THE CENTRAL NERVOUS
SYSTEM
THE BRAIN
EMBRYONIC DEVELOPMENT
• At three weeks’ gestation, the ectoderm
forms the neural plate, which invaginates,
forming the neural groove, flanked on either side
by neural folds
• By the fourth week of pregnancy, the neural
groove fuses, giving rise to the neural tube,
which rapidly differentiates into the CNS
• The neural tube develops constrictions that
divide the three primary brain vesicles:
– Prosencephalon (forebrain)
– Mesencephalon (midbrain)
– Rhombencephalon (hindbrain)
NEURAL TUBE
BRAIN DEVELOPMENT
Effect of Space Restriction
on
Brain Development
REGIONS AND ORGANIZATION
• The basic pattern of the CNS consists
of a central cavity surrounded by a gray
matter core, external to which is white
matter
• In the brain, the cerebrum and
cerebellum have an outer gray matter
layer, which is reduced to scattered gray
matter nuclei in the spinal cord
ARRANGEMENT
OF
GRAY and WHITE MATTER
VENTRICLES
• The ventricles of the brain are continuous
with one another, and with the central canal
of the spinal cord.
– They are lined with ependymal cells, and are filled
with cerebrospinal fluid
• The paired lateral ventricles lie deep within each cerebral
hemisphere, and are separated by the septum pellucidum
• The third ventricle lies within the diencephalon, and
communities with the lateral ventricles via two interventricular
foramina
• The fourth ventricle lies in the hindbrain and communicates
with the third ventricle via the cerebral aqueduct
BRAIN VENTRICLES
CEREBRAL HEMISPHERES
• The cerebral hemispheres form the superior part of the brain,
and are characterized by ridges and grooves (convolutions)
called gyri (elevated ridges of tissue) and sulci (hollow
grooves)
– Deeper grooves called Fissures separate large regions of the brain
• The cerebral hemispheres are separated along the midline by
the longitudinal fissure, and are separated from the cerebellum
along the transverse cerebral fissure
• The five lobes of the brain separated by specific sulci (all but the
last named for the cranial bone that overlie them) are: frontal,
parietal, temporal, occipital, and insula ( buried deep within the
lateral sulcus: equilibrium)
• The cerebral cortex is the location of the conscious mind,
allowing us to communicate, remember, and understand
CEREBRAL HEMISPHERES
• The two hemispheres are largely
symmetrical in structure but not
entirely equal in function
• There is a lateralization (specialization)
of cortical function
– NO function area of the cortex acts alone
and conscious behavior involves the entire
cortex in one way or another
LOBE FISSURES
BRAIN CONVOLUTIONS
NEUROIMAGING
NEUROIMAGING
• Shows that specific
motor and sensory
functions are localized
in discrete cortical
areas called DOMAINS
• Many higher mental
functions, such as
memory and language,
appear to have
overlapping domains
and are spread over very
large areas of the cortex
NEUROIMAGING
• PET scans:
– Positron emission
tomography
– Positron: a particle
having the same mass
as a negative electron
but possessing a
positive charge
– Shows maximal
metabolic activity
NEUROIMAGING
• MRI scans:
– Magnetic resonance
imaging
– Reveals blood flow
CEREBRAL HEMISPHERES
• The cerebral cortex has several motor areas
located in the frontal lobes, which control
voluntary movement:
– The primary motor cortex allows conscious control
of skilled voluntary movement of skeletal muscles
– The premotor cortex is the region controlling learned
motor skills
– Broca’s area is a motor speech area that controls
muscles involved in speech production
– The frontal eye field controls eye movement
CEREBRAL CORTEX
CEREBRAL CORTEX
• Primary motor area:
conscious control of
skilled voluntary
movement of skeletal
muscles
• Premotor cortex: region
controlling learned motor
behavior (typing, playing
musical instrument)
• Frontal eye field: eye
movement
CEREBRAL CORTEX
•
Prefrontal cortex:
–
–
–
–
–
–
–
–
Most complicated cortical region
Involved with intellect, complex
learning abilities (cognition), recall,
and personality
Production of abstract ideas,
judgment, reasoning, persistence, longterm planning, concern for others, and
conscience
In children matures slowly and is
heavily dependent on positive and
negative feedback
Closely linked to the emotional part
of the brain (limbic system)
Plays a role intuitive judgments and
mood
Tremendous elaboration of this region
sets humans apart from other animals
Language comprehension and word
analysis
CEREBRAL CORTEX
• Somatic sensation: receives
information from the general
(somatic) sensory receptors in
the skin and skeletal muscle
and integrates the different
sensory inputs (temperature,
pressure, etc.)
