Chapter 12 Part 1

Chapter 12Part 1

Anatomy & Physiology

The Central Nervous System

Brain DevelopmentBrain Development

Posteriolateral growth of the cerebral hemispheres encloses the diencephalon and superior aspect of the brain stem

Embryo at four weeks http://w-cpc.org/fetal1.html

Embryonic DevelopmentEmbryonic Development

Ectoderm thickens along dorsal midline to form the neural plate

The neural plate invaginates, forming a neural groove flanked by neural folds

The neural groove fuses dorsally and forms the neural tube which detaches from the surface ectoderm. The neural tube differentiates into the CNS. Neural crest cells form some PNS structures.

Embryonic DevelopmentEmbryonic Development

Neural Tube and Primary Brain VesiclesNeural Tube and Primary Brain VesiclesThe anterior (rostral) end of the neural tube expands and forms the three primary brain vesicles

Prosencephalon

Mesencephalon

Rhombencephalon

Secondary Brain VesiclesSecondary Brain VesiclesIn week 5 of embryonic development, secondary brain vesicles form

Telencephalon and Diencephalon arise from the prosenencephalon

Mesencephalon remains undivided

Metencephalon and Myelencephalon arise from the rhombencephalon

Adult Brain StructuresAdult Brain Structures

Secondary brain vesicles differentiate into adult brain structures

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

Diencephalon – thalamus, hypothalamus

Mesencephalon – brain stem: midbrain

Metencephalon – brain stem: pons

Myelencephalon – brain stem: medulla oblongata

Adult Brain StructuresAdult Brain Structures

Adult Neural Canal RegionsAdult Neural Canal Regions

The central cavity of the neural tube enlarges in four regions to form fluid-filled Ventricles

Telencephalon – Lateral Ventricles

Diencephalon – Third Ventricle

Mesencephalon – Cerebral Aqueduct

Metencephalon & Myelencephalon – Fourth Ventricle

Spinal Cord – Central Canal

Adult Neural Canal RegionsAdult Neural Canal Regions

Ventricles of the BrainVentricles of the Brain

Pair of C-shaped Lateral Ventricles

Third Ventricle in the diencephalon

Fourth Ventricle in the hindbrain dorsal to the pons

Cerebral HemispheresCerebral Hemispheres

Form the superior part of the brain and make up over 80% of its mass

Hemispheres are separated by the Longitudinal fissure and from cerebellum by the Transverse Cerebral fissure

Surface Features:

Ridges called Gyri (gyrus) Shallow grooves called Sulci (sulcus) Deeper grooves called Fissures

Cerebral Hemispheres - LobesCerebral Hemispheres - LobesFrontal, Parietal, Temporal, Occipital, and (Insula)

Central sulcus – separates the frontal and parietal lobes

Parieto-occipital sulcus – separates the parietal and occipital lobes

Lateral sulcus – separates the parietal and temporal lobes

Cerebral Hemispheres – 3 basic regionsCerebral Hemispheres – 3 basic regions

Cortex – superficial gray matter, 1-4.5 mm thick

White matter – inner, unmyelinated

Basal Nuclei – islands of gray matter within the white matter

Cortex (40% of brain mass) consists of neuron cell bodies, dendrites, and unmyelinated axons (plus glial cells and blood vessels), no fiber tracts, all neurons are interneurons

Cerebral CortexCerebral Cortex

Enables sensation, communication, memory, understanding, and voluntary movements

Each hemisphere controls the opposite (contralateral) side of the body

Hemispheres are not functionally equivalent (lateralization or specialization of cortical functions)

No functional area acts alone - conscious behavior involves the entire cortex

Cerebral CortexCerebral Cortex

Three kinds of functional areas:

Motor areas – control voluntary movement

Sensory areas – conscious awareness of sensation

Association areas – integrate diverse information, communicate “associate” with the motor cortex and sensory association areas to analyze input

Cerebral CortexCerebral Cortex

Cerebral CortexCerebral Cortex

Cerebral Cortex: Motor AreasCerebral Cortex: Motor Areas

Primary (somatic) motor cortex

Premotor cortex

Broca’s area

Frontal eye field

Primary Motor CortexPrimary Motor Cortex

Located in the precentral gyrus of the frontal lobe

Allows conscious control of voluntary movements

Composed of neurons called pyramidal cells - axons project to spinal cord and make up the voluntary motor tracts called corticospinal tracts

Primary Motor CortexPrimary Motor Cortex

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

Premotor CortexPremotor Cortex

Located anterior to the precentral gyrus

Controls learned, repetitious, or patterned motor skills

Coordinates simultaneous or sequential actions( directly or indirectly)

Involved in the planning of movements

Broca’s AreaBroca’s Area

Located anterior to the inferior region of the premotor area

Present in one hemisphere (usually the left)

A motor speech area that directs muscles involved in speech

Is active as one prepares to speak

Frontal Eye FieldFrontal Eye Field

Located anterior to the premotor cortex and superior to Broca’s area

Controls voluntary eye movement

Sensory AreasSensory Areas

Primary somatosensory cortex

Somatosensory association cortex

Visual and auditory areas

Olfactory, gustatory, and vestibular cortices

Primary Somatosensory CortexPrimary Somatosensory Cortex

Located in the postcentral gyrus of the parietal lobe

Receives information from somatic sensory receptors in the skin and proprioceptors in skeletal muscles

Exhibits spatial discrimination

Primary Somatosensory CortexPrimary Somatosensory Cortex

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

Somatosensory Association CortexSomatosensory Association Cortex

Located posterior to the primary somatosensory cortex

Integrates sensory information coming from the primary somatosensory cortex to produce an understanding (size, texture, and relationship of parts) of the stimulus

