1. The Central Nervous System
Honors Biology Chapter 12

2. CNS
brain & spinal cord
cephalization: concentration of sense organs and nervous control at the anterior end of the body, (rostral end) forming a head and brain, both during evolution and development of embryo

3. Embryonic Development of CNS
brain & spinal cord begin as embryonic structure called the neural tube
as neural tube forms rostral end expands  3 primary brain vesicles
Prosencephalon: forebrain
Mesencephalon: midbrain
Rhombencephalon:hindbrain
remaining caudal portion  spinal cord

4. Secondary Brain Vesicles
develop from the 3 primary vesicles
Forebrain  cerebral hemispheres, basal nuclei & the diencephalon (thalamus, hypothalamus, epithalamus, retina)
Midbrain does not divide
Hindbrain  brain stem, cerebellum

6. https://www.youtube.com/watch?v=Cu4lQ YbOzzY

7. Development of the Brain
Brain grows more rapidly than the membranous skull surrounding it causing folding to occupy available space
pment-human-embryonic-brain

8. Ventricles of the Brain
spaces in brain filled with CSF
are continuous w/each other
connected to subarachnoid space (around brain & spinal cord) and central canal of spinal cord
paired lateral ventricles
3rd ventricle
4th ventricle

9. Lateral Ventricles
anteriorly are very close separated only by a thin membrane called the septum pellucidum
each communicates with 3rd ventricle via channel called interventricular foramen

10. 3rd Ventricle
continuous with 4th ventricle through canal-like cerebral aqueduct which runs through midbrain

11. 4th Ventricle continuous with central canal of spinal cord inferiorly
3 openings which connect this ventricle to the subarachnoid space (fluid-filled space surrounding brain & spinal cord
1.median apeture in roof
2 & 3: paired lateral apertures on sides

13. CSF: Cerebral Spinal Fluid
forms liquid cushion in & around brain & spinal cord
gives buoyancy to brain reducing its weight by 97%
prevents injury to delicate nervous tissue from trauma
provides nourishment
carries chemical signals from 1part of brain to another
clears waste products or unnecesssary solutes
watery broth similar to blood plasma with less protein & a different ion composition
> Na+, Cl-, H+
< Ca++ and K+

14. Choroid Plexus hangs from top of each ventricle
broad, thin-walled capillaries
leaky capillaries
filter fluid from blood  CSF

15. CSF volume in adults ~150 mL (4 oz)
replaced every8 hrs forming ~500 mL/day
moves freely thru ventricles  subarachnoid spaces (4th ventricle) where it bathes outer surfaces of brain & spinal cord  returns to blood in the dural sinuses via arachnoid villi

17. Brain: unremarkable appearance ~ 3 lbs 4 major regions

18. 1. Cerebral Hemispheres: Gross Structures
right & left connected by large fiber tract: corpus callosum
cover most of other 3 parts (83% of total brain mass)
surface: elevated ridges = gyri separated by shallow grooves = sulci
fissures deeper grooves separate regions of brain

19. Gyri, Sulci, & a Fissure

20. Longitudinal Fissure
separates cerebral hemispheres
other fissures separate brain into lobes

21. Cerebral Cortex “conscious mind”
awareness, memory, communication, understanding, initiation of voluntary movements
composed of gray matter
neuron cell bodies with associated glial cells, dendrites, blood vessels, (no fiber tracts)
~40% of total brain mass
convolutions triple its surface area

23. Gray Matter of the Brain

24. PET Scans Positron Emission Tomography
using radioactive tracer to show activity in brain

25. MRI of Brain
reveals blood flow

26. Lobes of the Cerebral Cortex

27. The Brain’s Functional Areas
Motor Areas
Sensory Areas
Association Areas

28. 3 Functional Areas of Cerebral Cortex

29. Motor Areas Primary(Somatic) Motor Cortex Premotor Cortex
control precise or skilled voluntary movements of skeletal muscles
long axons form voluntary motor tracts called pyramidal or corticospinal tracts
Premotor Cortex
anterior to precentral gyrus
planning of movements/ coordination of different muscle groups

30. Motor Areas continued 3. Broca’s Area 4. Frontal Eye Field
anterior to inferior region of premotor area
usually only in left hemisphere
directs muscles involved with speech (becomes active even when thinking of saying something)
4. Frontal Eye Field
partially in & anterior to premotor cortex/ superior to Broca’s
controls voluntary motion of the eyes

