Title: Chapter 14 Part 1
1Chapter 14Part 1
- The Brain and Cranial Nerves
- Lecture Outline
2INTRODUCTION
- 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.
3Chapter 14The Brain and Cranial Nerves
- Largest organ in the body at almost 3 lb.
- Brain functions in sensations, memory, emotions,
decision making, behavior
4OVERVIEW 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
5Principal Parts of the Brain
- Cerebrum
- Diencephalon
- thalamus hypothalamus
- Cerebellum
- Brainstem
- medulla, pons midbrain
6Blood 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
7Blood 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.
8BBB
- 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.
9Protective 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.
10Protective 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
11CEREBROSPINAL FLUID
- Cerebrospinal fluid (CSF) is a clear, colorless
liquid that protects the brain and spinal cord
against chemical and physical injuries.
12Cerebrospinal 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
13Ventricles
- 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.
14Origin of CSF
- Choroid plexus capillaries covered by
ependymal cells - 2 lateral ventricles, one within each cerebral
hemisphere - roof of 3rd ventricle
- fourth ventricle
15Drainage of CSF from Ventricles
- One median aperture two lateral apertures allow
CSF to exit from the interior of the brain
16Flow of Cerebrospinal Fluid
17Reabsorption 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
18Hydrocephalus
- 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
19THE BRAIN STEM
20Medulla 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.
21Ventral 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
22Dorsal 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
23XII Hypoglossal Nerve
- Controls muscles of tongue during speech and
swallowing - Injury deviates tongue to injured side when
protruded - Mixed, primarily motor
24XI Spinal Accessory Nerve
- Cranial portion
- arises medulla
- skeletal mm of throat soft palate
- Spinal portion
- arises cervical spinal cord
- sternocleidomastoid and trapezius mm.
25X Vagus Nerve
- Receives sensations from viscera
- Controls cardiac muscle and smooth muscle of the
viscera - Controls secretion of digestive fluids
26IX Glossopharyngeal Nerve
- Stylopharyngeus m. (lifts throat during
swallowing) - Secretions of parotid gland
- Somatic sensations taste on posterior 1/3 of
tongue
27VIII 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)
28Injury 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
29Pons
- 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).
30Pons
- 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
31VII Facial Nerve
- Motor portion
- facial muscles
- salivary nasal and oral mucous glands tears
- Sensory portion
- taste buds on anterior 2/3s of tongue
32VI Abducens Nerve
- Lateral rectus eye muscle
33V Trigeminal Nerve
- Motor portion
- muscles of mastication
- Sensory portion
- touch, pain, temperature receptors of the face
- ophthalmic branch
- maxillary branch
- mandibular branch
34Midbrain
- One inch in length
- Extends from pons to diencephalon
- Cerebral aqueduct connects 3rd ventricle above to
4th ventricle below
35Midbrain 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
36Dorsal Surface of Midbrain
- Corpora quadrigemina superior inferior
colliculi - coordinate eye movements with visual stimuli
- coordinate head movements with auditory stimuli
37IV Trochlear Nerve
- Superior oblique eye muscle
38III 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
39Reticular 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
40Cerebellum
- 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
41Cerebellum
- Transverse fissure between cerebellum cerebrum
- Cerebellar cortex (folia) central nuclei are
grey matter - Arbor vitae tree of life white matter
42Cerebellar 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
43THE DIENCEPHALON
44Diencephalon Surrounds 3rd Ventricle
- Surrounds 3rd ventricle
- Superior part of walls is thalamus
- Inferior part of walls floor is hypothalamus
45Thalamus
- 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.)
46Thalamus
- 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
47Thalamic 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)
48Hypothalamus
- 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.
49Hypothalamus
- 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
50Epithalamus
- 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.
51Epithalamus
- Pineal gland
- endocrine gland the size of small pea
- secretes melatonin during darkness
- promotes sleepiness sets biological clock
- Habenular nuclei
- emotional responses to odors
52Subthalamus
- 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.
53Circumventricular 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.
54THE 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)