Contraction is stimulated by a signal from a nerve cell.
The sarcomere must be shortened for a muscle cell to contract.
Thin and thick filaments do not shorten.
They slide by one another, causing the sarcomere to shorten.
The sliding is accomplished when the myosin head is temporarily bound to an actin filament next to it and through a change in the shape of the myosin head.
The myosin head relaxes and then drags the actin filaments along with it.
It contracts because of the activity of many binding sites and movements within the sarcomere.
The contraction of the entire muscle cell is caused by the coordinated contraction of many sarcomeres in myofibril.
The movement of the myosin head requires energy.
This is what you can see.
Your nervous system is performing several functions at the same time.
The visual system is processing what is seen on the page; the motor system is controlling eye movements and the prefrontal cortex is keeping an eye on it.
The nervous system controls the functions of breathing and body temperature.
One of the two systems that control the body's organs is the nervous system.
The nervous system has more control than the hormonal system.
The signals are communicated through cells rather than through the circulatory system.
The combination of chemical and electrochemical signals is used to cover long distances.
The nervous system acquires information from sensory organs, processes it, and may initiate a response either through motor function, or in a change in the organism's state.
Sea sponges lack a true nervous system.
Flatworms have a central nervous system made up of a ganglion and two nerve cords, and a peripheral nervous system made up of nerves that extend throughout the body.
The insect nervous system is very complex.
There is a brain, nerve cord, and ganglia.
The brain can't control these movements.
The nervous systems of animals are more complex and specialized than those of humans.
The basic structure of the nervous system is made up of a brain and spinal cord and peripheral sensory and motor nerves.
The nerve cords of many animals are located to the side of the stomach, whereas the nerve cords of many animals are located to the back.
There is debate among evolutionary biologists as to whether the different nervous system plans evolved separately or whether the invertebrate body plan arrangement somehow "flipped" during the evolution of vertebrates.
Different parts of the nervous system have different types of neurons and glia.
The mouse has 75 million and the octopus has 300 million.
The nervous systems of these animals control many of the same behaviors, from basic reflexes to more complex behaviors like courting mates.
The ability of cells to communicate with each other is what underlies all of these behaviors.
Different types of neurons have different sizes and shapes that relate to their functional roles.
Each neuron has a cell body that contains a nucleus, smooth and rough reticulum, Golgi apparatus, and other cellular components.
Most of the neurons have at least one dendrite.
The neuron is surrounded by a bilayer lipid membrane.
Ions must pass through the ion channels to enter or exit the neuron.
The ion channels need to be opened to allow the ion to pass into or out of the cell.
The environment can affect the shape of these ion channels.
Ion channels that change their structure in response to voltage changes are called voltage-gated ion channels.
The total charge between the inside and outside of the cell is called the membrane potential.
The inside of a cell is more negatively charged than the outside.
The resting membrane potential is caused by differences in the concentrations of ion inside and outside the cell.
The different ion concentrations inside and outside of the cell can be produced by bringing in two K+ ion and removing three Na+ ion.
Each turn, one molecule of the pump's action is used.
Up to 50 percent of a neuron's ATP is used to maintain its resting potential.
The net negative charge inside the cell is caused by the loss of positive charge in the cell.
The driving force to enter is low, but the movement is less free.
When a slight change in the potential causes their channels to open, they are voltage dependent.
If the input is strong enough, a neuron can send the signal to the downstream neurons.
A neurotransmitter is a chemical that diffuses from the axon of one neuron to the dendrite of another.
When neurotransmitters bind to the dendrites, they open ion channels in the dendrite.
When a signal is received by the dendrite, it travels to the cell body.
A large amount of neurotransmitters will reach the axon.
This will cause Na+ channels further down the axon to open and more positive ion to enter the cell.
An action potential can either happen or not.
The threshold must be reached for the neuron to fire.
Depolarization reverses the charge across the membrane form -70mv to +30mV as sodium ion rush into the cell.
The change in the potential causes the K+ channels to open and the K+ to leave the cell.
The Na+ channels inactivate so no more Na+ enters the cell.
The K+ ion leaves the cell and the potential returns to the resting potential.
The K+ channels close at the resting potential.
It travels in only one direction because the sodium channels have been shut down and can't be opened again until the potential is close to resting.
The release of neurotransmitter onto the dendrite of another neuron occurs when the action potential reaches the axon terminal.
The process begins again when signals are released at axon terminals.
Some neurons do not have any axons.
