Download 14-1

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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Principal Parts of the Brain
• Cerebrum
• Diencephalon
– thalamus &
hypothalamus
• Cerebellum
• Brainstem
– medulla, pons &
midbrain
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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
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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
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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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Origin of CSF
• Choroid plexus = capillaries covered by ependymal cells
– 2 lateral ventricles, one within each cerebral hemisphere
– 3rd ventricle
– 4th ventricle
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Brain Stem
Medulla Oblongata
Pons
Midbrain
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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
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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, 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
• Function
– correct voluntary muscle contraction and posture based on
sensory data from body about actual movements
– sense of equilibrium
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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
• 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
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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
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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
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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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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
• Each hemisphere is subdivided into 4 lobes
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Limbic System
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
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