13 The Brain, Cranial Nerves, and Sensory and Motor Pathways Lecture Presentation by Lori Garrett
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Section 1: Functional Anatomy of the Brain and Cranial Nerves Learning Outcomes 13.1 Describe the origins of the different regions of the brain from the embryonic neural tube. 13.2 Name the four major regions of the brain, and describe their functions. 13.3 Explain how the brain is protected and supported and how cerebrospinal fluid forms and circulates. 13.4 List the main components of the medulla oblongata, and specify their functions.
Section 1: Functional Anatomy of the Brain and Cranial Nerves Learning Outcomes (continued) 13.5 List the main components of the pons, and specify their functions. 13.6 List the main components of the cerebellum, and specify the functions of each. 13.7 List the main components of the midbrain, and specify the functions of each. 13.8 List the main components of the diencephalon, and specify the functions of each.
Section 1: Functional Anatomy of the Brain and Cranial Nerves Learning Outcomes (continued) 13.9 Identify the main components of the limbic system, and specify the locations and functions of each. 13.10 Describe the structure and function of the basal nuclei of the cerebrum. 13.11 Identify the major superficial landmarks of the cerebrum, and cite the location of each.
Section 1: Functional Anatomy of the Brain and Cranial Nerves Learning Outcomes (continued) 13.12 Identify the locations of the motor, sensory, and association areas of the cerebral cortex, and discuss the functions of each. 13.13 Discuss the significance of the white matter of the cerebral hemispheres. 13.14 Clinical Module: Discuss the origin and significance of the major categories of brain waves seen in an electroencephalogram (EEG). 13.15 Identify the cranial nerves by name and number, and cite the functions of each.
Module 13.1: The brain develops from a hollow neural tube Brain anatomy Typical brain volume 1200 ml, but size varies On average, male brain ~ 10% larger than female s because of body size difference No correlation between brain size and intelligence
Module 13.1: Brain development Brain development Central nervous system begins as hollow cylinder neural tube Visible by fourth week of development
Module 13.1: Brain development Primary brain vesicles = three swellings at cephalic end of tube Prosencephalon = forebrain; anterior tip of neural tube Mesencephalon = midbrain; caudal to prosencephalon Rhombencephalon = hindbrain; most caudal part; continuous with spinal cord
Module 13.1: Brain development Secondary brain vesicles By week 5 of development: Primary brain vesicles subdivide; form secondary brain vesicles
Module 13.1: Brain development Secondary brain vesicles (continued) Prosencephalon subdivides into: Diencephalon becomes major relay/processing center for information headed to/from cerebrum Telencephalon expands rapidly; forms cerebrum Cerebrum continues enlarging to become largest part of brain and cover other regions
Module 13.1: Brain development Secondary brain vesicles (continued) Rhombencephalon subdivides into: Metencephalon caudal to midbrain (mesencephalon) Forms cerebellum and pons of adult brain Myelencephalon becomes medulla oblongata
Brain development
Module 13.1: Review A. Name the three primary brain vesicles. B. Which structures form the secondary brain vesicles? C. Which embryonic brain vesicle develops into the largest region of the adult brain? Learning Outcome: Describe the origins of the different regions of the brain from the embryonic neural tube.
Module 13.2: Each region of the brain has distinct structural and functional characteristics Four major brain regions 1. Cerebrum 2. Cerebellum 3. Diencephalon 4. Brainstem
Module 13.2: Major brain regions Cerebrum Left and right cerebral hemispheres; divided by deep fissures Surface Gyri (folds) and sulci (grooves) increase surface area
Module 13.2: Major brain regions Cerebral cortex Superficial layer of gray matter Thin 1.5 4.5 mm thick Major cortical functions Conscious thought Memory storage and processing Sensory processing Control of skeletal muscles
Module 13.2: Major brain regions Cerebellum Partially hidden by cerebral hemispheres Second largest brain structure Makes up 10 percent of brain s volume, but > 50 percent of its neurons Major cerebellar functions Coordinate/modulate motor commands from cerebral cortex
Module 13.2: Major brain regions Diencephalon Structural/functional link between cerebral hemispheres and rest of CNS Two parts 1. Thalamus Sensory relay/ processing 2. Hypothalamus has centers involved with: Emotions Autonomic function Hormone production
Module 13.2: Major brain regions Brainstem Three parts midbrain, pons, and medulla oblongata Midbrain contains nuclei that: Process visual and auditory information Control reflexes triggered by them Helps maintain consciousness Pons connects cerebellum/ brainstem Tracts and relay centers Somatic and visceral motor control
Module 13.2: Major brain regions Brainstem (continued) Three parts (continued) Medulla oblongata Relays sensory information through brainstem and to the thalamus Regulates many autonomic functions
Module 13.2: Major brain regions
Module 13.2: Major brain regions Ventricles of the brain Chambers formed by neural tube expansion during development Filled with cerebrospinal fluid; lined by ependymal cells
Module 13.2: Major brain regions Ventricular system components Lateral ventricles two, one in each cerebral hemisphere Interventricular foramen connect lateral ventricles to third ventricle Third ventricle located in diencephalon Cerebral aqueduct slender canal within midbrain; connects third ventricle to fourth ventricle Fourth ventricle extends from metencephalon upper part of medulla oblongata Narrows to become the central canal of spinal cord
Module 13.2: Major brain regions
Module 13.2: Major brain regions Interconnections between ventricles Corpus callosum thick tract of white matter that interconnects the cerebral hemispheres Septum pellucidum thin partition separating lateral ventricles
Module 13.2: Review A. Describe the role of the medulla oblongata. B. Which region of the brain contains two ventricles? C. Compare the corpus callosum with the septum pellucidum. D. Which region of the brain is enclosed or hidden by the cerebrum? Learning Outcome: Name the four major regions of the brain, and describe their functions.
