Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
APHY 101 Exam 5a
Ch. 11 Neurons and the Nervous System
| Question | Answer |
|---|---|
| what is the nervous system | the master controlling and communicating system of the body |
| what are afferent nerves | take sensory input and it ARRIVES at the brain/CNS |
| what are efferent nerves | take signals from the brain that EXIT the brain/CNS to EXECUTE motor outputs via the body |
| what are the first two divisions of the nervous system? | central and peripheral |
| what is the central nervous system (CNS)? | brain and spinal cord making up the integration and command center |
| what is the peripheral nervous system (PNS)? | paired spinal and cranial nerves carrying messages to and from the spinal cord and brain |
| what are the 2 functional (sub)divisions of the peripheral nervous system (PNS)? | sensory/afferent and motor/efferent division |
| what does the sensory (afferent) division of the PNS do? | somatic afferent fibers carry impulses from skin, skeletal muscles, and joints to the brain, while visceral afferent fibers transmit impulses from visceral organs to the brain (such as stomach pain) |
| what does the motor (efferent) division of the PNS do? | transmits impulses from the CNS to effector organs, such as in the somatic motor system |
| what are the 2 further subdivisions of the motor division of the PNS? | somatic nervous system and autonomic nervous system |
| what does the somatic nervous system do? | conscious control of skeletal muscles [matilda drawing] |
| what does the autonomic nervous system do? | regulates smooth muscle, cardiac muscle, and glands, and is further divided into two subdivisions for these |
| what are the 2 subdivisions of the autonomic nervous system? | sympathetic and parasympathetic nervous system |
| regarding histology, what are the two principal cell types of the nervous system? | neurons and supporting cells |
| what are neurons? | excitable cells that transmit electrical signals |
| what are supporting cells? | cells that surround and/or wrap neurons (aka neuroglia or glial cells) |
| what are the 6 types of neuroglial cells? | astrocytes, microglia, ependymal, oligodendrocytes, Schwann cells, satellite cells |
| what are the 4 functions of supporting cells? | providing a supporting scaffolding for neurons, segregating and insulating neurons, guiding young neurons to the proper connections (i.e. in the embryonic brain), and promoting health and growth |
| what are astrocytes and what do they do? | astrocytes are the MOST ABUNDANT, versatile, and highly branched glial cells. they cling to neurons and their synaptic endings, and cover capillaries |
| what are 4 further but still important functions of astrocytes? | they support and brace neurons, anchor neurons to their nutrient supplies, guide migration of young neurons, and control the chemical environment by forming the BBB--blood brain barrier (starred) |
| what does the BBB/blood brain barrier do? | acts as a protective filter to keep (polar) pathogens and (unfortunately) most large molecules like therapeutic drugs out of the CSF (cerebrospinal fluid) surrounding brain tissue |
| notice about astrocytes in the picture: | the astrocyte branches out and touches the outside of the capillaries with its perivascular feet, and the neuron is in the background nearby |
| what are microglia? | small, ovoid cells with spiny processes; they are also phagocytes that monitor the health of neurons |
| what are ependymal cells? | cells that secrete *CSF* (cerebrospinal fluid), and line the central cavities of the brain and spinal column. they range in shape from squamous to columnar |
| what are oligodendrocytes? | remember that oligo means few. they are branched cells that wrap *CNS* nerve fibers with MYELIN (layers of cell membrane have different names depending on location) |
| what are Schwann cells? | aka neurolemmocytes, these surround fibers of the PNS and myelinate them |
| what are satellite cells? | cells that surround neuron cell bodies IN ganglia |
| what is a collection of cell bodies called in the CNS? in the PNS? | nuclei in the CNS, ganglia in the PNS |
| what is a collection of axons (processes) called in the CNS? in the PNS? | tracts in the CNS (fasciculus), nerves in the PNS (cordlike organ of peripheral axons enclosed by connective tissue) |
| what are myelinating cells called in the CNS? in the PNS? | oligodendrocytes in the CNS, Schwann cells/neurolemmocytes in the PNS |
| note in the picture of oligodendrocytes | the picture has the oligodendrocyte in a pale blue, with a process sticking out in between the oligo's body and a "jelly roll" of the oligo around the axons |
| true or false, only axons are myelinated and the myelination makes the axons white | true |
