CENTRAL NERVOUS SYSTEM -BRAIN

BRAIN REGIONS

• Cerebrum - cerebral hemispheres • Diencephalon – hypothalamus, thalamus• Brainstem

– Consists of midbrain, pons, and medulla oblongata– Spinal cord continuous with medulla oblongata

• Cerebellum

CEREBRUMSURFACE ANATOMY

• Gyrus – elevated ridges of tissue– Precentral gyrus – motor area– Postcentral gyrus – somatosensory area

• Sulcus – shallow groove separating gyrus– Central sulcus – separates frontal from parietal

lobe– Lateral sulcus – separates temporal lobe from

parietal and frontal• Fissures – deep grooves separating brain regions

– Longitudinal – separates hemispheres– Transverse – separates cerebrum from cerebellum

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Figure 12.4c Lobes, sulci, and fissures of the cerebral hemispheres.

Frontal lobe

Postcentralgyrus

Parietal lobe

CentralsulcusPrecentral

gyrus

Lateral sulcus

Temporal lobeOccipital lobe

Transversefissure

Pons

Spinal cordFissure(a deepsulcus)

Gyrus

Cortex (gray matter)

Sulcus

White matter

Lobes and sulci of the cerebrum

Medulla oblongata

Cerebellum

GROSS ANATOMY OF CEREBRUM

• Divided into 2 halves – cerebral hemispheres• Composed of 3 layers

– Cerebral cortex - outer layer of gray matter associated with consciousness (voluntary behavior)

– Cerebral white matter – communication between cerebral areas and cortex to lower CNS centers• Ex. Corpus callosum connects 2 hemispheres

integrating information– Basal Nuclei (ganglia) -Core of gray matter that

controls subconscious contractions of skeletal muscle

CEREBRAL CORTEX

• Anatomically divided into 4 lobes – frontal, parietal, occipital, temporal

• Contains 3 functional areas – motor, sensory, association

• Each hemisphere “controls” opposite (contralateral) part of body– Cerebral dominance – 1 hemisphere

dominant for language (usually left side)

FUNCTIONAL SPECIALIZATION AREAS

• Motor area – Controls voluntary movement– located in posterior part of frontal lobe

• Sensory area– Receive sensory information– Involved in perception – conscious awareness of a

sensation• Association areas

– Involved in more complex integrative functions like memory, intelligence, personality

MOTOR AREAS

• Primary motor cortex– Located in precentral gyrus of frontal lobe– Controls skeletal muscle movement

• Premotor cortex – anterior to precentral gyrus– Helps plan movements (skilled motor activities)

• Broca’s area (motor speech area)– Located in inferior/lateral area of frontal lobe– Controls muscles of tongue, throat and lips to form

words– Most people – on left side

SENSORY AREAS IN PARIETAL LOBE

• Primary somatosensory area - in postcentral gyrus of parietal lobe– Receives sensory information from skin and

skeletal muscles and identifies part of body being stimulated – called spatial discrimination

– Integrates and analyzes different sensory inputs and evaluates what is being felt

– Receives information on joint and muscle position - Proprioception

• Gustatory cortex – located at base of postcentral gyrus– Receives impulses for taste– Involved in gustatory (taste) perception

SENSORY AREAS

• Visual area – posterior occipital lobe– Receives visual information from retinas– Interprets and evaluates visual stimuli

• Auditory area – superior temporal lobe– Auditory stimuli from cochlea evaluated for pitch,

rhythm, loudness– Identifies sound

• Olfactory cortex – medial aspect of temporal lobe– Conscious awareness of odors

ASSOCIATION AREAS

• Prefrontal cortex (Anterior association area)– anterior part of frontal lobe– Involved with intellect, complex learning ability

(cognition), personality, working memory (abstract ideas, reasoning and judgment)

• Somatosensory association cortex - posterior to primary somatosensory area (parietal lobe)– Stores memory of sensory experiences– Allows you to recognize objects without seeing

them

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Figure 12.6a Functional and structural areas of the cerebral cortex.

