Transcript Major Concepts of Anatomy and Physiology

Central Nervous
System (CNS)
Part 3: Integration & Control
Central Nervous System

Central Nervous System (CNS): The portion of
the nervous system made up of the brain and
spinal cord.
 Acts
as the Central Processing Unit (CPU) of the
human nervous system.
 Incoming data is processed and coordinated
 Outgoing data is developed and sent out to the rest of
the body

Four C’s of the CNS:
 Communicate
 Command
 Control
 Coordinate
The Brain

4 Major Parts of the Brain:
 Cerebrum:
The largest part of the brain, controls
complex activities, including complex motor control.
 Cerebellum: Controls muscle movements, regulates
posture & balance, and plays a role in cognition.
 Diencephalon: Relays sensory information to the
cerebrum & controls the Autonomic Nervous System
(ANS).
 Brain Stem: Relays motor impulses, is involved in
vital system control, & contributes to sensory organ
control.
Protecting The Brain
Skull: Provides physical protection from
traumatic injury.
 Blood-Brain Barrier: Prevents the
passage of harmful substances from the
blood stream into the brain.

 Created
by a tight junction between the
capillary cells & by astrocytes.
 Permeable to lipid-soluble substances (O2,
CO2, alcohol, anesthetics).
Protecting The Brain

Meninges: 3 layers of protective
coverings surrounding the brain & spinal
cord.
 Dura

Matter: Outermost layer
Subdural Space: Separates the dura & arachnoid
matter.
 Arachnoid

Matter: Middle layer
Subarachnoid space: Separate the arachnoid &
pia matter.
 Pia
Matter: Innermost layer
Protecting the Brain
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Cerebrospinal Fluid (CSF): Clear liquid contained
within the skull & spinal column to protect the CNS from
chemical and physical injury.
Contained within 4 ventricles:
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Lateral Ventricles: One on each side of the brain.
Third & Fourth Ventricles: Connected through the cerebral
aqueducts.
Choroid Plexuses: Networks of capillaries in the walls
of the ventricles where CSF is produced.
Arachnoid Villi: Location where CSF is reabsorbed and
dumped into the brain's sinus cavities for drainage.
Hydrocephalus: Marked by a failure to drain CFS,
resulting in increased intracranial pressure.
Brain Blood Flow
Blood flow to the brain requires 20% of the
body’s oxygen & glucose.
 4 minutes of oxygen deprivation is enough
to cause irreversible brain damage.

Embryonic Development

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Ectoderm: The tissue layer that develops into the neural
plate.
Neural Plate: Flat layer of nervous tissue that will then
develop into the neural tube.
Neural Tube: The neural plate rolls into the neural tube
that develops into the brain & spinal cord.

“Head” end develops into three primary areas/primary brain
vesicles:
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
Prosencephalon develops into the forebrain
Mesencephalon develops into the midbrain
Rhombencephalon develops into the hindbrain
These three primary brain vesicles will develop into secondary
vesicles that will in turn develop into all of the parts of the brain.
The Brain Stem

Brain Stem: The area of the brain which lies
between the spinal cord and the diencephalon.
 Composed
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of 3 regions:
Medulla Oblongata
Pons
Midbrain
Retuicular Formation: A network of grey &
white matter interspersed & extending
throughout the brainstem. Functions to maintain
muscle tone & arouse us from deep sleep!
The Brain Stem

Medulla Oblongata: Regulates vital body
functions and nonvital functions.
 Located
directly above the spinal cord.
 Vital functions: heartbeat and breathing.
 Nonvital functions: Reflexes, controlling
sneezing, coughing, hiccuping, sweating,
vomiting.
 Pyramids: Projections of white matter formed
by the motor tracts passing into the spinal
cord from the cerebrum. Most of these
decussate (cross) to the opposite side.
The Brain Stem

Pons: Relays impulses between the
medulla & midbrain.
 Contains
origins of the Cranial Nerves 5-8.
 Contains pneumotaxic & apneustic areas
which help to control breathing.
The Brain Stem

Midbrain (Mesencephalon): Relays….
 Motor
impulses from cerebral cortex to pons
 Sensory impulses from the spinal cord to the
thalamus
 Superior collicili coordinates eye movements
with incoming visual stimuli
 Inferior colliculi coordinates head and trunk
movements with auditory stimuli
 Contains the origins of Cranial Nerves 3 & 4
The Cerebellum
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Cerebellum: The 2nd largest part of the brain that
actually contains half of the CNS’s total neurons.
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Divides into…
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Considered part of the hindbrain
Coordinates skilled movement
May play a role in learning, cognition, & language processing.
Right Cerebellar Hemisphere
Left Cerebellar Hemisphere
Vermis: Connects the right & left cerebellar hemispheres
to the brainstem via 3 pairs of cerebellar peduncles.
Folia: Ridges lining the outer gray matter of the
cerebellum.