Module 13.3: The cranial meninges and cerebrospinal fluid protect and support the brain Protection of the brain Cranial bones Cerebrospinal fluid Blood brain barrier Cranial meninges
Module 13.3: The cranial meninges and cerebrospinal fluid protect and support the brain Cranial meninges Continuous with spinal meninges Three layers 1. Dura mater 2. Arachnoid mater 3. Pia mater
Module 13.3: Protection of the brain Dura mater Two fibrous layers; mostly fused Periosteal layer (outer layer) fused to periosteum of cranial bones No epidural space Meningeal layer (inner layer) In some areas, including dural venous sinuses, layers are separated by gap containing fluid and blood vessels
Module 13.3: Protection of the brain Arachnoid mater Arachnoid membrane closest to dura mater Arachnoid trabeculae fibrous strands through subarachnoid space; connect to the pia mater Subarachnoid space between arachnoid membrane/pia mater
Module 13.3: Protection of the brain Pia mater Bound to surface of brain by astrocyte processes (sticks to the brain) Extends into every fold Accompanies branches of cerebral blood vessels as they penetrate the surface into the brain
Module 13.3: Protection of the brain Dural folds Inward extensions of inner dural layer Stabilize/support the brain Three large dural folds 1. Falx cerebri 2. Tentorium cerebelli 3. Falx cerebelli
Module 13.3: Protection of the brain Dural venous sinuses Large collecting veins located within dural folds Superior sagittal sinus is the largest
Module 13.3: Protection of the brain Falx cerebri Dural fold between cerebral hemispheres Runs from crista galli of ethmoid bone (anteriorly) to internal occipital crest of occipital bone (posteriorly) Contains the superior and inferior sagittal sinuses
Module 13.3: Protection of the brain Tentorium cerebelli Separates cerebral hemispheres from cerebellum Falx cerebelli Separates cerebellar hemispheres along midsagittal line Inferior to tentorium cerebelli
Module 13.3: Protection of the brain Cerebrospinal fluid (CSF) Three functions 1. Support weight of brain 2. Cushion brain/spinal cord from physical trauma 3. Transport nutrients, chemical messengers, wastes Produced/maintained by choroid plexus (ependymal cells with tight junctions, and capillaries) A choroid plexus is in each ventricle
Module 13.3: Protection of the brain Cerebrospinal fluid (continued) CSF circulates from choroid plexus through ventricles into central canal of spinal cord
Module 13.3: Protection of the brain Cerebrospinal fluid (continued) Materials diffuse between CSF and interstitial fluid of CNS
Module 13.3: Protection of the brain Cerebrospinal fluid (continued) CSF is absorbed into venous circulation at arachnoid granulations Fingerlike extensions of arachnoid membrane Penetrate meningeal layer of dura mater Extend into superior sagittal sinus
Formation, circulation, and functions of CSF
Module 13.3 Review A. From superficial to deep, name the layers that make up the cranial meninges. B. What brain tissues have tight junctions? C. How would decreased diffusion across the arachnoid granulations affect the volume of cerebrospinal fluid in the ventricles? Learning Outcome: Explain how the brain is protected and supported and how cerebrospinal fluid forms and circulates.
Module 13.4: The medulla oblongata contains autonomic reflex centers, relay stations, and ascending and descending tracts Medulla oblongata All communication between brain and spinal cord travels in ascending and descending tracts through medulla oblongata Coordinates complex autonomic reflexes and visceral functions
Module 13.4: Medulla oblongata Medulla oblongata contains: Autonomic centers for vital functions Relay stations along sensory and motor pathways Nuclei associated with five cranial nerves Structures Olive olive-shaped bulge on anterolateral surface Pyramids contain tracts of motor fibers from cerebral cortex Some fibers cross to opposite side of medulla (decussation)
Module 13.4: Medulla oblongata
Organization of the medulla oblongata
Module 13.4: Medulla oblongata
Module 13.4: Review A. Describe the pyramids of the medulla oblongata and a decussation. B. Which medulla oblongata components relay somatic sensory information to the thalamus? C. What is the function of the ascending and descending tracts in the medulla oblongata? Learning Outcome: List the main components of the medulla oblongata, and specify their functions.
Module 13.5: The pons links the cerebellum to the brain and spinal cord and has vital autonomic reflex centers Pons links cerebellum with midbrain, diencephalon, cerebrum, medulla oblongata, spinal cord Four groups of structures 1. Ascending, descending, transverse tracts 2. Nuclei controlling respiration 3. Sensory and motor nuclei of cranial nerves 4. Nuclei/tracts that process/relay information sent to/from cerebellum
Module 13.5: Pons Reticular formation contains nuclei/centers regulating vital autonomic functions; spans from medulla oblongata to midbrain
Organization of the Pons
Module 13.5: Pons
Module 13.5: Review A. List the four groups of pontine structures. Learning Outcome: List the main components of the pons, and specify their functions.
Module 13.6: The cerebellum coordinates learned and reflexive patterns of muscular activity at the subconscious level Cerebellum Automatic processing center Monitors proprioceptive, visual, tactile, balance, and auditory sensations
Module 13.6: The cerebellum Cerebellum (continued) Two primary functions 1. Adjusting postural muscles Modifies activities of brainstem centers 2. Programming/fine-tuning movements controlled at conscious/subconscious levels Refines learned movement patterns Compares motor commands with proprioceptive information, makes adjustments as needed
Module 13.6: The cerebellum Cerebellum anatomy Anterior and posterior lobes, separated by primary fissure Two hemispheres Surface covered by thin layer of gray matter = cerebellar cortex Separated by narrow band of cortex called the vermis (worm) Folia = folds of the surface; less prominent than cerebral gyri
Module 13.6: The cerebellum Cerebellar cortex Outer molecular layer Inner granular layer Intermediate Purkinje layer with stacked Purkinje cells Highly branched cells (extensive dendrites) Receive input from up to 200,000 synapses Relay motor commands The only axons leaving cerebellar cortex are from Purkinje cells
Module 13.6: The cerebellum Internal organization and peduncles Arbor vitae: tree of life = branching cerebellar white matter Cerebellar peduncles Tracts linking cerebellum with brain stem, cerebrum, and spinal cord Three on each side 1. Superior peduncle carries most cerebellar output 2. Middle and inferior carry most cerebellar input Ataxia results from cerebellum damage/impairment Inability to coordinate muscle movement If severe, person cannot sit or stand without assistance
Organization of the cerebellum
Module 13.6: The cerebellum
Module 13.6: Review A. Identify the components of the cerebellar gray matter. B. Describe the arbor vitae, including its makeup, location, and function. C. Describe ataxia. Learning Outcome: List the main components of the cerebellum, and specify the functions of each.