| note in the picture of a sensory neuron with Schwann cells and satellite cells | these are PNS axons, and Schwann cells form the myelin sheath while the cell body of neuron sticks out like a lollipop perpendicularly, and satellite cells are the purple candy coating of the lollipop around the cell body of the neuron |
| what are neurons and what are they composed of? | neurons are structural units (!) of the nervous system composed of a body, axon, and dendrites; they are long-lived, amitotic (don't divide) and have a high metabolic rate |
| note in the picture of a typical, myelinated neuron in PNS | Nissl bodies and axon hillock are at the cell body; voltage-gated channels are at the axon near the cell body, the impulse direction goes away from the body, and terminal branches (telodendria) of the axon terminals (secretory component) are at the right |
| about the nerve cell body: | it is called the soma or PERIKARYON; contains the nucleus and nucleolus, and is the major *biosynthetic* center as the focal point for the outgrowth of neuronal processes |
| what does the nerve cell body contain? | contains an axon hillock (cone-shaped area from which the axon arises), and the decision to make an action potential occurs here; has well-developed Nissl bodies (rough ER), but has NO centrioles (hence its amitotic nature) |
| what are processes? | armlike extensions from the soma, can be either 1. axons or 2. dendrites |
| what are dendrites of motor neurons? | short, tapering, and diffusely branched processes that are the RECEPTIVE or INPUT regions of the neuron. importantly, electrical signals are conveyed by these as graded local potentials, not as action potentials |
| between ligand gated and voltage gated channels, which are associated with which potentials? | ligand gated -> local potentials, voltage gated -> action potentials |
| what is the structure of an axon? | an axon is a slender process of uniform diameter arising from the hillock, and long axons are called NERVE FIBERS (remember that this is part of the nerve, not its own cell like a muscle fiber would be its own cell) |
| true or false, usually there is only one unbranched axon per neuron | true |
| what is it called on the rare occasion there is a branched axon? | axon collaterals |
| what is the branched terminus of an axon called? | axon terminal |
| what is the function of an axon? | to generate and transmit action potentials, secreting neurotransmitters from the axon terminals |
| what are the 2 types of movement occurring along *and within* axons? | anterograde and retrograde - toward and away from axonal terminal |
| what is a myelin sheath? | whitish, fatty (protein-lipoid), segmented sheath around most long axons (made by oligodendrocytes in the CNS and Schwann cells in the PNS) |
| what are the 3 functions of a myelin sheath? | protect the axon, electrically insulate fibers from one another, and increase the speed of nerve impulse transmission - note that unmyelination controls speed of nerve impulse transmission by making it slower |
| how are myelin sheath and neurilemma different? | the myelin sheath is the inner portion of these wrappings (approximately 100 layers of plasma membrane), and the outermost layer that contains the nucleus and cytoplasm is the neurilemma |
| what are myelin sheaths and neurilemmas formed by? | they are formed by Schwann cells in the PNS; a Schwann cell has concentric layers of membrane that make up the myelin sheath, while the neurilemma is the outer turn on the cell containing the remaining nucleus and cytoplasm of a Schwann cell |
| true or false, regeneration is possible where there are Schwann cells (PNS) | true, but axons lost in the CNS are GONE |
| true or false, a single turn of a Schwann cell = unmyelinated axon | true, notedly: around & around = sheath |
| what is the other name for nodes of Ranvier? | neurofibral nodes |
| what are nodes of Ranvier? | gaps in the myelin sheath between adjacent Schwann cells: they are the sites where axon collaterals can emerge (remember: the rare occasion when axon branches) |
| what comprises the instance of an unmyelinated axon? | a Schwann cell partially enclose 15 or more axons, where the Schwann cell surrounds nerve fibers (axons) BUT coiling does not take place! |
| true or false, axons of the CNS have a neurilemma | false - remember, they can't regenerate fibers |
| what are 4 features of CNS axons? | both myelinated and unmyelinated fibers are present; myelin sheaths are formed by oligodendrocytes; nodes of Ranvier are WIDELY spaced; no neurilemma |
| regarding regions of the brain and spinal cord, what are white and gray matter? | white matter = dense collections of myelinated fibers; gray matter = mostly soma an unmyelinated fibers |
