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BIO-220
LECTURE 13: BRAIN AND SPINAL CORD FALL 2006
THE BRAIN
I. Brain Development and brain division
Cerebrum, diencephalon, mesencephalon, cerebellum, pons, medulla oblongata
II. The covering of the brain = cranial meninges
A. Dura mater – dense irregular CT
B. Arachnoid mater – reticular CT
C. Subarachnoid space – filled with cerebrospinal fluid (CSF)
D. Pia mater – loose areolar CT
III. Ventricles of the brain = central cavities filled with CSF
A. Four ventricles continuos with each other & with the central canal of the spinal cord
B. Three openings in the wall of IV ventricle: 2 lateral apertures, 1 median aperture, three openings connect
ventricles with subarachnoid space
C. Cerebrospinal fluid (CSF)
IV. Cerebrum:
A. Accounts for most of brain’s mass, 2 cerebral hemispheres
B. Cortex = gray matter: 1.3 mm thick; contains billions of cell bodies; has gyri (ridges), sulci (shallow
groves) & fissures (deep groves)
Divisions: frontal lobe, parietal lobe, occipital lobe, temporal lobe
C. Medulla = white matter: consists of myelinated fibers (association fibers, commisural fibers, projections
fibers)
D. Basal nuclei: cluster of gray matter located deep within white matter
E. Corpus callosum: transverse fibers connecting right & left hemispheres
F. Functions: perceive, communicate, remember, understand, initiate voluntary movements
G. Differences b/w left & right hemisphere
1. Left hemisphere: right hand/foot control, spoken & written language, scientific skills, numerical skills,
reasoning skills, sort out parts
2. Right hemisphere: left hand/foot control, appreciation of music & art, recognition of faces & other 3dimentional shapes, insight & imagination
V. Diecephalon
A. Thalamus: intermediate relay & processing center for all sensory info (except smell) going to cerebrum
B. Hypothalamus: controls & integrate ANS, center for emotional response & behaviour, temperature
regulation, food intake regulation, water & electrolyte balance, regulation of sleep-wake cycle, endocrine
control. Produces and secretes MSH, controlling tanning (melanocytes production)
i. Infundibulum is the stalk connecting pituitary gland to hypothalamus
ii. Pituitary gland, divided into two portions:
α. Anterior pituitary (glandular origin), produces, stores and secretes GH, TSH, ACTH, FSH, LH, and Pro
β. Posterior pituitary (neuronal origin) stores and sectretes ADH and Oxy (produced by hypothalamus)
C. Epithalamus: contains pineal gland (controls body rhythms). Produces, stores and secretes melatonin as
product of light exposure; organ is geomagnetically sensitive in birds, accounts for homing
VI. Midbrain
A. Functions – conduit for many major nerves into and out of brain; many neurotransmitters are produced here,
including dopamine from melanin (the skin pigment chemical).
VII. Pons
A. Functions – major link and conduit between higher brain and spinal cord; links cerebrum with cerebellum;
produces many important neurotransmitters (i.e. serotonin in raphe nuclei).
VIII. Medulla oblongata
A. Crossing of motor fibers takes place in here, that is why left brain controls right side of the body
B. Cardiovascular center (controls heart rate, force of heart contraction & vasoconstriction)
C. Respiratory center (controls respiratory rate, depth of respiration, rhythm of breathing)
D. Vomiting center
E. Some cranial nerves controlled from here: hypoglossal, glossopharyngeal, vagus, and auditory.
IX. Cerebellum (small brain)
A. Structure: consists of 2 hemispheres, and a vermis,
B. Functions: coordination of skeletal muscles; maintenance of normal muscle tone & body equilibrium
X. Cranial nerves (12 pairs)
1. Cranial nerves:
A. These are nerves that originate in the brain and govern control of senses (i.e., olfactory, optic) or motor (i.e.,
facial, trigeminal) functions directly: does not require receptor-spinal cord-brain sequence.
