HUMAN BRAIN
(Anatomy)

BRAIN FACTS & FIGURES

Average Brain Weights (in grams)
Species	Weight (g)		Species	Weight (g)
adult human	1,300 - 1,400		newborn human	350 - 400
sperm whale	7,800		fin whale	6,930
elephant	6,000		humpback whale	4,675
gray whale	4,317		killer whale	5,620
bowhead whale	2,738		pilot whale	2,670
bottle-nosed dolphin	1,500 - 1,600		walrus	1,020 - 1,126
Pithecanthropus Man	850 - 1,000		camel	762
giraffe	680		hippopotamus	582
leopard seal	542		horse	532
polar bear	498		gorilla	465 - 540
cow	425-458		chimpanzee	420
orangutan	370		California sea lion	363
manatee	360		tiger	263.5
lion	240		grizzly bear	234
sheep	140		baboon	137
adult rhesus monkey	90-97		dog (beagle)	72
aardvark	72		beaver	45
shark (great white)	34		shark (nurse)	32
cat	30		porcupine	25
squirrel monkey	22		marmot	17
rabbit	10-13		platypus	9
alligator	8.4		squirrel	7.6
opossum	6		flying lemur	6
fairy anteater	4.4		guinea pig	4
ring-necked pheasant	4.0		hedgehog	3.35
tree shrew	3		fairy armadillo	2.5
owl	2.2		grey partridge	1.9
rat (400 g body weight)	2		hamster	1.4
elephant shrew	1.3		house sparrow	1.0
european quail	0.9		turtle	0.3-0.7
bull frog	0.24		viper	0.1
goldfish	0.097		green lizard	0.08

Average number of neurons in the brain = 100 billion
Number of neurons in brain (octopus) = 300 million (from How Animals See, S. Sinclair, 1985)
Number of neurons in Aplysia nervous system = 18,000-20,000
Number of neurons in each segmental ganglia in the leech = 350
Volume of the brain of a locust = 6mm³ (from The Neurobiology of the Insect Brain, Burrows, M., 1996)
% of brain that is white matter = 60%
% of cerebral oxygen consumption by white matter = 6%
% of brain that is gray matter = 40%
% of cerebral oxygen consumption by gray matter = 94%
Average number of glial cells in brain = 10-50 times the number of neurons

(For more information about the number of neurons in the brain, see R.W. Williams and K. Herrup, Ann. Review Neuroscience, 11:423-453, 1988)

Number of neocortical neurons (females) = 19.3 billion (Pakkenberg, B., Pelvig, D., Marner,L., Bundgaard, M.J., Gundersen, H.J.G., Nyengaard, J.R. and Regeur, L. Aging and the human neocortex. Exp. Gerontology, 38:95-99, 2003 and Pakkenberg, B. and Gundersen, H.J.G. Neocortical neuron number in humans: effect of sex and age. J. Comp. Neurology, 384:312-320, 1997.)
Number of neocortical neurons (males) = 22.8 billion (Pakkenberg et al., 1997; 2003)
Average loss of neocortical neurons = 85,000 per day (~31 million per year) (Pakkenberg et al., 1997; 2003)
Average loss of neocortical neurons = 1 per second (Pakkenberg et al., 1997; 2003)
Average number of neocortical glial cells (young adults ) = 39 billion (Pakkenberg et al., 1997; 2003)
Average number of neocortical glial cells (older adults) =36 billion (Pakkenberg et al., 1997; 2003)
Length of myelinated nerve fibers in brain = 150,000-180,000 km (Pakkenberg et al., 1997; 2003)
Number of synapses in cortex = 0.15 quadrillion (Pakkenberg et al., 1997; 2003)
Difference number of neurons in the right and left hemispheres = 186 million MORE neurons on left side than right side (Pakkenberg et al., 1997; 2003)

	Proportion by Volume (%)
	Rat	Human
Cerebral Cortex	31	77
Diencephalon	7	4
Midbrain	6	4
Hindbrain	7	2
Cerebellum	10	10
Spinal Cord	35	2
(Reference: Trends in Neuroscience, November 1995)

Composition of Brain and Muscle
	Skeletal Muscle (%)	Whole Brain (%)
Water	75	77 to 78
Lipids	5	10 to 12
Protein	18 to 20	8
Carbohydrate	1	1
Soluble organic substances	3 to 5	2
Inorganic salts	1	1
(Reference: McIlwain, H. and Bachelard, H.S., Biochemistry and the Central Nervous System, Edinburgh: Churchill Livingstone, 1985)

Total surface area of the cerebral cortex = 2,500 cm² (2.5 ft²; A. Peters, and E.G. Jones, Cerebral Cortex, 1984)

Total surface area of the cerebral cortex (lesser shrew) = 0.8 cm²
Total surface area of the cerebral cortex (rat) = 6 cm²
Total surface area of the cerebral cortex (cat) = 83 cm²
Total surface area of the cerebral cortex (African elephant) = 6,300 cm²
Total surface area of the cerebral cortex (Bottlenosed dolphin) = 3,745 cm² (S.H. Ridgway, The Cetacean Central Nervous System, p. 221)
Total surface area of the cerebral cortex (pilot whale) = 5,800 cm²
Total surface area of the cerebral cortex (false killer whale) = 7,400 cm²
(Reference for surface area figures: Nieuwenhuys, R., Ten Donkelaar, H.J. and Nicholson, C., The Central nervous System of Vertebrates, Vol. 3, Berlin: Springer, 1998)
Total number of neurons in cerebral cortex = 10 billion (from G.M. Shepherd, The Synaptic Organization of the Brain, 1998, p. 6). However, C. Koch lists the total number of neurons in the cerebral cortex at 20 billion (Biophysics of Computation. Information Processing in Single Neurons, New York: Oxford Univ. Press, 1999, page 87).
Total number of synapses in cerebral cortex = 60 trillion (yes, trillion) (from G.M. Shepherd, The Synaptic Organization of the Brain, 1998, p. 6). However, C. Koch lists the total synapses in the cerebral cortex at 240 trillion (Biophysics of Computation. Information Processing in Single Neurons, New York: Oxford Univ. Press, 1999, page 87).

