What is the difference between irritability and membrane conductivity

Student Performance Objectives - for the lecture 1. State the functions of the nervous system. Identify the 3 structural and the 3 functional types of neuron.

Given a diagram of a "typical" neuron, identify and state the function of: a. Nissl bodies i. Schwann cells j. Explain the reason a unipolar neuron is said to have a single branched axon, and no dendrites. Explain the formation of the myelin sheath in the peripheral and central nervous systems.

Explain the functions of the 5 different types of neuroglial cells. Define each of the following terms as related to nervous tissue: irritability, conductivity. Explain the importance of neurotubules, kinesin and dynein within the axon as related to the process of axon transport. Explain the factors that cause the measurement of mv as the potential across the cell membrane of a resting neuron. Explain what is meant by local potentials developing along the dendrites and cyton of a neuron.

Explain an action potential in terms of the ion movements occurring across the neuronal cell membrane during depolarization and repolarization. Explain the importance of membrane pumps in the continuous, lifelong ability of neurons to maintain the resting membrane potential RMP. Describe what a nerve impulse is. Describe why nerve impulses travel at higher velocities in myelinated nerve fibers compared with unmyelinated nerve fibers. Draw a labeled diagram of a chemical synapse. Describe the transmission of a signal across an excitatory chemical synapse.

Explain the importance of neurotransmitter breakdown soon after synaptic transmission. Explain the difference between an excitatory and inhibitory synapse on the basis of the functioning of the receptor on the postsynaptic membrane. Explain how the nervous system codes for the quality and intensity of stimuli. Explain the difference between a convergent and divergent neuronal circuit. Student Required Nervous System Items- for Laboratory Practical Examinations items will be added or removed at your laboratory instructor's discretion.

For each item, identify its position in a neuron model or on a microscopic slide of a neuron and indicate its function.

Properties - irritability and conductivity a. Irritability refers to the ability of neurons cells of the nervous system to detect and to respond to a stimulus. Conductivity refers to the ability of neurons to transmit signals from one neuron to other neurons and from a neuron to muscles and glands.

Functions a. Provide sensory awareness through electrochemical input to the central nervous system CNS from peripheral receptors. The word "peripheral" refers to parts of the body e. Provide motor responses to sensory input: e. Analysis in its highest form occurs in the brain and can result in a long delay between a sensory input and a motor response. Memory - the ability to recall and integrate previous experiences into the analysis of information.

The nervous system is broadly organized into the central nervous system CNS - brain and spinal cord, and the peripheral nervous system PNS - the 12 pairs of cranial nerves and 31 pairs of spinal nerves. Other broad, functional divisions of the nervous system include the somatic nervous system SNS and the antonomic nervous system ANS.

The SNS includes all neural pathways involved in the conscious sensing of stimuli e. The ANS includes all neural pathways involved in the innervation and control of the smooth muscles of the body's internal organs e. At the cellular level of organization, the nervous system is based on the fundamental cellular unit -the neuron. It is estimated that there are about 1 trillion neurons in the nervous system. These highly irregularly shaped cells possess the nervous system's basic properties - irritability and conductivity.

Also at the cellular level are the specialized connective tissue cells of the nervous system - the neuroglia. There are at least 10 neuroglial cells for every one neuron in the nervous system. They come in different types each performing different functions that serve the activities of the neurons: a.

Schwann cells - synthesize myelin for the nerve fibers of the PNS. Oligodendrocytes - synthesize myelin for the nerve tracts of the CNS. Astrocytes - form structurally supportive and protective barriers around the neurons shielding them from direct contact with substances carried in the blood. Astrocytes form the basis of the blood-brain barrier and help regulate the chemical composition of the interstitial fluid directly bathing the neurons. They appear to communicate with neurons electrochemically and through their secretion of neuronal growth factors.

Microglia - protect neurons from microbes and can remove unwanted material dead cells from nervous tissue by phagocytosis. Ependyma - cells lining the brains cavities ventricles that secrete and help circulate cerebrospinal fluid. Each nerve fiber axon of the PNS is surrounded by Schwann cells and possibly a myelin sheath surrounded by a thin layer of connective tissue, the endoneurium.