• Gustatory cortex: taste
• General interpretation area:
– Found in one hemisphere
only (usually left)
– Receives input from all
incoming signals and focuses
into a single thought or
understanding of the
situation
CEREBRAL CORTEX
• Visual association
area: recognizes a
flower or a person’s
face
• Auditory
association area:
memories of sounds
CEREBRAL CORTEX
LANGUAGE AREAS:LEFT HEMISPHERE
•
Broca’s area:
–
–
–
•
Wernicke’s area:
–
–
–
•
•
Motor speech area that controls muscles
(tongue, lips, throat) involved in speech
production
Considered to be present in only one
hemisphere (usually the left)
Becomes active as we prepare to speak and
even when we think about (plan) many
voluntary motor activities other than speech
Language comprehension and articulation
Believed to be the area responsible for
understanding written and spoken language
Involved in sounding out unfamiliar words
Prefrontal cortex: language comprehension
and word analysis
Lateral and Ventral parts of temporal
lobe: coordinate auditory and visual aspects
of language when reading
CORRESPONDING AREA
RIGHT HEMISPHERE
• Non-language dominance
• Involved in body language and non-verbal
emotional (affective) components of
language rather than speech mechanics
• Allows the lift and tone of our voice and our
gestures to express our emotions when we
speak
• Permits us to comprehend the emotional content
of what we hear ( a soft response to your
question conveys quite a different meaning than
a sharp reply)
LATERALIZATION
• We use both cerebral hemispheres for
almost every activity, and the
hemispheres appear nearly identical
– BUT, there is division of labor, and each
hemisphere has unique abilities not shared by
its partner (LATERALIZATION)
• Although one cerebral hemisphere or the other
“dominates” each task, the term cerebral
dominance designates the hemisphere that is
dominant for language
LATERALIZATION
• Right Hemisphere:
– 10% of people
– Non-language dominant
– Visual-spatial skills, intuition, emotion, artistic
and musical skills, poetic, creative
– Most left-handed
– More often males
LATERALIZATION
• Left Hemisphere:
– 90% of people
– Greater control over language abilities, math
and logic
– Most right handed
LATERALIZATION
• BILATERAL:
– Ambidextrous
– Could be cerebral confusion: Is it your turn or
mine?
– Learning disabilities (dyslexia, etc.)
CEREBRAL CORTEX
CEREBRAL CORTEX
CEREBRAL HEMISPHERES
• There are several sensory areas of the cerebral cortex that
occur in the parietal, temporal, and occipital lobes
– The primary somatosensory cortex allows spatial discrimination
and the ability to detect the location of stimulation
– The somatosensory association cortex integrates sensory
information and produces an understanding of the stimulus being
felt
– The primary visual cortex and visual association area allow
reception and interpretation of visual stimuli
– The primary auditory cortex and auditory association area allow
detection of the properties and contextual recognition of sound
– The olfactory cortex allows detection of odors
– The gustatory cortex allows perception of taste stimuli
– The vestibular cortex is responsible for conscious awareness of
balance
Motor and Sensory Areas
of the
Cerebral Cortex
CEREBRAL CORTEX
• Do not confuse the sensory and motor
areas of the cortex with sensory and motor
neurons: All neurons in the cortex are
interneurons
Motor and Sensory Areas
of the
Cerebral Cortex
• Red: Primary (somatic)
motor cortex
– Located in the precentral
gyrus of the frontal lobe of
each hemisphere
• Central sulcus: groove
between Red/Blue
• Blue: Primary
somatosensory cortex
– Located on the postcentral
gyrus of the parietal lobe,
just posterior to the
premotor cortex
Motor and Sensory Areas
of the
Cerebral Cortex
• The body is typically
represented upside
down: the head at the
inferolateral part of
the precentral gyrus,
and the toes at the
superomedial end
Motor and Sensory Areas
of the
Cerebral Cortex
• PRIMARY MOTOR CORTEX
– The motor innervation of the
body is contralateral
(opposite)
– The left primary motor gyrus
controls muscles on the
right side of the body, and
vice versa
– Misleading: a given muscle is
controlled by multiple spots on
the cortex and that individual
cortical motor neurons actually
send impulses to more than
one muscle
• In other words: individual
motor neurons control
muscles that work together in
a synergistic way (so that one
does not over react)
Motor and Sensory Areas
of the
Cerebral Cortex
• PRIMARY
SOMATOSENSORY
CORTEX:
– Receives information from
the general (somatic)
sensory receptors located
in the skin and from
proprioceptors in skeletal
muscles (locomotion,
posture, and tone)
– Right hemisphere receives
input from the left side of
the body and vice versa
FIBER TRACTS
FIBER TRACTS
CEREBRAL HEMISPHERES
• Several association areas are not connected to any
sensory cortices
– The prefrontal cortex is involved with intellect, cognition, recall,
and personality, and is closely linked to the limbic system
– The language areas involved in comprehension and articulation
include Wernicke’s area, Broca’s area, the lateral prefrontal
cortex, and the lateral and ventral parts of the temporal lobe
– The general interpretation area receives input from all sensory
areas, integrating signals into a single thought
