Extends from brain stem through vertebral canal
31 pairs of spinal nerves emerge from spinal cord through spaces formed between arches of adjacent vertebrae Named for region of vertebral column from which they emerge 8 pairs cervical (neck) nerves 12 pairs thoracic (chest) nerves 5 pairs lumbar (abdominal) nerves 5 pairs sacral (pelvic) nerves 1 pair coccygeal (tailbone) nerves

Spinal Nerves

Spinal Cord Two vital functions Neuronal link between brain and PNS
Integrating center for spinal reflexes

Reflex Reflex Two types of reflexes
Any response that occurs automatically without conscious effort Two types of reflexes Simple, or basic, reflexes Built-in, unlearned responses Acquired, or conditioned, reflexes Result of practice and learning

Reflex Arc Neural pathway involved in accomplishing reflex activity
Five basic components Receptor Afferent pathway Integrating center Efferent pathway effector

Crossed Extensor Reflex Coupled with the Withdrawal Reflex

Cerebrum (the right hemisphere, At the longitudinal fissure
Between it and the left hemisphere) Hypothalamus Thalamus Pineal gland Corpus callosum Optic chiasm Figure 5.7: Brain of human cadaver. (a) Dorsal view looking down on the top of the brain. Note that the deep longitudinal fissure divides the cerebrum into the right and left cerebral hemispheres. (b) Sagittal view of the right half of the brain. All major brain regions are visible from this midline interior view. The corpus callosum serves as a neural bridge between the two cerebral hemispheres. Midbrain Brain stem Pons Medulla Cerebellum Fig. 5-7, p. 142

Fig. 5-7, p. 142

Figure 5.11: Somatotopic map of the primary motor cortex.
(a) Top view of cerebral hemispheres. Fig. 5-11a, p. 145

Front Left Right hemisphere hemisphere Frontal lobe Primary motor
cortex Central sulcus Top view Parietal lobe Somato- sensory cortex Occipital lobe Back Fig. 5-11a, p. 145

Motor homunculus Left hemisphere Cross-sectional view Temporal lobe
Fig. 5-11a, p. 145

Figure 5.12: Cortical pathway for speaking a written word or naming a visual object.
The red arrows and circled numbers with accompanying explanation indicate the pathway used to speak about something seen. Similarly, appropriate muscles of the hand can be commanded to write the desired words. Fig. 5-12, p. 148

(somatosensory, 1o visual,
Sensory input Primary sensory areas (somatosensory, 1o visual, 1o auditory cortices) Higher sensory areas Association areas Higher motor areas Primary motor areas Motor output Stepped art Fig. 5-13, p. 149

Eyes closed Eyes open Eyes closed Alpha waves Beta waves Alpha waves
Fig. 5-14, p. 150

(part of hypothalamus)
Right cerebral hemisphere Left cerebral hemisphere Cerebral cortex (gray matter) White matter Corpus callosum Lateral ventricles Caudate nucleus Basal nuclei (gray matter) Thalamus Putamen Third ventricle Globus pallidus Claustrum Mamillary bodies (part of hypothalamus) Fig. 5-15a, p. 152

Fig. 5-15b, p. 152 Figure 5.15: Frontal section of the brain.
(b) Photograph of a frontal section of the brain of a cadaver. Fig. 5-15b, p. 152

Top Part of the limbic system Corpus callosum Cerebral cortex Front of
brain Thalamus (wall of third ventricular cavity) Bridge that connects the two halves of the thalamus Pineal gland Hypothalamus Cerebellum Pituitary gland Brain stem Spinal cord Fig. 5-16, p. 153

Table 5-3, p. 156

Habituation (in Aplysia) Sensitization (in Aplysia)
Repetitious indifferent stimulus Strong or noxious stimulus Release of serotonin from facilitating interneuron Cyclic AMP in presynaptic neuron Blockage of K+ channels in presynaptic neuron Prolongation of action potential in presynaptic neuron Closing of Ca2+ channels in presynaptic neuron Ca2+ channels in presynaptic neuron kept open longer Ca2+ influx Ca2+ influx Output of transmitter from presynaptic neuron Output of transmitter from presynaptic neuron Postsynaptic potential in efferent neuron Postsynaptic potential in efferent neuron Reduced behavioral response to indifferent stimuli Enhanced behavioral response to mild stimuli Fig. 5-18, p. 160

Figure 5.19: Possible pathways for long-term potentiation.
Fig. 5-19, p. 162

Figure 5.19: Possible pathways for long-term potentiation.
Fig (1), p. 162

Presynaptic neuron Nitric oxide Glutamate release release Ca2+ NMDA
receptor AMPA receptor Ca2+ entry (increases availability of AMPA receptor) Ca2+-dependent second messenger system Excitatory postsynaptic potentials (brings about nitric oxide release) Postsynaptic neuron Fig (1), p. 162

