Download NAS 150 The Skeletal System Brilakis Fall, 2003

Bio 102 Section Four
Dr. Kate Brilakis
Part One: The Skeletal System
1.Functions: Protection, Support, Movement, Blood Cell Production, Mineral
Storage/Exchange, Lipid Storage
2.Types of Bones: Long bones, Short bones, Flat bones, Irregular Bones
3. Long Bone Structure: diaphysis, epiphyses, metaphyses, articular cartilage, medullary
cavity, periosteum, and endosteum.
4. Osseous (Bone)Tissue
Matrix contains crystallized mineral salts, collagen fibers and water. Cells may be:
Osteoblasts which build bone be creating collagen fibers for the matrix. Osteoblasts
become trapped by the secreted matrix, turning into…
Osteocytes which are responsible for regulating nutrient exchange.
Osteoclasts are large cells made when many white blood cells (monocytes) fuse.
They are found in the endosteum and secrete enzymes which digest the matrix.
Osteoblasts BUILD bone…Osteoclasts digest bone
5.Compact vs. Spongy Bone Structure
Compact Bone is composed of multiple Osteons each with a single central canal
containing blood vessels and surrounding, concentric lamellae. Spaced along the
lamellae are lacuna which contain the trapped osteocytes. Osteons are arranged in
bundles in the bone, with the whole bone surrounded by periosteum.
Spongy Bone is found in the epiphyses of long bones, lining the medullary cavity and
in large quantity in the short, flat and irregular bones. Spongy Bone contains
trabeculae (webbing) with osteocytes in lacuna but do NOT exhibit the classic osteon
structure seen in compact bone.
Embryonic skeletons are initially just cartilage and connective tissue. During the 6th/7th
week of life, ossification begins with the appearance of osteoblast cells. Endochondral
ossification occurs when the fetal skeleton made of cartilage is replaced by bone.
1. Stem cells differentiate into chondroblasts which secrete the hyaline cartilage matrix.
2. The chondroblasts differentiate into chondrocytes which enlarge, then rupture and
change the pH of the matrix which triggers.
3. Osteogenic (stem) cells in the connective tissue surrounding the cartilage differentiate
into osteoblasts and invade the matrix. Bone growth occurs from the middle outside of
the long bone to the inside and towards the bone’s ends. Osteoblasts secrete bone matrix,
forming bone within the decaying cartilage. As the osteoblasts secrete the matrix, they
become trapped, becoming osteocytes. Meanwhile, osteoclasts, formed by the fusion of
macrophages (blood cells), break down some of the bone in the center, forming a
medulary cavity where bone marrow will be stored.
4. Secondary ossification sites called epiphsyseal plates develop near opposite ends the
ends of the long bone and are responsible for the lengthening of long bones. At puberty,
hormones deactivate these ossification areas, turning them to bone. The epiphyseal plate
then becomes the epiphyseal line and growth stops.
Bone remodeling is the replacement of old bone with new bone. Osteoclasts, huge cells
with many vacuoles containing enzymes, break down and then reabsorb the bone matrix,
removing minerals and protein collagen fibers and depositing these materials back into
the bloodstream. Simultaneously, osteoblasts deposit minerals and protein collagen
fibers
Osteoclast activity must balance osteoblast activity.
Bone metabolism for repair, growth, and remodeling requires:
1. minerals including calcium, phosphorous, magnesium
2. vitamins D,C and A which help enzymes and other regulators function during bone
formation
3. Hormones including:
human growth hormone (hGH) produced by the pituitary gland
calcitonin produced by the thyroid gland which inhibits osteoclast activity
parathyroid hormone (PTH) which encourages osteoclast activity.
4. weight bearing exercises which increase mechanical stress derived from the pull of
skeletal muscles and the pull of gravity. Absence of such stressors weakens bone while
too much produces denser bones.
In the normal Feedback loop, if parathyroid receptors detect decreased blood Ca++
levels, the parathyroid will produce more PTH. This PTH enhances osteoclast activity.
Osteoclasts dissolve bone matrix, resulting in increased blood CA++ levels. Increased
Ca++ levels tells parathyroid gland to reduce PTH production. PTH levels decrease.
If Ca++ levels are to high, the thyroid gland receptors are triggered to produce calcitonin
which decreases osteoclast activity. Less osteoclast activity, less Ca++ release into the
blood. Blood Ca++ levels return to normal.
Parathyroid tumors desensitize Ca++ receptors. PTH is permanently “turned on”
despite high calcium levels (hyperparathyroidism). Very high blood calcium results
causing a variety of physiological and neurological symptoms.
Calcitonin, acting to inhibit osteoclast activity, is part of the antagonistic homeostatic
control of blood Calcium levels.
Joints/Articulations:
Your skeleton has more than 200 joints, areas where bones come together. Ligaments
are bands of connective tissue that hold bones together at joints. In your two wrists and
two hands you have about eighty joints! Some joints are freely moving (shoulder), others
slightly moving like your vertebra and still others that don’t move at all like the sutures in
your skull. Cartilage covers the ends of bones which helps prevent bones that articulate
from rubbing against each other and wearing down.
Bone Marrow:
There are two types of bone marrow. Red marrow consists mainly of hematopoietic
tissue (blood cell producing stem cells). Yellow marrow is mainly made up of fat cells.