The axon from a human motor neuron can be as long as a meter from the base of the spine to the toes.
glial cells produce the myelin sheath.
There are gaps in the myelin sheath along the axon.
The signal is charged when it travels along the axon.
Neural communication is dependent on the connections that neurons make with one another, as well as with other cells.
A single neuron may have dendrites that receive synaptic contact from many other neurons.
The Purkinje cell in the cerebellum is thought to have as many as 200,000 other neurons.
The nucleus and mitochondria are common to other cells.
They have more specialized structures such as dendrites and axons.
Scientists used to think that people were born with all the brain cells they would ever have.
The birth of new neurons continues into adulthood according to research performed in the last few decades.
Songbirds produce new neurons when they learn songs.
The hippocampus is a brain structure involved in learning and memory for mammals.
While most of the new neurons will die, researchers found that an increase in the number of surviving new neurons correlated with how well rats learned a new task.
Both exercise and antidepressants promote the growth of the hippocampus.
The opposite effect is caused by stress.
Research in this area may lead to new treatments for disorders such as Alzheimer's, stroke, and epilepsy.
A researcher can inject a compound into the brain of an animal.
BrdU will only be incorporated into newly generated cells that are in the S phase.
A technique called immunohistochemistry can be used to attach a fluorescent label to the incorporated BrdU, and a researcher can use fluorescent microscopy to visualize the presence of BrdU in brain tissue.
The image shows a rat.
The red glow in the micrograph is caused by new neurons tagged with BrdU.
There is an interactive laboratory simulation and a video that explains how BrdU labels new cells.
The number of glial cells in the brain is more than the number of neurons.
glial cells are vital to the function of the neuron.
The OpenStax book is free and can be found at http://cnx.org/content/col11487/1.9.
Most brain tumors are caused by defects in glia.
All functions performed by the nervous system require communication with one another.
When an action potential reaches the end of an axon it stimulates the release of neurotransmitters into the synaptic cleft between the synaptic knob of the axon and the dendrite or soma of the next cell.
The neurotransmitter is released through exocytosis.
The neurotransmitter diffuses across the synaptic cleft.
The ion channels are regulated by the receptor molecule.
An action potential may be initiated in the next cell if enough neurotransmitter has been released, but this is not guaranteed.
The nerve signal will die if insufficient neurotransmitter is released.
There are a number of different neurotransmitters that are used in the brain.
The inner layer is the pia mater, which contacts and covers the brain and spine, and the middle layer is the web-like arachnoid mater.
The brain floats in the CSF.
The cerebral cortex is covered by three layers of meninges.
The brain is the part of the central nervous system that is located in the skull.
The cerebral cortex, limbic system, thalamus, hypothalamus, brainstem, and retinas are included.
The two cerebral hemispheres are made up of the cerebral cortex and limbic system.
The functions of the two hemispheres are redundant, even though there are some brain functions that are more specific to one hemisphere than the other.
Sometimes an entire hemisphere is removed to treat severe seizure.
When the surgery is performed on children who have very immature nervous systems, patients can have surprisingly few problems.
The corpus callosum is cut instead of removing the entire hemisphere in some surgeries.
The split-brain condition gives insights into the unique functions of the two hemispheres.
The Body's Systems object is presented to patients' left visual field, and they may not be able to name it.
The speech center in the left side of the brain can't be signaled from the left visual field because it crosses the right hemisphere.
If a split-brain patient is asked to pick up a specific object out of a group of objects with the left hand, the patient will be able to do so but will still be unable to identify it.
You can learn more about split-brain patients and play a game where you can model split-brain experiments of your own.
Each hemisphere has regions that are involved in different functions.
The cerebral cortex can be broken down into four parts: frontal, parietal, temporal, and ).
The cerebral cortex includes the frontal, parietal, temporal, and occipital lobes.
The olfactory bulb is in this lobe.
The motor cortex is important for planning and implementing movement.
The cognitive functions that are controlled by the frontal cortex include maintaining attention, speech, and decision-making.
Studies show that parts of the brain that have been damaged are involved in personality and risk assessment.
The parietal brain is involved in speech and reading.
The sense of how parts of the body are oriented in space is one of the functions of the parietal lobe.
It is mostly involved in seeing, recognizing, and identifying the visual world.
The role of the hippocampus in memory was partially determined by studying a famous epileptic patient who had both sides of his hippocampus removed.
He could no longer form new memories because of his seizures, although he could remember some facts from before his surgery.
The thalamus helps regulate sleep and consciousness.
The hypothalamus sends signals to the pituitary.
