Biology 2121 – Chapter 12
Additional Lecture Notes
I.
Embryonic Development of the Brain
Topic
Notes-What to Know
1. Early Development
 At three weeks the primary germ layer called the ectoderm thickens and forms the neural
plate
 A groove forms between the plates called the neural groove.
 As it deepens, the folds fuse and form the neural tube.
 The neural tube detaches and falls below the ectoderm. This is formed by the fourth week.
The entire CNS will come from this tube!
 Anterior end of neural tube – three vesicles form.
 Prosencephalon – forebrain- develops into the telencephalon which becomes the cerebrum .
Also develops into the diencephalon which contains the thalamus, epithalamus and
hypothalamus.
 Mesencephalon – brain stem : midbrain
 Rhombencephalon – brainstem: medulla oblongata and pons
 Posterior region of the neural tube develops into the spinal cord
II. Brain Waves, Sleep and Memory
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1. Brain Waves and
EEG
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EEG records brain wave activity.
Alpha waves (8-13 Hz): low-amplitude, regular waves, calm and relaxed state of mind.
Beta waves (14-30 Hz): not as regular as alpha, higher frequency; concentrating and
mental alertness.
Theta waves (4-7): irregular, abnormal in waking adults
Delta waves (4 or less): seen during sleep; If seen in awake adults indicates brain damage.
All recorded on an EEG
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2. Epileptic events
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3. Sleep
4. Sleep Patterns
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5. Narcolepsy
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Caused by uncontrolled brain wave activity; person unable to receive messages or
comprehend; may be genetic or via injury to the head, stroke, tumor, etc. Petit mal
seizures are mild and only last for seconds; may disappear as the person ages; Grand mal
seizures the person looses consciousness.
Anticonvulsive drug treatment or newer vagus nerve stimulator
Sleep is defined as partial unconsciousness
Comas are defined as total unconsciousness
NREM sleep, REM are types of sleep defined by EEG.
There are 4 stages of NREM sleep; We pass through them during the first 90 minutes of
sleep; After the NREM stage, the EEG begins to show marked differences
REM sleep the EEG brain waves become irregular.
HR, breathing and blood pressure increase, oxygen use by brain increases.
Eyes move rapidly; dreaming occurs; skeletal muscles of the body go limp; Some adultsmales get an erection during this time and females experience engorgement of the
clitoris.
24-hour circadian rhythm.
Reticular activating activity begins to decline. RAS is not completely turned off. Adult
sleep alternates between periods of REM and NREM sleep. REM recurs every 90 minutes
or so. REM sleep becomes longer with each cycle.
Slow theta and delta waves occur during deep sleep.
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Condition in which people will lapse into REM sleep at any time. Last minutes at the time.
Sometime people lose control of all voluntary muscle functions called cataplexy.
Cause uncertain at this time.
6. Insomnia
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Person unable to sleep consistently. Easy to awaken
7. Sleep Apnea
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Temporary stoppage of breathing. Due to blocked, weight, etc. Person experiences
hypoxia or loss of oxygen. May occur throughout the night. Snoring is often a result of
the blockage.
8. Memory
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Memory storage involves two events.
Short-term (STM): or working memory; remembering a telephone number, etc.
LTM: ability to store information for long periods.
STM can be converted to LTM
LTM is affected by emotion; rehearsal or repetition; association; automatic memory
which is not consciously formed but stored.
9. Brain Structures
involved in memory
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After processing by the association cortex in the cerebral cortex, information may be sent
to the temporal lobe which communicates with the prefrontal cortex and thalamus
10. Damage to the brain
and memory
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Damage to the hippocampus and on either medial temporal lobe side may result in
memory loss. If both sides are damaged this may cause amnesia.
Loss of memory means the person can receive new imput but old memories are lost.
They live in the now!
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III. White Matter and Pathways to the brain
1. Sensory Neurons
 Sensory neurons will take sensory information from an organ, tissue, etc. back to the CNS. A
first-order sensory neuron runs from the organ or tissue to the spinal cord. It will (1).
Synapse with a second-order neuron in the dorsal horn or (2). Synapse with an interneuron
for a spinal reflex.
 Second-order neurons proceed through the spinal cord, brain stem and synapse with thirdorder neurons in the thalamus.
 Second-order neurons in the thalamus synapse with third-order neurons which proceed to
the somatosensory cortex of the brain.
2. Specific vs. Non-specific
pathways
 Page 476
 Specific pathways: discriminative touch and proprioception. Let’s the brain know exact
locations, positions, type of stimulus. White matter associated with specific pathways:
Fasciculus gracilis, spinocerebellar pathway, medial lemniscal tract, posterior spinocerebellar
tract
 Nonspecific: crude touch, pain temperature; White matter tracts: spinothalamic, lateral
spinothalamic
3. Descending Pathways
 These are motor pathways page 480
 Direct: include pyramidal or corticospinal tracts; originates with the pyramidal neurons in the
precentral gyrus; Signals sent down the pyramidal tracts, cross over in the medulla and
synapse in the dorsal horn of the spinal cord (with interneuron or with ventral motor horn
neurons). Involves smooth movements which are fine and or fast
 Indirect: All tracts except for the pyramidal tracts. “Extrapyramidal tracts”. Regulate muscles
that are involved in balance, posture, course limb movement, head, neck and eye
movements. Tracts involved are reticulospinal and vestibulospinal tacts.