About half of adult bone marrow is red and half yellow. Red marrow is found mainly in
the flat bones like the pelvis, sternum, ribs etc. It’s also in the spongy bone at the
epiphyseal ends of long bones like the femur and humerus. Yellow marrow is found in
the medullary cavity of these long bones.
FYI…
The smallest bone of the human body is found in the ear, called the stirrup. It is not larger
than a single grain of rice.
The longest bone in the body is the femur and makes up one-quarter of your body's
height.
The largest bone of the human skeletal system is the pelvis bone or hip bone. The pelvis
is made up of six bones that are joined to each other firmly.
Over half the body's bones are in the hands and feet.
The only jointless bone in your body is the hyoid bone in your throat.
Your nose and ears are not made up of bones but rather cartilage.
There are 27 bones in the human hand and 14 bones in your face.
The number of bones in your neck = the number of bones in a giraffe's neck.
There are about 230 movable and semi-movable joints in your body.
Part Two: The Muscular System
Functions:
movement-integrating muscle, bones and joints
body allignment and stabalization- coordinated actions of muscle groups
heat production- due to muscle contraction
movement of products within body- blood, urine, feces,gametes
regulating organ volume- sphincter action…hope it works
Histology:
Connective Tissue Component:
Sub-Q superficial fascia = areolar connective tissue and adipose tissue
broad band around muscles and covering organs
Deep fascia = dense fibrous irregular connective tissue
holds muscle groups together
epimysium wraps entire muscle
perimysium around fascicles
endomysium around muscle fibers
collectively extend beyond muscle as a tendon
Muscle fiber (cell) anatomy:
sarcolemma, sarcoplasm, T-tubes, sarcoplasmic reticulum,
myofibrils (actin and myosin)
actin: thin filaments attached to Z discs / exhibit myosin binding sites
myosin: thick filaments with heads that interact with myosin binding
sites
Movement:
Skeletal muscle relies on the coordinated effort of connective tissue and muscle.
Muscle pulls on tendons which pull on bones. Contraction moves one bone towards
another at a joint. One end of the target bone remains stationary (origin) and the other
moves (insertion).
Movement occurs via the actions of groups of muscles. Muscles which cause the desired
action are called agonists…muscles which oppose this action are called antagonists.
Anatagonists will relax as agonists contract.
ex.: biceps contracts = agonists…triceps relaxes and stretches = antagonists
result…arm flexes at elbow
if triceps contracts = agonist and biceps relaxes = antagonist
result…arm extends at elbow
if both muscles contract simultaneously…isometric contraction occurs
result…no movement at elbow
Muscles which help prime movers are called synergists.
Muscles which stabalize the origin of primary movers are called fixators.
Muscle Contraction:
Actin (thin filaments) and myosin (thick filaments) exhibit a sliding mechanism. This is
triggered by an action potential (electrical nerve impulse) received from a motor neuron
across a neuromuscular junction.
Neuromuscular Junction (NMJ)
Nerve cell axon with transmits signal to synapse. Synaptic vesicles at end of axon secrete
a neurotransmitter into the synaptic cleft. Receptors across the cleft on the muscle bind
the neurotransmitter (ACh = acetylcholine). This triggers ion channels in the muscle to
open, releasing Na+ (sodium). A muscle action potential is generated. Eventually,
Acetylcholinesterase breaks down the neurotransmitter
Physiology of Muscle Contraction:
After the Muscle Action Potential travels along the sarcolemma and through the T
tubules, Ca++ is released by the sarcoplasmic reticulum into the sarcoplasm. This
Calcium binds to molecules called troponin which are attached to the binding sites of the
actin filaments. The troponin, along with another protein called tropomysin, detach from
the binding sites. Now, they are free to accept the myosin heads during a contraction
cycle. The filaments slide across one another following a sequence of events. ATP splits
(forming ADP and P and releasing energy) and the energy is used by the myosin heads to
attach to the myosin binding sites on the actin filaments by forming crossbridges. The
myosin head swivels, sliding the thin filament past the thick filament into the H zone.
This is called the power stroke. The myosin heads detach from their binding sites. This
sequence is repeated as long as there is Ca++ and ATP. Picture the myosin heads
“walking” along the actin filaments, coming closer to the Z discs.
Relaxation occurs when the Ach is broken down by it’s enzyme. The action potential
stops. Ca++ is transported back into the sarcoplasmic reticulum and it’s Ca++ release
channels close. Troponin binds to myosin binding sites, shutting down their function. The
thin filaments slip back into their relaxed position.
Where does the energy come from?
ATP is stored in only enough quantity to sustain a few second burst of contraction.
Additional ATP must be synthesized if the contraction is to be sustained.
a. Creatine phosphate is made using ATP energy. The P from ATP is transferred to
creatine for “safe keeping” and can be summoned when energy is needed. This source of
energy lasts about 15 seconds.
b. Glycolysis/ anaerobic respiration produces 2 ATP molecules as glucose is
broken down into pyruvic acid. The glucose is supplied by the stored glycogen in your
muscles. This supplies enough energy for about 45 seconds. (if oxygen is absent, this
process continues as lactic acid is formed)
c. Aerobic respiration provides the rest of the ATP, assuming oxygen is present.
The process occurs in the mitochondria and uses oxygen that diffuses into the muscle
fibers or oxygen that has been stored by the myoglobin. This supplies enough ATP for
about 10 minutes of contraction. After that, if oxygen levels are still high, the body relies
on stored lipids for energy, using these lipids as precursors for aerobic respiration.
