The Central Nervous SystemChapter 12

Regions and Organization of the CNS

Adult brain regions1. Cerebral hemispheres2. Diencephalon3. Brain stem (midbrain, pons, and medulla)4. Cerebellum

Figure 12.3d

Cerebellum

Diencephalon

Cerebralhemisphere

(d) Birth

Brain stem• Midbrain• Pons• Medullaoblongata

Ventricles of the Brain

• Connected to one another and to the central canal of the spinal cord

• Lined by ependymal cells• 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

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

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

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

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 and sends output to multiple areas

• Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take

• 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

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

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• Includes: cingulate gyrus, parahippocampal

gyrus, and hippocampus• Provides emotional impact that helps establish

memories

Lateralization of Cortical Function

• Lateralization – Division of labor between hemispheres– Left hemisphere • Controls language, math, and logic

– Right hemisphere• Insight, visual-spatial skills, intuition, and artistic skills

• Cerebral dominance– Designates the hemisphere dominant for language

(left hemisphere in 90% of people)

Cerebral White Matter

• Myelinated fibers and tracts• Communication between cerebral areas, and

between cortex and lower CNS – Association fibers— horizontal; connect different

parts of same hemisphere– Commissural fibers— horizontal; connect gray

matter of two hemispheres – Projection fibers— vertical; connect hemispheres

with lower brain or spinal cord

Basal Nuclei (Ganglia)

• Subcortical nuclei (caudate nucleus, putamen, globus pallidus)

• Functionally associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain)

© 2013 Pearson Education, Inc.

Figure 12.9b Basal nuclei.

Cerebral cortex

Cerebral white matter

Corpus callosum

Anterior hornof lateral ventricle

PutamenGlobus pallidus

Thalamus

Third ventricle

Inferior hornof lateral ventricle

Head of caudate nucleus

Tail of caudate nucleus

Anterior

Posterior

Functions of Basal Nuclei

• Functions thought to be: – Influence muscle movements – Role in cognition and emotion– Regulate intensity of slow or stereotyped

movements– Filter out incorrect/inappropriate responses– Inhibit antagonistic/unnecessary movements

Diencephalon

• Three paired structures– Thalamus– Hypothalamus– Epithalamus

• Encloses the third ventricle

Figure 12.12

Thalamus(encloses third ventricle)

Pineal gland(part of epithalamus)

Hypothalamus

Thalamus• 80% of diencephalon• 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 to help direct the motor

cortical areas• Mediates sensation, motor activities, cortical arousal,

learning, and memory

Hypothalamus

• Autonomic control center for many visceral functions

• Center for emotional response• 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• Pineal gland—extends from the posterior

border and secretes melatonin– Melatonin—helps regulate sleep-wake cycles

Brain Stem

• Controls automatic behaviors necessary for survival

• Associated with 10 of the 12 pairs of cranial nerves

• Three regions– Midbrain– Pons– Medulla oblongata

Figure 12.14

Pons

Medullaoblongata

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

Midbrain

• Located between the diencephalon and the pons

• Cerebral aqueduct– Channel between third and fourth ventricles

• Nuclei that control cranial nerves III (oculomotor) and IV (trochlear)

• Releases dopamine from the substantia nigra

Pons

• 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)• Nuclei that help maintain normal rhythm of

breathing

Medulla Oblongata• Joins spinal cord at foramen magnum• Crossover of the corticospinal tracts

(decussation of the pyramids)• Cranial nerves VIII, X, and XII are associated

with the medulla• 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

• Additional centers regulate– Vomiting – Hiccupping – Swallowing – Coughing– Sneezing

Figure 12.17b

(b)

Medullaoblongata

Flocculonodularlobe

Choroidplexus offourth ventricle

Posteriorlobe

Arborvitae

Cerebellar cortex

Anterior lobe

Cerebellarpeduncles• Superior• Middle• Inferior

Cerebellum

The Cerebellum

• 11% of brain mass• Dorsal to the pons and medulla• Subconsciously provides precise timing and

appropriate patterns of skeletal muscle contraction

• Two hemispheres connected by vermis• Folia—transversely oriented gyri• Arbor vitae—distinctive treelike pattern of the

cerebellar white matter

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

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

• 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

• Motor function– Helps control coarse limb movements– Reticular autonomic centers regulate visceral

motor functions

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)

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

Alpha: 8-13 Hz

Beta: 14-30 Hz

Theta: 4-7 Hz

Delta: ≤ 4 Hz

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) is a signal that brain function is impaired

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 Patterns

• Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm (via Hypothalamus)

• Typical = alternates b/w REM and NREM

Language

• Language implementation system–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

Categories of Memory

1. Declarative (fact) memory– Explicit information– Related to conscious thoughts and language ability– Stored in LTM with context in which learned

2. 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

Figure 12.21a Proposed memory circuits.

