The Brain Muse spring 2430 lecture 15 7/12/10. Embryonic Development Neural plate forms from...
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Transcript of The Brain Muse spring 2430 lecture 15 7/12/10. Embryonic Development Neural plate forms from...
The Brain
Muse spring 2430lecture 157/12/10
Embryonic Development
• Neural plate forms from ectoderm
• Neural plate invaginates to form a neural groove and neural folds
Figure 12.1, step 1
The neural plate forms from surface ectoderm.1
Head
Tail
Surfaceectoderm
Neuralplate
(a)Neuraltube
(b) Primary brainvesicles
Anterior(rostral)
Posterior(caudal)
Rhombencephalon(hindbrain)
Mesencephalon(midbrain)
Prosencephalon(forebrain)
Figure 12.2a-b
(d) Adult brainstructures
(c) Secondary brainvesicles
Spinal cord
Cerebellum
Brain stem: medullaoblongata
Brain stem: pons
Brain stem: midbrain
Diencephalon(thalamus, hypothalamus,epithalamus), retina
Cerebrum: cerebralhemispheres (cortex,white matter, basal nuclei)
Myelencephalon
Metencephalon
Mesencephalon
Diencephalon
Telencephalon
Central canal
Fourthventricle
Cerebralaqueduct
Third ventricle
Lateralventricles
(e) Adultneural canalregions
Figure 12.2c-e
Figure 12.3a
Metencephalon
Anterior (rostral) Posterior (caudal)
MesencephalonDiencephalon Midbrain
Cervical
Spinal cord
Flexures
TelencephalonMyelencephalon
(a) Week 5
Figure 12.3b
MidbrainCerebellumPonsMedulla oblongata
Spinal cord
Cerebral hemisphere
Outline of diencephalon
(b) Week 13
Figure 12.3c
CerebellumPonsMedullaoblongata Spinal cord
Cerebralhemisphere
(c) Week 26
Figure 12.3d
Cerebellum
Diencephalon
Cerebralhemisphere
(d) Birth
Brain stem• Midbrain• Pons• Medullaoblongata
Ventricles of the Brain
• Contain cerebrospinal fluid
• Two C-shaped lateral ventricles in the cerebral hemispheres
• Third ventricle in the diencephalon
• Fourth ventricle in the hindbrain, dorsal to the pons, develops from the lumen of the neural tube
Figure 12.5
Anterior horn
Interventricularforamen
Inferiorhorn
Lateralaperture
(b) Left lateral view
Lateral ventricle
Septum pellucidum
Third ventricle
Cerebral aqueduct
(a) Anterior view
Fourth ventricleCentral canal
Inferior horn
Posteriorhorn
MedianapertureLateralaperture
Cerebral Hemispheres
• Surface markings
• Ridges (gyri), shallow grooves (sulci), and deep grooves (fissures)
• Five lobes
• Frontal
• Parietal
• Temporal
• Occipital
• Insula
Cerebral Hemispheres
• Surface markings
• Central sulcus
• Separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe
• Longitudinal fissure
• Separates the two hemispheres
• Transverse cerebral fissure
• Separates the cerebrum and the cerebellum
PLAYPLAY Animation: Rotatable brain
Figure 12.6a
Postcentralgyrus
Centralsulcus
Precentralgyrus
Frontallobe
(a)
Parietal lobeParieto-occipital sulcus(on medial surfaceof hemisphere)Lateral sulcus
Transverse cerebral fissure
Occipital lobeTemporal lobe
CerebellumPons
Medulla oblongataSpinal cord
Cortex (gray matter)
Fissure(a deepsulcus)
Gyrus
SulcusWhite matter
Figure 12.6b
Centralsulcus
(b)
Frontal lobe
Temporal lobe(pulled down)
Gyri of insula
Figure 12.6c
Parietallobe
Frontal lobe
Right cerebralhemisphere
Occipitallobe
Left cerebralhemisphere
Cerebral veinsand arteriescovered byarachnoidmater
Longitudinalfissure
Posterior(c)
Anterior
Figure 12.6d
Left cerebralhemisphere
TransversecerebralfissureCerebellum
Brain stem
(d)
Cerebral Cortex
• Thin (2–4 mm) superficial layer of gray matter
• 40% of the mass of the brain
• Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding
• Each hemisphere connects to contralateral side of the body
• There is lateralization of cortical function in the hemispheres
Functional Areas of the Cerebral Cortex
• The three types of functional areas are:
• Motor areas—control voluntary movement
• Sensory areas—conscious awareness of sensation
• Association areas—integrate diverse information
• Conscious behavior involves the entire cortex
Motor Areas
• Primary (somatic) motor cortex