– The visceral association area is involved in conscious visceral
sensation
CEREBRAL CORTEX
CEREBRAL CORTEX
CEREBRAL HEMISPHERES
• There is lateralization of cortical functioning, in
which each cerebral hemisphere has unique abilities
not shared by the other half:
– One hemisphere (often the left) dominates language
abilities, math, and logic, and the other hemisphere (often
the right) dominates visual-spatial skills, intuition, emotion,
and artistic and musical skills
• Cerebral white matter is responsible for communication
between cerebral areas and the cerebral cortex and
lower CNS centers
• Basal nuclei consist of a group of subcortical nuclei,
which play a role in motor control and regulating
attention and cognition
BASAL NUCLEI
BASAL NUCLEI
•
•
•
•
The precise role of the basal
nuclei has been elusive because
of their inaccessible location and
because their functions overlap to
some extent with those of the
cerebellum
Role in motor control is complex
Plays a role in regulating
attention and in cognition
(reasoning/thinking)
Important in starting, stopping,
and monitoring movements
executed by the cortex
– Inhibit unnecessary movements
•
Disorders result in either too
much or too little movement as
exemplified by Huntington’s and
Parkinson’s disease
BASAL NUCLEI
MIDSAGITTAL REGION
(Diencephalon and Brain Stem)
DIENCEPHALON
• The diencephalon is a set of gray matter
areas, and consist of the thalamus,
hypothalamus, and epithalamus
– The thalamus plays a key role in mediating
sensation, motor activities, cortical arousal, learning,
and memory
– The hypothalamus is the control center of the body,
regulating ANS activity such as emotional response,
body temperature, food intake, sleep-wake cycles,
and endocrine function
– The epithalamus includes the pineal gland, which
secretes melatonin and regulates the sleep-wake
cycle
DIENCEPHALON
VENTRAL BRAIN
BRAIN STEM
• The brain stem, consisting of the midbrain,
pons, and medulla oblongata, produces rigidly
programmed, automatic behaviors necessary for
survival
– The midbrain is comprised of the cerebral peduncles,
corpora quadrigemina, and substantia nigra
– The pons contains fiber tracts that complete
conduction pathways between the brain and spinal
cord
– The medulla oblongata is the location of several
visceral motor nuclei controlling vital functions such
as cardiac and respiratory rate
BRAIN STEM
BRAIN STEM
•
•
Just above the medulla-spinal
cord junction, most of the fibers
cross over to the opposite side
before continuing their descent
into the spinal cord or ascent
into the brain
This crossover point is called
the Decussation of the
Pyramids (longitudinal ridges of
the medulla)
– Formed by the large pyramidal
tracts descending from the motor
cortex
•
Consequence of this crossover
is that each cerebral
hemisphere chiefly controls the
voluntary movements of
muscles on the opposite
(contralateral) side of the body
BRAIN STEM
BRAIN STEM
BRAIN STEM NUCLEI
BRAIN STEM NUCLEI
CEREBELLUM
• The cerebellum processes inputs from several structures and
coordinates skeletal muscle contraction to produce smooth
movement
– There are two cerebellar hemispheres consisting of three lobes
each;
• Anterior and posterior lobes coordinate body movements and the
flocculonodular lobes adjust posture to maintain balance
– Three paired fiber tracts, the cerebellar peduncles, communicate
between the cerebellum and the brain stem
• Cerebellar processing follows a functional scheme in which the
frontal cortex communicates the intent to initiate voluntary
movement to the cerebellum, the cerebellum collects input
concerning balance and tension in muscles and ligaments, and the
best way to coordinate muscle activity is relayed back to the
cerebral cortex
CEREBELLUM
CEREBELLUM
FUNCTIONAL BRAIN SYSTEMS
• Functional brain systems consist of neurons
that are distributes throughout the brain but
work together:
– The limbic system is involved with emotions, and is
extensively connected throughout the brain, allowing
it to integrate and respond to a wide variety of
environmental stimuli
– The reticular formation extends through the brain
stem, keeping the cortex alert via the reticular
activating system, and dampening familiar, repetitive,
or weak sensory inputs
LIMBIC SYSTEM
LIMBIC SYSTEM
•
Limbic (ring) system (shown in
orange)
–
–
–
–
–
Group of structures located on the
medial aspect of each cerebral
hemisphere and diencephalon
Amygdala: recognizes angry or fearful
facial expressions, assesses danger,
and elicits the fear response
Cingulate gyrus: plays a role in
expressing our emotions through
gestures and resolving mental conflicts
when we are frustrated
Interacts with the hypothalamus: as a
result people with emotional stress may
have visceral problems (high blood
pressure, heartburn) referred to as
psychosomatic illnesses
Interacts with the prefrontal lobes:
intimate relationship between our
feelings and our thoughts
•
Explains why emotions sometimes
override logic and, conversely, why
reason can stop us from expressing
our emotions in inappropriate
situations
RETICULAR FORMATION
RETICULAR FORMATION
• Extends through the
central core of the
medulla oblongata,
pons, and midbrain
• Filters the flow of
sensory impulses so
there is no overload
– Drug LSD interferes
creating sensory overload
– Depressed by alcohol,
sleep-inducing drugs, and
tranquilizers
