Exam 4 Flashcards
these 2 systems share responsibility for maintaining homeostasis throughout the body.
The nervous system and the endocrine system
is specialized for rapid transmission of signals from one part of the body to another part of the body by way of nerves
nervous system
is specialized for sending chemical messengers from glands to target cells by way of blood stream
endocrine system
Sensory receptors
detect internal and/or external stimuli.
Incoming sensory information
gets processed and analyzed by neural integration.
Outgoing signals
are sent to effectors, which carry out the required response.
The central nervous system (CNS) consists of
the brain and the spinal cord.
The central nervous system (CNS)
integrates and correlates sensory information, generates thoughts and emotions, forms and stores memories, stimulates muscles to contract and glands to secrete
The peripheral nervous system (PNS) consists of
cranial nerves and spinal nerves that are located outside of the central nervous system.
somatic nervous system (SNS)sensory (afferent) component
carry towards the CNS
somatic nervous system (SNS) motor (efferent) component
carry away from the CNS
autonomic nervous system (ANS) sensory (afferent) component
contains neurons that carry information from visceral receptors toward CNS
autonomic nervous system (ANS) motor (efferent) component
contains neurons that conduct nerve signals from CNS to smooth muscle, cardiac muscle, glands
autonomic nervous system (ANS) motor (efferent) component sympathetic division
controls processes that tend to arouse the body and involve the expenditure of energy
autonomic nervous system (ANS) motor (efferent) component parasympathetic division
controls processes that tend to have a calming effect on the body and restore/conserve energy
Excitability
describes the ability of a nerve cell to respond to environmental stimuli.
Conductivity
describes the ability of a nerve cell to transmit signals to another nerve cell.
Nerve cells (neurons)
highly specialized components of the nervous system. (they are long lived; they cannot divide, so they cannot be replaced; they have a high metabolic rate)
Functional Classification of Neurons
is based upon the direction that a nerve signal travels in reference to the central nervous system.
Sensory (afferent) neurons
transmit signals about light, heat, pressure, and/or chemicals from various receptors toward the cental nervous system.
Interneurons (association neurons)
within the cental nervous system carry out integrative function by transferring signals between sensory neurons and motor neurons.
Motor (efferent) neurons
send signals away from the cental nervous system to various effectors, such as muscles or glands.
the cell body (soma; perikaryon) contains
a single, centrally located nucleus surrounded by cytoplasm and most of the organelles.
cytoskeleton
contains microtubules and actin neurofibrils that form Nissl bodies, compartments in rough ER
Nissl bodies
dark staining regions involved in protein synthesis
mature neurons
lack centrioles, which renders them incapable of undergoing mitosis
Unspecialized cells in CNS
can develop new neurons
Dendrites
short, branching processes with enormous surface area that allows them to receive signals from adjacent neurons.
Axons
long and thin cylindrical processes that conduct signals away from a cell body.
axon originates
from a conical elevation of the soma called an axon hillock
axoplasm
lacks Nissl bodies and Golgi apparatus; surrounded by axolemma
distal end of an axon
branches extensively and each axon terminal ends in a synaptic knob
synaptic knobs
contain synaptic vesicles that store chemical neurotransmitters
Proteins that are needed for a neuron to function properly
are synthesized in the cell body and transported to the axon.
slow axonal transport
moves materials down the axon and supplies new axoplasm needed for developing or regenerating neurons
fast axonal transport
uses protein “motors” to move materials and organelles in both directions between soma and axon terminals
Some pathogens can invade nervous system
by entering synaptic knobs and using fast axonal transport to travel to soma (herpes simplex virus, rabies virus, polio virus, tetanus toxin)
Neurons can be classified structurally
according to number of processes that extend from the soma.
unipolar neurons
have a single axon that extends away from the soma
location of unipolar neurons
Usually found in nerves that carry sensory signals to spinal cord
bipolar neurons
have a single axon and a single dendrite
location of bipolar neurons
Found in retina of eye, inner ear, nose
multipolar neurons
have a single axon and many dendrites
location of multipolar neurons
Most common neurons in brain and spinal cord
anaxonic neurons
have no axon and multiple dendrites
location of anaxonic neurons
Found in retina of eye
Neuroglia (glial cells)
fill spaces between neurons and provide support for neurons.
Neuroglia (glial cells) numbers
There may be 10 trillion neurons in body; glial cells may outnumber neurons 50 to 1 and they retain their ability to divide throughout life
gliomas
malignant brain tumors made of glial cells that actively undergo mitosis
Astrocytes
the most abundant glial cells in the cental nervous system.
Astrocytes description
star-shaped cells with many processes that cover the brain and form a support framework for nervous tissue
Astrocytes form
tight junctions with endothelial cells of blood capillaries to produce a blood-brain barrier that can regulate passage of materials into brain
Astrocytes maintain
the proper balance of potassium ions for generating nerve impulses
Astrocytes produce
scar tissue when neurons are damaged
Oligodendrocytes
also found in the cental nervous system.
possess fewer processes than astrocytes, but wrap around neurons to produce a myelin sheath, which forms insulating layer around neuron
Ependymal cells
also found in the cental nervous system.
resemble cuboidal epithelial cells and line cavities in the brain and spinal cord where they secrete cerebrospinal fluid that circulates through CNS
Microglia
small macrophages scattered throughout the cental nervous system.
phagocytize bacteria that invade the CNS and remove debris caused by tissue damage
Schwann cells
found in the PNS, where they form a neurilemma around neurons.
produce a myelin sheath around neurons in the PNS
assist in regenerating peripheral neurons
Satellite cells
found in the PNS around nerve cell bodies.
Myelin
a lipoprotein that forms an insulating sheath around an axon in order to increase the speed at which a nerve signal travels along a neuron.
myelin composition
20% protein and 80% lipid; fat intake is essential during childhood
In the peripheral nervous system, Schwann cells
wrap around the axons of neurons and form myelin sheaths that have multiple layers.
cytoplasm of the Schwann cell
gradually squeezed out, so the myelin sheath consists of many concentric layers of Schwann cell membranes with outermost forming a neurilemma that contains nucleus
Around neurilemma
endoneurium of fibrous connective tissue
nodes of Ranvier
narrow gaps in the myelin sheath between Schwann cells
In the cental nervous system, oligodendrocytes
spiral around axons to form myelin sheaths.
Neither neurilemma nor endoneurium form around neurons in CNS
If a neuron in the peripheral nervous system gets damaged
it can be regenerated if its cell body and some of the neurilemma remain intact.
regeneration tube
formed by neurilemma and endoneurium across the damaged area, which guides growth of new axonal processes
If a neuron in the central nervous system gets damaged,
it is not likely to be regenerated because it lacks the neurilemma and the endoneurium that are needed to form the regeneration tube.
Neurons
excitable cells and they communicate with one another by using electrical potentials and electrical currents.
electrical potential
the difference in concentration of charged particles on either side of the membrane of a neuron
electrical current
involves a flow of charged particles from one point to another
When a neuron is stimulated,
the electrical potential can change suddenly and produce local potentials and/or action potentials.
Potentials occur because
of ion channels in membrane of neuron
Ion channels allow
electrolytes to flow across the membrane, which establishes a current.
leakage channels
always open and allow sodium and potassium ions to flow
gated channels open and close in response to some stimulus
voltage-gated channels-
open and close in response to some kind of stimulus
ligand-gated channels
open and close in response to specific chemical stimulus
mechanically gated channels
open and close in response to vibration, pressure, or tissue stretching
There is a difference in electrical charges between extracellular fluid and intracellular fluid because
of an unequal distribution of ions on either side of the membrane of the neuron.
plasma membrane of the neuron is
selectively permeable
ions diffuse down their concentration gradient through the
plasma membrane
there is an electrical attraction between
cations and anions
The plasma membrane of a neuron
more permeable to potassium than any other ions.
concentration of potassium ions is higher in
the ICF than in the ECF
large organic anions
trapped inside the neuron and tend to draw some potassium ions back into neuron along electrical gradient
concentration of sodium ions is higher in
the ECF than in the ICF, so sodium ions tend to diffuse into neuron down their concentration and electrical gradients
inside of a neuron
is negative with respect to the outside and is polarized
Diffusion of sodium ions into the neuron and diffusion of potassium ions out of the neuron would
eventually eliminate the resting membrane potential.
ATP-driven membrane pump
actively transports three sodium ions out of the neuron and two potassium ions into the neuron per molecule of ATP spent to keep the RMP at -70 millivolts
A local potential
a small change in the resting membrane potential of a neuron caused by a stimulus that opens a ligand-regulated sodium gate in the membrane of the neuron.
local potential typically begins
at a dendrite, spreads through soma, then travels from axonal trigger zone to synaptic knob
local potentials are useful …
only for short-distance communication
Local potentials are graded because
they vary in size according to the stimulus strength.
strong stimulus causes a greater change in membrane potential and more gates open; allows current to flow further
Local potentials are decremental
because they become weaker as they spread away from the point of stimulation.
Plasma membrane is permeable to ions, so charge is lost and current dies out
Local potentials are reversible
because the resting membrane potential gets restored if the stimulation ceases prematurely.
A local potential is excitatory
if it depolarizes the plasma membrane of the neuron, which makes the potential difference less negative.
A local potential is inhibitory
if it hyperpolarizes the plasma membrane of the neuron, which makes the potential difference more negative.
An action potential
a dramatic change in the membrane potential of a neuron resulting from opening and closing voltage-gated ion channels during an interval of 1 millisecond.
An excitatory stimulus applied to a neuron
will generate an excitatory local potential that depolarizes the membrane and causes resting membrane potential to be less negative.
if the excitatory local potential spreads to the “trigger zone” and remains strong enough,
it can open enough voltage-regulated gates to generate an action potential
If the plasma membrane reaches a critical threshold voltage of about -55 mV,
voltage-gated sodium channels open.
Sodium ions rush into the neuron
and establish positive feedback that depolarizes the membrane potential from -55 mV to zero to +35 mV.
Depolarization
causes slow sodium inactivation gates to close, which prevents any more sodium ions from entering the neuron.
At peak depolarization,
slow voltage-gated potassium channels open and potassium ions rush out of the neuron to repolarize membrane potential from +30 mV to zero to -70 mV.
Voltage-gated potassium channels remain open longer than voltage-gated sodium channels,
so a loss of potassium ions may cause after-hyperpolarization; this makes membrane potential more negative than resting membrane potential until voltage gated potassium channels close and restore RMP
some of the characteristics of an action potential:
they follow an all-or-none principle because any stimulus that depolarizes membrane to threshold will generate action potential
they do not become weaker as they spread away from the point of stimulation
they are irreversible
The refractory period
a brief period of time during which a neuron may not be able to generate another action potential.
