A2 Biology – The nervous system The structure and function of the brain.

A2 Biology – The nervous system

The structure and function of the brain

By the end of this lesson I will be able to:

• Describe the gross structure of the brain.

• Outline the functions of the cerebrum, hypothalamus, cerebellum and the medulla oblongata.

The Brain – some The Brain – some facts!facts!

• weighs 1300 - 1400 g

• made up of about 100 billion neurons

• “the most complex living structure on the universe” Society for Neuroscience

• makes us who we are

Why is it appropriate to say the weight of the brain determines

intelligence?

Animal Wt. of Brain Brain/Body wt ratio

• Whale 15 lbs 1/10000

• Elephant 13 lbs 1/1000

• Human 3 lbs 1/50

The human brain is more developed and has a larger weight in proportion to total body weight.

Very basic brain Very basic brain structurestructure

Cerebrum

cerebellum

hypothalamus

Pituitary glandMedulla oblongata

If our brain is so important, how do we protect it?

• Cranium (skull bones)• Meninges (protective membrane that surrounds the

brain)What about our spinal cord?• Protected by bones called vertebrae

The Vertebrate Brain

• Forebrain– •cerebrum~memory, learning,

emotion

– •cerebral cortex~sensory and motor nerve cell bodies

– •corpus callosum~connects left and right hemispheres

– •thalamus; hypothalamus

• Midbrain •inferior (auditory) and

superior (visual) colliculi• Hindbrain

•cerebellum~coordination of movement •medulla oblongata/ pons~autonomic, homeostatic functions

Parts of the Cerebrum

Words and Colors

• Read the image aloud--but rather than reading the words, say the colour of the ink that was used to write each word. It's not easy; the written words have a surprisingly strong influence over the actual colour.

Do you see the Phantom Spots?

• You may see spots where the white lines intersect, but if you try looking right at one, it will disappear. The spots, of course, aren't really there. They're caused by the way your eyes respond to light and dark areas. When an area is surround by light, your eye compensates by "turning down" the brightness a bit, making you see darkened blobs. In this grid, the areas surrounded by the most white are at the intersections of the white lines. Since this phenomenon works best in your peripheral vision, the spots disappear when you look right at them.

• Left & Right sides are separate

• Corpus Callosum : major pathway between hemispheres

• Some functions are ‘lateralized’– language on left– math, music on right

• Lateralization is never 100%

Brain has 2 Hemispheres

LeftHemisphere

Corpus callosumRight

Hemisphere

Right versus left Cerebrum

Sensory Information sent to opposite hemisphere

• Principle is Contralateral Organisation

• Sensory data crosses over in pathways leading to the cortex

• Visual Crossover– left visual field to right

hemisphere– right field to left

• Other senses similar

Left visualfield

Right visualfield

Opticnerves

CorpusCallosum

Left VisualCortex

Right VisualCortex

Contralateral Motor Control• Movements

controlled by motor area

• Right hemisphere controls left side of body

• Left hemisphere controls right side

• Motor nerves cross sides in spinal cord

Somatosensory CortexMotor Cortex

Each hemisphere is divided into 4 lobes

Frontal

Parietal

Occipital

Temporal

Corpus Callosum• Major ( but not only)

pathway between sides• Connects comparable

structures on each side• Permits data received on

one side to be processed in both hemispheres

• Aids motor coordination of left and right side

Corpus Callosum

Medial surface of right hemisphere

Corpus Callosum

• What happens when the corpus callosum is cut?

• Sensory inputs are still crossed

• Motor outputs are still crossed

• Hemispheres can’t exchange data

The ‘Split Brain’ studies• Surgery for epilepsy :

cut the corpus callosum

• Roger Sperry, 1960’s• Special apparatus

– picture input to just one side of brain

– screen blocks objects on table from view Nonverbal

righthemisphere

Verballefthemisphere

Nonverbalrighthemisphere

Verballefthemisphere

??

“What didyou see?”

• Picture to left brain– can name the object– left hand cannot

identify by touch

• Picture to right brain– can’t name the object

– left hand can identify by touch

“Using your left hand,Pick up what you saw.”

The ‘Split Brain’ studies

I saw anapple.

“What didyou see?”

Nonverbalrighthemisphere

Verballefthemisphere

Localisation of function

Frontal

Parietal

Occipital

Temporal

Occipital Lobe

• Input from Optic nerve

• Contains primary visual cortex– most is on surface

inside central fissure

• Outputs to parietal and temporal lobes

OccipitalLobe

VisualLobe

Temporal Lobe

• Inputs are auditory, visual patterns– speech recognition– face recognition– word recognition– memory formation

• Outputs to limbic System, basal Ganglia, and brainstem

Contains primary auditory area

TemporalLobe

TemporalLobe

AuditoryCortex

ParietalLobe

SomatosensoryCortex

Parietal Lobe

• Inputs from multiple senses

contains primary somatosensory cortex

borders visual & auditory cortex

Outputs to Frontal lobe

hand-eye coordination

eye movements

attention

FrontalLobe

Frontal Lobe

• Contains primary motor cortex

MotorCortexMotorCortexBroca’s

Area

MotorCortex

WorkingMemory

• No direct sensory input

• Important planning and sequencing areas

Broca’s area for speech

• Prefrontal area for working memory

Frontal Lobe Disorders

• Broca’s area– productive aphasia

• Prefrontal area– lose track of ongoing context– fail to inhibit inappropriate responses

• Often measured with the Wisconsin Card Sorting Task

Wisconsin Card Sorting Task

• Patient is given a deck of 64 different cards

• Told to place each card under the one it best matches

• Told correct or incorrect after each card

• Row of 4 example cards set out

• Must deduce what the underlying rule is.

Correct!

Hypothalamus

• Controls autonomic NS and some endocrine glands.

• Hypothalamus Controls Temperature

• The hypothalamus is like your brain's inner thermostat.

• Your body should be (about 98.6 degrees Fahrenheit or 37 degrees Celsius).

• If your body is too hot, the hypothalamus tells it to sweat.

• If you're too cold, the hypothalamus gets you shivering..

The pituitary gland

• The pituitary gland is very small - only about the size of a pea!

• Its job is to produce and release hormones into your body.

• This gland is a big player in puberty too.

The cerebellum the very basics!• Next up is the cerebellum. • It controls balance, movement, and

coordination (how your muscles work together).

• Because of your cerebellum, you can stand upright, keep your balance, and move around.

• Think about a surfer riding the waves on his board. What does he need most to stay balanced? The best surfboard? The coolest wetsuit? Nope - he needs his cerebellum!

The medulla oblongata

• Controls breathing, heart rate and blood pressure