Heavy breathing after exercise is your bodies way of “resupplying” the myoglobin with
oxygen, converting lactic acid back into stored glycogen and replacing lost creatine
phosphate. Much of the replacement relies on stored energy…burning of lipids to replace
the “quick” energy sources.
We all possess different amounts of different types of muscle fibers:
a. Slow oxidative fibers allow for prolonged, sustained contraction and don’t
fatigue easily, producing ATP via aerobic respiration only.
b. Fast oxidative./glycolytic fibers (FOG) contract and relax more quickly than SO’s
and can produce ATP by aerobic and anaerobic respiration.
c. Fast, glycolytic fibers (FG) generate ATP by glycolysis anaerobically and produce
the fastest and strongest contractions.
The percent of each type of fiber that you have is genetically determined. Would cross
country runners and sprinters use different fibers?
Cardiac muscle exhibits autorhythmicity, the intrinsic rhythm of heart contractions.
Specific cardiac muscle fibers act as a pacemaker that initiates each contraction cycle.
The speed can be affected by hormones. The intercalated discs assist in spreading the
action potential from fiber to fiber.
Smooth muscle contains intermediate filaments in addition to the actin and mysosin.
It exists as sheets that are also rhythmically contracted. This contraction is affected also
by hormones as well as stretching, pH, gas levels, and temperature.
Part Three: The Nervous System
Functions:
a. Sensory: sensory receptors carry information via afferent neurons to your brain and
spinal cord.
b. Integrative: information is processed, analyzed and stored and appropriate responses
are determined via the interneurons.
c. Motor: efferent neurons respond to the integrative decisions by sending impulses to
effectors.
Subsystems of the Nervous System:
a. CNS (Central Nervous System) with brain and spinal cord
b. PNS (Peripheral Nervous System)
Structures:
Brain has 1 x 10*11 neurons with 12 pairs of cranial nerves which extend from the
base of the brain. Each nerve has 100’s-1000’s of axons bundles together.
Spinal Cord connects to the brain and has 1 x 10*6 neurons. 31 pairs of spinal nerves
extend from the cord, each serving a specific region of the body.
Sensory neurons monitor external and internal stimuli and send signals to CNS.
Motor neurons relay to effectors response to stimuli from CNS
CNS:
Brain:
Your brain weighs about 3 lbs and contains trillions of neurons and neuroglial cells.
A human brain exhibits:
1. brain stem with medulla oblongata, pons, midbrain and reticular formation:
Medulla oblongata: connects brain to spinal cord. Regulates heart beat and blood
vessel diameter, regulates and adjusts breathing, controls the reflexes for swallowing,
vomiting, coughing, sneezing.
Pons: serves as a connection from the medulla to cerebrum and helps medulla to
control breathing.
Midbrain: connects Pons to diencephalons. Exhibits a relay station which relays
the info from several reflex arcs associated with the eye and startle reflex as well as
relays auditory information.
Reticular Formation: processing center for sensory information en route to
cerebrum which participate in your state of “consciousness”. Partial uncounsciousness…
ie sleep is an inactivation of the reticular system. (what is a coma?)
2. diencephalons with thalamus, hypothalamus, and pineal gland:
Thalamus:
essential for cognition/learning. Relays sensory info to cerebrum. Assists in
regulating autonomic functions.
Hypothalamus: important for maintaining homeostasis.
1. regulates ANS- smooth, cardiac muscle and glands.
2. controls pituitary gland- integrates nervous and endocrine systems.
3. regulates behavior- pain, anger, pleasure
4. regulates eating and drinking- contains thirst center by monitoring osmotic levels
5. controls body temperature- monitors blood temp and stimulates activites that
promote heat loss or heat retention.
6. regulates circadian schedule.
Pineal Gland: produces melatonin which induces sleep.
3. cerebellum
Exhibits two hemispheres. Regulates coordination by integrating cerebral directions to
muscles with environmental information. Maintains balance, posture, and all
coordinated movements. (What happens when you drink alcohol…can u touch your
nose?)
4. cerebrum with cerebral cortex
Exhibits two hemispheres connected by an axon rich Corpus Callosum that connects
the two halves. Many folds/convolutions give the brain it’s characteristic appearance.
Four lobes are present in the cerebrum:
Frontal lobe: located at the front of the brain and is associated with reasoning, motor
skills, higher level cognition, and language. At the back of the frontal lobe is the motor
cortex which receives information from other lobes of the brain and utilizes this
information to carry out body movements. Damage to the frontal lobe can lead to changes
in personality, socialization, and attention and increase risk-taking.
Parietal lobe: located in the middle/lateral areaof the brain and is associated with
processing tactile sensory information such as pressure, touch, and pain. A portion of the
brain known as the somatosensory cortex is located in this lobe and is essential to the
processing of the body's senses. Damage to the parietal lobe can result in problems with
verbal memory, an impaired ability to control eye gaze and problems with language.
Temporal lobe: located on the bottom/lateral section of the brain. This lobe is also the
location of the primary auditory cortex, which is important for interpreting sounds and
the language we hear. The hippocampus is also located in the temporal lobe, which is
why this portion of the brain is also heavily associated with the formation of memories.
Damage to the temporal lobe can lead to problems with memory, speech perception, and
language skills.
