Brain Facts and Figures

These data were obtained from several textbooks. Note that all data are estimates and averages. Check literature for appropriate references. All numbers are for humans unless otherwise indicated.



Brain

 

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

Reference for many of these brain weights:

  1. Blinkov, S.M. and Glezer, I.I. The Human Brain in Figures and Tables. A Quantitative Handbook, New York: Plenum Press, 1968.
  2. Demski, L.S. and Northcutt, R.G. The brain and cranial nerves of the white shark: an evolutionary perspective. In Great White Sharks. The Biology of Carcharodon carcharias, San Diego: Academic Press, 1996.
  3. Nieuwenhuys, R., Ten Donkelaar, H.J. and Nicholson, C. The Central Nervous System of Vertebrates. Vol. 3, Berlin: Springer, 1998.
  4. Berta, A., et al. Marine Mammals. Evolutionary Biology, San Diego: Academic Press, 1999.
  5. Mink, J.W., Blumenschine, R.J. and Adams, D.B. Ratio of central nervous system to body metabolism in vertebrates: its constancy and functional basis. Am. J. Physiology, 241:R203-R212, 1981.
  6. Rehkamper, G., Frahm, H.D. and Zilles, K. Quantitative development of brain and brain structures in birds (Galliformes and Passeriforms) compared to that in mammals (Insectivores and Primates). Brain Beh. Evol., 37:125-143, 1991.
  7. Ridgway, S.H. and Harrison, S., Handbook of Marine Mammals, Vol. 3, London: Academic Press, 1985.

% brain of total body weight (150 pound human) = 2%
Average brain width = 140 mm
Average brain length = 167 mm
Average brain height = 93 mm

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 on 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 sq. cm (2.5 sq.ft.; A. Peters, and E.G. Jones, Cerebral Cortex, 1984)

Total surface area of the cerebral cortex (lesser shrew) = 0.8 sq. cm
Total surface area of the cerebral cortex (rat) = 6 sq. cm
Total surface area of the cerebral cortex (cat) = 83 sq. cm
Total surface area of the cerebral cortex (African elephant) = 6,300 sq.
Total surface area of the cerebral cortex (Bottlenosed dolphin) = 3,745 sq. cm (S.H. Ridgway, The Cetacean Central Nervous System, p. 221)
Total surface area of the cerebral cortex (pilot whale) = 5,800 sq. cm
Total surface area of the cerebral cortex (false killer whale) = 7,400 sq. cm
(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 sq. cm (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 cubic mm
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 sq. cm

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 cubic mm.
Red Blood cell count in CSF = 0-5 per cubic mm.
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

III- oculomotor

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

IV- trochlear

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

V- trigeminal

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

VI- abducens

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

VII- facial

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

VIII-vestibulocochlear
IX- glossopharyngeal
X- vagus

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

XI- spinal accessory
XII- hypoglossal

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


Spinal Cord

Number of neurons in human spinal cord = 1 billion (from Kalat, J.W., Biological Psychology, 6th Edition, 1998, page 24)
Length of human spinal cord = 45 cm (male); 43 cm (female)
Length of human vertebral column = 70 cm
Length of cat spinal cord = 34 cm
Length of rabbit spinal cord = 18 cm

Weight of human spinal cord = 35 g
Weight of rabbit spinal cord = 4 g
Weight of rat spinal cord (400 g body weight) = 0.7 g
Maximal Circumference of cervical enlargement = 38 mm
Maximal Circumference of lumbar enlargement = 35 mm
Pairs of Spinal Nerves = 31
Number of Spinal Cord segments = 31

8 cervical segments
12 thoracic segments
5 lumbar segments
5 sacral segments
1 coccygeal segment


Sensory Apparatus

Audition

Surface area of the tympanic membrane = 85mm2 (Statistics from "Hearing. Its Physiology and Pathophysiology" by A.R. Moller, San Diego, Academic Press, 2000.)
Length of the eustachian tube = 3.5 to 3.9 cm (Statistics from "Hearing. Its Physiology and Pathophysiology" by A.R. Moller, San Diego, Academic Press, 2000.)
Number of hair cells in cochlea = 10,000 inner hair cells; 30,000 outer hair cells (Statistics from "Hearing. Its Physiology and Pathophysiology" by A.R. Moller, San Diego, Academic Press, 2000. However, in the same book, Moller states that there are only 3,500 inner hair cells and 12,000 outer hair cells.)
Number of fibers in auditory nerve = 28,000-30,000
Length of auditory nerve = 2.5 cm
Number of neurons in cochlear nuclei = 8,800 (Northern, J.L. and Downs, M.P., Hearing in Children, 5th edition, Philadelphia: Lippincott Williams & Wilkins, 2002.)
Number of neurons in inferior colliculus = 392,000 (Northern, J.L. and Downs, M.P., Hearing in Children, 5th edition, Philadelphia: Lippincott Williams & Wilkins, 2002.)
Number of neurons in medial geniculate body = 570,000
Number of neurons in auditory cortex = 100,000,000
Hearing Range (young adult human) = 20 to 20,000 Hz
Hearing Range (elderly human) = 50 to 8,000 Hz (Guyton, A.C., Textbook of Medical Physiology, 1986)
Hearing Range (rat) = 1,000 to 50,000 Hz
Hearing Range (cat) = 100 to 60,000 Hz
Most sensitive range of human hearing = 1,000-4,000 Hz
Length of external auditory meatus = 2.7 cm
Diameter of external auditory meatus = 0.7 cm
Weight of malleus = 23 mg
Weight of incus = 25 mg
Weight of stapes = 2-4 mg
Length of cochlea = 35 mm
Width of cochlea = 10 mm
Number of turns in the cochlea = 2.2-2.9
Length of basilar membrane = 25-35 mm
Width of basilar membrane = 150 microns (at base of cochlea) (Statistic from "Hearing. Its Physiology and Pathophysiology" by A.R. Moller, San Diego, Academic Press, 2000.)
Auditory Pain Threshold = 130 db
Threshold for hearing damage = 90 db for an extended period of time

