Chapter 11 - The Nervous System

Which type of glial cells is responsible for microorganism phagocytosis?

Microglial cells - immune response eats bacteria & protects the CNS

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction

Relative Refractory Period

A period after firing when a neuron is returning to its normal polarized state and will fire again only if the incoming message is much stronger than usual

Steps of a Chemical Synapse

AP arrives at axon terminal. Voltage-gated Ca2+ channels open & Ca2+ enters the axon terminal. Synaptic vesicles release a neurotransmitter (chemical) that diffuses & binds to receptors on the postsynaptic membrane. This causes ion channels to open creating a graded potential. Then the neurotransmitters effects are terminated.

How does a synapse work?

Action potential sends an electrical message to the end of an axon, then the message hits the synapse (junction) where it is converted to a different type of signal that is sent to another neuron

Sensory Division

Afferent; Fibers transmit impulses from receptors to CNS; picks up sensory stimuli

Resting State

All gated Na+ and K+ channels are closed meaning that there are no ions moving.

Peripheral NS

All the nerves that branch off the brain & spinal cord for communication

Resting Membrane Potential

An electrical potential established across the plasma membrane of all cells by the Na+/K+ and the K+ leak channels. (In most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell.)

Amitotic

As neurons assume their roles as communicating links of the nervous system, they lose their ability to divide.

Which factors determine the conduction velocity of action potentials?

Axon diameter - Larger axons conduct more rapidly because they offer less resistance to the flow of local currents, bringing adjacent areas of the membrane to threshold more quickly. Degree of Myelination - The presence of a myelin sheath dramatically increases the speed of propagation. The conduction velocity increases with the degree of myelination—lightly myelinated fibers conduct more slowly than heavily myelinated fibers.

Inhibitory Postsynaptic Potential

Binding of neurotransmitters at inhibitory synapses reduces a postsynaptic neuron's ability to generate an AP. Most inhibitory neurotransmitters hyperpolarize the postsynaptic membrane by making the membrane more permeable to K+ or Cl−. Hyperpolarizes the postsynaptic neuron by making the inside more negative driving its charge down away from the threshhold. The message doesn't get passed along and it is even harder to excite that portion of the neuron now.

Name 2 examples of biogenic amines that function as neurotransmitters. Which neurotransmitter is found in neuromuscular junctions?

Biogenic amines - are low molecular weight organic nitrogen compounds Catecholamines - dopamine, epinephrine Indolamines - serotonin and histamine Acetylcholine - it is released at neuromuscular junctions

Central NS

Brain and spinal cord

(1) Astrocytes

CNS, support & regulate ions by assisting in the exchanges between blood capillaries & neurons

(3) Ependymal Cells

CNS; line cavities of the brain and spinal cord circulate cerebrospinal fluid that fills the cavities & cushions organs (Cerebrospinal fluid - a clear watery fluid between membranes)

(2) Microglial Cells

CNS; move toward injured neurons & can transform to phagocytize microorganisms (eat bacteria) & neuronal debris The main source of immune defense against invading microorganisms in the brain & spinal cord

(4) Oligodendrocytes

CNS; wrap around neurons producing an insulating barrier called the myelin sheath *Line up along the thicker nerve fibers in the CNS & wrap their processes tightly around the fibers, producing the myelin sheath.

Efferent

Carrying away or away from, especially a nerve fiber that carries impulses away from the CNS

Afferent

Carrying to or toward a center

Neurotransmitters

Chemical messengers that cross the synaptic gaps between neurons transmitting information one neuron to the other

What activates opening of chemically gated, voltage-gated and mechanically gated channels, respectively?

Chemically-Gated Channel - the channel opens when a neurotransmitter latches onto a receptor such as serotonin or a hormone Voltage-Gated Channel - open and closes in response to changes in the membrane potential Mechanically-Gated Channel - open in response physical deformation of the receptor (sensory receptors for touch & pressure)

Serial Processing

Cognitive process involving considering each input one at a time in steps Stimulus -> receptor -> sensory neuron -> integration center -> motor neuron -> effector -> response

Somatic (Voluntary)

Conscious control of skeletal muscles

Name the special characteristics of neurons (conduct impulses, longevity, amitotic, high metabolic rate)

Longevity, amitotic, high metabolic rate, conduct impulses

How do neurotransmitters exert their function in the target cells?

Direct and indirect actions Direct Action - neurotransmitters (chemicals b/w neurons) bind to open ion channels which causes a rapid response in post synaptic cells by altering the membrane potential (The voltage across a cell's plasma membrane.) Indirect Action - neurotransmitters promote, broader, longer lasting effects by acting through intracellular second-messenger molecules like the G-protein pathways.