An absolute refractory period
lasts from threshold until repolarization is complete.
a neuron cannot be restimulated by a stimulus of any strength because voltage gated sodium channels open and are then inactivated
A relative refractory period
lasts until hyperpolarization ends.
a neuron can be restimulated if a stimulus is larger than threshold
Supra threshold stimulus
If one neuron is to going to communicate with another neuron,
the nerve signal must travel the length of the axon.
nerve signal is a traveling wave of excitation produced by a self-propagating chain of action potentials moving in only one direction
In unmyelinated fibers,
there is a step-by-step depolarization of each adjacent area of the plasma membrane, which produces continuous conduction; propagation is slow, but not decremental; last action potential generated at synaptic knob has same voltage as first action potential generated at trigger zone
In myelinated fibers
the nerve signal appears to “leap” along the neuron from one node of Ranvier to the next node of Ranvier by saltatory conduction.
propagation is much faster, but it is decremental
Signal gets weaker, but reaches next node of Ranvier just in time to open voltage-gated sodium channels to generate new action potential
Propagation speed
not determined by the strength of a stimulus, but by the presence or absence of myelin, by the diameter of the fiber, and by the temperature.
large diameter fibers
conduct signals faster than small diameter fibers because large fibers tend to be myelinated and small fibers tend to be unmyelinated; large diameter fibers conduct signals faster because there is more surface area
nerve fibers conduct signals faster when the temperature is warm
A synapse
a junction between two neurons across which a nerve signal is conducted.
pre-synaptic neuron
conducts information towards a synapse and a post-synaptic neuron conducts information away from the synapse
Synaptic knob of presynaptic neuron
separated from postsynaptic neuron by a narrow synaptic cleft
single neuron in the cerebellum of the brain
may have 100,000 synapses
synapse may be
axodendritic or axosomatic or axoaxonic
At an electrical synapse,
a nerve signal is transmitted by the flow of ions from one cell to another through gap junctions.
these synapses allow fast communication, synchronization among multiple neurons or muscle fibers, and two-way transmission of signals
At a chemical synapse,
a nerve signal is transmitted by small organic neurotransmitters.
neurotransmitter is synthesized by the pre-synaptic neuron and stored in vesicles
neurotransmitters are released from a pre-synaptic neuron in response to a stimulus
neurotransmitters bind to specific receptors on the post-synaptic neuron
neurotransmitters alter the physiology of the post-synaptic neuron
There are more than 100 substances that have been classified as
neurotransmitters
acetylcholine (ACh)
the most familiar and it can be excitatory or inhibitory
Responsible for neuromuscular activity
amino acids
can be excitatory or inhibitory
Glutamate
excitatory neurotransmitter involved in learning and memory (amino acid)
GABA
inhibitory neurotransmitter in brain (amino acid)
biogenic amines
modified amino acids that may be excitatory or inhibitory
Serotonin or catecholamines (dopamine, epinephrine, norepinephrine ) play roles in emotional behavior or operation of ones 'biological clock'
neuropeptides
amino acid chains that may be excitatory or inhibitory
Some neuropeptides are neuromodulators because they function like hormones
Neuropeptides may be responsible for
craving fat and/or sugar and may be a cause of some eating disorders
Substance P
mediates pain
Endorphins and enkephalins
act as natural opiates to reduce perception of pain (‘runners euphoria’; placebo effect)
Acetylcholine
the neurotransmitter at an excitatory cholinergic synapse. (Neuromuscular junction)
GABA
the neurotransmitter at an inhibitory synapse.
GABA works like acetylcholine, except it opens chloride channels and hyperpolarizes the post-synaptic membrane making it harder to generate action potential
Norepinephrine
the neurotransmitter at an excitatory adrenergic synapse.
norepinephrine operates through a second-messenger system that activates a transmembrane G protein and binds it to adenylate cyclase
adenylate cyclase catalyzes the conversion of ATP to cyclic AMP (cAMP)
cAMP binds to a ligand-regulated ion gate on the inside of the membrane and opens it to depolarize the membrane
cAMP activates cytoplasmic enzymes that catalyze changes in metabolic reactions
cAMP also induces transcription
Neurotransmitters
must be removed from synaptic cleft to stop the transmission of nerve signals.
they can diffuse out of the synaptic cleft into the extracellular fluid where they get absorbed by astrocytes to be returned to pre-synaptic neuron
they can be actively transported back into the neuron that released them
acetylcholine can be degraded in the synaptic cleft by acetylcholinesterase
Postsynaptic potentials
graded potentials, so their size varies according to the strength of the stimulus and the amount of neurotransmitter that was released.
If a neurotransmitter causes depolarization of the post-synaptic membrane,
an excitatory postsynaptic potential (EPSP) occurs because sodium ions flow into the cell.
membrane potential approaches threshold so neuron is easier to stimulate
If a neurotransmitter causes hyperpolarization of the post-synaptic membrane,
an inhibitory postsynaptic potential (IPSP) occurs because chloride ions flow into the cell or potassium ions flow out of the cell.
membrane potential moves away from threshold so neuron is harder to stimulate
A typical neuron receives signals from thousands of pre-synaptic neurons and integrates them at the trigger zone through a process known as
summation
Whether post synaptic neuron fires depends on
NET input of EPSPs and IPSPs
a typical EPSP is too weak and too short-lived to
depolarize the membrane to threshold
Temporal summation
occurs at a single synapse because each EPSP is generated at such a short interval that the previous EPSP hasn’t decayed.
if enough EPSPs are generated to depolarize the post-synaptic membrane to threshold, an action potential is generated
Spatial summation
occurs when several pre-synaptic neurons generate EPSPs at the same time.
a single synapse only allows a small number of sodium ions into the post-synaptic membrane, but if multiple synapses allow enough sodium ions to enter and the post-synaptic membrane is depolarized to threshold, an action potential can be generated
Several neurons may cooperate through _____________ to enhance the effects of one another.
facilitation
One pre-synaptic neuron may suppress another pre-synaptic neuron by
pre-synaptic inhibition in order to halt the transmission of a nerve signal.
Alzheimer disease
characterized by reduced attention span, progressive memory loss, disorientation, and a dramatic change in personality, resulting in dementia.
Alzheimer disease is due to
the degeneration of cholinergic neurons causing a deficiency in acetylcholine
Alzheimer disease treatment modalities include
acetylcholinesterase inhibitors and nerve growth factor
Alzheimer disease diagnosis
can only be confirmed by an autopsy that detects beta-amyloid plaques around neurons and neurofibrillary tangles inside brain neurons
Parkinson disease
involves a progressive loss of motor function that leads to involuntary tremors, facial rigidity, “gawking”, shuffling gait, slurred speech, and illegible handwriting.
Parkinson disease is due to
the degeneration of dopamine-releasing neurons in the brain; might be caused by exposure to environmental toxins
Parkinson disease treatment modalities include
drugs or dopamine-rich tissue transplants or surgery to remove brain tissue that might be responsible for the tremors
Gray matter contains
cell bodies, dendrites, unmyelinated axons, and neuroglia.
Gray matter nuclei
clusters of nerve cell bodies
gray matter is
the main site of synaptic contact between neurons
White matter contains
myelinated axons.
White matter tracts
bundles of myelinated axons that carry nerve signals within the CNS
The brain is divided into several principal _________
REGIONS
brainstem-
continuous with spinal cord; components include medulla oblongata, pons, mid brain, reticular formation
cerebellum-
posterior to brainstem; divided into hemispheres
diencephalon-
components include thalamus, hypothalamus, epithalamus
cerebrum-
occupies most of cranium; divided into hemispheres; components include basal nuclei and limbic system
Meninges
fibrous connective tissue coverings surrounding the brain and spinal cord.
The outermost meninx is the
dura mater, which consists of dense irregular connective tissue that lines the cranial cavity and surrounds the spinal cord.
between the dura mater and the wall of the vertebral canal is an ___________________________filled with blood vessels, adipose tissue, loose connective tissue
epidural space
cranial dura mater
lies tightly against the cranial bones and consists of two layers
Extensions of dura mater separate major parts of brain
The middle meninx is the
arachnoid mater, which consists of delicate collagen fibers and some elastic fibers.
arachnoid mater is separated from the dura mater by a fluid-filled
subdural space
The inner meninx is the
pia mater, which is a thin layer of transparent collagen and elastic fibers that adhere to the spinal cord and brain.
between the arachnoid mater and the pia mater is a _____________________ filled with cerebrospinal fluid
subarachnoid space
Meningitis
inflammation of the arachnoid mater and/or pia mater caused by bacteria and/or viruses that invade the central nervous system via the nose or throat.
Meningitis extremely serious disease among
infants and children between ages of 3 months and 2 years
in bacterial meningitis,
brain swells, ventricles enlarge, and brainstem may start to hemorrhage
Symptoms include go fever, stiff neck, drowsiness, intense headache, coma
Death may occur within hours of onset
Ventricles
four fluid-filled chambers in the brain.
What are the four ventricles in the brain?
two lateral ventricles extend into the cerebral hemispheres
third ventricle is located along the midline of the brain and it connects to the lateral ventricles by way of an interventricular foramen
fourth ventricle is connected to the third ventricle by the cerebral aqueduct
cerebral aqueduct
forms a central canal that extends through the spinal cord
These ventricles and canals are lined with
ependymal cells and capillary networks to form choroid plexuses that produce and secrete up to 500 mL of cerebrospinal fluid each day.
cerebrospinal fluid is constantly reabsorbed, so circulating volume is
100-160 mL
Cerebrospinal fluid (CSF)
a clear, colorless liquid containing proteins, glucose, urea, salts, and various ions that serves several useful purposes.
Cerebrospinal fluid (CSF) provides
provides buoyancy so the brain “floats” in the cranial cavity; a medium for exchanging nutrients and wastes between blood and nerve tissue
Cerebrospinal fluid (CSF) functions
a shock absorber to protect the brain and spinal cord from jolts
Cerebrospinal fluid circulates through the ventricles, into the central canal of the spinal cord, and into the subarachnoid space where it is gradually
reabsorbed into the blood.
Any obstruction or inflammation of the brain that interferes with the circulation of cerebrospinal fluid can cause
hydrocephalus
hydrocephalus
an accumulation of fluid in the ventricles that can compress delicate nervous tissue and damage the brain.
The brain must be well-supplied with oxygen and nutrients because it is
one of the most metabolically active organs of the body.