• Premotor cortex
• Broca’s area
• Frontal eye field
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Primary Motor Cortex
• Large pyramidal cells of the precentral gyri
• Long axons pyramidal (corticospinal) tracts
• Allows conscious control of precise, skilled, voluntary movements
• Motor homunculi: upside-down caricatures representing the motor innervation of body regions
Figure 12.9
Toes
Swallowing
Tongue
Jaw
Primary motorcortex(precentral gyrus)
MotorMotor map inprecentral gyrus
Posterior
Anterior
Premotor Cortex
• Anterior to the precentral gyrus
• Controls learned, repetitious, or patterned motor skills
• Coordinates simultaneous or sequential actions
• Involved in the planning of movements that depend on sensory feedback
Broca’s Area
• Anterior to the inferior region of the premotor area
• Present in one hemisphere (usually the left)
• A motor speech area that directs muscles of the tongue
• Is active as one prepares to speak
Frontal Eye Field
• Anterior to the premotor cortex and superior to Broca’s area
• Controls voluntary eye movements
Sensory Areas
• Primary somatosensory cortex
• Somatosensory association cortex
• Visual areas
• Auditory areas
• Olfactory cortex
• Gustatory cortex
• Visceral sensory area
• Vestibular cortex
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Primary Somatosensory Cortex
• In the postcentral gyri
• Receives sensory information from the skin, skeletal muscles, and joints
• Capable of spatial discrimination: identification of body region being stimulated
Figure 12.9
Genitals
Intra-abdominal
Primary somato-sensory cortex(postcentral gyrus)
SensorySensory map inpostcentral gyrus
Posterior
Anterior
Somatosensory Association Cortex
• Posterior to the primary somatosensory cortex
• Integrates sensory input from primary somatosensory cortex
• Determines size, texture, and relationship of parts of objects being felt
Visual Areas
• Primary visual (striate) cortex
• Extreme posterior tip of the occipital lobe
• Most of it is buried in the calcarine sulcus
• Receives visual information from the retinas
Visual Areas
• Visual association area
• Surrounds the primary visual cortex
• Uses past visual experiences to interpret visual stimuli (e.g., color, form, and movement)
• Complex processing involves entire posterior half of the hemispheres
Auditory Areas
• Primary auditory cortex
• Superior margin of the temporal lobes
• Interprets information from inner ear as pitch, loudness, and location
• Auditory association area
• Located posterior to the primary auditory cortex
• Stores memories of sounds and permits perception of sounds
OIfactory Cortex
• Medial aspect of temporal lobes (in piriform lobes)
• Part of the primitive rhinencephalon, along with the olfactory bulbs and tracts
• (Remainder of the rhinencephalon in humans is part of the limbic system)
• Region of conscious awareness of odors
Gustatory Cortex
• In the insula
• Involved in the perception of taste
Visceral Sensory Area
• Posterior to gustatory cortex
• Conscious perception of visceral sensations, e.g., upset stomach or full bladder
Vestibular Cortex
• Posterior part of the insula and adjacent parietal cortex
• Responsible for conscious awareness of balance (position of the head in space)
Figure 12.8a
Gustatory cortex(in insula)
Primary motor cortex
Premotor cortex
Frontal eye field
Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks
Broca’s area(outlined by dashes)
Solving complex,multitask problems
(a) Lateral view, left cerebral hemisphere
Motor areas
Prefrontal cortex
Sensory areas and relatedassociation areas
Central sulcus
Primary somatosensorycortexSomatosensoryassociation cortex
Somaticsensation
Taste
Wernicke’s area(outlined by dashes)
Primary visualcortexVisualassociation area
Vision
Auditoryassociation areaPrimaryauditory cortex
Hearing
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Figure 12.8b
Frontal eye field
