Bio211 Lecture 19

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Mariebs Human Anatomy and Physiology Marieb w
Hoehn
Chapter 12 The Central Nervous System Lecture 19
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Lecture Overview

• The brain
• Overview
• Protection
• Meninges
• Ventricles and the CSF
• The structure of the major parts of the brain
• Functional areas of the brain
• The spinal cord
• Spinal meninges, and spinal reflexes
• Ascending and descending spinal tracts

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Divisions of the Nervous System
You are here
CNS
PNS
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Brain Embryology Overview
Table Figure From Marieb Hoehn, Human
Anatomy Physiology, 9th ed., Pearson, 2013
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Overview of the Brain

• Functions
• regulates visceral activities
• coordinates muscular movements
• interprets sensations
• determines perception
• stores memory
• carries out reasoning
• makes decisions
• determines personality

• Major Parts
• diencephalon
• thalamus
• hypothalamus
• brain stem
• midbrain (mesencephalon)
• pons
• medulla oblongata
• cerebellum
• cerebrum (two hemispheres)

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Protection of the Brain

• The brain is protected
• Mechanically by
• The skull bones
• The meninges
• The cerebrospinal (CSF) fluid
• Biochemically by the blood-brain barrier
• Capillaries interconnected by tight junctions
• Astrocytes/ependymal cells control permeability
  of general capillaries/choroid capillaries
• May be obstacle to delivery of drugs
• May become more permeable during stress

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Meninges of the Brain
- dura mater outer, tough (anchoring dural
folds) - arachnoid mater web-like - pia
mater inner, delicate
Singular of meninges is meninx
- Subdural space like interstitial fluid
- Subarachnoid space CSF
Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Dural Folds
Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
Falx Cerebri within longitudinal fissure
separates cerebral hemispheres Tentorium
Cerebelli above cerebellum separates occipital
lobe from cerebellum
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Ventricles of the Brain

• interconnected cavities
• within cerebral hemispheres and brain stem
• continuous with central canal of spinal cord
• filled with cerebrospinal fluid (CSF)

• lateral ventricles (1, 2)
• third ventricle (3)
• fourth ventricle (4)
• cerebral aqueduct

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Cerebrospinal Fluid

• secreted by choroid plexus of ventricles (500
  ml/day)
• circulates in ventricles, central canal of
  spinal cord, and subarachnoid space
• completely surrounds brain and spinal cord
• clear liquid (more Na and Cl-, but less K,
  Ca2, glucose, and protein than plasma)
• nutritive and protective
• helps maintain stable ion concentrations in CNS

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Flow of CSF
(Monro)
(Luscka)
(Magendie)
Know
Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Overview of the Cerebrum of the Brain
Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013

• Over 85 of brain mass, with about 14 billion
  multipolar neurons in cortex
• Lobes named for overlying bones. (See sulci
  above for divisions)

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The BRAIN Initiative
Last week April, 2013, President
Obama announced the BRAIN Initiative, a
10-year project to map the human brain. BRAIN,
which stands for Brain Research through Advancing
Innovative Neurotechnologies, will bring together
scientists from private and public institutions
to investigate how the brains 100 billion cells
interact with each other. Many researchers
believe that brain mapping could unlock the
secrets behind complex diseases like Alzheimers
and autismat a price tag of 100 million in 2014
and up to 3 billion over the next decade.
From http//cognoscenti.wbur.org/2013/04/09/b
rain-initiative-ravi-parikh
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Functions of Cerebrum

• interpretation
• initiating voluntary movements
• storing memory
• retrieving memory
• reasoning
• center for intelligence and personality

