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Title: Chapter 14 Part 1


1
Chapter 14Part 1
  • The Brain and Cranial Nerves
  • Lecture Outline

2
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.

3
Chapter 14The Brain and Cranial Nerves
  • Largest organ in the body at almost 3 lb.
  • Brain functions in sensations, memory, emotions,
    decision making, behavior

4
OVERVIEW OF 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

5
Principal Parts of the Brain
  • Cerebrum
  • Diencephalon
  • thalamus hypothalamus
  • Cerebellum
  • Brainstem
  • medulla, pons midbrain

6
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

7
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.

8
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.

9
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.

10
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

11
CEREBROSPINAL FLUID
  • Cerebrospinal fluid (CSF) is a clear, colorless
    liquid that protects the brain and spinal cord
    against chemical and physical injuries.

12
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

13
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.

14
Origin of CSF
  • Choroid plexus capillaries covered by
    ependymal cells
  • 2 lateral ventricles, one within each cerebral
    hemisphere
  • roof of 3rd ventricle
  • fourth ventricle

15
Drainage of CSF from Ventricles
  • One median aperture two lateral apertures allow
    CSF to exit from the interior of the brain

16
Flow of Cerebrospinal Fluid
17
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

18
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

19
THE BRAIN STEM
20
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.

21
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

22
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

23
XII Hypoglossal Nerve
  • Controls muscles of tongue during speech and
    swallowing
  • Injury deviates tongue to injured side when
    protruded
  • Mixed, primarily motor

24
XI Spinal Accessory Nerve
  • Cranial portion
  • arises medulla
  • skeletal mm of throat soft palate
  • Spinal portion
  • arises cervical spinal cord
  • sternocleidomastoid and trapezius mm.

25
X Vagus Nerve
  • Receives sensations from viscera
  • Controls cardiac muscle and smooth muscle of the
    viscera
  • Controls secretion of digestive fluids

26
IX Glossopharyngeal Nerve
  • Stylopharyngeus m. (lifts throat during
    swallowing)
  • Secretions of parotid gland
  • Somatic sensations taste on posterior 1/3 of
    tongue

27
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)

28
Injury to the Medulla
  • Hard blow to the back of the head may be fatal
  • Cranial nerve malfunctions on same side as
    injuryloss of sensation or paralysis of throat
    or tongue irregularities in breathing and heart
    rhythm

29
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).

30
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

31
VII Facial Nerve
  • Motor portion
  • facial muscles
  • salivary nasal and oral mucous glands tears
  • Sensory portion
  • taste buds on anterior 2/3s of tongue

32
VI Abducens Nerve
  • Lateral rectus eye muscle

33
V Trigeminal Nerve
  • Motor portion
  • muscles of mastication
  • Sensory portion
  • touch, pain, temperature receptors of the face
  • ophthalmic branch
  • maxillary branch
  • mandibular branch

34
Midbrain
  • One inch in length
  • Extends from pons to diencephalon
  • Cerebral aqueduct connects 3rd ventricle above to
    4th ventricle below

35
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

36
Dorsal Surface of Midbrain
  • Corpora quadrigemina superior inferior
    colliculi
  • coordinate eye movements with visual stimuli
  • coordinate head movements with auditory stimuli

37
IV Trochlear Nerve
  • Superior oblique eye muscle

38
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

39
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

40
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

41
Cerebellum
  • Transverse fissure between cerebellum cerebrum
  • Cerebellar cortex (folia) central nuclei are
    grey matter
  • Arbor vitae tree of life white matter

42
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

43
THE DIENCEPHALON
44
Diencephalon Surrounds 3rd Ventricle
  • Surrounds 3rd ventricle
  • Superior part of walls is thalamus
  • Inferior part of walls floor is hypothalamus

45
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.)

46
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

47
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)

48
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.

49
Hypothalamus
  • Dozen or so nuclei in 4 major regions
  • mammillary bodies are relay station for olfactory
    reflexesinfundibulum suspends the pituitary
    gland
  • Major regulator of homeostasis
  • receives somatic and visceral input, taste, smell
    hearing information monitors osmotic pressure,
    temperature of blood

50
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.

51
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

52
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.

53
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.

54
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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