Prefrontalcortex
Processes emotionsrelated to personaland social interactions
(b) Parasagittal view, right hemisphere
Olfactory bulbOrbitofrontalcortex
Olfactory tractFornix
Temporal lobe
Corpuscallosum
Premotor cortexPrimarymotor cortex
Cingulategyrus Central sulcus
Primary somatosensorycortex
Parietal lobe
Parieto-occipitalsulcus
Somatosensoryassociation cortex
OccipitallobeVisualassociationarea
Calcarine sulcusParahippocampalgyrus
UncusPrimaryolfactory cortex
Primaryvisual cortex
Primary motor cortex Motor association cortex Primary sensory cortex
Sensory association cortex Multimodal association cortex
Multimodal Association Areas
• Receive inputs from multiple sensory areas
• Send outputs to multiple areas, including the premotor cortex
• Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take
Multimodal Association Areas
• Three parts
• Anterior association area (prefrontal cortex)
• Posterior association area
• Limbic association area
Anterior Association Area (Prefrontal Cortex)
• Most complicated cortical region
• Involved with intellect, cognition, recall, and personality
• Contains working memory needed for judgment, reasoning, persistence, and conscience
• Development depends on feedback from social environment
Posterior Association Area
• Large region in temporal, parietal, and occipital lobes
• Plays a role in recognizing patterns and faces and localizing us in space
• Involved in understanding written and spoken language (Wernicke’s area)
Limbic Association Area
• Part of the limbic system
• Provides emotional impact that helps establish memories
Lateralization of Cortical Function
• Lateralization
• Division of labor between hemispheres
• Cerebral dominance
• Designates the hemisphere dominant for language (left hemisphere in 90% of people)
Lateralization of Cortical Function
• Left hemisphere
• Controls language, math, and logic
• Right hemisphere
• Insight, visual-spatial skills, intuition, and artistic skills
• Left and right hemispheres communicate via fiber tracts in the cerebral white matter
Cerebral White Matter
• Myelinated fibers and their tracts
• Responsible for communication
• Commissures (in corpus callosum)—connect gray matter of the two hemispheres
• Association fibers—connect different parts of the same hemisphere
• Projection fibers—(corona radiata) connect the hemispheres with lower brain or spinal cord
Figure 12.10a
Corona radiata
Projectionfibers
Longitudinal fissure
Gray matter
White matter
Associationfibers
Lateralventricle
Fornix
Thirdventricle
Thalamus
Pons
Medulla oblongataDecussationof pyramids
Commissuralfibers (corpus callosum)
Internalcapsule
Superior
Basal nuclei• Caudate• Putamen• Globuspallidus
(a)
Basal Nuclei (Ganglia)
• Subcortical nuclei
• Consists of the corpus striatum
• Caudate nucleus
• Lentiform nucleus (putamen + globus pallidus)
• Functionally associated with the subthalamic nuclei (diencephalon) and the substantia nigra (midbrain)
Figure 12.11a
Fibers ofcorona radiata
Corpusstriatum
(a)
Projection fibersrun deep to lentiform nucleus
Caudatenucleus Thalamus
Tail ofcaudatenucleus
Lentiformnucleus• Putamen• Globus pallidus (deep to putamen)
Figure 12.11b (1 of 2)
Corpus callosumAnterior hornof lateral ventricleCaudate nucleusPutamen
Lentiformnucleus
(b)
Globuspallidus ThalamusTail of caudate nucleusThird ventricle
Cerebral cortexCerebral white matter
Anterior
Posterior
Inferior hornof lateral ventricle
Figure 12.11b (2 of 2)
Corpus callosumAnterior hornof lateral ventricleCaudate nucleus
Lentiform nucleus
(b)
Thalamus
Third ventricle
Cerebral cortexCerebral white matter
Inferior hornof lateral ventricle
Functions of Basal Nuclei
• Though somewhat elusive, the following are thought to be functions of basal nuclei
• Influence muscular control
• Help regulate attention and cognition
• Regulate intensity of slow or stereotyped movements
• Inhibit antagonistic and unnecessary movements
Diencephalon
