Transcript THE CENTRAL NERVOUS SYSTEM

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
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Prefrontal cortex:
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Most complicated cortical region
Involved with intellect, complex
learning abilities (cognition), recall, and
personality
Production of abstract ideas, judgment,
reasoning, persistence, long-term
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 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
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Broca’s area:
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Wernicke’s area:
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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 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
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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
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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
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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
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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
RETICULAR FORMATION
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
• Patterns of electrical activity are called
brain waves, and fall into four types: alpha,
beta, theta, and delta waves
BRAIN WAVES
CONSCIOUSNESS
• Consciousness encompasses conscious
perception of sensations, voluntary
initiation and control of movement, and
capabilities associated with higher mental
processing
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
– 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
MEMORY
• Memory is the storage and retrieval of information
– Short-term memory, or working memory, allows the memorization of a
few units of information for a short period of time
– Long-term memory allows the memorization of potentially limitless
amounts of information for very long periods
– 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
– Fact memory entails learning explicit information, is often stored with the
learning context, and is related to the ability to manipulate symbols and
language
– Skill memory usually involves motor skills, is often stored without details
of the learning cortex, and is reinforced through performance
– Learning causes changes in neuronal RNA, dendritic branching,
deposition of unique proteins at LTM synapses, increase of presynaptic
terminals, increase of neurotransmitter, and development of new
neurons in the hippocampus
MEMORY PROCESS
MEMORY CIRCUITS
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
DURA MATER
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
CEREBROSPINAL FLUID
CEREBROSPINAL FLUID
HYDROCEPHALUS
The blood-brain barrier is a
protective mechanism that helps
maintain a protective
environment for the brain
HOMEOSTATIC IMBALANCES OF
THE BRAIN
• Traumatic head injuries can lead to brain injuries of varying severity:
concussion, contusion, and subdural or subarachnoid hemorrhage
• Cerebrovascular accidents (CVAs), or strokes, occur when blood
supply to the brain is blocked resulting in tissue death
• Alzheimer’s disease is a progressive degenerative disease that
ultimately leads to dementia
• Parkinson’s disease results from deterioration of dopaminesecreting neurons of the substantia nigra, and leads to a loss in
coordination of movement and a persistent tremor
• Huntington’s disease is a fatal hereditary disorder that results from
deterioration of the basal nuclei and cerebral cortex
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
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
SPINAL CORD
SPINAL CORD
Organization
of the
Gray Matter of the Spinal Cord
CROSS-SECTIONAL ANATOMY
• Ascending pathways conduct sensory impulses upward through a
chain of three neurons
– Nonspecific ascending pathways receive input from many different
types of sensory receptors, and make multiple synapses in the brain
– Specific ascending pathways mediate precise input from a single type of
sensory receptor
– Spinocerebellar tracts convey information about muscle and tendon
stretch to the cerebellum
• 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
ASCENDING/DESCENDING
TRACTS
ASCENDING PATHWAY
ASCENDING PATHWAY
DESCENDING PATHWAY
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
LUMBAR MYELOMENINGOCELE
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
• 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