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Chapter 13 Central Nervous System 1 Mosby items and derived items © 2007, 2003 by Mosby, Inc. Coverings of the Brain and Spinal Cord Two protective coverings: Outer covering is bone Inner covering is the meninges continues inside the spinal cavity beyond the end of the spinal cord 2 Coverings of the Brain and Spinal Cord Meninges 3 membranous layers Dura mater strong, white fibrous tissue outer layer of meninges and inner periosteum of the cranial bones Arachnoid mater delicate, cobwebby layer between the dura mater and pia mater 3 Coverings of the Brain and Spinal Cord Meninges 3 membranous layers (cont.) Pia mater innermost, transparent layer adheres to the outer surface of the brain and spinal cord 4 5 Cerebrospinal Fluid Functions Provides a supportive, protective cushion Reservoir of circulating fluid, which is monitored by the brain to detect changes in the internal environment Fluid spaces Cerebrospinal fluid— found around the brain and spinal cord 6 Cerebrospinal Fluid Fluid spaces (cont.) Ventricles— fluidfilled spaces within the brain; four ventricles within the brain 7 Spinal Cord Structure of the spinal cord Oval cylinder that tapers slightly from above downward Two bulges, one in the cervical region and one in the lumbar region 8 9 Spinal Cord Structure of the spinal cord (cont.) Nerve roots Fibers Carry sensory information into the spinal canal Fibers of dorsal nerve root of ventral nerve root Carry motor information out of the spinal cord Interneurons are located in the spinal cord’s gray matter core 10 Ventral (anterior) nerve root Dorsal (posterior) nerve root 11 Spinal Cord Structure of the spinal cord (cont.) Gray matter Consists predominantly of cell bodies of interneurons and motor neurons In transverse section, looks like an H White matter Surrounds the gray matter consists of a large bundle of axons divided into tracts 12 Spinal Cord Functions of the spinal cord Provides conduction routes to and from the brain Ascending tracts (sensory)— conduct impulses up the cord to the brain Descending tracts (motor)— conduct impulses down the cord from the brain Bundles of axons compose all tracts 13 Spinal Cord Functions of the spinal cord (cont.) Important ascending (sensory) tracts = BLUE crude touch, pain, and temperature pressure discriminating touch and conscious kinesthesia (proprioception) subconscious kinesthesia touch related to visual reflexes 14 Spinal Cord Functions of the spinal cord (cont.) Important descending (motor) tracts voluntary movements on opposite side of the body voluntary movements on same side of body maintain posture during movement transmit impulses that coordinate body movements and maintenance of posture head and neck movements during visual reflexes coordination of posture and balance Spinal cord— reflex center for all spinal reflexes reflex centers are located in the gray matter of the cord 15 16 The Brain Structures of the brainstem Medulla oblongata Lowest part of the brainstem Composed of white matter and a network of gray and white matter called the reticular formation Nuclei— clusters of neuron cell bodies located in the reticular formation 17 The Brain Structures of the brainstem (cont.) Pons Located above the medulla and below the midbrain Composed of white matter and reticular formation Midbrain Located above the pons and below the cerebrum; forms the midsection of the brain Composed conduct Red of white tracts and reticular formation impulses between the midbrain and cerebrum nucleus and substantia nigra (“black matter”) clusters of cell bodies of neurons involved in muscular control 18 The Brain Functions of the brainstem Performs sensory, motor, and reflex functions Nuclei in medulla— contain reflex centers Of primary importance— cardiac, vasomotor, and respiratory centers Nonvital reflexes— vomiting, coughing, sneezing, etc. Pons— help regulate respiration 19 The Brain Structure of the cerebellum Gray matter makes up the cortex, and white matter predominates in the interior Cerebellum has numerous sulci (groove) and delicate, gyri (raised areas) 20 The Brain Functions of the cerebellum coordinates movements to produce the intended action General functions produce skilled movements by coordinating the activities of muscles maintains balance Controls posture smooth movements and make movements efficient and coordinated Processes sensory information 21 Stand Up! 22 The Brain Diencephalon Located between the cerebrum and the midbrain Consists of several structures: thalamus, hypothalamus, pineal gland, and several others Thalamus Dumbbell-shaped mass of gray matter made up of many nuclei plays role in processing auditory and visual input 23 24 The Brain Thalamus (cont.) Serves as a major relay station for sensory impulses on their way to the cerebral cortex Performs the following primary functions: Two parts for sensations: conscious recognition of the crude, less critical sensations of pain, temperature, and touch Neurons relay all kinds of sensory impulses, except possibly olfactory, to the cerebrum emotions by associating sensory impulses with feeling of pleasantness and unpleasantness arousal mechanism 25 The Brain Diencephalon (cont.) Hypothalamus lies beneath (hypo) the thalamus Small but functionally important area of the brain, performs many functions of greatest importance for survival and enjoyment Links mind and body Links nervous system to endocrine system 26 The Brain Hypothalamus (cont.) Summary of hypothalamic functions Regulator and coordinator of autonomic activities Major relay station between the cerebral cortex and lower autonomic centers crucial part of the route by which emotions can express themselves in changed bodily functions maintaining water balance arousal mechanism regulating appetite maintaining normal body temperature 27 The Brain Diencephalon (cont.) Pineal gland Involved in regulating the body’s biological clock Produces melatonin as a “timekeeping hormone” Melatonin is made from the neurotransmitter serotonin Melatonin levels increase when sunlight is absent and decreases when sunlight is present, thus regulating the circadian (daily) biological clock (Figure 13-15) Melatonin is the “sleep hormone” 28 29 The Brain Structure of the cerebrum Cerebral cortex Largest and uppermost division of the brain consists of right and left cerebral hemispheres each hemisphere is divided into four lobes: Frontal lobe Parietal lobe Temporal lobe Occipital lobe 30 31 The Brain Cerebral cortex (cont.) Cerebral cortex— outer surface made up of six layers of gray matter Gyri— raised areas Sulci— shallow grooves 32 The Brain Cerebral cortex (cont.) Fissures— deeper grooves, divide each cerebral hemisphere into lobes Central sulcus— groove between frontal and parietal lobes Lateral fissure— groove between temporal lobe below and parietal lobes above 33 Structure of the cerebrum Basal nuclei (or cerebral nuclei) Basal nuclei— islands of gray matter located deep inside the white matter of each hemisphere Unsure of exact function but important in regulating voluntary motor functions, especially repetitive actions Example: maintaining posture, walking 34 The Brain Functions of the cerebral cortex Certain areas of cortex have certain functions Transverse gyrus— auditory area Occipital lobe— visual areas Precentral gyrussomatic motor Postcentral gyrussomatic sensory 35 The Brain Functions of the cerebral cortex (cont.) Sensory functions of the cortex Cortex contains a “somatic sensory map” of the body Senses send information to primary sensory areas, as well as to other parts of the brain 36 The Brain Motor functions of the cortex For normal movements to occur, many parts of the nervous system must function Precentral gyrus primary somatic motor area controls individual muscles Secondary motor area (premotor) in the gyrus immediately anterior to the precentral gyrus activates groups of muscles simultaneously 37 The Brain Integrative functions of the cortex Consciousness State of awareness of one’s self, one’s environment, and other beings Depends on excitation of neurons from the reticular formation Two about reticular activating system: Functions as the alert system for the cerebral cortex Its functioning is crucial for maintaining consciousness 38 The Brain Integrative functions of the cortex (cont) Language Ability to speak and write words AND ability to understand spoken and written words Left cerebral hemisphere contains speech centers in approximately 90% of the population FYI: Explains Broca’s and Wernicke’s area 39 The Brain Integrative functions of the cortex (cont.) Emotions Limbic system— also known as the “emotional brain” hippocampus Have primary connections with other parts of the brain, such as thalamus, amygdaloid nucleus, and hypothalamus FYI: removal of hippocampus causes inability to recall new info 40 The Brain Integrative functions of the cortex (cont) Memory One of the major human mental activities Cortex is capable of storing and retrieving both short- and long-term memory Temporal, parietal, and occipital lobes are among the areas responsible for short- and long-term memory Cerebrum’s limbic system plays a key role in memory 41 The Brain Right and left hemispheres of the cerebrum specialize in different functions Both sides communicate with each other to accomplish complex functions Left hemisphere is responsible for: Language functions Dominating control of certain hand movements Right hemisphere is responsible for: Auditory Tactual perception Perceiving and visualizing spatial relationships 42 Cycle of Life: Central Nervous System The development and degeneration of the CNS is the most obvious functional change over the life span Development of the brain and spinal cord begins in the womb Lack of development in the newborn is evidenced by lack of: Language- both speech and reading Comprehension of spatial relationships Complex motor skills- walking 43 Cycle of Life: Central Nervous System Complex functions develop by adulthood Late adulthood— tissues degenerate Profound degeneration— unable to perform complex functions Milder degeneration— temporary memory lapse or difficulty with complex motor tasks 44 The Big Picture: The Central Nervous System and the Whole Body Central nervous system ultimate regulator of the body essential to survival Able to integrate bits of information from all over the body, make sense of them, and make decisions 45