Occipital lobe: located at the back of the brain and is associated with interpreting visual
stimuli and information. The primary visual cortex, which receives and interprets
information from the retinas of the eyes, is located in the occipital lobe. Damage to this
lobe can cause visual problems such as difficulty recognizing objects, an inability to
identify colors, and trouble recognizing words.
Encircling the corpus callosum and the diencephalons is the limbic system. It controls
most of the involuntary actions associated with survival and plays an important role in
behavior and memory. Damage to the limbic system can cause amnesia.
Protection:
Your brain (and spinal cord) is protected by the layers of protective connective tissue
called meninges.
1.dura mater: outermost,dense,layer covering fat cushioning over cord
2.arachnoid mater: fibrous middle layer
* sub-arachnoid space:contains circulating cerebrospinal fluid
3.pia mater: inner highly vascular layer
The brain uses 20% of your oxygen, and must be continuously supplied with glucose for
ATP synthesis. Cerebrospinal fluid circulates in the sub-arachnoid space and in four
cavities that allow access to deep brain tissue. CSF carries gasses and nutrients and
removes toxins.
How does your brain work?
Somatic sensory neurons carry information to the brain. Interneurons in the brain process
this information. Somatic motor nerves carry a response to the effector. The left
hemisphere of the brain receives impulses from and sends motor signal to the right side
of the body and visa versa. Both hemispheres are not identical, however. The left side
controls spoken and written language, reasoning and numerical skills while the right
controls spatial recognition, music, mental imagery.
Memory is just stored information much like what is found in a computer. Retrieval
encourages memory by establishing pathways that are accessed over and over.
Spinal Cord:
Length approx. 42-45 cm, extending from the brain’s medulla oblongata to the top of
the second lumbar vertebra, after which, the column contains the cauda equina.
The spinal cord is divided into two halves by anterior median fissure and posterior,
median sulcus with central canal. The gray matter resembles an interior horn; the white
matter the surrounding tissue. Running parallel within the cord to and from the brain are
bundles of axons called tracts that run in pathways.
Sensory tracts run up.
Motor tracts run down.
Spinal nerves enter and exit the cord from specific regions on the body. They split into
roots, bundles of axons that enter and exit the cord.
Posterior roots with sensory axons enter the cord and the signal runs up.
Anterior roots with somatic motor neurons exit the cord and the signal runs down.
Reflexes are fast, involuntary responses to stimulus. When the gray matter of the spinal
cord integrates the information received from a receptor, the reflex is called a spinal
reflex. They may be inborn (withdrawal reflex) or learned (think learning to drive). The
reflex path is called the reflex arc. For ex.: patellar reflex:
1. sensory receptor is the muscle spindle which senses stretching of the muscle
fibers of quad muscle…tap on the knee
2. impulse from receptor travels along sensory neuron to it’s axon terminus
located in gray matter of the cord. The brain is informed but does not
contribute to initial response.
3. Gray matter integrates signal. Patellar reflex has single synapse between
sensory and motor neuron. Other reflexes have one or more interneurons.
4. Impulse exits motor neuron, travelling to effector located in the quads.
5. Effector muscle responds to impulse. Quad contracts and muscle stretch is reduced.
The patellar reflex is a somatic reflex because its effector is a skeletal muscle. Other
reflexes may be autonomic or visceral, when the effector is a smooth muscle, cardiac
muscle or gland.
Lack of a patellar reflex indicates damage to spinal cord, sensory or motor neurons.
Absence of other reflexes, such as the pupillary light reflex, may indicate brain damage.
What can go wrong?
Spinal cord injury, Brain injury (TBI), Concussion, Stroke (CVA cerebrovascular
incident), TIA (transient ischemic attack) , Parkinson’s (degeneration of dopamine
releasing neurons), Shingles (herpes virus goes lysogenic), Alzheimer’s (plaques)
Nerve Impulses:
Nerve impulses work like dominos. Each neuron receives an impulse and must pass it on
to the next neuron. The dendrites pick up an impulse. It travels through the cell body
through to the axon then transmitted to the next neuron. The entire impulse passes
through a neuron in about seven milliseconds, faster than lightening…literally!
Here’s the big picture:
Selectively permeable neuron membranes exhibit membrane channel/carrier proteins.
Sodium ions (Na+) are concentrated in the interstitial space outside of the cell while
potassium ions (K+) are concentrated in the cell cytoplasm. A neuron has a resting
negative charge (-70 mvolts). A stimulus deforms the cell membrane at the point of
impact, disrupting the ionic balance by allowing Na+ to travel into the cell. This increases
the + charge inside the cell, causing the release of K+ to the outside of the cell in an
attempt to return to the - charge status. This flow of ions into and out of the cell sends a
propagation signal down the dendrite, through the cell body, out through the axon to the
synaptic space where the ion flow causes the release of neurotransmitter into the synaptic
cleft. As the ionic transfer occurs, K+/Na+ pumps use ATP to reassign the ions to their
correct side of the cell membrane.
If you like to think of this process in a step by step fashion…
1.A polarized membrane.
Sodium is on the outside, and potassium is on the inside.
When a neuron is “at rest”, its membrane is polarized. Polarized means the electrical
charge on the outside of the cell is positive while the electrical charge on the inside of the
cell is negative but they are balanced. Outside the cell there are excess sodium ions while
inside of the cell there are excess potassium ions. There are sodium and potassium
channels that are gated (can regulate movement) in the membrane that can move Na and
K across the membrane. When the neuron is inactive/ polarized, it's said to be at its
resting potential. It stays this way until a stimulus comes along.