| what are the 3 structural classifications of neurons? | multipolar (3+ processes, are most common/abundant), bipolar (rare. 2 processes only: axon and dendrite), and unipolar (PNS. single, short process) Table 11.1 |
| what are the 3 functional classifications of neurons? | sensory(afferent), motor(efferent), and interneurons(association neurons) |
| how do sensory/afferent neurons function? | transmit impulses toward the CNS [arrive] |
| how do motor/efferent neurons function? | carry impulses away from the CNS [exit] |
| how do interneurons(association neurons) function? | shuttle signals through CNS pathways, between sensory and motor neurons |
| notes relaying structural and functional classes of neurons | most multipolar neurons = interneurons, but some are motor neurons. all bipolar neurons are sensory neurons in special sense organs. and most unipolar neurons are sensory neurons conducting impulses along afferent pathways to the CNS for interpretation |
| what are the 3 types of plasma membrane ion channels? | passive/leakage, chemically/ligand gated, voltage-gated |
| when is a passive/leakage channel open? | always |
| when is a ligand-gated (chemical) channel open? | if/when a specific neurotransmitter binds to it |
| when is a voltage-gated channel open? | in response to membrane potential |
| what is resting membrane potential (Vr)? | the potential difference, about -70mV, across the membrane of a resting neuron |
| how is resting membrane potential generated? | different concentrations of Na+, K+, Cl-, and protein anions (A-) |
| why do ionic differences at the cell membrane occur? (2 reasons) | 1. differential permeability of the neurilemma to Na+ and K+, 2. operation of the sodium-potassium pump |
| what are the 2 ways membrane potential is maintained? | K+ leakage channels and Na+-K+ pump |
| what are membrane potential signals used for? | used to integrate, send, and receive information |
| what produces membrane potential changes? | changes in membrane permeability to ions, and, alterations of ion concentrations across the membrane |
| what are the 2 types of membrane potential signals? | graded potentials and action potentials |
| what are graded potentials? | short-lived, local changes in membrane potential that decrease in intensity with distance [decremental]. they travel over short distances and magnitude varies directly with the strength of the stimulus (graded); dependent on threshold |
| describe the importance of the threshold for a graded (local) potential | excitatory graded potentials depolarize but may not meet threshold; sufficiently strong graded potentials can initiate action potentials |
| what is an action potential? (AP) | the principal means of neural communication; a brief reversal of membrane potential in the axon of a neuron with a total amplitude (range) of 100 mV, only generated by muscle cells and neurons, do not decrease in strength over distance |
| changes in membrane potential are caused by what 3 events? | depolarization, repolarization, hyperpolarization |
| what is depolarization? | inside of the membrane becomes less negative (more positive) -- Na+ gates open |
| what is repolarization? | the membrane returns to its resting membrane potential (same direction as depolarization) -- Na+ gates close, K+ gates open |
| what is hyperpolarization? | the inside of the membrane becomes more negative than the resting potential -- K+ gates stay open a little "too" long, then K+ gates close |
| what is important to note about the sodium-potassium pump and repolarization? | while repolarization may restore the resting electrical conditions of the neuron, it does not restore the resting ionic conditions, so the sodium-potassium pump is what redistributes ions back to resting conditions |
| how is an AP propagated? | Na+ influxes at the spot where the AP is occurring and the nerve impulse is propagated down the axon one patch of membrane at a time whenever the voltage-gated Na+ gates open next door--new APs occurs at the new patches of membrane...! |
| how much is the membrane depolarized by to reach threshold? | about 15-20 mV |
| true or false, weak (subthreshold) stimuli are relayed into action potentials | false - only strong (threshold) stimuli are relayed into action potentials |
| is there such a thing as a "weak" action potential? | no, the all-or-none phenomenon of action potentials is such that APs either happen completely at full strength or not at all |
| what is the absolute refractory period? | the time from the opening of the Na+ activation gates until the closing of Na+ activation gates (and simultaneous reopening of the Na+ inactivation gates) |
