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Central nervous system, spinal
and cranial nerves
or ...let's get brainy on this page
"The central nervous system (CNS) consists of the brain and
the spinal cord,
while the
spinal nerves and cranial nerves are part of the peripheral nervous system (PNS)"
Objectives:
-
Be able to describe the protective layers of the
spinal cord as well as its structures and function
- know that the
meninges
are connective tissue coverings that extend
around the
spinal cord and the brain; the meninges consist of
3 layers which are:
1. Dura
mater
- outermost covering
- extends beyond the length of the spinal cord
2. Arachnoid mater
- middle layer
- collagen and elastic fibers
3. Pia
mater
- innermost layer
- transparent layer made up from collagen and elastin fibers
- when any of the meninges becomes invaded by a microbe, e.g. a bacterium,
the often resulting
infection is called meningitis;
-
The
spinal cord ends at approx. the 2. lumbar vertebrae
- know that the cerebrospinal fluid circulates in the
subarachnoid
space
- know that the spinal is about 42-45 cm (16 - 18 inches) long and
originates at the
medulla oblongata part of the brain
- know that the inferior, highly branched out part of the spinal cord is called
cauda equina
- know that the nerve cells of the
cervical enlargement of the
spinal cord supply
the upper limbs, while the nerves of the
lumbar enlargement innervate the
lower limbs
- there are 31 spinal segments of the spinal cord each of
which gives rise to a
pair of
spinal nerves
- each spinal nerve is only about
1 cm long
- almost immediately after emerging from the spinal
cord, each spinal nerve
divides into dorsal and ventral
rami
- rami contain both, efferent motor and afferent sensory
fibers
- the smaller dorsal rami serve the skin and muscles of the
posterior
body trunk
- the larger ventral rami of spinal nerves T2 - T12 pass
anteriorly as the
intercostal nerves;
they supply the muscles of the intercostal spaces and
the skin and muscles of the anterior and
lateral trunk;
- the ventral rami of all other spinal nerves form complex
nerve networks called
plexuses,
which serve the motor and sensory needs of the upper and lower limbs;
- from the plexuses the nerves
diverge again to form
peripheral nerves;
-
4 major nerve plexuses
are found, which - together with their peripheral nerves -
are described below:
1.
Cervical plexus
- arises from
the ventral rami of C1 - C5
- supplies
muscles of the shoulder and neck
- major motor
branch is the
phrenic nerve
- arises from C3 - C5
- innervates the diaphragm
"The primary danger of a 'broken neck' is
that the phrenic nerve may have been
severed, leading to paralysis, cessation of breathing and death ..."
2.
Brachial plexus
- arises from
ventral rami of C5 - C8, and T1
- subdivides
into 5 major peripheral nerves which are:
1.
Axillary nerve
- serves the muscles and skin of the shoulder, e.g. deltoid muscle
-
damage causes paralysis and atrophy of deltoid
2.
Radial nerve
- large peripheral nerve which innervates all extensor muscles of the
arm, forearm and hand; and all the skin along the way;
- e.g. triceps brachialis
-
damage causes wrist drop and inability to extend
hand at wrist;
3.
Median nerve
- runs down anterior of the arm
- supplies most of the flexor muscles in the forearm and several
muscles in the lateral part of the hand;
-
damage causes inability to pick up small objects
due to decreased
ability to flex and abduct thumb and index finger;
4.
Musculocutaneous nerve
- innervates the arm muscles that flex the forearm and of the skin
of the lateral surface of the forarm;
-
damage leads to decreased ability to flex the
forearm;
5.
Ulnar nerve
- runs down along the postero-medial surface of the arm;
- supplies the flexor carpi ulnaris muscle and all intrinsic muscles
of the hand not served by the median nerve;
-
damage causes typical "clawhand" with inability to
spread fingers
apart;
3.
Lumbar plexus
- arises from
the central rami of L1 - L4;
- innervates
the lower abdominal region and the anteromedial thigh;
- the largest
nerve of this plexus is the
femoral nerve;
- innervates the anterior thigh muscles, lower abdomen, buttocks,
and the skin of the anteromedial leg and thigh;
-
damage causes inability to extend leg and to flex
the hip;
- another
important nerve associated with this plexus is the
obturator nerve;
- innervates the adductor muscles of the medial thigh and small hip
muscles; also serves the skin of the medial thigh and hip joint;
-
damage leads to inability to adduct the thigh;
4.
Sacral plexus
- arises from L4 - S4
- peripheral nerves of this plexus innervate the buttock, the posterior
thigh
and virtually all of the leg and foot;
- the major nerve of this plexus is the
sciatic nerve;
- it is the largest nerve of the human body!
- travels through the greater sciatic notch of the hip bone down to the
posterior thigh;
- innervates the lower trunk and the posterior surface of thigh and leg;
-
damage leads to inability to extend hip and to
flex the knee --> "sciatica"
- divides in the popliteal region into the:
1.
Common fibular nerve
- innervates the lateral aspect of the leg and foot;
-
damage leads to inability to dorsiflex the foot
--> "footdrop"
and
2.
Tibial nerve
- innervates the posterior aspect of the leg and foot;
-
damage leads to inability to plantar flex and
invert the foot --> "shuffling gait";
- another important nerve of this plexus is the
superior and inferior gluteal nerve;
- innervates the gluteal muscles of the hip;
-
Know the difference between
white and grey matter of the spinal cord:
1. Grey matter
- cell bodies
of neurons, neuroglia, unmyelinated axons, dendrites of
interneurons and
motor neurons
- anterior
grey horn
- cell bodies of somatic motor neurons
- posterior
grey horn
- cell bodies of somatic and autonomic sensory neurons
- lateral
grey horns
- cell bodies of autonomic motor neurons (innervate smooth muscles,
cardiac
muscle and glands)
2. White matter
- strands of
unmyelinated and myelinated axons of sensory neurons, motor
neurons and interneurons
-
anterior
white columns
-
lateral
white columns
-
posterior
white columns
- also
contains
tracts:
- ascending tracts
= axons that conduct nerve impulses up
to the brain
-
descending or motor tracts = axons
that conduct nerve impulses down the
spinal cord
"Spinal nerves are the path of communication
between the spinal cord and
the nerves that innervate specific regions of
the body ..."