Motor Division

Efferent; Sends directions from your brain (away from CNS) to your muscles & your glands

Understand how neurons are functionally and structurally classified.

Functionally - classify them based on their function or the way that the impulse travels through a neuron in relation to the brain and spine. Neurons are grouped structurally according to the number of processes extending from their cell body

Identify and describe the location and function of the six (6) types of neuroglia (glial cells).

Glial cells - non-excitable cells of the neural tissue that support, protect, insulate neurons

Compare and contrast graded potentials and action potentials.

Graded potentials - an incoming signal or impulse coming over a short distance with "graded" strength Action potentials - an incoming signal or impulse coming over a long distance with the same strength each time

Catecholamines

Hormones secreted by the adrenal medulla that affect the sympathetic nervous system in stress response Dopamine, norepinephrine, epinephrine

What determines whether postsynaptic neurons of a simple neuronal pool will fire action potentials?

How closely related/associated the neurons are with the incoming fiber because they release the bulk of synaptic contacts

Sensory Input

Information gathered by sensory receptors (ex - skin) about internal and external changes

Spatial Summation

Integration by a postsynaptic neuron of inputs (EPSPs and IPSPs) from multiple sources.

Chemical Synapse

More common than electrical synapses; They are more controlled (precise) and move slower. These synapses in particular will use neurotransmitters or chemical signals to diffuse the signal across the synaptic gap to successfully deliver the message/signal. The signal moves from an electrical signal to chemical signal to electrical signal. The signal can be modified, amplified, split, etc. at these junctions.

Describe the effects of multiple sclerosis on myelinization and action potentials.

Multiple Sclerosis - demyelinating disorder of the central nervous system causing patches of the brain and spinal cord to harden Multiple sclerosis gradually destroys myelin sheaths in the CNS, reducing them to nonfunctional hardened lesions called scleroses. The loss of myelin short-circuits the current so that successive gaps are excited more and more slowly, and eventually impulse conduction ceases. However, the axons themselves are not damaged and growing numbers of Na+ channels appear spontaneously in the demyelinated fibers.

Compare multipolar, bipolar and unipolar neurons with regards to structure and location.

Multipolar - 3 or more processes sticking out from the cell body (dendrites (2 or more stems w/ branches), axon, soma) *major neuron type in CNS Bipolar - 2 or more processes (containing an axon, dendrite (1 stem)) *special senses - eye, nasal (PNS) Unipolar - only 1 process; have a single short process that emerges from the cell body and divides T-like into proximal and distal branches *located in the ganglia (PNS)

Compare how myelination occurs in the CNS and PNS. Which cells are implicated?

Myelination PNS - The myelin sheath is formed by Schwann cells. The Schwann cells first wrap loosely around the axon of the neuron and slowly start to squeeze the axon squeezing the cytoplasm from in between each membrane. The Schwann cells wrap around the axon multiple times creating the myelin sheath on the axon. Myelination CNS - Oligodendrocytes wrap around the axon in layers creating the myelin sheath. However, oligodendrocytes can attach themselves up to 60 axons at a time and create myelin sheaths on more than one.

Excitatory Postsynaptic Potential

Neurotransmitter binding depolarizes the postsynaptic membrane. Chemically gated ion channels open on postsynaptic membranes causing the inside to become more positive bringing it closer to the action potential threshhold = more likely to fire off the signal to the other neuron. Each channel allows Na+ and K+ to diffuse simultaneously through the membrane but in opposite directions.

Discriminate between the nucleus and ganglion.

Nucleus - A collection of neuron cell bodies in the CNS Ganglion - A collection of neuron cell bodies in the PNS

(5) Satellite Cells

PNS; surround neuron cell bodies in ganglia (cell masses containing cell bodies of neurons and glial cells supported by connective tissue) support, nutrition

(6) Schwann Cells

PNS; wrap around all nerve fibers of the PNS & form myelin sheaths (insulation) by wrapping around the thicker nerve fibers *Vital to regeneration of damaged peripheral nerve fibers.

Electrical Synapse

Synapse - functional junction or point of close contact between two neurons or between a neuron and an effector cell Sends an ion current flowing directly from the cytoplasm of one nerve cell to another through gap junctions. These are super fast signals because they are not created into another form at the junction. They use raw electricity to send these signals and impulses that transmitted directly by neurons.

What neural process causes us to smell something and remember something that happened in the past?

