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A.2 The Human Brain
Understandings
The anterior part of the neural tube expands to form the brain
Different parts of the brain have specific roles
The autonomic nervous system controls involuntary processes in the body using centers located in the medulla
oblongata
The cerebral cortex forms a larger portion of the brain and is more highly developed in humans than other animals
The human cerebral cortex has become enlarged principally by an increase in total area with extensive folding to
accommodate it within the cranium
The cerebral hemispheres are responsible for higher order functions
The left cerebral hemisphere receives sensory input from sensory receptors in the right side of the body and the right
side of the visual field in both eyes, and vice versa for the right hemisphere
The left cerebral hemisphere controls muscle contraction in the right side of the body, and vice versa for the right
hemisphere
Brain metabolism requires large energy inputs
Application
Visual cortex, Broca’s area, nucleus accumbens as areas of the brain with specific functions
Swallowing, breathing, and heart rate as examples of activities coordinated by the medulla
Use of the pupil reflex to evaluate brain damage
Use of animal experiments,autopsy, lesions, and fMRI to identify the role of different brain parts
Skill
Identification of parts of the brain in a photograph, diagram, or scan of the brain
Analysis of correlations between body size and brain size in different animals
Brain Formation: nerve cells migrate to outer edge - harden
Anterior end (forebrain)
expands  cerebral
hemispheres
Posterior end  other
parts of brain and spinal
cord
Most complex organ in body
• Weighs 1.4kg
• Produces: thoughts, feelings, actions, memories
• Contains: 100 billion neurons, thousands of synapses
• Connections: store memories, learning, personality traits
• No two brains same, changes throughout lifetime
• Regulates and monitors: blood pressure, heart rate,
breathing
• Controls: balance, muscle coordination, most voluntary
movement, speech, emotions, problem solving
Cerebral Hemisphere:
Integrating center for high
complex functions – learning,
memory, emotions
Pituitary gland:
Posterior lobe – stores,
releases hormones regulating
body functions
Hypothalamus:
Maintains homeostasis,
coordinates nervous/endocrine
systems, secretes hormones
Cerebellum:
Two hemispheres, highly
folded surface,
coordinates unconscious
functions (balance and
movement)
Medulla:
Controls automatic and hemostatic activities –
swallowing, digestion, vomiting, breathing, heart activity
Role of Medulla:
Swallowing – coordinates muscles of mouth, pharynx, larynx
Send food down esophagus and not trachea
Breathing – monitors CO2 levels in blood
Increase CO2 breathing rate increases (intake more O2)
Cardiovascular – cardioinhibitory center (slows heart rate) vs cardioaccelerator
center (increase heart rate)
Connected by thick band of axons (corpus callosum)
Left Hemisphere:
Important for communication
Stroke (broken or blocked
blood vessels) can cause
damage
Difficulty: speaking, doing
complicated movements
with hands/arms
Broca’s area – interferes with
vocalizing words
Wernicke’s area – affects ability
of creating sentences
Right Hemisphere:
Helps understand words
Specializes in receiving and
analyzing information
Lesions – problems identifying
faces, locating objects in space
(spacial awareness)
Studied severed corpus callosum  used to relieve
symptoms of epilepsy
Card with dot in middle – spoon may appear on left or
right of dot
Right side  left hemisphere identifies as spoon
Left side  right hemisphere sees nothing (no
language ability) – but knows what to do with it
fMRI (Functional magnetic resonance imaging)
Use Radio waves and strong magnetic field
See blood flow in brain as it is occurring
Determine regions of active brain and how long stay active
Used to determine:
Plan for surgery
Treatment for stroke
Placements of radiation therapy for brain tumor
Effects of degenerative brain disease
Diagnosing how diseased or injured brain works
Animal Experimentations
Expose animals to addictive substances in controlled situations
Findings