10 second interruption of blood flow can cause
loss of consciousness
1-2 minute interruption of blood flow can
impair neurological function
4 minute interruption of blood flow can
produce irreversible brain damage
There is a brain barrier system that is
highly permeable to water, glucose, oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anaesthesia, but it blocks the delivery of most drugs.
blood-brain barrier forces
materials that leave the blood to pass through cells rather than pass between them, because brain capillaries are less permeable than most other capillaries
blood-CSF barrier regulates
the passage of materials from cerebrospinal fluid into the brain
medulla oblongata
the inferior brainstem continuous with the spinal cord.
The anterior surface of the medulla oblongata
exhibits two large, bulging pyramids.
pyramids
contain large motor tracts that connect the brain to the spinal cord
Fibers from left pyramid
cross to body’s right side i n phenomenon of decussation
fibers from right pyramid
cross to body’s left side in phenomenon of decussation
Lateral to each pyramid
an oval olive that contains nuclei to relay sensory information from the brain and/or spinal cord to the cerebellum.
The medulla oblongata contains
several control centers that are vital to homeostasis.
cardiac center regulates heart rate
vasomotor center adjusts the diameter of blood vessels to regulate blood pressure
respiratory centers adjust the rate and depth of breathing; Other centers control reflexes associated with coughing, sneezing, swallowing, vomiting.
The pons lies…
lies superior to the medulla oblongata and anterior to the cerebellum.
The pons is
a “bridge” with tracts and nuclei that connect the brain with the spinal cord and also connect parts of the brain with each other.
some pontine nuclei
nuclei work with the medullary respiratory center to control respiration
other pontine nuclei are associated with equilibrium/posture, taste/swallowing, and hearing
The midbrain
extends from the pons to the lower portion of the diencephalon.
A pair of cerebral peduncles
anchor the cerebrum to the brainstem and contain tracts that run through the midbrain to carry motor signals to the medulla oblongata.
The main mass of the midbrain contains
a highly vascular red nucleus, which connects with the cerebellum to permit fine motor control.
The substantia nigra
is a darkly pigmented nucleus that controls subconscious muscle actions by relaying inhibitory signals to various parts of the brain.
Degeneration of neurons in substantia nigra produces
muscle tremors characteristic of Parkinson’s disease
The posterior portion of the midbrain is the
tectum
tectum contains _______ corpora quadrigemina that protrude from its roof
four
superior colliculi
serve as reflex centers for blinking, focusing eyes, moving head and neck to visually track moving objects
inferior colliculi
serve as reflex centers for movements of head in response to auditory stimuli (sudden loud sounds)
The reticular formation contains
more than 100 small areas of gray matter interspersed throughout the medulla oblongata, pons, and midbrain.
Somatic motor control maintains
balance and posture in response to sensory signals from the eyes and ears about body position and the position of nearby objects.
The reticular formation contributes to
cardiovascular control by integrating the cardiac center and the vasomotor center in the medulla oblongata.
The reticular formation plays a central role in
maintaining consciousness and awakening from sleep.
The reticular formation allows us to
ignore traffic sounds or other inconsequential noises, but causes us to respond quickly to an alarm clock or a flash of lightning
The reticular formation transmits
pain signals from the lower body to the cerebral cortex.
Damage to the reticular formation can
produce an irreversible coma.
The cerebellum is
the second-largest portion of the brain, comprising about 11% of the brain’s mass, and it occupies the inferior and posterior region of the cranial cavity.
Contains about 100 billion neurons
The right and left cerebellar hemispheres are linked by a
medial vermis.
surface of the cerebellum consists of
leaf-like folia consisting of gray matter
arbor vitae
a deeper “tree-like” mass consisting of white matter
The cerebellum attaches to
the brainstem by three pairs of cerebellar peduncles.
inferior pair of cerebellar peduncles
connects with the medulla oblongata to facilitate muscle performance
middle pair of cerebellar peduncles
transmits signals from the pons to coordinate muscle responses
superior pair of cerebellar peduncles
transmits motor signals through the midbrain and the thalamus
The cerebellum serves mainly as
a reflex center to coordinate subconscious movements of skeletal muscle that are necessary for muscle coordination, balance, and posture.
also involved in time-keeping and the perception of elapsed time
The cerebellum receives
sensory information about the position of limbs, joints, and other body parts in order to maintain unconscious control over walking, dancing, or catching a ball.
The thalamus is
the largest component of the diencephalon and it contains paired oval masses of gray matter located beneath each cerebral hemisphere.
is a “gateway to the cerebral cortex” and it filters sensory impulses arriving from the spinal cord, brainstem, or cerebellum before relaying them to the cerebral cortex.
thalamus
Nuclei within the thalamus carry out a variety of functions:
some nuclei receive and integrate auditory, visual, and taste information
some nuclei receive and integrate information about pain, temperature, light touch, pressure
some nuclei relay signals to motor control areas in the cerebrum
some nuclei are involved in emotion, memory, and cognition
The hypothalamus is
inferior to the thalamus and also contains many nuclei.
there are two small, round ____________________ that play a role in memory
mammillary bodies
stalk-like __________ attaches the pituitary gland to the hypothalamus
infundibulum
supraoptic and preoptic regions
are involved in autonomic and endocrine activities (hypothalamus)
The hypothalamus maintains
homeostasis by regulating internal processes through the autonomic nervous system and the endocrine system.
Nuclei within the hypothalamus- integrating center for the autonomic nervous system regulates
heart rate, blood pressure, digestion, urination, and other visceral activities
some nuclei within the hypothalamus produce and release
hormones to control the pituitary gland
hypothalamic thermostat
monitors the blood in order to control body temperature
“heat-losing center” controls vasodilation in skin and sweating
“heat-producing center” controls vasoconstriction, shivering, "goose bump" formation
“hunger” and “satiety” centers within the hypothalamus
monitor levels of glucose and amino acids in the blood in order to regulate food intake
“thirst” center within the hypothalamus
monitors osmolarity and dehydration to regulate fluid intake
hypothalamus connection with the reticular formation
regulates circadian rhythms associated with sleeping/waking
some nuclei within the hypothalamus
control anger, aggression, fear, pain, pleasure, sexual behavior
Epithalamus- A pineal gland
involved in maintaining the body’s biological clock.
Habenular nuclei (Epithalamus)
involved in emotional response to odors.
The cerebrum
the largest region of the brain and accounts for 83% of total brain mass.
Cerebrum- There is a superficial layer of gray matter called the
cerebral cortex.
all neurons in the cerebral cortex are
interneurons
gyri
folds or ridges at the surface of the cerebrum
Gyri function
increase surface area to improve information processing capabilities
sulci
shallow grooves between gyri
fissures
deep grooves between gyri
The cerebrum is divided into
left and right hemispheres by the longitudinal fissure.
two hemispheres are connected internally by the
corpus callosum
Each hemisphere can be subdivided into
frontal, parietal, temporal, and occipital lobes.
central sulcus separates
the frontal lobe from the parietal lobe
precentral gyrus
anterior to central sulcus
postcentral gyrus
posterior to central sulcus
lateral sulcus separates
parietal lobe from the temporal lobe
insula
a small mass of cortex located deep to the lateral sulcus
Most of the cerebrum is located
beneath the cerebral cortex and comprised primarily of white matter.
association tracts
transmit nerve signals between gyri in the same hemisphere
commissural tracts
transmit nerve signals from gyri in one hemisphere to the corresponding gyri in the opposite hemisphere by way of the corpus callosum
projection tracts
form ascending tracts to carry nerve signals up to the cerebrum and form descending tracts to carry motor signals to the brainstem and spinal cord
The basal nuclei
masses of gray matter located lateral to the thalamus.
The basal nuclei receive
input from the red nuclei and the substantia nigra of the midbrain in order to control muscle tone required for gross voluntary movements (walking).
Damage to the basal nuclei
can produce the involuntary muscle movements that are associated with Parkinson disease.
The limbic system
a ring of structures around the corpus callosum and the thalamus.
The limbic system includes
the amygdala and hippocampus nuclei, the fornix tract, and the cingulate gyrus
The amygdala
involved in emotion and behavior associated with pleasure and pain.
The hippocampus
involved in memory storage and may facilitate links between memory and emotions, particularly those memories associated with pleasure or pain or smell.
The cerebrum interprets
sensory impulses, controls voluntary motor responses, directs intellectual processes, stores memories, and governs personality traits.
Although the two cerebral hemispheres appear identical,
anatomical and functional differences between them lead to cerebral lateralization. ( highly correlated with “handedness” and somewhat correlated with gender
prone to change as a person grows older)
The left hemisphere
appears to be more important for right-hand control, spoken and written language, numerical and scientific skills, and logic.
The right hemisphere
appears to be more important for left-hand control, musical and artistic awareness, perception of patterns and spatial relationships, insight, imagination, and mental imagery of sights, sounds, smells, and tastes.
The primary somatosensory area
is located in the postcentral gyrus of each parietal lobe.
The primary somatosensory area receives
sensory information about joint and muscle position
also receives sensory information about touch and pain and temperature from skin and muscle receptors to determine exact point of origin
The primary visual area
located in the posterior occipital lobe.
The primary visual area receives
signals from the eyes about shape, color, and movement of visual stimuli
The primary auditory area
located in the superior temporal lobe and partly in the insula.
The primary auditory area interprets
basic characteristics of sound, such as pitch and rhythm
The primary olfactory area
located on the medial surface of the temporal lobe and the inferior surface of the frontal lobe.
The primary olfactory area receives
signals related to smell
The primary gustatory area
located at the base of the postcentral gyrus.
The primary gustatory area receives
signals related to taste
Motor areas
control voluntary movement of skeletal muscles.
The primary motor area
located in the precentral gyrus of the frontal lobe.
The primary motor arealarge pyramidal neurons
project to spinal cord and form pyramidal motor tracts, which control voluntary contractions of specific muscles or groups of muscles on opposite side of body
Broca’s area
located in the left frontal lobe and contains the motor speech area.
Broca’s area coordinates
complex muscle actions of the tongue, mouth, and larynx that enable a person to translate his/her thoughts into spoken words
injury to Broca’s area can cause
aphasia
word deafness
inability to understand spoken words
word blindness
inability to recognize written words
The somatosensory association area
located in the parietal lobe behind the postcentral gyrus.
The somatosensory association area functions
integrates and interprets sensory information about the shape and/or texture of an object
makes us aware of the orientation of one object to another object and makes us aware of the position of our limbs
stores memories of past sensory experiences
The visual association area
located in the occipital lobe.
The visual association area function
allows us to recognize and evaluate what we see and what we have seen
The auditory association area
located in the superior temporal lobe.
The auditory association area functions
it helps us determine whether sound is speech or music or noise
it enables us to recall a song or melody; enables us to recognize a person’s voice
The premotor area
located in the frontal lobe, anterior to the primary motor area.
