Brain Facts and FiguresBrain Facts and FiguresThese 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 |
 SPINAL CORD |
 NEURON |
 SENSORY APPARATUS |
 BLOOD SUPPLY |
Species Weight (gm) ------- ----------- adult human 1,300 - 1,400 (about 3 pounds) newborn human 350 - 400 sperm whale 7,800 elephant 6,000 bottle-nosed dolphin 1,500 walrus 1,126 Pithecanthropus Man 850 - 1,000 camel 762 giraffe 680 hippopotamus 582 horse 532 polar bear 498 gorilla 465 - 540 cow 425-458 chimpanzee 420 orangutan 370 tiger 263.5 lion 240 grizzly bear 234 sheep 140 baboon 137 adult rhesus monkey 90-97 dog (beagle) 72 aardvark 72 beaver 45 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 hedgehog 3.35 tree shrew 3 fairy armadillo 2.5 owl 2.2 rat (400gm body weight) 2 hamster 1.4 elephant shrew 1.3 turtle 0.3 bull frog 0.24 viper 0.1 green lizard 0.08
Reference for many of these brain weights:
Average number of neurons in the brain = 100 billion
Number of neurons in brain (octopus) = 170 million
Number of neurons in Aplysia nervous system = 18,000-20,000
Number of neurons in each segmental ganglia in the leech = 350
% 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)
Proportion by Volume(%) ----------------------- Rat Human --- ----- Cerebral Cortex 31 77 Basal Ganglia 7 4 Diencephalon 6 4 Midbrain 4 1 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 78
Lipids 4 10
Protein 18 8
Carbohydrate 1 1
Inorganic salts 1 1
Other 3-5 2
(Reference: McIlwain, H. Biochemistry and the central nervous system.
Boston, Little, Brown, 1959)
Total surface area of the cerebral cortex = 2200-2400 sq. cm (2.5 sq.ft.)
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.
cm
Total surface area of the cerebral cortex (pilot whale) = 5,800 sq. cm
Total number of neurons in cerebral cortex = 10 billion (from
G.M. Shepard, The Synaptic Organization of the Brain, 1998, p. 6)
Total number of synapses in cerebral cortex = 60 trillion (yes, trillion)
(from G.M. Shepard, The Synaptic Organization of the Brain,
1998, p. 6)
Number of cortical layers = 6
Thickness of cerebral cortex = 1.5-4.5 mm
EEG - alpha wave frequency = 8 to 12 Hz
EEG - theta wave frequency = 3 to 7 Hz
EEG - delta wave frequency = 0.5 to 2 Hz
World record, time without sleep = 264 hours (11 days) by Randy Gardner
in 1963
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
Combined synaptic surface area of dendritic branchlet = 222,000 sq. micron
Weight of adult human cerebellum = 150 gm
Surface area of cerebellar cortex = 50,000 sq. cm (from G.M.
Shepard, The Synaptic Organization of the Brain, 1998, p. 255)
Weight of newborn human cerebellum = 21 gm
Number of Purkinje cells = 15-26 million
Number of synapses made on a Purkinje cell = up to 200,000
Weight of hypothalamus = 4 gm
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
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
More on Cranial
Nerves
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 = 13,500,000
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 gm
Weight of rabbit spinal cord = 4 gm
Weight of rat spinal cord (400 gm body weight) = 0.7 gm
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
Number of hair cells in cochlea = 3500 inner hair cells; 12-20,000 outer
hair cells
Number of fibers in auditory nerve = 28,000-30,000
Number of neurons in medial geniculate body = 570,000
Number of neurons in auditory cortex = 100,000,000
Hearing Range (young adult human) = 20 Hz to 20,000 Hz
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
Auditory Pain Threshold = 130 db
Threshold for hearing damage = 90 db for an extended period of time
Decibel Sound Scale
----------------------------
Decibles Sound
-------- ---------------
160 Jet plane engine
130 Pain threshold
120 Discomfort
100 Subway
80 Heavy motor vehicle traffice
60 Normal conversation
20 Whisper conversation
0 Threshold of hearing
Total number of human taste buds (tongue, palate, cheeks) = 10,000
Number of taste buds on the tongue = 9,000
Number of receptors on each taste bud = 50-150
Diameter of taste receptor = 10 micron
Diameter of taste fiber = less than 4 micron
Taste threshold for quinine sulfate = 3.376 mg/liter water
Number of human olfactory receptor cells = 40 million
Number of rabbit olfactory receptor cells = 100 million
Number of dog olfactory receptor cells = 1 billion
Area of olfactory mucosa per nostril = 2.5 sq. cm
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
Length of eyeball = 24.5 mm
Average time between blinks = 2.8 seconds
Average duration of a single blink = 0.3 seconds
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 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
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
More Facts and
Figures about the Human Retina from WebVision.