Thalamus

Basalforebrain

Prefrontalcortex

Smell

Touch

Hearing

Vision

Hippocampus

Taste

Sensoryinput

Associationcortex

Thalamus

Medial temporal lobe(hippocampus, etc.)

Prefrontalcortex

ACh releasedby basalforebrain

Declarative memory circuits

© 2013 Pearson Education, Inc.

Figure 12.21b Proposed memory circuits.

Sensory andmotor inputs

Associationcortex

Basalnuclei

Thalamus Premotorcortex

Dopamine releasedby substantia nigra

Basalnuclei

Substantianigra

Thalamus

Premotorcortex

Procedural (skills) memory circuits

Protection of the Brain

• Bone (skull)• Meninges• Cerebrospinal fluid• Also…..Blood-brain barrier

Major Protective Structures

Meninges

• Cover and protect the CNS• Protect blood vessels and enclose venous

sinuses• Contain cerebrospinal fluid (CSF)• Form partitions in the skull• Three layers– Dura mater– Arachnoid mater– Pia mater

Dura Mater

• Two layers of fibrous connective tissue– Periosteal and meningeal layers– Layers separate to form dural venous sinuses

• Dural septa limit excessive movement of the brain

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

Dural septa!

Arachnoid Mater

• Middle layer with weblike extensions• Subarachnoid space contains CSF and blood

vessels• Arachnoid villi protrude into the superior

sagittal sinus and permit CSF reabsorption

Pia Mater

• Layer of delicate vascularized connective tissue that clings tightly to the brain

Cerebrospinal Fluid (CSF)

• Composition– Watery solution – Less protein and different ion concentrations than

plasma• Functions– Gives buoyancy to the CNS organs– Protects the CNS from blows and other trauma– Nourishes the brain and carries chemical signals

Choroid Plexuses

• Produce CSF at a constant rate • Hang from the roof of each ventricle

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

Blood-Brain Barrier

• Helps maintain a stable environment for the brain

• Separates neurons from some bloodborne substances

Blood-Brain Barrier

• Composition– Continuous endothelium of

capillary walls– Basal lamina– “Feet of astrocytes”

Blood-Brain Barrier: Functions

• Selective barrier– Allows nutrients to move by facilitated diffusion– Allows any fat-soluble substances to pass,

including alcohol, nicotine, and anesthetics • Absent in some areas, e.g., vomiting center

and the hypothalamus, where it is necessary to monitor the chemical composition of the blood

Spinal Cord

• Location– Begins at the foramen magnum, ends (conus

medullaris) at L1

• Functions• Two-way communication to/from the brain, spinal

reflex centers• Protection– Bone, meninges, and CSF

Figure 12.29a

Cervicalenlargement

Dura andarachnoidmater

LumbarenlargementConusmedullarisCaudaequina

Filumterminale

Cervicalspinal nerves

Lumbarspinal nerves

Sacralspinal nerves

Thoracicspinal nerves

(a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.

Spinal Cord

• Spinal nerves– 31 pairs

• Cervical and lumbar enlargements– The nerves serving the upper and lower limbs

emerge here• Cauda equina– The collection of nerve roots at the inferior end of

the vertebral canal

Cross-Sectional Anatomy

• Two lengthwise grooves divide cord into right and left halves – Ventral (anterior) median fissure – Dorsal (posterior) median sulcus

• Gray commissure—connects masses of gray matter; encloses central canal

Figure 12.31b

(b) The spinal cord and its meningeal coverings

Dorsal funiculus

Dorsal median sulcus

Central canal

Ventral medianfissure

Pia mater

Arachnoid mater

Spinal dura mater

Graycommissure Dorsal horn Gray

matterLateral hornVentral horn

Ventral funiculusLateral funiculus

Whitecolumns

Dorsal rootganglion

Dorsal root(fans out into dorsal rootlets)

Ventral root(derived from severalventral rootlets)

Spinal nerve

Figure 12.32

Somaticsensoryneuron

Dorsal root (sensory)

Dorsal root ganglion

Visceralsensory neuron

Somaticmotor neuron

Spinal nerve

Ventral root(motor)

Ventral horn(motor neurons)

Dorsal horn (interneurons)

Visceralmotorneuron

Interneurons receiving input from somatic sensory neurons

Interneurons receiving input from visceral sensory neurons

Visceral motor (autonomic) neurons

Somatic motor neurons

Pathway Generalizations

• Pathways decussate (cross over)• Most consist of two or three neurons (a relay)• Most exhibit somatotopy (precise spatial

relationships)• Pathways are paired symmetrically (one on

each side of the spinal cord or brain)

See figures 12.30 and 12.31, Table 12.2

Spinal Cord Trauma

• Functional losses– Parasthesias (abnormal sensation)– Paralysis (loss of motor function)

• Transection– Cross sectioning of the spinal cord at any level– Results in total motor and sensory loss in regions

inferior to the cut– Paraplegia—transection between T1 and L1

– Quadriplegia—transection in the cervical region