32. Humunculus: Primary Motor Cortex

33. Homeostatic Imbalances
1◦ Motor Cortex
damage  paralysis of area
motor tracts cross so damage to left motor cortex  paralysis on right
Premotor Cortex
loss of motor skills programmed by region damaged
does not impair muscle strength or ability to do the activity just the agility or speed (activity can be re-learned by using undamaged neurons in area)

35. Sensory Areas Primary Somatosensory Cortex
in postcentral gyrus (just posterior to 1◦ motor cortex)
neurons receive info from:
general (somatic) sensory receptors
proprioceptors in skeletal muscles, joints & tendons
spatial discrimination: identification of area being stimulated

36. Humunculus:Primary Somatosensory

37. Sensory Areas continued
2. Somatosensory Association Cortex
lies posterior to 1◦ Somatosensory Cortex
integrates sensory inputs (from #1) & makes sense of info
3. 1◦ Visual Area
extreme posterior tip of occipital lobe& deep w/in the occipital lobe
receives info from retina
optic tracts partially cross so there is a contralateral map

38. Sensory Areas continued
4. Visual Association Area
surrounds 1◦ Visual Cortex
uses past visual experiences to interpret visual stimuli
complex visual processing involves entire posterior ½ of hemispheres
5. 1◦ Auditory Cortex
superior margin of temporal lobe
receives impulses from inner ear
interpret pitch, loudness, & location

39. Sensory Areas continued
6. Auditory Association Area
posterior to #5
storage of memories of sound

40. Sensory Areas continued
7. Vestibular Cortex
posterior part of insula & adjacent parietal cortex
conscious awareness of balance & position of head
8. Olfactory Cortex
medial aspect of temporal lobe
afferent fibers from smell receptors  olfactory tract  here
conscious awareness of odors

41. Sensory Areas continued
8. Gustatory Cortex
insula deep to temporal lobe
perception of taste
9. Visceral Sensory Area
just posterior to gustatory cortex in insula
conscious awareness of visceral sensations (nausea, feeling your bladder is full)

42. Homeostatic Imbalances of 1◦ Visual Cortex
damage results in functional blindness
in contrast a damaged visual association area  can see but cannot interpret what they see

43. Lateralization of Cortical Functioning
division of labor in cerebral hemispheres:
cerebral dominance: designates the hemisphere that is dominant for language
~90% people have left dominance
~10%: right dominance or equally functioning
generally: rt dominance people are males & left handed / equally functioning: ambidexterous
2 hemispheres instantly communicate via connecting fiber tracts

45. Cerebral White Matter internal to gray matter
responsible for communication w/in brain & between brain and lower CNS centers (brainstem & spinal cord)
consists mainly of myelinated fibers bundled into large tracts
classified (#3)according to direction in which they run

46. Association Fibers connect different parts of same hemisphere
short: connect adjacent gyri
long: bundled into tracts connecting different lobes

47. Commisural Fibers
connect corresponding gray areas of the 2 hemispheres
Corpus Callosum: largest commissure
superior to lateral ventricles , deep w/in longitudinal fissure
anterior & posterior commissures: smaller

49. Projection Fibers
enter cerebral cortex from lower brain or cord centers or descend from cortex to lower areas
sensory info reaches cortex & motor output leaves cortex thru these tying cortex to rest of nervous system
run vertically

51. Basal Nuclei (Ganglia)
group of subcortical gray matter
receive input from entire cerebral cortex & each other thru thalamus
functions:
motor: starting, stopping, & monitoring intensity of movements
disorders: Huntington’s chores (too much movement) Parkinson’s (too little movement)
cognition
emotion

53. Diencephalon forms central core of forebrain 3 paired structures:
Thalamus
Hypothalamus
Epithalamus

55. Thalamus
bilateral egg-shaped nuclei joined (in most people) by intermediate mass
form superolateral walls of 3rd ventricle
information received (motor, sensory, cortical arousal, learning, memory) is sorted, “edited”, then relayed via internal capsule to specific cortical association areas
allows for stimulus localization & discrimination

56. Thalamus
relay station for sensory impulses passing thru to sensory cortex

58. Hypothalamus below thalamus
caps brain stem forming inferrolateral walls of 3rd ventricle
extends from optic chiasma (crossover point of optic nerves)  mammary bodies (nuclei that bulge anteriorly from hypothalamus & are relay stations in olfactory pathway)
infundibulum: stalk of hypothalamus that connects to pituitary gland