The premotor area function
enables us to “plan” the degree and sequence of muscle actions needed for learned motor activities that are complex and sequential (writing, typing, speaking)
Wernike’s area
located in the left temporal lobe, posterior to the lateral sulcus.
Wernike’s area function
responsible for recognizing speech and written language
Brain cells generate
considerable amount of electrical activity from nerve signal transmission and an electroencephalogram (EEG) can provide a record of the brain waves that result.
alpha waves
occur in individuals who are awake or resting with closed eyes
They disappear when person becomes mentally engaged or falls asleep
beta waves
present when a person is alert and mentally active
theta waves
normally occur in children or in sleeping adults
Presence in adults who are awake indicate emotional stress or brain disorders
delta waves
present in alert infants and in adults during deep sleep
Presence in adults who are awake may indicate serious brain damage
Sleep
a state of temporary unconsciousness from which an individual can be aroused.
cycle of sleep and waking
one of our circadian rhythms that repeats at 24 hour intervals
Timing of this cycle is controlled by nuclei in hypothalamus and brainstem
non-rapid eye movement (NREM).
One type of sleep in the sleep cycle
NREM Stage 1
a transition between wakefulness and sleep when we relax and close our eyes and let our mind wander
NREM Stage 2
(“light sleep”) is characterized by sleep spindle brain waves; more difficult to arouse individual
NREM during Stage 3
(“moderate sleep”), body temperature and blood pressure decrease and pulse and breathing rate slow down
NREM during Stage 4
(“deep sleep”), muscles are very relaxed
Nightmares, night terrors, bed-wetting, sleepwalking may occur in this stage
rapid eye movement (REM)
Another type of sleep in the sleep cycle, which begins about 90 minutes after sleep begins provided NREM stage 4 has been achieved
most individuals experience ________ episodes of REM during each sleep cycle
three to five (Eyes dart back and forth under closed eyelids)
vital signs during REM
increase and brain becomes more active; most dreaming occurs during REM sleep
Skeletal muscles during REM
inhibited and go limp to prevent one from ‘acting out’ his/her dreams
REM episodes
get progressively longer as the sleep cycle lengthens
REM sleep may give the brain
an opportunity to organize and/or strengthen desirable memories and/or forget unwanted memories
The spinal cord conducts
sensory information from the periphery of the body to the brain, and it conducts motor signals from the brain to peripheral effectors.
The spinal cord triggers
repetitive, coordinated muscle contractions necessary for walking.
The spinal cord establishes
reflex pathways.
The spinal cord
a slender cylindrical column extending from the medulla oblongata, through the foramen magnum into the vertebral canal, down to second lumbar vertebra.
The spinal cord is covered by
spinal meninges that extend from meninges that cover brain
spinal dura mater
not attached to the walls of the vertebral column, but is surrounded by a fat-filled epidural space
two conspicuous enlargements of the spinal cord
cervical enlargement and lumbar enlargement
cervical enlargement
extends from the fourth cervical vertebra to the first thoracic vertebra; nerves arise to innervate upper extremities
lumbar enlargement
extends from the ninth through the twelfth thoracic vertebrae; nerves arise to innervate pelvic region and lower limbs
Below the lumbar enlargement the spinal cord tapers to form the _____________________ which is anchored to the base of the spine by fibrous connective tissue.
medullary cone
spinal nerves that arise from the lower part of the spinal cord form the
cauda equina (‘horses tail’);
cauda equina innervates
pelvic organs and lower limbs
The spinal cord is separated into right and left symmetrical halves by
an anterior median fissure and a posterior median sulcus.
hollow central canal running the length of the cord is filled with
cerebrospinal fluid
A butterfly-shaped mass of ____________ contains nerve cell bodies, unmyelinated axons, and dendrites of association neurons and motor neurons.
gray matter
forms the “center of the butterfly”
gray commissure
anterior (ventral) gray horns
contain the cell bodies of motor neurons
posterior (dorsal) gray horns
contain interneurons
lateral gray horns are present only in
the thoracic and lumbar regions
White matter surrounding the gray “butterfly” consists of
bundles of myelinated axons of sensory neurons and motor neurons that form tracts.
White matter is arranged into
anterior (ventral), posterior (dorsal), and lateral white columns (funiculi)
Ascending tracts
carry sensory signals from peripheral receptors up the spinal cord to the brain.
dorsal column (Ascending tracts)
carries signals for vibration, touch, proprioception, and visceral pain
spinothalamic tract (Ascending tracts)
carries signals for pain, temperature, touch, and pressure
spinocerebellar tracts (Ascending tracts)
carry signals for proprioception to the cerebellum
Sensory information conveyed to the central nervous system must be
integrated with other information before a response can be initiated.
Descending tracts
carry motor signals from the brainstem down the spinal cord to skeletal muscles in the periphery.
corticospinal tracts (Descending tracts)
transmit signals from cerebral cortex that control precise limb movements
tectospinal tract (Descending tracts)
transmits signals from the midbrain for reflex movements of the head needed to respond to sights or sounds
reticulospinal tracts (Descending tracts)
transmit signals from the reticular formation to the limbs to maintain posture and balance
vestibulospinal tract (Descending tracts)
transmits signals from the brainstem to the limbs to maintain posture/ balance
Multiple sclerosis
involves the deterioration of oligodendrocytes and myelin sheaths in the brain and spinal cord, which is followed by replacement with scar tissue.
Multiple sclerosis- loss of myelin causes
“short circuits” that produce less excitation at successive nodes of Ranvier, until the conduction of nerve impulses eventually ceases
Multiple sclerosis- disruption of nerve conduction depends on
the specific part of CNS that is affected
Multiple sclerosis symptoms include
double vision, blindness, speech defects, tremors, and numbness
Multiple sclerosis occurs between the ages of
20 and 40, more often in females than in males; cycles of mild to severe symptoms may occur until patient becomes bedridden
Multiple sclerosis- death
may occur from 7 years to 32 years following the onset of symptoms
Multiple sclerosis may be caused by
a virus that triggers an autoimmune response; treatment includes immunosuppressive drugs
Epilepsy
characterized by seizures initiated by massive discharge of brain neurons.
Epilepsy seizures
can produce hallucinations, anxiety, “religious ecstasy”, loss of consciousness, spasmodic stiffening/jerking
Epilepsy may be triggered by
flickering lights sudden loud noises, the sound of a specific voice or song, emotional stress, or even doing math problems
Epilepsy may be caused by
brain trauma at birth, metabolic disturbances, infections, toxins, or tumors
Epilepsy treatment
uses a variety of anti-epileptic drugs
Cerebral palsy
a group of motor disorders that cause loss of voluntary muscle control and coordination.
Cerebral palsy can also include
seizure disorders, mental retardation, deafness, and visual impairment
Cerebral palsy often detected in
infants who exhibit breathing abnormalities, sucking and/or swallowing disorders, or delays in walking followed by stiff/awkward limb movements
Cerebral palsy- damage to motor areas can be caused by
exposure to the rubella virus or from radiation during fetal development or by oxygen deprivation during birth or by hydrocephalus during infancy
Spina bifida
a congenital defect occurring in 1 out of 1000 babies because the vertebral column fails to completely enclose the spinal cord.
Spina bifida- lower portion of spinal cord
doesn’t function, so it causes a lack of bowel control, bladder paralysis, and paralysis of the lower limbs
Spina bifida may be caused by
insufficient folic acid in the mother’s diet during early pregnancy
Poliomyelitis
caused by a virus that destroys motor neurons in the brainstem and ventral gray horns of the spinal cord.
Poliomyelitis symptoms include
muscle pain and weakness, loss of reflexes followed by paralysis, muscle atrophy, and respiratory failure
Poliomyelitis vaccines
have almost eliminated polio
Amyotrophic lateral sclerosis (ALS)
involves degeneration of motor neurons and atrophy of muscles due to the formation of scar tissue in lateral regions of spinal cord.
ALS- astrocytes
fail to reabsorb the neurotransmitter glutamate, which leads to toxic accumulation
ALS symptoms include
muscle weakness, difficulty speaking and/or swallowing, and difficulty using one’s hands
Nerves consist of
bundles of axons enclosed within a connective tissue covering.
individual axons are wrapped in
endoneurium
groups of axons are arranged in
a fascicle, which is wrapped in a perineurium
several fascicles are wrapped in
an outer epineurium, which forms a whole nerve
ganglion
a cluster of nerve cell bodies outside of the central nervous system.
Each ganglion is wrapped in
epineurium continuous with that of nerve
___ pairs of cranial nerves arise from the base of the brain and connect with muscles and sense organs in the head and neck.
12
each pair of cranial nerves is identified by
a name and a Roman numeral
sensory fibers associate with
receptors in the head and neck
motor fibers associate with
nuclei in the brainstem that lead to muscles and glands
mixed cranial nerves contain
both sensory and motor fibers
most cranial nerves are
mixed nerves because motor nerves typically contain afferent fibers for proprioception
The olfactory nerve (I)
a sensory cranial nerve that links odor-detecting receptors in the nose with an olfactory bulb that is located in the frontal lobe of the cerebrum.
The optic nerve (II)
a sensory cranial nerve that links visual receptors in the retina of the eye with an optic tract that terminates in the thalamus.
The oculomotor nerve (III)
primarily a motor cranial nerve that innervates muscles to move eyelid and eyeball, control amount of light that enters the eye, and focus the lens on near and far objects.
The trochlear nerve (IV)
primarily a motor cranial nerve that innervates muscles to move eyeball.
The trigeminal nerve (V)
a mixed cranial nerve with three branches.
trigeminal nerve (V)- ophthalmic branch
transmits sensory signals from the eyes and forehead for touch, temperature, pain
trigeminal nerve (V)- maxillary branch
transmits sensory signals from the mouth region for touch, temperature, pain
trigeminal nerve (V)- mandibular branch
contains motor fibers that innervate muscles used in chewing
The abducens nerve (VI)
primarily a motor cranial nerve that innervates muscles to move eyeball.
