Download CHAPTER 35 Human Body Systems: The levels of organization in

CHAPTER 35
Human Body Systems: The levels of organization in humans include cells, tissues, organs, and organ systems.
Cells- Tend to be specialized, and are uniquely suited to perform a particular function.
Tissues- A group of cells that perform a single function- like connecting muscle to bone. There are 4 basic types of tissue:
1. Epithelial- cover internal and external body surfaces.
2. Connective- provide support for body and connects the parts.
3. Nervous- transmits nerve impulses.
4. Muscle- enables body to move.
Organs- A group of different types of tissue that work together to perform a single function. Eye is made up of all 4 types of
tissue that work together for sight.
Organ Systems- A group of organs that perform closely related functions. Like your stomach and intestines are different
organs, but work together for digestion.
Homeostasis: the process by which organisms keep internal conditions relatively constant despite changes in external
environments.
A non-living example is a thermostat. It is controlled by feedback inhibition. The environment gives "feedback" to the heating
system, which then raises or lowers the temperature in response to that feedback.
Just as the thermostat maintains homeostasis within your home, even on the coldest of days, your organ systems work
together to keep your body a controlled, stable environment. From blood clotting to seal a cut, you breathing deeply when
you climb a hill, or maintaining your body temperature, organ systems work together to maintain homeostasis.
The nervous system controls and coordinates functions throughout the body and responds to internal and external stimuli.
-Neurons: Cells that transmit electrical impulses. 3 types:
1. Sensory: Carry impulses from sense organs to spinal cord & brain.
2. Motor: carry impulses from brain/spinal cord to muscles and glands.
3. Interneurons: connect sensory and motor neurons.
Neurons have certain structures in common. Largest part is a cell body that contains the nucleus and much of the cytoplasm.
Out from the cell body are short branches called dendrites that carry impulses to the cell body. The long fiber that carries
impulses away from the cell body is called the axon.
Nerve Impulse- A nerve impulse is similar to the flow of electrical current through a wire. The wire is the neuron. First, let's
talk about a neuron at rest. When a neuron is a rest (not transmitting an impulse), the outside of the cell has a + charge and
the inside has a - charge.
How does this charge difference happen? Using active transport, the sodium-potassium pump in the cell membrane uses the
energy of ATP to pump 3 Na+ out of the cell and at the same time pump 2 K+ in. Combined with the - proteins and Cl in the
cell, this creates the - charge inside. This maintains what we call resting potential.
A neuron remains at rest until it receives a stimulus from another neuron or the environment to start a nerve impulse. Once it
begins, the impulse moves rapidly down the axon. To go from resting potential to action potential, "gates" open that allow the
Na+ ions to flow into the cel. This reverses the charge inside the cell from - to +. When the impulse passes, the cell goes
back to resting potential.
The strength of an impulse is always the same- there's either an impulse or there's not. No such thing as a partial impulse.
The stimulus must be strong enough to cause an impulse to happen. The minimum level of a stimulus needed to initiate an
impulse is called the threshold. Think of the domino example. Dominoes are the neurons, your finger is the stimulus. If you
don't push the first domino hard enough, it won't fall. Once you do push it hard enough though, it falls and starts the reaction.
At the end of each neuron, the impulse reaches an axon terminal. There is a tiny space between the axon terminals of one
cell and the dendrites of the next. This space is called a synapse. It is filled with chemical neurotransmitters that transmit the
impulse across the synapse and to the next cell.
Neurons do not act alone- they are joined together to form the nervous system. The nervous system is separated into two
major divisions: Central Nervous System and Peripheral Nervous System.
-Central Nervous System: relays messages, processes, information, and analyzes information. Consists of the brain and
spinal cord. Both are wrapped in 3 layers of connective tissue called meninges. Between this layer and the central nervous
system is a space filled with cerebrospinal fluid that acts as a shock absorber and for the exchange of nutrients/waste
products with the blood and nervous tissue.
The brain has about 100 BILLION neurons! The largest region is the cerebrum which is responsible for voluntary activities of
the body. Each half of the body is controlled by the opposite half of the cerebrum. There are 2 layers- outer cerebral cortex
(gray matter) that processes information from the sense organs and controls body movement and the inner white matter layer
that connects the cerebral cortex with the brain stem.
The cerebellum is the second largest region of the brain, and it coordinates and balances the actions of the muscles so that
the body can move efficiently.
The brain stem connects the brain and spinal cord, and includes the pons and medulla oblongata. This regions controls
involuntary functions like breathing, heart rate, swallowing, etc...
The thalamus and hypothalamus are found between the brain stem and cerebrum. The thalamus receives messages from all
of the sensory receptors in the body and relays the information to the proper region of the cerebrum for further processing.