2. Action potential occurs:
Sodium ions move inside the membrane.
When a stimulus reaches a resting neuron, the gated ion channels open suddenly and
allow the Na+ that was on the outside of the cell rush in. As this happens, the neuron
goes from being polarized to being depolarized. As more Na+ rush in, the inside becomes
positive, and the cell is no longer polarized. Each neuron has a point at which there's no
turning back called its threshold level. At this point, more and more ion channels open
and allow more Na+ inside the cell. This causes the neuron to become completely
depolarization and an action potential to be created.
3.Repolarization:
Potassium ions move outside, and sodium ions stay inside the membrane.
After the inside of the cell becomes stuffed with Na+, the potassium gated channels open
to allow the K+ to move from inside the cell to outside the cell and the sodium channels
close. With K+ moving to the outside, the charge imbalance is restored although it's the
opposite of the initial polarized membrane that had Na+ on the outside and K+ on the
inside.
4. Hyperpolarization:
Now potassium ions are on the outside and sodium ions on the inside.
The potassium gates close, but after there are slightly more K+ is on the outside than Na+
is on the inside. At this point, the cell is said to be hyperpolarized. This is a really quick
stage (although they are allll really quick…remember lightning!) and the cell soon returns
to its normal, resting, polarized state.
5.Refractory period…
Everything back from where they came…K+ returns inside; Na+ outside.
The refractory period is when the Na+ and K+ are returned to their original sides: Na+ on
the outside and K+ on the inside. While the neuron is busy returning everything to
normal, it doesn't respond to any incoming stimuli. After the ion pumps return the ions to
their correct side of the neuron's cell membrane, the neuron is once again polarized and at
its resting potential until per chance another impulse comes along.
How does the signal move from one neuron to another?
There is a space called a synapse or synaptic cleft that separates the axon of one neuron
and the dendrites of the next neuron. Neurons don't physically touch one another.
The signal has to cross the synapse to continue on its way through the nervous system.
Here’s the way it happens:
1.Calcium gates open.
When the signal reaches the end of the axon and the membrane there depolarizes,
calcium ions (Ca2+) are allowed to rush into the axon via other gated channels.
2.A neurotransmitter is released.
As the calcium ions rush in, this triggers vacuoles in the axon to release a
neurotransmitter (like acetylcholine) into the synapse.
3.The neurotransmitter binds with receptors on the dendrites of the neighboring neuron.
The neurotransmitter moves across the synapse and binds to receptors on the dendrites
membrane. Different receptors are activated by different neurotransmitters. After the
neurotransmitter does its job, it is released by the receptor and can be reused by the cell
after it returns to its vacuole across the synapse.
4. The excitation of the receiving neuron’s membrane starts.
The neurotransmitter causes the Na+ channels to open…depolarizing the cell and starting
the entire cascade of events to occur again in this cell.
What are Neurotransmitters?
Neurotransmitters are chemical messenger that transmit, amplifies or affects the
signals between neurons and other neurons, muscle cells or other cells in the body.
Neurotransmitters are released from the end of the axon and travel across the synaptic
cleft where it interacts with a receptor on the surface of the next cell. It has been
postulated that there are over 100 different neurotransmitters which are able to control
nerve functions.
Neurotransmitters are usually categorized by how they function:
1. excitatory neurotransmitters excite the neighboring cell and include epinephrine and
norepinephrine.
2. inhibitory neurotransmitters inhibit the neighboring cell and include serotonin and
GABA
3. excitatory AND inhibitory neurotransmitters such as acetylcholine and dopamine can
both excite and inhibit based on the receptor present.
Neurotransmitters can also be categorized by their type:
1.Acetylcholine is found in neuromuscular junctions connecting motor nerves to muscles
and
permit muscle movement. The paralytic arrow-poison curare acts by blocking
transmission at
these synapses.
2. Amino acids: Gamma-aminobutyric acid (GABA) and Glycine, Glutamate, Aspartate.
Glutamate is the most common excitatory neurotransmitter in the brain and spinal
cord.
Excessive glutamate release can lead to overstimulation and cell death.
GABA is a common neurotransmitter used in inhibitory synapses. Many sedatives
enhance the action of GABA.
3. Neuropeptides: Oxytocin,endorphins, vasopressin, etc.
4. Monoamines: Epinephrine, norepinephrine, histamine, dopamine and serotonin.
Dopamine is an important neurotransmitter for brain function. It helps to regulate
coordinated movement, your pleasure center and emotional arousal. It is also been found
t o play a significant role in the reward system. Low levels of dopamine are found in
people with Parkinson's disease while high levels are found in people with schizophrenia.
Parkinson's disease is partly due to poorly producing dopaminergic cells in the brain.
Levodopa is a precursor of dopamine and as such is an effective drug used to treat
Parkinson's disease.
Serotonin helps regulate appetite, sleep, memory and learning, temperature, mood,
behavior, muscle contraction, and function of the cardiovascular system and endocrine
system. It is also thought to be responsible for some forms of depression since
some depressed patients are seen to have lower concentrations of serotonin.