IV. Cerebral Cortex – Motor and Sensory areas
Area
Primary Motor
Cortex
Location
Pre-central gyrus
(frontal lobe of
the brain)
Premotor Cortex
Anterior to precentral gyrus
Broca’s area
Anterior to the
inferior region of
the premotor area
Functions/Description
 Contains large multipolar neurons called pyramidal cells
 Long axons group together and form large pyramidal (corticospinal tracts) that
are voluntary tracts(affects skeletal muscles)
 Face tongue and hands (allocated most neurons of this type because fine
control is needed)
 Controls learned motor skills that are repetitious or patterned
 Supplies 15% of the corticospinal tracts
 Involved in planning movements
 Only found in the left hemisphere
 Motor speech area
Frontal Eye Field
Primary
Somatosensory
Cortex
Somatosensory
Association Cortex
Visual Cortex
and overlaps the
Broadman’s areas
44 and 45
Superior to
Broca’s area
Post-central gyrus
of the parietal
lobe (Broadman’s
1-3)
Posterior to
primary
somatosensory
cortex
Posterior tip of
occipital lobe
Auditory Cortex
Superior margin of
the temporal lobe
Olfactory Cortex
Medial aspect of
the temporal lobe
(piriform lobe)
Insula
Cortex of the
insula posterior to
gustatory cortex
Gustatory Cortex
Visceral Sensory
Area
 Controls voluntary eye movement
 Receive info from sensory receptors in skin, proprioceptors in skeletal
muscles, joints, tendons
 Neurons can identify the body region being stimulated – spatial discrimination
 Face, fingertips have most neurons assigned to them (most sensitive)
 Integrates sensory inputs such as temperature, pressure, ect.
 Information relayed to this area and it produces an understanding of what is
being felt or sensed.
 Largest of all cortical sensory areas
 Receives visual information from the retina
 Visual association area surrounds the cortex area and communicates with the
primary visual cortex. It uses past visual experiences to interpret visual stimuli
such as color, form, movement, etc.). Helps us to recognize a flower, face, etc.
 Receptors in the cochlea of the inner ear send info via CN VIII to this area
 Interprets pitch, loudness and location
 Auditory Association Area – gives us a perception of the sound we are hearing
 Receives afferent fibers from the oolfactgory tracts
 Sense of smell
 Perception of taste stimuli
 Perception of visceral stimuli (stomach pains, bladder sensations, lungs and
breathing ,etc.)
Vestibular Cortex
Posterior insula
 Balance and equilibrium sensations
VII. Cerebral Cortex – Multimodal Association Areas
Area
Anterior Association
Area
Location
Frontal lobe or
prefrontal cortex
Posterior Association
Area
In temporal,
parietal, and
occipital lobes
Cingulated gyrus,
parahippocampal
gyrus,
hippocampus
(limbic system)
Limbic Association
Areas
Description
 Involved with intellect; complex learn or cognition; recall, personality
 Working memory, formation of abstract ideas, judgement, reasoning,
persistence; planning
 Develop slowly in children
 Role in recognizing patterns, faces, our surroundings in space
 Makes sense of emotional information; sense of danger, memories of good
and bad incidences
VIII. Cerebrospinal Fluid
Characteristics
Function
Contents
Description
 Allows for the brain to float or be suspended to reduce brain weight
 Protection from blows and damage to the head
 Keeps proper chemicals supplied to brain cells
 Similar to plasma in blood
 Less protein than plasma
 Great deal of water
 Contains higher levels of Na, Cl and H ions and less Ca and K ions
Formation
 By choroid plexus which are clusters of thin-walled capillaries enclosed by pia
mater and ependymal cells
 Tight junction by ependymal cells so high filtering takes place. Controls ion
concentration, etc.
 Formed daily; 150 ml replaced every 8 hours
Volume
 150 ml in adults
Circulation
 Moves through the ventricles and central canal of the spinal cord
 Most enters the subarachnoid space via the lateral median apertures in the
walls of the fourth ventricles
 Cilia of the ependymal cells keep it moving
 Drains out and back into the venous system of blood via the dural sinuses by
way of the arachnoid villi
 Hydrocephalus – condition in which newborn baby head enlarges due to
excess fluid on the brain
 Skull has not fused at early ages and this cause the head to expand
 Caused by obstructions or problems with drainage or circulations (arachnoid
villi possibly)
 Adults bones are fused so pressure is internalized and causes brain damage.
Disorder
IX. Blood Brain Barrier
Function
Structure
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Keeps stable environment for the brain
Keeps hormones, amino acids and ions in balance
Keeps K ions in check
Capillaries in brain area have a continuous endothelium and a thick basal
lamina surrounding the external face of each capillary; feet of the astrocyte
glia cells attach to the capillaries and form tight junctions
 Least permeable capillaries in the body
Characteristics
 Areas around the 3rd and 4th ventricles the blood brain barrier is absent and
the capillary endothelium is permeable allowing entrance of molecules; this is
where the vomiting center is located in the brain stem
 Selective in nature
 Allows for passive movement via facilitated diffusion for glucose, essential
amino acids and some electrolytes
 Waste, toxins and most drugs are denied passage or entry into brain tissue
 Small nonessential amino acids and K ions are denied passage but are also
actively pumped out
 Not effective against fats, fatty acids, oxygen, carbon dioxide and fat-soluble
molecules; alcohol and nicotine can gain entrance very easily