Decibel Sound Scale

Decibels

Sound

160

Jet plane engine

130

Pain threshold

120

Discomfort

100

Subway

80

Heavy motor vehicle traffic

60

Normal conversation

20

Whisper conversation

0

Threshold of hearing

Taste

Total number of human taste buds (tongue, palate, cheeks) = 10,000
Number of taste buds on the tongue = 9,000
Height of taste bud = 50-100 microns (From: Farbman, A.I., Taste Bud, in G. Adelman, eds., Encyclopedia of Neuroscience, 1987)
Diameter of taste bud = 30-60 microns (From: Farbman, A.I.)
Number of receptors on each taste bud = 50-150 (Boron, W.F. and Boulpaep, E.L., Medical Physiology. A Cellular and Molecular Approach, Philadelphia: Saunders, 2003)
Diameter of taste receptor = 10 micron
Diameter of taste fiber = less than 4 micron
Taste threshold for quinine sulfate = 3.376 mg/liter water

Smell

Number of human olfactory receptor cells = 40 million
Number of rabbit olfactory receptor cells = 100 million
Number of dog olfactory receptor cells = 1 billion
Surface area of olfactory epithelium (contains olfactory receptor cells) in humans = 10 cm2 (Bear, M.F., Connors, B.W. and Pradiso, M.A., Neuroscience: Exploring the Brain, 2nd edition, Baltimore: Lippincott Williams and Wilkins, 2001, p. 269)
Area of olfactory epithelium in some dogs = 170 cm2 (Bear, M.F., Connors, B.W. and Pradiso, M.A., Neuroscience: Exploring the Brain, 2nd edition, Baltimore: Lippincott Williams and Wilkins, 2001, p. 269)
Area of olfactory epithelium in cats = 21 sq. cm (Bradshaw, J., Behavioral biology, in The Waltham Book of Dog and Cat Behaviour, ed. C. Thorne, Oxford: Pergamon Press, 1992)
Thickness of olfactory epithelium mucous layer = 20-50 microns. (Boron and Boulpaep, 2003)
Diameter of olfactory receptor axons = 0.1-0.2 micron
Diameter of distal end olfactory receptor cell = 1 micron
Diameter of olfactory receptor cell = 40-50 micron
Number of cilia per olfactory receptor cell = 10-30
Length of cilia on olfactory receptor cell = 100-150 micron
Concentration for detection threshold of musk = 0.00004 mg/liter air

Vision

Length of eyeball = 24.5 mm (from Spaide, R.F., 1999)
Volume of eyeball = 5.5 cm3
Weight of eyeball = 7.5 g
Average time between blinks = 2.8 seconds
Average duration of a single blink = 0.1-0.4 seconds (Schiffman, H.R., Sensation and Perception. An Integrated Approach, New York: John Wiley and Sons, Inc., 2001)
Thickness of cornea = 0.54 mm in center; 0.65 in periphery
Diameter of cornea = 11.5 mm
Thickness of lens = 4 mm
Diameter of lens = 9 mm
Composition of lens = 65% water; 35% protein
Number of retinal receptor cells = 5-6 million cones; 120-140 million rods
Number of retinal ganglion cells = 800 thousand to 1 million
Density of cones in fovea = 200,000 per square mm
Peak density of rods = 175,000 per square mm
Peak density of rods (cat) = 400,000 per square mm
Number of fibers in optic nerve = 1,200,000
Number of neurons in lateral geniculate body = 570,000
Number of cells in visual cortex (area 17) = 538,000,000
Wavelength of visible light (human) = 400-700 nm
Amount of light necessary to excite a rod = 1 photon
Amount of light necessary to excite a cone = 100 photons
Location of the greatest density of rods = 20 degrees from fovea
Highest density of rods = 160,000 per mm2
Density of cones in fovea = 200,000 per mm2
Diameter of fovea = 1.5 mm
Intraocular pressure = 10-20 mm Hg
Volume of orbit = 30 ml
Area of retina = 2,500 square mm
Thickness of retina = 120 microns (ranges from 100 to 230 microns)
Production rate of aqueous humor = 2 microliters/min
Turnover of aqueous humor = 15 times/day
% volume of eye occupied by the vitreous = 80%
Maximal sensitivity of red cones = 570 nm
Maximal sensitivity of green cones = 540 nm
Maximal sensitivity of blue cones = 440 nm
More Facts and Figures about the Human Retina from WebVision.

Touch

Weight of skin (adult human) = 9 lb.(4-5 kg) (Source: Schiffman, H.R., Sensation and Perc