60. Hypothalamus Functions
main visceral control center of body (homeostasis)
controls ANS
initiates physical response to emotions
regulates body temperature
regulates food intake
regulates sleep/wake cycles
controls endocrine function

62. Epithalamus most dorsal part of diencephalon
forms roof of 3rd ventricle
includes Pineal Gland (pinecone- shaped)which secretes melatonin which is released in response to darkness  helps regulate sleep cycle

64. Brain Stem 3 major regions connects brain to spinal cord Midbrain Pons
Medulla Oblongata
connects brain to spinal cord

65. Midbrain
smallest, uppermost part of brain stem
cerebral aquaduct: tiny canal that runs thru midbrain connecting 3rd & 4th ventricles
contains reflex centers for vision, hearing

66. Midbrain

67. Pons
“bridge”
rounded structure that protrudes below midbrain
contains apneustic (produces deep, prolonged inspirations) & pneumotatic center (inhibits inspiration)

69. Medulla Oblongata
most inferior part of brain stem
with the pons form the ventral wall of 4th ventricle
inferior border merges into spinal cord
site where corticospinal tracts cross
centers: heart rate, BP, breathing, swallowing, vomiting

70. Cerebellum “small brain” ~11% brain mass
dorsal to pons & medulla protruding under occipital lobe (separated by transverse cerebral fissure)
Functions: (all unconscious)
processes input from motor cortex, brain stem nuclei, & sensory receptors
provides timing & patterns of skeletal muscle allowing smooth, coordinated movements & agility

71. Cerebellar Anatomy bilaterally symmetrical
vermis (worm-like)connects the 2 cerebellar hemispheres
surface is convoluted with pleat-like gyri called folia (“leaves”)
thin outer cortex of gray matter, internal white matter with small, deeply situated paired masses of gray matter: dendate nuclei

74. Purkinje Cells
large cells with extensively branched dendrites called arbor vitae
*only cortical neurons that send axons through white matter to synapse with central nuclei in cerebellum

76. loss of ability to control body movements
Ataxia
loss of ability to control body movements
occurs with damage to cerebellum
cannot touch finger to nose with eyes closed
have trouble keeping balance
appear drunk

77. Limbic System
group of structures in medial aspect of each cerebral hemisphere & diencephalon
encircle upper brain stem (limbus = ring)
includes:
amygdaloid body
important in emotions
hypothalamus
fornix :
fiber tract connecting limbic regions
cingulate gyrus
important in expressing emotions thru gestures & resolving mental conflicts when frustrated

79. The Emotional Brain (Limbic System)
odors often trigger emotions/memories
due to extensive connections with lower& higher regions of brain its able to respond to a variety of stimuli
connections with frontal lobe account for intimate relationship between feelings & thought
output from limbic system  hypothalamus
psychosomatic illnesses: emotion-induced illness
example: stress headaches, high blood pressure

81. The Reticular Formation
loosely clustered neurons in white matter extending through central portion of brainstem
their axons  diencephalon, cerebral cortex, cerebellum, spinal cord
Reticular Activating System or RAS sends continuous stream of impulses to cerebral cortex
keeps cortex alert & conscious
filters ascending sensory information but sends unusual, significant, or strong impulses to reach awareness

83. Reticular Activating Center
inhibited by:
sleep centers(hypothalamus, epithalamus))
alcohol
sleep-inducing drugs
tranquilizers
irreversible coma (twisting injury to brainstem)

84. Reticular Activating Center continued
motor function: helps control skeletal muscles during coarse limb movements
autonomic functions: vasomotor, cardiac, respiratory centers (medulla)  regulate visceral motor functions

86. EEG electroencephalogram: recording of electrical activity of brain
electrodes placed on scalp measure voltage differences between different cortical areas
patterns called brain waves: generated by synaptic activity at surface of cortex

89. Normal EEG

90. EEG during a Seizure

91. Epilepsy
Seizures: reflect a torrent of electrical charges by groups of brain neurons
while happening no other messages can get through
1% of world population affected
causes: head trauma, tumor, stroke, infection, metabolic, fever

92. Types of Epilepsy Absence / Petit Mal Tonic-Clonic/ Grand Mal
mild form: patient gets blank expression for few seconds
unconscious during this
most commonly seen in young children, often resolve when >10 yo
Tonic-Clonic/ Grand Mal
most severe
loss of consciousness, possibly injure self, loss of bowel/bladder, biting of tongue

