Chapter 11

Question 0

What are the 3 functions of the nervous system?

Answer 0

1- Sensory input: gathered information from millions of its sensory receptors that monitor changes occurring both inside & outside the body.

2- Integration: this processes and interprets sensory input and decides what should be done, happens at CNS level.

3- Motor Output: this causes a response, and activates the effector organs(muscles & glands).

Question 1

Describe the nervous system.

Answer 1

• It is the master controlling and communicating system of the body.
• Every thought, action, and emotion reflects its activity.
• Cells communicate by electrical and chemical signals,which are rapid and specific, and cause immediate response.

Question 2

What are the two principal parts of the nervous system?

Answer 2

1) Central Nervous System (CNS): which consists of the brain and spinal cord, that occupy the dorsal body cavity.
2) Peripheral Nervous System (PNS): is part of the nervous system outside the CNS, consists mainly of the nerves(bundles of axons) that extend from the brain and the spinal cord.

Question 3

What are two nerves that make up the PNS?

Answer 3

1) spinal nerves: they carry impulses to and from the spinal cord.
2) cranial nerves: they carry impulses to and from the brain.

Question 4

What are the two functional subdivisions of the Peripheral Nervous System?

Answer 4

1- The Sensory Division: “Afferent Division” responsible for sending impulses to CNS, from various sensory receptors. Has two fibers (Somatic and Visceral fibers).

2-The motor “Efferent Division” transmit impulses from the CNS to effector organs which are muscles and glands.the impulses activate muscles to contract and glands to secrete.

Question 5

What are the 2 subdivisions of the motor “efferent division”?

Answer 5

1) Somatic Nervous System aka voluntary nervous system- composed of somatic nerve fibers that conduct impulses from the CNS to skeletal muscles. Allows us to consciously control our skeletal muscles.
2) Autonomic Nervous Sysytem- involuntary nervous system. consists of Visceral motor nerve fibers that regulate activity of smooth muscle, cardiac muscle, and glands.

Question 6

What are the 2 functional subdivisions of the the ANS?

Answer 6

1) sympathetic division-gets heart to beat faster, blood flowing. Fight or flight.
2) parasympathetic division-rest and digest

These Divisions work in opposition to each other. Whatever one stimulates the other inhibits.

Question 7

What is a neuron?

Answer 7

Main nerve cells that are responsive to stimuli and transmit electrical signals.

Question 8

What are neuroglia?

Answer 8

Aka glial cells. They are supporting small cells that surround and wrap the more delicate neurons.

Question 9

How many neuroglia are found in the CNS and PNS?

Answer 9

There are 6 total. The CNS has 4 and the PNS has 2.

Question 10

What are Astrocytes?

Answer 10

Neuroglia in the CNS “star cells”most abundant and versatile glial cells. they support brace the neurons and anchor them to their nutrient supply lines.their most important job is mopping up leaked potassium ions and recapturing and recycling release neurotransmitters

Question 11

What are microglial cells?

Answer 11

Defensive cells in the CNS. Small have long thorny processes.their processes touch nearby neurons monitoring their health. Microglia cells transform into a type of macrophage that phagocytize invading microorganisms or neuro debris.

Question 12

What are Ependymal cells?

Answer 12

Ependymal cells line cerebrospinal fluid-filled cavities in the CNS. Range in shape from squamous to columnar and are ciliates. Their cilia help circulate the CSF that cushions the brain and spinal cord.

Question 13

What are oligodendrocytes?

Answer 13

have few processes that form Myelin sheaths around CNS nerve fibers. They line up along thick nerve fibers and wrap their processes around the fibers producing insulating covering called a myelin sheath.

Question 14

What are the 2 kinds of neuroglia in the PNS?

Answer 14

1) Satelite cells- surround the neuron cell body.have same functions as Astrocytes.
2) Schwann cells- surround all nerve fibers in PNS. They form myelin sheaths around the thicker nerve fibers. They are vital to regeneration of damaged peripheral nerve fibers.

Question 15

What are neurons?

Answer 15

Neurons are “nerve cells” are the structural units of the nervous system. They are large and conduct messages in the form of nerve impulses from one part of the body to another.

Question 16

What are 3 characteristics neurons have?

Answer 16

1) neurons have extreme longevity given good nutrition.
2) neurons are amitotic. Neurons can not be replaced if they die.
3) neurons have high metabolic rate and require continuous and abundant supplies of oxygen and glucose.

Question 17

What is the neuron cell body? Aka soma aka perikaryon.

Answer 17

The neuron cell body consists of a nucleus with a nucleolus surrounded by cytoplasm. It contains the usual organelles needed to synthesize proteins and other chemicals. Most cell bodies aready located in the CNS where they are protected by bone.

Question 18

What are cluster of cell bodies in the CNS and PNS called?

Answer 18

In the CNS they are called nuclei and in the PNS they are called ganglia.