Flocculonodular Lobe: Maintains posture & balance
Diencephalon

Diencephalon: The part of the forebrain
extending from the brain stem to the cerebrum
 Plays
a crucial role in the vital systems of the human
body
 Primarily responsible for sensory relay & controlling
the autonomic nervous system (ANS)

Made up of 4 parts:
 Thalamus
 Hypothalamus
 Epithalamus
 Subthalamus
Thalamus
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Comprises 80% of the diencephalons
Considered the “Gateway to the Cerebral
Cortex”
Located in the very center of the brain.
Nearly all incoming sensory information passes
through the Thalamus.
 Primary
relay station for sensory data
 Responsible for crude perception of touch, pressure,
pain, & temperature, & helps regulate some
autonomic activities.
 Contributes to motor function as well.
Hypothalamus
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Located inferior to the thalamus
Major control center for the autonomic nervous
system & the endocrine system.
Regulates many basic body functions & is
crucial to maintaining homeostasis.
 Includes
food & water intake, temperature, circadian
rhythms, & emotional & behavioral patterns.
 Also produces hormones critical to homeostasis

Control center of the Autonomic Nervous System
 Regulates
the gastrointestinal tract, urinary tract, &
cardiovascular system
Epithalamus
Superior & posterior to the thalamus.
 Consists of the…

 Pineal
Gland: Endocrine gland that secretes
hormones (including melatonin)
 Habenular Nuclei: Involved in olfaction
(smell) and especially the emotional response
to odors.
Subthalamus
Located directly below the thalamus
 Controls body movement
 Contains nuclei that work together with the
basal ganglion cerebellum
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The Cerebrum
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Cerebrum: Largest part of the brain & the part we use
the most for cognition.
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Divided into 2 hemispheres:
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Responsible for all the higher brain functions
Gyri: Convolutions/folds that increase the surface area – the
result of gray matter forming more rapidly than white matter
during the embryonic stage.
Right Cerebral Hemisphere
Left Cerebral Hemisphere
Longitudinal Fissure: Divides the two hemispheres of
the cerebrum.
Corpus Collosum: Broad band of white matter
containing axons that connect the two halves of the brain
& allow for communications between the hemispheres.
The Cerebrum
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Each hemisphere is divided into 5
functional regions/lobes by…
 Fissures:
Deep grooves
 Sulci: Shallow grooves
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5 Lobes:
 Frontal
Lobe
 Parietal Lobe
 Occipital Lobe
 Temporal Lobe
 Insula
The Cerebrum
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Central Sulcus: Valley thatr runs from side to
side across both central hemispheres.
 This
is the area of separation between the motor and
sensory cortex.
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Postcentral Gyrus: Primary somatosensory
area located in the parietal lobe.
Precentral Gyrus: Primary motor area
contained in the frontal lobe.
 Contralateral:
The left hemisphere coordinates the
muscle movement of the right side of the body
beginning below the neck and vice versa.
The Cerebrum

Cerebral Cortex: Outer portion of the
brain comprised of gray matter.
 Gray
Matter: Contains mainly nerve cell
bodies and unmyelinated fibers.
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Cerebral cortex is made up of two kinds of
neurons:
 Stellate
Cells: Rceive sensory imput and
project it for short distances.
 Pyramidal Cells: Acts as the output neurons
of the cerebelum.
The Cerebrum
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The cerebellum contains white matter
underneath the cerebral cortex.
 White
Matter: Contains mainly myelinated axons and
appears to be white.
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Contains axons in 3 types of tracts:
 Association
Tracts: Conduct impulses between gyri
located in the same hemisphere.
 Commissural Tracts: Conduct nerve impulses from
gyri in one hemisphere to corresponding gyri in the
other hemisphere.
 Projection Tracts: Conduct nerve impulses from the
cerebrum to the lower portions of the CNS.
The Cerebrum

Basal Nuclei or Basal Ganglia: Masses
of gray matter buried deeply in the
cerebral hemisphere.
 This
is an exception to the rule that ganglia
are located outside the CNS!
 These form the areas that contribute to motor
control:
Globus Pallidus
 Corpus Seriatum