Motor areas

Primary motor cortex

Premotor cortex

Broca's area(outlined by dashes)

Prefrontal cortex

Lateral view, left cerebral hemisphere

Sensory areas and relatedassociation areasPrimary somatosensorycortexSomatosensoryassociation cortex

Gustatory cortex

Somatic sensation

Taste

Wernicke's area(outlined by dashes)

Primary visualcortexVisualassociation area

Auditoryassociation area

Primary auditory cortex

Vision

Hearing

Central sulcus

Primary motorcortex

Motor associationcortex

Primary sensorycortex

Sensoryassociation cortex

Multimodal associationcortex

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Figure 12.5 Functional neuroimaging (fMRI) of the cerebral cortex.Central sulcus

Longitudinalfissure

Left frontallobe

Left temporallobe

Areas activein speech andhearing (fMRI)

DIENCEPHALON

• Extends from brainstem to cerebrum• Surrounds 3rd ventricle• Includes thalamus, hypothalamus

THALAMUS

• Bilateral masses of gray matter in center of brain• Functions include:

– Relay station for all sensory impulses and relayed to appropriate area

– Transmits motor information from cerebellum to primary motor area

– Helps maintain consciousness– Interprets some sensory information (pain,

pressure, touch)– Learning and memory

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Figure 12.10 Midsagittal section of the brain.

Cerebral hemisphere

intermediatemass of Thalamus

HypothalamusOptic chiasma

Pituitary gland

PonsMedulla oblongataSpinal cord

Corpus callosum

Choroid plexus

Thalamus(encloses third ventricle)

Pineal gland

Midbrain

Arbor vitae (of cerebellum)Fourth ventricleChoroid plexusCerebellum

Lateral ventricle

Third ventricle

Hypothalamus

Corpus callosum

Thalamus

Midbrain

Arbor vitae

Fourth ventricle

Cerebellum

Medulla oblongataPons

Optic chiasma

HYPOTHALAMUS

• Inferior to thalamus• Connected to pituitary gland by infundibulum• Functions include:

– Control of autonomic nervous system to regulate homeostasis

– Initiates physical response to emotions – increased heart rate, etc. when scared

– Regulates body temperature– Regulates food and water intake– Regulates sleep-wake cycle– Controls endocrine function by producing

hormones that act on pituitary gland

BRAINSTEM

• Located between cerebrum and spinal cord• Contain tracts and nuclei

– Tracts (bundles of axons) conduct impulses– Nuclei - contain cell bodies of 10 cranial nerves

• Three sections:– Midbrain – inferior to diencephalon– Pons – superior to medulla, anterior to cerebellum– Medulla oblongata – most inferior part that is

continuous inferiorly with spinal cord

MIDBRAIN

• Tracts include:– Motor tracts descending from motor area to spinal

cord– Sensory tracts ascending to thalamus

• Nuclei include:– Reflex center for startle reflex (visual and auditory

involvement)– Contains cell bodies for oculomotor (III) and

trochlear (IV) cranial nerves– Substantia nigra – releases dopamine to control

subconscious muscle movements (loss = Parkinson’s)

PONS

• Tracts include:– Conduction between cerebrum and

cerebellum – Connects 2 sides of cerebellum

• Nuclei include:– Pneumotaxic center – regulates normal

rhythm of breathing– Contains cell bodies for trigeminal (V),

abducens (VI) and facial (VII) cranial nerves

MEDULLA OBLONGATA• Hypothalamus relays instructions through medulla for visceral

function:– Cardiovascular center – regulates heart beat and blood

pressure– Respiratory center – generates respiratory rate– Controls reflexes for vomiting, sneezing, swallowing,

hiccups, etc. (autonomic reflexes)• Tracts include:

– Decussation (crossing over) of motor tracts occurs here – explains contralateral control of hemispheres

• Nuclei include:– Contains cranial nerve bodies for vestibulocochlear (VIII),

glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII)

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Thalamus

Hypothalamus

Midbrain

Pons

Medulla oblongata

Diencephalon

Brain stem

View (b)

View (a) View (c)

Diencephalon• Thalamus• Hypothalamus

Oculomotor nerve (III)

Trochlear nerve (IV)

Abducensnerve (VI)Vestibulocochlearnerve (VIII)

Decussation ofpyramids

Optic chiasma

Optic nerve (II)

Optic tract

Infundibulum

Pituitary gland

Midbrain

Trigeminal nerve (V)

PonsFacial nerve (VII)

Abducens nerve (VI)

Glossopharyngeal nerve (IX)

Hypoglossal nerve (XII)

Vagus nerve (X)

Accessory nerve (XI)

Spinal cord

Ventral view

Thalamus

Trochlear nerve (IV)

Vestibulocochlear nerve (VIII)Olive

Left lateral view

Figure 12.13a–b Three views of the brain stem (green) and the diencephalon (purple).

CEREBELLUM

• Located posterior to pons and medulla, inferior to occipital lobe

• contains inner layer of white matter tracts called arbor vitae – conducts impulses between cerebellum and cerebrum

• Functions: – Provide smooth coordinated movements of

skeletal muscles– Regulates posture and balance

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Figure 12.15 Cerebellum.

