Brain and Cranial Nerves | Anatomy ppt

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Brain and Cranial Nerves | Anatomy ppt

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Human Anatomy, First Edition
McKinley & O’Loughlin

Chapter 15 Lecture Outline:

Brain and Cranial Nerves


Brain and Cranial Nerves

An adult brain weighs between 1.35 and 1.4 kilograms (kg) (around 3 pounds) and has a volume of about 1200 cubic centimeters (cc).

Brain size is not directly correlated with intelligence

It is not the physical size of the brain that determines intelligence—it is the number of active synapses.

The Brain’s 4 Major Regions

Cerebrum, the diencephalon, the brainstem, and the cerebellum.

The cerebrum is divided into two halves, called the left and right cerebral hemispheres.

Each hemisphere is subdivided into five functional areas called lobes.

Outer surface of an adult brain exhibits folds called gyri (gyrus) and shallow depressions between those folds called sulci (sulcus).

The brain is associated with 12 pairs of cranial nerves.



The Brain’s 4 Major Regions

Prosencephalon (forebrain)

Telencephalon: cerebrum

Diencephalon: epithalamus, thalamus,hypothalamus

Mesencephalon (midbrain)

Mesencephalon: cerebral peduncles, colliculi

Rhombencephalon (hindbrain)

Metencephalon: pons, cerebellum

Myelencephalon: medulla oblongata



Organization of Brain Tissue

Gray matter:

motor neuron and interneuron cell bodies, dendrites, axon terminals

unmyelinated axons.

White matter:

composed primarily of myelinated axons.

During brain development, an outer, superficial region of gray matter forms from migrating peripheral neurons.

External sheets of gray matter, called the cortex, cover the surface of most of the adult brain (the cerebrum and the cerebellum).

Organization of Brain Tissue

White matter lies deep to the gray matter of the cortex.

Within the masses of white matter:

discrete innermost clusters of gray matter called cerebral nuclei (or basal nuclei).

are oval, spherical, or sometimes irregularly shaped clusters of neuron cell bodies.

Support and Protection of the Brain

The brain is protected and isolated by multiple structures:

bony cranium


Protective connective tissue membranes

surround and partition portions of the brain.

Cerebrospinal fluid (CSF)

acts as a cushioning fluid.

Blood-brain barrier:

prevents entry of harmful materials from the bloodstream.


Cranial Meninges

Three dense regular connective tissue layers:

separate the soft tissue of the brain from the bones of the cranium.

Enclose and protect blood vessels that supply the brain.

Contain and circulate cerebrospinal fluid.

Parts of the cranial meninges form some of the veins that drain blood from the brain.

From superficial to deep, the cranial meninges are the dura mater, the arachnoid, and the pia mater.

Dura Mater

Tough membrane composed of two fibrous layers.

Strongest of the meninges.

Dura mater is composed of two layers.

periosteal layer, the more superficial layer, attaches to the periosteum of the cranial bones

meningeal layer lies deep to the periosteal layer

The meningeal layer is usually fused to the periosteal layer

Exception: in specific areas where the two layers separate to form large, blood-filled spaces called dural venous sinuses.


Also called the arachnoid mater or the arachnoid membrane.

Lies immediately internal to the dura mater.

Partially composed of a delicate web of collagen and elastic fibers, termed the arachnoid trabeculae.

Between the arachnoid and the overlying dura mater is the subdural space.

Immediately deep to the arachnoid is the subarachnoid space.

Pia Mater

The innermost of the cranial meninges.

Thin layer of delicate connective tissue that tightly adheres to the brain and follows every contour of the brain surface.


Cranial Dural Septa

The meningeal layer of the dura mater extends as flat partitions (septa) deep into the cranial cavity;

at four locations

called cranial dural septa.

Membranous partitions separate specific parts of the brain and provide additional stabilization and support to the entire brain.

falx cerebri

tentorium cerebelli

falx cerebelli

diaphragma sellae

Brain Ventricles

Cavities or expansions within the brain that are derived from the lumen (opening) of the embryonic neural tube.