Module 13.7: The midbrain regulates auditory and visual reflexes and controls alertness Midbrain Most complex/integrative part of brainstem Can direct complex motor patterns at subconscious level Influences level of activity in entire nervous system
Module 13.7: The midbrain Corpora quadrigemina two pairs of sensory nuclei 1. Superior colliculus (colliculus, hill) Receives visual input from thalamus Controls reflex movements of eyes, head, and neck in response to visual stimuli 2. Inferior colliculus Receives auditory input from medulla oblongata and pons Controls reflex movements of head, neck, and trunk in response to auditory inputs
Module 13.7: The midbrain Reticular activating system (RAS) Specialized part of the reticular formation Stimulation increases alertness and attentiveness Damage to the RAS produces unconsciousness Red nucleus Red from rich blood supply Receives information from cerebrum and cerebellum Sends subconscious motor commands for upper limb position and muscle tone
Module 13.7: The midbrain Substantia nigra (nigra, black) Contains darkly pigmented cells Inhibits activity in cerebral basal nuclei Cerebral peduncles Nerve fiber bundles with descending fibers Go to cerebellum, via pons Carry voluntary motor commands from cerebral cortex
Organization of the midbrain
Module 13.7: The midbrain Internal midbrain structures Tectum Roof of the midbrain Region posterior to the cerebral aqueduct Tegmentum Region anterior to the cerebral aqueduct
Origins of cranial nerves from the brainstem
Module 13.7: The midbrain
Module 13.7: Review A. Identify the sensory nuclei contained within the corpora quadrigemina. B. Give the functions of the superior colliculi and inferior colliculi. C. Which cranial nerves arise from the brainstem? D. What part of the midbrain influences the activity of the entire nervous system? Learning Outcome: List the main components of the midbrain, and specify the functions of each.
Module 13.8: The diencephalon consists of the epithalamus, thalamus, and hypothalamus Three parts 1. Epithalamus 2. Thalamus 3. Hypothalamus
Module 13.8: Diencephalon Anterior commissure Connects cerebral hemispheres Optic chiasm Where optic nerves (II) cross; enter brain Interthalamic adhesion Bumplike extension of gray matter into third ventricle from sides of thalamus; no fibers cross Missing in about 20 percent of human brains
Location of the diencephalon
Module 13.8: Diencephalon Epithalamus Roof of diencephalon; superior to third ventricle Contains extensive choroid plexus that extends through interventricular foramina
Module 13.8: Diencephalon Epithalamus (continued) Pineal gland Endocrine structure secretes melatonin Located in posterior epithalamus Melatonin regulates day night cycles and reproductive functions
Module 13.8: Diencephalon Thalamus Superior to midbrain Filters sensory information, passing on only small portion Final relay for ascending sensory information being projected to cerebral cortex Each thalamic region connected to specific areas in cortex
Major relay areas of the thalamus
Module 13.8: Diencephalon Thalamus (continued) Lateral geniculate body Receives visual information from optic tract Sends signals to midbrain and occipital lobe Medial geniculate nucleus Relays auditory information from receptors in inner ear to appropriate areas in cerebral cortex
Module 13.8: Diencephalon
Module 13.8: Diencephalon Hypothalamus Contains important control and integrative centers May be stimulated by: 1. Sensory information from cerebrum, brainstem, spinal cord 2. Changes in composition of CSF and interstitial fluid 3. Chemicals in circulating blood (lacks blood brain barrier) Infundibulum connects it to pituitary gland (endocrine)
Organization of the hypothalamus
Module 13.8: Diencephalon
Module 13.8: Review A. Damage to the lateral geniculate bodies of the thalamus would interfere with what particular function? B. Which component of the diencephalon is stimulated by changes in body temperature? Learning Outcome: List the main components of the diencephalon, and specify the functions of each.
Module 13.9: The limbic system is a functional group of tracts and nuclei located in the cerebrum and diencephalon Limbic system Functional grouping of tracts and nuclei along border of cerebrum and diencephalon Functions include: 1. Establishing emotional states 2. Linking conscious, intellectual functions of cerebral cortex with unconscious and autonomic functions of brainstem 3. Facilitating memory storage/retrieval 4. Affecting motivation
Module 13.9: Limbic system Major components of limbic system Diencephalic components Thalamus anterior thalamic nuclei from mammillary body (in hypothalamus) to cingulate gyrus Hypothalamus hypothalamic nuclei, mammillary body Emotions (rage, fear, pain, sexual arousal, pleasure) Produce general alertness/excitement or lethargy/sleep via stimulation from reticular formation
Module 13.9: Limbic system Major components of limbic system (continued) Cerebral components Limbic lobe cortical areas (three cerebral gyri) Cingulate gyrus Dentate gyrus Parahippocampal gyrus Tracts Fornix = tract of white matter connecting hippocampus and hypothalamus
Module 13.9: Limbic system Major components of limbic system (continued) Cerebral components (continued) Nuclei Amygdaloid body interface between limbic system, sensory systems, and cerebrum; role in regulating heart rate, fight-or-flight response, and linking emotions and memories Hippocampus learning, especially storage/retrieval of long-term memories
Organization of the limbic system
The functional components of the limbic system
Module 13.9: Review A. List the primary functions of the limbic system. B. What are some functions of the amygdaloid body? C. Which region of the limbic system is particularly important for the storage and retrieval of longterm memories? Learning Outcome: Identify the main components of the limbic system, and specify the locations and functions of each.