-
Know that the roots connect the spinal nerves to a segment
of the spinal cord
1. posterior (dorsal) root
- contains only sensory axons
2. anterior (ventral) root
- contains axons of somatic motor neurons
- know the function of the spinal cord in the human body; there are two
major
functions:
1. biological highways or "pathways"
for nerve impulse conduction
(= white matter)
2. site of integration of reflexes (=
gray matter)
- know that a reflex is a very
fast involuntary sequence of actions in the body in
response to a particular
stimulus; some reflexes, e.g. the eye lid or patellar
knee jerk reflex, are inborn and
don't have to be trained
- be able to name the difference between a spinal and a cranial reflex
-
Know the different basic components and the path of nerve impulse in a
typical
reflex arc; the
components are:
1. Sensory receptor
- located at distal ends of sensory neurons
2. Sensory (afferent) neuron
- axonal conduction of nerve impulse from receptor to the gray matter of the
spinal cord
3. Integrating center
- interaction of synapse of sensory neuron with a motor neuron; sometimes
including interneurons
4. Motor (efferent) neuron
- axonal conduction of nerve impulse from spinal cord to responding area of
the body, e.g. a skeletal muscle
5. Effector
- the part of the body that responds to the (efferent) nerve impulse of the
motor neuron
- can be a skeletal muscle (= somatic reflex), or
cardiac muscle, smooth muscle or gland (= visceral reflex)
- know the
important examples of reflexes of the human body, which are:
1. Patellar (or knee jerk) reflex
-
assesses the function of the S1 and S2 spinal nerves;
- sensory
receptors are in the quadriceps femoris muscle;
- effector
muscle is the quadriceps femoris;
2.
Plantar reflex
-
another important neurological test which probes the integrity of the
corticospinal tract (= major voluntary motor tract);
-
elicited by stimulating receptors in the sole of the foot;
- effector
muscles are flexor muscles in the toes which flex and move closer
together;
-
damage to the corticospinal tract elicits the "Babinski's
sign";
- as a consequence the toes flare
and the great toe moves upward!
3. Eye lid reflex
4. Corneal reflex
-
tests the normal functioning of the trigeminal nerve (=
cranial nerve V);
-
absence of this reflex often indicates damage to
the brain stem;
5. Gag reflex
- tests the
normal motor responses of the cranial
nerves IX & X (= vagus);
- receptors
are in the oral mucosa on the side of the uvula;
- effector
function (= response) is the rise of the oral mucosa;
-
absence of this reflex often indicates damage to
the brain stem;
6. Pupillary light reflex
-
retina of the eye is the receptor;
- tests
function of the sensory (afferent) optic nerve (=
cranial nerve I)
and of the
efferent oculomotor nerve (= cranial
nerve III)
-
effector muscles are the smooth muscles of the iris;
- many
CNS centers involved;
-
absence of normal pupillary reflex is late
indication of severe trauma or
deterioration of the brain stem;
7. Consensual reflex
-
retina of the eye is the receptor;
- tests
function of the sensory (afferent) optic nerve (=
cranial nerve I)
and of the
efferent oculomotor nerve (= cranial
nerve III)
-
effector muscles are the smooth muscles of the iris;
- many
CNS centers involved;
-
Be able to describe the
composition, coverings and locations of spinal nerves within
the human body
- know that spinal nerves connect the CNS to sensory receptors located
in muscles and
glands in the human body
- know that there are 31 pairs of spinal nerves which are named after the
region and level
of the vertebral column from which they originate (see overview figure below or in
your textbook); the
spinal
nerves are sub-grouped into:
1. Cervical nerves
= 8 pairs
- first
spinal nerve pair emerges from the spinal cord above the atlas
2. Thoracic nerves
= 12 pairs
3. Lumbar nerves
= 5 pairs
4. Sacral nerves
= 5 pairs
5. Coccygeal nerve
= 1 pair
- all spinal nerves (exception C1) leave the vertebral column
via the intervertebral
foramina
- know the 2 attachments points of spinal nerves with the spinal cord which
are:
1. posterior root
- sensory
(afferent) axons run there
2. anterior root
- motor
(efferent) axons run there
- know that a mixed (spinal) nerve
contains both, afferent and efferent, axons
- know the names of the
protective connective tissue coverings
of spinal
(and cranial)
nerves, which are (from outer to inner):
1. Epineurium
- covering
around the entire nerve
- fuses with
the dura mater of the spinal meninges after passage through the
intervertebral foramina
2. Fascicles
3. Perineurium
4. Endoneurium
-
Know that the spinal nerves (after passing through the intervertebral
foraminae) divide
into several branches, some of which are fusing with neighboring branches to form
functional networks,
called
plexi
(sing. plexus)
- know the names of major and important plexi
of the human body, which are:
1. Cervical plexus
- innervates
posterior head, neck, upper part of shoulders and diaphragm
(major
nerve =
phrenic
nerve)
2. Brachial plexus
- innervates
upper limbs, parts of the neck and shoulder muscles
3. Lumbar plexus
- innervates
abdominal wall, external genitals, parts of the lower limbs
- branching
out are the
ilioinguinal, femoral and obturator nerves
4. Sacral plexus
- innervates
the buttocks, perineum, and lower limbs
- branching
out are the
gluteal, sciatic, and pudental nerves
- know that the spinal nerves T2 - T11 (instead of forming a plexus) build
the
intercostal nerves, which innervate the muscles between the ribs
-
Be able to name the
protective coverings of the brain and be able to explain the nature and
function of the blood-brain barrier; rehearse the function of the
cerebrospinal fluid (CSF)
- the human brain is protected by the cranium (skull bones) and the
cranial meninges
- know that the cranial meninges
have the same names as the spinal meninges, which are (from outer to
innermost):
1. Dura mater
2. Arachnoid mater
3. Pia mater
- know that the
cerebrospinal fluid (CSF)
is a clear, colorless liquid that carries oxygen,
glucose, and other important
nutrients from the blood the the neurons and neuroglia
- it also serves the function to remove metabolic wastes from the brain back
to the blood
- know that the site of CSF production in the human brain is the
choroid
plexus
via ependymal cells
- know that the CSF circulates within the human body (CSF
circulation) following a distinctive
route:
1. Choroid
plexus = site of active CSF secretion
2. Third
ventricle
3. Fourth
ventricle
4. Central
canal (spinal cord)
5.
Subarachnoid space (spinal cord)
6.