The facial nerve (VII)
a mixed cranial nerve.
facial nerve (VII)- sensory fibers
transmit signals from taste buds on the tongue
facial nerve (VII)- motor fibers
innervate muscles to control facial expression, salivation, and production of tears
The vestibulocochlear nerve (VIII)
primarily a sensory cranial nerve.
vestibulocochlear nerve (VIII)- cochlear branch
links receptors in the ear with the auditory areas
vestibulocochlear nerve (VIII)- vestibular branch
transmits signals from the inner ear about balance and equilibrium
The glossopharyngeal nerve (IX)
a mixed cranial nerve.
glossopharyngeal nerve (IX)- sensory fibers
transmit signals about taste from the tongue and transmit signals about touch, pain, and temperature from the tongue, pharynx ,and outer ear
glossopharyngeal nerve (IX)- motor fibers
innervate muscles to control swallowing and speech and muscles to stimulate the secretion of saliva
The vagus nerve (X)
a mixed cranial nerve that belongs to autonomic nervous system.
vagus nerve (X)- sensory fibers
transmit signals about taste, touch, pain ,and temperature from the throat, and transmit signals about blood pressure, respiration, and gastrointestinal function from visceral receptors
vagus nerve (X)- motor fibers
innervate skeletal muscles to control swallowing, coughing, and speech; innervate smooth muscles that control the gastrointestinal tract; innervate cardiac muscle that slows heart rate
The accessory nerve (XI)
primarily a motor cranial nerve that innervates muscles to control swallowing and innervates other muscles to move the head, neck, and shoulders.
The hypoglossal nerve (XII)
primarily a motor cranial nerve that innervates muscles to move the tongue during speech, chewing, and swallowing.
______ pairs of spinal nerves emerge from the spinal cord through intervertebral foramina.
31
Spinal nerves are mixed nerves with ____ points of attachment to the spinal cord.
two
dorsal root
contains afferent neurons to conduct sensory impulses from peripheral receptors to the dorsal gray horn of the spinal cord
Cell bodies form
dorsal root ganglia
ventral root
contains efferent neurons to conduct motor signals from the ventral gray horn of the spinal cord to peripheral effectors
After a spinal nerve passes through its intervertebral foramen, it divides into branches called
rami
dorsal ramus innervates
deep muscles and skin of the dorsal surface of the trunk
ventral ramus innervates
muscles and skin of the lateral and ventral surfaces of the trunk; gives rise to nerves that innervate limbs
meningeal branch
re-enters the vertebral canal and innervates the meninges, blood vessels, and ligaments of the spinal cord
Ventral rami in the thorax
form an intercostal nerve to innervate muscles for breathing.
Varicella virus
causes childhood chickenpox; it takes up lifelong residence in dorsal root ganglia, which might cause shingles (Herpes zoster) in individuals older than 50.
shingles- immune system
fails to keep the virus under control, so it travels down sensory nerves and produces skin discoloration and painful, fluid-filled vesicles along these nerves
Shingles usually appears in
chest and waist on one side of body
Shingles - heal and cure
vesicles may heal spontaneously within 3 weeks, but there is no cure for shingles
Ventral rami typically branch and merge to form
interconnected plexuses, except in the thoracic region of the spinal cord.
Cervical plexus
(C1 - C5) is located on the side of the neck beneath the sternocleidomastoid muscle.
Cervical plexus- nerves
nerves innervate the skin and muscles of the head, neck, upper shoulders, and chest
Cervical plexus- phrenic nerve
conducts motor impulses to the diaphragm to control breathing
Brachial plexus
(C4 - T2) is located deep in the shoulder between the neck and armpit.
Brachial plexus- nerves
nerves innervate the skin and muscles of the arms, forearms, and hands.
nerves that arise from the brachial plexus
axillary, radial, median, and ulnar nerves
Lumbar plexus
(L1-L4) is located in the lower back.
Lumbar plexus- nerves
nerves innervate the skin and muscles of the abdominal wall, external genitalia, thighs, and lower limbs
Sacral plexus
(L4-S4) is located on the side of the sacrum.
Sacral plexus - nerves
nerves innervate the skin and muscles of the buttocks and lower extremities.
Sacral plexus - sciatic nerve
the largest nerve in the body and consists of the tibial nerve and the fibular nerve wrapped in a common sheath
Reflexes
fast, involuntary, predictable responses to environmental changes that maintain homeostasis and enhance one’s chances for survival.
somatic reflexes
involve contraction of skeletal muscles
autonomic (visceral) reflexes
involve contraction of smooth muscle, contraction of cardiac muscle, or glandular secretion
reflex arc
used during a somatic reflex.
reflex arc- sensory receptor
in the skin, in a muscle, or in a tendon responds to a stimulus
reflex arc- sensory neuron
carries that signal from the receptor to a dorsal gray horn in the spinal cord
reflex arc- interneurons
act as an integrating center in the central nervous system
reflex arc- motor neuron
carries a motor signal from the integrating center to an effector
reflex arc- effector
a skeletal muscle that responds to the motor signal
Somatic reflexes use
proprioception to monitor status of muscles, tendons, and joints.
proprioception
the awareness of the degree of muscle contraction, to the amount of tension in a tendon, to changes in joint position, or to changes in the position of the head
Proprioception permits us to
perform activities without thinking about them
Somatic reflexes- muscle spindles
located between skeletal muscle fibers; they indicate degree and speed of change in muscle length (This information is relayed to cerebrum so we are conscious of limb position and is relayed to cerebellum so muscle contractions can be coordinated )
Somatic reflexes - tendon organs
located at the junction of a tendon and a muscle; they protect against damage from excessive tension
Somatic reflexes -joint kinesthetic receptors
located within the capsule of a synovial joint; they indicate excessive strain placed on that joint
A stretch reflex
a monosynaptic reflex arc that helps maintain equilibrium and posture.
stretch reflexes operate as
feedback mechanisms to control muscle length by causing contractions in synergistic or antagonist muscles
flexion of a joint creates
stretch reflex in extensor muscles
extension of a joint creates
stretch reflex in flexor muscles
stretch reflex- important in
coordinating vigorous and precise movements (dancing)
stretch reflex- depends on
reciprocal inhibition to prevent muscles from working against one another
A tendon reflex
a monosynaptic reflex arc that occurs when a muscle is suddenly stretched because a tendon is tapped.
tapping the patellar tendon causes
femoris quadriceps muscle to suddenly stretches and stimulate “knee-jerk” response that extends the leg
tapping the calcaneal tendon causes
plantarflexion of the foot
tapping the triceps brachii tendon causes
extension of the elbow
tapping the masseter tendon cause
the jaw to clench
A flexor (withdrawal) reflex
a polysynaptic reflex arc that produces quick contraction of flexor muscles, which causes immediate withdrawal from a painful or dangerous stimulus.
flexor (withdrawal) reflexes tend to be
complex with polysynaptic reflex arc (at least one interneuron)
A crossed-extensor reflex produces
contractions of extensor muscles in the limb that is opposite to the one withdrawn in order to maintain balance following a withdrawal reflex.
The Golgi tendon reflex
a response to excessive tension on a tendon that controls the contraction of a muscle before it can damage the tendon.
component of the peripheral nervous system functions without conscious control to maintain homeostasis by increasing or decreasing visceral activity in response to internal changes.
AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system is responsible for
visceral reflexes.
The autonomic nervous system- sensory input
transmitted by general visceral sensory (afferent) neurons from special visceral receptors
The autonomic nervous system- visceral responses
regulated by general visceral motor (efferent) neurons that either excite or inhibit visceral effectors
The autonomic nervous system consists of
a sympathetic division and a parasympathetic division.
sympathetic division
prepares the body for physical action
sympathetic division effects
Increases heart rate, blood pressure, and respiration rate
parasympathetic division
concerned with activities that conserve energy and/or restore energy to the body
autonomic tone
the balance between these divisions in response to the changing needs of the body
Autonomic motor pathways
use two motor neurons to carry signals to effectors.
preganglionic neuron
extends from its soma in the brain or spinal cord to an autonomic ganglion by way of a cranial or spinal nerve: tend to be thin and myelinated
postganglionic neuron
lies completely outside the central nervous system and extends from an autonomic ganglion to its effector
Preganglionic neurons of the sympathetic (thoracolumbar) division
arise from the lateral gray horns of the thoracic and lumbar regions of the spinal cord.
short preganglionic fibers
connect with sympathetic chain ganglia, which are located along either side of vertebral column
short preganglionic fibers may—
may synapse immediately with postganglionic neuron; may synapse with other ganglia and form sympathetic trunk; may continue to other ganglia without forming any synapses
long postganglionic fibers
connect with various effectors
illustrates neuronal divergence
each preganglionic fiber may branch and synapse with many postganglionic fibers;
illustrates neuronal convergence
each postganglionic fiber may receive synapses from many preganglionic fibers
Motor neurons of the sympathetic division
connect with the adrenal glands and control the secretion of adrenal hormones.
Preganglionic neurons of the parasympathetic (craniosacral) division
arise from cranial nerves in the brainstem and from the sacral region of the spinal cord.
Preganglionic neurons of the parasympathetic (craniosacral) division- long preganglionic fibers
connect with terminal ganglia in or near an effector
Preganglionic neurons of the parasympathetic (craniosacral) division- short postganglionic fibers
connect to the target organ
Preganglionic neurons of the parasympathetic (craniosacral) division- oculomotor nerve
carries fibers that control the lens and the pupil of the eye
Preganglionic neurons of the parasympathetic (craniosacral) division- facial nerve
carries fibers that regulate salivation and crying
Preganglionic neurons of the parasympathetic (craniosacral) division- glossopharyngeal nerve
carries fibers that are involved in salivation
Preganglionic neurons of the parasympathetic (craniosacral) division- vagus nerve
carries about 90% of the preganglionic fibers to visceral organs
The enteric nervous system
innervates smooth muscle and glands in the digestive tract to regulate the movement of food through the intestines and also to control the secretion of digestive enzymes.
Cholinergic fibers release
acetylcholine, which produces brief, localized effects.
all sympathetic and parasympathetic preganglionic neurons are
cholinergic
all parasympathetic postganglionic neurons are
cholinergic
a few sympathetic postganglionic neurons are
cholinergic
Cholinergic receptors bind
acetylcholine in order to open ligand-gated ion channels.
nicotinic receptors are found on
postsynaptic neurons in all autonomic ganglia, in the adrenal medulla, and in neuromuscular junctions (activation by ACh causes depolarization and excitation of post synaptic cell)
muscarinic receptors are found on
cardiac muscle, smooth muscle, and glands
activation by ACh causes excitation of smooth muscle in intestines, but inhibition of cardiac muscle
Adrenergic fibers produce
norepinephrine (NE), which produces longer lasting and more widespread effects than acetylcholine.
most sympathetic postganglionic neurons are
adrenergic
Adrenergic receptors bind
norepinephrine
alpha receptors
are usually excitatory when bound with norepinephrine
alpha receptors causes
vasoconstriction of blood vessels
beta receptors
are usually inhibitory when bound with norepinephrine
beta receptors relaxes
bronchioles to enhance airflow
knowing location of adrenergic and cholinergic receptors
allows drugs to target specific organs
Most visceral organs receive neurons from
both the sympathetic division and the parasympathetic division, so they have dual innervation.
sympathetic signals and heart activity
sympathetic signals increase heart activity,
parasympathetic signals and heart activity
parasympathetic signals decrease heart activity
sympathetic signals and digestive activities
sympathetic signals inhibit digestive activities,
parasympathetic signals and digestive activities
parasympathetic signals increase digestive activities
Sensory receptors
specialized for detecting environmental stimuli and converting them into action potentials.