Putamen
 Caudate Nucleus

Cerebral Cortex Areas

Divided into 3 basic areas based on
function:
 Sensory
Areas: Receive & interpret sensory
impulses.
 Association Areas: Handle the more
complex integrative functions, e.g. emotion,
memory, intellegence, reasoning, judgement,
and personality traits.
 Motor Areas: Initiate movement.
Functional Areas of the Cerebral
Cortex
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Broca’s Area: Controls the planning and production of
speech. Localized in the left frontal lobe.
Wernicke’s Area: Interprets the meaning of speech by
recognizing spoken words and turning them into
thoughts & adding emotional content. Localized to the
temporal and parietal lobes.
Primary Visual Area #17: Recieves impulse messages
for vision.
Primary Auditory Areas #41 & #42: Interprets pitches,
rhythm, and the basic characteristics of sound.
Primary Gustatory Area #43: Receives impulses for
taste.
The Limbic System
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Limbic System: Composed of a ring of
structures that encircle the upper part of the
brainstem & the corpus collosum.
Two primary nuclei:
 Amygdala:
Important in the regulation of emotions.
 Hippocampus: Important in memory functions.
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Contains the olfactory bulbs.
Limbic system considered the “emotional brain”.
Hemispheric Lateralization
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The two hemispheres tend to be similar in
structure and function.
Each have specializes in certain functions.
Right Hemisphere: Musical and artistic ability,
space and pattern recognition, emotional
content of language, odor discrimination.
Left Hemisphere: Numeric & scientific
processes, spoken and written language, logical
reasoning.
Lateralization is somewhat less pronounced in
females than males.
Brain Waves
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Brain Waves: Electrical signals from action potentials
that occur rhythmically and can be detected by
electrodes & recorded by electroencephalogram
(EEG).
4 Categories of Brain Waves:
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Alpha: Produced when awake but resting with eyes closed, not
present during sleep.
Beta: Present when nervous system is active & person is
engaged in awake mental activity.
Delta: Present in awake infants and sleeping adults, indicative of
brain damage in awake adults.
Theta: Present in children & adults during emotional stress, may
be a sign of brain disorder.
Brain Death: A complete absence of brain waves.
Higher Brain Functions
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Sleep: Hypothalamus controls the need for sleep while
the brainstem controls sleep patterns.
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Rapid Eye Movements: Period of sleep in which the eyes track
in a set pattern and dreaming occurs.
Cognition: Association areas responsible for
awareness, thinking, assimilating knowledge. Processed
in the parietal, temporal and frontal lobes.
Emotion: Prefrontal cortex helps control emotions, but
hypothalamus and amygdala provide emotional source.
Sensation: Postcentral gyrus is the primary
somatosensory area, but cerebral cortex contains
specific sense areas.
Motor Control: Precentral gyrus is the primary motor
area.
Higher Brain Functions
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Memory: Hippocampus and limbic system responsible
for consolidation and housing of the long-term memories.
Amnesia:
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Anterograde Amnesia: Inability to store new information.
Retrograde Amnesia: Inability to recall previously known
information.
Alzheimer’s Disease: Loss of the neurons secreting
acetylcholine, beta-amyloid pllaques, and neurofibrillary
tangles causes memory loss, confusion, developmental
regression, and personality changes.
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Affects more than 10% of elderly over 65 years of age.
Is the 4th leading cause of death among the elderly as the ANS
systems degrade.
Spinal Cord
Spinal Cord: The outer portion of the
CNS that functions in propagating
impulses, integrating information, and
processing reflexes.
 Spinal Nerves: Connect the sensory
receptors to the CNS.
 Divisions: Divides into cervical, thoracic,
lumbar, & sacral regions just like the
vertebral column.
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Major Structures of the Spinal Cord
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Foramen Magnum: Opening at the base of the
skull where the spinal cord begins & attaches to
the medulla oblongata.
Second Lumbar Vertebra (Superior Border):
Where the spinal cord ends.
Meninges: Layers of protective membrane
surrounding the spinal cord.
 Dura
Matter, Arachnoid Matter, & Pia Matter
separated by the subdural & subarachnoid spaces.

Cervical & Lumbar Enlargements: Points
where the spinal cord connects to the nerves
that lead out to the appendages.
Major Spinal Cord Structures
Conus Medullaris: The tapering ends of
the spinal cord between the 1st & 2nd
lumbar vertebrae.
 Cauda Equina: The “horse’s tail”
comprised of a bundle of nerve roots
extending downward from the end of the
cord.
 Epidural Space: The space between the
dura matter and the wall of the vertebral
canal.
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Internal Anatomy of the Spinal Cord

Under a cross section of the internal gray
matter we can see…
2
Dorsal Horns (Posterior Horns): Contain
somatic and autonomic sensory nuclei
 2 Ventral Horns (Anterior Horns: Contain
motor neurons.
 Gray Commisure: Connects the left & right
halves of the spinal cord.
 Central Canal: A central canal filled with
cerebrospinal fluid.
Internal Anatomy of the Spinal Cord

Under a cross section of the external white
matter we can see..
 Anterior Columns
 Posterior Columns
 Lateral Columns
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Each column contains tracts of axons..
 Ascending
Tracts: Carry sensory impulses toward
the brain.
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Examples: Gracile fasciculus, cuneate fasciculus, dorsal &
ventral spinocerebellar tracts, spinothalamic tract.
 Descending
Tracts: Carry motor impulses from the
brain.

