Glossary
735
nuclear chain fi
ber
specialized stretch receptor in
skeletal muscle spindles that responds in direct
proportion to the length of a muscle
nuclear envelope
double membrane surrounding
cell nucleus
nuclear pore
opening in nuclear envelope
through which molecular messengers pass
between nucleus and cytoplasm
nucleic acid
(noo-KLAY-ik) nucleotide polymer
in which phosphate of one nucleotide is
linked to the sugar of the adjacent one; stores
and transmits genetic information; includes
DNA and RNA
nucleolus
(noo-KLEE-oh-lus) densely staining
nuclear region containing portions of DNA
that code for ribosomal proteins
nucleosome
(NOO-clee-oh-some) nuclear
complexes of several histones and their
associated coils of DNA
nucleotide
(NOO-klee-oh-tide) molecular
subunit of nucleic acid; purine or pyrimidine
base, sugar, and phosphate
nucleus
(NOO-klee-us) (pl. nuclei) (cell) large
membrane-bound organelle that contains cell’s
DNA; (neural) cluster of neuron cell bodies in
CNS
O
obligatory water loss
minimal amount of water
required to excrete waste products
occipital lobe
(ok-SIP-ih-tul) posterior region of
cerebral cortex where primary visual cortex is
located
odorant
molecule received by the olfactory system
that induces a sensation of smell
Ohm’s law
current (
I
) is directly proportional
to voltage (
E
) and inversely proportional to
resistance (
R
) such that
I = E/R
olfaction
(ol-FAK-shun) sense of smell
olfactory
(ol-FAK-tor-ee) pertaining to sense of
smell
olfactory bulb
(ohl-FAK-tor-ee) anterior
protuberance of the brain containing cells that
process odor inputs
olfactory cortex
region on the inferior and medial
surface of the frontal lobe of the cerebral
cortex where information about the sense of
smell is processed
olfactory epithelium
mucous membrane in upper
part of nasal cavity containing receptors for
sense of smell
oligodendrocyte
(oh-lih-goh-DEN-droh-site)
type of glial cell; responsible for myelin
formation in CNS
oncogene
(ON-koh-jeen) altered gene that can
lead to cancer
oogenesis
(oh-uh-JEN-ih-sis) gamete production
in female
oogonium
(oh-uh-GOH-nee-um) primitive germ
cell that gives rise to primary oocyte
opioid
(OH-pee-oid)
see
endogenous opioid
opponent color cell
ganglion cells in the retina
that are inhibited by input from one type of
cone photoreceptor but activated by another
type of cone photoreceptor
opsin
(OP-sin) protein component of
photopigment
opsonin
(op-SOH-nin) any substance that binds
a microbe to a phagocyte and promotes
phagocytosis
opthalmoscope
medical instrument with
magnifying lenses and light, designed for
viewing the interior of the eye through the pupil
optic chiasm
(KYE-azm) place at base of brain at
which optic nerves meet; some neurons cross
here to other side of brain
optic disc
region of the retina where neurons to
the brain exit the eye; lack of photoreceptors
here results in a “blind spot”
optic nerve
bundle of neurons connecting the eye
to the optic chiasm
optic tract
bundle of neurons connecting the
optic chiasm to the lateral geniculate nucleus of
the thalamus
optimal length (L
0
)
sarcomere length at which
muscle fi ber develops maximal isometric tension
organ
collection of tissues joined in structural unit
to serve common function
organ of Corti
(KOR-tee) structure in inner ear
capable of transducing sound-wave energy into
action potentials
organelle
see
cell organelle
organic
pertaining to carbon-containing
substances;
compare
inorganic
organ system
organs that together serve an
overall function
orgasm
(OR-gazm) inner emotions and systemic
physiological changes that mark apex of sexual
intercourse, usually accompanied in the male
by ejaculation
orienting response
behavior in response to
a novel stimulus; that is, the person stops
what he or she is doing, looks around, listens
intently, and turns toward stimulus
osmol
(OZ-mole) 1 mole of solute ions and