Subarachnoid space (brain)
7. Blood (via
arachnoid villi and the superior sagittal sinus)
8. Choroid
plexus
-
Be able to name the major
brain structures and their known biological functions
"The brain - one of the largest organs of the human
body - consists of about 100 billion neurons
and 10 - 50 trillion (!!) neuroglial cells with a mass of about 1,300 grams (almost 3 lb)...."
- be able to name the
5 major parts of the human brain, which are:
1. Brain stem (BS)
2. Diencephalon (DE)
3. Cerebellum (CB)
4. Cerebrum (C)
5. Cerebral cortex (CC)
Be able to find and name the most
important brain structures
of the human brain, its brain
regions, glands
and ventricles with the help of the table and the figures below; also know the most important biological
functions
for each of the brain structures and glands.
- know that the white matter of the brain consists of myelinated and
unmyelinated axons
- despite making up only about 6% of the weight of the human body, the brain
takes up more
than 20% of the human blood supply due to its high demand in primarily glucose;
- the nutrients and the necessary oxygen is
delivered to the brain via three major arteries which are:
1. External & internal carotid artery
2. Vertebral arteries
3. Basilar artery
Table: Important brain regions and their
biological functions
| |
Brain region/area |
Biological function |
|
BS |
Medulla oblongata |
contains several nuclei:
- Cardiovascular center (reg. of heart beat, blood vessels)
- Medullary rhythmicity area (control
of breathing)
- Posterior part (touch, pressure, vibration sensation)
- other nuclei (reflex control, swallowing, vomiting) |
| BS |
Pons |
contains nuclei and bundles of axons
- connective function and relay station (cortex into cerebellum)
- nuclei associated with cranial nerves V, VI, VII and VIII |
| BS |
Midbrain |
connects pons with diencephalon; contains tracts
and nuclei
- Cerebral peduncules (contain efferent and afferent axons)
- Substantia nigra (motor control, high concentration of
dopaminergic neurons; nerve cell loss in PD patients)
- Red nucleus (coordination of muscular movements)
- oculomotor nucleus
- Reticular formation (afferent axons in reticular activating
system (RAS);
site of "wakefulness & consciousness" of the brain; "sleep center")
- Superior & inferior colliculi (passage site of several
reflex arcs) |
| DE |
Thalamus |
the neuronal filter or "brain switch board";
cross point of sensory &
motor neurons
- awareness & "cognition center" of the brain |
| DE |
Hypothalamus |
controls many important and basic body functions:
- Control of the autonomous nervous system (ANS)
- Control of the anterior and posterior lobe of the
pituitary gland
- Modulation of appetite & drives, e.g. eating and drinking,
sexual
reproduction (FSH) via hormones --> hormonal regulation
- Control of body temperature (via ANS)
- preoptic area (rostral tip) is temperature sensitive
- neurons in medial preoptic region have inhibitory effect
on thermogenesis (heat production) in the brown fat
tissue
- paraventricular and dorsomedial nuclei have
excitatory effect
on thermogenesis
- adrenergic receptors on brown fat tissue
mediate production
of
uncoupling proteins (UCPs) in mitochondria which
lead to increased heat instead
of ATP production
- input to brainstem and spinal areas via the Raphe pallidus
- Regulation of circadian rhythms
- Regulation of states of consciousness |
| DE |
Suprachiasmatic Nucleus
(SCN) |
- brain region located in the hypothalamus
- the body's "master time keeper" or circadian
(day/night) rhythms,
incl. sleep-wake cycle
- connected with the light-perceiving retina
- the light-activated SCN prevents secretion of the "sleep and
depression hormone" melatonin from the pineal gland (see below) |
| DE |
Pineal gland |
seat of the "biological clock" of the human body
- Control of important biological rhythms (day/night cycles)
- Secretes melatonin which promotes sleepiness |
| CB |
Cerebellum |
important relay and muscular movement
coordination center
- consists of 2 cerebellar hemispheres
- compares intended with actual body movements
- sensory inputs from muscles, tendons, joints and receptors |
| |
Tentoricum |
Separation of cerebellum and cerebrum |
| C |
Cerebrum
(& cerebral cortex) |
- consists of cerebral cortex (grey matter) &
internal region (white matter)
- "seat" of all higher body functions and abilities
- has folds called gyri & deep grooves called
fissures
- consists of two (right and left) hemispheres
- each hemisphere shows 4 major lobes:
1. Frontal lobe
2. Parietal lobe
3. Temporal lobe
4. Occipital lobe
- fifth part of the cerebrum is the insula (deep
brain location)
- each hemisphere shows 3 nuclei (grey matter areas)
1. Basal ganglia (see below)
2. Globus pallidus
3. Caudate nucleus |
| C |
Corpus callosum |
- part of the limbic system;
- massive axon bundles that connect the two (left and right) brain hemispheres |
| |
|
|
| C |
Amygdala |
"Seat" of emotional memory
& part of the limbic system (see below);
- plays an important role in anxiety and fear behavior
- axons of autonomous efferent neurons reach into the hypothalamus
and brain stem and trigger autonomic fear expression |
| C |
Limbic system |
"Seat" of the
"emotional brain"
- has complex nervous and biochemical interactions with the
cerebral cortex;
- role in the control of a range of emotions (pain, pleasure,
affection,
anger), appetite, emotions, and memory
- electric stimulation of some limbic areas triggers reactions of
anger,
anxiety, excitement, sexual interest , colorful visions, deep thoughts
and relaxation;
- place of the body's "reward" and "punishment" centers;
- consists of:
1. Amygdala
- associated with aggressive
behavior
- allows distinction between
positive and negative memories;
2. Hippocampus
- "Seat" of the long-term
memory of the brain;
- loss of nerve functions
in this region observed in AD patients;
(for more info on AD --> see Medical section at the end of this page)
3. Transparent septum
- associated with pleasure
4. Cingulate gyrus
5. Body of Fornix
6. Anterior commisure
- role in internal
inter-communication
7. Maxillary bodies
- role in creation of memory;
8. Corpus callosum
9.
