Chapter 11 - The Peripheral Nervous System

What is the nervous system composed of?

It is made up of the brain
and spinal cord, and the nerves that emerge
from them and connect them to the rest of
the body

What is the main function of the nervous system?

The main function is to make sure that the body maintains homeostasis by ensuring that the body responds to multiple internal as well as external stimuli and appropriately regulate these responses

What two branches are the nervous system divided into?

The peripheral nervous system and central nervous system

What two pathways does the peripheral nervous system divide into?

Sensory pathways and motor pathways

What do the motor pathways branch off into?

The somatic nervous system and autonomic nervous system

What does the term “somatic” mean?

• Provide examples of things that the somatic nervous system controls

• What other functions is the somatic nervous system responsible for other than voluntary movements?

Under conscious control, meaning it is something we can regulate voluntarily

• Examples include muscle movement and speaking

• Processing sensory input such as touch, temperature, and pain and sends that information to the brain

What does the term “autonomic” mean?

• Provide examples of things that the autonomic nervous system controls

Under unconscious control, meaning it is something we control without the use of any voluntary bodily movements

• Examples include regulating of blood pressure, heart rate, digestion and respiratory rate

What two branches does the autonomic nervous system divide into?

The sympathetic and parasympathetic nervous system

What is the main function of the sympathetic nervous system?

The main function is to be activated whenever the body is in a stressful situation. This is also known as activating the body’s “fight or flight” mode like when it believes it is in danger.

What is the main function of the parasympathetic nervous system?

The main function is to be activated after the body goes through a stressful situation/ This is also known as the body’s “rest and digest” mode.

What are the basic structural and functional units of the nervous system?

Neurons

What are the functions of neurons?

Their functions are to respond to physical and chemical stimuli, conduct electrochemical signals and release chemicals that regulate various body processes. In other words:

• Sensory Input

• Integration

• Motor Output

What are nerves?

They are cordlike bundles of fibres that make up neurons

What are the three main types of neurons

• Sensory Neurons

• Motor Neurons

• Interneurons/Association Neurons

Sensory Neurons are…

• In which part of the nervous system?

• Are they myelinated or unmyelinated?

• What is their function?

• Peripheral Nervous System

• Myelinated

• Send nerve impulses from the body’s sensory organs to the brain and spinal cord

Motor Neurons are…

• In which part of the nervous system?

• Are they myelinated or unmyelinated?

• What is their function

• In the peripheral nervous system

• Myelinated

• Send nerve impulses from the brain and spinal cord to the effectors (muscles and glands)

Interneurons/Association Neurons are…

• In which part of the nervous system?

• Are they myelinated or unmyelinated?

• What is their function

• Central Nervous System

• Unmyelinated

• relay messages between sensory and motor neurons

What are effectors?

Effectors are primarily muscles and glands that respond to signals from neurons, enabling movement and physiological processes

What are receptors?

Receptors are specialized structures that detect and respond to various stimuli such as light, sound and temperature. They convert energy from external and internal environments into electrical impulses that are then transmitted for processing. They are primarily found in sensory organs

What are glial cells and their functions?

Glial cells are a type of neuron that account for about half of the nervous system’s volume. They nourish the neuron, remove any waste, defend against any infections and provide a supporting framework for nervous system tissue.

What are Schwann Cells?

Schwann cells are a type of glial cell that have the function of creating myelin, which is what is composed within the myelin sheath in sensory and motor neurons.

Describe the structure of motor neurons

• Cell body is connected to dendrites

• Connected to an effector

• Has a myeline sheath

• Contain nodes of Ranvier

Describe the structure of sensory neurons

• Cell body is located in the middle of the axon instead of connecting to the dendrites

• Connected to a sensory receptor

• Has a myelin sheath

• Contain nodes of Ranvier

Describe the structure of interneurons

• Cell body located at the end near the dendrites

• No myelin sheath

• Do not have nodes of Ranvier

What is the nerve impulse transmission pathway in order?

• Stimulus

• Sensory Receptor

• Sensory Neuron

• Interneuron

• Motor Neuron

• Effectors

• Response

What is neurilemma?

Neurilemma is a membrane produced by the Schwann cells in the peripheral nervous system and promotes the regeneration of damaged axons

What three parts of the neuron are essential for informational flow in exact order?

Dendrites, Cell Body and Axon

What is the function of dendrites?

Receive signals from other neurons or sensory receptors and relay the impulse to the cell body

What is the function of the cell body?

Contains the nucleus and other organelles, serving as the site of metabolic cell reactions. Also processes input from dendrites and if the input received is large enough will relay it to the axon where an impulse is initiated

What is the function of the axon?

Responsible for transmitting impulses away from the cell body along its length to the next neuron

What are reflex arcs?

• The simplest neural pathway that occur within the body

• Involve very few neurons which therefor allow us to respond to particular stimuli such as danger very rapidly

• Does not require the brain to participate, hence such a fast reaction

• The response by the effector, such as movement, occurs before the brain even processes information about what had happened

Describe the entire reflex arc process in order

• Stimuli

• Sensory Receptor

• Sensory Neuron

• Interneuron (in spinal cord)

• Motor Neuron

• Effector Muscle

• Response

What are the five main stages in a nerve impulse?

• Resting potential

• Depolarization

• Repolarization

• Hyperpolarization

• Refractory period

Describe what happens during resting potential in terms of:

• What is within the cell and what is out of the cell at this stage?

• What is the electrical potential at the point within the nerve impulse?

• What is being actively transported?

