THE CENTRAL NERVOUS SYSTEM

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THE CENTRAL NERVOUS SYSTEM
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THE BRAIN
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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)

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NEURAL TUBE
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BRAIN DEVELOPMENT
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Effect of Space Restriction on Brain Development
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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

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ARRANGEMENT OF GRAY and WHITE MATTER
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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

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BRAIN VENTRICLES
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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

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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

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LOBE FISSURES
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BRAIN CONVOLUTIONS
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NEUROIMAGING
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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

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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

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NEUROIMAGING

• MRI scans
• Magnetic resonance imaging
• Reveals blood flow

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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
• Brocas area is a motor speech area that controls
  muscles involved in speech production
• The frontal eye field controls eye movement

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CEREBRAL CORTEX
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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

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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, 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

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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

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CEREBRAL CORTEX

• Visual association area recognizes a flower or a
  persons face
• Auditory association area memories of sounds

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CEREBRAL CORTEXLANGUAGE AREASLEFT HEMISPHERE

• Brocas 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
• Wernickes area
• 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

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CORRESPONDING AREARIGHT 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)

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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

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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

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LATERALIZATION

• Left Hemisphere
• 90 of people
• Greater control over language abilities, math and
  logic
• Most right handed

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LATERALIZATION

• BILATERAL
• Ambidextrous
• Could be cerebral confusion Is it your turn or
  mine?
• Learning disabilities (dyslexia, etc.)

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CEREBRAL CORTEX
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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

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Motor and Sensory Areas of the Cerebral Cortex
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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

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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

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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

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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)

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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

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FIBER TRACTS
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FIBER TRACTS
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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 Wernickes area, Brocas
  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

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CEREBRAL CORTEX
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CEREBRAL CORTEX
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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

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BASAL NUCLEI
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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 Huntingtons and
  Parkinsons disease

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BASAL NUCLEI
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MIDSAGITTAL REGION(Diencephalon and Brain Stem)
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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

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DIENCEPHALON
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VENTRAL BRAIN
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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

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BRAIN STEM
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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

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BRAIN STEM
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BRAIN STEM
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BRAIN STEM NUCLEI
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BRAIN STEM NUCLEI
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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

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CEREBELLUM
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CEREBELLUM
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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

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LIMBIC SYSTEM
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RETICULAR FORMATION
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HIGHER MENTAL FUNCTIONS
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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

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BRAIN WAVES
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CONSCIOUSNESS

• Consciousness encompasses conscious perception of
  sensations, voluntary initiation and control of
  movement, and capabilities associated with higher
  mental processing

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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

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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

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MEMORY PROCESS
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MEMORY CIRCUITS
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PROTECTION OF THE BRAIN
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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

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MENINGES
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MENINGES
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DURA MATER
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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

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CEREBROSPINAL FLUID
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CEREBROSPINAL FLUID
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HYDROCEPHALUS
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The blood-brain barrier is a protective mechanism
that helps maintain a protective environment for
the brain
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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
• Alzheimers disease is a progressive degenerative
  disease that ultimately leads to dementia
• Parkinsons disease results from deterioration of
  dopamine-secreting neurons of the substantia
  nigra, and leads to a loss in coordination of
  movement and a persistent tremor
• Huntingtons disease is a fatal hereditary
  disorder that results from deterioration of the
  basal nuclei and cerebral cortex

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THE SPINAL CORD
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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

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EMBRYONIC SPINAL CORD
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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

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SPINAL CORD
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SPINAL CORD
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LUMBAR TAP
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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

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SPINAL CORD
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SPINAL CORD
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Organization of the Gray Matter of the Spinal
Cord
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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

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ASCENDING/DESCENDING TRACTS
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ASCENDING PATHWAY
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ASCENDING PATHWAY
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DESCENDING PATHWAY
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DESCENDING PATHWAY
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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
  Gehrigs, disease is a neuromuscular condition
  that involves progressive destruction of anterior
  horn motor neurons and fibers of the pyramidal

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LUMBAR MYELOMENINGOCELE
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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 Alzheimers disease

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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