Visual AreasVisual Areas

Primary visual (striate) cortex - located on the posterior tip of the occipital lobe, most of it is buried in the calcarine sulcus - receives visual information from the retinas

Visual association area - surrounds the primary visual cortex - interprets visual stimuli (e.g., color, form, and movement)

Auditory AreasAuditory Areas

Primary auditory cortex - located in the superior margin of the temporal lobe -receives information related to pitch, rhythm, and loudness

Auditory association area - located posterior to the primary auditory cortex -stores memories of sounds and permits perception of sounds

Other Sensory AreasOther Sensory Areas

Olfactory (smell) cortex – small area of frontal lobe above the orbit and in medial temporal lobe (piriform lobe and uncus)

Gustatory (taste) cortex – in parietal lobe deep to temporal lobe

Other Association AreasOther Association Areas

Prefrontal cortex

Language areas

General (common) interpretation area

Visceral association area

Prefrontal CortexPrefrontal Cortex

Located in the anterior portion of the frontal lobe

Involved with intellect, cognition, recall, personality, judgment, reasoning, and conscience

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

Language AreasLanguage Areas

Located in a large area surrounding the left (or language-dominant) lateral sulcus

Broca’s area – speech preparation and production

Wernicke’s area – involved in sounding out unfamiliar words

Lateral prefrontal cortex – language comprehension and word analysis. Lateral and ventral temporal lobe – coordinate auditory and visual aspects of language

Broca’s area Wernicke’s area

General (Common) Interpretation Area (?)General (Common) Interpretation Area (?)

Ill-defined region including parts of the temporal, parietal, and occipital lobes

Found in one hemisphere, usually the left

Integrates incoming signals into a single thought

Involved in processing spatial relationships

Visceral Association Area (?)Visceral Association Area (?)

Located in the cortex of the insula

Involved in conscious perception of visceral sensations

Lateralization of Cortical FunctionLateralization of Cortical Function

Lateralization – each hemisphere has abilities not shared with the other hemisphere

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

Cerebral White MatterCerebral White Matter

Consists of myelinated fibers and their tracts

Responsible for communication between areas of the cerebrum amd between the cerebral cortex and lower CNS centers

Cerebral White Matter Fiber TractsCerebral White Matter Fiber Tracts

Commissures – connect corresponding gray areas of the two hemispheres (corpus callosum , anterior and posterior commissures)

Association fibers – connect different parts of the same hemisphere

Projection fibers – enter the hemispheres from lower brain or cord centers

Commissures and Association fibers – horizontal Projection fibers – vertical

Fiber Tracts in White MatterFiber Tracts in White Matter

Fiber Tracts in White MatterFiber Tracts in White Matter

Basal NucleiBasal Nuclei

Masses of gray matter found deep within the cortical white matter

Corpus striatum:

Caudate nucleus (amygdala- tail of caudate)

Lentiform nucleus – composed of the putamen and the globus pallidus

Fibers of internal capsule run between and through caudate and lentiform nuclei, giving them a striped appearance

Basal NucleiBasal Nuclei

Basal NucleiBasal Nuclei

Functions of Basal NucleiFunctions of Basal Nuclei

Possible functions of basal nuclei:

Influence muscular activity

Regulate attention and cognition

Regulate intensity of slow or stereotyped movements

Inhibit antagonistic and unnecessary movement

Diencephalon and Brain StemDiencephalon and Brain Stem

DiencephalonDiencephalon

Central core of the forebrain surrounded by the cerebral hemispheres

Consists of three paired structures – thalamus, hypothalamus, and epithalamus

Collectively, these gray matter areas enclose the third ventricle

ThalamusThalamus

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

Connected at the midline by the interthalamic adhesion (intermediate mass)

Contains four groups of nuclei - anterior, ventral, dorsal, and posterior - project and receive fibers from the cerebral cortex

ThalamusThalamus

Thalamus – “gateway” to the cerbral cortexThalamus – “gateway” to the cerbral cortex

Afferent impulses from all senses converge and synapse in the thalamus

Impulses of similar function are sorted out, “edited”, and relayed as a group to the appropriate area of the sensory cortex or association areas

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

HypothalamusHypothalamus

Below the thalamus, it caps the brainstem and forms the inferolateral walls of the third ventricle

Mammillary bodies - small, paired nuclei bulging anteriorly from the hypothalamus - relay stations for olfactory pathways

Infundibulum – stalk of the hypothalamus connecting to the pituitary gland

Main visceral control center of the body, important to overall body homeostasis

Hypothalamic NucleiHypothalamic Nuclei

Hypothalamic FunctionHypothalamic Function

Regulates blood pressure, rate and force of heartbeat, digestive tract motility, respiratory rate and depth, pupil size, and many other visceral activities

Center for emotional response - involved in perception of pleasure, fear, rage

Regulates body temperature – the body’s “thermostat”

Regulates food intake - feelings of hunger and satiety

Regulates sleep-wake cycle

Regulates ANS by controlling activity of centers in brains stem and spinal cord

Endocrine Functions of the HypothalamusEndocrine Functions of the Hypothalamus

Releasing hormones control the secretion of hormones by the anterior pituitary

Stimulates ADH release from the posterior pituitary

Anti-diuretic hormone- causes kidneys to retain water

EpithalamusEpithalamus

Most dorsal portion of the diencephalon; forms roof of the third ventricle

Pineal gland – extends from the posterior border and secretes melatonin, a hormone involved with sleep regulation, sleep-wake cycles, and mood

Choroid plexus – a structure that secretes cerebral spinal fluid (CSF) [all ventricles have a choroid plexus]