The body's thermostat is one of the functions that the hypothalamus performs.
The hypothalamus regulates sleep cycles.
It plays a role in the formation of memories.
Both for the sensation of fear and for recognizing fearful faces, the two amygdala are important.
The cerebellum helps with coordination and learning new motor tasks.
The coordination required by flight makes the cerebellum of birds large.
The brain and spine are connected by the spinal cord.
The brain and the body are connected by a thick bundle of nerve tissue in the spine.
The meninges and bones of the vertebral column contain the spine cord, which is able to communicate signals to and from the body through its connections with the peripheral nervous system.
A gray butterfly-shape is found in a cross-section of the spine.
The signals from the brain to the body are transmitted by the xes and cell bodies.
The motor reflexes are controlled by the spine.
These reflexes are similar to removing a hand from a hot object.
Local synaptic connections are what make reflexes so fast.
A sensory neuron and a motor neuron are connected by a single sphinx to control the knee reflex.
The information from the interneurons in the spine can be relayed to the brain via one or two synapses.
A cross-section of the spine shows gray matter and white matter.
In the nervous system, a preganglionic neuron from the central nervous system goes to a neuron in a ganglion that goes to a target organ.
The sympathetic nervous system is activated.
The parasympathetic nervous system causes the release of acetylcholine.
The central nervous system relays information between the internal organs.
The lungs, the heart, and smooth muscle are all controlled by it.
The control of these organs is largely by the autonomic nervous system, which can continuously monitor the conditions of these different systems and implement changes as needed.
In order to signal to the target tissue, there are two synapses: a preganglionic neuron in the central nervous system and a neuron in a ganglion.
The sympathetic nervous system and the parasympathetic nervous system have opposing effects on the autonomic nervous system.
One way to remember this is to think of the "fight-or-flight" response a person feels when confronted with a snake.
An accelerated heart rate and inhibited digestion are some of the functions controlled by the sympathetic nervous system.
These functions help prepare an organisms body for the physical strain needed to escape a potentially dangerous situation or fend off a predator.
The sympathetic and parasympathetic nervous systems have different effects.
One way to remember is to think that the parasympathetic nervous system is in control during a picnic, and both "picnic" and "parasympathetic" start with "p".
There are cell bodies in the brain and the spine.
Slowing of heart rate, lowered blood pressure, and stimulation of digestion are some of the effects of the parasympathetic nervous system.
The sensory-somatic nervous system is made up of cranial and spine nerves.
The sensory information is sent to the central nervous system.
Motor neurons communicate with the central nervous system to make the muscles contract.
Without the sensorysomatic nervous system, an animal would not be able to process information about its environment and would not be able to control its motor movements.
Unlike the autonomic nervous system, which usually has two connections between the central nervous system and the target organ, sensory and motor neurons only have one connection.
Homeostasis is maintained in the body.
It is constantly adjusting to the changes in the systems.
Body functions are kept within a normal range, with some fluctuations around a set point.
The main osmoregulatory organs in mammals are the kidneys and their function is to filter blood and maintain dissolved ion concentrations.
They are made up of three distinct regions.
The inferior vena cava and the aorta are the blood vessels that transport blood into and out of the kidneys.
The kidneys filters blood and excretes urine.
The urine is stored in the bladder.
There is a void in the urethra.
There are many organs that work together to digest food.
The mouth is where the mechanical and chemical breakdown of food begins.
The amylase in saliva breaks down sugars.
The stomach is very acidic.
The stomach has pepsin in it.
In the small intestine there is further digestion and absorption.
The large intestine stores waste until it is eliminated.
The primary components of food are sugars and fats.
It is not possible for the animal body to produce essential nutrients for cellular function.
These include vitamins, minerals, and some acids.
Food intake in more than necessary amounts is stored in the cells of the body.
Excess storage of fat can lead to health problems.
Respiratory systems are used to facilitate gas exchange.
In mammals, air is warm and humid.
Air goes down the pharynx and into the lungs through the trachea.
The OpenStax book is available for free through the branching bronchi, reaching the respiratory bronchioles.
The bronchioles open into the alveolar ducts.
The surface area for gas exchange is large because there are so many alveoli and alveolar sacs in the lung.
The circulatory system of the mammal is a closed system with double circulation.
The network of vessels contains blood that circulates because of the pressure differences in the heart.
The heart has two pumps that move blood.
There are two heart valves on the right side and two on the left side.