• Three paired structures
• Thalamus
• Hypothalamus
• Epithalamus
• Encloses the third ventricle
PLAYPLAY Animation: Rotatable brain (sectioned)
Figure 12.12
Corpus callosum
Choroid plexusThalamus(encloses third ventricle)
Pineal gland(part of epithalamus)
Posterior commissure
CorporaquadrigeminaCerebralaqueductArbor vitae (ofcerebellum)Fourth ventricleChoroid plexusCerebellum
Septum pellucidum
Interthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissure
Hypothalamus
Optic chiasma
Pituitary gland
Cerebral hemisphere
Mammillary bodyPonsMedulla oblongata
Spinal cord
Mid-brain
Fornix
Thalamus
• 80% of diencephalon
• Superolateral walls of the third ventricle
• Connected by the interthalamic adhesion (intermediate mass)
• Contains several nuclei, named for their location
• Nuclei project and receive fibers from the cerebral cortex
Figure 12.13a
Dorsal nuclei
Medial
Anteriornucleargroup
Reticularnucleus
Ventralanterior
Ventrallateral
Ventralpostero-lateral
Lateralgeniculatebody
Medialgeniculatebody
Pulvinar
Lateraldorsal
Lateralposterior
(a) The main thalamic nuclei. (The reticular nuclei that “cap” thethalamus laterally are depicted as curving translucent structures.)
Ventral nuclei
Thalamic Function
• Gateway to the cerebral cortex
• Sorts, edits, and relays information
• Afferent impulses from all senses and all parts of the body
• Impulses from the hypothalamus for regulation of emotion and visceral function
• Impulses from the cerebellum and basal nuclei to help direct the motor cortices
• Mediates sensation, motor activities, cortical arousal, learning, and memory
Hypothalamus
• Forms the inferolateral walls of the third ventricle
• Contains many nuclei
• Example: mammillary bodies
• Paired anterior nuclei
• Olfactory relay stations
• Infundibulum—stalk that connects to the pituitary gland
Figure 12.13b
Preopticnucleus
SupraopticnucleusSupra-chiasmatic nucleus
Anteriorhypothalamicnucleus
Dorsomedialnucleus
Paraventricularnucleus
FornixAnteriorcommissure
PosteriorhypothalamicnucleusLateralhypothalamicareaVentromedialnucleus
OpticchiasmaInfundibulum(stalk of thepituitary gland)
Pituitarygland
Mammillarybody
(b) The main hypothalamic nuclei.
Arcuatenucleus
Hypothalamic Function
• Autonomic control center for many visceral functions (e.g., blood pressure, rate and force of heartbeat, digestive tract motility)
• Center for emotional response: Involved in perception of pleasure, fear, and rage and in biological rhythms and drives
Hypothalamic Function
• Regulates body temperature, food intake, water balance, and thirst
• Regulates sleep and the sleep cycle
• Controls release of hormones by the anterior pituitary
• Produces posterior pituitary hormones
Epithalamus
• Most dorsal portion of the diencephalon; forms roof of the third ventricle
• Pineal gland—extends from the posterior border and secretes melatonin
• Melatonin—helps regulate sleep-wake cycles
Figure 12.12
Corpus callosum
Choroid plexusThalamus(encloses third ventricle)
Pineal gland(part of epithalamus)
Posterior commissure
CorporaquadrigeminaCerebralaqueductArbor vitae (ofcerebellum)Fourth ventricleChoroid plexusCerebellum
Septum pellucidum
Interthalamicadhesion(intermediatemass of thalamus)Interven-tricularforamenAnteriorcommissure
Hypothalamus
Optic chiasma
Pituitary gland
Cerebral hemisphere
Mammillary bodyPonsMedulla oblongata
Spinal cord
Mid-brain
Fornix
Brain Stem
• Three regions
• Midbrain
• Pons
• Medulla oblongata
Brain Stem
• Similar structure to spinal cord but contains embedded nuclei
• Controls automatic behaviors necessary for survival
• Contains fiber tracts connecting higher and lower neural centers
• Associated with 10 of the 12 pairs of cranial nerves
Figure 12.14
Frontal lobeOlfactory bulb(synapse point ofcranial nerve I)Optic chiasmaOptic nerve (II)Optic tractMammillary body
Pons
MedullaoblongataCerebellum
Temporal lobe
Spinal cord
Midbrain
Figure 12.15a
Optic chiasmaView (a)
