human anatomy fourth edition marieb | mallatt | wilhelm copyright © 2005 pearson education, inc.,...

HUMAN ANATOMYfourth edition

MARIEB | MALLATT | WILHELM

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

PowerPoint® Lecture Slides prepared by Leslie Hendon,

University of Alabama, Birmingham

13

The CentralNervous System

PART 1


The Central Nervous System

• Central nervous system – the brain and spinal cord

• Directional terms unique to the CNS• Rostral – toward the nose

• Caudal – toward the tail


Embryonic Development of the Brain

• Brain arises from the rostral part of the neural tube

• Three primary brain vesicles in 4-week embryo• Prosencephalon – the forebrain

• Mesencephalon – the midbrain

• Rhombencephalon – the hindbrain



• Secondary brain vesicles• Prosencephalon

• Divides into telencephalon and diencephalon

• Mesencephalon – remains undivided

• Rhombencephalon • Divides into metencephalon and myelencephalon



• Structures of the adult brain• Develop from secondary brain vesicles

• Telencephalon the cerebral hemispheres

• Diencephalon thalamus, hypothalamus, and epithalamus

• Metencephalon pons and cerebellum

• Myelencephalon medulla oblongata



• Brain stem includes:• The midbrain, pons, and medulla oblongata

• Ventricles • Central cavity of the neural tube enlarges



Figure 13.2a-e



• Brain grows rapidly, and changes occur in the relative position of its parts• Cerebral hemispheres envelop the diencephalon

and midbrain

• Wrinkling of the cerebral hemispheres • More neurons fit within limited space


Brain Development from Week 5 to Birth

Figure 13.3a-d


Basic Parts and Organization of the Brain

• Divided into four regions• Cerebral hemispheres

• Diencephalon

• Brain stem: midbrain, pons, and medulla

• Cerebellum



Figure 13.4



• Organization • Centrally located gray matter• Externally located white matter• Additional layer of gray matter external to white

matter• Due to groups of neurons migrating externally

• Cortex – outer layer of gray matter• Formed from neuronal cell bodies• Located in cerebrum and cerebellum



Figure 13.5


Ventricles of the Brain

• Expansions of the brain’s central cavity

• Filled with cerebrospinal fluid

• Lined with ependymal cells

• Continuous with each other

• Continuous with the central canal of the spinal cord



• Lateral ventricles – located in cerebral hemispheres• Horseshoe-shaped from bending of the cerebral

hemispheres

• Third ventricle – lies in diencephalon • Connected with lateral ventricles by

interventricular foramen



• Cerebral aqueduct – connects 3rd and 4th ventricles

• Fourth ventricle – lies in hindbrain• Connects to the central canal of the spinal cord



Figure 13.6a, b






13


PART 2


The Cerebral Hemispheres

• Account for 83% of brain mass• Fissures – deep grooves – separate major regions

of the brain• Transverse fissure – separates cerebrum and

cerebellum

• Longitudinal fissure – separates cerebral hemispheres



• Sulci – grooves on the surface of the cerebral hemispheres

• Gyri – twisted ridges between sulci

• Prominent gyri and sulci are similar in all people



• Deeper sulci divide cerebrum into lobes

• Lobes are named for the skull bones overlying them

• Central sulcus separates frontal and parietal lobes• Bordered by two gyri

• Precentral gyrus

• Postcentral gyrus



Figure 13.7a



• Parieto-occipital sulcus • Separates the occipital from the parietal lobe

• Lateral sulcus • Separates temporal lobe from parietal and frontal

lobes

• Insula – deep within the lateral sulcus



Figure 13.7b, c



• Frontal section through forebrain• Cerebral cortex

• Cerebral white matter

• Deep gray matter of the cerebrum (basal ganglia)



Figure 13.8


The Cerebral Cortex

• Home of our conscious mind

• Enables us to: • Be aware of ourselves and our sensations

• Initiate and control voluntary movements

• Communicate, remember, and understand


The Cerebral Cortex

• Composed of gray matter• Neuronal cell bodies, dendrites, and short axons

• Folds in cortex – triples its size

• Approximately 40% of brain’s mass

• Brodmann areas – 52 structurally distinct areas


Functional and Structural Areas of the Cerebral Cortex

Figure 13.11a


Functional and Structural Areas of the Cerebral Cortex

Figure 13.11b


The Cerebral Cortex

• Functional regions• Traditionally – studied brain-injured people and

animals• New discoveries – PET and fMRI

• Regions of the cerebral cortex • Perform distinct motor and sensory functions

• Memory and language spread over wide area


The Cerebral Cortex

• Three kinds of functional areas• Motor areas

• Sensory areas

• Association areas


Motor Areas – Primary Motor Cortex

• Controls motor functions• Primary motor cortex (somatic motor area)