Olfactory tract
10. Stria medullaris &
terminalis
|
| C |
Dendate gyrus |
One of the few places in the brain where
neurogenesis takes place |
| C |
Caudate nucleus |
Motor functions & Emotional modulation |
| C |
Putamen |
Motor functions & Emotional modulation |
| C |
Globus pallidus |
Motor functions & Emotional modulation |
| C |
Nucleus accumbus |
Emotional modulation |
| |
Basal ganglia |
Helps to initiate and terminate body movements
- has connection to the substantia nigra
Regulation of muscle tone
Subconscious muscle movements |
| |
Neocortex |
Newer, evolutionary youngest part of the brain |
| |
Cortex |
Generally means the gray matter of the human brain |
| |
Paleocortex |
Older, more primitive cortical area |
| |
Temporal lobe |
Neocortical brain region associated with
understanding speech and hearing |
| |
Angular gyrus |
Neocortical brain area responsible for the
ability to read and write |
| |
Brodmann's area 10 |
Expanded area in the human brain
- involved in
undertaking initiatives and planning future actions -
"higher
cognitive center" |
| |
Prefrontal cortex |
A higher brain region that allows us to
appropriately control our
behaviors,
thoughts, and emotions using representational
knowledge;
Cortical area critical for motivation, learning
in response to reward,
and working memory;
Regions of this brain area play a role in processing and retrieving
information
related to self awareness ("ego", "free will") and
maintaining sense of self; important
sub-regions are:
- Medial prefrontal cortex
- "memory of self" region
- Precuneus
- retrieves "autobiographic memories"
- Anterior insula
- creates/stores visual pictures of self
Damage (lesions) to this area produces symptoms of impulsivity,
distractibility,
and poor judgment;
Prefrontal cortex deficits are associated with thought disorder,
hallucinations,
bipolar disorder and schizophrenia
|
| |
rostral Anterior Cingulate
Cortex (rACC) |
One of the brains pain centers |
Legend: BS = Brain Stem
DE = Diencephalon C = Cerebrum
Figure 10-1: Important structures and regions of the human
brain
Figure 10.2. Elements of the limbic system of the human
brain
Anatomically, the human brain shares
many basic structures and brain areas with the brains of other animals. For
example,
in the much smaller sheep
brain (see
Image below), one
observes a cerebrum, a brain stem, cerebellum, medulla oblongata
and glands, such as the pineal gland and the pituitary gland.
- like the human brain it's surface is also thrown into many
convolusions, called gyri and fissures.
- it possesses a rather large olfactory bulb, a pronounced
optic nerve (CN II) and an optic chiasma.
- cerebral peduncles are found on the ventral aspect of the
midbrain, posterior to the mammilary body.
- the same number of cranial nerves, which is 12, emerge from
the base of the brain.
- internally, the sheep brain reveals a thalamus, a corpus
callosum, ventricles, hypothalamus, the corpora quadrigemina
of the midbrain, the pineal gland, and the pons.
The inner anatomy of a sheep brain
Click on the interactive button below to access the file
for the "Anatomy of the Sheep Brain".
- Know
the names and location of the different functional (sensory, motor &
association)
areas of the cerebral cortex, which are:
(see also Figure 10-3 below)
1. Sensory areas
-
areas
posterior to the central sulcus
- the individual areas are:
1. Primary somatosensory area
2. Primary visual area
3. Primary auditory area
4. Primary olfactory area
2. Motor areas
- areas
anterior to the central sulcus = Primary motor area, Premotor
area
3. Association areas
Figure 10-3: Lobes and functional areas of the
human cerebrum
-
Know that within the sensory
cortex and the motor cortex the neurons are communicating
with different regions of the human body; the number of neurons and
neuron density is
different for the different regions of the human body
- see and study the
maps of the human sensory and motor
cortex below
- the hands, feet and face are over-proportionally
represented in the sensory cortex
- the hands and face (especially the lips and tongue) are are
over-proportionally represented
in the motor cortex
-
Know the difference between
the somatic sensory and somatic motor pathway of the cerebrum.
All
efferent somatic motor information
descends mainly from the primary
motor area of the
cortex via the brain stem to the skeletal muscles.
- they control all voluntary and involuntary movements of the
body
- route: axons of motor neurons begin in
primary motor area
→ internal capsule →
upper motor neurons
→
pons →
medulla → left lateral corticospinal tract or
right anterior corticospinal
tract → lower motor neurons (brain stem
or in anterior grey horn of spinal cord) →
spinal cord →
muscle
- axons converge at the lower motor neurons located in the brain
stem
or in anterior grey horn of spinal cord
- lower motor neurons receive modulatory signals from other
neurons such as:
1. "local
interneurons"
- rhythmic muscle activity, e.g. walking
2. upper
motor neurons
- control of voluntary movements
3. basal
ganglia
- help to initiate and terminate movements, control muscle tone, suppression
of unwanted movements
4. cerebellum
neurons
- help to coordinate body movements
Pathology
"Damage or disease (e.g. viruses) of
LOWER MOTOR NEURONS
leads to flaccid
paralysis
of muscles on the SAME SIDE of the body. Under these
conditions, muscles lack voluntary control
and reflexes; the muscles remain flaccid (limp) due to decreased or lost
muscle tone.
Injury or disease of UPPER MOTOR NEURONS
causes spastic
paralysis
of muscles
located on the opposite side of the body; in this condition the muscle tone
is increased, reflexes
are exaggerated, and pathological reflexes appear."
-
All
afferent) somatic sensory information
from the body surface
ascends to the primary somatosensory
area of the cerebral cortex via 2 main somatic sensory pathways, which are:
1. The posterior column -
medial lemniscus pathway
- carries
nerve signals or fine touch,
proprioception and vibration from somatic sensory receptors
in
peripheral body parts towards the primary somatosensory area of cortex;
- nerve
impulses conducted along the posterior column-medial lemniscus pathway give
rise to three
main types of sensations:
I. Fine touch
- ability to recognize what point on the body is touched
- recognition of shape, size and texture
II. Proprioception
- awareness of the precise position of body parts
- signals the awareness of the directions of body movements =
kinesthesia
III. Vibratory sensations
- signals of rapidly fluctuating touch stimuli
2. The anterior spinothalamic pathway
- carries
nerve signals from peripheral receptors for
pain,
hot and cold temperature,
tickle,
and itch
sensations via two spinal cord tracts towards the primary somatosensory area
of the cerebral cortex.
