The Brain

Muse Spring2430Lecture #107/16/12

An Introduction to the Brain and Cranial Nerves

• The Adult Human Brain

– Ranges from 750 cc to 2100 cc

– Contains almost 97% of the body’s neural tissue

– Average weight about 1.4 kg (3 lb)

The Brain• Six Regions of the Brain– Cerebrum

– Cerebellum

– Diencephalon

– Mesencephalon

– Pons

– Medulla oblongata

The Brain

Figure 14–1 An Introduction to Brain Structures and Functions.

Figure 12.6c

Parietallobe

Frontal lobe

Right cerebralhemisphere

Occipitallobe

Left cerebralhemisphere

Cerebral veinsand arteriescovered byarachnoidmater

Longitudinalfissure

Posterior(c)

Anterior

The Brain

Figure 14–2 Ventricles of the Brain.

Brain Protection and Support• Cerebrospinal Fluid (CSF)

– Surrounds all exposed surfaces of CNS

– Interchanges with interstitial fluid of brain

– Functions of CSF

• Cushions delicate neural structures

• Supports brain

• Transports nutrients, chemical messengers, and waste

products

Brain Protection and Support

Figure 14–4 The Formation and Circulation of Cerebrospinal Fluid.

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.)

Brain Protection and Support

• Blood Supply to the Brain

– Supplies nutrients and oxygen to brain

– Delivered by internal carotid arteries and

vertebral arteries

– Removed from dural sinuses by internal jugular

veins

Brain Protection and Support

Figure 21–23 Arteries of the Brain.

Brain Protection and Support• Blood–Brain Barrier

– Isolates CNS neural tissue from general circulation

– Formed by network of tight junctions

– Between endothelial cells of CNS capillaries

– Lipid-soluble compounds (O2, CO2), steroids, and

prostaglandins diffuse into interstitial fluid of brain and

spinal cord

– Astrocytes control blood–brain barrier by releasing

chemicals that control permeability of endothelium

Figure 11.3a

(a) Astrocytes are the most abundantCNS neuroglia.

Capillary

Neuron

Astrocyte

Brain Protection and Support• Four Breaks in the BBB– Portions of hypothalamus• Secrete hypothalamic hormones

– Posterior lobe of pituitary gland• Secretes hormones ADH and oxytocin

– Pineal glands• Pineal secretions

– Choroid plexus• Where special ependymal cells maintain blood–CSF

barrier

The Medulla Oblongata• The Medulla Oblongata

– Allows brain and spinal cord to communicate

– Coordinates complex autonomic reflexes

– Controls visceral functions

– Nuclei in the Medulla

• Autonomic nuclei: control visceral activities

• Sensory and motor nuclei: of cranial nerves

• Relay stations: along sensory and motor pathways

The Medulla Oblongata

Figure 14–5a The Diencephalon and Brain Stem.

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

• Functions of the Cerebellum

– Adjusts postural muscles

– Fine-tunes conscious and subconscious

movements

The Cerebellum• Structures of the Cerebellum

– Purkinje cells

• Large, branched cells

• Found in cerebellar cortex

• Receive input from up to 200,000 synapses

– Arbor vitae

• Highly branched, internal white matter of cerebellum

• Cerebellar nuclei: embedded in arbor vitae:

– relay information to Purkinje cells

The Cerebellum

Figure 14–7b The Cerebellum.

Figure 12.17d

(d)

Anteriorlobe

Posteriorlobe

Vermis(d)

The Cerebellum

• Disorders of the Cerebellum

– Ataxia

• Damage from trauma or stroke

• Intoxication (temporary impairment)

• Disturbs muscle coordination

The Diencephalon

• Integrates sensory information and motor commands

• Thalamus, epithalamus, and hypothalamus

– The pineal gland

• Found in posterior epithalamus

• Secretes hormone melatonin

The Diencephalon• The Hypothalamus– Mamillary bodies

• Process olfactory and other sensory information

• Control reflex eating movements

– Infundibulum• A narrow stalk

• Connects hypothalamus to pituitary gland

– Tuberal area• Located between the infundibulum and mamillary bodies

• Helps control pituitary gland function

The Diencephalon

Figure 14–10a The Hypothalamus in Sagittal Section.