| what 3 things does the absolute refractory period accomplish? | prevents the neuron from generating an action potential for about 1 ms, ensures that each action potential is separate, and enforces one-way transmission of nerve impulses |
| what is the relative refractory period? (3 "when"s) | the relative refractory period is the interal following the absolute refractory period. here, sodium gates are closed, K gates open, and repolarization occurs |
| what is the exception to the relative refractory period? | it takes a particularly strong stimulus to be able to reopen the newly reset Na+ gates to start another AP, so only strong stimuli can increase the frequency of AP events (cause another AP) |
| true or false, conduction velocities vary widely armong neurons | true |
| what determines rate of impulse propagation? | myelination (insulation) and axon diameter |
| what is saltatory conduction? | the rapid jumping of an AP current passing through a myelinated axon at the nodes of Ranvier, where voltage-gated Na+ channels are concentrated. much faster than conduction along unmyelinated axons Fig. 11.16 |
| what are the 3 classifications of nerve fibers? | diameter, degree of myelination, and speed of conduction |
| what is a synapse? | a junction that mediates information transfer from one neuron either to another neuron or to an effector cell |
| what does a presynaptic neuron do? | conducts impulses toward the synapse |
| what does a postsynaptic neuron do? | transmits impulses away from the synapse |
| what are 2 important types of synapses? | axodendritic and axosomatic |
| what is an axodendritic synapse? | synapse between the axon of one neuron and the dendrite of another (as the name suggests) |
| what is an axosomatic synapse? | synapse between the axon of one neuron and the soma of another (as the name suggests) |
| what are other types of synapses whose names also suggest what type of synapse they are? | axoaxonic, dendrodendritic, dendrosomatic |
| what is an electrical synapse, and how common is it? | electrical synapses correspond to GAP JUNCTIONS found in other cell types, and are less common than chemical synapses |
| electrical synapses are important in the CNS for what 4 things? | arousal from sleep; mental attention; emotions and memory; ion and water homeostasis |
| what are chemical synapses? | synapses specialized for the release and reception of neurotransmitters |
| what are the 2 parts of a chemical synapse? | axonal terminal of the presynaptic neuron, which contains synaptic vesicles, and, the receptor region of the dendrite(s) or soma of the postsynaptic neuron |
| what is the synaptic cleft? | fluid-filled space separating the presynaptic and postsynaptic neurons |
| what does the synaptic cleft do? | prevents nerve impulses from directly passing from one neuron to the next |
| what are the features of transmissions across the synaptic cleft? | is a chemical event, not electrical, and ensures unidirectional communication between neurons |
| how is information transferred across a synaptic cleft (1 of 4)? | nerve impulses reach the axonal terminal of the presynaptic neuron and open Ca2+ channels |
| how is information transferred across a synaptic cleft (2 of 4)? | neurotransmitter is released into the synaptic cleft via exocytosis in response to synaptotagmin |
| how is information transferred across a synaptic cleft (3 of 4)? | neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic neuron |
| how is information transferred across a synaptic cleft (4 of 4)? | postsynaptic membrane permeability changes, causing an excitatory or inhibitory effect (it might be a K+ or Cl- channel |
| what are 3 things to note about a neurotransmitter bound to a postsynaptic neuron? | 1. produces a continuous postsynaptic effect 2. blocks reception of additional "messages" like a finger holding a doorbell 3. must be removed from receptor (chop the finger off) |
| what 3 things occur for removal of neurotransmitters? | they diffuse from the synaptic cleft, then they are degraded by enzymes, and they are reabsorbed by astrocytes or presynaptic terminals |
| what is synaptic delay? | the rate-limiting step of neural transmission that limits the speed at which neural transmission can occur |
| why is the concept of synaptic delay significant? | the neurotransmitter must be released, then diffuse across the synapse, and bind to receptors, and this takes time (0.3-5.0 ms) |
| postsynaptic potentials have 2 types, what are they? | EPSP - excitatory postsynaptic potential, and IPSP - inhibitory postsynaptic potential |
| changes in the membrane potential are mediated by neurotransmitter receptors according to what 2 factors? | the amount of NT released, and the amount of TIME the neurotransmitter is bound to receptors |
