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Central Nervous System (CNS)  (download here)

Central Nervous System (CNS)

•      CNS – composed of the brain and spinal cord

The Brain  

•      Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem

*FYI* Primary Brain Vesicles

•      The anterior end of the neural tube expands and constricts to form the three primary brain vesicles

•    Prosencephalon – the forebrain

•    Mesencephalon – the midbrain

•    Rhombencephalon – hindbrain

Adult Brain Structures

•      Fates of the secondary brain vesicles:

•    Telencephalon –> cerebrum:  cortex, white matter, and basal nuclei

•    Diencephalon –> thalamus, hypothalamus, and epithalamus

•    Mesencephalon –> brain stem: midbrain

•    Metencephalon –> brain stem: pons

•    Myelencephalon –> brain stem: medulla oblongata

Brain Stem  see illustration above  From superior to inferior

•      Consists of three regions – midbrain, pons, and medulla oblongata

•      Similar to spinal cord but contains embedded nuclei

•      Controls automatic behaviors necessary for survival

•      Provides the pathway for tracts between higher and lower brain centers

•      Associated with 10 of the 12 pairs of cranial nerves

Thalamus

•      Paired, egg-shaped masses that form the superolateral walls of the third ventricle

•      Connected at the midline by the intermediate mass

•      Contains four groups of nuclei – anterior, ventral, dorsal, and posterior

•      Nuclei project and receive fibers from the cerebral cortex

Thalamic Function - relay station

•      Afferent impulses from all senses converge and synapse in the thalamus

•      Impulses of similar function are “sorted out,” edited, and relayed as a group

•      All inputs ascending to the cerebral cortex pass through the thalamus

•      Plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory

Hypothalamus

•      Located below the thalamus

•      Mammillary bodies:

•    Small, paired nuclei bulging anteriorly from the hypothalamus

•    Relay station for olfactory pathways

•      Infundibulum – stalk of the hypothalamus; connects to the pituitary gland

•    Main visceral control center of the body

Hypothalamic Function

•      Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of breathing, and many other visceral activities

•      Is involved with perception of pleasure, fear, and rage

•      Controls mechanisms needed to maintain normal body temperature

•      Regulates feelings of hunger and satiety

Midbrain

•      Located between the diencephalon and the pons

•      Midbrain structures include:

•    Cerebral peduncles – two bulging structures that contain descending pyramidal motor tracts

•    Various nuclei

Midbrain Nuclei

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

•      Corpora quadrigemina – four domelike protrusions of the dorsal midbrain

•      Superior colliculi – visual reflex centers

•      Inferior colliculi – auditory relay centers

Pons

•      Bulging brainstem region between the midbrain and the medulla oblongata

•      Fibers of the pons:

•    Connect higher brain centers and the spinal cord

Medulla Oblongata

•      Most inferior part of the brain stem

Medullary Nuclei

•      Cardiovascular control center – adjusts force and rate of heart contraction

•      Respiratory centers – control rate and depth of breathing

Ventricles of the Brain

•      The ventricles are:

•    The paired C-shaped lateral ventricles

•    The third ventricle found in the diencephalon

•    The fourth ventricle found in the hindbrain dorsal to the pons

 

Cerebral Hemispheres

•      Form the superior part of the brain and make up 83% of its mass

•      Contain ridges (gyri) and shallow grooves (sulci)

•      Contain deep grooves called fissures

•      Are separated by the longitudinal fissure

•      Have three basic regions: cortex, white matter, and basal nuclei

Major Lobes, Gyri, and Sulci of 
the Cerebral Hemisphere

•      Deep sulci divide the hemispheres into five lobes:

•    Frontal, parietal, temporal, occipital

•      Central sulcus – separates the frontal and parietal lobes

•      Lateral sulcus – separates the parietal and temporal lobes

•      The precentral and postcentral gyri border the central sulcus

Cerebral Cortex

•      The cortex – superficial gray matter; accounts for roughly 40% of the mass of the brain

•      It enables sensation, communication, memory, understanding, and voluntary movements

•      Each hemisphere acts contralaterally (controls the opposite side of the body)

•      Hemispheres are not equal in function

•      No functional area acts alone; conscious behavior involves the entire cortex

Functional Areas of the Cerebral Cortex

•      Three types of functional areas are:

•    Motor areas – control voluntary movement

•    Sensory areas – conscious awareness of sensation

•    Association areas – integrate diverse information

Cerebral Cortex: Motor Areas

•      Primary (somatic) motor cortex

•    Wernicke’s area –  involved in sounding out unfamiliar words  See above illustration

•    Broca’s area – speech preparation and production

•      Motor homunculus – caricature of relative amounts of cortical tissue devoted to each motor function

Premotor Cortex

•      Located anterior to the precentral gyrus

Primary Somatosensory Cortex

•      Located in the postcentral gyrus, this area:

•    Receives information from the skin and skeletal  muscles

•      Somatosensory homunculus – caricature of relative amounts of cortical tissue devoted to each sensory function