The Diencephalon

• Eight Functions of the Hypothalamus

– Provides subconscious control of skeletal muscle

– Controls autonomic function

– Coordinates activities of nervous and endocrine systems

– Secretes hormones

• Antidiuretic hormone (ADH) by supraoptic nucleus

• Oxytocin (OT; OXT) by paraventricular nucleus

The Diencephalon• Eight Functions of the Hypothalamus

– Produces emotions and behavioral drives

• The feeding center (hunger)

• The thirst center (thirst)

– Coordinates voluntary and autonomic functions

– Regulates body temperature

• Preoptic area of hypothalamus

– Controls circadian rhythms (day–night cycles)

• Suprachiasmatic nucleus

The Limbic System

• The Limbic System

– Is a functional grouping that

• Establishes emotional states

• Links conscious functions of cerebral cortex with autonomic

functions of brain stem

• Facilitates memory storage and retrieval

The Limbic System

Figure 14–11a The Limbic System.

The Limbic System• Components of the Limbic System– Amygdaloid body• Acts as interface between the limbic system, the

cerebrum, and various sensory systems

– Limbic lobe of cerebral hemisphere• Cingulate gyrus

• Dentate gyrus

• Parahippocampal gyrus

• Hippocampus

The Limbic System• Components of the Limbic System– Fornix• Tract of white matter• Connects hippocampus with hypothalamus

– Anterior nucleus of the thalamus• Relays information from mamillary body to cingulate

gyrus

– Reticular formation• Stimulation or inhibition affects emotions (rage, fear,

pain, sexual arousal, pleasure)

The Limbic System

Figure 14–11b The Limbic System.

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

The limbic system

The Cerebrum

• The Cerebrum

– Is the largest part of the brain

– Controls all conscious thoughts and intellectual

functions

– Processes somatic sensory and motor information

The Cerebrum

• Gray matter

– In cerebral cortex and basal nuclei

• White matter

– Deep to basal cortex

– Around basal nuclei

The Cerebrum

Figure 14–12c The Brain in Lateral View.

The Cerebrum• Special Sensory Cortexes– Visual cortex • Information from sight receptors

– Auditory cortex • Information from sound receptors

– Olfactory cortex • Information from odor receptors

– Gustatory cortex • Information from taste receptors

The Cerebrum

Figure 14–15a Motor and Sensory Regions of the Cerebral Cortex.

The Cerebrum

Figure 14–16 Hemispheric Lateralization.

The Cerebrum

• Monitoring Brain Activity

– Brain activity is assessed by an

electroencephalogram (EEG)

• Electrodes are placed on the skull

• Patterns of electrical activity (brain waves) are printed

out

The Cerebrum• Four Categories of Brain Waves– Alpha waves

• Found in healthy, awake adults at rest with eyes closed– Beta waves 12-30 Hz

• Higher frequency• Found in adults concentrating or mentally stressed

– Theta waves• Found in children• Found in intensely frustrated adults• May indicate brain disorder in adults

– Delta waves 1-4 Hz• During sleep• Found in awake adults with brain damage

The Cerebrum

Figure 14–17a-d Brain Waves.

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

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

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)

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

Consciousness

• Clinically defined on a continuum that grades behavior in response to stimuli– Alertness– Drowsiness (lethargy)– Stupor– Coma

Consciousness

• Clinically defined on a continuum that grades behavior in response to stimuli– Alertness– Drowsiness (lethargy)– Stupor– Coma

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

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

memory

Higher-Order Functions

• Amygdaloid body and hippocampus

– Are essential to memory consolidation

– Damage may cause

• Inability to convert short-term memories to new long-

term memories

• Existing long-term memories remain intact and

accessible

memory

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).

• Combination of potentiation and new synapse formation

Increase the learning of this chapter!

– Emotional state—best if alert (beta wave), motivated, surprised, and aroused. Chocolate while studying!

– Rehearsal—repetition and practice – Association—tying new information with old

memories. Connect lecture to lab. Draw!!!– Automatic memory—subconscious information

stored in LTM. Test yourself– Get some sleep. Repeat often

Review Guide for The Final will be posted on Blackboard and on the Website.

Pick up any old exams including you last exam in your lab sections or open labs

Open labs this week 11-1 today 11-1 Thursday