Question 19

What are bundles of neuron processes called in the CNS and PNS?

Answer 19

They are called tracts in the CNS and nerves in the PNS.

Question 20

Name the 2 types of neuron processes:

Answer 20

1) Dendrites- branching extensions are the main receptive or input regions.they have spiked ends which represent points of close contact (synapses) with other neurons.
2) Axons- each neuron has a single axon. The axon region arises from the axon hillock then narrows . Any long axon is called a nerve fiber.

Question 21

What are the functional characteristics of the axon?

Answer 21

The axon is the conducting region of the neuron. It generates impulses and transmits them away from the cell body along the axolemma(plasma membrane). In motor neurons the nerve impulse is generated at the axon hillock, conducted along the axon to the axon terminals( secretory regions of the neuron). Then neurotransmitters are released into extracellular space.the NT either excite or inhibit neurons.

Question 22

What are the 3 groups that neurons are structurally classified as?

Answer 22

1) multipolar neurons- have three or more processes.they are the major near and type in the CNS.
2) Bipolar neurons- have 2 processes an Axon and a dendrite that extend from opposite sides of the cell body.they are rare and found in some of the special sense organs like the retina and in olfactory mucosa.
3) Unipolar neurons- have a single short process that emerges from the cell body and divides T-like into proximal and distal branches.

Question 23

What are the 3 functional classifications of neurons? ( the direction in which the nerve impulse travels relative to the CNS).

Answer 23

1) sensory(afferent) neurons- transmit impulses from sensory receptors in the skin or internal organs toward or into the central nervous system. Almost all sensory neurons are unipolar.
2) motor neuron( efferent)- Carry impulses away from the CNS to the effector organs (muscles and glands) of the body periphery. Motor neurons are multipolar with a few exceptions.
3) interneurons (association neurons)- lie between motor and sensory neurons in neural pathways and shuttle signals through The CNS pathways where integration occurs.Most interneurons are confined within the CNS they make up over 99% of the neurons of the body. most interneurons are multipolar and their structures are dynamic.

Question 24

What is membrane potential?

Answer 24

When a neuron is stimulated and electrical impulse is generated and conducted on its axon.This response is called the action potential.

Question 25

What is the Resting membrane potential?

Answer 25

The voltage that exist across the plasma membrane during the resting state of an excitable cell. Inside cell is negative and outside is positive. Ranges from -40mv to -90mv. The average is -70mv and the membrane is polarized.

Question 26

What 2 factors generate resting membrane potential?

Answer 26

1) differences in ionic composition- differences of ions inside the cell compared to outside.
2) difference in plasma membrane permeability- permeability of plasma membrane to the ions.

Question 27

What is the difference in ionic composition?

Answer 27

The cell cytosol contains a lower concentration of sodium and a high concentration of potassium the net extracellular fluid. Negatively charged (anionic) proteins help to balance the positive charges of intracellular cations (primarily potassium). In the extracellular fluid the positive charges of sodium and other cat ions are balanced by chloride ions.potassium plays the most important role in generating the membrane potential.

Question 28

What is the difference in plasma membrane permeability?

Answer 28

Potassium ions diffuse out of the cell along the concentration gradient much more easily than sodium ions can enter the cell. Potassium flowing out of the cell cause the cell to become more negative inside.sodium trickling into the cell makes the cell slightly more positive than it would be if only potassium flowed.therefore the negative interior of the cell is due to a much greater ability for potassium to diffuse out of the cell then for sodium to diffuse into the cell. There is never an equal concentration of sodium and potassium inside and outside the cell because of the sodium potassium pump. this pump ejects 3 Sodium from the cell and then transports 2 potassium back into the cell.

Question 29

What is depolarization?

Answer 29

Depolarization is a decrease in the membrane potential. The inside of the cell becomes less negative (moves closer to 0 mv).

Question 30

What is hyperpolarization?

Answer 30

Hyperpolarization is an increase in membrane potential: the inside of the cell membrane becomes more negative than the resting potential.

Question 31

What are the 2 types of signals produced when membrane potential changes?

Answer 31

1) Graded potential- incoming signals operating over short distances. Causes depolarization or hyperpolarization.the stronger the stimulus the more voltage changes and the farther the current flows. Graded potentials are triggered a change in the neurons environment that opens up gated ion channels.
2) Action potentials AKA nerve impulse-long-distance signals of axons.only neurons and muscle cells can generate action potentials.total amplitude is about 100mv. Depolarization is followed by depolarization and often a short period of hyperpolarization.unlike grades potential, action potentials don’t decay with distance.