- the two,
ascending nerve signals conducting spinal cord tracts are:
I. Anterior spinothalamic tract
II. Lateral spinothalamic tract
-
Know that (despite the brain symmetry) there exist functional differences
between
the two brain hemispheres, which is termed:
Hemispheric laterization:
1. Left hemisphere
- receives sensory signals from
right
body side
- controls motor functions of right
body side
- important for spoken and written
language, numerical and scientific skills
- important for reasoning in most
people
2. Right hemispere
- receives sensory signals from
left
body side
- controls motor functions of left
body side
- important for musical and artistic
awareness
- important for spatial and pattern
perception
- recognition of faces and emotional
content of language
- generates mental images of sight,
sound, touch, taste and smell
- know that
memory is the capacity and great
achievement of the brain to store
and retrieve information once acquired through learning or experience
- know that the parts of the brain important for memory
include:
1. association cortex of the
frontal, parietal, occipital and temporal lobes
2. parts of the limbic system
3. parts of the diencephalon
4. basal ganglia & cerebellum
(→ memory of motor skills)
-
Know that brain functions,
e.g. consciousness, can be altered by a series of drugs and
pharmaceuticals
- drugs (legal of illegal)
as well as pharmaceuticals
can interfere with nervous transmission
and in many cases can cause the long-term development of habit or a
drug addiction;
- some can induce immediate mental alterations and hallucinations, e.g. LSD,
cocaine, and show
measurable changes in brain functions (--> see
PET Figures
below);
- all of them cause tolerance or addiction;
- in tolerance higher drug doses are required to achieve the
same effect;
- in addiction lack of drug access can cause severe
physiological and psychological
problems;
- drugs can be divided into 3 major groups which are:
1. Popular, legal drugs
- e.g. caffeine, nicotine (tobacco),
alcohol
2. Pharmaceutics
- sold in pharmacies with a medical
prescription
- e.g. stimulants, sleeping pills,
sedatives, pain killers
3. Prohibited, illegal
substances/drugs
- e.g. heroin, cocaine, amphetamines,
cannabis (ashis/marijuana), hallucineogens
(e.g. LSD, mescal,
ecstasy)
-
Be able to identify the 12
pairs of cranial nerves (by name and numbers) and know their biological
functions
- the 12 pairs of cranial nerves
(CN)
which are designated with roman numerals (CN I →
CN
XII), are part of the PNS
- the names, components and biological function of the cranial nerves are
summarized in the Table and
Figure below
- the 12 pairs of cranial nerves primarily serve the head and neck and only
the Vagus nerve (CN X),
which is part of the
ANS, extends into the thoracic and abdominal cavities.
- with the exception of CN I & CN II, all cranial nerves are mixed nerves,
which means, that they are containing motor AND
sensory nerve fibers.
- Techniques for testing cranial nerve
function/condition is an important part
of routine neurological examination of
patients for traumatic injury of the brain.
- An easy way to remember the sequence of cranial nerves within the human
brain is the following catchy saying:
"On
occasion
our
trusty
truck
acts
funny
- very
good
Vehicle
anyhow"
| Number |
Name |
Components
(Receptors/Axons) |
Function
|
| I |
Olfactory nerve |
Purely sensory (Nose) |
Transmission of sense of smell
via olfactory bulb |
| II |
Optic nerve |
Purely sensory
(Retina) |
Vision |
| III |
Oculomotor nerve |
Sensory
(Eye balls)
Motor part (muscles of eye balls) |
Proprioception (= muscle sense)
of eye balls
Movement of skeletal muscles controlling eyelid and eye balls;
Parasympathic control of ciliary muscle of eye ball
and of smooth muscles sphincter muscle of iris |
| IV |
Trochlear nerve |
Sensory part
(Superior oblique muscle)
Motor part (Superior oblique muscle) |
Proprioception of
superior oblique muscles
Movement of the eye balls |
| V |
Trigeminal nerve |
Sensory part
1. Ophthalmic nerve (scalp/forehead)
2. Maxillary nerve (lower eyelid, nose,
upper teeth, upper lip & pharynx
3. Mandibular nerve (tongue, lower teeth
& lower side of face)
Motor part (motor control of chewing muscles) |
Touch, pain and temperature
sensations from
skin of face and anterior scalp, mucosae of mouth
and nose;
+ proprioception
(Test: Patient's facial
sensation of pain, touch, and temperature
are tested with the help of safety pins, hot and cold objects)
Activation of chewing muscles
(Test: Patient is asked to clench teeth, open mouth against
resistance, and to move jaw side to side) |
| VI |
Abducens nerve |
Sensory part
(lateral rectus muscles, eye ball positioning)
Motor part (lateral rectus muscles) |
Proprioception of
lateral rectus muscle
Control of movement of eye balls |
| VII
|
Facial nerve |
Sensory part
(Taste buds on tongue, proprioceptors of muscles of face and scalp)
Motor part (facial, scalp and neck muscles
Control of lacrimal and salivary glands) |
Taste & Proprioception
(Test: Anterior two thirds of
tongue is tested for
ability to taste sweet, salty, sour and bitter substances)
1. Control of facial expressions via
skeletal muscles
(Test: Patient is asked to close eyes, smile, whistle,
etc.)
