Unit 3 Chapter 12 (Intro to Nervous System)

Question 1

What are the functions of the nervous system

Answer 1

-receiving information about the environment and generating responses to that information
-combines sensory perceptions and higher cognitive functions such as memories, learning, and emotion to produce a response

Question 2

How is the nervous system organized

Answer 2

-divided into 2 parts: somatic nervous system (SNS) and autonomic nervous system (ANS)
-SNS is responsible for conscious perception and voluntary motor responses (skeletal muscles)
-ANS is responsible for involuntary control of the body for the sake of maintaining homeostasis (cardiac and smooth muscles, breathing and sweating) and is divided into sympathetic and parasympathetic systems
-sympathetic system is associated with the fight-or-flight response
-parasympathetic activity is referred to by the epithet of rest and digest

Question 3

What are the functions of neurons and neuroglia

Answer 3

-neurons are the computation and communication of the nervous system, they’re electrically active and release chemicals to target cells
-neuroglia play a supporting role for the neurons, differentiated by location between CNS and PNS along with function

Question 4

Describe the cell body of a neuron

Answer 4

-cell body contains nucleus and most major organelles
-processes are extensions of cell membrane
-have one axon that projects out of the cell membrane and to target cells
-dendrites receive information from other cells, synapses are on the end to make contact with other cells to receive that information
-axon hillock is “beginning” of the axon and is a special region where reactions start
-myelin is made of neuroglia cells and wraps around the axon and acts as an insulator
-gaps in myelin are called Nodes of Ranvier, which help electric signal travel down the axon
-axon segment is the length of the axon between each segment of myelin
-axon terminal is at the end of the axon and has many branches to reach out to the target cell

Question 5

What are the functions of sensory neurons, interneurons, and motor neurons

Answer 5

-sensory neurons transmit impulses from a receptor (eye, ear) to a more central location in the nervous system (brain, spinal cord)
-interneurons are the “middle-man” and connect the input from sensory neurons to the output for motor neurons
-motor neurons carry a signal from the CNS to an effector cell, which then carries out the desired response

Question 6

What are multipolar neurons, bipolar neurons, and unipolar neurons

Answer 6

-unipolar neurons have one end of the axon that are dendrites, and at the other end, the axon forms synaptic connections with a target
-bipolar neurons extend from each end of the cell body opposite to each other. One is the axon and one the dendrite
-multipolar neurons have one axon and two or more dendrites

Question 7

What are the functions of the 5 neuroglia cells

Answer 7

-Astrocyte (CNS): Support
-Oligodendrocyte (CNS): Insulation, myelination
-Schwann cell (PNS): Insulation, myelination
-Microglia (CNS): Immune surveillance and phagocytosis
-Ependymal cell (CNS): Creating CSF (cerebrospinal fluid)

Question 8

How is the myelin sheath formed around a PNS neuron

Answer 8

A Schwann cell wraps itself around only a portion of one axon segment where the outermost layer of the cell membrane contains cytoplasm and the nucleus of the cell as a bulge on one side of the myelin sheath

Question 9

What is the difference between the composition of white matter and gray matter

Answer 9

-gray matter is regions of the nervous system containing cell bodies of neurons with few or no myelinated axons
-regions of the nervous system containing mostly myelinated axons, making the tissue appear white because of the high lipid content of myelin

Question 10

Summarize neuron communication from the moment of receptor stimulation to the response of an effector

Answer 10

-cell membrane of the thermoreceptors changes its electrical state, amount of change is known as graded potential
-voltage at which such a signal is generated is called the threshold, and the resulting electrical signal is called an action potential
-action potential travels along the axon from the axon hillock to the axon terminals and into the synaptic end bulbs. When this signal reaches the end bulbs, it causes the release of a neurotransmitter.
-neurotransmitter diffuses across the short distance of the synapse and binds to a receptor protein of the target neuron
-target of this neuron is another neuron in the thalamus of the brain, the part of the CNS that acts as a relay for sensory information
-thalamus then sends the sensory information to the cerebral cortex where conscious perception of stimulus
-information is processed among many neurons, integrating the stimulus
-cerebral cortex sends a command out to your body to move muscles based on stimulus