The hypothalamus is the control center for hunger, thirst, fatigue, anger, and body temperature.
The spinal cord is the link between the brain and rest of the body. 31 pairs of spinal nerves branch out from the cord.
Reflexes-a quick, automatic response to a stimulus- are processed directly in the spinal cord.
-Peripheral Nervous System: All of the nerves that are not a part of the brain or spinal cord. It has two divisions:
1. Sensory division- transmits impulses from sense organs to the central nervous system.
2. Motor division- transmits impulses from the central nervous system to the muscles or glands.
The motor division is split into 2 systems.
1. Somatic Nervous System: regulates activities under conscious control. Wiggle a toe or make a fist.
2. Autonomic Nervous System: regulates involuntary responses- will speed up your heart rate when you are running. The
Autonomic nervous system has 2 parts:
Sympathetic nervous system and parasympathetic nervous system. Most organs are under control of both systems, and each
system has an opposite effect. For example, heart rate is increased by the sympathetic nervous system and decreased by
the parasympathetic nervous system. Having 2 systems allows the autonomic nervous system to quickly speed up organs
activities or slam on the brakes if necessary.
The Senses
Sensory receptors are neurons that react directly to stimuli in the environment such as light, sound, motion, and temperature.
They are throughout the body, but concentrated in the sense organs (eyes, ears, nose, mouth, skin). There are five
categories of sensory receptors:
1. Pain receptors: Throughout body except not in brain. Respond to chemicals released by damaged cells.
2. Thermoreceptors: in skin, body core, and hypothalamus. Detect temperature differences.
3. Mechanoreceptors: in skin, skeletal muscles, inner ear. Sensitive to touch, pressure, stretching of muscles, sound, and
motion.
4. Chemoreceptors: in nose and taste buds. Sensitive to chemicals in the external environment.
5. Photoreceptors: in eyes. Sensitive to light.
Vision
Light enters eye through cornea, which helps focus the light. Then it passes through a fluid filled chamber called the aqueous
humor. Behind that is the iris, which is the colored part of the eye. The center of the iris is the pupil. Tiny muscles in the iris
adjust the size of the pupil. Low light= bigger pupil. Bright light= smaller pupil.
Behind the iris is the lens. Muscles attached to the lens change its shape to help you focus on near or distant objects. Behind
the lens is another fluid filled chamber called the vitreous humor. The lens focuses light on the retina, where photoreceptors
convert light energy into nerve impulses. Two types of photoreceptors:
1. Rods: sensitive to light, but not color
2. Cones: respond to light of different colors, producing color vision.
The impulses assembled leave each eye through the optic nerve, which takes the signals to the brain for interpretation as a
visual image. (Know eye anatomy diagram on p. 907)
The ear has 2 functions- hearing and balance.
Hearing: Sound is vibrations. The ears can distinguish both the pitch and loudness of the vibrations. Vibrations enter the ear
through the auditory canal, where they cause the tympanum (eardrum) to vibrate. Three tiny bones, the hammer, anvil, and
stirrup, pickup these vibrations. The stirrup transmits vibrations to the oval window where pressure waves are created in the
fluid filled cochlea of the inner ear. The cochlea is lined with tiny hair cells that move back and forth by the waves, and
produce nerve impulses that are sent to the brain via the cochlear nerve.
Balance: Within the inner ear, above the cochlea, there are 3 fluid filled semicircular canals that monitor the position of your
body. As the fluid changes position, the hair cells bend, sending impulses to the brain that enable it to determine body motion
and position and adjust accordingly.
Smell and Taste are chemical senses. Without smell, you can not taste. The sense organs that detect taste are taste buds
which can detect salty, bitter, sweet, and sour.
Touch: Your largest sense organ is your skin. Areas with greater densities of sensory receptors are more sensitive- fingers,
toes, face.
Drugs are any substance, other than food, that change the structure or function of the body. Most drugs interfere with the
neurotransmitters in the synapses. Let's look at some of them.
Stimulants: Amphetamines, cocaine, nicotine, caffine. Increase heart rate, blood pressure, and breathing rate. Also increase
the release of neurotransmitters, leading to a feeling of energy and well-being. When the effect wears off, the brain's supply
of neurotransmitters has been depleted, causing fatigue and depression. Long term use causes circulatory problems,
hallucinations, and depression.
Depressants: Alcohol, marijuana, opiates. Slow down heart and breathing rates, lower blood pressure, relax muscles, relieve
tension. Prevents nerve cells from starting action potential, so are are constant rest potential. Calms parts of the brain that
sense fear and relaxes the person. Over time, user relies on these drugs to deal with everyday anxieties. With alcohol, can
cause death when respiration stops.