Optic nerve (II)
Mammillary body
Oculomotor nerve (III)
Crus cerebri ofcerebral peduncles (midbrain)
Trigeminal nerve (V)
Abducens nerve (VI)Facial nerve (VII)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Ventral root of firstcervical nerve
Trochlear nerve (IV)
PonsMiddle cerebellarpeduncle
Pyramid
Decussation of pyramids
(a) Ventral view
Spinal cord
Vestibulocochlearnerve (VIII)
Glossopharyngeal nerve (IX)
Diencephalon• Thalamus• Hypothalamus
Diencephalon
Brainstem
Thalamus
Hypothalamus
Midbrain
Pons
Medullaoblongata
Figure 12.15b
View (b)
Crus cerebri ofcerebral peduncles (midbrain)
InfundibulumPituitary gland
Trigeminal nerve (V)
Abducens nerve (VI)
Facial nerve (VII)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Pons
(b) Left lateral view
Glossopharyngeal nerve (IX)
Diencephalon
Brainstem
Thalamus
Hypothalamus
Midbrain
Pons
Medullaoblongata
Thalamus
Superior colliculusInferior colliculusTrochlear nerve (IV)
Superior cerebellar peduncle
Middle cerebellar peduncle
Inferior cerebellar peduncle
Vestibulocochlear nerve (VIII)Olive
Figure 12.15c
View (c)
Diencephalon
Brainstem
Thalamus
Hypothalamus
Midbrain
Pons
Medullaoblongata
Pineal gland
Diencephalon
Anterior wall offourth ventricle
(c) Dorsal view
Thalamus
Dorsal root offirst cervical nerve
Midbrain• Superior
colliculus• Inferior
colliculus• Trochlear nerve (IV)• Superior cerebellar peduncle
Corporaquadrigeminaof tectum
Medulla oblongata• Inferior cerebellar peduncle• Facial nerve (VII)• Vestibulocochlear nerve (VIII)• Glossopharyngeal nerve (IX)• Vagus nerve (X)• Accessory nerve (XI)
Pons• Middle cerebellar peduncle
Dorsal median sulcus
Choroid plexus(fourth ventricle)
Midbrain
• Located between the diencephalon and the pons
• Cerebral peduncles
• Contain pyramidal motor tracts
• Cerebral aqueduct
• Channel between third and fourth ventricles
Midbrain Nuclei
• Nuclei that control cranial nerves III (oculomotor) and IV (trochlear)
• Corpora quadrigemina—domelike dorsal protrusions
• Superior colliculi—visual reflex centers
• Inferior colliculi—auditory relay centers
• Substantia nigra—functionally linked to basal nuclei
• Red nucleus—relay nuclei for some descending motor pathways and part of reticular formation
Figure 12.16a
Dorsal
Cerebral aqueduct
Superiorcolliculus
Reticular formation
Crus cerebri ofcerebral peduncle
Ventral
Fibers ofpyramidal tract
Substantianigra
(a) Midbrain
Rednucleus
Mediallemniscus
Oculomotornucleus (III)
Periaqueductal graymatter
Tectum
Pons
• Forms part of the anterior wall of the fourth ventricle
• Fibers of the pons
• Connect higher brain centers and the spinal cord
• Relay impulses between the motor cortex and the cerebellum
• Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial)
• Some nuclei of the reticular formation
• Nuclei that help maintain normal rhythm of breathing
Figure 12.16b
Reticularformation
Trigeminalnerve (V)
Pontinenuclei
Fibers ofpyramidaltract
Middlecerebellarpeduncle
Trigeminal mainsensory nucleus Trigeminalmotor nucleus
Superior cerebellarpeduncle
Medial lemniscus
Fourthventricle
(b) Pons
Medulla Oblongata
• Joins spinal cord at foramen magnum
• Forms part of the ventral wall of the fourth ventricle
• Contains a choroid plexus of the fourth ventricle
• Pyramids—two ventral longitudinal ridges formed by pyramidal tracts
• Decussation of the pyramids—crossover of the corticospinal tracts
Medulla Oblongata
• Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellum
• Cranial nerves VIII, X, and XII are associated with the medulla
• Vestibular nuclear complex—mediates responses that maintain equilibrium
• Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory information
Medulla Oblongata
• Autonomic reflex centers
• Cardiovascular center
• Cardiac center adjusts force and rate of heart contraction
• Vasomotor center adjusts blood vessel diameter for blood pressure regulation
Medulla Oblongata
• Respiratory centers
• Generate respiratory rhythm