HIGHER MENTAL FUNCTIONS
BRAIN WAVE PATTERNS
• Normal brain functions results from continuous
electrical activity of neurons, and can be recorded
with an electroencephalogram, or EEG
• Electrodes measure electrical potential differences
between cortical areas
• Patterns of electrical activity are called brain waves, and
fall into four types: alpha, beta, theta, and delta waves
• Unique as fingerprints
• Used for diagnosis: brain: tumors, lesions, infections,
infarction (area of dead tissue), abscesses
• Clinical dead: flat EEG
BRAIN WAVES
BRAIN WAVES
• Alpha:
– Low-amplitude, slow,
synchronous waves
– Calm, relaxed state of
wakefulness
• Beta:
– Rhythmic but more
irregular than alpha
– Higher frequency than
alpha
– Awake and mentally alert
– concentration
BRAIN WAVES
• Theta:
– Irregular
– Common in children
– Abnormal in adults who are
awake
• Delta:
– High amplitude with low
frequency
– Sleep
– Anesthesia
– Awake adults: brain
damage
CONSCIOUSNESS
• Consciousness encompasses conscious
perception of sensations, voluntary initiation
and control of movement, and capabilities
associated with higher mental processing
(memory, logic, judgment, perseverance)
• Defined on a continuum that grades levels of
behavior in response to stimuli
– Alert, drowsy, lethargy, stupor, coma
• Still a mystery
SLEEP
AND
SLEEP-AWAKE CYCLES
• Sleep is a state of partial unconsciousness from which a
person can be aroused, and has two major types that alternate
through the sleep cycle
– Non-rapid eye movement (NREM) sleep has four stages
• Most nightmares occur during stage 3/4
– Rapid eye movement (REM) sleep is when most dreaming occurs
• Sleep patterns change throughout life, and are regulated by the
hypothalamus
• NREM sleep is considered to be restorative, and REM sleep allows
the brain to analyze events or eliminate meaningless information
• Hypothalamus is responsible for the timing of the sleep cycle
• SIDS: sudden infant death syndrome
• A typical nights sleep alternates between NREM and REM with
REM time increasing during the night
– Longest dreaming in the wee hours of the morning
HOMEOSTATIC IMBALANCES OF SLEEP
• Narcolepsy: lapse abruptly into sleep from the awake
state
• Insomnia: chronic inability to obtain the amount or
quality of sleep
• Sleep apnea: temporary cessation of breathing during
sleep
– Various causes:
• Elderly: stimulating effects of carbon dioxide buildup on breathing
declines with age
• Upper respiratory blockage: swallow glands
• Alcohol
• High blood pressure
• Obesity
• Nasal congestion
MEMORY
• Memory is the storage and retrieval of information
– Short-term memory (STM), or working memory, allows the
memorization of a few units of information for a short period of
time
• Capacity limited to 7 or 8 chunks of information
– Long-term memory allows the memorization of potentially
limitless amounts of information for very long periods
• Limitless capacity
– Transfer of information from short-term to long-term memory can
be affected by a high emotional state, repetition, association of
new information with old, or the automatic formation of memory
while concentrating on something else
MEMORY PROCESS
MEMORY PROCESS
•
Skill memory is less conscious
usually involving motor skills and
is often stored without details of
the learning cortex
– reinforced through performance
(ride a bike, play music
instrument, tie your shoe)
•
Learning causes changes in
neuronal RNA, dendritic
branching, deposition of unique
proteins at Long-term memory
(LTM) synapses, increase of
presynaptic terminals, increase of
neurotransmitter, and
development of new neurons in
the hippocampus
MEMORY CIRCUITS
BRAIN STRUCTURES INVOLVED
IN MEMORY
• Knowledge of memory
comes mainly from two
sources:
– Experiments with macaque
monkeys
– Amnesia in humans
• Specific pieces of memory
are stored in the regions of
input (e.g. visual (occipital) /
music (temporal)
– Memory of a loved one (scent
of their perfume/cologne,
softness of their skin)
• Found in bits and pieces
scattered all over your cortex
BRAIN STRUCTURES INVOLVED
IN MEMORY
•
Fact memory (names, faces,
words, dates) entails learning
explicit information, is often stored
with the learning context, and is
related to our conscious thoughts
and our ability to manipulate
symbols and language
– Hippocampus and amygdala (both
part of the limbic system)
– Diencephalon (thalamus and
hypothalamus)
– Ventromedial prefrontal cortex
(cortical region tucked beneath
the front of the brain)
– Basal forebrain (cluster of Achsecreting neurons anterior to the
hypothalamus)
BRAIN STRUCTURES INVOLVED
IN MEMORY
•
•
•
•
Basal forebrain closes the
memory loop by sending
impulses back to the sensory
cortical areas initially forming
the perception
Feedback presumably causes
changes that transform the new
perception into a more durable
memory
Hippocampus: oversees the
circuitry for learning and
remembering spatial relationships
Amygdala: responsible for
associating memories formed
through different senses and
linking them to emotional states
generated in the hypothalamus
BRAIN HOMEOSTATIC
IMBALANCE
• Anmesia: loss of memory
• Calcium appears to promote activation of
several enzymes in the postsynaptic cells,
including proteases and protein kinases causing
NMDA (n-methyl-D-aspartate) receptors (named
after the chemical used to detect them) changes
