Neurons Physiology

Refers to a separation of charges across the membrane or to a difference in the relative number of cations and anions in the ICF and ECF.

The membrane potential is maintained by the Na+/K+ pump.

The Na+/K+ pump is found in the membranes of many types of cells. In particular, it plays a very important role in nerve cell membranes.

Notice that 3 positive ions (Na+) are pumped out of the cell (towards ECF) for every 2 positive ions (K+) pumped into the cell (towards ICF). This means that there is more positive charges leaving the cell than entering it. As a result, positive charge builds up outside the cell compared to inside the cell. The difference in charge between the outside and inside of the cell allows nerve cells to generate electrical impulses which lead to nerve impulses.

About 50 to 75 times more permeable to K+ than to Na+.

It is the difference of electrical potential between two points

The flow of electrical charges

the membrane potential that exists when an excitable cell is not displaying an electrical signal. (Positive outside/negative inside- difference across the concentration gradient)

Neurons and muscles are excitable tissue

Also known as the soma, houses the nucleus and organelles.

Extensions coming from the cell body, typically project like antennae to increase the surface area available for receiving signals from other nerve cells. Carry signals toward the cell body, and contain protein receptors for binding chemical messengers from other neurons.

A nerve fiber, a single, elongated, tubular extension that conducts action potentials away from the cell body and eventually terminates at other cells.

Local changes in membrane potential that occurs in varying grades or degrees of magnitude or strength.

Graded potentials are usually produced by a specific triggering event that causes gated ion channels to open in a specialized region of the excitable cell membrane. (The stronger the triggering event, the more gated channels that open, the greater the positive charge entering the cell, and the larger the depolarizing graded potential at the point of origin. Also, the longer the duration of the triggering event, the longer the duration of the graded potential)

Brief, rapid, large (100mV) changes in membrane potential during which the potential actually reverses, so that the inside of the excitable cell transiently becomes more positive than the outside.

A change in potential that makes the membrane less polarized (less negative) that at resting potential. Depolarization decreases membrane potential, moving it closer to 0mV.

The membrane potential returns to resting potential after having been depolarized.

A change in potential that makes the membrane more polarized (more negative) that at resting potential. Hyperpolarization increases membrane potential, moving it even further from 0mV, more charges are separated than at resting potential.

the critical potential that must be reached before an action Totential is initiated in an excitable cell. Typically between -50mV and -55mV.

An excitable membrane either responds to a stimulus with a maximum action potential that spreads nondecrementally throughout the membrane or does not respond with an action potential at all.

The means by which an action potential is propagated throughout a myelinated fiber, with the impulse jumping over the mylinated regions from one node of Ranvier to the next.

Oligodendrocyte in CNS- (the brain and spinal cord) myelin forming cells.

Schwann cells in PNS- (nerves running between the CNS and the various regions of the body) myelin forming cells.

The portions of a myelinated neuronal axon between the segments of insulative myelin; the axonal regions where the axonal membrane is exposed to the ECF and membrane potential exists.

The process by which a new action potential cannot be initiated by normal events in a region that has just undergone an action potential.

The specialized junctions between two neurons where an action potential in the presynaptic neuron influences the membrane potential of the postsynaptic neuron by means of the release of a chemical messenger that diffuses across the small cleft that separates the two neurons.

A small depolarization of the postsynaptic membrane in response to neurotransmitter binding, bringing the membrane closer to the threshold.

A small hyperpolarization of the postsynaptic membrane in response to neurotransmitter binding, therby moving the membrane farther from the threshold.

A composite of all EPSP’s and IPSP’s occurring at approximately the same time.

A conversion of the electrical signal in the presynaptic neuron to an electrical signal in the postsynaptic neuron by chemical means takes time. It is usually between 0.5 to 1 msec.

Neurotransmitters must be inactivated or removed after it has produced the appropriate response in the postsynaptic neuron, however, so that the postsynaptic “slate” is wiped clean, “leaving it ready to receive additional messages from the same or other postsynaptic inputs.

The summing of several postsynaptic potentials occurring very close together in time because of successive firing of a single presynaptic neuron.

The summing of several postsynaptic potentials arising from the simultaneous activation of several excitatory (or several inhibitory) synapses.

The converging of many presynaptic terminals from thousands of other neurons on a single neuronal cell body and its dendrites so that activity in the single neuron is influenced by the activity in many other neurons.

The diverging, or branching, of a neuron’s axon terminals, so that activity in this single neuron influences the many other cells with which its terminals synapse.