• Control rate and depth of breathing, with pontine centers
Medulla Oblongata
• Additional centers regulate
• Vomiting
• Hiccuping
• Swallowing
• Coughing
• Sneezing
Figure 12.16c
Choroidplexus
Fourth ventricle
PyramidMedial lemniscus
Inferior olivarynucleus
Nucleusambiguus
Inferior cerebellarpeduncle
Cochlearnuclei (VIII)
Vestibular nuclearcomplex (VIII)
Solitarynucleus
Dorsal motor nucleusof vagus (X)
Hypoglossal nucleus (XII)
(c) Medulla oblongata
LateralnucleargroupMedialnucleargroupRaphenucleusRet
icu
lar
form
atio
n
The Cerebellum
• 11% of brain mass
• Dorsal to the pons and medulla
• Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction
Anatomy of the Cerebellum
• Two hemispheres connected by vermis
• Each hemisphere has three lobes
• Anterior, posterior, and flocculonodular
• Folia—transversely oriented gyri
• Arbor vitae—distinctive treelike pattern of the cerebellar white matter
Figure 12.17b
(b)
Medullaoblongata
Flocculonodularlobe
Choroidplexus offourth ventricle
Posteriorlobe
Arborvitae
Cerebellar cortex
Anterior lobe
Cerebellarpeduncles• Superior• Middle• Inferior
Figure 12.17d
(d)
Anteriorlobe
Posteriorlobe
Vermis(d)
Cerebellar Peduncles
• All fibers in the cerebellum are ipsilateral
• Three paired fiber tracts connect the cerebellum to the brain stem
• Superior peduncles connect the cerebellum to the midbrain
• Middle peduncles connect the pons to the cerebellum
• Inferior peduncles connect the medulla to the cerebellum
Cerebellar Processing for Motor Activity
• Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction
• Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum
• Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction
• A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei
Cognitive Function of the Cerebellum
• Recognizes and predicts sequences of events during complex movements
• Plays a role in nonmotor functions such as word association and puzzle solving
Functional Brain Systems
• Networks of neurons that work together and span wide areas of the brain
• Limbic system
• Reticular formation
Limbic System
• Structures on the medial aspects of cerebral hemispheres and diencephalon
• Includes parts of the diencephalon and some cerebral structures that encircle the brain stem
Figure 12.18
Corpus callosum
Septum pellucidum
Olfactory bulb
Diencephalic structuresof the limbic system
•Anterior thalamic nuclei (flanking 3rd ventricle)•Hypothalamus•Mammillary body
Fiber tractsconnecting limbic system structures
•Fornix•Anterior commissure
Cerebral struc-tures of the limbic system
•Cingulate gyrus•Septal nuclei•Amygdala•Hippocampus•Dentate gyrus•Parahippocampal gyrus
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
• Puts emotional responses to odors
• Example: skunks smell bad
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
• Hippocampus and amygdala—play a role in memory
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
Figure 12.19
Visualimpulses
Reticular formation
Ascending generalsensory tracts(touch, pain, temperature)
Descendingmotor projectionsto spinal cord
Auditoryimpulses
Radiationsto cerebralcortex
Electroencephalogram (EEG)
• Records electrical activity that accompanies brain function
• Measures electrical potential differences between various cortical areas
Figure 12.20a
(a) Scalp electrodes are used to record brain waveactivity (EEG).
Brain Waves
• Patterns of neuronal electrical activity
• Generated by synaptic activity in the cortex
• 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)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain
• Beta waves (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert
• Theta waves (4–7 Hz)—more irregular; common in children and uncommon in adults
• Delta waves (4 Hz or less)—high-amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage
Figure 12.20b
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 intofour general classes.
