BIO 25 Exam 2 Study Questions

What molecule is the main component of cell membranes?

Phospholipids

What type of molecules cannot cross the cell membrane without help? Why can’t they cross?

Large polar molecules and ions (charged molecules). They aren’t attracted to the hydrophobic tail

region of the phospholipid bilayer, but are attracted to the water on either side of the membrane.

What are 4 functions of membrane proteins?

Structure

• Transporters and channels

• Enzymes

• Signaling proteins

• Receptors

If a molecule can’t cross a membrane on its own, what transport mechanisms would allow it to

cross?

Either facilitated diffusion or active transport. Both use proteins to help the molecule across.

What is the difference between facilitated diffusion and active transport?

Active transport requires energy and moves molecules against their concentration gradients.

What is osmosis?

The diffusion of water from areas of low solutes (molecules) to areas of high solutes.

If a solution had an osmolarity of 400 mOsm, what would be its relative osmolarity to a typical cell?

Hyperosmotic

If a solution caused a cell to expand, what would be the tonicity of the solution?

Hypotonic

What layer of the epidermis contains melanocytes?

The stratum basale.

What layer of the epidermis is only found in thick skin (soles of feet and palms of hands)?

The stratum lucidum.

What are 4 functions of the integumentary system?

Protection from dehydration, protection from foreign invaders causing infection, synthesis of

vitamin D, sensory feedback about the external environment, and assisting in thermoregulation.

If all of a person’s melanocytes in their skin died off, what disadvantage would that person have?

They would be unable to create melanin and so would be at more at risk from ultraviolet (UV)

damage

What is the name of the epidermis layer that is in contact with the environment and what type of

cells it is it composed of?

The stratum corneum, which is made up of dead stratified squamous cells.

If a burn damages or destroys the epidermis and dermis layers of a part of the skin, what type of

burn would that be?

A third degree burn since it went all the way through the dermis layer.

For how long does a typical hair grow?

2-7 years

What is the sensory cell type found in the epidermis that detects light touch?

Merkel’s cells

In what epidermis layer do the cells begin linking up with desmosomes?

The stratum spinosum.

What is the predominant cell type found in the dermis, and what function do these cells serve?

Fibroblasts, which secrete into the dermis collagen, elastic, and reticular fibers.

Besides the cell type in the previous question, what other cell types are found in the dermis?

Mast cells, white blood (immune) cells, adipose (fat) cells, as well as sensory cells.

What is something eccrine, apocrine, and sebaceous glands have in common?

They all secrete a substance that makes its way to the skin’s surface.

Where are eccrine glands found and what is their main purpose?

They are found all over the skin, but are especially abundant in the palms of the hands and soles of

the feet. They secrete sweat needed to cool the body.

Why do armpits tend to have body odor over time?

They have a large concentration of apocrine glands which secrete a sweat that has chunks of cell

pieces in it, containing lipids, proteins, and carbohydrates. Bacteria then feed on the nutrients and

their waste products produce an odor.

What is the purpose of sebaceous glands?

To act as a moisturizing and water-proofing agent for the skin and hair.

Where are Pacinian corpuscles found and what purpose do they serve?

They are found deep in the dermis and are used to detect deep pressure on the skin.

if the body temperature of a person was 89.5 °F, what effectors would be activated?

the effectors that warm the body would be activated. These include: the

thyroid gland releasing more thyroid hormone to increase metabolism and heat production; the

muscles shivering to increase heat production; the blood vessels in the skin constricting so that less

blood goes to the skin’s surface (to help retain heat); arrector pili muscles will contract to pull hairs

upright to increase the air-insulation layer around the skin; and behavioral centers of the brain

would increase the motivation to seek out warmth.

What is the name of the brain area that is the integrator for thermoregulation?

The hypothalamus

What are three effectors that are used (only with the opposite effect) for both hypothermia and

hyperthermia?

The thyroid gland – decrease thyroid hormone production when hot, increase it when cold.

Blood vessels in the skin – dilate when hot, constrict when cold.

Behavioral centers in brain – seek cold when hot, seek warmth when cold.

if a person had a tumor on their thyroid gland that caused the gland to secrete way too much

thyroid hormone, what would be the consequence?