Weight of skin (adult human) = 6 lb.(2.7 kg)
Area of skin (adult human) = 20 sq. ft.
Number of tactile receptors in the hand = 17,000
Number of nerve endings in hand = 1,300 per sq. in.
von Frey threshold (Face) = 5 mg
2 point threshold (Finger) = 2-3 mm
Length of Meissner corpuscle = 90 - 120 micron
Density of receptors on finger tips = 2,500 per sq.cm
Density of Meissner's corpuscles on finger tips = 1,500 per sq. cm
Density of Merkel's cells on finger tips = 750 per sq. cm
Density of Pacinian corpuscles on finger tips = 75 per sq. cm
Density of Ruffini's corpuscles on finger tips = 75 per sq. cm
Thermal pain threshold = 45 degrees centigrade
Neurons
Number of synapses for a "typical" neuron = 1,000 to 10,000
Diameter of neuron = 4 micron (granule cell) to 100 micron (motor neuron
in cord)
Diameter of neuron nucleus = 3 to 18 micron
Length of Giraffe primary afferent axon (from toe to neck) = 15 feet
Resting potential of squid giant axon = -70 mV
Conduction velocity of action potential = 0.6-120 m/s (1.2-250 miles/hr)
Single sodium pump maximum transport rate = 200 Na ions/sec; 130 K ions/sec
Typical number of sodium pumps = 1000 pumps/square micron of membrane surface
(from Willis and Grossman, Medical Neurobiology, Mosby,
St. Louis, 1981, p. 36)
Total number of sodium pumps for a small neuron = 1 million
Density of sodium channels (squid giant axon) = 300 per sq. micron (from Hille, B., Ionic Channels of Excitable Membranes, Sinauer,
Sunderland, 1984, p. 210.)
Number of voltage-gated sodium channels at each node = 1,000 to 2,000 per
sq. micron (from Nolte, J., The Human Brain, Mosby,
1999, p. 163.)
Number of voltage-gated sodium channels between nodes = 25 per sq. micron
(from Nolte, J., The Human Brain, Mosby, 1999, p. 163.)
Number of voltage-gated sodium channels in unmyelinated axon = 100 to 200
per sq. micron (from Nolte, J., The Human Brain, Mosby,
1999, p. 163.)
Diameter of microtubule = 20 nanometer
Diameter of microfilament = 5 nanometer
Diameter of neurofilament = 10 nanometer
Thickness of neuronal membrane = 5 nanometer
Thickness of squid giant axon membrane = 50-100 A
Typical synaptic cleft distance = 10-20 nanometers across
% neurons stained by Golgi
method = 5%
Slow axoplasmic transport rate = .2-4 mm/day (actin, tubulin)
Intermediate axoplasmic transport rate = 15-50 mm/day (mitochondrial protein)
Fast axoplasmic transport rate = 200-400 mm/day (peptides, glyolipids)
Number of molecules of neurotransmitter in one synaptic vesicle = 10,000-100,000
Diameter of synaptic vesicle = 50 nanometer (small); 70-200 nanometer (large)
Diameter of neurofilament = 7 - 10 nm
Diameter of microtubule = 25 nm
Internodal Length = 150 - 1500 microns (depends on fiber diameter
% composition of myelin = 70-80% lipid; 20-30% protein
% brain utilization of total resting oxygen = 20%
% blood flow from heart to brain = 15-20%
Blood flow through whole brain (adult) = 750 ml/min
Blood flow through whole brain (adult) = 54 ml/100 gm/min
Blood flow through whole brain (child) = 105 ml/100 gm/min
Oxygen consumption whole brain = 46 cubic cm/min
Oxygen consumption whole brain = 3.3 ml/100 gm/min
Blood flow rate through each internal carotid artery = 180 ml/min
Blood flow rate through basilar artery = 380 ml/min
Diameter of vertebral artery = 2-3 mm
Diameter of common carotid artery (adult) = 6 mm
Diameter of common carotid artery (newborn) = 2.5 mm