1-second interval
Brain Waves: State of the Brain
• Change with age, sensory stimuli, brain disease, and the chemical state of the body
• 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
Epilepsy
• A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking
• Epilepsy is not associated with intellectual impairments
• Epilepsy occurs in 1% of the population
Epileptic Seizures
• Absence seizures, or petit mal
• Mild seizures seen in young children where the expression goes blank
• 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 can keep electrical activity of the brain from becoming chaotic
Consciousness
• Conscious perception of sensation
• Voluntary initiation and control of movement
• Capabilities associated with higher mental processing (memory, logic, judgment, etc.)
• Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired
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 (defined by EEG patterns)
• Nonrapid eye movement (NREM)
• Rapid eye movement (REM)
Sleep
• First two stages of NREM occur during the first 30–45 minutes of sleep
• Fourth stage is achieved in about 90 minutes, and then REM sleep begins abruptly
Figure 12.21a
Awake
(a) Typical EEG patterns
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: IrregularEEG with sleep spindles (short high- amplitude bursts); arousal is more difficult.
NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline.
NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur.
Sleep Patterns
• Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm
• RAS activity is inhibited during, but RAS also mediates, dreaming sleep
• The suprachiasmatic and preoptic nuclei of the hypothalamus time the sleep cycle
• A typical sleep pattern alternates between REM and NREM sleep
Figure 12.21b
(b) Typical progression of an adult through onenight’s sleep stages
Awake
REM
Stage 1
Stage 2NonREM Stage 3
Stage 4
Time (hrs)
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
• REM sleep may be a reverse learning process where superfluous information is purged from the brain
• Daily sleep requirements decline with age
• Stage 4 sleep declines steadily and may disappear after age 60
Sleep Disorders
• Narcolepsy
• Lapsing abruptly into sleep from the awake state
• Insomnia
• Chronic inability to obtain the amount or quality of sleep needed
• Sleep apnea
• Temporary cessation of breathing during sleep
Language
• Language implementation system
• Basal nuclei
• Broca’s area and Wernicke’s area (in the association cortex on the left side)
• Analyzes incoming word sounds
• Produces outgoing word sounds and grammatical structures
• Corresponding areas on the right side are involved with nonverbal language components
Memory
• Storage and retrieval of information
• Two stages of storage
• Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information
• Long-term memory (LTM) has limitless capacity
Figure 12.22
Outside stimuli
General and special sensory receptors
Data transferinfluenced by:
ExcitementRehearsalAssociation ofold and new data
Long-termmemory(LTM)
Data permanentlylost
Afferent inputs
Retrieval
Forget
Forget
Data selectedfor transfer
Automaticmemory
Data unretrievable
Temporary storage(buffer) in cerebral cortex
Short-termmemory (STM)
Transfer from STM to LTM
• Factors that affect transfer from STM to LTM
• Emotional state—best if alert, motivated, surprised, and aroused
• Rehearsal—repetition and practice
• Association—tying new information with old memories
• Automatic memory—subconscious information stored in LTM
Categories of Memory
• Declarative memory (factual knowledge)
• Explicit information
• Related to our conscious thoughts and our language ability
• Stored in LTM with context in which it was learned
Categories of Memory
• Nondeclarative memory
• Less conscious or unconscious
• Acquired through experience and repetition
• Best remembered by doing; hard to unlearn
• Includes procedural (skills) memory, motor memory, and emotional memory
Brain Structures Involved in Declarative Memory
• Hippocampus and surrounding temporal lobes function in consolidation and access to memory
• ACh from basal forebrain is necessary for memory formation and retrieval
Figure 12.23a
Smell
Basal forebrain
Prefrontal cortex
Taste
Thalamus
Touch
Hearing
Vision
Hippocampus
Thalamus
Prefrontalcortex
Basalforebrain
Associationcortex
Sensoryinput
ACh ACh
Medial temporal lobe(hippocampus, etc.)