• Located in precentral gyrus (Brodmann area 4)

• Pyramidal cells – large neurons of primary motor cortex


Motor Areas – Primary Motor Cortex

• Corticospinal tracts descend through brainstem and spinal cord• Axons signal motor neurons to control skilled

movements

• Contralateral – pyramidal axons cross over to opposite side of the brain


Motor Areas

• Specific pyramidal cells control specific areas of the body

• Face and hand muscles – controlled by many pyramidal cells

• Motor homunculus – body map of the motor cortex

• Somatotopy – body is represented spatially in many parts of the CNS


Motor Areas

Figure 13.10


Motor Areas – Premotor Cortex

• Located anterior to the precentral gyrus

• Controls more complex movements

• Receives processed sensory information• Visual, auditory, and general somatic sensory

• Controls voluntary actions dependent on sensory feedback

• Involved in the planning of movements






13


PART 3


Sensory Areas

• Cortical areas involved in conscious awareness of sensation

• Located in parietal, temporal, and occipital lobes

• Distinct area for each of the major senses


Sensory Areas – Primary Somatosensory Cortex

• Located along the postcentral gyrus• Corresponds to Brodmann areas 1-3

• Involved with conscious awareness of general somatic senses

• Spatial discrimination – precisely locates a stimulus



• Projection is contralateral • Cerebral hemispheres

• Receive sensory input from the opposite side of the body

• Sensory homunculus – a body map of the sensory cortex



Figure 13.10


Association Areas

• Make associations between different types of sensory information

• Associate new sensory input with memories of past experiences

• New name for association areas – higher order processing areas


Association Areas – Prefrontal Cortex

• Large region of the frontal lobe anterior to motor areas

• Performs cognitive functions• All aspects of thinking and perceiving

• Remembering and recalling information

• Also related to mood

• Has close links to the limbic part of the forebrain


Association Areas – Prefrontal Cortex

• Anterior pole of frontal cortex • Active in solving the most complex problems


Lateralization of Cortical Functioning

• The two hemispheres control opposite sides of the body

• Hemispheres are specialized for different cognitive functions


Lateralization of Cortical Functioning

• Left cerebral hemisphere – more control over:• Language abilities, math, and logic

• Right cerebral hemisphere – more involved with:• Visual-spatial skills

• Reading facial expressions

• Intuition, emotion, artistic and musical skills


Cerebral White Matter

• Different areas of the cerebral cortex communicate:• With each other

• With the brainstem and spinal cord

• Fibers are usually myelinated and bundled into tracts



• Types of tracts• Commissures – composed of commissural fibers

• Allows communication between cerebral hemispheres

• Corpus callosum – the largest commissure

• Association fibers • Connect different parts of the same hemisphere



Figure 13.13a



• Types of tracts (continued) • Projection fibers – run vertically

• Descend from the cerebral cortex

• Ascend to the cortex from lower regions



Figure 13.13b


Projection Tracts

Figure 13.14a






13


PART 4


The Diencephalon

• Forms the center core of the forebrain

• Surrounded by the cerebral hemispheres

• Composed of three paired structures:• Thalamus, hypothalamus, and epithalamus

• Border the third ventricle

• Primarily composed of gray matter


The Diencephalon and Brainstem

Figure 13.15


The Diencephalon

Figure 13.16a


The Diencephalon

Figure 13.16b


The Diencephalon – The Thalamus

• Makes up 80% of the diencephalon

• Contains approximately a dozen major nuclei

• Send axons to regions of the cerebral cortex

• Nuclei act as relay stations for incoming sensory messages


The Diencephalon – The Thalamus

• Afferent impulses converge on the thalamus• Synapse in at least one of its nuclei

• Is the “gateway” to the cerebral cortex

• Nuclei organize and amplify or tone down signals


The Thalamus

Figure 13.17b


The Diencephalon – The Hypothalamus

• Lies between the optic chiasm and the mammillary bodies

• Pituitary gland projects inferiorly

• Contains approximately a dozen nuclei

• Main visceral control center of the body


The Diencephalon – The Hypothalamus

• Functions include the following: • Control of the autonomic nervous system• Control of emotional responses• Regulation of body temperature• Regulation of hunger and thirst sensations• Control of behavior• Regulation of sleep-wake cycles• Control of the endocrine system• Formation of memory