Want more substance
Spends lots of time and energy getting it
Keep taking it despite adverse conditions
Have withdrawal symptoms
Go back when stressed
Can shed light on ways drugs
promote abuse and addiction
Limitations
Never replicate complete picture of human
interactions
Social factors are not considered
Autopsy
Determine what brain parts are involved in certain functions
Important in emergency
Important in returning to normal
Response is ‘fight or flight’
Response is to relax
NT is noradrenaline
NT is acetylcholine
Excitatory
inhibitory
Pupil Reflex
Reflex (just like pain reflex)
Cranial reflex (not tied to spinal cord)
Caused by acetylcholine (NT)
Use atropine – blocks acetylcholine
Axons of ciliary ganglion
stimulate the circular muscle of
the iris  contraction
Oculomotor nerves synapse on the ciliary ganglion (small circle)
From the pretectal
nucleus, a message is
sent to the EdingerWestphal nucleus
(triangle), whose axons
run along the
oculomotor nerves
back to the eye
Optic nerve receives
message from retina tin
back of eye
Optic nerve connects with pretectal
nucleus of brain stem (rectangle)
Definition of brain death:
Time when a physician(s) has determined that the brain and brain stem
have irreversibly lost all neurological function
Examination includes:
Movement of extremities: arms and legs are raised, let fall
Eye movement: eyes must remain fixed showing lack of
brain-to-motor-nerve reflex
Corneal reflex: must be absent
Pupil reflex: must be absent
Gag reflex: must be absent
Respiration (breathing) response: must be absent
Definition of brain death:
Time when a physician(s) has determined that the brain and brain stem
have irreversibly lost all neurological function
Cerebral blood flow (CBF) study
Radioactive isotope is injected into
bloodstream
Electroencephalogram (EEG)
Measures brain activity in microvolts
Very sensitive test
Cerebrum
Largest part of mature brain
Cerebral hemispheres covered in grey matter – cerebral cortex
No myelin sheath
Largest part of mature brain
75% body’s neurons
Tasks:
Reasoning
Language
Complex thought
Visual processing
Motor movement
Remembering
Speech
Correlation between body and brain size
Rough findings for vertebrates:
larger animal – smaller brain
Intelligence??
E = brain weight
S = body weight
C = constant
r = exponential constant
E = CSr
Establish relative brain capacity
Establish value “C” for each species  find EQ
(encephalization quotient)
Ratio between actual brain size and predicted
brain mass for an animal of a given size
EQ = C/average mammalian value
Greater cognitive ability, more advanced behavior associated with increase cerebral cortex
Limited space in skull  folding of cerebral cortex
Increase folding – more surface area – more
complex behaviors
Plans, executes
movements
Processes information
related to touch
Processes sensory information of
perceptions or multisensory
information
Coordinates
movements
Organizes thoughts,
solves problems, format
strategies
Processes visual information
Recognizes visual stimuli
Broca’s area: produces
speech, language
Understands written, spoken language
Detects sound quality
(loudness/tone)
Processes auditory
information
Ventral tegmental area synthesizes
dopamine – sends to nucleus
accumbens
Reward circuit
Responds to two NT
Dopamine – promotes desire
Production is associated with
anticipation of reward
Drugs can increase dopamine
production - addiction
Serotonin – inhibits desire
Left cerebral hemisphere receives sensory information from the right side of the body, vice versa
Myelinated neurons white matter
Left cerebral hemisphere controls muscle contraction in right side of the body, vice versa
Motor cortex controls voluntary movements
Stroke – occurs on left or right hemisphere
Due to blocked/ruptured blood vessels
Causes loss of oxygen
Location of paralysis pinpoints location of
stroke
Brain metabolism requires large energy inputs
Neurons always in state of high metabolic activity due to
Repair, rebuild, communication (requires 2x energy than normal cells)
Glucose primary energy source
Must be carried in by blood
Increase mental activity –
increase glucose intake
Age correlates to successfully
supply glucose intake to
neurons