2. Parasympathetic control of secretion of tears and saliva
(Test: Patient's ability to produce tears is tested with
the
help of ammonia fumes) |
| VIII |
Vestibulocochlear nerve |
Sensory part
(Vestibule)
Motor part (Vestibule)
Sensory part (Cochlea)
Motor part (Cochlea) |
Sensation of Equilibrium
Sensitivity of hair cells adjustment
Sensation of hearing
(Test: Patient's hearing ability is checked
by air and bone
conduction using tuning forks)
Modulation of cochlear hair cell responses |
| IX |
Glossopharyngeal
nerve |
Sensory part
(Taste buds on posterior third, of tongue, swallowing proprioception, carotid sinus,
carotid body)
Motor part (swallowing muscles, throat, salivary gland) |
Taste, touch, pain, temperature
sensation from tongue;
blood pressure monitoring, oxygen and CO2
monitoring,
Actions: Somatic motor neurons activate swallowing
muscles;
Parasympathetic axons stimulate secretion of saliva
(Test: Patient is checked for gag and swallowing reflexes;
patient is asked to speak and cough; |
| X
|
Vagus nerve
(also major part of
the parasympathetic
division of the ANS) |
Sensory portion
(Proprioception of muscles of neck and throat, carotid sinus;
Stretch and chemoreceptors in carotid body and carotid sinus;
Visceral sensory receptors in organs of thoracic and abdominal cavities
Motor portion (Muscles of throat and neck, smooth muscles in the
airways, esophagus, stomach, small intestines, most of large intestine,
gall bladder, cardiac muscle, glands of GI tract) |
Taste, touch & temperature
sensation from throat and pharynx;
monitoring of blood pressure;
Monitoring of blood oxygen and CO2
level; sensations from visceral organs
Swallowing, coughing and voice production; smooth muscle contraction &
relaxation of GI tract organs;
slowing of heart rate;
secretion of digestive fluids |
| XI
|
Accessory nerve |
Sensory part
(Proprioceptors in muscles of throat and voice box)
Motor part (Muscles of throat and neck; provides motor fibers
to sternocleidomastoid and trapezius muscle) |
Proprioception
Actions: Swallowing; rotation of head and
movement
of shoulders
(Test: patient is asked to rotate head and elevate shoulder
against resistance) |
| XII |
Hypoglossal
nerve |
Sensory part
( Proprioceptors in tongue muscles)
Motor part ( Motor fibers serve muscles
of tongue) |
Proprioception
Actions:
Movement of tongue during speech and swallowing
(Test: Patient is asked to protrude and retract tongue) |
Figure 10-3: Brain stem and the cranial nerves of the human
brain
Medicine & Pathology:
-
Make yourself familiar with
the meaning of the following conditions, diseases and disorders connected to
the functions of the tissues of the central nervous system (CNS):
Key term
Neurology scientific study of
nerve tissue & brain function
Neurogenesis
The biological process through which new neurons
are created; very limited in the adult human brain
Neuralgia
severe pain that occurs along a nerve
with unknown cause;
may occur as repeated stabs of pain in the teeth, sinuses, eyes, tongue
face, or throat;
occurs most frequently in two cranial nerves:
1. Trigeminal nerve (= CN V)
- pain in eyes, face, sinuses, and teeth
2. Glossopharyngeal nerve (= CN IX)
- pain in the back of tongue and throat
Neuritis
is a painful inflammation of a nerve
usually caused by disease or
injury;
infection by bacteria (tuberculosis, syphilis), viruses (Herpes zoster),
bad diet habits, vitamin deficiency and certain diseases (diabetes) can
cause neuritis;
if a neuritis remains untreated and continues for a long period, the
affected nerve(s) can become damaged beyond repair;
Primary Amebic Meningo-
human disease caused by the
waterborne protozoan Naegleria fowleri;
encephalitis (PAM)
it is characterized by an infection of the meninges and other parts of the
central nervous system; the disease usually occurs in children or young
adults after swimming in lakes or pools, bathing in natural hot springs, or
after water skiing in waters carrying the pathogenic microbe;
after nasal infection the protozoan reaches the brain where it initiates the
-
often fatal - inflammatory reaction;
Electroencephalogram (EEG) Technical
recording of the nerve signals of the
brain
Positron emission tomography
Very
sensitive medical technology that uses
radioactive
(PET)
tracers to visualize brain function; brain scans of measured
subjects' reveal the overall
brain activity while they perform
certain tasks, e.g. working memory, or during exposure to
certain
drugs, such as cocaine or amphetamine (see
Figure below);
Magnetic Resonance
sensitive method to monitor changes in brain functions and activities
Imaging (MRI)
Hydrocephalus
Painful brain abnormality characterized by elevated
CSF pressure
of the brain;
the pressure increase is due to defective or blocked
drainage of the CSF
from the ventricles into the sub-
arachnoid space and the resulting fluid build-up;
Ataxia muscle coordination disorder caused by traumatic, drug
or disease damage to
the
cerebellum;
people cannot touch the tip of their nose; changed
speech pattern due to uncoordinated speech muscles;
symptoms are staggering or abnormal walking movements
Spinocerebellar ataxia type I
neurodegenerative disease characterized by balance and
coordination
difficulties due to destruction of Purkinje-
fibers in the
cerebellum;
triggered by mutation of a gene which codes for a
cell-regulatory protein called
ataxin;
- ataxin regulates other cell proteins by attaching multiple
glutamine
residues
to these proteins (= Poly-glutamine regulation)
Prion diseases
rare and inexorably fatal human
neurodegenerative disorder;
includes variant Creutzfeld-Jacob disease
and Kuru-Kuru;
can appear sporadic, dominantly heritable and in
transmissible forms (e.g. BSE and Scrapie);
the cause of this type of neurological disease and the
pathogenic mechanism are still unknown;
but scientists have evidence that a highly infectious
and protease-resistant version (PrPSC)
of a brain-
specific protein called prion (PrP)
plays a pivotal
role in the outbreak of the disease;
Basal ganglia damage
brain damage resulting in uncontrollable shaking
(= tremor), muscular
rigidity, and
involuntary muscle movements
Aphasia
Disorder caused by
damage to the language areas
of the
cerebral cortex;
patients show inability to use or comprehend words;
Nonfluent aphasia: = damage to Broca's speech
area;
inability to form words
Fluent aphasia:
= damage to common integrative
or auditory association area
patients have faulty understanding
of spoken or written words
Paralysis
Damage or disease of motor neurons in the human
body; muscles
lack voluntary control
and
reflexes
two types of paralysis are described:
1. Flacid paralysis:
- damage of lower motor neurons
- decreased or lost muscle tone of muscles on
same side; limp muscles
2. Spastic paralysis:
- damage of upper motor neurons
- increased muscle tone and exaggerated reflexes
on opposite side of body
Autosomal recessive
human genetic disorder which represents the most
common
or X-linked syndromic
human cognitive dysfunction disorder;
mental retardation (MR)
affected
humans show a lower IQ (< IQ 70);
possible causes of MR are diverse and include factors such as:
environmental factors/teratogens
chromosomal anomalies
for autosomal recessive MR, scientists
associated a
4-basepair deletion (mutation) of the gene for the neuronal
serine protease neurotrypsin
with the disorder;
- neurotrypsin is involved in learning and memory
- located in pre-synaptic nerve endings
Hereditary neuralgic
an inherited
painful neurological disorder