Nuclei of the Hypothalamus

Figure 13.18


The Diencephalon – The Epithalamus

• Forms part of the “roof” of the third ventricle

• Consists of a tiny group of nuclei

• Includes the pineal gland (pineal body)• Secretes the hormone melatonin

• Under influence of the hypothalamus






13


PART 5


The Brain Stem

• Includes the midbrain, pons, and medulla oblongata

• Several general functions• Produces automatic behaviors necessary for

survival• Passageway for all fiber tracts running between the

cerebrum and spinal cord• Heavily involved with the innervation of the face

and head• 10 of the 12 pairs of cranial nerves attach to it


Ventral View of the Brain – Diencephalon and Brain Stem

Figure 13.19


The Brain Stem – The Midbrain

• Lies between the diencephalon and the pons

• Central cavity – the cerebral aqueduct

• Cerebral peduncles located on the ventral surface of the brain• Contain pyramidal (corticospinal) tracts

• Superior cerebellar peduncles• Connect midbrain to the cerebellum


The Brain Stem and Diencephalon

Figure 13.20a, b

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.21a


• Periaqueductal gray matter surrounds the cerebral aqueduct• Involved in two

related functions • Fright-and-flight

reaction

• Mediates response to visceral pain



• Corpora quadrigemina – the largest nuclei• Divided into the superior and inferior colliculi

• Superior colliculi – nuclei that act in visual reflexes

• Inferior colliculi – nuclei that act in reflexive response to sound


The Brain Stem – Dorsal View

Figure 13.20c


The Brain Stem – The Pons

• Located between the midbrain and medulla oblongata

• Contains the nuclei of cranial nerves V, VI, and VII


The Brain Stem – The Pons

Figure 13.21.b


The Brain Stem – The Medulla Oblongata

• Most caudal level of the brain stem• Continuous with the spinal cord

• Choroid plexus lies in the roof of the fourth ventricle

• Pyramids of the medulla – lie on its ventral surface • Decussation of the pyramids – crossing over of

motor tracts

• Cranial nerves VIII–XII attach to the medulla


The Brain Stem – The Medulla Oblongata

• The core of the medulla contains:• Much of the reticular formation

• Nuclei influence autonomic functions

• Visceral centers of the reticular formation include:• Cardiac center

• Vasomotor center

• The medullary respiratory center

• Centers for hiccupping, sneezing, swallowing, and coughing


The Cerebellum

• Located dorsal to the pons and medulla• Smoothes and coordinates body movements

• Helps maintain equilibrium


The Cerebellum

• Consists of two cerebellar hemispheres

• Surface folded into ridges called folia• Separated by fissures

• Hemispheres each subdivided into:• Anterior lobe

• Posterior lobe

• Flocculonodular lobe


The Cerebellum

Figure 13.22a


The Cerebellum

• Composed of three regions• Cortex – gray matter• Internal white matter• Deep cerebellar nuclei – deeply situated gray

matter

• Cerebellum must receive information • On equilibrium • On current movements of limbs, neck, and trunk• From the cerebral cortex


The Cerebellum – Cerebellar Peduncles

• Thick tracts connecting the cerebellum to the brain stem• Superior cerebellar peduncles

• Middle cerebellar peduncles

• Inferior cerebellar peduncles

• Fibers to and from the cerebellum are ipsilateral• Run to and from the same side of the body






13


PART 6


Functional Brain Systems

• Networks of neurons functioning together• The limbic system – spread widely in the forebrain

• The reticular formation – spans the brain stem


Functional Brain Systems – The Limbic System

• Location • Medial aspect of cerebral hemispheres

• Also within the diencephalon

• The fornix and other tracts link the limbic system together



Figure 13.23



• The “emotional brain”• Cingulate gyrus

• Allows us to shift between thoughts

• Interprets pain as unpleasant


Functional Brain Systems – The Reticular Formation

• Runs through the central core of the medulla, pons, and midbrain



Figure 13.21c



• Widespread connections • Ideal for arousal of the brain as a whole

• Reticular activating system (RAS) • Maintains consciousness and alertness

• Functions in sleep and arousal from sleep



Figure 13.24


Protection of the Brain

• The brain is protected from injury by• The skull

• Meninges

• Cerebrospinal fluid

• Blood-brain barrier


Protection of the Brain – Meninges

• Cover and protect the CNS

• Enclose and protect the vessels that supply the CNS

• Contain the cerebrospinal fluid


The Dura Mater

• Strongest of the meninges

• Composed of two layers• Periosteal layer

• Meningeal layer• Two layers are fused except to enclose the dural

sinuses


The Dura Mater

Figure 13.25a


The Dura Mater

• Largest sinus – the superior sagittal sinus

• Dura mater extends inward to subdivide the cranial cavity

Figure 13.26


The Arachnoid Mater

• Located beneath the dura mater

• Subdural space • Potential space between dura and arachnoid mater

• Subarachnoid space• Filled with CSF

• Contains the blood vessels that supply the brain

• Arachnoid villi • Allow CSF to pass into the dural blood sinuses


The Pia Mater

• Delicate connective tissue

• Clings tightly to the surface of the brain• Follows all convolutions of the cortex