Arbor vitaeCerebellum

Pons

Fourth ventricle

Medulla oblongata Choroid plexus

Medulla oblongata

Choroid plexus offourth ventricle

Arbor vitae

Cerebellum

Anteriorlobe

Posteriorlobe

OTHER BRAIN SYSTEMS

• Limbic system– encircles midbrain and corpus callosum– Center for emotions (pain or pleasure

centers), memory and olfaction• Reticular formation

– Located throughout brainstem– Contains the RAS which maintain

consciousness, active during awakening– Filters out repetitive stimuli– Regulates muscle tone

PROTECTION OF BRAIN

• Meninges – 3 connective tissue membranes that cover and protect CNS

• Cerebrospinal fluid (CSF) – liquid cushion for CNS

• Blood Brain Barrier - maintains stable environment of brain

MENINGES

• Dura mater – tough double-layered outer membrane– Outer layer connects to crista galli of ethmoid– Contains dural venous sinuses which collects blood from

brain and sends it to jugular veins – head trauma can cause bleed into Subdural space (between

dura and arachnoid mater) • Arachnoid mater – spidery middle layer

– Subarachnoid space – filled with CSF– Contains largest blood vessel to brain

• Pia mater – – attached directly to brain– Highly vascular

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Figure 12.22 Meninges: dura mater, arachnoid mater, and pia mater.

Skin of scalpPeriosteum

Bone of skullDura mater• Periosteal layer• Meningeal layer

Arachnoid materPia mater

Blood vessel

Subduralspace

Subarachnoidspace

CEREBROSPINAL FLUID (CSF)

• Colorless fluid surrounding brain and spinal cord– Contains water, glucose, albumin, gases (oxygen

and carbon dioxide) and metabolic wastes (urea, creatine)

– No red blood cells or platelets, some white blood cells may be present

• Provides buoyancy to reduce brain weight • Provides chemical stability for nervous tissu• Cushions and nourishes nervous tissue• Produced by choroid plexus that hang from roof of

ventricles (cavities in brain)

BLOOD BRAIN BARRIER

• Maintains stable environment – prevents overstimulation

• Brain capillaries impermeable to most substances – allows nutrients (glucose, amino acids)– Lipid soluble substances can also enter –

oxygen, carbon dioxide, fats, alcohol, nicotine, anesthetics

CENTRAL NERVOUS SYSTEM - SPINAL CORD

GENERAL FUNCTIONS OF SPINAL CORD

• Provides two way conduction pathway to and from brain

• Initiates complex patterns of motor activities like walking

• Major reflex center

GROSS ANATOMY

• Vertebrae – bone surrounding spinal cord

• Meninges – connective tissue coverings that protect spinal cord

• Spinal cord – nervous tissue

VERTEBRAE

• Surround and protect spinal cord• 31 pairs of spinal nerves exit via

intervertebral foramen• C1 to C7 nerves leave cord superior to

vertebrae, rest of nerves leave inferior to vertebrae

MENINGES

• Epidural space – space between vertebra and dura mater filled with

fat and blood vessels– Cushions and protects spinal cord from vertebra

• Same layers as brain– dura (single layer), arachnoid and pia mater (contains blood vessels)

• Subarachnoid space contains CSF• Extends to S2 – creates sac of CSF (used in lumbar

puncture or spinal tap)

SPINAL CORD • Contains gray and white matter

– Gray matter is butterfly shaped area containing unmyelinated multipolar neurons

– White matter – myelinated nerve fibers surrounding gray matter

• Roots - sensory and motor axons that exit spinal cord via intervertebral foramen

• Central canal – cavity in center of gray matter that contains CSF

• Cord ends around L1 – spinal taps done below L3

• Cauda equina – lumbar and sacral nerve roots at end of spinal cord

GRAY MATTER

• Ventral (anterior) horn – contains cell bodies of somatic motor neurons

• Lateral horns – contain autonomic motor neurons that serve visceral organs (only in thoracic and upper lumbar)

• Dorsal (posterior) horn – contains cell bodies of association neurons

• ** Sensory neuron cell bodies are outside the spinal cord in the Dorsal (posterior) root ganglion**

WHITE MATTER

• Ascending tracts– sensory axons running up to brain

• Descending tracts– motor axons running down from brain

• Transverse (commissural) tracts– cross from 1 side of cord to the other

SPINAL ROOTS

• Dorsal – contains sensory axons that run from sensory cell bodies in dorsal (posterior) root ganglion to dorsal (posterior) horns

• Ventral – contain motor axons exiting from ventral (anterior) horn

• Ventral Root unites with Sensory nerve distal to dorsal (posterior) root ganglion to form Spinal nerve which exit through intervertebral foramen out to body