Question 32

How is an action potential generated? (4 steps)

Answer 32

1) resting (polarized) state: all Na and K channels are closed.only leakage channels are open.
2) depolarization: Na channels open. Na rushes into the cell. The positive charge depolarizers that patch of the membrane further, opening more Na channels so the cells interior becomes less negative.this phase puts the “action” into action potential.
3) Repolarization: Na channels are inactivating, and ️K channels open. The AP spike stops rising! K rushes out of the cell and this restores the internal negativity of the resting neuron (Repolarization) both A decline in Na and an increase of K contribute to Repolarization.
4) Hyperpolarization: some K channels remain open, and Na channels reset. The period of increase K permeability typically lasts longer than needed to restore the resting state. Hyperpolarization is seen on the AP curve as a slight dip following the spike. At this point Na channels begin to reset to their original position by changing shape to reopen their inactivation gates and close their activation gates. Small ionic changes are quickly corrected because an axon membrane has thousands of sodium potassium pumps.

Question 33

What determines the threshold point?

Answer 33

Threshold is a membrane potential at which the outward current created by K movement is exactly equal to the inward currant created by Na movement. Threshold is reached when the membrane has been depolarized by 15 to 20 MV from the resting value.if stimulus doesn’t reach threshold an action potential won’t occur.

Question 34

What is the all- or -none phenomenon?

Answer 34

Action potential either happens completely or doesn’t happen at all.

Question 35

What is propagation of an action potential?

Answer 35

The action potential generated at the axon hillock propagates as a wave along the axon. The currents flowing inwards at a point on the axon during an action potential spread out along the axon, and depolarize the adjacent sections of its membrane.

Question 36

What is a refractory period?

Answer 36

When a patch of neuron membrane is generating an AP and it’s voltage gated sodium channels are open , the neuron cannot respond to another stimulus.

Question 37

What is absolute refractory period?

Answer 37

The period from the opening of the sodium channels until the sodium channels begin to reset to their original resting state.

Question 38

What is relative refractory period?

Answer 38

the interval following the absolute refractory period. Most sodium channels have returned to their resting state ,and some potassium channels are still open and Repolarization is occurring.strong stimuli trigger more frequent APs by intruding into the relative refractory period.

Question 39

What is a synapse?

Answer 39

A junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell- it’s where the action is.

Question 40

What is a axodendritic synapse?

Answer 40

Synapses between the axon endings of one neuron and the dendrites of other neurons.

Question 41

What are axosomatic synapses?

Answer 41

Those between Exxon endings of one neuron and cell bodies of other neurons.

Question 42

What is a presynaptic neuron?

Answer 42

The neuron conducting impulses toward the synapse.sends the information.

Question 43

What is a postsynaptic neuron?

Answer 43

The neuron transmitting the electrical signal away from the synapse. Receives the information.

Question 44

What are chemical synapses?

Answer 44

They allow the release and reception of chemical neurotransmitters.

Question 45

What are the two parts that make up a chemical synapse?

Answer 45

1) presynaptic neuron- contains tiny membrane bounded sac called synaptic vesicles which has thousands of Neurotransmitter molecules.
2) Neurotransmitter receptor region- found on the post synaptic neuron’s membrane usually located on a dendrite or the cell body.

Question 46

What is the synaptic cleft?

Answer 46

Synaptic cleft is a small fluid filled space found between the pre and post synaptic neuron.

Question 47

How does information transfer across chemical synapses? (6 steps)

Answer 47

1) action potential arrives at axon terminal.
2) voltage gated calcium channels open and calcium enters the axon terminal.
3) calcium entry causes synaptic vesicles to release neurotransmitter by exocytosis.
4) Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.
5) binding of Neurotransmitter opens ion channels creating graded potentials.
6) Neurotransmitter effects are terminated.

Question 48

What are excitatory postsynaptic potentials (EPSPs)?

Answer 48

Local graded depolarization events occur at excitatory postsynaptic membranes.

Question 49

What are inhibitory synapses(IPSPs)?

Answer 49

Hyperpolarizing changes in potential.

Question 50

Define neurotransmitters.

Answer 50

neurotransmitters are the language of the nervous system -the means by which each neuron communicates with others to process and send messages to the rest of the body.

Question 51

What are the classifications of neurotransmitters by chemical structure? (3)

Answer 51

1) Acetylcholine(ACH)
2) biogenic Amines
3) gases

Question 52

What are the two neurotransmitter receptors?

Answer 52

1) Channel link receptors- are ligand gated ion channels that mediate direct neurotransmitter action. As the ligand binds to the receptor subunits, the proteins change shape. This Opens the central channel and allows ions to pass, leading to fast changes in membrane potential.
2) G protein linked receptors- indirect, complex, and slow. When a neurotransmitter binds to a G protein linked receptor, the G protein is activated. Activated G proteins work by controlling the production of second messengers such as cyclic AMP, cyclic GMP, Diacylglycerol,or calcium. These second messengers act as go-between to regulate(open/close) ion channels or activate kinase enzymes. Some second messengers activate/ inactivate other proteins including channel proteins, by attaching phosphate groups to them. Others interact with nuclear proteins that activate genes and induce synthesis of new proteins in the target cell.