The cerebrum can be divided into several
functional areas - Motor (frontal cortex) -
Sensory (parietal, occipital, and temporal
cortex) - Association (all lobes)
Points to keep in mind - Each cerebral
hemisphere receives information from, and sends
information to, the opposite side of the body -
Although symmetrical, the cerebral hemispheres
are not entirely equal in function
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Functions of Parts of Brain
Part of Brain Major Function
Motor areas
Primary motor cortex (Precentral gyrus) Voluntary control of skeletal muscles
Brocas area (motor speech area) Controls muscles needed for speech
Frontal eye field Controls muscles needed for eye movement
Sensory areas
Cutaneous Sensory Area (postcentral gyrus) Receives somatic sensations
Visual area (occipital lobe) Receives visual sensations
Auditory area (temporal lobe) Receives auditory sensations
Association areas (all lobes) Analyze and interpret sensory experiences coordinate motor responses memory, reasoning, verbalization, judgment, emotions
Basal nuclei Subconscious control certain muscular activities, e.g., learned movement patterns (a nucleus is a collection of neuron cell bodies in the CNS) putamen, globus pallidus, caudate
Limbic system controls emotions , produces feelings, interprets sensory impulses, facilitates memory storage and retrieval (learning!)
Diencephalon
Thalamus gateway for sensory impulses heading to cerebral cortex, receives all sensory impulses (except smell)
Hypothalamus Vital functions associated with homeostasis
Brainstem
Midbrain Major connecting center between spinal cord and brain and parts of brainstem contains corpora quadrigemina (visual and auditory reflexes)
Pons Helps regulate rate and depth of breathing, relays nerve impulses to and from medulla oblongata and cerebellum
Medulla Oblongata Contains cardiac, vasomotor, and respiratory control centers, contains various nonvital reflex control centers (coughing, sneezing, vomiting)
Reticular formation (system) Filters incoming sensory information habituation , modulates pain, arouses cerebral cortex into state of wakefulness (reticular activating system)
Cerebellum Subconscious coordination of skeletal muscle activity, maintains posture
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Brain Sensory and Motor Areas

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(Gnostic)
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Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
Somatosensory Somesthetic
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Cerebral Cortex Motor/Sensory Homunculi
Notice the relative amount of cortical tissue
devoted to each sensory function.
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Hemispheric (Cerebral) Lateralization
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
Categorical hemisphere
Representational hemisphere
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Basal Nuclei (formerly basal ganglia)

• nuclei are masses of gray matter in CNS
• deep within cerebral hemispheres
• three nuclei caudate nucleus and putamen,
  (together called the striatum), and the globus
  pallidus
• subconscious control certain muscular
  activities, e.g., learned movement patterns

1. Receive input from entire cerebral cortex.
2. Relay motor impulses originating in the
   substantia nigra, along with their own output,
   through the thalamus to the motor cortex to
   influence muscle movement.

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Brain Cerebral White Matter

• Three types of myelinated tracts form cerebral
  white matter
• 1. Association same hemisphere
• 2. Commisural between corresponding gyri in
  opposite hemispheres
• 3. Projection Ascending and descending tracts

Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Limbic System

• Consists of
• portions of frontal lobe
• portions of temporal lobe
• hypothalamus
• thalamus
• basal nuclei
• other deep nuclei
• associated with sense of smell (less
  significant)

• Functions
• controls emotions
• produces feelings
• interprets sensory impulses
• facilitates memory storage and retrieval
  (learning!)

Figure from Saladin, Anatomy Physiology,
McGraw Hill, 2007
The motivational system
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Memory

• A Memory is the persistence of knowledge that
  can be accessed (we hope!) at a later time.
• Memories are not stored in individual memory
  cells or neurons they are stored as pathways
  called engrams, or memory traces that use
  strengthened or altered synapses.
• Immediate memory lasts a few seconds, e.g.,
  remembering the earliest part of a sentence to
  make sense of it.
• Short-term memory (STM) lasts a few seconds to a
  few hours
• Working memory is a form of this (repeating a
  phone number over to yourself just long enough to
  dial it and then forget it!)
• Limited to a few bits of information (about
  7-9). So, chunk up!
• Long-term memory (LTM) can last a lifetime
• Can hold much more information that STM
• Declarative (events and facts)
• Procedural (motor skills)

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Diencephalon

• between cerebral hemispheres and brainstem
• surrounds third ventricle

• thalamus
• hypothalamus
• epithalamus
• optic tracts
• optic chiasm
• infundibulum
• posterior pituitary
• mammillary bodies
• pineal gland

(Tectum)
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Diencephalon - Thalamus
Ventral nuclei - Posterior relay for taste
- Anterior and Lateral voluntary motor