5. Purines: Adenosine, ATP.
6. Lipids and gases: Nitric oxide, cannabinoids.
Some drugs affect neurotransmitter function. Cocaine blocks the reuptake of dopamine
back into the presynaptic neuron, leaving the neurotransmitter in the synaptic cleft for a
longer period of time. Since the dopamine remains in the synapse longer, the
neurotransmitter continues to bind to the receptors on the postsynaptic neuron, eliciting a
pleasurable emotional response. Physical addiction to cocaine may result from prolonged
exposure to excess dopamine in the synapses, which leads to the downregulation of some
postsynaptic receptors. After the effects of the drug wear off, one might feel depressed
because of the decreased probability of the neurotransmitter binding to a receptor.
Prozac is a selective serotonin reuptake inhibitor (SSRI), which blocks re-uptake of
serotonin by the presynaptic cell. This increases the amount of serotonin present at the
synapse and allows it to remain there longer.
Sensory Receptors
Receptors may be:
Thermoreceptors, Pain Receptors, Chemoreceptors, Osmoreceptors, Photoreceptors
They may be Somatic (not isolated to one area) or in an category as Special Senses
With all of these receptors, an action potential delivers information to the brain. Your
interpretation/response is based on :
a. which pathway the signal travels
b. the frequency of the signal
c. the number of axons stimulated to relay the signal
Body Surface Receptors:
a. Free nerve ending receptors: chemo/pain/thermo receptors.
b. Encapsulated receptors: touch/pressure/thermo
Pain:
a. somatic: pain receptors in skin/muscles/joints
b. visceral: internal stimulation due to muscle spasms, chemical stimulation, distension or
inadequate blood flow
Cell damage causes the release of chemical that may bind to pain receptors and/or trigger
the inflammatory response( histamine) and trigger the release of endorphins from the
hypothalamus to help alleviate the pain.
Special Senses:
1. Chemical Receptors: Smell and Taste
Sense of taste and smell related.
Taste: >10,0001 papillae (taste buds) on your tongue which are triggered by five basic
chemical stimulants which are interpreted as salty, sweet, bitter, sour, and umami.
Papillae contain gustatory hairs, receptor cells (not neurons), supporting cells, taste pore,
basal cells, and sensory neurons.
Smell: olfactory receptors detect gasses via 5 x 10*6 receptors which protrude from the
mucous lining of your nose. These receptor’s axons join, once through the cribform plate
of the ethmoid plate in your skull, to become the olfactory bulb which enters the brain via
the olfactory tract.
2. Mechanical Receptors Balance/Equilibrium:
Static balance: Vestibule with utricle and saccule which contain the axons of sensory
neurons covered with hair cells on which a gelatinous membrane containing otoliths
rests.
Motion: three semicircular canals each have a crista in their base. The crista contain a
cupula, a mound of gelatinous matrix into which tiny sensory hairs project. As the head
tilts, the fluid in the semicircular canals flows over the cupula, bending it and triggering
the hair cells to begin an action potential.
3. Mechanical Receptors: Hearing
(See ear structure tutorial)
Outer ear: auricle, auditory canal with hairs and ceruminous glands, tympanic
membrane
Middle ear: auditory (Eustachian) tube, auditory ossicles called malleus, incus, stapes,
oval window
Inner ear: bony labrinth exhibits cochlea with vestibule, utricles and saccule, and
semicircular canals
Middle ear designed for sound amplification with stirrup, anvil and hammer bones which
react to vibrating tympanic membrane by vibrating oval window in cochlea. Vibration
sets up wave action in cochlea which compresses membrane in organ of corti and
stimulates ciliated sensory cells to send impulse to brain.
Frequency and pitch distinguished by intensity and pattern of wave action.
4. Photoreceptors: Sight:
Light enters eye via the cornea and stimulates the rod (dim light vision) and cone (color
and day light vision) receptors to transmit energy signal (light absorbtion alters rhodopsin
shape, triggering ion channels in membrane) to optic ganglion cells which converge into
an optic nerve.
Accessory eye structures include: eyebrows, lashes, lids, muscles (rectus and oblique),
lacrimal apparatus with lacrimal glands.
Eyeball structures include: Fibrous tunic with cornea, sclera, conjunctiva,
vascular tunic with choroids, ciliary body, lens, iris, pupil, retina with neural layer
containing photoreceptors (rods for black and white and cones for color), bipolar cells
and ganglion cell, optic disc (blind spot), central fovea (acuity spot), pigmented layer
Aqueous(anterior) and vitreous (posterior) body
Visual pathway to brain via optic nerves and optic chiasma.
Nearsightedness (myopia)= focal point anterior of the retina (long eyeball or
overstretched lens)
Farsightedness (hyperopia)= focal point posterior of the retina (short eyeball or loss of
lens flexibility with age)
And if we have time…
Brain Function, Intelligence and Behavior
Genes just code for proteins, not behaviors! Or do they…?
By knocking out a gene in an organism, researchers can see if that absent or altered gene
disrupts the organism’s behavior. The first gene linked to behavior was identified in
drosophila in the early 1970’s and was called “period”. “Period” plays an important role
in circadian rhythms and was also found to affect courtship behavior. Drosophila play
unique courtship songs played using their wings in an attempt to attract mates. When a
part the period gene was transferred from D. simulans to D. melanogaster, the
melanogaster males began singing the simulans song. La la la la la…
Drosophila also exhibit two alleles for a gene that determines foraging behavior. 70%
of flies express the dominant allele in a phenotype which exhibits “roving” behavior.
