Study Guide: Nervous system & synapse

Describe the mechanism that allows information to travel in only one direction in an axon

ACTION POTENTIAL

-List the general functions of the nervous system.

-1. Sensory input: gathering information. Monitors changes occurring inside and outside the body. Homeostasis-balanced internal environment (controlled by NS and Endocrine system). 2. Integration: process and interpret the sensory input and decide if action is needed. 3. Motor output: a response to integrated stimuli and the response activates muscles or glands.

Identify different types of glia cells and explain their functions (astrocytes, Schwann cells, oligodendrocytes, microglia, ependymal cells)

-Astrocytes- protect nerves from harmful substances in the blood. Microglia- phagocytes that dispose of dead cells Ependymal cells- circulate CSF Oligodendrocytes- responsible for myelin sheaths Schwann cells- creates myelin sheaths in the PNS Satalite cells- act as protective cushioning cells

Distinguish between the CNS, PNS, and ANS

-CNS: Occupy the dorsal body cavity and act as the integrating and command centers of the NS.- Brain (cerebrum, cerebellum, and brainstem.)-The Midbrain(medulla and pons.) Diencephalon: (thalamus and hypothalamus) PNS: the part of the NS outside the CNS, consists mainly of the nerves that extend from the brain and spinal cord.

-Describe the general structure of a neuron and name its important anatomical regions (dendrites, axon, axonal terminals)

-a cell body with nerve processes that transmit signals from one neuron to another. Nerve processes exist as either dendrites or axons. The cell body of the neuron contains the nucleus. The nucleus of the neuron's cell body contains its DNA, or genetic material. Dendrites and axons both extend from the cell body and function to transmit signals to and from the cell. Dendrites receive signals to the cell body, while axons carry signals away from the cell body. Axons may be covered in a layer made of cells called the myelin sheath. The sheath is made up of either oligodendrocytes or Schwann cells, both of which are types of glial cells. Myelin sheath increases the speed at which nerve impulses are transmitted from one nerve cell to another. Gaps between each section of myelin sheath on the axon are known as Nodes of Ranvier. Sodium/potassium (Na+/K+) pumps are located here and play a role in transmitting action potentials down a neuron. At the end of the axon is the axon terminal. Neurotransmitters are released from this location and travel to an adjacent neuron. There are three types of neurons: sensory, motor and interneurons.

-Differentiate between sensory, motor neurons and interneurons

1.Sensory (afferent) neurons conduct impulses from sensory receptors to the CNS; most cell bodies are in the ganglia in the PNS.2. Motor (efferent) neurons transmit impulses from the cNS to effectors in the body periphery. 3. Interneurons (association neurons) complete the communication pathway between sensory and motor neurons: their cell bodies reside in the CNS2.Sensory Neurons: Detect stimuli, and transmit information to the CNS Interneurons: Connect incoming sensory pathways with outgoing motor pathways Motor Neurons: Relay messages from the brain to the muscle or gland cells

Structural Classification

All nervous system structures are classified as part of the CNS (brain and spinal cord) or PNS (nerves and ganglia) Functional2. Motor nerves of the PNS are classified on the basis of whether they stimulate skeletal muscles (somatic division) or smooth/cardiac muscle and glands (autonomic division)-Central nervous system and Peripheral nervous system. The PNS is divided into somatic and autonomic branches. Autonomic contains the Sympathetic and parasympathetic systems.There are sensory neurons which carry information to the CNS and motor neurons which carry information from the CNS

Explain how the conduction speed changes between A, B and C fibers

B filter: At 30mv the B fiber was 7.78 m/s slower than the A fiber. C Filter: At 3omv the C fiber fiber was slower than the B fiber because the C fiber has a small diameter and less myelination.

Explain the significance of the blood-brain barrier (how is it formed, what type of molecules can pass through)

CSF (cerebrospinal fluid) protects fragile nervous tissue from trauma. The blood-brain barrier separates neurons from blood borne substances. 1. Cerebrospinal fluid -Similar to blood plasma composition -Formed by choroid plexus -Forms a watery cushion to protect the brain - Circulated in the arachnoid space, ventricles, central canal of the spinal cord 2.Blood Brain Barrier -Includes the least permeable capillaries of the body -Excludes many potentially harmful substances -Useless against some substances Fats and fat soluble molecules Respiratory gases Alcohol Nicotine Anesthesia

Differentiate between all-or-none (action potentials) and graded potentials Graded Potentials

Graded response, No threshold, Can be added together, Has no refractory period, Decremental conduction Action Potentials All-or-none response, Has threshold, Not added together, Has refractory period, Non-decremental conduction

Explain the effect of magnesium ions in neurotransmitter release.

Magnesium blocks the effects of extracellular calcium by blocking the calcium channels and limiting the release of neurotransmitters.

Explain synaptic transmission and the role of calcium ions in neurotransmitter release.

