The Brain

The Brain StemCorpus Callosum

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• smallest and from an evolutionary viewpoint, the oldest and most primitive part of the brain.

• continuous with the spinal cord, and is composed of the parts of the hindbrain and midbrain.

• The medulla oblongata and pons control heart rate, constriction of blood vessels, digestion, swallowing, vomitting and respiration.

• The midbrain consists of connections between the hindbrain and forebrain, & visual and auditory reflexes. Mammals use this part of the brain only for eye reflexes.

The Brain Stem

• The Reticular System, Arousal, and Sleep.– The reticular activating system (RAS) of the reticular

formation.• Regulates sleep

and arousal.• Acts as a

sensory filter.

CerebellumCorpus Callosum

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Cerebellum

• 3rd part of the hindbrain, but it is not considered part of the brain stem.

• Functions include fine motor coordination and body movement, posture, and balance.

• This region of the brain is enlarged in birds and controls muscle action needed for flight.

FOREBRAIN

Divided into 2 general regions:

•Diencephalon•Cerebrum

Corpus Callosum

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Diencephalon

• The thalamus and hypothalamus are the parts of the diencephalon.

• The thalamus acts as a switching center for nerve messages.

• The hypothalamus is a major homeostatic center having both nervous and endocrine functions for control of hormones.

Cerebrum

• largest part of the human brain, is divided into left and right hemispheres connected to each other by the corpus callosum.

• hemispheres are covered by a thin layer of gray matter known as the cerebral cortex, the most recently evolved region of the vertebrate brain.

• Fish have no cerebral cortex, amphibians and reptiles have only rudiments of this area.

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The cortex in each hemisphere of the cerebrum is between 1 and 4 mm thick. Folds divide the cortex into four lobes: occipital, temporal, parietal, and frontal. No region of the brain functions alone, although major functions of various parts of the lobes have been determined.

Sensory Regions of the Cerebrum

Frontal Lobe•Speech•Emotions•Motor control

Parietal Lobe•Speech•Somatosensory Areas & taste•Reading

Temporal Lobe•Smell•hearing

Occipital Lobe•vision

Motor Cortex Map•Developed by Dr. William Penfield (Canadian from McGill Univ.)•Maps motor (or sensory areas) on the cerebral cortex of each hemisphere of the brain.•Each hemisphere of the brain controls the opposite sides of the body.

HOMUNCULUS MODELS•Homunculus models are sculptures of the human body•each body part is shown in proportion to the amount of brain area dedicated to its motor control or sensory control

What does the homunculus tell us?

1. The human brain is ‘heavy handed’.– WHY?

2. Mouth parts are also very important.– WHY?

What about other animals?Platypus

Brain ComparisonsEQ

Brain to Body size Ratio

Development of Cerebral Cortex

Endocasts