They move about when food is present while they eat. 30% of flies are “sitters”. They
plop down in one place to eat. The for gene codes for a protein kinase (PKG) which
activates several molecules in intercellular signaling pathway. Rovers have more PKG,
permitting them to indentify new odors (food) faster than sitters…but these flies also
forget these odors faster leading to this roving behavior.
How a gene is regulated can also affect behavior. Look at the mating behavior of the
vole. Prairie voles are monogomous. Montane voles are not. The sequence for the
hormone that controls this behavior is the same in both species. So is the sequence for the
hormone's receptor. The regulatory sequence, however, is longer in the prairie vole.
When the faithful gene AND its regulatory sequence were transferred between the prairie
vole and the montane vole, the males exhibited monogamy.
Can behavior be transferred between populations? Hybridization occurred between the
African and European honey bee. The term "Africanized" is applied to all progeny
resulting from mating between European and African bees. Honey bees from Africa were
imported to Brazil around 1950 in order to blend the genomes of these bees which are
tropically adapted with the genomes of the resident European bees. In 1957, a few of the
“Africanized” queen bees were accidentally released. These queens quickly established
colonies. Over the next forty years, these bees extended their range, entering Texas in the
early 1990s. Often sensationalized as “killer” bees, they defend their nests very
aggressively, are VERY sensitive to vibrations and other disturbances and will swarm
over a mile in response. This behavior is an evolutionary advantage to their natural
competitors. The European honey bee is less aggressive, having been bred domestically
for centuries, stressing traits which increase honey production and decrease swarming.
Researchers at the University of California and Purdue identified such a gene by
measuring the speed and intensity of stinging behavior in 162 colonies of hybrid bees.
They then located gene markers on the chromosomes of the aggressive hybrid bees and
compared the genes with those of non-aggressive hybrid bees. They made a genetic map
of the honey bee (locus mapping). The researchers identified five genes that are linked to
aggressive behavior. They are now developing specific genetic marker that could identify
queen bees with and without the “mean” genes, making it easier for breeders to avoid
using these queens. Next, they are looking to clone the genes to gain an understanding of
how the genes affect behavior.
http://extension.entm.purdue.edu/beehive/pdf/Sting-2.pdf
The production of hormone and hormone receptors are regulated by an organism’s
DNA. Pheromones are chemicals produced by an insect to send a signal to other insects
of the same species. These messengers are volatile chemicals that can be detected from
afar. Hybridized bees are much more sensitive to pheromones, leading to more intense
and prolonged swarming behavior.
http://www.ibra.org.uk/articles/Response-to-alarm-pheromone-by-European-andAfricanized-honeybees
http://extension.entm.purdue.edu/beehive/pdf/JChem_Ecol03.pdf
Animals will vary their behavior towards their offspring and mate, reducing their
aggressiveness and increasing pair bonding in the presence of a hormone called oxytocin.
OT blockers can alter this behavior. Knocking out the OT gene receptor will decrease
maternal instinct along with targeted lactation and monogamy. The number and
distribution of OT receptors explain differences in mating systems.
Similarly, insertion of ADH (antidiuretic hormone) receptor genes into the forebrain
of male voles (via a viral vector) reduced promiscuity and increased bonding.
Could it be that the biological capacity for bonding is one way nature prepares us for
offspring who are born helpless and require parenting in order to survive. Would social
bonds improve the odds? The rewards for these bonds are the feelings of pleasure and
satisfaction that our brains supply us when we experience love.
Instinctive behavior:
Instincts are fixed patterns of behavior triggered by very specific stimuli that continue
until completion such as hibernation, migration, nesting.
Instincts have limitations when it comes to species success. A single stimulus does not
always permit for a variation in response despite the response being detrimental to the
species. For example, observe the cuckoo bird, a brood parasite.
The tricked foster mother only recognizes a gaping mouth as the stimulus to trigger the
feeding response and not the fact that the bird is not her own.
BTW…Brood parasitic birds like the cuckoo lay eggs that mimic those of their hosts to
try to trick them into accepting the egg and raising the cuckoo chick. The University of
Cambridge has found that some finch species parasitised by the cuckoo have evolved
strategies to fight back. One is for host females to lay different colored and patterned
eggs. This makes it harder for the cuckoo to find a host next. Female cuckoos always lay
the same type of egg.
Learned behavior :
Learned behavior is behavior capable of being altered through experience. Some
monkeys have an instinctive ability to swim but learn how to avoid crocodile infested
water from their parents. Some learned behavior can be modified throughout the
organisms life when new information is presented. Others have a fixed time period
in which the behavior is set. For example: Imprinting (are you my mother?)
First described by Konrad Lorenz, imprinting occurs when innate behaviors are released
in response to a learned stimulus. Imprinting often secures the survival of newborn
animals and influences their future breeding activities. Imprinting exhibits a critically
sensitive time period, usually early in life. Ducks and geese imprint in the first 24-48
hours after hatching. This is when the 'following response' is learned. A bebe duck
learns to follow his mother, the first large moving animal he sees. This visual stimulus
does not necessarily have to be momma. Imprinting can occur on any object within a
certain size range regardless of its color or shape.
http://www.youtube.com/watch?v=6-HppwUsMGY
In China, farmers for centuries have relied on the ability to imprint in making ducks
more effective in the control of snails that otherwise damage rice crops. By imprinting
ducklings onto a special stick, they take the brood out to the rice fields and, by planting
the stick different parts of the field, they can ensure that the snails in all parts of the field
will be eaten.