Nerve impulse causes Calcium ions to enter presynaptic neurone. Entry of calcium ions causes fusion of vesicles with presynaptic membrane and the neurotransmitter is released by exocytosis

Explain the terms depolarization, repolarization and hyperpolarization

Once an action potential has been triggered, it takes place in three phases. •Depolarization: During this stage the membrane potential changes from -70mv to +35mv At rest. The inside of the neuron is 70mv more negative than the outside. At the start of an action potential. Na+ voltage-regulated gates open. Na+ rushes in This causes The inside of the neuron to become more positive• The outside of the neuron to become less positive Thus the difference in charge between the inside and the outside of the neuron is reduced• The membrane becomes less polar or depolarized• The membrane potential reaches zero As more Na+ moves out • The membrane potential reverses

Explain what a resting membrane potential is and how it is formed

Resting membrane potential is the electrical potential energy (voltage) that results from separating opposite charges across the plasma membrane when those charges are not stimulating the cell (cell membrane is at rest). The inside of a cell membrane is more negative than outside. Na+-K+ ATPase pump - This pump pushes only 2K+ into the cell for every 3Na+ it pumps OUT of the cell. Therefore, its activity results in a net loss of positive charges within the cell. Na+ channels are closed when the plasma membrane is at rest. That is because Na+ always wants to go IN, as a result of gradient differences (inside Na+ concentration is lower than outside).K+ leakage channels- concentration of K+ is higher inside the plasma membrane than outside, therefore, K+ wants to go out. These leakage channels allows K+ to go out only in small amounts, and that also helps to maintain the inside more negative than out.

Name the specific types of neurons that connect the CNS with skeletal muscles, sensory receptors, the heart, smooth muscle, and glands

Somatic motor neurons: originating in the central nervous system, these neurons project their axons to the skeletal muscle Sensory neurons carry signals from the outer parts of your body (periphery) into the central nervous system. Motor neurons (motoneurons) carry signals from the central nervous system to the outer parts (muscles, skin, glands) of your body. Interneurons connect various neurons within the brain and spinal cord.

Describe the effect of tetrodotoxin and lidocaine on the voltage-gated Na+ channel.

TTX irreversibly blocks the voltage-gated sodium channels so that sodium ions cannot enter. It blocks the action potential from R1 to R2. Lidocaine blocks the voltage-gated sodium channels, keeping sodium ions from entering. Unlike TTX, the effects of lidocaine are reversible. Synapses•Identify the structures of a synapse (presynaptic neuron, postsynaptic neuron, synaptic cleft, vesicle, neurotransmitter, receptor) Presynaptic Neuron- The neuron conducting impulses toward the synapse Postsynaptic Neuron-The neuron transmitting the electrical signal away from the synapse Synaptic Cleft-A fluid filled space approximately 30-50nm wide Neurotransmitter - They are chemical messengers inside the body that carry messages between neurons. Vesicles - membranes which store most neurotransmitters in the terminal Receptors: liganda molecule of the correct shape that can fit into a particular receptor protein and activate or block the channel

Distinguish between temporal and spatial summation

Temporal Summation is synaptic potentials produced by ONE SINGLE pre -synaptic neuron and Spatial Summation is synaptic potentials produced by DIFFERENT (more then 1) pre-synaptic neurons.

Differentiate between the absolute and refractory periods

The absolute refractory period is the period in which the sodium-gated ion channels are completely inactive the relative refractory period is the time span where the inactive sodium channels transit to the active form to acceptthe second signal.

Explain the effect of myelination and axonal diameter on the conduction velocity

The effect of myelination: The larger the axon diameter the greater the conduction velocity. The effect of axonal diameter: The greater amount of myelination, the greater the conduction velocity.

Explain EPSPs, IPSPs and how they contribute to generation of an action potential

The two types of postsynaptic potentials are EPSP and IPSP. EPSP stands for the Excitatory Postsynaptic Potential and IPSP stands for the Inhibitory Postsynaptic Potential. EPSP is a temporary depolarization that is caused by the flow of positively-charged ions into the postsynaptic cell while IPSP is a hyperpolarization caused by the flow of negatively-charged ions into the postsynaptic cell. The main difference between EPSP and IPSP is that EPSP facilitates the firing of an action potential on the postsynaptic membrane whereas IPSP lowers the firing of the action potential.

Explain in detail what happens during an action potential, where it is formed and its characteristics

a wave of electricity that travels down the axon of neuron from the cell body to the axon terminals This wave of electricity is actually a brief change in the resting membrane potential of the neuron from -70mv to +35mv Then the membrane returns to its resting potential of -70mv. In the resting neuron, special channels for Na+ and K+ allow A small amount of Na+ to diffuse into the cell A small amount of K+ to diffuse out of the cell An action potential works by Briefly opening more membrane gates for Na+ and then for K+ Thus making the neuron cell membrane More permeable first to Na+ Then to K+ This causes a change in the numbers of plus charges inside and outside the cell membrane. Changing the cell membrane potential