which symptoms
amyotrophy (HNA) include chronic pain in the arms and
shoulders as well as
weakness, loss of sensation, and
muscle wasting;
it is caused by short-circuits of the brachial plexus,
a peripheral
nerve center formed by a network of
over 100,000 nerves that branches from the spinal
cord;
researchers believe that mutations in a gene named
SEPT9 is responsible for the symptoms of this disorder;
- SEPT9, which is located on chromosome #17,
codes
for septin, a protein that plays a crucial role
in the cytokinesis phase of
cell division;
mutated septin proteins are further implicated in
certain abnormal cell
divisions that lead to tumor
formation, including breast cancer
Multiple sclerosis (MS)
devastating,
progressive neurological
autoimmune disorder ;
characterized by brain destruction and formation
of brain
lesions due to
inflammatory processes;
brains of MS patients show demyelination of nerve
fibers and production of pro-inflammatory hormones
(cytokines); immune
cells, e.g. lymphocytes and
monocytes gain access to the CNS by breaking through
the blood brain barrier at the inflammatory sites
Parkinson's disease (PD)
progressive neurodegenerative disorder;
patients show uncontrollable shaking and movement
disruptions due to nerve
cell degeneration of neurons
that extend from the
substantia nigra, to the
putamen
and caudate
nucleus;
PD is characterized by the accumulation of protein
tangles and plaques (= Lewis bodies) in
the
damaged neurons;
the protein plaques contain fibrils of a mutated protein
called α-synuclein;
PD patient brain biopsies show cell death of dopaminergic
neurons located in the
substantia nigra of the brain;
patients show inability to control and stop certain movements
(dyskinesias)
and other motor dysfunctions;
patients are often treated with the dopamine precursor
molecule
L-Dopa
Shingles
acute infection of the PNS caused by the Herpes zoster virus
which homes into the posterior
root ganglion;
the reactivated virus interferes with the normal function
of sensory axons
to the skin;
pain, skin discoloration and characteristic line of
skin blisters
Schizophrenia
a
severe mental illness which is marked by hallucinations
and
delusions of the affected persons due to impaired
functions of dopaminergic areas in the
prefrontal
cortex;
it affects one percent of the human population and is treated
with
antipsychotic drug (e.g. Zyprexa) that block release of the
neurotransmitter
dopamine;
Chorea-Huntington's disease
neurodegenerative disease caused by the brain accumulation
of an abnormal protein called
huntingtin;
huntingtin protein has abnormally expanded poly-
glutamine sequences
Alzheimer's disease (AD)
progressive human neurodegenerative disorder affecting elderly;
characterized by
the deposition of protein-made plaques
(= amyloid
protein) and tangles
(=
tau protein) in the hippocampus,
amygdala;
and
neocortex;
there is a sporadic and a less prevalent inherited form
of AD known;
AD patients show a loss of cholinergic neurons;
the gradual build up amyloid plaques made up from abnormal
shaped
amyloid
β
peptide, seems to be responsible
for the
progressive cognitive impairment and memory
loss in AD
patients;
- amyloid-β
is generated by proteolytic cleavage of the
larger amyloid precursor protein (APP);
- amyloid-β
is a normal nerve cell secreted peptide
with currently unknown function;
- the proteases which cleave APP are
γ- and
β-secretase;
tau protein
observed in the AD typical tangles is a protein
involved in microtubule assembly and stabilization;
- missense mutations
of the tau gene reduce the ability of
tau to properly interact with microtubules;
- some mutations also promote tau aggregation into tangles-
forming filaments and its
hyperphosphorylation;
mutations in the gene for
apolipoprotein E (APOE)
is a risk factor linked to
the late-onset Alzheimer disease
form (=
LOAD), the most common type of AD, which
onset is above the
age of 65;
mutations in three genes which code for beta-amyloid
precursor protein
(APP),
presenilin 1, and
presenilin 2
cause the
autosomal dominant inherited (very rare)
form of
familial AD;
- APP gene is located on chromosome #21;
- mutations lead to increased amyloid-β
production;
"According to the amyloid cascade hypothesis,
an increase in amyloid-β
42 triggers all
cases of AD, the tau-tangles appear later ..."
major risk factors for AD are old age, environmental factors,
habits (alcoholism?);
currently, there
is no cure for AD; there are only 5 FDA-
approved drugs available
for management and delay of
this debilitating disease;
- all of them are cholinesterase inhibitors, such as:
- Aricept, Reminyl,
Exelon & Memantine
- they increase the level of acetylcholine
"In 2006, there were more
than 20 million reported AD cases worldwide ..."
MDMA & Ecstacy
MDMA stands for the chemical
methyl-enedioxymethamphetamine
which is
used to make the illegal drug Ecstasy;
MDMA is a derivative of the
more common drug
methamphetamine, a chemical that has been reported to
have destructive
effects on dopaminergic neurons of
primate brains;
some scientists believe that there is a connection between
"Met" overuse and
predisposition to Parkinson disease
development in later years
Fronto-Temporal
Dementia
a
human neurodegenerative disorder which is linked
(FTD)
with Parkinsonism-like symptoms; as with many other
neurodegenerative disease, a key characteristic of FTD
is the
accumulation of mis-folded proteins
in the cytoplasm
and nuclei of neurons of the CNS;
FTDs are clinically, genetically and pathologically very
heterogenous and are (after Alzheimer's disease) the
most common cause of dementia under the age of 65;
affected human individuals show progressive changes in
social, behavioral and/or language dysfunction;
more than 30% of all FTDs have a genetic background and
are associated with genetic defects on chromosome #17
(=
FTDP-17);
- especially pathological mutations of the
tau gene
product seem to play a role in the manifestation of
of FTDP-17
- the tau gene (located on Chromosome 17; therefore:
FTDP-17) codes for the
microtubule-associated
protein Tau;
affected neurons
of FTD patients show
(like in AD)
tau protein
aggregates as typical intraneuronal
deposits known as
"neurofibrillary tangles" (NFT)
α
- Mannosidosis
a rare, inherited human disorder that causes severe
mental retardation
and
leads to a short life expectancy; a type of lysosomal storage disorder
(such as Tay-Sachs
disease);
lysosomes of neurons of affected individuals carry a vaulty version of a
gene coding for the sugar degrading enzyme
alpha-mannosidase;
Lou-Gehrig's disease
or currently
an incurable and progressively paralyzing human
Amyotrophic Lateral
neurodegenerative disorder; ALS is
characterized by the
Sclerosis (ALS) death
of motor neurons in the spinal cord and brain stem;
affected neurons show signs of
oxidative stress and
apoptosis (= programmed cell death);
the cause(s) of ALS is/are unknown;
the most prominent known cause of the (rare) inherited
(= familial) form of ALS are dominant mutations in the
the
gene coding for the oxidative stress-protecting
enzyme
Cu/Zn superoxide dismutase (SOD);
several hypotheses have been put forward by scientists,
including mitochondrial dysfunction, protein aggregate formation,
excitotoxicity, axonal transport malfunction, SOD-mutant-
derived cell damage and and inflammation, to explain
the typical motor neuron degeneration observed in
ALS patients;
Over 5,600
people in the U.S. are diagnosed with amyotrophic lateral sclerosis (ALS) or
Lou Gehrig's disease each year.
