Transcript Slide 1
The Cerebellum • 11% of brain mass • Dorsal to the pons and medulla • precise timing and appropriate patterns of skeletal muscle contraction • Sports Cognitive Function of the Cerebellum • sequences of events during complex movements • nonmotor functions such as word association and puzzle solving Anterior lobe Cerebellar cortex Arbor vitae Cerebellar peduncles • Superior • Middle • Inferior Medulla oblongata (b) Flocculonodular lobe Posterior lobe Choroid plexus of fourth ventricle Figure 12.17b Limbic System • Emotional or affective brain – Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response – Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict • emotional responses to odors Limbic System: Emotion and Cognition • The limbic system interacts with the prefrontal lobes, therefore: – We can react emotionally to things we consciously understand to be happening – We are consciously aware of emotional richness in our lives Reticular Formation • Three broad columns along the length of the brain stem – Raphe nuclei – Medial (large cell) group of nuclei – Lateral (small cell) group of nuclei • Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord Reticular Formation: RAS and Motor Function • RAS (reticular activating system) – Sends impulses to the cerebral cortex to keep it conscious and alert – Filters out repetitive and weak stimuli (~99% of all stimuli!) – Severe injury results in permanent unconsciousness (coma) Reticular Formation: RAS and Motor Function • Motor function – Helps control coarse limb movements – Reticular autonomic centers regulate visceral motor functions • Vasomotor • Cardiac • Respiratory centers Radiations to cerebral cortex Visual impulses Auditory impulses Reticular formation Ascending general sensory tracts (touch, pain, temperature) Descending motor projections to spinal cord Figure 12.19 (a) Scalp electrodes are used to record brain wave activity (EEG). Figure 12.20a Brain Waves: State of the Brain • EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions • A flat EEG (no electrical activity) is clinical evidence of death Brain Waves • Patterns of neuronal electrical activity • Each person’s brain waves are unique • Can be grouped into four classes based on frequency measured as Hertz (Hz) Types of Brain Waves • Alpha waves (8–13 Hz)—“idling” brain • Beta waves (14–30 Hz)—mentally alert • Theta waves (4–7 Hz)—irregular; common in children and uncommon in adults • Delta waves (4 Hz or less)—deep sleep and when during anesthesia; may indicate brain damage 1-second interval Alpha waves—awake but relaxed Beta waves—awake, alert Theta waves—common in children Delta waves—deep sleep (b) Brain waves shown in EEGs fall into four general classes. Figure 12.20b Epilepsy • A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking • not associated with intellectual impairments • Epilepsy occurs in 1% of the population • Tonic-clonic (grand mal) seizures – Victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and severe biting of the tongue Control of Epilepsy • Anticonvulsive drugs • Vagus nerve stimulators implanted under the skin of the chest Consciousness • Conscious perception of sensation • Voluntary initiation and control of movement • Capabilities associated with higher mental processing (memory, logic, judgment, etc.) Consciousness • Clinically defined on a continuum that grades behavior in response to stimuli – Alertness – Drowsiness (lethargy) – Stupor – Coma Sleep • State of partial unconsciousness from which a person can be aroused by stimulation • Two major types of sleep – Nonrapid eye movement (NREM) – Rapid eye movement (REM) Awake REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs. NREM stage 1: Relaxation begins; EEG shows alpha waves, arousal is easy. NREM stage 2: Irregular EEG with sleep spindles (short high- amplitude bursts); arousal is more difficult. NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline. (a) Typical EEG patterns NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur. Figure 12.21a Importance of Sleep • Slow-wave sleep (NREM stages 3 and 4) is presumed to be the restorative stage • People deprived of REM sleep become moody and depressed • Daily sleep requirements decline with age • Stage 4 sleep declines steadily and may disappear after age 60 Sleep Disorders • Narcolepsy • Insomnia • Sleep apnea Memory • Storage and retrieval of information • Two stages of storage – Short-term memory – Long-term memory (LTM) • has limitless capacity Transfer from STM to LTM • Factors that affect transfer from STM to LTM – Emotional state—best if alert, motivated, surprised, and aroused – Rehearsal – Association – Automatic memory Protection of the Brain • • • • Bone (skull) Membranes (meninges) Watery cushion (cerebrospinal fluid) Blood-brain barrier Superior sagittal sinus Subdural space Subarachnoid space Skin of scalp Periosteum Bone of skull Periosteal Dura Meningeal mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only) Figure 12.24 Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord (a) CSF circulation 2 choroid plexus of each ventricle. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances Capillary Neuron Astrocyte (a) Astrocytes are the most abundant CNS neuroglia. Figure 11.3a Blood-Brain Barrier: Functions • Selective barrier – Allows nutrients to move by facilitated diffusion – Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Absent in some areas – where it is necessary to monitor the chemical composition of the blood Homeostatic Imbalances of the Brain • Degenerative brain disorders – Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia – Parkinson’s disease: degeneration of the dopaminereleasing neurons of the substantia nigra – Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex Spinal Cord • Location – Begins at the foramen magnum – Ends as conus medullaris at L1 vertebra • Functions – Provides two-way communication to and from the brain – Contains spinal reflex centers T12 Ligamentum flavum Lumbar puncture needle entering subarachnoid space L5 L4 Supraspinous ligament L5 Filum terminale S1 Intervertebral disc Arachnoid matter Dura mater Cauda equina in subarachnoid space Figure 12.30 Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Figure 12.29a Spinal Cord • Spinal nerves – 31 pairs • Cervical and lumbar enlargements – The nerves serving the upper and lower limbs emerge here • Cauda equina – The collection of nerve roots at the inferior end of the vertebral canal Dorsal median sulcus Dorsal funiculus White Ventral funiculus columns Lateral funiculus Dorsal root ganglion Gray commissure Dorsal horn Gray Ventral horn matter Lateral horn Spinal nerve Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater (b) The spinal cord and its meningeal coverings Figure 12.31b Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32 Ascending tracts Fasciculus gracilis Dorsal white Fasciculus cuneatus column Dorsal spinocerebellar tract Ventral spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Descending tracts Ventral white commissure Lateral reticulospinal tract Lateral corticospinal tract Rubrospinal tract Medial reticulospinal tract Ventral corticospinal tract Vestibulospinal tract Tectospinal tract Figure 12.33