The Brain

Some interesting brain factsBrain weighs 3 lbs

However, it is completely immersed in liquid (cerebrospinal fluid) and, as a result, its effective weight is 3 ounces.

Brain uses 20% of the body’s blood, 20% of its oxygen, and 70% of its glucose.

80% of the human brain is cortex Cortex is virtually absent in fish, reptiles, and birds 1/3 of the cortex is visible Cortex is 1/8” thick and, if spread out flat, is about the size of 1

sheet of newspaper (4 pages of a textbook)Localization of function vs. equipotentiality (mass action)

Broca’s area is in the frontal lobe; when destroyed, patient cannot produce language, but can comprehend language; Broca’s aphasia

Wernicke’s area is in the temporal lobe; when destroyed patient cannot comprehend language, but can produce language; Wernicke’s aphasia

Direction in the brain We are symmetrical around our midline: we have a left arm and a

right arm, a left ear and a right ear, etc. Medial: close to the midline Lateral: farther from the midline; closer to the “side” of the head

Some brain structure terminologySulcus (pl. sulci): any of the shallow grooves separating the

convolutions (bumps, ridges) on the surface of the brainFissure: a very deep groove that, typically, separates major

cortical structuresGyrus (pl. gyri): a convolution (bump, ridge) on the brain

surfaceCommisures: a fiber bundle that interconnects

corresponding regions on each side of the brainWhite matter (mylinated axons) and gray matter (cell

bodies)Cortical structures are specialized parts of the cortex.

Everything else under the cortex, but above the brainstem, is referred to as a subcortical structure.

Some brain organization terminologyHemispheres

The two relatively symmetrical halves of the brain; one on the left and one on the right

Contralaterality The left hemisphere receives sensory input from, and sends motor

messages to, the right side of the body; vice versa for the right hemisphere

Cerebral lateralization (hemispheric specialization) Instances in which one of the hemispheres is more responsible for

a particular cognitive function than the other hemisphere• Left hemisphere specialized for language and analytical thought• Right hemisphere specialized for visual-spatial tasks, music, face

recognition, and emotional statesCerebral dominance

In 90% of human beings, the left hemisphere is specialized for language and these individuals are right-handed; thus, the left hemisphere is said to be the dominant hemisphere

Brainstem Medulla

Vital involuntary functions

Pons Sleep and arousal

Reticular formation

Sleep, arousal, attention

Cerebellum Motor coordination Also involved in

planning, memory, language, and emotion

Another view of the brainstem

Limbic System I: Emotion and motivation

Hypothalamus Regulates

• Glands• Autonomic

system• Eating• Drinking• Sleeping• Sexual activity

Plays a role in emotion

Amygdala Forms learned

associations between objects and emotion, especially fear

Limbic system II: Cognitive functions

Thalamus Sensory relay

station

Hippocampus Formation of new

memories

Basal ganglia Putamen, globus

pallidus, caudate nucleus

Motor behavior Habit learning

Another view of both the limbic system and brain stem

Neglect Syndrome (Hemineglect)

A patient with a stroke in the right hemisphere was asked to copy the model drawings

Typical of neglect syndromes, the left side of the model is almost completely ignored

Primary motor cortex and somatosensory cortex

TheNervousSystem

The Autonomic Nervous System

“Fight or Flight” Restore Calm

The Endocrine System Endocrine system:

Ductless glands that regulate growth, reproduction, metabolism, mood, and some behavior

Hormones: chemical messengers secreted into the bloodstream

Chain of command Hypothalamus

commands the pituitary, which in turn releases hormones that command the other glands to release their hormones

Brain Change Plasticity

A property of the brain that allows it to change as a result of experience, drugs, or injury

Chemical signals guide growing connections. Experience fine-tunes neural connections.

Critical periods Rats in special environments have heavier brains with more synaptic

connections Change in the strength of connections underlies learning

Hebbian learning: “fire together, wire together” Neurogenesis: production of new brain cells in the adult brain Brain reorganization in response to overuse or underuse

Devoting more cortex to information that is pertinent for tasks at hand • Blind people who read Braille have much larger areas of cortex devoted to receiving

input from index fingers than do sighted individuals Brain reorganization in response to brain injury

Much more likely to occur in the young Treatment for brain injury or disease

Neural grafting, using stem cells