Imprinting seems more significant in precocial species, in which the offspring are less
dependent on their mothers for food and warmth, than in altricial species which often
confine their more vulnerable, and often hairless, young to nests. Altricial neonates learn
similar lessons rather later in life during what are called "socialisation periods". These
apply when the animal's sensory, motor and thermoregulatory systems are fully
functional and they learn to move away from their mother and to interact with others of
the same and other species. The window of opportunity for learning varies according on
the species. In dogs it is from 3-10 weeks and in cats 2-7 weeks, while in primates it is
usually 6-12 months.
If there is a genetic component to learning? If so, how can intelligence be defined?
Knowledge of events? Intuitive talent? Reasoning skills?
Leaning can be time sensitive with certain pathways set by maturity. Young songbirds
learn to sing by imitating adults. This behavior emerges as a product of genetic
predispositions coupled with exposure to specific experiences.
http://dels-old.nas.edu/ilar_n/ilarjournal/51_4/pdfs/v5104Fee.pdf
Conditioning:
Learning also involves associating a certain stimulus with a prepared response.
Negative or positive outcomes are expected and responses are developed accordingly.
Classical conditioning: a stimulus is associated with another event that occurs at same
time. Ex. Pavlov’s dogs heard a bell and found food present…salivation occured when
bell was rung.
Operant conditioning: animal changes behavior in response to stimulus.
ex. rat presses lever to get food. Initial press was accident. Repeat to learn associative
behavior.
Habituation: learning by a culmination of many experiences. Similar to accommodation
where animals learn to ignore stimuli knowing it is not harmful. Ex. Park pigeons
Observational learning: a skill is passed down by watching behavior. “teaching” occurs.
How does a young whale know how to enter the shallows to obtain prey?
http://www.youtube.com/watch?v=heHnm2uwRIM
Adaptive behavior often increases reproductive success. Can this behavior be altruistic?
Think of the honeybee drones. Drones are male bees that lack stingers. Drones have no
purpose other than to mate with passing queens. They eat the pollen and nectar collected
by the female workers, but don’t collect any themselves. When a drone mates with the
queen, his genitals snap off and he dies. Unmated drones are considered a drain on the
hive during the cold season, so are viciously attacked by worker bees and then shoved out
into the cold to starve.
The Theory of Inclusive Fitness states that altruistic behavior genes are selected for
because they increase the fitness (reproductive success) of the species.
Consider Humans and our offspring. Is our parental behavior genetic?
Being a parent consumes energy. More energy input translates into fewer offspring
produced.
R-selection favors traits that maximize number of offspring produced usually with little
parental involvement after birth.
K-selection favors traits that improve quality of offspring and lead to fewer offspring
produced with greater investment per offspring.
Males may assist. Some toads hold onto developing embryos, freeing up the female to
mate again. Females fight for access to males. This is rare. Only 5% of mammalian males
participate in a monogamous fashion to rear young.
When discussing human behavior, can we be as objective as when we discuss the
behavior of mole rats? Why or why not?
Does adaptive behavior necessarily translate into ethical or moral behavior?
Take infanticide. Populations practice this behavior to increase the reproductive success
of the population. Kill one offspring to ensure the survival of another. Male lions
eliminate the offspring of a won pride in order to bring the females into estrus and mate,
passing on his DNA, theoretically the DNA of a superior male.
Are humans any different? Fact: unrelated human males living with a mother of a child
under the age of two increases the chance that that child will perish by a factor of over
50. (http://pediatrics.aappublications.org/content/116/5/e687.full)
Group behavior:
Being a part of a group encourages a cooperative response to predators. Although this
behavior can be selfish such as trying to get into the center of a herd to avoid predation,
the chances of survival overall are greater in ANY herd.
Group behavior increases hunt efficiency and encourages learned behavior.
Ever see primates using a stick to get ants out of a hole?
Groups have the alpha and the subordinate. Is it better to be the subordinate than to go it
alone? Ultimately it is a cost benefit analysis.
More competition…but with greater security and access to mates.
Communication:
Communication among organisms requires signals:
Pheromones: chemical messengers that can be used to attract mates or warn of danger.
Acoustic: songbirds or the scream of warning by howler monkeys
Visual: hair standing on end to scare off threat
Some signals increase vulnerability of organism but continue if the signal is more
important than the threat. Singing increases chance of predation but the search for a mate
supersedes threat.
Tactile: honeybees dance to tell a story of where food can be found after a bee touches a
food source. http://www.youtube.com/watch?v=-7ijI-g4jHg
Sex selection involves many behaviors. Female “hangingflies” only mate with males that
offer a gift of food. She copulates only after she has started to eat the gift. The sperm
takes several minutes to make it into the reproductive tract of female. If gift is eaten
before this occurs, she leaves and finds a new mate. So, the larger the gift, the greater the
chance that a male will mate and pass on his DNA! Sounds familiar?
Fiddler crabs look for large claws.
Lionesses want virile manes.
Population Studies rely on demographics. Demographics include:
Size of the population
Age structure and reproductive base (affects population survival)
Density of the population
Distribution of the population (random, clumped, uniform, etc.)
Influences affecting populations include migration and the carrying capacity of the
environment (biotic potential of each niche)
Limiting factors may be:
density dependent (resources: food, refuge, safety, mates)
density independent = natural disasters that reduce pop size (fire/flood)
Why are these studies important? What do they tell us?