Module 13.10: The basal nuclei of the cerebrum adjust and refine ongoing voluntary movements Basal nuclei of the cerebrum Masses of gray matter within each cerebral hemisphere, deep to floor of lateral ventricles Subconscious control of skeletal muscle tone Help coordinate learned movement patterns Do not initiate movements; provide general pattern/rhythm
Module 13.10: Basal nuclei The basal nuclei consist of: Caudate nucleus Lentiform nucleus Medial globus pallidus Lateral putamen Internal capsule Bundles of axons linking cerebral cortex to diencephalon and brainstem; pass between and around the basal nuclei
Locations of the basal nuclei
13.10: Basal nuclei Roles of the basal nuclei in modifying ongoing movements Direct control over movement Stimulate motor nuclei (the red nucleus, superior and inferior colliculi, reticular formation) in the brainstem Example: control cycles of arm/thigh movements while walking Indirect modification of movement Send output to cerebral cortex after synapsing in thalamus Example: subconsciously adjust muscle tone as you begin a voluntary movement
Roles of the basal nuclei in movement
Module 13.10: Review A. Define basal nuclei. B. Describe the function of the caudate nucleus. C. What signs and symptoms would be present in a person who has basal nuclei damage? Learning Outcome: Describe the structure and function of the basal nuclei of the cerebrum.
Module 13.11: Superficial landmarks divide the cerebral hemispheres into lobes Overview of cerebral lobes Each cerebral hemisphere divided into regions lobes Named after overlying bones of the skull (except for the insula) Lobes of the cerebrum 1. Frontal lobe 2. Parietal lobe 3. Temporal lobe 4. Occipital lobe 5. Insula (insula, island)
Module 13.11: Lobes of the cerebrum Superficial landmarks Each person has unique pattern of gyri and sulci Lateral sulcus separates frontal lobe from temporal lobe Parieto-occipital sulcus separates parietal lobe from occipital lobe
Module 13.11: Lobes of the cerebrum Superficial landmarks (continued) Central sulcus separates frontal lobe from parietal lobe Precentral gyrus ridge anterior to central sulcus Contains primary motor cortex Controls voluntary movements Postcentral gyrus Posterior to central sulcus Contains primary somatosensory cortex Conscious awareness of somatosensory information
Lobes and superficial anatomy of the cerebrum
Module 13.11: Lobes of the cerebrum
Module 13.11: Lobes of the cerebrum
Module 13.11: Lobes of the cerebrum General facts about the cerebral hemispheres Each hemisphere receives sensory information from and sends motor commands to opposite side of body Crossing over occurs in brainstem and spinal cord Has no known functional significance Hemispheres may look identical and have similar functions, but still have important differences Imprecise mapping of specific functions and regions Boundaries are indistinct and overlap Some functions (such as consciousness) use multiple regions Normal individuals use ALL portions of the brain
Module 13.11: Review A. Identify the lobes of the cerebrum, and indicate the basis for their names. B. Describe the insula. C. What effect would damage to the left postcentral gyrus produce? Learning Outcome: Identify the major superficial landmarks of the cerebrum, and cite the location of each.
Module 13.12: The lobes of the cerebral cortex have regions with specific functions Cerebral cortex divided into six functional categories 1. Motor cortex sends voluntary commands to skeletal muscles 2. Sensory cortex receives general somatic sensory information 3. Visual cortex (vision) 4. Auditory cortex (hearing) 5. Olfactory cortex (smell) 6. Gustatory cortex (taste) Each sensory and motor region connected to nearby association area = region that interprets incoming data or coordinates motor response
Module 13.12: Functional regions of cerebral cortex 1. Motor cortex Primary motor cortex directs voluntary movement by controlling motor neurons in brainstem/spinal cord Premotor cortex (somatic motor association area) coordinates learned movements
Module 13.12: Functional regions of cerebral cortex 2. Sensory cortex Primary somatosensory cortex receives sensory information from receptors for touch, pressure, pain, vibration, or temperature Somatosensory association area monitors activity in primary somatosensory cortex; recognizes different sensations
Module 13.12: Functional regions of cerebral cortex 3. Gustatory cortex (taste) In insula receives information from taste receptors 4. Olfactory cortex (smell) Receives sensory information from olfactory receptors
Module 13.12: Functional regions of cerebral cortex 5. Auditory cortex (hearing) Primary auditory cortex monitors auditory information Auditory association area activity in auditory cortex; recognizes different sounds (such as speech)
Module 13.12: Functional regions of cerebral cortex 6. Visual cortex Primary visual cortex receives visual information from lateral geniculate bodies Visual association area monitors activity and patterns in visual cortex; interprets the information Example: Primary visual cortex sees symbols c, a, t; visual association area interprets as cat
Module 13.12: Functional regions of cerebral cortex Integrative centers Receive information from association areas Direct motor activities Perform analytical functions In lobes/cortical areas of both cerebral hemispheres Language areas typically associated with left hemisphere
Module 13.12: Functional regions of cerebral cortex Integrative centers (continued) Broca s area (motor speech area) speech production Regulates breathing/vocalization patterns for normal speech If damaged, can make sounds but not form words Prefrontal cortex integrates information from sensory association areas; performs intellectual functions
Module 13.12: Functional regions of cerebral cortex Integrative centers (continued) Frontal eye field controls learned eye movements Example: scanning lines of text Wernicke s area associated with language comprehension Receives information from somatosensory association areas Plays essential role in personality by linking sensory information to complex visual and auditory memories
Module 13.12: Functional regions of cerebral cortex Hemispheric lateralization Regional specialization of each hemisphere Left cerebral hemisphere Specialized language areas Language-based skills, such as reading, writing, speaking Premotor cortex for hand movements is larger on left side in right-handed people than in left-handed people Analytical tasks, such as math and logic
Module 13.12: Functional regions of cerebral cortex Hemispheric lateralization (continued) Right cerebral hemisphere Analyzes sensory information; relates body to it Interpretive centers for identifying familiar objects by touch, smell, sight, taste, or feel Facial recognition Understanding three-dimensional relationships Analyzes emotional context/tone of conversation
Hemispheric lateralization
Module 13.12: Functional regions of cerebral cortex Approximately 9 percent of the population is lefthanded Primary motor cortex of right hemisphere controls motor function for left hand, but left hemisphere usually still controls speech and analytical functions Seen in an unusually high percentage of musicians/artists
Module 13.12: Review A. Where is the primary motor cortex located? B. Which senses are affected by damage to the temporal lobes? C. Which brain region has been affected in a stroke victim who is unable to speak? Learning Outcome: Identify the locations of the motor, sensory, and association areas of the cerebral cortex, and discuss the functions of each.