Examples: Corticospinal tracts, lateral & medial reticulospinal
tracts, vestibulospinal tract, tectospinal tract.
Spinal Nerves
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Technically part of the perepheral nervous
system.
31 total pairs (62 nerves total):
 Each
nerve provides a path for communication
between the cord and the region of innervation,.

Consists of two roots (bundles of axons).
 Posterior (Dorsal) Root: Contains sensory axons.
 Anterior (Ventral) Root: Contains motor neurons.

Nerves correspond to the region and level of the
vertebral column they extend from.
 E.g.
thoracic nerves emerge through the intevertebral
foramina between the thoracic vertebra.
Protecting The Nerves

Cranial & Thoracic Nerves have protective
coverings.
 Endoneurium:
Wraps around an individual
axon.
 Perineurium: Wraps around fascicles
(bundles of neurons).
 Epineurium: Wraps around the entire nerve
fiber.
Branches of the Spinal Nerves
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Rami: Divisions/branches of the spinal nerves. Two
types: Anterior Rami & Posterior Rami
Plexus: A joining of the anterior rami and the adjacent
neurons, which then branch to serve a region of the
body. Most important plexuses:
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Cervical Plexus: Serves the skin & muscles in the head, neck,
shoulders & chest. Ex. Phrenic nerve.
Brachial Plexus: Serves the shoulders & upper limbs. Ex.
Axillary nerve.
Lumbar Plexus: Serves the abdominal wall, genitals, & parts of
the lower limbs. Ex. Femoral nerve.
Sacral & Coccygeal Plexuses: Serve the buttocks, perineum, &
lower limbs. Ex. Sciatic nerve (largest in the body).
Intercostal Nerves: Spinal nerves T2-T12 do not form
plexuses, and innervate the intercostal spaces.
Reflexes
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Reflex: A fast, involuntary action that occurs in response
to a stimuli.
Inborn Reflexes: Ones we’re born with!
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Learned Reflexes: Ones we have to actively learn to
integrate.
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Ex. Pulling away from heat
Ex. Slamming on car breaks.
Spinal Reflexes: Reflexes that are controlled by the
spinal cord.
Somatic Reflexes: Reflexes that involve skeletal
muscles.
Autonomic Reflexes: Reflexes that involve the viscera.
Cranial Reflexes: Reflexes that are controlled by the
brainstem.
Reflexes

Reflex Arc: The pathway the nerve
impulses take to produce a reflex.
 Begins
in the somatic receptors
 Travels across the afferent nerve fibers to
interneurons
 Travels from the interneurons across the
efferent nerve fibers to the appropriate
skeletal muscle.
Reflexes

5 Parts of a Reflex Arc:
 Sensory
Receptor: Serves as a sensory receptor.
 Sensory Neuron: Nerve impulses travel along the
axon terminal of the sensory neuron to the axon
terminals
 Integrating Center: A single synapse between a
sensory & motor neuron.
 Motor Neuron: Impulses from the integrating center
travel along the motor neuron to the part of the body
that needs to respond.
 Effector: The part of the body that responds to the
motor nerve impulse, e.g. the muscle cell or the
gland.
Reflexes
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Most common reflexes:
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Stretch Reflex: Contraction of skeletal muscle in response to
the stretching of the muscle.
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Golgi Tendon Reflex: Tension applied to a tendon will cause
relaxation of the muscle.
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Prevents muscle & tendon damage when muscle force is too
extreme.
Flexor Reflex: Withdrawal of a limb in response to pain stimuli.
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E.g. knee joint flexing when tapped with a hammer
E.g. rapidly removing hand from hot stove
Crossed Extensor Reflex: Contraction of muscles in the limb
opposite of the one experiencing a painful stimulus.

Contralateral reflex allows the body weight to shift as the supporting
limb is withdrawn.
Poliomyelitis

Poliomyelitis (Polio): Caused by a virus
that destroyes motor neurons in the spinal
cord & nuclei in the cranial nerves.
 Results:
Paralysis & loss of reflexes