– Increases their sensitivity to glutamate
– Understanding is still unclear
• The “mind” within the brain is always just a
bit beyond our grasp
PROTECTION OF THE BRAIN
MENINGES
• Meninges are three connective tissue
membranes that cover and protect the CNS,
protect blood vessels and enclose venous
sinuses, contain cerebrospinal fluid, and
partition the brain
– The dura mater is the most durable, outermost
covering that extends inward in certain areas to limit
movement of the brain within the cranium
– The arachnoid mater is the middle meninx that forms
a loose brain covering
– The pia mater is the innermost layer that clings tightly
to the brain
MENINGES
MENINGES
• The dura mater is the
most durable,
outermost covering that
extends inward in
certain areas to limit
movement of the brain
within the cranium
• The arachnoid mater is
the middle meninx that
forms a loose brain
covering
• The pia mater is the
innermost layer that
clings tightly to the brain
MENINGES
DURA MATER
HOMEOSTATIC IMBALANCE OF
MENINGES
• Meningitis: inflammation of the meninges
– E.g: bacteria/virus
• Encephalitis: inflammation due to
bacteria or virus that spread into the CNS
CEREBROSPINAL FLUID
• Cerebrospinal (CSF) is the fluid found within the
ventricles of the brain and surrounding the brain
and spinal cord
• CSF gives buoyancy to the brain, protects the brain
and spinal cord from impact damage, and is a
delivery medium for nutrients and chemical signals
• Similar in composition to blood plasma from which it
arises. However it contains:
– less protein
– Ion concentration is different
• CSF contains more sodium, chloride, and hydrogen ions
• CSF contains fewer calcium and potassium ions
CEREBROSPINAL FLUID
•
Formation:
– In the choroid plexuses that hang
from the roof of each ventricle
– Capillaries of the choroid plexuses
are fairly permeable, and tissue
fluid filters continuously from the
bloodstream
– Ependymal cells modify the filtrate
by actively transporting only
certain ions across their
membranes into the CSF pool
setting up ionic gradients that
cause water to diffuse into the
ventricles
– 150 ml replaced every 8 hours
• 500 ml formed daily
•
Circulates throughout the brain
and spinal cord
– Returns to the blood in the dural
sinuses via the arachnoid villi
CEREBROSPINAL FLUID
CEREBROSPINAL FLUID
Formation, Location, and Circulation
• Choroid plexus forms CSF
• Porous blood capillaries
surrounded by ependymal
cells
• Filtrate enters the ventricles as
CSF
• Arachnoid villi protude
superiorly through the
overlying dura mater and into
the superior sagittal sinus
– CSF is absorbed into the
venous blood of the sinus by
the villi
HOMEOSTATIC IMBALANCE OF
CSF
• Hydrocephalus:
– Obstruction of circulation or
drainage of CSF accumulating
and exerting pressure on the
brain
– Referred to as water on the
brain
– In children, since the skull
bones are not completely
fused the head enlarges
– In adults, more likely to result
in brain damage because the
skull is rigid and hard
• Accumulating fluid
compresses the blood
vessels serving the brain and
crushes the soft nervous
tissue
BLOOD-BRAIN BARRIER
• The blood-brain barrier is a protective
mechanism that helps maintain a protective
environment for the brain
• Brain cannot be exposed to constant chemical
variations (constant flux) as other parts of the
body:
– If the brain was exposed to such chemical variations,
the neurons would fire uncontrollably, because some
hormones and amino acids serve as
neurotransmitters and certain ions (particularly
potassium) modify the threshold for neuronal firing
BLOOD-BRAIN BARRIER
• Selective:
– Essential nutrients move passively by
facilitative diffusion through the endothelial
cell membranes
– Bloodborne metabolic waste, such as urea
and creatinine, as well as proteins, certain
toxins, and most drugs, are prevented from
entering brain tissue
– Nonessential amino acids and potassium ions
are actively pumped from the brain
BLOOD-BRAIN BARRIER
• Ineffective against fats, fatty acids, oxygen and
carbon dioxide, and other fat-soluble molecules
that diffuse easily through all plasma
membranes
– Explains why bloodborne alcohol, nicotine, and
anesthetics can affect the brain
• Not completely uniform:
– Some areas are more permeable than others
• Capillaries of the choroid plexuses are very porous
• Vomiting center: monitors the blood for poisonous
substances
• Hypothalamus: regulates water balance, body temperature,
and many metabolic activities
HOMEOSTATIC IMBALANCES OF
THE BRAIN
•
•
•
Traumatic head injuries can lead to brain injuries of varying severity:
concussion (partial or complete loss of function), contusion (bruise), and
subdural or subarachnoid hemorrhage
Cerebrovascular accidents (CVAs), or strokes (sudden loss of
neurological function, caused by vascular injury), occur when blood supply
to the brain is blocked resulting in tissue death
Dementia
– Progressive, irreversible decline in mental function marked by memory
impairment
•
Alzheimer’s disease is a progressive degenerative disease that
ultimately leads to dementia
– Chronic, progressive, degeneration cognition disorder (memory loss, personality
changes, speech and language problems)
– 60% of all dementias
– Causes functional disabilities
– Multiple causes including genetics, viruses, aluminum toxins
– Acetylcholine is reduced 75%