Module 13.13: White matter connects the cerebral hemispheres and the lobes of each hemisphere and links the cerebrum to the rest of the brain Functional grouping of white matter Interior of cerebral hemispheres mostly consists of white matter Organized into groups sharing common function
Module 13.13: Cerebral white matter Association fibers connect areas in same cerebral hemisphere Arcuate fibers shortest; curve in an arc to connect gyri Longest are organized in bundles, or fasciculi Longitudinal fasciculi connect frontal lobe to other lobes in same cerebral hemisphere
Module 13.13: Cerebral white matter Commissural fibers connect the two cerebral hemispheres Corpus callosum most important band of commissural fibers Allows communication/coordination between the two hemispheres > 200 million axons carrying about 4 billion impulses per second
Module 13.13: Cerebral white matter Commissural fibers (continued) Anterior commissure smaller tract also connecting the two hemispheres; becomes more important if corpus callosum injured
Module 13.13: Cerebral white matter Projection fibers link cerebral cortex to diencephalon, brainstem, cerebellum, and spinal cord All projection fibers pass through diencephalon Internal capsule = collection of ascending (sensory) and descending (motor) fibers passing through diencephalon
Module 13.13: Review A. What is the function of the longitudinal fasciculi? B. What special names are given to axons in the white matter of the cerebral hemispheres? Learning Outcome: Discuss the significance of the white matter of the cerebral hemispheres.
Module 13.14: Brain activity can be monitored using external electrodes; the record is called an electroencephalogram, or EEG Electrical activity of the brain Neural function depends on electrical events Electrical activity of all the neurons in the brain generates an electrical field, measurable by electrodes placed on scalp Printed report of that activity = electroencephalogram (EEG) Electrical patterns observed are called brain waves
Module 13.14: EEG Brain waves Alpha waves Occur in healthy, awake adults while resting with eyes closed Disappear during sleep Disappear with concentration on a specific task Beta waves Higher frequency than alpha waves Appear in people who are concentrating on a task, under stress, or in state of psychological tension
Module 13.14: EEG Brain waves (continued) Theta waves Appear transiently during sleep in normal adults Usually observed in children and intensely frustrated adults Presence under other circumstances may indicate brain disorder
Module 13.14: EEG Brain waves (continued) Delta waves Large-amplitude, low-frequency waves Normally seen during deep sleep in all ages Also seen in brains of infants (incomplete cortical development) Seen in awake adults when tumor, vascular block, or inflammation has damaged parts of the brain
Electroencephalogram (EEG) showing the brain waves
Module 13.14: EEG Abnormal brain activity Electrical activity in cerebral hemispheres usually synchronized by pacemaker that involves the thalamus Asynchrony may indicate localized damage or cerebral abnormality Example: tumor or injury in one hemisphere changes its pattern, losing alignment between hemispheres
Module 13.14: EEG Seizure = temporary cerebral disorder accompanied by unusual neural activity (movements, sensations, behaviors) Marked by change in pattern of electrical activity Epilepsies, or seizure disorders = clinical conditions characterized by seizures
Module 13.14: Review A. Name and describe the four wave types associated with an EEG. B. Differentiate between a seizure and epilepsy. Learning Outcome: Discuss the origin and significance of the major categories of brain waves seen in an electroencephalogram (EEG).
Module 13.15: The twelve pairs of cranial nerves are classified as sensory, special sensory, motor, or mixed nerves Twelve pairs of cranial nerves Numbered using Roman numerals (I XII) preceded by CN
Cranial nerve distribution
Module 13.15: Cranial nerves
Module 13.15: Cranial nerves
Module 13.15: Review A. Which cranial nerves are involved with the eye? B. Which cranial nerves have motor functions only? Learning Outcome: Identify the cranial nerves by name and number, and cite the functions of each.
Section 2: Sensory and Motor Pathways Learning Outcomes 13.16 Describe the basic events that occur along a sensory pathway. 13.17 Explain the ways in which receptors can be classified. 13.18 List the types of tactile receptors, and specify the functions of each. 13.19 Identify and describe the major sensory pathways. 13.20 Describe the components, processes, and functions of the somatic motor pathways.
Section 2: Sensory and Motor Pathways Learning Outcomes (continued) 13.21 Describe the levels of information processing involved in motor control. 13.22 Clinical Module: Describe the roles of the nervous system in referred pain, Parkinson s disease, rabies, cerebral palsy, amyotrophic lateral sclerosis, Alzheimer s disease, and multiple sclerosis.