Their metabolism would increase, generating more body heat. This would likely cause the person

too become hyperthermic, triggering activation of cooling effectors by the hypothalamus.

if a channel for a cation opened so that it could cross the cell membrane, would this cause a

depolarization of the cell or a hyperpolarization of the cell?

It depends on which way the net force of the ions was going. If the net force was pushing the

positive ion into the cell, it would cause a depolarization. If the net force was pushing the positive

ion out of the cell, it would cause a hyperpolarization.

If a cell has a positive membrane potential, would the electrical force of a negative ion be into or out

of the cell?

Into the cell. The negative ions would be attracted to the positivity inside the cell.

For a typical cell, if the potassium (K+ ) concentration outside the cell (in the ECF) was doubled, what

would happen to the concentration force acting on potassium?

A typical cell has a higher potassium concentration inside the cell (150 mM) than outside the cell (5

mM). If the concentration outside the cell was double to 10 mM, the concentration gradient (the

difference in concentration between the inside and outside of the cell would decrease.

What causes the concentration of sodium (Na+ ) to be high outside the cell and the concentration of

potassium to be high inside the cell?

The Na+ /K + -ATPase (also known as the Na + /K + pump).

What is meant when it is said that an ion is at equilibrium?

It means that all of the forces acting on the ion (the concentration force and the electrical force)

have cancelled each other out so that there is no net force acting on the ion.

When the Nernst equation is used to calculate an ion’s equilibrium potential, what does this value

represent?

The membrane potential (the charge inside the cell) at which the ion is at equilibrium. Said another

way, it is the charge inside the cell that would be needed to create an electrical force on the ion that

would exactly counteract the concentration force acting on the ion.

A cell is at the normal resting membrane potential of a typical cell. The ion X 2- (it has a charge of -2)

has a concentration in the extracellular fluid of 40 mM and a concentration in the intracellular fluid

of 4 mM. If an ion channel for X 2- were to open, in which direction would the ion move, into or out

of the cell?

If sodium is moving across the membrane to make the membrane potential +61mV and potassium is

moving across the membrane to make the membrane potential -90mV, what determines what the

actual membrane potential will be?

The relative permeabilities of each of the two ions.

What parts of a neuron would a person find chemically gated ion channels?

On the dendrites and, to a lesser degree, the cell body.

What would happen to a neuron if:

a. All its voltage-gated Na+ channel activation gates were stuck in the closed position?

graded potential causing the cell’s spike initiation zone to reach -55 mV would not result in the

cell firing an action potential. All neuronal communication would cease.

What would happen to a neuron if:

All its voltage-gated K + channel activation gates were stuck in the closed position?

If a cell fired an action potential, the membrane potential would become very positive as Na +

rushed in. Normally, the membrane potential is “reset” back to a negative value as K + leaves the

cell through open voltage-gated K + channels. But, if these channels were blocked, the

membrane potential would stay positive for a long time (until the leak channels and Na + /K +

pump slowly returned it back to -70mV). Neurons would release lots of neurotransmitter from

just a single action potential.

What would happen to a neuron if:

All its voltage-gated Ca2+ channel activation gates were stuck in the closed position?

Neuron could reach the threshold potential and fired action potentials, but the action potentials

would have no effect. The axon terminals would not release any neurotransmitter once action

potentials arrived there. All neuronal communication would stop.

What would happen to a neuron if:

All its chemically gated channel gates were stuck in the closed position?

neurons would not

be able to receive input from other neurons (so they would have no graded potentials to trigger

any action potentials). All neuronal communication would stop.

What is an action potential and where in a neuron does it start?

An action potential is a brief switching of the membrane’s polarity (negative to positive, and then

back to negative) that travels down a neuron’s axon. It starts at the spike initiation zone.

What is the threshold potential?

-55mV.

What is a graded potential?

is a change to the cell’s membrane potential

During an action potential, while Na + is rushing into the cell, why isn’t K + rushing out of the cell?

The influx of Na + ions and the efflux of K + ions don’t happen at the same time because of the time

delay of the K + activation gate. The Na + activation gate opens without a delay, allowing Na + to rush

into the cell. A millisecond later, the Na + inactivation gate closes (so no more Na + can come into the

cell) and the K + gate finally opens to allow K + to leave the cell.