Sensory Receptors- stimuli produce
a receptor potential that may release a neurotransmitter or cause a nerve signal to be sent to the central nervous system
sensory receptors transmit
information about the type of stimulus, the location of the stimulus, the intensity of the stimulus, and length of time that the stimulus lasts
Receptive fields
vary in size and in number of neurons
Sensory receptors can be classified according to
the type of stimulus that triggers them.
chemoreceptors
respond to various chemicals
mechanoreceptors
respond to touch, pressure, vibration
nociceptors
respond to pain
photoreceptors
respond to light
thermoreceptors
respond to heat and cold
Tactile sensations are detected by
encapsulated and unencapsulated nerve endings that are located under the skin and in mucous membranes.
encapsulated nerve endings
are enclosed in connective tissue capsules and mostly serve as mechanoreceptors
unencapsulated nerve endings
are “naked” and mostly serve as nociceptors throughout the body
Touch sensations are detected by
mechanoreceptors
crude touch
the ability to perceive contact with the skin, while discriminative touch refers to the ability to recognize exactly where that contact has occurred
Merkel discs and Meissner corpuscles in skin detect
discriminative touch
Krause end bulbs in mucous membranes detect
discriminative touch
hair receptors at base of hair follicles respond to
touch that bends a hair
Pressure
a sustained sensation that is felt over a larger area than touch.
pressure is detected by
Pacinian corpuscles deep in the dermis
Vibrations
result from rapid repetition of sensory signals coming from Pacinian corpuscles.
Itch sensations
result from the stimulation of free nerve endings by chemicals.
Thermoreceptors
are free nerve endings located in epithelial tissue and connective tissue throughout the skin.
“Cold” receptors
respond to falling temperatures.
“Warm” receptors
respond to rising temperatures.
Prolonged stimuli from very low or very high temperatures can produce
pain sensations.
Pain sensations are detected by
free nerve endings that serve as nociceptors in almost all organs, but they tend to be especially dense in the skin and mucous membranes.
nociceptors respond to
any stimulus that is strong enough to cause tissue damage
tissue irritation or tissue injury
releases chemicals that stimulate nociceptors; causes pain sensations to linger until these chemicals are removed
bradykinin
chemical that produces most potent pain stimulus
serotonin, prostaglandins, and histamine
also stimulate nociceptors
Fast pain
sharp, localized, and conducted by myelinated pain fibers. (Needle pricks)
Slow pain
dull, long-lasting, and conducted by unmyelinated pain fibers.
May gradually increase in intensity until it becomes excruciating (toothache)
somatic pain
Pain arising from receptors in the skin, muscles, or joints
pain arising from visceral receptors
visceral pain.
visceral pain
may be mistakenly “felt” in the skin as referred pain, due to convergence of neuronal pathways in CNS
phantom pain
itching or tingling or pain that is experienced by someone who has had a limb amputated
Pain travels by
diverse and complex routes and pain sensations can originate anywhere along these routes.
pain travels from the head region along cranial nerves
V, VII, IX, and X
pain travels from the trunk along the
spinothalamic tract and the spinoreticular tract
Pain can be modulated by
the central nervous system or by drugs that have analgesic mechanisms.
There are approximately __________ located on the tongue, cheeks, soft palate, and throat that serve as chemoreceptors for gustatory (taste) sensations.
10,000 taste buds
taste buds
found in several types of lingual papillae
each taste bud consists of _________ ,which fall into one of three categories
40 to 60 cells
gustatory cells
contain tuft of gustatory hairs that project into a taste pore
taste buds are easily damaged by
heat or friction and get replaced every 7 to 10 days
Chemical substances get dissolved in saliva in order to enter a
taste pore.
gustatory hairs
are stimulated and generate receptor potentials
There are five primary taste sensations
sweet, sour, salty, bitter, umami - that tend to be more correlated with some regions of the tongue than with others.
receptors for bitter taste
at the back of the tongue are the most sensitive
Trigger gagging and/or retching to protect against ingesting harmful substance
receptors for bitter taste
receptors for sweet taste
at the tip of the tongue are less sensitive
receptors for salty taste
along the lateral surface of the tongue are less sensitive
all “tastes” are
actually combinations of these sensations and can be detected from any area with taste buds
Taste signals
conducted from the taste buds along the facial, glossopharyngeal and vagus nerves to the medulla oblongata.
conducted to thalamus which relays them to primary gustatory area to be interpreted
Taste signals
Taste dislikes
may be a protective mechanism
taste preferences
may have homeostatic value to ensure intake of nutrients, vitamins, minerals
The chemoreceptors for olfactory (smell) sensations
are located in the olfactory mucosa of the nasal passages.
olfactory receptors
are bipolar neurons equipped with olfactory hairs
olfactory glands
produce mucus to moisten the olfactory epithelium and dissolve odoriferous chemicals
Gases enter the nose
and stimulate olfactory hairs to generate receptor potentials.
Nerve signals are carried along the olfactory nerves to
olfactory bulbs beneath the frontal lobes of the cerebral cortex.
-olfactory tract then carries these signals to the primary olfactory area in the temporal lobe without transmitting them through thalamus
The sense of smell
poorly understood, but smells seem to evoke vivid memories and strong emotional responses, which may be due to the proximity of the olfactory centers to the limbic system in the cerebral cortex.
______ of all sensory receptors are in our eyes and nearly ____ of the cerebral cortex is involved in visual processing.
70%; 50%
Eyebrows
protect the eyeballs from foreign objects, perspiration, and direct sunlight.
Eyelids
shade the eyes during sleep, protect the eyes from excessive light and foreign objects, and blink every 3 to 5 seconds to spread lubricating secretions over the eyeballs.
eyelashes
highly innervated guard hairs that keep debris out of our eyes and trigger the blink reflex
conjunctiva
a transparent mucous membrane lining the inner surface of each eyelid that secretes a film of mucus to prevent the eyeball from becoming too dry.
irritation or infection of the conjunctiva can dilate blood vessels and produce
“bloodshot eyes”
The lacrimal apparatus
produces tears and drains them from the eye.
lacrimal glands
produce tears, which contain water, says, mucus, lysozyme
lacrimal ducts
carry tears to the conjunctiva to be spread over surface of eyeball
tears
eventually carried into the nasal cavity
Three pairs of extrinsic eye muscles
produce smooth, precise, and rapid movements of the eyeballs to coordinate focusing and prevent “double vision” from occurring.
The fibrous tunic
the outer layer of the eyeball.
sclera
dense white connective tissue that covers most of the eyeball
makes the eyeball more rigid and protects its internal components
anterior cornea
a nonvascular, transparent region that covers the iris
convex curvature enables it to bend light
The vascular tunic
the middle layer of the eyeball.
choroid
a highly vascular and deeply pigmented layer of tissue
ciliary body
an extension of the choroid at the front of the eye
ciliary processes
secrete watery aqueous humor
ciliary muscle
circular band of smooth muscle that alters shape of lens to permit near vision or far vision
pigmented iris
an adjustable diaphragm that controls the diameter of the pupil (the pupil is not a structure, it is the opening at the center of the iris, the iris is the structure)
radial smooth muscle fibers
dilate pupil when more light is needed
circular smooth muscle fibers
constrict pupil when less light is needed
The nervous tunic
the inner layer of the eyeball.
retina
a thin transparent membrane pressed tightly against the choroid
macula lutea
a patch of cells with a small depressed fovea centralis; located at exact center of visual axis of eye
optic disc
occurs where the optic nerve exits the eyeball
Lacks photoreceptor cells; produces blind spot where no image can form
trauma to the head
may detach a retina and cause distorted vision or even blindness
Aqueous humor fills an anterior chamber
between the cornea and the iris and a posterior chamber between the iris and the lens.
aqueous humor
is reabsorbed into the blood by way of the canal of Schlemm; maintains proper intraocular pressure and provides nutrients to the lens and cornea
excessive intraocular pressure
can cause glaucoma, which can lead to degeneration of retina and cause blindness
The lens
a non-vascular, transparent structure made up of crystalline proteins.
suspensory ligaments
attach the lens to the ciliary body and hold it in position behind the pupil
cataracts
cloud the lens because of aging, injury, overexposure to the sun, long-term use of steroids, or diabetes; can cause loss of transparency
The vitreous body
a jelly-like substance located between the lens and the retina.
maintains shape of eyeball and keeps retina flush against the internal portions of the eyeball
The pupil
uses a parasympathetic reflex arc to control the amount of light entering the eye.
contraction of circular smooth muscle fibers in the iris
constricts the pupil to screen out light rays at the edge of the lens to create sharp image of a close object
photopupillary reflex
is consensual, because both pupils will constrict even if only one eye is exposed to light
Light rays enter the eye
and are refracted by the cornea and the lens until they are focused on the central fovea of the retina to produce an image that is inverted and reversed.
in general, the closer the object is to the eye,
the more that light rays must be refracted to be focused on central fovea and produce a clear image
Increasing the curvature of the lens bends the light rays coming from close objects and focuses them on the retina through
accommodation.
ciliary muscles contract,
which causes suspensory ligaments to relax, thus reducing tension on the lens to make it more spherical and refract light rays more sharply
Medial rotation of both eyeballs by the extrinsic eye muscles
produces convergence, which permits both eyes to focus on a single object.
in myopia
(nearsightedness) either the eyeball is too long or the lens is too thick, so light rays focus in front of the retina and produce blurred vision (corrected by using concave lens)
in hypermetropia
(farsightedness) either the eyeball is too short or the lens is too thin, so light rays focus behind the retina and produce blurred vision (corrected by using a convex lens)
astigmatism
due to an irregular curvature of the cornea or the lens; causes unequal focusing and blurred vision
presbyopia
occurs when the lens loses elasticity, which reduces one’s ability to accommodate lens and focus on near objects (corrected with bifocals)
The conversion of light energy into action potentials occurs in the
retina
layer of darkly pigmented cuboidal cells
forms pigment epithelium to absorb stray light rays and prevent reflection and scattering of light within the eyeball
Photoreceptor cells
absorb light energy and generate chemical or electrical signals.
rods
specialized for black-and-white vision in dim light; allow for discrimination among shapes and various shades of gray
rods contain
the light-sensitive photopigment rhodopsin; consists of opsin protein and retinal, derivative of vitamin A absorbed from blood by pigment epithelium
cones
specialized for color vision in bright light and visual acuity
cones contain
the light sensitive photopigment photopsin; various forms respond differently to blue, green, yellow-orange light
rods and cones
send chemical signals to bipolar neurons
bipolar neurons send signals to
ganglion cells whose axons form the optic nerve
When rhodopsin is exposed to light,
it splits into opsin and retinal and becomes colorless because of bleaching.
bleaching
triggers chemical reactions that signal a bipolar neuron that a rod has absorbed light
when bipolar neurons detect variations in light intensity
they stimulate ganglion cells
for rods to continue functioning,
they must regenerate rhodopsin at a rate that keeps pace with bleaching
Light adaptation
occurs when someone in a dark environment is exposed to bright light.