Module 13.16: Sensations carried by sensory pathways to the CNS begin with transduction at a sensory receptor Sensory terminology Sensory receptors = specialized cells or cell processes that alert CNS about conditions in/out of your body General senses temperature, pain, touch, pressure, vibration, proprioception (position); receptors distributed throughout body Sensory pathways begin at peripheral receptors, end within CNS
Module 13.16: Sensory pathways Sensory terminology (continued) Sensation = information carried by a sensory pathway Perception = conscious awareness of a sensation Receptive field = area monitored by single receptor cell Larger the receptor field, less able to localize stimulus
Module 13.16: Sensory pathways Basic events along sensory and motor pathways Depolarization of receptor Physical/chemical stimulus results in graded change in receptor cell (transduction)
Module 13.16: Sensory pathways Action potential generation If receptor cell depolarizes to threshold, triggers action potential Greater depolarization = greater frequency of action potentials
Module 13.16: Sensory pathways Propagation over labeled line Labeled line = axons carrying information about one type of stimulus (touch, pressure, temperature) CNS interprets stimulus based on which line carries it
Module 13.16: Sensory pathways CNS processing Occurs at every synapse along labeled line Line may branch repeatedly, distributing sensory information to multiple nuclei/centers in spinal cord and brain
Module 13.16: Sensory pathways CNS processing can trigger motor response Involuntary motor pathways immediate involuntary response even before sensations reach cerebral cortex Example: reflex response
Module 13.16: Sensory pathways Voluntary motor pathways Perception only ~ 1 percent of arriving sensations are relayed to primary sensory cortex, where perception occurs Can initiate voluntary response not immediate; can moderate, enhance, supplement simple reflexive response
Module 13.16 Review A. Define the term general senses. B. Relate receptive field size to stimulus localization. Learning Outcome: Describe the basic events that occur along a sensory pathway.
Module 13.17: Receptors are classified by function or response to the stimulus Free nerve endings Tips of branching dendrites of sensory neurons Simplest receptors Respond to many different stimuli, so not much receptor specificity Example: pain receptors stimulated by chemicals, pressure, temperature, or trauma
Module 13.17: Receptor classification Nociceptors = pain receptors Free nerve endings with large receptive fields and broad sensitivity Do not adapt quickly Two axon types carry pain information 1. Myelinated type A fibers 2. Unmyelinated type C fibers
Module 13.17: Receptor classification Nociceptors (continued) Two axon types carry pain signals 1. Myelinated type A fibers fast pain (prickling pain) Sensations quickly reach primary somatosensory cortex for conscious awareness; often trigger somatic reflexes Can usually localize the stimulus
Module 13.17: Receptor classification Nociceptors (continued) 2. Unmyelinated type C fibers slow pain Burning/aching General activation of reticular formation and thalamus Aware of pain but just general idea what area is affected
Module 13.17: Receptor classification Thermoreceptors = temperature receptors Free nerve endings in dermis, skeletal muscles, liver, hypothalamus Cold receptors three to four times more numerous than warm receptors No structural differences between warm and cold thermoreceptors
Module 13.17: Receptor classification Chemoreceptors respond to water-soluble and lipid-soluble substances dissolved in body fluids (interstitial fluid, blood, CSF)
Module 13.17: Receptor classification Mechanoreceptors respond to physical distortion of their plasma membranes Membranes have mechanically gated ion channels that open/close in response to stretching, compression, twisting, etc. Three types of mechanoreceptors 1. Proprioceptors 2. Baroreceptors 3. Tactile receptors
Module 13.17: Receptor classification Mechanoreceptors (continued) Three types (continued) 1. Proprioceptors monitor position of joints/muscles most complex of general sensory receptors Example: muscle spindle 2. Baroreceptors detect pressure changes in blood vessels and in digestive, respiratory, and urinary tracts 3. Tactile receptors provide sensations of touch (shape/texture), pressure, and vibration Fine touch and pressure receptors give detailed information; extremely sensitive Crude touch and pressure receptors give little information; poor localization
Module 13.17: Receptor classification
Module 13.17: Receptor classification Receptors categorized by nature of their response to stimulation Tonic receptors Slow-adapting; always active Action potential frequency reflects level of stimulation Increased stimulus = increased action potential frequency
Module 13.17: Receptor classification Phasic receptors Fast-adapting; normally inactive Become active for short time when a change occurs in what they are monitoring
Module 13.17: Receptor classification Adaptation = reduction in sensitivity with constant stimulus Two types 1. Peripheral adaptation occurs when level of receptor activity changes; receptor first responds strongly, then activity declines Especially characteristic of phasic receptors Example: temperature not noticed much unless it changes
Module 13.17: Receptor classification 2. Central adaptation occurs along sensory pathways in CNS; involves inhibition of nuclei along a sensory pathway Example: new smell once it is initially detected, awareness almost stops even though neurons are still sending signals
Module 13.17: Review A. List the four types of general sensory receptors based on function, and identify the type of stimulus that excites each type. B. Describe the three classes of mechanoreceptors. C. Explain adaptation, and differentiate between peripheral adaptation and central adaptation. Learning Outcome: Explain the ways in which receptors can be classified.