• What causes the inside of the neuron to be negative?

• High levels of sodium surround the outside of the cell (the extracellular space) while high levels of potassium ions are within the inside of the cell (intracellular space)

• Electrical Potential is at -70mV

• Carrier proteins are actively transporting 3 sodium ions out of the neuron while also actively transporting 2 potassium ions into the neuron due to an ATP sodium-potassium exchange pump

• The inside of the neuron is negative due to the small amount of negatively charged chloride ions passing through a nearly impermeable membrane within the neuron

Describe what happens during depolarization in terms of:

• What is within the cell and what is out of the cell at this stage?

• What is the electrical potential at the point within the nerve impulse?

• What channel stays open and what channel stays closed?

• What does this stage make the inside o f the neuron?

• What must be reached in order for the stimulus to generate an impulse?

• Small amounts of sodium are in the extracellular space while a large majority of sodium as well as potassium ions are within the intracellular space

• Electrical potential is at -55mV

• Voltage gated sodium channels stay open while potassium gates are still closed, making them stay in the neuron

• This stage makes the inside of the neuron more positive due to the the ratio of sodium and potassium ions versus negative chloride ions

• In order for a stimulus to generate this kind of impulse for depolarization to occur, a threshold potential must be reached

Describe what happens during repolarization in terms of:

• What is within the cell and what is out of the cell at this stage?

• What is the electrical potential at the point within the nerve impulse?

• What channel stays open and what channel stays closed?

• Sodium ions stay within the cell (intracellular space) while potassium ions begin to travel outside of the cell (extracellular space), moving down the concentration gradient

• At this point, electrical potential starts making its way down to about -90mV

• Sodium channels stay closed while voltage gated potassium channels open

Describe what happens during hyperpolarization in terms of:

• What is within the cell and what is out of the cell at this stage?

• What is the electrical potential at this point within the nerve impulse/What channel stays open?

• Sodium ions stay within the cell (intracellular space) while potassium ions begin to travel outside of the cell (extracellular space), moving down the concentration gradient

• Voltage gated potassium channels stay open until a membrane potential of -90mV has been reached

Describe what happens during the refractory period in terms of:

• What is within the cell and what is out of the cell at this stage?

• What is the electrical potential at this point within the nerve impulse?

• What cannot happen during this time period?

• Because the axon is currently at -90mV which is way under from it’s resting potential, the sodium-potassium exchange pump powered by ATP will naturally active transport sodium and potassium ions in and out of the axon in order for the neuron to return back to it’s resting potential

• The electrical impulse at this point within the neuron is at -90mV and will continue to go back up to -70mV and reach resting potential due to the sodium-potassium pump

• For the next few milliseconds, the membrane cannot be stimulated to undergo another action potential. This allows for a uni-directional nerve impulse

What is saltatory conduction?

Saltatory conduction is a process in which action potentials are forced to “jump” from one node of Ranvier to the next in myelinated neurons. This allows for extremely quick transmission of nerve impulses compared to unmyelinated neurons where nodes of Ranvier are not present

What is multiple sclerosis?

Multiple sclerosis is a disease caused by the breakdown of the myelin sheath surrounding axons in the central nervous system

What are neurotransmitters?

• What are some examples of neurotransmitters?

Neurotransmitters are chemical signals that carry the neural signal from one neuron to another or form a neuron to an effector

• Dopamine, Serotonin , Endorphins, Norepinephrine and Acetylcholine

What is acetylcholine?

Acetylcholine is an excitory neurotransmitter

Why is acetylcholine such a crucial component in a nerve impulse?

In order for the post synaptic neuron or effector to become depolarized, there must be a sufficient amount of acetylcholine in the synaptic cleft which can bind to the receptor proteins present on the post synaptic dendrite or effector

What is acetylcholinesterase and why is it very important?

• What would happen if it were to not exist?

• Acetylcholinesterase is the enzyme that breaks down acetylcholine within the synaptic cleft

• It is crucial within a nerve impulse because it is used to breakdown any excess acetylcholine within the synaptic cleft that binds to a receptor and causes a post synaptic membrane excitation

• If acetylcholinesterase were to not exist, that would mean excess acetylcholine would be in such abundant amounts near the synaptic cleft and would always bind to the post synaptic membrane, initiating membrane excitation at a constant rate without giving it time to repolarize for the next action potential

Define summation

When more than 1 presynaptic neuron must release the neurotransmitter in order to reach threshold

Define neuromuscular junction

When a motor neuron synapses with an effector

What is the difference between an excitatory and inhibitory neurotransmitter?

• Excitatory neurotransmitters increase trans-membrane flow of the post synaptic neuron, triggering receptor proteins to open up ion channels such as sodium to flow into the post synaptic neuron making it slightly depolarized

• Inhibitory neurotransmitters decrease trans-membrane flow of of the post synaptic neuron, triggering receptor proteins that open up potassium channels to flow potassium ions out of the membrane, resulting in hyperpolarization

The sympathetic and parasympathetic nervous system work in opposition to each other in order to maintain ________

Which of these neurotransmitters are responsible for regulating body temperature, sensory perception and mood control?

Which of the following neurotransmitters affects the brain synapse in the control of bodily movements, links to sensations of pleasure and eating

Which of the following neurotransmitters acts as a natural painkiller in the synapse of the brain and also affects the brain’s emotional area

Which of the following neurotransmitters is used by the brain and some autonomic neurons as well as compliments actions of a certain hormone that readies the body to respond to danger or other stressful situations