B. Numbered using Roman numerals.
C. Nerves and their functions-I Olfactory (smell) somatic
II. Optic (vision) sensory
III. Oculomotor (moves eyeball) motor
IV. Trochlear (moves eyeball to look up) motor
V. Trigeminal (moves rear and lower face muscles; feels sensations in mouth, jaw, rear of face) motor and
sensory
VI. Abducens (moves eyeball inward--makes you cross-eyed) motor
VII. Facial (controls most muscles of face and mouth, including sensations) motor and sensory
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VIII. Vestibulomotor/Auditory/Acoustic/Statoacoustic (receives sensations of sound and balance) sensory
[This nerve has more aliases than Chevy Chase]
IX. Glossopharyngeal (taste and tongue movement; throat muscle control) motor and sensory
X. Vagus (controls larynx and speaking; controls gastrointestinal tract function; controls blood supply to and
from brain; helps regulate blood pressure and flow rate; sends sensory data from GI tract to brain; induces
vomiting; and other related tasks) motor and sensory
XI. Accessory (partial control of throat and larynx; controls muscles that turn head) motor
XII. Hypoglossal (operate tongue movement) motor
2. Some vocabulary assistance:
Oculo- means "of the eye"
Pharynx - means "throat"
Tri - means "3"
Glosso- means "tongue"
Gemin- means "branches" or "start points"
Hypo- means "under" or "beneath"
Vestibul - refers to the ear's organ of balance
Cochlea - refers to ear's organ of hearing
Moto, motor - means "moving"
THE SPINAL CORD
I. Spinal Cord
A. Longitudinal structure:
1. Continuous with medulla oblongata at foramen magnum, terminates at conus medullaris, the nerve root
inferior to that are called cauda equina, filum terminale is a fibrous tissue that connect conus medullaris to
coccygeal ligament
2. Cervical enlargement, lumbar enlargement
3. Covering of spinal cord = spinal meninges: dura mater, arachnoid, subarachnoid space (filled with CSF),
pia mater
4. Spinal tap, lumbar puncture
B. Cross-sectional structure
1. Anterior median fissure, posterior median sulcus, central canal,
2. Gray matter: cell bodies of neurons + glial cells + unmylinated axons
a) Posterior gray horns – contain somatic & visceral sensory nuclei (nuclei = groups of soma in CNS)
b) Lateral gray horns (located only in thoracic & lumbar segments) – contain visceral motor nuclei
c) Anterior gray horns – contain somatic motor nuclei
d) Gray commissures – contain axons that cross from one side of the cord to the other
3. White matter: myelinated & unmyelinated axons running in 3 directions: down from brain, up to brain,
one side of cord to the other
a) Divided into 3 regions: posterior white columns, lateral white columns, anterior white columns
b) Each column contains tracts (axons sharing the same functional & structural characteristics)
c) Ascending tracts carry sensory info toward the brain; descending tracts carry motor commends from
brain to spinal cord
4. Polio causes paralysis due to destruction of somatic motor neurons; physical damage to spinal cord at or
above C5 will eliminate sensation & motor control of upper/lower limbs (= quadriplegia); damage to
thoracic spinal cord results in paraplegia
C. Dorsal root ganglia: contains the cell bodies of sensory neurons
D. Dorsal roots: contain axons of sensory neurons (soma are located in dorsal root ganglia) & bring sensory
info into the axons of motor neurons
E. Ventral roots: contain axons of motor neurons (soma are located in the gray matter of spinal cord) that
extend into the periphery to control somatic & visceral effectors
F. Functions of spinal cord
1. Connecting link b/w brain & the body
2. Coordinating spinal reflex
II. Spinal Nerves:
A. Dorsal and ventral roots are bound together to form a spinal nerve
B. Are mixed nerves because they contain both sensory (afferent) & motor (efferent) fibers
C. Cross-sectional structure: epineurium, perineurimu, endopneurium, fascicles, arteries, veins
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D. 31 pairs: cervical spinal nerves (C1 - C8), thoracic spinal nerves (T1 - T12), lumbar spinal nerves (L1 - L5),
sacral spinal nerves (S1 - S5), coccygeal nerve (Co1)
E. Peripheral distribution of spinal nerves (Fig.13-6)
1. Rami communicates (gray ramus & white ramus), sympathetic ganglion
2. Ventral ramus
3. Dorsal ramus
F. Plexuses of spinal nerves
1. Cervical plexus (C1 – C4)
a) Innervation: skin / muscles of back, neck & diaphragm
b) Damage: paralysis of diaphragm → stop breathing → death
2. Brachial plexus (C5 – C8, T1)
a) Innervation: muscles / skin of neck & upper limb
b) Damage: quadriplegia
3. Lumbar plexus (L1 – L4)
a) Innervation: muscles / skin of abdominal wall
b) Damage: paraplegia, back pain
4. Sacral plexus (L4, L5, S1 – S3)
a) Innervation: buttock, lower limb
b) Damage: paraplegia
5. Coccygeal plexus (S4, S5, Co1)
a) Innervation: skin in coccyx region
b) Damage: no symptom
III. Reflexes
A. Definition: a reflex is a mechanism by means of which an organism responds to changes in its internal or
external stimuli, it is a rapid, autonomic & unconscious activity; two types: neural reflexes, endocrine
reflexes
B. Reflex Arc of neural reflexes
1. Arrival of stimulus & activation of a receptor → activation of a sensory neuron → info processing →
activation of a motor neuron → response of a peripheral effector
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BIO 220
ANATOMY & PHYSIOLOGY I
FALL 2006
ANTIDEPRESSANT DRUG PHARMOKINETICS
Depression is a common symptom for a variety of disorders that affect the brain’s neurotransmitters.
Conditions include bulimia, anorexia, obsessive-compulsive disorder, depression, attention deficit
disorder, and attention deficit hyperactivity disorder. Two classes of medications are used in therapies,
monoamine oxidase inhibitors, and selective serotonin reuptake inhibitors. Both act to supplement natural
brain enzymes that are either produced in insufficient or no quantities.