Module 13.18: Tactile receptors have a simple structure and are abundant in the skin Tactile sensory receptors = mechanoreceptors responding to touch, pressure, vibration Greatest diversity in the skin Six types of tactile receptors in the skin 1. Free nerve endings 2. Root hair plexuses 3. Tactile discs 4. Tactile corpuscles 5. Lamellar corpuscles 6. Bulbous corpuscles
Module 13.18: Tactile receptors Six types of tactile receptors in skin (continued) 1. Free nerve endings Branching dendrite tips of sensory neurons Nonspecific respond to touch, pressure, pain, temperature Most common receptors in skin
Module 13.18: Tactile receptors Six types of tactile receptors in skin (continued) 2. Root hair plexus Monitor distortion/movement of hair follicle Displacement of hair distorts sensory dendrites; generates action potentials Adapt rapidly
Module 13.18: Tactile receptors Six types of tactile receptors in skin (continued) 3. Tactile discs Fine touch and pressure Extremely sensitive tonic receptors Very small receptive fields A tactile disc is composed of a Merkel cell (large epithelial cell in stratum basale) and dendritic processes from single myelinated afferent fiber that are in contact with it
Module 13.18: Tactile receptors Six types of tactile receptors in skin (continued) 4. Tactile corpuscles (Meissner s corpuscles) Fine touch, pressure, low-frequency vibration Adapt within a second Abundant in eyelids, lips, fingertips, nipples, external genitalia Tactile corpuscles composed of dendrites surrounded by Schwann cells, all wrapped in fibrous capsule
Module 13.18: Tactile receptors Six types of tactile receptors in skin (continued) 5. Lamellar corpuscles (Pacinian corpuscles) Sensitive to deep pressure Fast-adapting most sensitive to pulsing or high-frequency vibration Large receptors up to 4 mm long and 1 mm in diameter Abundant in fingers, mammary glands, external genitalia, fasciae, joint capsules, some viscera (mesenteries, pancreas, urethra, and bladder) Lamellar corpuscles composed of single dendrite within concentric layers of collagen fibers and fibroblasts
Module 13.18: Tactile receptors Six types of tactile receptors in skin (continued) 6. Bulbous corpuscles (Ruffini corpuscles) Sensitive to pressure and distortion of deep dermis (skin stretched) Tonic receptors; little adaptation Ruffini corpuscles are composed of capsule around core of collagen fibers continuous with those of adjacent dermis, and inner network of dendrites wrapped around collagen fibers Tension/distortion of dermis stimulates dendrite
Module 13.18: Tactile receptors
Module 13.18: Review A. Which types of tactile receptors are located only in the dermis? B. Which is likely to be more sensitive to continuous deep pressure: a lamellar corpuscle or a bulbous corpuscle? Learning Outcome: List the types of tactile receptors, and specify the functions of each.
Module 13.19: Three major somatic sensory pathways carry information from the skin and muscles to the CNS Somatotopy = functional map of primary somatosensory cortex Sensory homunculus ( little human ) = somatotope showing the relative size of cortex devoted to any specific body area
Module 13.19: Somatic sensory pathways Three major somatic sensory pathways 1. Spinothalamic pathway 2. Posterior column pathway 3. Spinocerebellar pathway
Module 13.19: Somatic sensory pathways Spinothalamic pathway Anterior spinothalamic tracts Crude touch and pressure sensations from body Lateral spinothalamic tracts Pain and temperature sensations from body First-order neuron from receptor to spinal cord; synapses with second-order neuron in posterior gray horns Second-order neuron from posterior gray horn; crosses spinal cord; ascends to thalamus Third-order neuron from thalamus to primary sensory cortex
Module 13.19: Somatic sensory pathways
Module 13.19: Somatic sensory pathways Posterior column pathway Highly localized ( fine ) touch, pressure, vibration, proprioception From peripheral receptor to primary somatosensory cortex Sensory axons ascend in medial gracile fasciculus and lateral cuneate fasciculus Medial lemniscus tract leading from gracile nucleus and cuneate nucleus to the thalamus
Module 13.19: Somatic sensory pathways
Module 13.19: Somatic sensory pathways Spinocerebellar pathway Proprioceptive information about position of skeletal muscles, joints, and tendons; goes to cerebellum Axons of posterior spinocerebellar tracts do not cross to other side pass through inferior cerebellar peduncle on same side Anterior spinocerebellar tract axons do cross to opposite side of spinal cord
Module 13.19: Somatic sensory pathways
Module 13.19: Review A. Define somatotopy. B. Which spinal tracts carry action potentials generated by nociceptors? C. Which cerebral hemisphere receives impulses conducted by the right gracile fasciculus? Learning Outcome: Identify and describe the major sensory pathways.
Module 13.20: The somatic nervous system controls skeletal muscles through upper and lower motor neurons Somatic motor pathways Always involve at least two motor neurons 1. Upper motor neuron Cell body in a CNS processing center 2. Lower motor neuron Cell body in a nucleus of brainstem or spinal cord Upper motor neuron synapses on lower motor neuron, which then innervates a single motor unit of a skeletal muscle
Module 13.20: The somatic nervous system controls skeletal muscles through upper and lower motor neurons Motor homunculus = functional map of primary motor cortex Proportions reflect number of motor units innervated and degree of fine motor control in corresponding body region
Module 13.20: Motor pathways Corticospinal pathway Voluntary control of skeletal muscles Sometimes called the pyramidal system upper motor neurons start at pyramidal cells in primary motor cortex Upper motor neuron axons descend into brainstem and spinal cord Synapse with lower motor neurons that control skeletal muscles
Module 13.20: Motor pathways Tracts of the corticospinal pathway 1. Corticobulbar (bulbar, brainstem) tracts conscious control of skeletal muscles for eye, jaw, face, some muscles of neck/pharynx Synapse on lower motor neurons in cranial nerve motor nuclei 2. Corticospinal tracts conscious control of skeletal muscles Visible along ventral surface of medulla oblongata as pair of thick bands (pyramids) ~15 percent descend uncrossed as anterior corticospinal tracts; cross over in anterior white commissure before synapsing on lower motor neurons in anterior gray horns
Corticospinal pathways
Module 13.20: Motor pathways Two main pathways for subconscious motor commands Commands issued from cerebrum, diencephalon, brainstem 1. Lateral pathway muscle tone/precise movements of distal limb muscles Upper motor neurons start in red nucleus Axons cross to opposite side of brain; descend through rubrospinal (ruber, red) tracts
Module 13.20: Motor pathways 2. Medial pathway gross movements of trunk, proximal limb Upper motor neurons located in vestibular nuclei, superior and inferior colliculi, and reticular formation Three major sets of tracts in medial pathway 1. Reticulospinal tracts 2. Vestibulospinal tracts 3. Tectospinal tracts
Module 13.20: Motor pathways Medial pathway (continued) Reticulospinal tracts Axons of upper motor neurons in reticular formation Reticular formation receives input from almost every ascending/descending pathway and has extensive connections with cerebrum, cerebellum, and brainstem Vestibulospinal tracts Start at vestibular nuclei of CN VIII (vestibulocochlear nerve.) Get sensory information from internal ear about head position/movement; send motor commands to alter muscle tone and position of neck, head, eyes, limbs
Module 13.20: Motor pathways Medial pathway (continued) Tectospinal tracts Upper motor neurons in superior/inferior colliculi (midbrain) Reflex changes in position of head, neck, upper limb in response to bright light, sudden movement, loud noises
The Medial Pathway
Cross-section of spinal cord showing positions of the various motor tracts
Module 13.20: Review A. Describe the role of the corticobulbar tracts. B. Define corticospinal tracts. C. What effect would increased stimulation of the motor neurons of the red nucleus have on muscle tone? Learning Outcome: Describe the components, processes, and functions of the somatic motor pathways.