Anything that is not part of sensual nervous system. It is outside the brain and the spinal cord. It has to have inputs to the CNS.

Provides the input to the CNS. It is going to include sensory information. Has visceral and sensory

Affects the skeletal muscles, they are the effectors

Has 2 branches-- the sympathetic division (fight or flight) and the parasympathetic (rest and digest) They both affect the cardiac, smooth muscle and the glands, it is involuntary.

Monitor the concentration of solute particles

Produce a constant rate of firing as long as the stimulus is applied and maintained.

They adapt. when a stimulus first begins they respond with a burst of firing and they quickly reduce the levels of firing to a lower level. However when the stimulus stops they will respond with another burst of firing. First burst is called the called the OFF response.

Respond to all sorts of painful stimuli including chemicals released by damaged cells. When cells are damaged they are going to ultimately release prostoglandins, which amplify the pain and making pain receptors more responsive to the pain.

Skeletal. voluntary. somatic affects it via the motor neurons. refered to as mucle fibers. multi nucleated. striated.

Muscle--muslce fiber--myofibrils--sarcomerre

Made up of actin (spherical) that will bind together and twist into an actin helix. It has a binding site for myosin cross bridges that are covered by Tropomyosin so that no contraction can occur.

Troponin will stabalize the tropomyosin to cover the binding sites.

The protrusions on thick filaments are called cross bridges. Each cross bridge has 2 binding sites. 1 for actin and 1 for myosin ATPase.

As soon as the binding happens between a myson cross bridge and an actin molecule you will get a power stroke. The cross birdges will bend in causing the thin filaments to slide into the center of the sarcomere. This is contraction.

No, they only slide due to the sliding filament mechanism.

Calcium binds to the troponin which will expose the binding sites to break apart from the tropomyosin. As soon as the binding sites are exposed you will see a binding between the myosin cross bridge and the actin. Once this binding occurs you will get a power stroke.

The action potential travel the membrane and the t tubules. there are segments that lie on either side of the transverse tubules and those parts of the SR have a name called, lateral sacs.

In order for detachment to occur between the myosin cross bridges and the actin a fresh ATP has to bind to the cross bridge.

When we die we will run out of ATP. Rigor mortis sets in because there isn’t enough atp to bind to the cross bridges, so there is no attachment. Therefore the body is rigid. After a while the proteins will fall apart.

It is one motor neuron and all the muscle fibers that it innervates. They help make sure that not all parts of the muscle have to contract at the same time.

It refers to the activation of more and more motor units to develop more strength as needed. Once they are all acivated you have reached maximum strength of that muscle.

When you get a smooth sustansed contraction because you are firing the AP so fast that you don’t give it a chance to relax.

Due to the depleetion of energy reserves. and the build up of lactic acid. It is the muscle that can’t respond to stimulation with the same degree of contraction

The motor neurons that can’t synthesize the ACH fast enough to sustain the contraction.

It is the CNS that does not activate hte motor neurons which supply the muscle.

Classified two ways: the speed of contraction (fast and slow fibers) and the primary way that the fiber uses to synthesis ATP.

Gets ATP from electron transport chain (occurs in the mitochondria). These fibershave an abundace of mitochondria. Needs oxygen. Highly vascularized fibers. Have many molecules of moyglobin (help support the oxidative fibers). They are fatigue resistant because of how much ATP is makes. “red meat” fibers

SLOW. Gets ATP from electron transport chain (occurs in the mitochondria). These fibershave an abundace of mitochondria. Needs oxygen. Highly vascularized fibers. Have many molecules of moyglobin (help support the oxidative fibers). They are fatigue resistant because of how much ATP is makes. “red meat” fibers

Uses glycolysis. Occurs in the cytoplasm. Doesn’t need as many mitochondria then fast or slow oxidative fibers. Less vascularized. Less myoglobin. “white meat” fibers. They fatigue much easier.

We lose up to 30 percent of our muscle fibers. The motor unit size decreases. The diameter of it decreases. The neuroactivity to the muscle decreases because the motor neurons get less efficient at making ACH.

Our brain has to be aprised of the position of our muscles. So we have structures in our muscles called muscle spindles that relay muscle position. They have intrafussal fibers that have afferent innervation. When they are streched it causes an action potential to go to the CNS.

Important becasue they allow us to react very quickly. Spinal reflexes you react before the message gets to your brain. It is predictable.

One step process to get ATP. You get ATP + creatine