– Changes in associative areas of the cerebral cortex and the hippocampus
HOMEOSTATIC IMBALANCES OF
THE BRAIN
• Parkinson’s Disease
– Chronic degenerative disease of the CNS (central nervous
system) that produces movement disorders and changes in
cognition and mood
– Inhibition of motor drive
– Results from deterioration of dopamine-secreting neurons of the
substantia nigra (brain stem nucleus that project to the corpus
striatum), and leads to a loss in coordination of movement and a
persistent tremor
– Basal nuclei become overactive causing the classic tremors of
the disease (pill rolling, shuffling gait, stiff facial expression, slow
movement)
– Underlying cause unknown (genetics, pesticides, aluminum,
viruses)
– Treatment by enhancing dopamine production
HOMEOSTATIC IMBALANCES OF
THE BRAIN
• Huntington’s disease of the CNS is a fatal
hereditary disorder that results from
deterioration of the basal nuclei and cerebral
cortex
–
–
–
–
–
Dominant trait
Involuntary writhing dancelike muscular movements
Worsening emotional and behavioral disturbances
Dementia
Opposite of Parkinson
• Overstimulation
– Treated by blocking dopamine production
HOMEOSTATIC IMBALANCES OF
THE BRAIN
• Nursing Homes:
– 50% stroke
– 50% alzheimer
• Dopamine:
– Neurotransmitter (brain messenger)
– Implicated in some forms of psychosis
(mental disorder in which there is severe loss
of contact with reality) and abnormal
movement disorders
THE SPINAL CORD
EMBRYONIC DEVELOPMENT
• The spinal cord develops from the
caudal portion of the neural tube
• Axons from the alar plate form white
matter, and expansion of both the alar and
ventral plates gives rise to the central gray
matter of the cord
• Neural crest cells form the dorsal root
ganglia, and send axons to the dorsal
aspect of the cord
EMBRYONIC SPINAL CORD
GROSS ANATOMY
AND
PROTECTION
• The spinal cord extends from the foramen magnum
of the skull to the level of the first or second lumbar
vertebrae
– It provides a two-way conduction pathway to and from the
brain and serves as a major reflex center
• Fibrous extensions of the pia mater anchor the
spinal cord to the vertebral column and coccyx,
preventing excessive movement of the cord
• The spinal cord has 31 pairs of spinal nerves along
its length that define the segments of the cord
• There are cervical and lumbar enlargements for the
nerves that serve the limbs, and a collection of nerve
roots (caudal equine) that travel through the vertebral
column to their intervertebral foramina
SPINAL CORD
SPINAL CORD
ANATOMY OF SPINAL CORD
LUMBAR TAP
CROSS-SECTIONAL ANATOMY
• Two grooves partially divide the spinal cord into two halves:
the anterior and posterior median fissures
• Two arms that extend posteriorly are dorsal horns, and the two
arms that extend anteriorly are ventral horns
• In the thoracic and superior lumbar regions, there are also paired
lateral horns that extend laterally between the dorsal and ventral
horns
• Afferent fibers form peripheral receptors form the dorsal roots
of the spinal cord
• The white matter of the spinal cord allows communication between
the cord and brain
• All major spinal tracts are part of paired multineuron pathways that
mostly cross from one side to the other, consist of a chain of two or
three neurons, and exhibit somatotropy
CROSS-SECTIONAL ANATOMY
• Two grooves partially divide
the spinal cord into two
halves: the anterior and
posterior median fissures
• Two arms that extend
posteriorly are dorsal
(posterior) horns, and the
two arms that extend
anteriorly are ventral
(anterior) horns
• In the thoracic and superior
lumbar regions, there are also
paired lateral horns that extend
laterally between the dorsal
and ventral horns
SPINAL CORD
Organization
of the
Gray/White Matter of the Spinal Cord
Organization
of the
Gray/White Matter of the Spinal Cord
• In the thoracic and superior
lumbar regions, there are
also paired lateral horns that
extend laterally between the
dorsal and ventral horns
– Autonomic (sympathetic
division) motor neurons that
serve visceral organs
– Axons leave cord via ventral
root along with somatic motor
neurons
• Since the ventral roots
contain both somatic and
autonomic efferents, they
serve both motor divisions
of the peripheral nervous
system
Organization
of the
Gray/White Matter of the Spinal Cord
• Afferent fibers form
peripheral receptors
form the dorsal roots of
the spinal cord
– The nerve cell bodies of
the associated neurons are
found in an enlarged region
of the dorsal root called the
dorsal root ganglion (spinal
ganglion)
– Axons enter the cord and
take several different
routes
• Some enter the white
matter
Organization
of the
Gray/White Matter of the Spinal Cord
•
•
•
Gray matter consist of a mixture
of neuron cell bodies. Their
unmyelinated processes, and
neuroglia
Multipolar neurons
Two posterior (dorsal) horns
– Composed entirely of interneurons
•
Two anterior (ventral) horns
– Some interneurons but mainly
nerve cell bodies of somatic
motor neurons
• Send axons out via the ventral
root to the effector organs/skeletal
muscles
•
Two lateral horns
– Motor neurons that serve
visceral organs
– Leave cord via ventral root
Organization
of the
Gray/White Matter of the Spinal Cord
• The white matter of the
spinal cord allows
communication between
different parts of the cord
and brain
– Composed of myelinated