The nerve fibers making up nerves are arranged in groups called fascicles, with each fascicle surrounded by a slightly thicker layer of connective tissue, the perineurium. All the fascicles of the nerve are surrounded by a thicker layer of connective tissue, the epineurium. Functional Cell Types a. Sensory afferent neurons - conduct nerve impulses into the CNS from peripheral receptors connected to the body surface skin , major sense organs e.

Motor efferent neurons - conduct nerve impulses from the CNS to peripheral effectors e. Association neurons interneurons - these neurons are found only in the CNS and conduct nerve impulses among themselves as part of the analysis and memory functions of the nervous system.

They are the basis for the delay in response between an incoming sensory signal and an outgoing motor response. Structural Cell Types a. Multipolar neurons - these are the most commonly observed type of neuron possessing many dendrites and a single axon. Most association neurons are multipolar. Bipolar neurons - possess a single dendrite and a single axon. They are found in specialized locations associated with the delivery of sensory signals into the CNS - they are found in the olfactory epithelium of the nasal passages, the eye's retina, and in the inner ear.

Unipolar neurons - possess a single branched axon. They are the afferent neurons that bring sensory information into the spinal cord. Nerve Physiology. Nerve Impulses Neurons have two major functions:.

Irritability Irritability is the ability to respond to a stimulus and change it into an impulse. Conductivity Conductivity is the ability to transmit the impulse to other neurons, muscles and glands. Polarization of the Plasma Membrane Animation showing creation of resting membrane potential All cells have polarized plasma membranes.

This polarization results from the fact that there is an uneven distribution of ions, or charged particles, on either side of the membrane. The unequal distribution of ions also results in the plasma membrane being electrically polarized. Typically, the outside of the cell has more positive charges than the inside of the cell.

The electrical polarity across the plasma membrane is like a battery that contains energy in the form of volts. The charges involved are so small that this energy is actually expressed as thousandths of a volt, or millivolts. From the left atrium the blood is ejected into the left ventricle. The left ventricle then pumps the blood out of the heart into the general circulation.

The aorta is the first vessel to carry blood, and, at that same time, coronary arteries are fed oxygenated blood to circulate though the heart. The above is only a brief outline of the circulation of blood. Be sure you can trace the blood through the heart. Be sure that you can name all the valves and chambers of the heart as blood flows through. You should also be able to list the major arteries of the body. When you perform the assessment, it will be necessary for you to know these vessels and their location.

Myocardium: Following is a review of the physiology of muscle contraction. Muscle contraction is dependent upon the availability of calcium and other electrolytes.

The nervous system sends impulses to the muscle cells. As these energy bonds are formed with in the muscle cell, the sarcomere is shortened. Shortening of the sarcomere causes shortening of the muscle fiber cell , and hence the contraction of the entire muscle.

When the calcium in the cell is used up, the sarcomere returns to its normal length and so does the muscle. This is known as diastole. The muscle must replenish its calcium and energy. Cardiac muscle has special properties that not all other muscles have. As mentioned earlier in the text, the properties are:. In the body many conditions must be met before a muscle will have the ability to contract. We know that fluids and electrolytes are important as well as the condition of the body.

The preceding material is review of the anatomy and physiology of muscle contraction. It is important that you keep in mind the basic principles of muscle physiology. These principles will help you understand some of the following normal and abnormal ECG tracings. Represented next is the electrical pathway of the impulses through the heart.

Each wave on the ECG is related to a portion of those impulses. When the heart muscle is stimulated by the electoral impulses, blood is ejected from eh corresponding chamber of the heart. Pacemaker cells have one phase of action potential. This is the portion from the threshold to peak action potential i. Initiate stage of repolarization, it has a brief origin initial phase due to influx of C1- ion.

During the next 0. This period does not exist in skeletal muscle. This allows cardiac muscle to have a more sustained contraction isometric contraction; plateau phase. The relationship of resting membrane potential at excitation to the rate of depolarization during phase 0 of the action potential; normal resting membrane potential is 85 to 90 mv. Is dependent upon the integrity of the cell membrane; injury, ischemia, chemical intoxication and also radical temperature changes can alter membrane potential.

Some cells are polarized and others are not. A strong stimulus can produce a response in the polarized cells after P wave complex by T wave. A vector is a symbolic representation of a physical force. It has direction and magnitude, characterized by an arrow, Plus or Minus. Vector size varies; it depends upon muscle mass.