13


PART 7


Protection of the Brain – Cerebrospinal Fluid (CSF)

• Provides a liquid cushion for the brain and spinal cord

• The brain “floats” in CSF

• Formed in choroid plexuses in the brain ventricles



Figure 13.27a



Figure 13.27b


Protection of the Brain – Blood-Brain Barrier

• Prevents most blood-borne toxins from entering the brain• Impermeable capillaries

• Not an absolute barrier• Nutrients such as oxygen pass through

• Allows alcohol, nicotine, and anesthetics through


The Spinal Cord

• Runs through the vertebral canal

• Extends from the foramen magnum to the level of the vertebra L1 or L2

• Protected by bone, meninges, and CSF

• Dura mater of the spinal cord

• The spinal dural sheath – only one layer


The Spinal Cord

• Conus medullaris – the inferior end of the spinal cord

• Filum terminale – long filament of connective tissue• Attaches to the coccyx inferiorly

• Cervical and lumbar enlargements • Where nerves for upper and lower limbs arise

• Cauda equina – collection of nerve roots


The Spinal Cord

Figure 13.29a


The Spinal Cord

• Denticulate ligaments – anchor spinal cord to vertebrae

• Two deep grooves run the length of the cord• Posterior median sulcus

• Anterior median fissure


Anatomy of the Spinal Cord

Figure 13.30a


Anatomy of the Spinal Cord

Figure 13.30b


Gray Matter of the Spinal Cord and Spinal Roots

• Shaped like the letter H

• Gray commissure – contains the central canal

• Anterior horns – contain cell bodies of motor neurons

• Posterior horns – consist of interneurons

• Gray matter – divided according to somatic and visceral regions


Gray Matter of the Spinal Cord and Spinal Roots

Figure 13.32






13


PART 8


White Matter of the Spinal Cord

• Composed of myelinated and unmyelinated axons

• Three types of fibers• Ascending

• Descending

• Commissural


White Matter of the Spinal Cord

Figure 13.33


Sensory and Motor Pathways

• Most motor pathways:• Decussate at some point along their course

• Consist of a chain of two or three neurons

• Exhibit somatotopy• Tracts arranged according to the body region they

supply

• All pathways are paired• One of each on each side of the body


Ascending (Sensory) Pathways

• Conduct general somatic sensory impulses

• Chains of neurons composed of:• First-, second-, and third-order neurons

• Four main ascending pathways• Dorsal column pathway

• Spinothalamic pathway

• Posterior spinocerebellar pathway

• Anterior spinocerebellar pathway


Ascending Pathways

Figure 13.34a


Ascending Pathways

Figure 13.34b


Descending (Motor) Pathways

• Deliver motor instructions from the brain to the spinal cord

• Divided into two groups• Pyramidal, or corticospinal, tracts• Other motor pathways

• Tectospinal tracts• Vestibulospinal tract• Rubrospinal tract• Reticulospinal tract


Descending Motor Pathways

Figure 13.35a


Descending Motor Pathways

Figure 13.35b


Disorders of the Central Nervous System

• Brain dysfunction• Traumatic brain injuries

• Concussion – brain injury is slight

• Contusion – marked destruction of brain tissue



• Brain dysfunction (continued)• Degenerative brain diseases

• Cerebrovascular accident (stroke)• Blockage or interruption of blood flow to a brain region

• Alzheimer’s disease • Progressive degenerative disease leading to dementias



• Spinal cord damage• Paralysis – loss of motor function

• Parasthesia – loss of sensation

• Paraplegia – injury to the spinal cord is between T1 and L2

• Paralysis of the lower limbs

• Quadriplegia – injury to the spinal cord in the cervical region• Paralysis of all four limbs


The Central Nervous System Throughout Life

• Congenital malformations • Hydrocephalus

• Neural tube defects• Anencephaly – cerebrum and cerebellum are absent

• Spina bifida – absence of vertebral lamina

• Cerebral palsy – voluntary muscles are poorly controlled • Results from damage to the motor cortex

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