The pumping of the heart is a function of cardiomyocytes, muscle cells that are striated like skeletal muscle but pump rhythmically and involuntarily.
The signal causes the two atria to contract at the same time.
The blood from the heart is carried through the body by a complex network of blood vessels.
Cell changes are caused by hormones binding to target cells.
In response to hormone activity, the number ofreceptors on a target cell can increase or decrease.
Negative feedback controls the levels of hormones in order to prevent its further release.
The base of the brain is where the pituitary is located.
The hypothalamus sends signals to the anterior pituitary, which produces hormones.
The brain is an extension of the pituitary and it releases hormones.
The neck contains the two lobes of the thyroid gland.
The hormones are produced by the thyroid.
calcitonin is also produced by the thyroid.
The parathyroid hormone is produced on the surface of the thyroid.
The adrenal cortex and adrenal medulla are located on top of the kidneys.
The steroids are produced by the adrenal cortex.
The inner part of the adrenal glands is called the adrenal medulla.
Between the stomach and small intestine lies the pancreas.
The islets of Langerhans are made up of clusters of cells that release hormones.
Some organs have both primary and secondary functions.
Atrial natriuretic peptide is produced by the heart to reduce blood volume, pressure, and Na+ concentration.
Various hormones are produced in the gastrointestinal tract.
erythropoietin is produced by the kidneys.
The immune system is aided by the production of hormones.
testosterone and estrogen are produced in males and females by the gonads.
leptin stimulates satiety signals in the brain.
The human skeleton is composed of two parts.
The bones of the skull, ossicles of the ear, hyoid bone, vertebral column, and ribcage are part of the axial skeleton.
There are 14 facial bones and eight cranial bones in the skull.
There are six bones in the middle ear and one in the neck.
The spine is protected by the 26 bones and surrounds of the vertebral column.
The thoracic cage is made up of the sternum, ribs, thoracic vertebrae, and costal cartilages.
The upper and lower limbs make up the appendicular skeleton.
The clavicles and the scapulae make up the pectoral girdle.
There are 30 bones in the upper limb.
The lower limbs are attached to the skeleton.
The lower limb contains bones of the thigh, leg, and foot.
The structural classification of joints divides them into three categories.
The bones of the joints are held together.
The bones are connected in a cartilaginous joint.
There is a space between the adjoining bones.
The movement of the joints is done in two different ways.
The angle between the bones of a joint can change.
The movement of a bone is called rotational movement.
There are three types of muscle in the body.
The muscle fibers are composed of individual cells.
Muscle fibers are composed of myofilaments composed of the actin and myosin.
When the myosin heads bind to the actin fibers, they move past each other and contract the muscle.
The nervous system is made up of cells.
The cells that send electrical and chemical signals are called neurones.
Dendrites and axons send signals to other parts of the brain.
The glial cells in the nervous system support signaling and development.
There are different types of glia.
When a signal from another neuron is strong enough, an action potential may be carried along the neuron to a synapse with another neuron.
Transmitters carry signals to another neuron.
The brain and the spine are protected by three meninges.
The brain has regions that are functionally defined.
The cortex can be broken down into four primary functional lobes: frontal, temporal, occipital, and parietal.
Language and sleep are examples of functions that involve multiple brain regions.
The brain and the rest of the body are connected through the spinal cord.
It controls motor reflexes and transmits sensory and motor input.
The peripheral nervous system has two nervous systems.
The sympathetic and parasympathetic nervous systems are part of the autonomic nervous system.
The animal is prepared for a fight-orflight response when the sympathetic nervous system is activated.
The parasympathetic nervous system is active.
The sensory-somatic nervous system is made of cranial and spine nerves that transmit sensory information from the skin to the central nervous system.
Whenbacteria are destroyed by leukocytes, gas exchange between the lungs and blood takes place.
The place in the alveolus was reset.
There is blood in the vein.
The inferior vena cava has blood in it.
Goiter is a disease caused by iodine b.
Food enters the large intestine before the small deficiency results.
The body tries to compensate by producing more TSH.
Which emulsifies fats.
Air travels from sweating to increased heart rate when we breathe in.
The bronchioles are part of the body.
An endothermic animal will respond to a sudden drop in environmental temperature by increasing muscle activity.
The c. in the blood heart is during the systolic phase of the cardiac cycle.
The bile from the body is delivered.
The b stimulates muscle growth.
The b. provides body tissues with oxygen and carbon.
The pecthora supports the _____.
The c. cerebellum can receive signals from other neurons.
The part of the brain that controls movement is called the _____.