• Forms wall of third ventricle
• Crude interpretation center for pain, touch,
  pressure, temperature

Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
Relay for hearing
Relay for vision
The gateway to the cerebral cortex. Major relay
for sensory information coming into the cerebral
cortex, roles in cortical arousal, learning, and
memory
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Diencephalon - Hypothalamus
Hypothalamus - maintains homeostasis by
regulating visceral activities (see list below
for examples)

• Heart rate and blood pressure- Body temperature
• Stimulation of the pituitary (links nervous and
  endocrine) - Water balance (ADH)
• SM contraction (OT)- Feeding/satiety centers-
  Movement/secretions of glands and intestines-
  Sleep and wakefulness
• Rage/aggression
• Psychosomatic illness

Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
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Brain Stem

• Three Parts
• Midbrain
• Pons
• Medulla Oblongata

(Tectum)
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Midbrain

• between diencephalon and pons
• contains bundles of fibers that join lower parts
  of brainstem and spinal cord with higher part of
  brain
• cerebral aqueduct
• cerebral peduncles bundles of nerve fibers
• contains red nucleus (rubro-) and substantia
  nigra
• corpora quadrigemina centers for visual and
  auditory reflexes

Major connecting center between spinal cord and
brain and parts of brainstem
(Tectum)
Figure from Saladin, Anatomy Physiology,
McGraw Hill, 2007
Origins of CN III, IV
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Pons

• rounded bulge on underside of brainstem
• between medulla oblongata and midbrain
• helps regulate rate and depth of breathing
• relays nerve impulses to and from
• medulla oblongata and brainstem via longitudinal
  tracts
• cerebellum via transverse tracts

Origins of CN V, VI, VII, VIII
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Medulla Oblongata

• enlarged continuation of spinal cord running
  through foramen magnum of skull
• conducts all ascending (olive) and descending
  (pyramids - decussation) impulses between brain
  and spinal cord
• contains cardiac, vasomotor, and respiratory
  control centers
• nucleus gracilis and nucleus cunneatus on dorsal
  side sensory info, cross over, then send to
  thalamus

Origins (nuclei) of CN IX, X, XI, and XII
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Reticular Formation

• complex network of nerve fibers scattered
  throughout the brain stem
• extends into the diencephalon
• connects to centers of hypothalamus, basal
  nuclei, cerebellum, and cerebrum
• filters incoming sensory information
  habituation
• modulates pain
• arouses cerebral cortex into state of wakefulness

Ascending portion is called the reticular
activating system(prefix reticulo-)
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Cerebellum

• integrates sensory information concerning
  position of body parts
• coordinates skeletal muscle activity
• helps to maintain posture
• May also be involved in several sensory,
  linguistic, emotional and non-motor functions
• virtually all fibers entering and leaving are
  ispsilateral

Figure from Saladin, Anatomy Physiology,
McGraw Hill, 2007
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Review of Major Brain Areas
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1
2
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4
5
10 (White part)
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Summary of Lower Brain
Part of Brain Major Function
Brainstem  
Medulla Oblongata (Embryology?) (Ventricles nearby?) Contains cardiac, vasomotor, and respiratory control centers Nucleus gracilis/cunneatus Origin of CN 9, 10, 11, 12
Pons (Embryology?) (Ventricles nearby?) Bridge between medulla and midbrain via transverse tracts (to cerebellum) and longitudinal tracts(to medulla/midbrain) Helps regulate rate and depth of breathing Origin of CN 5, 6, 7, 8
Midbrain (Embryology?) (Ventricles nearby?) Major connecting center between spinal cord and brain and parts of brainstem Contains corpora quadrigemina (visual and auditory reflexes) Origin of CN 3 and 4 Location of red nucleus (rubrospinal tract) Origin of substantia nigra
Cerebellum (Embryology?) (Ventricles nearby?) Subconscious coordination of skeletal muscle activity, maintains posture Hemispheres separated by falx cerebelli and vermis Cerebellar peduncles (sup, middle, inf) attach to rest of brainstem
Diencephalon (Embryology?) (Ventricles nearby?)  
Thalamus Gateway (relay) for sensory impulses heading to cerebral cortex hearing, vision, taste Crude interpretation for pain, touch, pressure, and temperature relay for motor information (voluntary) Forms walls of third ventricle
Hypothalamus Vital functions associated with homeostasis, ANS, psychosomatic illness, feeding/satiety Connected to pituitary by infundibulum (pituitary stalk)
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Spinal Cord Structure