- pupils quickly constrict and the individual experiences momentary difficulty seeing because photopigment bleaching reduces supply of light sensitive pigments
Dark adaptation
occurs when an individual enters a darkened environment.
pupils dilate and visual sensitivity slowly increases as rhodopsin is regenerated, which may take 20 to 30 minutes
Color vision
perceived according to the number of each type of cone that is stimulated.
cones are less sensitive to light, so it requires
greater light intensity to activate them compared to stimulating rods
absence or deficiency of cone photopigments
can produce color blindness
Bipolar neurons in the retina
synapse with retinal ganglion cells in the optic nerve.
visual pathways- Nerve signals travel along the
optic nerve, cross the optic chiasm, enter the thalamus through the optic tracts, and eventually reach the primary visual area in the occipital lobe where they are interpreted and acted upon.
Sound
produced when a vibrating object creates disturbance in a medium (e.g., air).
Pitch
determined by the frequency at which an object vibrates.
Loudness
the perception of sound intensity determined by the energy of the vibration.
involves the sensations of balance and motion.
Equilibrium
static equilibrium
the orientation of the head when the body is stationary
dynamic equilibrium
the perception of motion
The outer ear consists of
a fleshy auricle (pinna) and an external auditory canal that collect sound waves and direct them toward the eardrum.
external auditory canal
lined with hairs and ceruminous glands that secrete cerumen (earwax) to trap dust and foreign particles
The middle ear
occupies an air-filled tympanic cavity in the temporal bone.
tympanic membrane (eardrum)
a thin, semitransparent partition between the external auditory canal and the middle ear
shock waves, trauma, infection
can perforate eardrum
auditory (Eustachian) tube
connects the middle ear to the nasopharynx
air pressure
can be equalized on both sides of the tympanic membrane to ensure that eardrum vibrates freely when struck by sound waves
extending across the middle ear are
three small auditory ossicles
malleus
(hammer) attaches to tympanic membrane
incus
(anvil) is middle bone
stapes
(stirrup) attaches to oval window
The middle ear
occupies an air-filled tympanic cavity in the temporal bone.
tympanic membrane (eardrum)
a thin, semitransparent partition between the external auditory canal and the middle ear
shock waves, trauma, infection
can perforate eardrum
auditory (Eustachian) tube
connects the middle ear to the nasopharynx
air pressure
can be equalized on both sides of the tympanic membrane to ensure that eardrum vibrates freely when struck by sound waves
extending across the middle ear are
three small auditory ossicles
malleus
(hammer) attaches to tympanic membrane
incus
(anvil) is middle bone
stapes
(stirrup) attaches to oval window
____ small muscles insert on the auditory ossicles
two
The inner ear consists of
an outer bony labyrinth filled with perilymph and an inner membranous labyrinth filled with endolymph.
vestibule
forms the central portion of the bony labyrinth, and its membranous labyrinth contains two chambers
posterior utricle
connected by small duct to anterior saccule
above and behind the vestibule
three semicircular ducts in bony semicircular canals, arranged at right angles to one another
in front of the vestibule
the cochlea, which resembles a snail’s shell
scala vestibuli
superior chamber filled with perilymph
scala tympani
inferior chamber also filled with perilymph
cochlear duct
filled with endolymph; separated from scala vestibuli by vestibular membrane and from scala tympani by basilar membrane
resting on basilar membrane is
spiral organ of Corti
spiral organ of Corti contains
thousands of hair cells (stereocilia) covered with jelly-like tectorial membrane
auricle
directs sound waves into the external auditory canal, so they can move toward the tympanic membrane.
Sound waves strike the tympanic membrane and produce
vibrations with the same frequency and comparable intensity as the original sound waves.
Vibration of the stapes creates
enough force to cause vibration of the oval window.
Ossicles don’t amplify sound, but they
reduce transfer of energy to protect inner ear against loud sounds
Vibration of the oval window
sets up fluid pressure waves in the perilymph of the scala vestibuli.
Pressure waves push the vestibular membrane up and down,
creating pressure waves in the endolymph of the cochlear duct.
Pressure waves in the endolymph move the basilar membrane up and down,
causing the hair cells to move back and forth and trigger receptor potentials.
frequency of a sound depends on
which segment of the basilar membrane vibrates
loudness of a sound depends on
the intensity of the vibrations of the basilar membrane and the number of hair cells that generate receptor potentials
Spiral ganglia associated with the organ of Corti form
the cochlear branch of the vestibulocochlear nerve, which terminates in the brainstem.
Equilibrium
can be hard to describe because it is a response, often without awareness, to movements of the head.
The walls of the utricle and saccule contain
thickened maculae that serve as receptors for static equilibrium and linear acceleration.
otoliths
hair cells are embedded in a thick, gelatinous otolithic membrane, which is covered with a layer of calcium carbonate crystals called otoliths
when the position of the head changes,
the otolithic membrane and the otoliths shift position and stimulate the hair cells
hair cells initiate signals in the vestibular branch of the vestibulocochlear nerve which travel to
motor areas in the brainstem and cerebellum to maintain static equilibrium
In the ampulla of each semicircular canal
is a small elevated crista that serves as the receptor for dynamic equilibrium and rotation.
each crista contains
hair cells and supporting cells covered by a dome-shaped gelatinous cupula
when the head moves, endolymph pushes the cupula, which
stimulates the hair cells
hair cells form nerve signals that are carried by
the vestibular branch of the vestibulocochlear nerve to the cerebellum to maintain balance and coordination
The bony labyrinth
moves with the body, while fluids within the membranous labyrinth move at different rates.
Conduction deafness
occurs when the conduction of sound waves to the fluid-filled inner ear get blocked.
can be caused by a ruptured eardrum
otosclerosis fuses the auditory ossicles to one another or fuses the stapes to the oval window
Sensorineural deafness
results from damage to hair cells caused by aging or prolonged exposure to high-intensity sounds.
Tinnitus
a symptom of degeneration of the cochlear nerve, which produces phantom cochlear noise.
Meniere’s syndrome
a disorder of the labyrinth in the inner ear that can cause vertigo, nausea and vomiting, and the inability to stand up.
it is probably due to the overproduction and accumulation of endolymph
gap junctions
enable cells to communicate with adjacent cells by transmitting molecules from cytoplasm to cytoplasm through pores in plasma membrane
neurotransmitters diffuse across a synaptic cleft and
bind to postsynaptic receptors
paracrines
(local hormones) are secreted into the extracellular fluid and diffuse to nearby cells in the same tissue to exert physiological effect
circulating hormones
are secreted by endocrine glands and they travel through the blood to stimulate distant target cells
Endocrine glands
ductless glands that secrete hormones into the extracellular fluid, so the hormones can diffuse into the blood to be carried to target cells throughout the body.
hormones can only bind to
target cells that possess the correct receptors
target cells can adjust their sensitivity to a hormone by
changing the number of receptors
target cells can up-regulate by
increasing number of receptors to become more sensitive to hormone (uterus increases oxytocin receptors late in pregnancy)
target cells can down-regulate by
reducing number of receptors to become less sensitive to hormone (adipocytes reduce number of insulin receptors)
The endocrine system uses ________ to control the body, while the nervous system uses _____________ to control the body
hormones; nerve signals
Hormones travel through ______________, while nerve signals travel along _____________.
blood vessels; neurons
Hormones travel much more ____________ than nerve signals
slowly
Hormones affect _________________, while nerve signals usually affect __________________.
a variety of target cells; a specific group of effectors.
Hormones exert their effects over a __________ period of time than nerve signals.
longer
Steroid hormones
derived from cholesterol so they have a four-ring structure.
testosterone, estrogens, and cortisol differ in functional groups attached to ring
Peptide hormones
amino acid chains of variable lengths.
peptide hormones get synthesized like any other protein:::
Gene gets transcribed into mRNA; gets translated to form pre-prohormone
Rough ER removes portion of this peptide to create prohormone
Golgi apparatus cuts or splices prohormone to create functional hormone
insulin is synthesized as
inactive pre-proinsulin, which is modified into proinsulin, which is converted into the active hormone
Monoamines
(catecholamines) are modified from amino acids.
thyroid hormone is modified from tyrosine
Eicosanoids
local hormones derived from the fatty acid arachidonic acid.
prostaglandins
are the most diverse local hormones and they initiate contractions in smooth muscle
leukotrines
are signaling chemicals that play role in inflammation and allergies
Hormones must travel through ___________________ to reach their target cells
the bloodstream
hormones can alter
the permeability of the plasma membrane of the target cell
hormones can stimulate
protein synthesis by the target cell; and cell division
hormones can activate
or deactivate enzymes
hormones can trigger
secretion of chemicals by the target cell
Most peptide hormones and monoamines are
hydrophilic and can easily travel through the blood.
Steroid hormones and thyroid hormones must
bind to transport proteins before they can travel through blood.
Steroid hormones and thyroid hormones are lipid-soluble, so they can
diffuse through the phospholipid plasma membrane of the target cell into the cytoplasm.
Steroid hormones enter the nucleus and combine with
an intracellular receptor that is associated with the DNA of the target cell.
Transcription produces new mRNA, which directs
the synthesis of proteins that can alter the physiological activity of the target cell.
Peptide hormones and catecholamines cannot
diffuse through the phospholipid plasma membrane, so they bind to extracellular receptors on the outer surface of the target cell.
Designated as "first messengers"
A receptor-hormone complex activates
a “second messenger” system inside the cell.
G protein activates adenylate cyclase- which converts ATP into cyclic AMP (cAMP)
G protein activates phospholipase- which will break membrane phospholipids into diacylglycerol and inositol tri phosphate ( IP3)
cAMP and diacylglycerol activate protein kinase enzymes, which add
phosphate to a protein to activate or inhibit enzymes to alter the physiological response of the target cell.
IP3 opens
ligand-gated calcium channels to allow calcium ions to flood into the cytoplasm and alter the physiological response of the target cell.
Hormones that bind to extracellular receptors can
induce their effects at low concentration because they trigger a chain reaction of enzyme amplification.
