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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
Principal Parts of the Brain
• Cerebrum
• Diencephalon
– thalamus &
hypothalamus
• Cerebellum
• Brainstem
– medulla, pons &
midbrain
Protective Coverings of the Brain
• Bone, meninges & fluid
• Meninges same as around
the spinal cord
– dura mater
– arachnoid mater
– pia mater
Blood Supply to Brain
• 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
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
Origin of CSF
• Choroid plexus = capillaries covered by ependymal cells
– 2 lateral ventricles, one within each cerebral hemisphere
– 3rd ventricle
– 4th ventricle
Brain Stem
Medulla Oblongata
Pons
Midbrain
Medulla Oblongata
• 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
• Reflex centers for coughing, sneezing, swallowing
Ventral Surface of Medulla Oblongata
• Ventral surface bulge
– pyramids
– large motor tract
– decussation of most fibers
• left cortex controls right muscles
Dorsal Surface of Medulla Oblongata
• 5 cranial nerves arise from medulla -- 8 thru 12
XII = Hypoglossal Nerve
• Controls muscles of
tongue during speech
and swallowing
XI = Accessory Nerve
• Proprioception
X = Vagus Nerve
• Receives sensations
from viscera
• Controls cardiac muscle
and smooth muscle of
the viscera
• Controls secretion of
digestive fluids
IX = Glossopharyngeal Nerve
• Stylopharyngeus m.
(lifts throat during
swallowing)
• Somatic sensations &
taste on posterior 1/3
of tongue
VIII = Vestibulocochlear Nerve
• hearing
• if damaged deafness or
tinnitus (ringing) is produced
• sense of balance
• vertigo (feeling of rotation)
• ataxia (lack of coordination)
Pons
• One inch long
• help control breathing
• Cranial nerves 5 thru 7
VII = Facial Nerve
• facial muscles
• salivary & nasal and
oral mucous glands &
tears
VI = Abducens Nerve
• Movement of eye
V = Trigeminal Nerve
• muscles of mastication
• touch, pain, &
temperature receptors of
the face
Midbrain
• One inch in length
• Extends from pons to
diencephalon
IV = Trochlear Nerve
• Movement of eye
III = Oculomotor Nerve
• Movement of eye
Cerebellum
• 2 cerebellar hemispheres
• Function
– correct voluntary muscle contraction and posture based on
sensory data from body about actual movements
– sense of equilibrium
Cerebellum
• Cerebellar cortex = grey matter
• Arbor vitae = tree of life = white matter
Diencephalon Surrounds 3rd Ventricle
• Surrounds 3rd ventricle
• Superior part of walls is thalamus
• Inferior part of walls & floor is hypothalamus
Thalamus
• 1 inch long mass of gray mater in each half of brain
• Relay station for sensory information on way to cortex
• Crude perception of some sensations
Hypothalamus
• 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
Functions of Hypothalamus
• Controls and integrates activities of the ANS which
regulates smooth, cardiac muscle and glands
• Synthesizes regulatory hormones that control the
anterior pituitary
• Contains cell bodies of axons that end in posterior
pituitary where they secrete hormones
• Regulates rage, aggression, pain, pleasure & arousal
• Feeding, thirst & satiety centers
• Controls body temperature
• Regulates daily patterns of sleep
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
Cerebrum
(Cerebral Hemispheres)
• Cerebral cortex is gray matter
overlying white matter
– 2-4 mm thick containing billions
of cells
– grew so quickly formed folds
(gyri) and grooves (sulci or fissures)
• Longitudinal fissure separates left
& right cerebral hemispheres
• Corpus callosum is band of white matter connecting
left and right cerebral hemispheres
• Each hemisphere is subdivided into 4 lobes
Lobes and Fissures
•
•
•
•
•
•
Longitudinal fissure (green)
Frontal lobe
Central sulcus (yellow)
Parietal lobe
Occipital lobe
Temporal lobe
Limbic System
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
II -- Optic Nerve
• Connects to retina
supplying vision
I -- Olfactory Nerve
• Extends from
olfactory mucosa of
nasal cavity to
olfactory bulb
• Sense of smell