Principles of Human Anatomy and Physiology, 11e 1 Chapter 14 Part 1 The Brain and Cranial Nerves Lecture Outline.

Principles of Human Anatomy and Physiology, 11e

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Chapter 14Part 1

The Brain and Cranial Nerves

Lecture Outline


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INTRODUCTION

The brain is the center for registering sensations, correlating them with one another and with stored information, making decisions, and taking action.

It is also the center for intellect, emotions, behavior, and memory.

It also directs our behavior towards others. In this chapter we will consider the principal parts of

the brain, how the brain is protected and nourished, and how it is related to the spinal cord and to the 12 pairs of cranial nerves.


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The Brain and Cranial Nerves

Largest organ in the body at almost 3 lb. Brain functions in sensations, memory, emotions, decision

making, behavior


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OVERVIEW: BRAIN ORGANIZATION AND BLOOD SUPPLY

The major parts of the brain are the brain stem, diencephalon, cerebrum, and cerebellum (Figure 14.1).

The CNS develops from an ectodermal neural tube Three primary vesicles: prosencephalon,

mesencephalon, and rhombencephalon develop from the neural tube. (Figure 14.29)

The embryologic development of the CNS is summarized in table 14.1


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Principal Parts of the Brain

Cerebrum Diencephalon

thalamus & hypothalamus Cerebellum Brainstem

medulla, pons & midbrain


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Blood Supply to Brain Arterial blood supply is branches from circle of Willis on

base of brain Vessels on surface of brain----penetrate tissue Uses 20% of our bodies oxygen & glucose needs

blood flow to an area increases with activity in that area deprivation of O2 for 4 min does permanent injury

at that time, lysosome release enzymes

Blood-brain barrier (BBB) protects cells from some toxins and pathogens

proteins & antibiotics can not pass but alcohol & anesthetics do

tight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries


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Blood Flow and the Blood-Brain Barrier An interruption of blood flow for 1 or 2

minutes impairs neuronal function. A total deprivation of oxygen for 4 minutes

causes permanent injury. Because carbohydrate storage in the brain is

limited, the supply of glucose to the brain must be continuous. Glucose deficiency may produce mental

confusion, dizziness, convulsions, and unconsciousness.


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BBB

A blood-brain barrier (BBB) protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage of many substances from the blood to the brain.

An injury to the brain due to trauma, inflammation, or toxins causes a breakdown of the BBB, permitting the passage of normally restricted substances into brain tissue.

The BBB may also prevent entry of drugs that could be used as therapy for brain cancer or other CNS disorders, so research is exploring ways to transport drugs past the BBB.


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Protective Covering of the Brain

The brain is protected by the cranial bones (Figure 7.4) and the cranial meninges (Figure 14.2). The cranial meninges are continuous with the

spinal meninges and are named dura mater, arachnoid, and pia mater.

Three extensions of the dura mater separate parts of the brain: the falx cerebri, falx cerebelli, and the tentorium cerebelli.


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Protective Coverings of the Brain

Bone, meninges & fluid Meninges same as

around the spinal cord dura mater arachnoid mater pia mater

Dura mater extensions falx cerebri tentorium cerebelli falx cerebelli


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CEREBROSPINAL FLUID

Cerebrospinal fluid (CSF) is a clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries.


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Cerebrospinal Fluid (CSF)

80-150 ml (3-5oz) Clear liquid containing glucose, proteins, &

ions Functions

mechanical protection floats brain & softens impact with bony walls

chemical protection optimal ionic concentrations for action potentials

circulation nutrients and waste products to and from

bloodstream


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Ventricles

There are four CSF filled cavities within the brain called ventricles (Figure 14.3). A lateral ventricle is located in each

hemisphere of the cerebrum. The lateral ventricles are separated by the septum pellucidum.

The third ventricle is a narrow cavity along the midline superior to the hypothalamus and between the right and left halves of the thalamus.

The fourth ventricle is between the brain stem and the cerebellum.


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Origin of CSF

Choroid plexus = capillaries covered by ependymal cells 2 lateral ventricles, one within each cerebral hemisphere roof of 3rd ventricle fourth ventricle


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Drainage of CSF from Ventricles

One median aperture & two lateral apertures allow CSF to exit from the interior of the brain


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Flow of Cerebrospinal Fluid


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Reabsorption of CSF

Reabsorbed through arachnoid villi grapelike clusters of arachnoid penetrate dural venous sinus

20 ml/hour reabsorption rate = same as production rate Reabsorption of CSF

Reabsorbed through arachnoid villi grapelike clusters of arachnoid penetrate dural venous sinus

20 ml/hour reabsorption rate = same as production rate


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Hydrocephalus

Blockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injury) Continued production cause an increase in

pressure --- hydrocephalus In newborn or fetus, the fontanels allow this

internal pressure to cause expansion of the skull and damage to the brain tissue

Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen


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THE BRAIN STEM


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Medulla Oblongata

Continuation of spinal cord Ascending sensory tracts Descending motor tracts Nuclei of 5 cranial nerves Cardiovascular center

force & rate of heart beat diameter of blood vessels

Respiratory center medullary rhythmicity area sets basic rhythm of breathing

Information in & out of cerebellum Reflex centers for coughing, sneezing, swallowing etc.