(a) Declarativememory circuits
Brain Structures Involved in Nondeclarative Memory
• Procedural memory
• Basal nuclei relay sensory and motor inputs to the thalamus and premotor cortex
• Dopamine from substantia nigra is necessary
• Motor memory—cerebellum
• Emotional memory—amygdala
Figure 12.23b
Dopamine
Thalamus Premotorcortex
Substantianigra
Associationcortex
Basalnuclei
Sensory andmotor inputs
Premotorcortex
ThalamusSubstantia nigra
Basal nuclei
(b) Procedural (skills) memory circuits
Molecular Basis of Memory
• During learning:
• Altered mRNA is synthesized and moved to axons and dendrites
• Dendritic spines change shape
• Extracellular proteins are deposited at synapses involved in LTM
• Number and size of presynaptic terminals may increase
• More neurotransmitter is released by presynaptic neurons
Molecular Basis of Memory
• Increase in synaptic strength (long-term potentiation, or LTP) is crucial
• Neurotransmitter (glutamate) binds to NMDA receptors, opening calcium channels in postsynaptic terminal
Molecular Basis of Memory
• Calcium influx triggers enzymes that modify proteins of the postsynaptic terminal and presynaptic terminal (via release of retrograde messengers)
• Enzymes trigger postsynaptic gene activation for synthesis of synaptic proteins, in presence of CREB (cAMP response-element binding protein) and BDNF (brain-derived neurotrophic factor)
Meninges
• Three layers
• Dura mater
• Arachnoid mater
• Pia mater
Figure 12.24
Skin of scalpPeriosteum
Falx cerebri(in longitudinalfissure only)
Blood vesselArachnoid villusPia materArachnoid mater
Duramater Meningeal
Periosteal
Bone of skull
Superiorsagittal sinus
Subduralspace
Subarachnoidspace
Dura Mater
• Strongest meninx
• Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses
Dura Mater
• Dural septa limit excessive movement of the brain
• Falx cerebri—in the longitudinal fissure; attached to crista galli
• Falx cerebelli—along the vermis of the cerebellum
• Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure
Figure 12.25a
Falx cerebri
Superiorsagittal sinus
Straightsinus
Crista galliof theethmoid bone
Pituitarygland
Falxcerebelli
(a) Dural septa
Tentoriumcerebelli
Arachnoid Mater
• Middle layer with weblike extensions
• Separated from the dura mater by the subdural space
• Subarachnoid space contains CSF and blood vessels
• Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption
Figure 12.24
Skin of scalpPeriosteum
Falx cerebri(in longitudinalfissure only)
Blood vesselArachnoid villusPia materArachnoid mater
Duramater Meningeal
Periosteal
Bone of skull
Superiorsagittal sinus
Subduralspace
Subarachnoidspace
Pia Mater
• Layer of delicate vascularized connective tissue that clings tightly to the brain
Figure 12.26a
Superiorsagittal sinus
Arachnoid villus
Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater
Right lateral ventricle(deep to cut)Choroid plexusof fourth ventricle
Central canalof spinal cord
Choroidplexus
Interventricularforamen
Third ventricle
Cerebral aqueductLateral apertureFourth ventricleMedian aperture
(a) CSF circulation
CSF is produced by thechoroid plexus of eachventricle.
1
CSF flows through theventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.
2
CSF flows through thesubarachnoid space. 3
CSF is absorbed into the dural venoussinuses via the arachnoid villi. 4
1
2
3
4
Choroid Plexuses
• Produce CSF at a constant rate
• Hang from the roof of each ventricle
• Clusters of capillaries enclosed by pia mater and a layer of ependymal cells
• Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes
Figure 12.26b
Ependymalcells
Capillary
Connectivetissue ofpia mater
Wastes andunnecessarysolutes absorbed
Sectionof choroidplexus
(b) CSF formation by choroid plexuses
Cavity ofventricle
CSF forms as a filtratecontaining glucose, oxygen, vitamins, and ions(Na+, Cl–, Mg2+, etc.)
Blood-Brain Barrier
• Composition
• Continuous endothelium of capillary walls
• Basal lamina
• Feet of astrocytes
• Provide signal to endothelium for the formation of tight junctions
Figure 11.3a
(a) Astrocytes are the most abundantCNS neuroglia.
Capillary
Neuron
Astrocyte