Brain Chapter 11 Nervous System II Spinal cord Meninges of the brain Meninges membranes surrounding CNS protect CNS three layers dura mater outer, tough arachnoid mater thin, weblike pia mater inner, very thin 1 2 Meninges of the Spinal Cord interconnected cavities within cerebral hemispheres and brain stem continuous with central canal of spinal cord filled with cerebrospinal fluid (CSF) Ventricles lateral ventricles third ventricle fourth ventricle cerebral aqueduct 3 4 1
Cerebrospinal Fluid Spinal Cord secreted by choroid plexus circulates in ventricles, central canal of spinal cord, and subarachnoid space completely surrounds brain and spinal cord clear liquid nutritive and protective helps maintain stable ion concentrations in CNS slender column of nervous tissue continuous with brain extends downward through vertebral canal begins at level of foramen magnum and terminates near first and second lumbar 5 6 Cross Section of Spinal Cord Functions of Spinal Cord center for spinal reflexes conduit for nerve impulses to and from the brain 7 8 2
Reflex Arcs Reflex Arcs Reflexes automatic, subconscious responses to stimuli within or outside the body 9 10 General Components of a Spinal Reflex Tracts of the Spinal Cord Ascending tracts conduct sensory impulses to the brain Descending tracts conduct motor impulses from the brain to motor neurons reaching muscles and glands 11 12 3
Brain Brain Functions Major Parts interprets sensations cerebrum determines perception two hemispheres stores memory basal nuclei reasoning diencephalon makes decisions brainstem coordinates muscular cerebellum movements regulates visceral activities determines personality 13 14 Structure of Cerebrum corpus callosum connects cerebral hemispheres convolutions bumps or gyri sulci shallow grooves fissures Deep grooves longitudinal fissure separates hemispheres transverse fissure separates cerebrum from cerebellum 15 Lobes of Cerebral Hemispheres Frontal Parietal Temporal Occipital Insula 16 4
Functions of the Cerebrum interpreting impulses initiating voluntary movements storing information as memory retrieving stored information reasoning seat of intelligence and personality Functional Regions of Cerebral Cortex Cerebral Cortex thin layer of gray matter that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system 17 18 Sensory Areas Association Areas Cutaneous Sensory Area parietal lobe interprets sensations on skin Visual Area occipital lobe interprets vision Auditory Area temporal lobe interprets hearing Sensory Area for Taste near bases of the central sulci Sensory Area for Smell arise from centers deep within the cerebrum regions that are not primary motor or primary sensory areas widespread throughout the cerebral cortex analyze and interpret sensory experiences provide memory, reasoning, verbalization, judgment, emotions 19 20 5
Association Areas Hemisphere Dominance Frontal Lobe Association Areas concentrating planning complex problem solving Parietal Lobe Association Areas understanding speech choosing words to express thought Temporal Lobe Association Areas interpret complex sensory experiences store memories of visual scenes, music, and complex patterns Occipital Lobe Association Areas analyze and combine visual images with other sensory experiences The left hemisphere is dominant is most individuals Dominant hemisphere controls speech writing reading verbal skills analytical skills computational skills Nondominant hemisphere controls nonverbal tasks motor tasks understanding and interpreting musical and visual patterns provides emotional and intuitive thought processes 21 22 Primary Motor Areas frontal lobes control voluntary muscles Broca s Area anterior to primary motor cortex usually in left hemisphere controls muscles needed for speech Frontal Eye Field above Broca s area controls voluntary movements of eyes and Motor Areas masses of gray matter deep within the cerebral hemispheres interact with other areas of the brain to facilitate voluntary movement Basal Nuclei eyelids 23 24 6
Memory Memory is a consequence of leaning Brain Waves Recordings of the activity of the cerebral cortex Short Term Thought to be electric in nature working memory closed neuronal circuit circuit is stimulated over and over when impulse flow ceases, memory does also unless it enters long-term memory via memory consolidation Long Term changes structure or function of neurons enhances synaptic transmission 25 Alpha waves - awake by resting Beta waves (higher frequency) - person is actively engaged in mental activity or under tension Theta waves (lower frequency) - normal in children, some adults produce them in early stages of sleep or times of emotional stress Delta waves - occur during sleep 26 Diencephalon between cerebral hemispheres and above the brainstem surrounds third ventricle thalamus hypothalamus optic tracts optic chiasma infundibulum posterior pituitary mammillary bodies pineal gland 27 Diencephalon Thalamus gateway for sensory impulses heading to cerebral cortex receives all sensory impulses (except smell) channels impulses to appropriate part of cerebral cortex for interpretation Hypothalamus maintains homeostasis by regulating visceral activities links nervous and endocrine systems Other parts Optic tract and optic chiasma, infundibulum, pituitary gland, mammillary bodies, and pineal gland 28 7