and unmyelinated nerve
fibers
– Fibers run in three
directions
• Ascending: up to higher
centers (sensory inputs)
• Descending: down to the
cord from the brain or within
the cord to lower levels
(motor outputs)
• Transverse (commissural
fibers): across from one side
of the cord to the other
Organization
of the
Gray/White Matter of the Spinal Cord
•
•
•
•
•
•
In terms of processing sensory
and motor activity, the gray
matter can be divided into a
sensory half dorsally and a
motor half ventrally
SS: interneurons receiving input
from somatic sensory neurons
VS: interneurons receiving input
from visceral sensory neurons
VM: visceral motor (autonomic)
neurons
SM: somatic motor neurons
Note that the dorsal and ventral
roots are part of the PNS
Peripheral Nervous System, not of
the spinal cord
NEURAL INTEGRATION
•
Ascending pathways conduct sensory impulses upward through a
chain of three neurons successive neurons to various areas of the
brain (note that the 2nd and 3rd order neurons are interneurons)
– First-order neurons:
• Cell bodies reside in a ganglion (dorsal root or cranial)
• Conduct impulses from the cutaneous receptors of the skin and from proprioceptors to
the spinal cord or brain stem, where they synapse with 2nd order neurons
• Impulses from the facial area are transmitted by cranial nerves
• Spinal nerves conduct somatic sensory impulses from the rest of the body to the CNS
– Second-order neurons:
• Cell bodies reside in the dorsal horn of the spinal cord or in medullary nuclei
• Transmit impulses to the thalamus or to the cerebellum where they synapse
– Third-order neurons:
• Located in the thalamus and conduct impulses to the somatosensory cortex of the
cerebrum
• There are no 3rd order neurons in the cerebellum
ASCENDING/DESCENDING
TRACTS
ASCENDING TRACTS
•
Somatosensory information is
conveyed along three main
pathways on each side of the
spinal cord:
– Two of these pathways
(nonspecific and specific)
transmit impulses to the
sensory cortex:
• Nonspecific crosses over in spinal
cord
• Specific crosses over in the
medulla
– Collectively the inputs of these
sister tracts provide us with
discriminative touch and
conscious proprioception
– Third pathway (spinocerebellar)
tracts to the cerebellum:
• Hence does not contribute to
sensory perception
ASCENDING PATHWAYS
•
a:Somatosensory information is
conveyed along three main
pathways on each side of the
spinal cord
– Specific pathways for
discriminative touch and
conscious proprioception (limb
and joint position) to the cortex
– Specific ascending pathways
mediate precise input from a
single type of sensory receptor
– Interacts with the nonspecific
ascending pathway
• Allows information to be handled
in different ways
• Provides alternate pathways (if
one is damaged)
– Decussates in the medulla
ASCENDING PATHWAYS
• a: Spinocerebellar Tract
– Tract extends only to the
cerebellum
– Spinocerebellar tracts convey
information about muscle and
tendon stretch to the
cerebellum
– Conveys information from
proprioceptors (muscle and
tendon) to the cerebellum
– Coordinates skeletal muscle
activity
– Does not contribute to
conscious sensation since
somatosensory cortex is not
involved
– Does not decussate or cross
over twice
ASCENDING PATHWAY
Specific/Spinocerebellar
ASCENDING PATHWAY
• b:Nonspecific:
– Nonspecific ascending
pathways receive input
from many different types
of sensory receptors, and
make multiple synapses in
the brain
– Ascending pathway for
pain, temperature, and
crude touch
– Crossover of fibers occurs
in the spinal cord
– Involved in emotional
aspects of perception
(pleasure, arousal, and
pain)
ASCENDING PATHWAY
Nonspecific
ASCENDING PATHWAY
Specific/Spinocerebellar
• First order neurons:
– Cell bodies reside in a
ganglion (dorsal root or
cranial)
– Conduct impulses from
cutaneous receptors of the
skin and proprioceptors to
the spinal cord or brain
stem, where they synapse
with second-order neurons
• Impulses from the facial
area are transmitted by
cranial nerves to CNS
• Impulses (somatic
sensory) from the rest of
the body are transmitted
by spinal nerves to CNS
ASCENDING PATHWAY
Specific/Spinocerebellar
• Second order
neurons:
– Cell bodies reside in
the dorsal horn of
the spinal cord or in
medullary nuclei
– Transmit impulses to
the thalamus or to the
cerebellum where they
synapse
ASCENDING PATHWAY
Specific/Spinocerebellar
• Third order neurons:
– Located in the
thalamus
– Conduct impulses to
the somatosensory
cortex of the cerebrum
– There are NO thirdorder neurons in the
cerebellum
DESCENDING TRACTS
• DESCENDING PATHWAYS
– Deliver efferent impulses from the brain to the
spinal cord
– Divided into two groups: Direct and Indirect
DESCENDING TRACTS
• Direct pathways:
– Equivalent to the pyramidal tracts ( major motor
pathways concerned with voluntary movement/descend
from the frontal lobes of each cerebral hemisphere)
– Send impulses through the brain stem via large
pyramidal tracts (corticospinal)
– Axons descend without synapsing from the pyramidal
neurons to the spinal cord
– Synapse with interneurons or directly with anterior horn
motor neurons activating the skeletal muscles with which
they are associated
– Regulates fast and fine movements such as those
performed by the fingers (threading a needle)
DESCENDING TRACTS
• Indirect pathways:
– Brain stem motor nuclei (midbrain, pons, medulla) and all motor
pathways except the pyramidal pathway
– Extrapyramidal tracts (indirect or multineuronal pathways)
originate in different subcortical motor nuclei of brain stem
•
•
•
•
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal
– Complex and multisynaptic
– Regulates axial muscles that maintain balance and posture
– Controls muscles involved in coarse movements of the proximal
portions of the limbs
– Controls head, neck, and eye movements that act to follow
objects in the visual field
DESCENDING TRACTS
• Descending pathways
involve two neurons: upper
motor neurons and lower
motor neurons:
– The direct, or pyramidal,
system regulates fast, finely
controlled, or skilled
movements
– The indirect, or
extrapyramidal, system
regulates muscles that
maintain posture and balance,
control coarse limb
movements, and head, neck,
and eye movements involved
in tracking visual objects
DESCENDING TRACTS
• Direct pathway: Pyramidal
Tracts
– Pyramidal tracts carry motor
impulses to skeletal muscles
– These neurons send impulses
through the brain stem via the
large pyramidal (corticospinal)
tracts
– Called direct because their
axons descend without
synapsing from the pyramidal
neurons to the spinal cord
where they synapse with
interneurons
– Regulates fast and fine
(skilled) movements such as
doing needlework or writing
DESCENDING PATHWAY
DESCENDING PATHWAY
•
Indirect (Extrapyramidal) Rubrospinal
tract:
– Includes brain stem motor nuclei and
all motor pathways except the
pyramidal
– Pathways complex and multisynaptic
– Regulate:
• Axial muscles that maintain
balance and posture
• Muscles that control coarse limb
movements
• Head, neck, and eye movements
that follow objects in the visual
field
– Control flexor muscles
• Heavily dependent on reflex
activity
– Helps regulate tone of muscles on
opposite sides of the body
• Maintain balance by varying the
tone of postural muscles
DESCENDING PATHWAY
SPINAL CORD
TRAUMA AND DISORDERS
• Any localized damage to the spinal cord or
its roots leads to paralysis (loss of motor
function) or paresthesias (loss of sensory
function)
• Poliomyelitis results from destruction of anterior
horn neurons by the polio virus
• Amyotrophic lateral sclerosis (ALS), or Lou
Gehrig’s, disease is a neuromuscular condition
that involves progressive destruction of anterior
horn motor neurons and fibers of the pyramidal
SPINAL CORD TRAUMA AND
DISORDERS
•
•
•
•
•
Paralysis: loss of motor function
Paresthesias: loss of sensory function
Flaccid paralysis: damage to ventral root or anterior horn resulting in skeletal
muscle served
Spastic paralysis: damaged to the upper motor neurons of the primary motor cortex
Transection (cross cutting): of spinal cord results in total motor and sensory loss in
the body regions inferior to the site of the injury
–
–
•
•
Hemiplegia: paralysis of one side of the body, usually reflects brain, rather than
spinal cord, injury
Poliomyelitis: inflammation of spinal cord resulting from destruction of anterior
(ventral) horn motor neurons by the poliovirus
–
•
Between T1 and L1: lower limbs affected: paraplegia
Cervical region: all limbs affected: quadriplegia
In most cases virus enters the body in feces-contaminated water (swimming pool)
Amyotrophic Lateral Sclerosis (Lou Gehrig”s Disease): destruction of the anterior
(ventral) horn motor neurons and fibers of the pyramidal tract
–
–
Loss of ability to speak, swallow, and breathe
Linked to abnoemal gene
LUMBAR MYELOMENINGOCELE
spina bifida cyst
HOMEOSTATIC IMBALANCE OF
CNS
• Cerebral palsy
– Neuromuscular disability in which the voluntary muscles are poorly
controlled or paralyzed as a result of brain damage
– Could result from a difficult delivery due to a temporary lack of oxygen
– Smoking during pregnancy: reduces oxygen to the brain
• Hydrocephalus
• Anencephaly
– Cerebrum and part of the brain stem never develop
• Spina bifida
– Incomplete formation of the vertebral arches and typically involves the
lumbosacral region
– 70% of cases are caused by inadequate amounts of the B vitamin folate
in maternal diet
• Added as folate supplements in all bread, flour, and pasta products sold in
the U.S.
DIAGNOSTIC PROCEDURES
FOR
ASSESSING CNS DYSTUNCTION
• Pneumoencephalography is used to diagnose
hydrocephalus, and allows X-ray visualization of the
ventricles of the brain
• A cerebral angiogram is used to assess the condition of
cerebral arteries to the brain in individuals that have
suffered a stroke or TIA (transient ischemic attack: mini
strokes)
• CT scans and MRI scanning techniques allow
visualization of most tumors, intracranial lesions,
multiple sclerosis plaquwes, and areas of dead brain
tissue
• PET scan can localize brain lesions that generate
seizures and diagnose Alzheimer’s disease
DEVELOPMENTAL ASPECTS
OF
THE CENTRAL NERVOUS SYSTEM
• The brain and spinal cord grow and mature throughout
the prenatal period due to influence from several centers
• Gender-specific areas of the brain and spinal cord
develop depending on the presence or absence of
testosterone
• Lack of oxygen to the developing fetus may result in
cerebral palsy, a neuromuscular disability in which
voluntary muscles are poorly controlled or paralyzed as
a result of brain damage
• Age brings some cognitive decline but losses are not
significant until the seventh decade