Continuous with one another as well as with the central canal of the spinal cord.

Four ventricles in the brain.

two lateral ventricles are in the cerebrum, separated by a thin medial partition called the septum pellucidum

within the diencephalon is a smaller ventricle called the third ventricle

each lateral ventricle communicates with the third ventricle through an opening called the interventricular foramen

The fourth ventricle is located within the pons and cerebellum.

Cerebrospinal Fluid

A clear, colorless liquid that circulates in the ventricles and subarachnoid space.

Bathes the exposed surfaces of the central nervous system and completely surrounds it.

Performs several important functions.



environmental stability

Formed by the choroid plexus in each ventricle.

Produced by secretion of a fluid from the ependymal cells that originate from the blood plasma.

Is similar to blood plasma.



Blood-Brain Barrier

Nervous tissue is protected from the general circulation by the blood-brain barrier.

Strictly regulates what substances can enter the interstitial fluid of the brain.

Prevents exposure of neurons in the brain to drugs, waste products in the blood, and variations in levels of normal substances (ions, hormones) that could adversely affect brain function.


Blood-Brain Barrier

Tight junctions prevent materials from diffusing across the capillary wall.

Astrocytes act as “gatekeepers” that permit materials to pass to the neurons after leaving the capillaries.

Is markedly reduced or missing in three distinct locations in the CNS: the choroid plexus, hypothalamus, and pineal gland.


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

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

Cerebrum: functional areas

Home of our conscious mind

Enables us to:

Be aware of ourselves and our sensations

Initiate and control voluntary movements

Communicate, remember, and understand


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 areas of the cortex

Three kinds of functional areas

Motor areas

Sensory areas

Association areas

Motor areas

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

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


Sensory cortex

Cortical areas involved in conscious awareness of sensation

Located in parietal, temporal, and occipital lobes

Distinct area for each of the major senses


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

Primary Somatosensory Cortex

Projection is contralateral

Cerebral hemispheres

Receive sensory input from the opposite side of the body

Sensory homunculus – a body map of the sensory cortex

Somatosensory Association Area

Lies posterior to the primary somatosensory cortex

Corresponds to Brodmann areas 5 and 7

Integrates different sensory inputs

Touch, pressure, and others

Draws upon stored memories of past sensory experiences


Sensory Areas – Visual Areas

Primary visual cortex

Corresponds to Brodmann area 17

Located deep within the calcarine sulcus

On the posterior and medial part of the occipital lobe

Receives visual information that originates on the retina

First of a series of areas that interprets visual input

Sensory Areas – Visual Areas

Visual association area

Surrounds the primary visual area

Coincides with Brodmann areas 18 and 19

Continues the processing of visual information

Complex visual processing extends into:

Temporal and parietal lobes

Sensory Areas – Auditory Areas

Primary auditory cortex

Function – conscious awareness of sound

Location – superior edge of the temporal lobe

Corresponds to Brodmann areas 41 and 42

Sensory Areas – Auditory Areas

Auditory association area

Lies posterior to the primary auditory cortex

Located within Brodmann area 22

Permits evaluation of different sounds

Lies in the center of Wernicke’s area

Involved in recognizing and understanding speech

Sensory Areas – Gustatory Cortex

Involved in the conscious awareness of taste stimuli

Corresponds to Brodmann area 43

Located on the “roof” of the lateral sulcus

Sensory Areas – Vestibular Cortex

Located in the posterior part of the insula

Deep to the lateral sulcus

Sensory Areas – Olfactory Cortex

Lies on the medial aspect of the cerebrum

Located in a region called the piriform lobe

Olfactory nerves transmit impulses to the olfactory cortex

Provides conscious awareness of smells

Sensory Areas – Olfactory Cortex

Part of the rhinencephalon – “nose brain”