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Ventral Surface of Medulla Oblongata

Ventral surface bulge pyramids large motor tract decussation of most fibers

left cortex controls right muscles

Olive = olivary nucleus neurons send input to

cerebellum proprioceptive signals gives precision to movements


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Dorsal Surface of Medulla Oblongata

Nucleus gracilis & nucleus cuneatus = sensory neurons relay information to thalamus on opposite side of brain

5 cranial nerves arise from medulla -- 8 thru 12


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XII = Hypoglossal Nerve

Controls muscles of tongue during speech and swallowing

Injury deviates tongue to injured side when protruded

Mixed, primarily motor


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XI = Spinal Accessory Nerve

Cranial portion arises medulla skeletal mm of throat & soft

palate Spinal portion

arises cervical spinal cord sternocleidomastoid and

trapezius mm.


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X = Vagus Nerve

Receives sensations from viscera

Controls cardiac muscle and smooth muscle of the viscera

Controls secretion of digestive fluids


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IX = Glossopharyngeal Nerve

Stylopharyngeus m. (lifts throat during swallowing)

Secretions of parotid gland

Somatic sensations & taste on posterior 1/3 of tongue


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VIII = Vestibulocochlear Nerve

Cochlear branch begins in medulla receptors in cochlea hearing if damaged deafness or

tinnitus (ringing) is produced Vestibular branch begins in

pons receptors in vestibular

apparatus sense of balance vertigo (feeling of rotation) ataxia (lack of coordination)


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Tests of Cranial Nerve FunctionNerve Name Function How to test

I Olfactory olfaction with an odorous substance

II Optical vision vision chart

III Oculomotor most eye muscles "follow the moving finger"

IV Trochlear superior oblique look down at the nose

V Trigeminalfacial sensation touch the face

muscles of mastication clench the teeth

VI Abducens lateral rectus look to the side

VII Facialfacial expression smile, raise the eyebrows

taste sugar or salt

VIII Vestibulocochlearhearing a tuning fork

balance look for vertigo

IX Glosopharyngeal pharynx sensation gag reflex

X VagusMuscles of larynx and pharynx,

parasympatheticcheck for hoarseness, open

wide and say "AH"

XI AccessoryTrapezius and

sternocleidomastoidtest shoulder raise or turning

the head

XII Hypoglossal tongue muscles stick out the tongue


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Injury to the Medulla

Hard blow to the back of the head may be fatal Cranial nerve malfunctions on same side as injury;

loss of sensation or paralysis of throat or tongue; irregularities in breathing and heart rhythm


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Pons

The pons is located superior to the medulla. It connects the spinal cord with the brain and links parts of the brain with one another by way of tracts (Figures 14.1, 14.5). relays nerve impulses related to voluntary skeletal

movements from the cerebral cortex to the cerebellum. contains the pneumotaxic and apneustic areas, which

help control respiration along with the respiratory center in the medulla (Figure 23.24).

contains nuclei for cranial nerves V trigeminal, VI abducens, VII facial, and VIII vestibulocochlear (vestibular branch only).(Figure 14.5).


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Pons

One inch long White fiber tracts

ascend and descend Pneumotaxic &

apneustic areas help control breathing

Middle cerebellar peduncles carry sensory info to the cerebellum

Cranial nerves 5 through 7


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VII = Facial Nerve

Motor portion facial muscles salivary & nasal

and oral mucous glands & tears

Sensory portion taste buds on

anterior 2/3’s of tongue


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VI = Abducens Nerve

Lateral rectus eye muscle


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V = Trigeminal Nerve

Motor portion muscles of

mastication Sensory portion

touch, pain, & temperature receptors of the face

ophthalmic branch maxillary branch mandibular branch


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Midbrain

One inch in length

Extends from pons to diencephalon

Cerebral aqueduct connects 3rd ventricle above to 4th ventricle below


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Midbrain in Section

Cerebral peduncles---clusters of motor & sensory fibers Substantia nigra---helps controls subconscious muscle activity Red nucleus-- rich blood supply & iron-containing pigment

cortex & cerebellum coordinate muscular movements by sending information here from the cortex and cerebellum


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Dorsal Surface of Midbrain

Corpora quadrigemina = superior & inferior colliculi coordinate eye movements with visual stimuli coordinate head movements with auditory stimuli


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IV = Trochlear Nerve

Superior oblique eye muscle


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III = Oculomotor Nerve

Levator palpebrae raises eyelid (ptosis)