• extends from the foramen magnum to 2nd lumbar
  vertebra
• cervical and lumbar enlargements
• cauda equina (horses tail) thin nerve fibers
  that exit at different level than they arise
  (note that spinal cord does not extend into this
  area of the lumbar spine). Begins around L2 and
  extends to S5. Good area for lumbar puncture and
  collection of CSF.

Figure from Saladin, Anatomy Physiology,
McGraw Hill, 2007
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Meninges of the Spinal Cord
Figures from Saladin, Anatomy Physiology,
McGraw Hill, 2007
Denticulate ligaments branches of pia mater
connecting to the arachnoid
Space between the dura mater and the vertebral
body is called the epidural space
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Cross Section of Spinal Cord
The spinal cord

• is a center for spinal reflexes
• aids in locomotion

• is a conduit for nerve impulses to and from the
  brain

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Organization of Spinal Gray Matter
You should know the major areas of gray matter of
within the spinal cord Posterior
sensory Lateral visceral motor Anterior
somatic motor
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Spinal Cord and Nerve Roots
Figure From Marieb Hoehn, Human Anatomy
Physiology, 9th ed., Pearson, 2013
Ventral root - axons of motor neurons whose cell
bodies are in spinal cord
Dorsal root - axons of sensory neurons in the
dorsal root ganglion
Dorsal root ganglion - cell bodies of sensory
neurons
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Organization of Spinal White Matter
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
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Tracts of the Spinal Cord

• Ascending tracts conduct sensory impulses to the
  brain
• Descending tracts conduct motor impulses from
  the brain to motor neurons reaching muscles and
  glands

All the axons in a tract share a common origin
and destination Tracts are usually named for
their place of origin (1st) and termination
(2nd) Most axons cross over during their travel.
What will this mean clinically?
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Ascending Tracts

• fasciculus cuneatus/gracilis - fine touch,
  pressure, body movement - cross
  (decussate) in medulla
• spinothalamic - crude pain, temperature,
  pressure, and touch - cross in spinal cord
• spinocerebellar - subconscious coordination
  of muscle movements (1st and 2nd order
  neurons) - ipsilateral

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2
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Decussation (crossing over)
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1st, 2nd, and 3rd Order Sensory Neurons
1st order neuron from receptor to the spinal
cord (cell bodies are located in the dorsal root
ganglion) 2nd order neuron from spinal cord to
thalamus 3rd order neuron from thalamus to
sensory cerebral cortex - terminate in the
cerebral cortex
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2
1
Decussation
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Descending Tracts

• corticospinal (direct, pyramidal) - voluntary
  movement of skeletal muscles - lateral
  cross in medulla - contralateral
• reticulospinal (indirect, extrapyramidal) -
  subconscious muscle tone, sweat glands
  - some lateral cross, anterior do not cross
• rubrospinal (indirect, extrapyramidal) -
  subconscious regulation of upper limb
  tone/movement - cross in brain (less
  important in humans)

Upper motor begin in precentral gyrus of cortex
Decussation
Lower
Upper MN Cerebral cortex to spinal cord Lower
MN Spinal cord to effector
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Review

• The brain is protected by the
• Skull bones
• Meninges
• CSF
• Blood-brain barrier
• The meninges of the brain and spinal cord consist
  of the
• Dura mater
• Arachnoid (membrane)
• Pia mater

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Review

• Important motor areas of cerebral cortex
• Precentral gyrus (Primary motor area)
• Brocas area
• Frontal eye field
• Important sensory areas of cerebral cortex
• Postcentral gyrus (Primary cutaneous sensory)
• Visual area (occipital lobe)
• Auditory area (temporal lobe)
• The spinal cord is a
• Center for spinal reflexes
• Conduit for nerve impulses to and from the brain

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Review
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Review
Spinal cord contains nerve tracts Ascending
sensory Descending motor