Diencephalon Brain Stem Limbic System Consists of portions of frontal lobe portions of temporal lobe hypothalamus thalamus basal nuclei other deep nuclei Functions controls emotions produces feelings interprets sensory impulses Three Parts 1. Midbrain 2. Pons 3. Medulla Oblongata 29 30 Midbrain Pons between diencephalon and pons contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain cerebral aqueduct cerebral peduncles bundles of nerve fibers corpora quadrigemina centers for visual and auditory reflexes rounded bulge on underside of brainstem between medulla oblongata and midbrain helps regulate rate and depth of breathing relays nerve impulses to and from medulla oblongata and cerebellum Transmits impulses between the cerebrum and centers within the cerebellum 31 32 8
Medulla Oblongata Reticular Formation enlarged continuation of spinal cord conducts ascending and descending impulses between brain and spinal cord contains cardiac, vasomotor, and respiratory control centers contains various nonvital reflex control centers (coughing, sneezing, swallowing, vomiting) complex network of nerve fibers scattered throughout the brain stem extends into the diencephalon connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum filters incoming sensory information arouses cerebral cortex into state of wakefulness 33 34 Types of Sleep Slow Wave Rapid Eye Movement (REM) non-rem sleep paradoxical sleep person is tired some areas of brain active decreasing activity of heart and respiratory rates reticular system irregular restful dreaming occurs dreamless reduced blood pressure and respiratory rate ranges from light to heavy alternates with REM sleep 35 inferior to occipital lobes posterior to pons and medulla oblongata two hemispheres vermis connects hemispheres cerebellar cortex gray matter arbor vitae white matter cerebellar peduncles nerve fiber tracts dentate nucleus largest nucleus in cerebellum integrates sensory information concerning position of body parts coordinates skeletal muscle activity maintains posture Cerebellum 36 9
Peripheral Nervous System Structure of a Peripheral Nerve Consists of the nerves that branch from the CNS Cranial nerves arising from the brain Somatic fibers connecting to the skin and skeletal muscles Autonomic fibers connecting to viscera Spinal nerves arising from the spinal cord Somatic fibers connecting to the skin and skeletal muscles Autonomic fibers connecting to viscera Connective tissue coverings epineurium outer, dense covering perineurium middle layer of loose connective tissue endoneurium inner layer made up of a small amount of loose connective tissue 37 38 Nerve Fiber Classification Nerve Fiber Classification Sensory Nerves conduct impulses into brain or spinal cord Motor Nerves conduct impulses to muscles or glands Mixed Nerves contain both sensory nerve fibers and motor nerve fibers; most nerves General somatic efferent fibers carry motor impulses from CNS to skeletal muscles General visceral efferent fibers carry motor impulses away from CNS to smooth muscles and glands General somatic afferent fibers carry sensory impulses to CNS from skin and skeletal muscles General visceral afferent fibers carry sensory impulses to CNS from blood vessels and internal organs 39 40 10
Nerve Fiber Classification Special somatic efferent fibers carry motor impulses from brain to muscles used in chewing, swallowing, speaking, and forming facial expressions Cranial Nerves Special visceral afferent fibers carry sensory impulses to brain from olfactory and taste receptors Special somatic afferent fibers carry sensory impulses to brain from receptors of sight, hearing, and equilibrium 41 42 Functions of Cranial Nerves Spinal Nerves mixed nerves 31 pairs 8 cervical (C1 to C8) 12 thoracic (T1 to T12) 5 lumbar (L1 to L5) 5 sacral (S1 to S5) 1 coccygeal (Co) 43 44 11
Dorsal root (posterior or sensory root) axons of sensory neurons in the dorsal root ganglion Spinal Nerves Ventral root (anterior or motor root) axons of motor neurons whose cell bodies are in spinal cord Spinal Nerves Dorsal root ganglion cell bodies of sensory neurons whose axons conduct impulses inward from peripheral body parts Spinal nerve union of ventral root and dorsal root 45 46 Autonomic Nervous System Autonomic Nerve Fibers functions without conscious effort controls visceral activities regulates smooth muscle, cardiac muscle, and glands efferent fibers typically lead to ganglia outside CNS Two Divisions sympathetic prepares body for fight or flight situations parasympathetic prepares body for resting and digesting activities Most organs have dual innervation 47 all are neurons are motor (efferent) preganglionic fibers axons of preganglionic neurons neuron cell bodies in CNS postganglionic fibers axons of postganglionic neurons neuron cell bodies in ganglia 48 12
Control of Autonomic Activity Controlled largely by CNS Medulla oblongata regulates cardiac, vasomotor and respiratory activities Hypothalamus regulates visceral functions, such as body temperature, hunger, thirst, and water and electrolyte balance Limbic system and cerebral cortex control emotional Life-Span Changes Brain cells begin to die before birth Over average lifetime, brain shrinks 10% Most cell death occurs in temporal lobes By age 90, frontal cortex has lost half its neurons Number of dendritic branches decreases Decreased levels of neurotransmitters Fading memory Slowed responses and reflexes Increased risk of falling Changes in sleep patterns that result in fewer sleeping hours responses 49 50 Clinical Application Cerebral Injuries and Abnormalities Concussion brain jarred against cranium loss of consciousness temporary loss of memory mental cloudiness headache recovery usually complete Cerebrovascular Accident stroke sudden interruption in blood flow brain tissues die Cerebral Palsy motor impairment at birth caused by blocked cerebral blood vessels during development seizures learning disabilities 51 13