| what are EPSPs? | (excitatory postsynaptic potentials) are graded potentials that can initiate an action potential in an axon via summation at the axon hillock - use only chemically gated channels where sodium and potassium flow in opposite directions at the same time |
| note about EPSPs | postsynaptic membranes of the dendrites or soma do not generate action potentials - the membrane at the axon hillock does |
| what are IPSPs? | (inhibitory postsynaptic potentials) are a temporary hyperpolarization of a postsynaptic neuron's membrane potential, decreasing the likelihood of an action potential firing. caused by the release of inhibitory neurotransmitters which open ion channels |
| when an NT binds to a receptor at an inhibitory synapses, what 3 things happen? | the membrane becomes more permeable to K ions (rush out) and chlorine ions rush in; the inner surface is more negative, and the postsynaptic neuron's ability to produce an AP is reduced since the memrane potential ends up further away from threshold |
| how do EPSPs induce an action potential? | a single EPSP cannot induce an action potential, so EPSPs must summate (add up) to induce one |
| what are IPSPs effects on action potentials? | IPSPs make it harder to induce an action potential. whether postsynaptic neurons will fire or not is result of a vote by all the EPSPs and IPSPs (yes and no votes) |
| what are neurotransmitters? | chemicals used for neuronal communication with the body and brain |
| how many NTs have been identified? | 50, classified chemically and functionally |
| what are some common chemical neurotransmitters? (recognize these on a multiple choice) | acetylcholine (ACh), biogenic amines, amino acids such as NH2 (not nucleic acids), peptides (strings of amino acids), novel messengers such as ATP and dissolved gases NO (nitrous oxide) and CO (carbon monoxide - blocks hemoglobin from picking up O2) |
| what is important to know about acetylcholine? | it was the 1st neurotransmitter identified, and best understood, released at the NMJ (neuromuscular junction), synthesized and enclosed in synaptic vesicles, degraded by AChE (acetylcholinesterase) |
| where/what is ACh released by? | all neurons that stimulate skeletal muscle and some neurons in the autonomic nervous system |
| neurotransmitters - biogenic amines - include which? | catecholamines(!) such as dopamine, norepinephrine (NE), and epinephrine; indolamines such as serotonin and histamine |
| what are some features of biogenic amines? | they are broadly distributed in the brain, and play roles in emotional behaviors and our biological clock |
| what are 2 functional classifications of neurotransmitters? | excitatory and inhibitory |
| what do excitatory NTs cause? | depolarizations e.g. the amino acid glutamate |
| what do inhibitory NTs cause? | hyperpolarizations e.g. the amino acids GABA and glycine |
| true or false, acetylcholine is only excitatory | false, ACh has both excitatory and inhibitory effects determined by the receptor type of the postsynaptic neuron - i.e., ACh is excitatory at NMJ with skeletal muscle (sodium channel) and inhibitory for cardiac muscle (chloride channel) |
| what is a neuron classified as if it has at least two dendrites? | multipolar |
| what is a pseudounipolar neuron? | a neuron structurally classified as having 1 process but functioning as though it has 2 |
| bipolar and unipolar neurons both seem to have a dendrite and axon coming off it. what makes the difference between them? | it's what's coming off the cell body that counts (Table 11.1.1) |
| what visual cue signals a Purkinje cell of the cerebellum? | very extensive dendritic trees, ridiculously so |
| which cranial nerve would correspond to a bipolar olfactory nerve cell? | cranial nerve 1 |
| which cranial nerve would correspond to a bipolar retinal nerve cell? | cranial nerve 2 |
| where are unipolar (psuedounipolar) neurons found? | dorsal root ganglion |
| which potentials are associated with ligand/chemically gated channels? | local/graded potentials |
| which potentials are associated with voltage-gated channels? | they make the *action potential* once threshold is readied |
| true or false, a very strong stimulus can overcome the relative refractory period | true |
| true or false, a very strong stimulus can overcome the absolute refractory period | false |
| true or false, it's the FREQUENCY of action potentials that determines the strength of a stimulus | true |
| does saltatory conduction have anything to do with salt? | no, saltar means to jump or hop in Spanish, describes how action potentials jump from one node to the next on myelinated axons |
| why doesn't retrograde action affect previous nodes while saltatory conduction is happening? | because the previous node is in its absolute refractory period |
Created by:
elianayu
Popular Neuroscience sets