93. Aura of Seizures
many epileptics experience a sensory hallucination (smell, flashes of light, taste) just prior to onset

94. Epilepsy Treatment Anticonvulsants
various drugs
may require >1
Vagus Nerve Stimulator or Deep Brain Stimulator
possible treatment options if drugs fail
deliver pulses to vagus nerve or directly to the brain in effort to stabilize brain’s electrical activity

95. Protection of the Brain
Nervous tissue: very delicate and easily damaged
Protection:
Skull
Meninges (membranes)
cover &protect the CNS
protect blood vessels & enclose venous sinuses
contain CSF
form partitions in the skull
CSF

96. Meninges
3 layers:
Dura Mater
Arachnoid Mater
Pia Mater

97. Dura Mater “tough mother” tough, leathery, fibrous CT
surrounds brain in 2 layers
Dura Septa: #3,extend inward to form flat partitions that subdivide the cranial cavity
Falx cerebri: dips into longitudinal fissure between hemispheres
Falx cerebelli: along vermis of cerebellum
Tentorium cerebelli: horizontal fold extends between cerebellar hemispheres

99. Arachnoid Mater web-like
projections span subarachnoid space & attach to pia mater
subarachnoid space filled with CSF
spinal taps insert needle into this space between lumbar vertebrae to either;
withdraw fluid for analysis
inject anesthetic (spinal anesthesia)
inject medications that cannot cross blood brain barrier (bbb)

101. Pia Mater “gentle mother”
delicate CT layer clinging tightly to brain and spinal cord

102. Meningitis inflammation of meninges bacterial or viral
could spread to brain tissue
diagnosed by spinal lumbar tap & examining for WBC’s and microbes

103. Blood Brain Barrier
protective mechanism that helps maintain a stable environment for the brain
all blood-borne substances in capillaries in brain must pass through 3 layers b/4 reaching neurons:
endothelium of capillary: held together by tight jcts  key to BBB
relatively thick basal lamina surrounding capillary
astrocytes clinging to cappilary

106. BBB selective barrier pumps removing
allows fats, fatty acids, O2, CO2, other small, fat-soluble molecules
pumps removing K+
nonessential amino acids
passing via facilitated diffusion:
glucose
essential amino acids
some electrolytes

107. BBB absent in tissue around 3rd & 4th ventricles examples:
Vomiting Center
monitors blood for poisonous substances
Hypothalamus
monitors: temperature, water balance, other metabolic activities

108. Traumatic Brain Injuries (TBI)
head injuries are leading cause of accidental death in North America
victim suffers a coup and a contra-coup

109. Concussion
alteration in brain function, usually temporary, following a blow to the head
multiple concussions over time can produce cumulative damage
symptoms:
+/- dizziness
+/- loss of consciousness

111. Brain Contusion bruising of brain tissue
+/- remain conscious if injury in brain
if involves brain stem  coma (hours to lifetime) depending on damage to RAS

112. Subdural or Subarachnoid Hemorrhage
injury that involves bleeding from ruptured vessels in spaces betwee dura mater & arachnoid mater or between arachnoid mater and pia mater
treatment: surgically removing hematoma & repairing ruptured vessels

114. Cerebral Edema swelling of the brain
usually associated with contusion but also 2◦ to infection

115. Cerebral Vascular Accidents (CVA)
strokes
single most common nervous system disorder and the #3 cause of death in North America
occur when blood circulation to area of brain is blocked  tissue dies
#1 cause: blood clots block a cerebral artery
clot could form inside brain artery or travel to brain
less commonly CVA 2◦ to bleeding within brain causing compression

116. Transient Ischemic Attacks
TIA’s or “minnie strokes”
temporary episodes of reversible brain ischemia ( deprivation of blood supply to any tissue)
characterized by temporary:
numbness or tingling
paralysis
impaired speech

117. Alzheimer’s Disease progressive degenerative disease of brain
leads to dementia
~50%nursing home patients
5- 15% > 65 yo / ~50% >85 yo
Symptoms:
memory loss: past > recent
shortened attention span
disorientation
eventually loss of language
confusion, irritability
+/- hallucinations

118. Alzheimer’s Disease Pathology: extracellular plaques of amyloid
1 form ass’c with gene mutation (codes for precursor molecule to amyloid)
Prion (infective protein) may
neurofibillary tangles inside neurons
eventually kill neuron  brain shrinks