Percentage of total cerebral cortex volume (human): frontal lobe = 41%; temporal lobe = 22%; parietal lobe = 19%; occipital lobe = 18%. (Caviness Jr., et al. Cerebral Cortex, 8:372-384, 1998.)

Number of cortical layers = 6
Thickness of cerebral cortex = 1.5-4.5 mm
Thickness of cerebral cortex (Bottlenosed dolphin) = 1.3-1.8 mm (S.H. Ridgway, The Cetacean Central Nervous System, p. 221)

EEG - beta wave frequency = 13 to 30 Hz
EEG - alpha wave frequency = 8 to 13 Hz
EEG - theta wave frequency = 4 to 7 Hz
EEG - delta wave frequency = 0.5 to 4 Hz
World record, time without sleep = 264 hours (11 days) by Randy Gardner in 1965. Note: In Biopsychology (by J.P.J. Pinel, Boston: Allyn and Bacon, 2000, p. 322), the record for time awake is attributed to Mrs. Maureen Weston. She apparently spent 449 hours [18 days, 17 hours] awake in a rocking chair. The Guinness Book of World Records [1990] has the record belonging to Robert McDonald who spent 453 hours, 40 min in a rocking chair.
Time until unconsciousness after loss of blood supply to brain = 8-10 sec
Time until reflex loss after loss of blood supply to brain = 40-110 sec

Rate of neuron growth (early pregnancy) = 250,000 neurons/minute
Length of spiny terminals of a Purkinje cell = 40,700 micron
Number spines on a Purkinje cell dendritic branchlet = 61,000
Surface area of cerebellar cortex = 50,000 cm² (from G.M. Shepherd, The Synaptic Organization of the Brain, 1998, p. 255)
Number of Purkinje cells = 15-26 million
Number of synapses made on a Purkinje cell = up to 200,000
Weight of hypothalamus = 4 g
Volume of suprachiasmatic nucleus = 0.3 mm³
Number of fibers in pyramidal tract above decussation = 1,100,000
Number of fibers in corpus callosum = 250,000,000
Area of the corpus callosum (midsagittal section) = 6.2 cm²

Species	Cerebellum Weight (grams)	Body Weight (grams)
Mouse	0.09	58
Bat	0.09	30
Flying Fox	0.3	130
Pigeon	0.4	500
Guinea Pig	0.9	485
Squirrel	1.5	350
Chinchilla	1.7	500
Rabbit	1.9	1,800
Hare	2.3	3,000
Cat	5.3	3,500
Dog	6.0	3,500
Macaque	7.8	6,000
Sheep	21.5	25,000
Bovine	35.7	300,000
Human	142	60,000
Source: Sultan, F. and Braitenberg, V. Shapes and sizes of different mammalian cerebella. A study in quantitative comparative neuroanatomy. J. Hirnforsch., 34:79-92, 1993.

Total volume of cerebrospinal fluid = 125-150 ml
Half life of cerebrospinal fluid = 3 hours
Daily production of CSF = 400 to 500 ml
Specific gravity of cerebrospinal fluid = 1.007
Color of normal CSF = clear and colorless
White Blood cell count in CSF = 0-3 per mm³
Red Blood cell count in CSF = 0-5 per mm³
Normal intracranial pressure = 150 - 180 mm of water

Composition of Serum and Cerebrospinal Fluid (CSF)
	CSF	Serum
Water (%)	99	93
Protein (mg/dl)	35	7000
Glucose (mg/dl)	60	90
Osmolarity (mOsm/l)	295	295
Na (meq/l)	138	138
K (meq/l)	2.8	4.5
Ca (meq/l)	2.1	4.8
Mg (meq/l)	0.3	1.7
Cl (meq/l)	119	102
pH	7.33	7.41
(Reference: Fishman, R.A. Cerebrospinal Fluid in Disease of the Nervous System. Philadelphia: Saunders, 1980)

Number of cranial nerves = 12

I- olfactory

II- optic

Number of fibers in human optic nerve = 1,200,000
Number of fibers in cat optic nerve = 119,000
Number of fibers in albino rat optic nerve = 74,800
Length of optic nerve = 50 mm

Number of fibers in oculomotor nerve = 25,000-35,000

Number of fibers in trochlear nerve = 2,000-3,500
Number of neurons in nucleus of the trochlear nerve = 2,000-3,500

Number of fibers in motor root of trigeminal nerve = 8,100
Number of fibers in sensory root of trigeminal nerve = 140,000

Number of fibers in abducens nerve (at exit from brain stem) = 3,700

Number of fibers in facial nerve (at exit from brain stem) = 9,000-10,000
Length of nucleus of the facial nerve = 2 to 5.6 mm
Number of neurons in nucleus of the facial nerve = 7,000

Length of dorsal motor nucleus of the vagus nerve = 10 mm

Number of neurons in nucleus of the hypoglossal nerve = 4,500-7,500
Length of nucleus of the hypoglossal nerve = 10 mm