Fig. 5-20, p. 163 Figure 5.20: Cerebellum.
(a) Gross structure of the cerebellum. (b) Unfolded cerebellum, revealing its three functionally distinct parts. (c) Internal structure of the cerebellum. Fig. 5-20, p. 163

Reticular activating system Cerebellum Visual impulses Reticular
formation Brain stem Auditory impulses Spinal cord Ascending sensory tracts Descending motor tracts Fig. 5-22, p. 166

Table 5-4, p. 166

Slow-wave sleep, stage 4 Paradoxical sleep Awake, eyes open
Fig. 5-23, p. 167

Spinal cord Dorsal root ganglion Spinal nerve Meninges (protective
coverings) Vertebra Intervertebral disk Sympathetic ganglion chain Fig. 5-24, p. 168

Cervical Cervical cord nerves Vertebrae Thoracic nerves Thoracic cord
Lumbar nerves Lumbar cord Cauda equina Sacral nerves Sacral cord Coccygeal nerve Fig. 5-25, p. 169

White matter Gray matter Cell body of efferent neuron Interneuron
afferent neuron Dorsal root Dorsal root ganglion Efferent fiber From receptors To effectors Ventral root Spinal nerve Fig. 5-26, p. 170

Ascending tracts Descending tracts Dorsal surface Gray matter
Dorsal columns: 1. Fasciculus gracilis 2. Fasciculus cuneatus Dorsal spinocerebellar Ventral spinocerebellar Lateral spinothalamic Ventral spinothalamic Lateral corticospinal Rubrospinal Ventral corticospinal Vestibulospinal Gray matter Ventral surface Fig. 5-27, p. 170

Ascending tracts Descending tracts 1 2 3 4 5 6
Primary motor cortex Somatosensory area of cerebral cortex Thalamus 1 Cerebral cortex slice 1 2 3 4 Midbrain slice 2 5 Cerebellum slice 3 Ventral corticospinal tract Pons Ventral spinocerebellar tract slice 3 6 Lateral corticospinal tract Medulla slice 4 Muscle stretch receptor Fasciculus cuneatus Spinal cord slice 5 Pressure receptor in skin Spinal cord slice 5 Spinal cord slice 6 Fig. 5-28, p. 172

Dorsal horn (cell bodies of interneurons
on which afferent neurons terminate) Lateral horn (cell bodies of autonomic efferent nerve fibers) Central canal Ventral horn (cell bodies of somatic efferent neurons) Fig. 5-29, p. 173

Axon Myelin sheath Connective tissue around the axon Connective tissue
around a fascicle Connective tissue around the nerve Blood vessels Nerve fascicle (many axons bundled in connective tissue) Nerve Fig. 5-30, p. 173

= Inhibitory interneuron = Excitatory interneuron = Synapse = Inhibits
= Stimulates Components of a reflex arc Receptor Afferent pathway Integrating center Efferent pathway Effector organs Thermal pain receptor in finger Ascending pathway to brain Afferent Pathway Stimulus Biceps (flexor) contracts Efferent pathway Integrating center (spinal cord) Triceps (extensor) relaxes Hand withdrawn Effector organs Response Fig. 5-31, p. 174

Afferent pathway Efferent pathway Efferent pathway Integrating center
(spinal cord) Flexor muscle contracts Extensor muscle relaxes Flexor muscle relaxes Extensor muscle contracts Injured extremity (effector organ) Opposite extremity (effector organ) Pain receptor in heel Response Stimulus Response Fig. 5-32, p. 175

Neuroglia Oligodendroglia Schwann Astrocytes Microglia Ependymal
Wrap axons to form myelin One for many axons Wrap axons to form myelin 1:1 ratio 1000’s per long axon Remove debris Control K+,pH Diverse Regulate Neurotransmitters Regulation of pH Glial end feet Reactive- responds to injury Defensive cells Migrate to damaged vessels Epithelial lining of ventricles and canals

Subarachnoid space of brain
Cerebrospinal fluid Lateral ventricle (see next slide) Arachnoid villus Dural sinus Venous blood Cerebrum Vein Choroid plexus of lateral ventricle Choroid plexus of third ventricle Third ventricle Pia mater Arachnoid mater Cranial meninges Dura mater Cerebellum Aperture of fourth ventricle Choroid plexus of fourth ventricle Spinal cord Central canal Pia mater Arachnoid mater Spinal meninges Dura mater Brain stem Fourth ventricle Subarachnoid space of spinal cord Fig. 5-6, p. 137

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