About 30,000 Americans have the disease at any given time, and 10% of cases
are inherited
variant Creutzfeld-Jacob
infectious protein (= prion)-caused fatal degenerative disease affecting the human brain;
disease (vCJD)
a suspected critical event in pathogenesis of this disorder is the conversion of
the
normal form of a cellular prion protein (PrP) into an abnormal shaped,
protease-resistant form which forms fatal
nerve cell function corrupting
protein plaques
Gerstmann-Straussler-Sheinker
GSS is a fatal
familial prion disease that
causes movement disorders with
disease (GSS)
course of approximately 3 years;
the cause of GSS disease is unknown, but scientists believe that it is
caused
by mutations of the normally occurring cell proteins called prions.
Neurofibromatosis (NF)
Neurofibromatosis is an incurable
inherited human disorder, that affects
("Elephant's man disease")
the nervous system and the skin;
two types of NF are known:
1. NF-1 or "von Recklinghausen's
disease"
- NF1 is characterized
by the development of multiple benign tumors
in the nervous system (neurofibromas)
and flat, light brown spots on the skin;
- tumors arise from defective glial cells (Schwann cells) of the peripheral
nervous
system;
- affected humans have germline mutations in the
NF1 gene which codes for a
tumor
suppressor protein;
- most common form of NF (1/4000 births)
2. NF-2 or Bilateral Acoustic
Neurofibromatosis
- characterized by tumors of the brain, spinal cord and nerves that control
hearing;
- tumors may lead to deafness, chronic head ache, vision problems and
partial
paralysis; often fatal;
- there seems to be a genetic background (children from NF patients have a
50%
of inheriting NF); NF patients often show mutations in a gene coding for the
protein neurofibromin;
- it is the less common type of NF (1/50,000 births)
Kuru-kuru A severe and fatal
human neurodegenerative infectious disease (often called
the "laughing disease"),
which outbreak is connected with forms of tribal
cannibalism;
a prion protein
disorder, which in the 1960s (remember: prions are infectious
proteins) killed almost 10% of population
of the "Fore", a small
New Guinea tribe which until then had a tradition of eating parts of their
dead;
Asperger syndrome (AS)
a
mild version of autism observed in humans;
affected humans show high problem-solving intelligence
(e.g. in mathematics,
physics), but show signs of
mild to severe
deficiencies in "social" intelligence;
AS patients are often unable to sense the
emotions of others;
the scientists Isaac Newton and Albert Einstein are suspected to have
been affected by AS;
Autism
a
severe neuropsychiatric disorder;
it is characterized
by impaired social interaction and communication and by
repetitive and stereotyped interests and behavioral patterns;
it includes mental retardation in up to 70% and seizures in 20-
25% of all cases;
autism shows a broad spectrum of clinical manifestations
and a heterogenous genetic background; it is highly
heritable
but the gene(s) responsible for this disorder is/are
not known
to date;
- the great majority of identified autism genes show high
high rates of mutations and chromosomal anomalies,
including submicroscopic deletions and duplications;
Addiction
Brain-controlled craving for a certain drug or repetitive
behavioral pattern
(see section further below)
Rett syndrome (RS)
a childhood neuro-developmental disorder which
affects
primarily females;
RS is characterized by decreased head growth, progressive
autism and mental retardation;
80% of all patients show mutations in the gene coding
for the methyl-CpG (DNA)-binding protein MECP2
which seems to play a role in gene activity
regulation;
Tourette's Syndrome (TS)
a (most likely) polygenic inherited developmental
neuropsychiatric
disorder;
it is characterized by the combination of persistent
vocal and
motor tics; some TS patients also suffer from
obsessive-
compulsive disorder (OCD), show attention
deficits, forms of
depression and other
"strange habit" disorders;
in the U.S., TS affects as many as 1 in 100 individuals;
scientists observed frameshift mutations and inversions
in several genes, e.g. for SLITRK,
located on different chromosomes;
Human temporal lobe
a severe and life-threatening
neurological
disorder;
epilepsy characterized by synchronous discharges
of neurons
located in certain temporal lobe areas, i.e.
the subiculum
(an output region of the hippocampus projecting to the
temporal cortex), and by sclerosis of CA regions of the
hippocampus;
Anosognosia partial or complete loss of self-awareness and emotional
control due to frontal lobe damage;
Seasonal affective disorder (SAD)
a usually winter time-appearing
depression-like human disorder
which affects
more than 1-10% of people living north or south of the northern or southern
30th parallel;
clinical symptoms include: diminished pleasure in life, sadness, gloomy
mood,
difficulty concentrating, extended sleep demand & lower sex drive;
therapy is the common
"light therapy" where people expose themselves once a
day to sunlight or the light emitted from "light boxes"
likely triggered by a lower "light-dependent" activation of the Supra-
chiasmatic Nucleus (SCN) of the hypothalamus
Wernicke's aphasia
Neurological disorder caused by damage, e.g. stroke or trauma, to the Wernicke's
Area;
affected persons are not able to comprehend and understand the meaning of
another person's spoken word
Fetal alcohol syndrome (FAS)
alcohol-induced damage of the fetal brain which manifests itself in impaired
fetal growth,
facial deformations and configurations, learning disabilities and other
neuro-
developmental anomalies
Familial advanced sleep phase
hereditary sleep disorder of humans; affected human individuals are typical
"morning
syndrome (FASPS)
larks" and show shortened sleep periods
caused by mutations of the gene for the enzyme casein kinase
Transcranial magnetic stimulation
Invented non-invasive device (Sony) which uses a magnetic field technique to
stimulate
(TMS) sensory association areas of the brain to trigger sensory experiences and
sensations
Brain, Addiction & Genes
The brain has a lot to do with human addictions for legal or illegal drugs,
such as caffeine, nicotine, morphine, cocaine,
amphetamines, heroine;
In recent years scientists unraveled the connection between the role of
certain molecules and genes in different
forms of addictions. For example,
the brain of alcoholics and cocaine addicted individuals show high
concentrations of the neurotransmitter glutamate and a biological clock gene
named Per2 seems to play a role in the
alcoholism in humans.
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