What is the relative refractory period and why does it occur?

The relative refractory is the time during an action potential during which generating another action

potential is possible but relatively more difficult. This is because the membrane potential has been

made very negative due to the efflux of K + , so the membrane potential is farther away from the

threshold potential compared to when the cell is at rest.

What triggers the exocytosis of the neurotransmitter from the synaptic vesicles?

An increase in the concentration of calcium in the cytosol of the axon terminal.

If a chemically gated channel on a postsynaptic neuron allowed Cl- to enter the cell, would this

cause an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic potential (IPSP)?

It would cause an IPSP because the Cl - entering the cell would move the spike initiation zone of the

postsynaptic cell farther away from threshold (-55mV).

What is it called when the effects of two different postsynaptic neurons overlap in time and sum

together in a postsynaptic neuron?

Spatial summation.

What type of neuron (classified by shape) are the sensory neurons in your skin?

Unipolar neurons.

What is the most common type of neuron (classified by function) and what is it shuttling signals

between?

Interneurons. An interneuron shuttles information between two other neurons.

What is the most common neurotransmitter in the body?

Glutamate is the most abundant excitatory neurotransmitter while GABA is the most abundant

inhibitory neurotransmitter

What is the absolute refractor period and why does it occur?

The absolute refractory period is the time during an action potential during which generating

another action potential is absolutely not possible because the Na + inactivation gate has already

been triggered to close. Another action potential cannot occur until the Na + inactivation gate

reopens.

Is the brain stem part of the central or peripheral nervous system, and what function does it serve?

It is part of the central nervous system and controls vital functions like breathing and blood

pressure.

What are the functions of the cerebellum?

The cerebellum maintains balance and creates/stores/modifies complex motor programs for actions

like typing, riding a bike, playing tennis, etc.)

In what lobe of the brain is the primary somatosensory cortex and what does this brain area do?

It is located in the anterior portion of the parietal lobe, just behind the central sulcus. It receives

information from the skin, muscles, and joints about touch, pain, itch, temperature, muscle length,

and muscle tension.

In what lobe of the brain is the visual association area and what does this brain area do?

It is in the occipital lobe and functions to put visual information into context (associate the colors

and shapes with some “thing”).

Relative to the central sulcus, where is the pre-motor cortex and what does this brain area do?

The pre-motor cortex sits anterior to the central sulcus (in the frontal lobe) and functions to plan

conscious movements.

Where is the thalamus located and what function does it serve?

The thalamus lies near the center of the cerebrum. It acts as a sensory relay station (nearly all

incoming sensory information first comes to the cerebellum) and a sensory filter for filtering out

sensory information that the thalamus deems not important enough to make higher brain areas

aware of (e.g., the weight of your clothes on your body).

What is the difference between a neuron and a nerve?

A nerve is a bundle of neurons covered with a connective tissue sheath.

How many thoracic spinal nerves are there on each side of the body?

12.

In the spinal cord, what is the difference between the gray matter and white matter?

Gray matter is mostly cell bodies of neurons, while white matter is mostly axons of neurons running

up/down the spinal cord.

What does the dorsal root ganglia contain?

It is a cluster of cell bodies of sensory neurons in your skin, muscles, and joints.

What is the difference between a reflex and a reaction?

are hardwired, unlearned, involuntary motor responses to sensory input. Reflexes do not

involve any conscious decision-making by the brain. A reaction is a voluntary action the brain

decided to take

What are two reasons why a myotatic stretch reflex faster than a withdrawal reflex?

The myotatic stretch reflex is faster because it 1) does not have any interneurons to slow it down,

and 2) its sensory neurons are much faster than the pain sensory neurons used for the withdrawal

reflex.

In a withdrawal reflex, what does the inhibitory interneuron release its neurotransmitter on?

The dendrites of alpha-motor neurons going to the extensors of the limb.

What two factors can affect the conduction velocity of a neuron?

The diameter of a neuron and whether or not the neuron is myelinated. Myelination and larger

diameters both speed up the conduction velocity of a neuron.

What is frequency coding?

is how a neuron conveys the magnitude of the signal it is sending. Low frequency

firing of action potentials signals a small signal whereas high frequency firing of action potentials

signals a large signal.