Parallel Processing the processing of many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. The stimulus (aka the smell) promotes many responses beyond simple awareness of the smell. Parallel processing is not repetitious because the pathways do different things with the information. Each pathway or "channel" is decoded in relation to all the others to produce a total picture. A single neuron sends information along several pathways instead of just one, so you process a large amount of information much more quickly.

Saltatory Conduction

Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, (gap to gap) skipping the myelin-sheathed regions of the membrane.

Autonomic (Involuntary)

Refers to actions that happen automatically; beyond your control - heart beating, lungs breathing, stomach churning

Continuous Conduction

Relatively slow; it occurs along the whole un-myelinated axon. There are Na+ voltage-gated channels that are opening releasing large amounts of Na+ that is rushing to the cell causing harsh currents.

High Metabolic Rate

Require continuous and abundant supplies of oxygen & glucose - they cannot survive for more than a few minutes without oxygen.

Explain the events of a nerve impulse (action potential), including the various ions and channels involved.

Resting State Depolarization Re-polarization Hyper-polarization

Repolarization

Return of the cell to resting state, caused by reentry of potassium into the cell while sodium exits the cell. Na+ channels are inactive. K+ channels open, allowing K+ to exit the cell. Na+ channels are blocked by the inactivation gate soon after they open. K+ channels open by depolarization, after a short delay. Repolarization caused by K+ flowing out of the cell. The change in membrane potential returns it to negative

Simple Reflex Arc

Sensory & motor neurons Stimulus > receptor > sensory neuron > intermediate neuron > motor neuron > effector > response

Describe the major overlapping functions of the nervous system.

Sensory input, integration, motor output

Indolamines

Serotonin and histamine

Describe the structures of the typical neuron and their respective functions.

Soma, dendrites, axon Soma - cell body, life support of the neuron that contains the nucleus, DNA, mitochondria, etc. Dendrites - pick up messages from other cells & convey that information to the cell body Axon - extension fiber that can short/long that transmit electrical impulses away from the cell body to other cells

How does the CNS determine whether a stimulus is intense or weak?

Strong stimuli generate nerve impulses more often in a given time interval than do weak stimuli. Stimulus intensity is coded for by the number of impulses per second—that is, by the frequency of action potentials—rather than by increases in the strength (amplitude) of the individual APs.

Temporal Summation

Summation by a postsynaptic cell of input (EPSPs or IPSPs) from a single source over time.

Synapse

The junction between the axon tip of the sending neuron & the dendrite or cell body of the receiving neuron - the meeting point between 2 neurons. Their strength & purpose lies in their connections

Absolute Refractory Period

The minimum length of time after an action potential during which another action potential cannot begin.

Hyperpolarization

The movement of the membrane potential of a cell away from rest potential in a more negative direction. (The inside of the cell becomes more negative than the resting potential) Some K+ channels remain open & some Na+ channels reset caused by K+ continuing to leave the cell.

Motor Output

The nervous system activates effector organs—the muscles and glands—to cause a response.

Integration

The nervous system processes and interprets sensory input and decides what should be done at each moment.

Myelination

The process by which axons become coated with myelin, a fatty substance that speeds the transmission of nerve impulses from neuron to neuron and insulates the axon.

Depolarization

The process during the action potential when sodium is rushing into the cell causing the interior to become more positive. Na+ channels open allowing Na+ to enter the cell. There is a decrease in membrane potential

Parallel Processing

The processing of several aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. Reflexes occur on neutral pathways called reflex arcs

Membrane Potential

The voltage across a cell's plasma membrane.

Discriminate between the nerve and tract.

Tract - a collection of axons in the central nervous system having the same origin, termination, & function (a major anatomical passageway) Nerve - a collection of axons in the peripheral nervous system

True or False? Acetylcholine is excitatory in neuromuscular junctions of skeletal muscles and inhibitory in the cardiac muscle.

True

True or False? Neurotransmitters can be excitatory or inhibitory.

True

Name the two principal parts of the nervous system and describe the functions of the various divisions of the NS. Which divisions are voluntary and which involuntary?

Two major parts - Central & Peripheral NS Peripheral - sensory (afferent) & motor (efferent) division Motor (efferent) Division - somatic (voluntary) & autonomic (involuntary) Autonomic (involuntary) - parasympathetic & sympathetic division

Neuron Longevity

With good nutrition they can live and function for a lifetime

pre-synaptic neuron

a neuron that delivers a signal to a synapse (The junction between the axon tip of the sending neuron & the dendrite or cell body of the receiving neuron - the meeting point between 2 neurons.)

post-synaptic neuron

the neuron on the receiving end for the signal of the synapse (The junction between the axon tip of the sending neuron & the dendrite or cell body of the receiving neuron - the meeting point between 2 neurons.)