The responsiveness of a target cell to a hormone depends on
number of receptors it has, concentration of hormone, influences exerted by other hormones
Synergistic effects
involve two or more hormones that work together to produce cumulative effect greater than effect that either hormone can produce separately
Estrogens and follicle stimulating hormone act together to stimulate follicle maturation in ovaries
Permissive effects
occur when particular hormone acts on target cell to enhance the target cells response to one or more additional hormones
Uterus must be exposed to estrogens before progesterone prepares it for pregnancy
Antagonistic effects
occur when one hormone directly opposes effect that different hormone has on same target cell
Insulin lowers blood glucose levels, but glucagon raises blood glucose levels
Negative feedback occurs when
blood levels of hormone increase and suppress further secretion of that hormone
When blood levels of that hormone drop, endocrine function resumes
Some endocrine glands secrete hormones in response to
nerve signals / releasing hormones
Positive feedback occurs when
hormone- induced response intensifies initial stimulus and causes release of additional hormones
The hypothalamus forms
the floor of the diencephalon.
The hypothalamus produces
releasing hormones and inhibiting hormones to control activities of the pituitary gland
The pituitary gland
a pea-shaped structure in the sella turcica of the sphenoid bone.
suspended from the hypothalamus by the infundibulum
The adenohypophysis
(anterior lobe of the pituitary gland) is connected to the hypothalamus by hypophyseal portal veins.
these blood vessels transport hormones from the hypothalamus to the anterior lobe of the pituitary gland
The neurohypophysis
(posterior lobe of the pituitary gland) is a mass of neuroglia and nerve fibers connected to the hypothalamus by specialized neurosecretory cells.
nerve signals are sent along the axons of these neurons to release hormones that were produced by the hypothalamus, but stored in the posterior lobe
The anterior lobe of the pituitary gland
synthesizes and secretes tropic hormones along a hypothalamo-pituitary-gonadal axis, a hypothalamo-pituitary-thyroid axis, or a hypothalamo-pituitary- adrenal axis to stimulate other endocrine glands to release their hormones.
Growth hormone
(GH) is secreted by somatotropes, which are the most abundant cells in the anterior lobe of the pituitary gland.
GH principal function is
to promote mitosis and cellular differentiation for tissue growth
other GH functions:
stimulates the liver and other tissues to secrete insulin-like growth factors (IGF)
stimulates protein synthesis and inhibits protein breakdown
increases fat breakdown to release energy from free fatty acids
reduces the rate of glucose usage during ATP production
promotes electrolyte balance
GH secretion usually occurs while
we sleep and is regulated by hypothalamic releasing hormones and inhibiting hormones
hyposecretion of GH during childhood growth
causes pituitary dwarfism; limits child’s height to about 4 feet without affecting normal Body proportions
Can be treated with genetically engineered GH
hypersecretion of GH during childhood
can result in gigantism
GH stimulates epiphyseal plates that are already active; can produce heights of 8 feet
hypersecretion of GH during adulthood
because of a tumor in the adenohypophysis can cause acromegaly
Bones and soft tissue in hands, feet, face, becomes abnormally thick
Thyroid-stimulating hormone
(TSH), or thyrotropin, is secreted by thyrotropes.
Adrenocorticotropic hormone
(ACTH), or corticotropin, is secreted by corticotropes.
Follicle-stimulating hormone
(FSH) is a gonadotropin secreted by gonadotropes.
TSH stimulates:
growth of the thyroid gland and its release of thyroid hormones
ACTH stimulates:
the cortex of the adrenal gland to secrete corticosteroids
FSH in females
stimulates the monthly development of egg-containing ovarian follicles
FSH in males
stimulates sperm production in the testes
Prolactin
(PRL) is secreted by lactotropes, which increase in size and number during pregnancy
PRL after females gives birth
stimulated mammary glands which were previously prepared by other hormones, to produce milk and maintain its production
PRL in males
makes testes more sensitive to LH; enhances testosterone secretion
Antidiuretic hormone
(ADH)- or vasopressin, acts on kidneys to increase water retention from urine and decrease urine volume to prevent dehydration
Hyposecretion of ADH
causes diabetes insipidus, characterized by excretion of large amounts of dilute urine
Results in dehydration and chronic thirst
Oxytocin
(OT)- stimulates contractions of smooth muscles in walls of uterus and in contractile cells in mammary glands
release of OT
Released in response to distension of cervix during labor and establishes positive feedback cycle to facilitate childbirth
Release in response to stimulation of nipple during nursing, so milk release can continue though positive feedback
Release during sexual arousal and climax and it propels semen through urethra
The pineal gland
a small cone of endocrine tissue located in the epithalamus.
pineal gland size and secretions
Much larger in children than in adults
It's secretions peak by age 5, decline 75% by end of puberty
The pineal gland produces
serotonin during the day and melatonin during the night.
melatonin
seems to be associated with the body’s diurnal dark-light cycle
overproduction of melatonin
may contribute to seasonal affective disorder (SAD) a type of depression that arises during winter when day length is short
may also contribute to pre-menstrual syndrome
The thymus gland
a large gland above the heart in infants, but it shrinks after puberty.
The thymus gland secretes
hormones to develop white blood cells called T-lymphocytes.
The thyroid gland
a butterfly-shaped gland divided into two lateral lobes that lie on either side of the trachea just below the larynx.
The thyroid gland- follicular cells
produce and secrete triiodothyronine (T3) and thyroxine (T4)
The thyroid gland- C cells
produce and secrete calcitonin (CT)
T3 and T4
released in response to TSH in order to increase one’s metabolic rate.
T3 and T4 use
more oxygen, which creates a calorigenic effect that produces body heat
Secretion increases in cold weather to compensate for heat loss
T3 and T4 increase
fat breakdown and the use of glucose to produce ATP
T3 and T4 combine with
GH and insulin to accelerate body growth
Calcitonin
lowers blood levels of calcium by inhibiting osteoclasts from breaking down bone and by increasing the activity of osteoblasts that deposit calcium in bone.
hyposecretion of thyroid hormones during infancy
can cause cretinism, condition characterized by dwarfism and severe mental retardation
goiter
an enlarged thyroid gland due to insufficient iodine in the diet
Grave’s disease
occurs when auto-antibodies mimic the effect of TSH and cause thyroid hypertrophy and hypersecretion
Grave’s disease consequences
increases the metabolic rate leading to weight loss
increases heart rate
produces abnormal heat sensitivity and increased sweating
causes bulging eyeballs
The parathyroid glands
four small, round masses of tissue attached to the posterior surface of each lateral lobe of the thyroid gland.
Parathyroid hormone
(PTH) raises blood calcium levels by promoting calcitriol synthesis
PTH increases
the number and activity of osteoclasts that break down bone and release calcium into blood
the rate at which the kidneys remove calcium from urine
Hypoparathyroidism
typically occurs as a consequence of trauma or thyroid surgery and causes a calcium deficiency, which impairs neuromuscular activity and leads to muscle twitches, spasms, and the convulsions associated with tetany.
Hyperparathyroidism
a relatively rare condition that causes the removal of large quantities of calcium from the bones, leaving them brittle and susceptible to spontaneous fractures.
Also contributes to the formation of kidney stones
Each adrenal gland is located
in a mass of fat above each kidney and it is organized into an outer adrenal cortex and an inner adrenal medulla.
The adrenal medulla
does not mature until age 3 when a sympathetic ganglion consisting of hormone-producing chromaffin cells responds to sympathetic preganglionic neurons by secreting epinephrine and norepinephrine.
epinephrine and norepinephrine supplement the effects produced by
the sympathetic division of ANS, but their effects lasts longer
epinephrine and norepinephrine increase
blood pressure, heart rate, and the rate of respiration
metabolism by converting glycogen to glucose during glycogenolysis; by synthesizing glucose from amino acids and fatty acids during gluconeogenesis
epinephrine and norepinephrine inhibit
insulin secretion to reduce glucose consumption by muscles
The adrenal cortex
divided into zones, each of which secretes different corticosteroids.
outer zona glomerulosa
secretes mineralocorticoids; regulate concentration of electrolytes in ECF
aldosterone-
increases reabsorption of sodium ions and excretion of potassium ions by kidneys
middle zona fasciculata
secretes glucocorticoids
cortisol and corticosterone-
promote breakdown of proteins and lipids into amino acids and fatty acids, respectively, to make more glucose available so body is alert and prepared to deal with stress
anti-inflammatory compounds-
relieve swelling and other signs of inflammation
inner zona reticularis
secretes androgens that get converted into testosterone
androgens-
contribute to onset of puberty, development of secondary sexual characteristics, sex drive, sexual behavior in males and females
overproduction of adrenal androgens by females
can cause adrenogenital syndrome, which results in formation of male sexual characteristics
The pancreas
a flattened organ located inferior/ posterior to the stomach.
Pancreas has both ________________ functions
exocrine and endocrine
Endocrine functions are performed by
pancreatic islets (of Langerhans).
alpha cells (pancreas)
secrete glucagon, which activates glycogenolysis in liver and release of glucose into blood
glucagon secretion (pancreas)
is regulated by negative feedback from low blood sugar levels trigger its release from alpha cells to increase blood levels of glucose
beta cells (pancreas)
secrete insulin; activates cells to absorb glucose and store it as glycogen for later use
insulin secretion (pancreas)
is regulated by negative feedback when high blood sugar levels trigger its release from beta cells to reduce blood levels of glucose
delta cells (pancreas)
secrete somatostatin, which inhibits secretion of glucagon and insulin and slows absorption of nutrients from gastrointestinal tract
Hypoglycemia
( low blood sugar ) results from overproduction of insulin
Hypoglycemia Symptoms
include anxiety, sweating, weakness
Hypoglycemia consequences
Depriving brain cells of glucose causes mental disorientation, convulsions, unconsciousness, which can quickly lead to death
Diabetes mellitus
a group of disorders that lead to elevated levels of glucose in the blood (hyperglycemia), which can produce excess glucose in the urine (glucosuria).
Diabetes
most prevalent metabolic disease and leading cause of adult blindness, renal failure, limb amputation
Symptoms of diabetes mellitus
include excessive urine production (polyuria), excessive thirst (polydipsia), excessive appetite (polyphagia)
type I Diabetes
about 10% of all cases are type I, or insulin-dependent diabetes (IDDM), which appears to be an autoimmune disease that destroys insulin-producing beta cells
type II diabetes
known as non-insulin-dependent diabetes (NIDDM), and it occurs most often among people over 40 who are overweight
type II diabetes- target cells
do not respond to insulin
type II diabetes- adipocytes
secrete substances that interfere with glucose transport into cells
last card!!
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