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

Hypothalamus: Maintains homeostasis, coordinates nervous/endocrine systems, secretes hormones Cerebral Hemisphere: Integrating center for high complex functions – learning, memory, emotions Cerebellum: Two hemispheres, highly folded surface, coordinates unconscious functions (balance and movement) Pituitary gland: Posterior lobe – stores, releases hormones regulating body functions 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 Right Hemisphere: Helps understand words Specializes in receiving and analyzing information Lesions – problems identifying faces, locating objects in space (spacial awareness) Broca’s area – interferes with vocalizing words Wernicke’s area – affects ability of creating sentences

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

Oculomotor nerves synapse on the ciliary ganglion (small circle) Axons of ciliary ganglion stimulate the circular muscle of the iris  contraction From the pretectal nucleus, a message is sent to the Edinger-Westphal 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 Coordinates movements Processes sensory information of perceptions or multisensory information 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 Serotonin – inhibits desire Production is associated with anticipation of reward Drugs can increase dopamine production - addiction

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