Somatosensory Association Area

•      Located posterior to the primary somatosensory cortex

•      Integrates sensory information

Auditory Areas

•      Primary auditory cortex

•    Located at the superior margin of the temporal lobe

Prefrontal Cortex

•      Involved with intellect, cognition, recall, and personality

•      Necessary for judgment, reasoning, persistence, and conscience

•      Closely linked to the limbic system (emotional part of the brain)

Lateralization of Cortical Function

•      Lateralization – each hemisphere has abilities not shared with its partner

•      Cerebral dominance – designates the hemisphere dominant for language

•      Left hemisphere – controls language, math, and logic

•      Right hemisphere – controls visual-spatial skills, emotion, and artistic skills

Basal Nuclei

•      Masses of gray matter found deep within the cortical white matter

*FYI* Functions of Basal Nuclei

•      Though somewhat elusive, the following are thought to be functions of basal nuclei:

•    Influence muscular activity

•    Regulate attention and cognition

•    Regulate intensity of slow or stereotyped movements

•    Inhibit antagonistic and unnecessary movement


The Cerebellum

•      Located dorsal to the pons and medulla

•      Provides precise timing and appropriate patterns of skeletal muscle contraction

•      Cerebellar activity occurs subconsciously

Anatomy of the Cerebellum

•      Two bilaterally symmetrical hemispheres connected medially by the vermis

•      Folia – transversely oriented gyri

•      Each hemisphere has three lobes – anterior, posterior, and flocculonodular

•      Neural arrangement – gray matter cortex, internal white matter, scattered nuclei

•      Arbor vitae – distinctive treelike pattern of the cerebellar white matter

Cerebellar Peduncles

•      Three paired fiber tracts that connect the cerebellum to the brain stem

•      All fibers in the cerebellum are ipsilateral

•      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 Cognitive Function

•      Plays a role in language and problem solving

•      Recognizes and predicts sequences of events


*FYI* Limbic System

•      Structures located on the medial aspects of cerebral hemispheres and diencephalon

•      Includes the rhinencephalon, amygdala, hypothalamus, and anterior nucleus of the thalamus

•      Parts especially important in emotions:

•    Amygdala – deals with anger, danger, and fear responses

•    Cingulate gyrus – plays a role in expressing emotions via gestures, and resolves mental conflict

•      Puts emotional responses to odors – e.g., skunks smell bad

Limbic System: Emotion and Cognition

•      The limbic system interacts with the prefrontal lobes, therefore:

•    One can react emotionally to conscious understandings

•    One is consciously aware of emotion in one’s life

•      Hyppocampal structures – convert new information into long-term memories


Meninges

•      Three connective tissue membranes that lie external to the CNS – dura mater, arachnoid mater, and pia mater

•      Functions of the meninges include:

•    Cover and protect the CNS

•    Protect blood vessels and enclose venous sinuses

•    Contain cerebrospinal fluid (CSF)

Dura Mater

•      Leathery, strong meninge composed of two fibrous connective tissue layers

Arachnoid Mater

•      The middle meninge, which forms a loose brain covering

•      It is separated from the dura mater by the subdural space

•      Beneath the arachnoid is a wide subarachnoid space filled with CSF and large blood vessels

•      Arachnoid villi protrude superiorly and permit CSF to be absorbed into venous blood

Pia Mater

•      Deep meninge composed of delicate connective tissue that clings tightly to the brain


Spinal Cord

•      CNS tissue is enclosed within the vertebral column from the foramen magnum to L1

•      Provides two-way communication to and from the brain

•      Protected by bone, meninges, and CSF

•      Epidural space – space between the vertebrae and the dural sheath (dura mater) filled with fat and a network of veins

•      Conus medullaris – terminal portion of the spinal cord

•      Filum terminale – fibrous extension of the pia mater; anchors the spinal cord to the coccyx

•      Denticulate ligaments – delicate shelves of pia mater; attach the spinal cord to the vertebrae

•      Spinal nerves – 31 pairs attach to the cord by paired roots

•      Cervical and lumbar enlargements – sites where nerves serving the upper and lower limbs emerge

•      Cauda equina – collection of nerve roots at the inferior end of the vertebral canal

Cross-Sectional Anatomy of the Spinal Cord

•      Anterior median fissure – separates anterior funiculi

•      Posterior median sulcus – divides posterior funiculi

Gray Matter and Spinal Roots

•      Gray matter consists of soma, unmyelinated processes, and neuroglia

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

•      Posterior (dorsal) horns – interneurons

•      Anterior (ventral) horns – interneurons and somatic motor neurons

•      Lateral horns – contain sympathetic nerve fibers

Gray Matter: Organization

•      Dorsal half – sensory roots and ganglia

•      Ventral half – motor roots

•      Dorsal and ventral roots fuse laterally to form spinal nerves

•      Four zones are evident within the gray matter – somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM)

White Matter in the Spinal Cord

•    Fiber tract names reveal their origin and destination

•    Fiber tracts are composed of axons with similar functions

White Matter: Pathway Generalizations

•      Pathways decussate – cross to the contralateral side

•      Most consist of two or three neurons – two on the motor side, three on the sensory side

 

 

The CNS

The notes are your study guide!

 

 

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