MAOs -- Neurotransmitters are generally monoamines, enzymes with a single amino acid. When released
into the synapse, neurotransmitters are a) reabsorbed into the presynaptic bulbs of the transmitting nerve,
or b) destroyed by digestive enzymes called monoamine oxidase (MAO), released by the target cell into
the synaptic cleft. Clinical depression is related to decreases in concentration of the neurotransmitters.
Drugs that can either block the reuptake of neurotransmitters (e.g., cyclic antidepressants, newer selective
serotonin reuptake inhibitors) or interfere with the breakdown of the monoamines within the synaptic cleft
(monoamine oxidase inhibitors, or MAOIs) can restore brain neuronal functions to normal or near
normal activity.
There are two types of MAO. MAO-A is found primarily in the liver and gastrointestinal tract, with trace
amounts occurring in the monoaminergic neurons (nerve cells that release monoamine neurotransmitters).
MAO-A in the liver is involved in eliminating ingested monoamines such as dietary tyramine.
Monoamines circulating in the blood, such as epinephrine, norepinephrine, and dopamine, are inactivated
when they pass through a liver rich in MAO-A. MAO-B, on the other hand, is found primarily in the brain
and in platelets.
The older MAOIs, such as phenelzine (Nardil), isocarboxazid (Marplan), and tranylcypromine (Parnate),
bond irreversibly to both MOA-A and MOA-B inhibitors, while the newer MAOIs bind reversibly and
competitively, and are specific inhibitors of either MAOI-A or MAOI-B.
The MAOI agents currently available in the United States include phenelzine sulfate (Nardil),
tranylcypromine sulfate (Parnate), isocarboxazid (Marplan), and selegiline (specific for the MAO-B
enzyme), all of which irreversibly bind to MAO. Reversible inhibitors of MAO are available in Europe
(e.g., brofaromine, cimoxatone, clorgyline, lazabemide, moclobemide). Substances, such as St. John's
wort, that may have MAOI-like activity are frequently used for self-treatment of depression. Use of both
MAOI and selective serotonin uptake inhibitors may induce lethal effect.
SSRIs -- Selective serotonin reuptake inhibitors (SSRIs) are widely prescribed medications,
representing the majority of all antidepressants prescribed in the United States. SSRIs include fluoxetine
(Prozac), sertraline (Zoloft), paroxetine (Paxil), citalopram (Celexa), escitalopram (Lexapro), and
fluvoxamine (Luvox). SSRI toxicity and other adverse drug reactions can occur with overdose, in
combination with other medications, or infrequently at therapeutic doses.
SSRIs have a high therapeutic to toxicity ratio and are associated with less toxicity than tricyclic
antidepressants (TCAs). However, they are often involved in co-ingestions that can precipitate the
potentially lethal "serotonin syndrome" (SS). SS is characterized by mental status changes, neuromuscular
hyperactivity, and autonomic instability. SS is often caused by combinations of SSRIs with other
proserotonergic agents, including monoamine oxidase inhibitors (MAOIs), TCAs, trazodone (Desyrel),
lithium, opioids, and amphetamines, including 3,4 methylenedioxymethamphetamine (MDMA, Ecstasy),
cocaine, and herbal dietary supplements or nutraceuticals (St. John's wort, ginseng, and S-adenosylmethionine). Less frequently, SS can be precipitated by overdose of a single SSRI.
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Venlafaxine (Effexor) and duloxetine (Cymbalta) are serotonin-norepinephrine reuptake inhibitors
(SNRIs) that are also associated with serotonin toxicity, as is the tetracyclic drug mirtazapine (Remeron),
a blocking agent that causes increased norepinephrine and serotonin release in addition to blocking
serotonin receptors. Trazodone (Desyrel) is a tetracyclic drug that blocks serotonin reuptake and also has
an antagonistic effect at the serotonin 5-HT2 receptor site.
Serotonin, or 5-hydroxytryptamine (5HT), is a neurotransmitter found in both the central and peripheral
nervous system. It is an organic compound (C10H12N2O) formed from tryptophan, an amino acid.
Serotonin is produced in the brainstem raphe nucleus from L-tryptophan and is then stored in presynaptic
vesicles. Nerve impulses release 5HT into the synapse. Excess serotonin is taken back into the presynaptic
vesicles by an active transport mechanism, or is locally metabolized by monoamine oxidase (MAO) to 5hydroxyindoleacetic acid.
Metabolism in the body is through liver mixed function oxidases (MFOs). Inhibition of MFOs by other
medications or plant materials (e.g., grapefruit) may cause increased drug effect from decreased
metabolism. Seven distinct 5HT receptors with further specific subtypes exist, and they produce several
physiologic effects, including multiple symptoms of toxicity.
In addition to its neurotransmitter functions, serotonin stimulates the smooth muscles, and regulates cyclic
body processes, such as sleep and activity levels.
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