Question

5. Draw a diagram of the preganglionic neuron, postganglionic neuron, and effector for both Sympathetic Nervous System and Parasympathetic Nervous System. indicate which neurotransmitter is released by each neuron and label the receptors at all locations for the neurotransmitter. 6. Which cells have a resting membrane potential? Which cells can have an action potential? 7. Circle which of the following choices pertain to a Graded Potential. (1) Localized or Widespread (2) Gradations or All-or-None (3) Threshold or Not (4) Short distance or Long distance

Answer 1

5). Preganglion neuron- The autonomic nervous system is the part of the peripheral nervous system that regulates the basic visceral processes needed for the maintenance of normal bodily functions. It operates independently of voluntary control, although certain events, such as stress, fear, sexual excitement, and alterations in the sleep-wake cycle, change the level of autonomic activity. The autonomic system usually is defined as a motor system that innervates three major types of tissue: cardiac muscle, smooth muscle, and glands. However, it also relays visceral sensory information to the central nervous system and processes it so that alterations can be made in the activity of specific autonomic motor outflows, such as those that control the heart, blood vessels, and other visceral organs. It also stimulates the release of certain hormones involved in energy metabolism (e.g., insulin, glucagon, and epinephrine [also called adrenaline]) or cardiovascular functions (e.g., renin and vasopressin). These integrated responses maintain the normal internal environment of the body in an equilibrium state called homeostasis.

The autonomic system consists of two major divisions: the sympathetic nervous system and the parasympathetic nervous system. These often function in antagonistic ways. The motor outflow of both systems is formed by two serially connected sets of neurons. The first set, called preganglionic neurons, originates in the brainstem or the spinal cord, and the second set, called ganglion cells or postganglionic neurons, lies outside the central nervous system in collections of nerve cells called autonomic ganglia. Parasympathetic ganglia tend to lie close to or within the organs or tissues that their neurons innervate, whereas sympathetic ganglia are located at more distant sites from their target organs. Both systems have associated sensory fibres that send feedback into the central nervous system regarding the functional condition of target tissues.

Postganglionic neuron - In the autonomic nervous system, fibers from the ganglion to the effector organ are called postganglionic fibers.

Preganglionic neuron Sympathetic chain Lateral horn Postganglionic neuron < Effector organ Effector organ < Effector organ Chromaffin cell 15 Adrenal medulla Effector organ Thoracic and lumbar spinal cord Collateral ganglion

The neurotransmitters of postganglionic fibers differ:

• In the parasympathetic division, neurons are cholinergic. That is to say Choline is the primary neurotransmitter responsible for the communication between neurons on the parasympathetic pathway.
• In the sympathetic division, neurons are mostly adrenergic (that is, epinephrine and norepinephrine function as the primary neurotransmitters). Notable exceptions to this rule include the sympathetic innervation of sweat glands and arrectores pilorum muscles where the neurotransmitter at both pre and post ganglionic synapses is acetylcholine. Another notable structure is the medulla of the adrenal gland, where chromaffin cells function as modified post-ganglionic nerves. Instead of releasing epinephrine and norepinephrine into a synaptic cleft, these cells of the adrenal medulla release the catecholamines into the blood stream as hormones.
  Brain Parasympathetic (Vagal) Medulla Heart Preganglionic Postganglionic Sympathetic Blood Vessels Symp Ganglia Spinal Cord
  

(6)All cells within the body have a characteristic resting membrane potential depending on their cell type. Of primary importance, however, are neurons and all three types of muscle cells: smooth, skeletal, and cardiac.

Neurons and muscle cells are excitable cells such that these cell types can transition from a resting state to an excited state. The resting membrane potential of a cell is defined as the electrical potential difference across the plasma membrane when that cell is in a non-excited state.

• A resting (non-signaling) neuron has a voltage across its membrane called the resting membrane potential, or simply the resting potential.

• The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.

  Maintaining Resting Potential K+ and Nat can't diffuse across bilayer Nat pumped out K+ leaks out nler silial Fluid otside membrane leul O'S plasma membrane Na-leaks 2001 Erooks Cole Thomson Leam cyloplasm next rote membrane K+ pumped in K+ leaks in

• The resting membrane potential is determined by the uneven distribution of ions (charged particles) between the inside and the outside of the cell, and by the different permeability of the membrane to different types of ions.

the main excitable cell is the neuron, which also has the simplest mechanism for the action potential. Neurons are electrically excitable cells composed, in general, of one or more dendrites, a single soma, a single axon and one or more axon terminals.

Action potential Nations in Voltage (mv) Depolarization Repolarization Kions out Threshold Failed initiations Resting state 5 Stimulust Hyperpolarization 23 Time (ms)

Neurons are a special type of cell with the sole purpose of transferring information around the body. Neurons are similar to other cells in that they have a cell body with a nucleus and organelles. However, they have a few extra features which allow them to be fantastic at transferring action potentials:

• dendrites: receive signals from neighboring neurons (like a radio antenna)
• axon: transmit signals over a distance (like telephone wires)
• axon terminal: transmit signals to other neuron dendrites or tissues (like a radio transmitter)
• myelin sheath: speeds up signal transmission along the axon.
• Action potentials (those electrical impulses that send signals around your body) are nothing more than a temporary shift (from negative to positive) in the neuron’s membrane potential caused by ions suddenly flowing in and out of the neuron. During the resting state (before an action potential occurs) all of the gated sodium and potassium channels are closed. These gated channels are different from the leakage channels, and only open once an action potential has been triggered. We say these channels are “voltage-gated” because they are open and closed depends on the voltage difference across the cell membrane. Voltage-gated sodium channels have two gates (gate m and gate h), while the potassium channel only has one (gate n).

(7) - 3 Threshold

A graded potential is produced when a ligand opens a ligand-gated channel in the dendrites, allowing ions to enter (or exit) the cell. For example, Na+ will enter the cell and K+ will exit, until they both reach equilibrium.In principle, graded potentials can occur in any region of the cell plasma membrane, however, in neurons, graded potentials occur in specialized regions of synaptic contact with other cells (post-synaptic plasma membrane in dendrites or soma), or membrane regions involved in receiving sensory stimuli.Graded potentials are changes in membrane potential that vary in size, as opposed to being all-or-none. They include diverse potentials such as receptor potentials, electrotonic potentials, subthreshold membrane potential oscillations, slow-wave potential, pacemaker potentials, and synaptic potentials, which scale with the magnitude of the stimulus. They arise from the summation of the individual actions of ligand-gated ion channel proteins, and decrease over time and space. They do not typically involve voltage-gated sodium and potassium channels.

A small stimulus causes a small depolarization of the cell membrane A larger stimulus causes more depolarization A stimulus of longer durations causes a longer lasting depolarization, but not of any greater strength than the previous stimulus Threshold A larger stimulus that depolarizes above the threshold may trigger an action potential in a postsynaptic neuron - - - - - - - Membrane potential (mV) LÚTO Some stimuli result in hyperpolarization, which depends on the specific ion channels activated in the cell membrane Depolarizing graded potential Hyperpolarizing graded potential -90 Time

These impulses are incremental and may be excitatory or inhibitory. They occur at the postsynaptic dendrite in response to presynaptic neuron firing and release of neurotransmitter, or may occur in skeletal, smooth, or cardiac muscle in response to nerve input. The magnitude of a graded potential is determined by the strength of the stimulus.