molecules
osmolarity
(oz-moh-LAR-ih-tee) total solute
concentration of a solution; measure of water
concentration in that the higher the solution
osmolarity, the lower the water concentration
osmoreceptor
(OZ-moh-ree-sep-tor) receptor
that responds to changes in osmolarity of
surrounding fl uid
osmosis
(oz-MOH-sis) net diffusion of water
across a selective barrier from region of
higher water concentration (lower solute
concentration) to region of lower water
concentration (higher solute concentration)
osmotic diuresis
increase in urine fl ow resulting
from increased solute excretion (e.g., glucose
in uncontrolled diabetes mellitus)
osmotic pressure
(oz-MAH-tik) pressure that
must be applied to a solution on one side of
a membrane to prevent osmotic fl ow of water
across the membrane from a compartment
of pure water; a measure of the solution’s
osmolarity
osteoblast
(OS-tee-oh-blast) cell type responsible
for laying down protein matrix of bone; called
osteocyte after calcifi ed matrix has been set down
osteoclast
(OS-tee-oh-clast) cell that breaks down
previously formed bone
osteocyte
cell transformed from osteoblast when
surrounded by mineralized bone matrix
osteoid
collagen matrix in bone that becomes
mineralized
otolith
(OH-toe-lith) calcium carbonate crystal
embedded in the mucus covering of the
auditory hair cell
outer segment
light-sensitive portion of the
photoreceptor containing photopigments
oval window
membrane-covered opening
between middle ear cavity and scala vestibuli of
inner ear
ovarian follicle
see
follicle
ovary
(OH-vah-ree) gonad in female
overshoot
part of the action potential in which
the membrane potential goes above zero
ovulation
(ov-you-LAY-shun) release of egg,
surrounded by its zona pellucida and granulosa
cells, from ovary
ovum
(pl. ova) gamete of female; egg
oxidative
(OX-ih-day-tive) using oxygen
oxidative deamination
(dee-am-ih-NAY-shun)
reaction in which an amino group (—NH
2
)
from an amino acid is replaced by oxygen to
form a keto acid
oxidative fi
ber
muscle fi ber that has numerous
mitochondria and therefore a high capacity for
oxidative phosphorylation; red muscle fi ber
oxidative phosphorylation
(fos-for-ih-LAY-shun)
process by which energy derived from reaction
between hydrogen and oxygen to form water is
transferred to ATP during its formation
oxygen-carrying capacity
maximum amount
of oxygen the blood can carry; in general,
proportional to the amount of hemoglobin per
unit volume of blood
oxygen debt
decrease in energy reserves during
exercise that results in an increase in oxygen
consumption and an increased production of
ATP by oxidative phosphorylation following
the exercise
oxygen-hemoglobin dissociation curve
S
-shaped
(sigmoid) relationship between the gas pressure
of oxygen (partial pressure of O
2
) and amount
of oxygen bound to hemoglobin per unit
blood (hemoglobin saturation)
oxyhemoglobin (HbO
2
)
(ox-see-HEE-moh-
gloh-bin) hemoglobin combined with oxygen
oxytocin
(ox-see-TOH-sin) peptide hormone
synthesized in hypothalamus and released from
posterior pituitary; stimulates mammary glands
to release milk and uterus to contract
P
pacemaker
neurons that set rhythm of biological
clocks independent of external cues; any
nerve or muscle cell that has an inherent
autorhythmicity and determines activity pattern
of other cells
pacemaker potential
spontaneous gradual
depolarization to threshold of some nerve and
muscle cells’ plasma membrane
pancreas
elongated gland behind the stomach
with both exocrine (secretes digestive enzymes
into the gastrointestinal tract) and endocrine
(secretes insulin into the blood) functions
papillary muscle
(PAP-ih-lair-ee) muscular
projections from interior of ventricular
chambers that connect to atrioventricular valves
and prevent backward fl ow of blood during
ventricular contraction
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