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