Includes – the piriform lobe, olfactory tract, and olfactory bulb

Connects the brain to the limbic system

Explains why smells trigger emotions

Orbitofrontal cortex

Involved with consciously identifying and recalling specific smells

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

Functional neuroimaging techniques

Reveal functions of specific parts of the prefrontal cortex

Anterior pole of frontal cortex

Active in solving the most complex problems

The farther rostrally one goes in the CNS, the more complex the neural functions

Association Areas – Prefrontal Cortex

Functional areas located on the medial side of the frontal lobe

Regions anterior to the corpus callosum

Involved in complex personal and social interactions

Regions superior to the corpus callosum

Involved in “mentalization

Association Areas – General Interpretation Area

Function is currently under investigation

Located at the interface of:

The visual, auditory, and somatosensory association areas

Newer studies show most of this region is involved in the visual processing of spatial relationships



Association Areas – Language Area

Surrounds the lateral sulcus in the left cerebral hemisphere

Five parts have been identified

Broca’s area – speech production

Wernicke’s area – speech comprehension

Lateral prefrontal cortex – conceptual analysis of spoken words

Association Areas – Language Area

Five parts have been identified (continued)

Most of the lateral and inferior temporal lobe

Coordination of auditory and visual aspects of language

Parts of the insula

Initiation of word articulation

Recognition of rhymes and sound sequences


Association Areas – Insula

Functions of its cortex – not well understood

Some parts function in language and the sense of balance

Other parts – visceral function

Conscious perception of:

Upset stomach

Full bladder

Some aspects of the sense of smell

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

Cerebral White Matter

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

Cerebral White Matter

Types of tracts (continued)

Projection fibers – run vertically

Descend from the cerebral cortex

Ascend to the cortex from lower regions

Projection tracts

Internal capsule – projection fibers form a compact bundle

Passes between the thalamus and basal nuclei

Corona radiata – superior to the internal capsule

Fibers run to and from the cerebral cortex

Basal nuclei

A group of nuclei deep within the cerebral white matter

Caudate nucleus – arches over the thalamus

Lentiform nucleus – “lens shaped”

Amygdala – sits on top of the caudate nucleus

Functionally belongs with the limbic system

Basal nuclei

Lentiform nucleus

Divided into two parts

Globus pallidus


Basal nuclei

Cooperate with the cerebral cortex in controlling movements

Receive input from many cortical areas

Evidence shows that they:

Start, stop, and regulate intensity of voluntary movements

In some way estimate the passage of time

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 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 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 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 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

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

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

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 – The Midbrain

Periaqueductal gray matter surrounds the cerebral aqueduct

Involved in two related functions

Fright-and-flight reaction

Mediates response to visceral pain

The Brain Stem – The Midbrain

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 – The Midbrain

Imbedded in the white matter of the midbrain

Two pigmented nuclei

Substantia nigra – neuronal cell bodies contain melanin

Functionally linked to the basal nuclei

Red nucleus – lies deep to the substantia nigra

Largest nucleus of the reticular formation

The Brain Stem – The Pons

Located between the midbrain and medulla oblongata

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

Two general groups of cranial nerve nuclei

Motor nuclei

Sensory nuclei

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


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

Fibers to and from the cerebellum are ipsilateral

Run to and from the same side of the body

Thick tracts connecting the cerebellum to the brain stem

Superior cerebellar peduncles

Middle cerebellar peduncles

Inferior cerebellar peduncles

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


Medial aspect of cerebral hemispheres

Also within the diencephalon

Composed of:

Septal nuclei, cingulate gyrus, and hippocampal formation

Part of the amygdala

The fornix and other tracts link the limbic system together

Functional Brain Systems – The Limbic System

The “emotional brain”

Cingulate gyrus

Allows us to shift between thoughts

Interprets pain as unpleasant

Hippocampal formation

Hippocampus and the parahippocampal gyrus

Functional Brain Systems – The Reticular Formation

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

Forms three columns

Midline raphe nuclei

Medial nuclear group

Lateral nuclear group

Functional Brain Systems – The Reticular Formation

Functional Brain Systems – The Reticular Formation

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

Functional Brain Systems – The Reticular Formation



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