119. AD Pathology

120. Parkinson’s Disease 50 -60 yo’s Cause: unknown Symptoms:
degeneration of dopamine-releasing neurons in substantia nigra (basal ganglion)
Symptoms:
tremor at rest  “pill-rolling”
forward – bent walking
initiating & executing movement

122. Parkinson’s Treatment
L-Dopa  crosses bbb converted to dopamine
if not working:
deep brain stimulation via implanted electrodes decreases abnormal brain activity
gene therapy insert normal genes into patient’s brain cells  secrete GABA a inhibitory neurotransmitter (same as implants)

123. The Spinal Cord

124. Gross Anatomy enclosed in vertebral column
extends from foramen magnum  L1-L2

125. Meninges same layers as CNS exceptions:
dura mater not attached to vertebrae so there is an epidural space (between bone & dura)

126. Meninges of Spinal Cord
other exceptions:
2. inferiorly, dural& arachnoid layers extend lower than spinal cord
cord ends ~L1 – L2
meninges extend to upper sacrum

127. Conus Medullaris / Filum Terminale
inferior border of spinal cord ends in cone-shaped point
fibrous extension of conus, covered by pia mater extends from conus to coccyx where it anchors the spinal cord
pegs of pia mater called denticulate ligaments secure cord to dura materthrough out its length

128. Spinal Nerves (PNS) 31 pair attach to cord by “roots”
nerves exit cord passing superior to its corresponding vertebra  part of body it innervates

129. Spinal Cord Enlargements

130. Cauda Equina
collection of nerve inferior end spinal cord

131. Transverse Section of Spinal Cord
2 grooves mark surface:
ventral median fissure
deeper of the 2
dorsal median fissure

132. Gray Matter of the Spinal Cord
butterfly shaped (or H) on cross section
lateral gray masses
dorsal horns
ventral horns
both columns of gray matter running entire length of cord
thoracic & upper lumbar have additional pair of gray columns = lateral horns
crossbar : gray commissure

134. Neurons in the Spinal Cord
*all neurons with cell bodies in spinal cord are multipolar neurons
*dorsal horns: all neurons are interneurons
*ventral horns: some interneurons but mostly somatic motor neurons  axons to skeletal muscle via ventral roots
larger in cervical & lumbar regions
*lateral horns contain cell bodies of sympathetic division of ANS serving visceral organs, axons  thru ventral root

136. Dorsal Roots
carry afferent fibers from all peripheral sensory receptors
dorsal root ganglion:
enlargement containing cell bodies of associated sensory neurons
their axons  enter spinal cord 
to dorsal white matter  higher cord or brain to synapse
synapse with interneurons in dorsal horn

137. Spinal Cord Trauma
cord slightly elastic but very sensitive to pressure
injury results in:
paralysis: loss of motor control
flaccid paralysis: motor neurons do not send impulses to skeletal muscle  no voluntary or involuntary movement
spastic paralysis: when only 1° motor cortex neurons damaged loss of voluntary control but still have spinal reflexes
paresthesias
abnormal sensations

139. Transection of Spinal Cord
spinal shock: transient period of functional loss following injury (most recover w/in 48 hrs, rest permanent paralysis)
depression of all reflexes caudal to injury
BP drops
all muscles below injury paralyzed & insensitive
depends on level
T1  L1 affect upper & lower limbs = paraplegia
any cervical level = quadriplegia
hemiplegia: paralysis one side of body due to brain injury only

140. Poliomyelitis polio – gray matter myelitis – inflammation
poliovirus: destroys ventral horn motor neurons

141. Polio (poliomyelitis) mainly affects children under 5 years of age.
One in 200 infections leads to irreversible paralysis. Among those paralysed, 5% to 10% die when their breathing muscles become immobilized.
Polio cases have decreased by over 99% since 1988, from an estimated cases then, to 359 reported cases in The reduction is the result of the global effort to eradicate the disease.
Today, only 2 countries (Afghanistan and Pakistan) remain polio-endemic, down from more than 125 in 1988.
As long as a single child remains infected, children in all countries are at risk of contracting polio. Failure to eradicate polio from these last remaining strongholds could result in as many as new cases every year, within 10 years, all over the world.

143. ALS: Amyotrophic Lateral Sclerosis
condition that progressively destroys ventral horn motor neurons + fibers of the corticospinal tracts
patient progressively loses ability to speak, swallow, breathe
death usually w/in 5 yrs
cause: environmental + genetic factors
10% have mutation: genes involved in RNA processing