4 extrinsic eye muscles 2 intrinsic eye muscles

accomodation for near vision (changing shape of lens during reading)

constriction of pupil


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Reticular Formation

Scattered nuclei in medulla, pons & midbrain Reticular activating system

alerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleep

maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles

Motor function is involvement with maintaining muscle tone


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Cerebellum

2 cerebellar hemispheres and vermis (central area) Function

correct voluntary muscle contraction and posture based on sensory data from body about actual movements

sense of equilibrium


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Cerebellum

Transverse fissure between cerebellum & cerebrum Cerebellar cortex (folia) & central nuclei are grey matter Arbor vitae = tree of life = white matter


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Cerebellar Peduncles

Superior, middle & inferior peduncles attach to brainstem inferior carries sensory information from spinal cord middle carries sensory fibers from cerebral cortex &

basal ganglia superior carries motor fibers that extend to motor control

areas


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THE DIENCEPHALON


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Diencephalon Surrounds 3rd Ventricle

Surrounds 3rd ventricle Superior part of walls is thalamus Inferior part of walls & floor is hypothalamus


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Thalamus

The thalamus is located superior to the midbrain and contains nuclei that serve as relay stations for all sensory impulses, except smell, to the cerebral cortex (Figure 14.9). seven major groups of thalamic nuclei on each side

(Figure 14.9 c and d). They are the Anterior nucleus, medial nuclei, lateral

group, ventral group, intralaminar nuclei, midline nucleus, and the reticular nucleus.

It also registers conscious recognition of pain and temperature and some awareness of light touch and pressure.

It plays an essential role in awareness and the acquisition of knowledge (cognition.)


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Thalamus

1 inch long mass of gray mater in each half of brain (connected across the 3rd ventricle by intermediate mass)

Relay station for sensory information on way to cortex Crude perception of some sensations


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Thalamic Nuclei

Nuclei have different roles relays auditory and visual impulses, taste and

somatic sensations receives impulses from cerebellum or basal

ganglia anterior nucleus concerned with emotions,

memory and acquisition of knowledge (cognition)


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Hypothalamus The hypothalamus

inferior to the thalamus, has four major regions (mammillary, tuberal, supraoptic, and preoptic)

controls many body activities, and is one of the major regulators of homeostasis (Figure 14.10).

The hypothalamus has a great number of functions. It controls the ANS. It produces hormones. It functions in regulation of emotional and behavioral

patterns. It regulates eating and drinking through the feeding center,

satiety center, and thirst center. It aids in controlling body temperature. It regulates circadian rhythms and states of consciousness.


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Hypothalamus

Dozen or so nuclei in 4 major regions mammillary bodies are relay station for olfactory reflexes;

infundibulum suspends the pituitary gland Major regulator of homeostasis

receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood


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Epithalamus

The epithalamus lies superior and posterior to the thalamus and contains the pineal gland and the habenular nuclei (Figure 14.7). The pineal gland secretes melatonin to

influence diurnal cycles in conjunction with the hypothalamus.

The habenular nuclei (Figure 14.7a) are involved in olfaction, especially emotional responses to odors.


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Epithalamus

Pineal gland endocrine gland

the size of small pea

secretes melatonin during darkness

promotes sleepiness & sets biological clock

Habenular nuclei emotional

responses to odors


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Subthalamus

The subthalamus lies immediately inferior to the thalamus and includes tracts and the paired subthalamic nuclei, which connect to motor areas of the cerebrum. The subthalamic nuclei and red nucleus and

substantia nigra of the midbrain work together with the basal ganglia, cerebellum, and cerebrum in control of body movements.

Table 14.2 summarizes the functions of the parts of the diencephalon.


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Circumventricular Organs

Parts of the diencephalon, called circumventricular organs (CVOs), can monitor chemical changes in the blood because they lack a blood-brain barrier.

CVOs include part of the hypothalamus, the pineal gland, the pituitary gland, and a few other nearby structures.

They function to coordinate homeostatic activities of the endocrine and nervous systems.

They are also thought to be the site of entry into the brain of HIV.


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THE CEREBRUM

The cerebrum is the largest part of the brain . The surface layer, the cerebral cortex, is 2-4 mm thick

and is composed of gray matter. The cortex contains billions of neurons.

The cortex contains gyri (convolutions), deep grooves called fissures, and shallower sulci. (Figure 14.11a)

Beneath the cortex lies the cerebral white matter, tracts that connect parts of the brain with itself and other parts of the nervous system.

The cerebrum is nearly separated into right and left halves, called hemispheres, by the longitudinal fissure. Internally it remains connected by the corpus callosum, a

bundle of transverse white fibers. Figure 14.12)


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Principles of Human Anatomy and Physiology, 11e 1 Chapter 14 Part 1 The Brain and Cranial Nerves Lecture Outline.

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