Question 11

Define neurotransmitter, resting membrane potential, and
current

Answer 11

-neurotransmitter is a chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell
-resting membrane potential is the difference in voltage measured across a cell membrane under steady-state conditions (-70 mV)
-current is the flow of charge

Question 12

Define electrochemical gradients and the term “polarized”

Answer 12

-electrochemical gradients are gradients of electrochemical potential, usually for an ion that can move across a membrane
-polarized is the cell’s state based on the flow of electrical signals along their membrane

Question 13

Describe the function of the sodium-potassium pump in
maintaining the resting membrane potential

Answer 13

-The sodium-potassium pump that moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell, thus regulating ion concentration on both sides of the cell membrane.
-Pump moves ions against the concentration gradient, which requires ATP, and also maintains the concentration gradients of both sodium and potassium, which helps maintain the resting membrane potential along with leakage channels

Question 14

Describe graded potentials, along with hyperpolarizing and depolarizing graded potentials

Answer 14

-graded potentials are local changes in the membrane potential, usually associated with dendrites of a neuron
-hyperpolarizing graded potentials can be caused by K+ leaving the cell or Cl- entering the cell; move away from threshold
-depolarizing graded potentials are often the result of Na+ or Ca2+ entering the cell; move towards threshold

Question 15

Describe action potentials (nerve impulses) including:
▪ Thresholds
▪ All-or-none principle
▪ Phases of action potential generation
▪ Refractory period (absolute and relative)

Answer 15

-threshold is the voltage needed for a signal to be generated
-all-or-none principle means that signal transmission between neurons is not dependent on the strength of the stimuli but, rather, only that the initial threshold is met
-the phases of action potential generation are depolarization, repolarization, and hyperpolarization
-absolute refractory period is part of the phase when another action potential will not start due to the inactivation gate of the voltage-gated Na+ channel
-relative refractory period is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before

Question 16

Describe nerve impulse propagation including:
▪ Continuous and saltatory conduction
▪ Factors affecting impulse speed
▪ Encoding stimuli intensities

Answer 16

-continuous conduction is propagation along an unmyelinated axon
-saltatory conduction is propagation along a myelinated axon
-factors that affect impulse speed are the axon diameter (higher conduction velocity) and the existence of a myelin sheath (electrical insulator).
-stimuli intensities are encoded in two ways:
1) frequency coding, where the firing rate of sensory neurons increases with increased intensity
2) population coding, where the number of primary afferents responding increases (recruitment)

Question 17

Distinguish between graded potentials and action potentials

Answer 17

-action potentials are a change in voltage of a cell membrane in response to a stimulus that results in transmission of an
electrical signal
-graded potentials are changes in the membrane potential that varies in size, depending on the size of the stimulus that elicits
it

Question 18

Describe synapses including:
▪ Components of a synapse
▪ How information is transferred from one neuron to another across a chemical synapse
▪ Excitatory and inhibitory postsynaptic potentials
▪ Summation of postsynaptic potentials

Answer 18

-components of a synapse are the presynaptic and postsynaptic membrane, synaptic cleft, neurotransmitter, receptor proteins, and neurotransmitter elimination or re-uptake
-information is transferred chemically by a neurotransmitter, which is released from one cell and it affects the other cell
-excitatory postsynaptic potentials is depolarization which results in the membrane potential moving towards threshold
-inhibitory postsynaptic potentials is hyperpolarization which results in the membrane potential to move away from threshold
-summation of postsynaptic potentials is the changes of either hyperpolarization or polarization that can lead to the neuron reaching threshold if the changes add together

Question 19

Why is neurotransmitter removal from the synaptic cleft important and what are the 3 ways it occurs

Answer 19

-it is important because it is done to prevent constant stimulation of the post-synaptic cell and an excessive firing of action potentials
-the 3 ways it occurs are reuptake, enzymatic degradation in the cleft, and diffusion

Question 20

Compare the ability of neurons in the PNS and CNS to repair

Answer 20

The chance of nerve regeneration is greater within the peripheral nervous system. This is because these neurons have a different lining, or sheath, made up of Schwann cells, which can help guide nerves to the regeneration tubes. The central nervous system does not have these cells. Schwann cells can help damaged nerves regenerate and restore function.