Module 13.21: There are multiple levels of somatic motor control Many nuclei in spinal cord and brain are involved in controlling skeletal muscle contractions Generally, the closer the motor center is to the cerebral cortex, the more complex the motor activity Cerebellum coordinates motor activities at multiple levels
Module 13.21: Levels of somatic motor control Levels of somatic motor control (least to most complex): 1. Brainstem/spinal cord 2. Pons/medulla oblongata 3. Hypothalamus 4. Thalamus/midbrain 5. Basal nuclei 6. Cerebellum 7. Cerebral cortex
Levels of motor control
Module 13.21: Levels of somatic motor control Preparing for movement Decision to move begins relay of information from: Frontal lobes premotor cortex basal nuclei/cerebellum
Module 13.21: Levels of somatic motor control As movement begins: Information is sent from premotor cortex to primary motor cortex Commands are modified by feedback from cerebellum/basal nuclei
Module 13.21: Levels of somatic motor control Effects of primary motor cortex damage Person loses fine motor control over skeletal muscles Some voluntary movements will still be controlled by basal nuclei with input from prefrontal cortex Cerebellum cannot fine-tune movements because corticospinal pathway is inoperative An individual is able to stand, balance, and walk, but movements are hesitant, awkward, poorly controlled
Module 13.21: Review A. Which brain regions control reflexes in response to visual and auditory stimuli that are experienced while viewing a movie? B. The basic reflex motor patterns related to eating and drinking are controlled by which region of the brain? C. During a tennis match, you decide how and where to hit the ball. Explain how the premotor cortex is involved in your decisions. Learning Outcome: Describe the levels of information processing involved in motor control.
Module 13.22: Nervous system disorders may result from problems with neurons, pathways, or a combination of the two Referred pain Sensation of pain in a part of the body other than its actual source Example: pain of a heart attack felt in left arm Strong visceral pain sensations arriving at a spinal cord segment can stimulate interneurons in spinothalamic pathway Stimulates primary sensory cortex Pain perceived pain as coming from corresponding part of body surface (see sensory homunculus)
13.22: Nervous system disorders Parkinson s disease Substantia nigra neurons damaged or secrete less dopamine Basal nuclei become more active, increasing muscle tone and producing stiffness and rigidity Starting movements is difficult because antagonistic muscle groups do not relax (must be overpowered) Every part of a movement must be voluntarily controlled through intense effort and concentration
13.22: Nervous system disorders Rabies Bite from rabid animal injects rabies virus into peripheral tissues; virus enters axon terminals Virus carried by axons back into CNS through retrograde flow Potentially fatal results Many toxins, pathogenic bacteria, and other viruses also bypass CNS defenses through axoplasmic transport
13.22: Nervous system disorders Cerebral palsy (CP) Number of disorders that affect voluntary movement Motor dysfunction is nonprogressive Appears during infancy/childhood; persists throughout life Cause may be: Trauma from premature/stressful childbirth Maternal exposure to drugs (including alcohol) Genetic defect disrupting motor pathway development
13.22: Nervous system disorders Amyotrophic lateral sclerosis (ALS) Progressive, degenerative disorder affecting motor neurons in spinal cord, brainstem, cerebrum Destroys upper/lower motor neurons Associated skeletal muscles atrophy Likely defect in axonal transport Also called Lou Gehrig s disease (famous Yankees player who died from it); Stephen Hawking, noted physicist, also afflicted with ALS
13.22: Nervous system disorders Alzheimer s disease (AD) Progressive disorder causing loss of higher-order cerebral functions AD patients have intracellular and extracellular abnormalities in hippocampus (affects memory processing) Most common cause of senile dementia, or senility
13.22: Nervous system disorders Alzheimer s disease (AD) (continued) Symptoms may appear at age 50 60 or later; also affects younger people Estimated 2 million people affected in United States (~15 percent of those over 65, ~50 percent of those over 85); ~100,000 deaths/year
13.22: Nervous system disorders Multiple sclerosis (sklerosis, hardness) (MS) CNS disease characterized by recurrent incidents of demyelination in axons of optic nerve, brain, spinal cord Common signs/symptoms include impairment of vision, speech, balance, general motor coordination (including urinary/bowel) Time between incidents and degree of recovery vary In about one-third of patients, disease progresses more functional impairment occurs with each incident Onset often occurs at age 30 40 years; 1.5 times more common in women