Chapter 12: Nervous Tissue

Contrast the two types of summation at a synapse.

temporal: intense stimulation by one presynaptic neuron spatial: simultaneous stimulation by several presynaptic neurons

What happens to Na+ when a neuron is stimulated on its dendrite? Why does the movement of the Na+ raise the voltage on the plasma membrane?

the neurotransmitter opens the Na+ ligand gated ion channels, which causes Na+ to move into the cell, positively charged influx causes a greater charge difference between the outside and inside)

How can a severed peripheral nerve fiber find its way back to the cells it previously innervated?

1. distal end of damaged nerve begins to die, macrophages clean up 2. soma swells, Nissl bodies disperse, proximal end sprouts numerous growth processes 3. Schwann cells form regeneration tube that produce nerve growth factors; once a growth process reaches a dendrite, other processes slow growth and support growth of the main process 4. synaptic connection is eventually reestablished 5. soma shrinks and denervation atrophy is reversed

Describe the 5 steps that occur between the arrival of an action potential at the synaptic knob and the trigger of an action potential in the postsynaptic neuron.

1. voltage change open Ca2+ channels 2. Ca2+ flows into the cells and triggers synaptic vesicles to attach to cell membrane and release neurotransmitter. 3. ligand-gated ion channels open in response to neurotransmitter 4. Na+ to flow into cell and K+ to flow out of cell 5. local potential is induced when Na+ spreads out; if it reaches the axon hillock with enough depolarization, signal will continue

List four ways in which action potential is different from local potential.

Irreversible (once it hits threshold, action potential is triggered and continued through a positive feedback loop) Nondecremental (signal maintains same strength) Non-graded (on or off situation) Produced by voltage-gated ion channels (initiated by local potential)

What causes K+ to diffuse out of the cell? What attracts it into the cell?

K+ moves down its concentration gradient out of the cell, but also creates a negative interior which attracts it back inward

What makes an action potential rise to +35 mV? What makes it drop again after this peak?

Na+ gates are closing from 0 mV to about +35 mV; K+ flows out of cell due to charge repulsion, repolarizing the cell

How is myelin produced in the CNS?

Oligodendrocytes extends around several nerve fibers and forms new layers underneath itself, no neurilemma or endoneurium

How is myelin produced in the PNS?

Schwann cell wraps repeatedly around axon (super tight with hardly any cytoplasm) finally wraps around last time with thicker wall (called neurilemma, contains all inclusions and cell body)

List the types and functions of glial cells in the PNS

Schwann cells: form neurilemma around all nerve fibers and myelin around most; aid in regeneration of damaged nerve fibers satellite cells: surround somas of neurons in the ganglia; provide electrical insulation and regulate chemical environment of neurons

Explain why myelinated fibers conduct signals much faster than unmyelinated fibers.

They function through saltatory conduction; very fast in the internodes, but decremental; very slow in nodes of Ranvier, but nondecremental

What is a receptor?

an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve.

What is another name for the visceral motor nervous system? What are its two subdivisions? What are their functions?

autonomic nervous system; divided into sympathetic and parasympathetic sympathetic stops digestion, constricts blood vessels, constrics pupillary dilators, increases respiratory airflow (dilates bronchioles), ATP production

Give two examples of effectors.

cardiac muscle, glands

Distinguish between the central and peripheral nervous systems, and between visceral and somatic divisions of the sensory and motor systems.

central nervous system contains brain and spinal cord, while peripheral nervous system contains nerves and ganglia somatic sensory sends info from skin, muscle, bones, and joints to cns visceral sensory sends info from thoracic and abdominal cavities to cns somatic motor send info from cns to skeletal muscles visceral motor (aka autonomic nervous system) sends info from cns to smooth muscle, cardiac muscle, and glands

Contrast the effects of acteylcholine, GABA, and norepinephrine.

cholinergic: releases ACh, can act as excitatory or inhibitory, receptor channel is K+/Na+ channel GABA-ergic: releases gamma-aminobutyric acid, inhibitory, Cl- channels as receptor channel adrenergic: employs norepinephrine, receptor is a transmembrane protein-- also, enzyme amplification

What is the functional difference between a dendrite and an axon?

dendrites receive info from other cells and are incapable of producing action potentials, relatively branched axon transmits action potentials, relatively unbranched

Describe 3 mechanisms that stop synaptic transmission.

diffusion: neurotransmitter gets lost in extracellular fluid or consumed by astrocyte reuptake: monoamine oxidase breaks down enzymes that are taken back into the synaptic knob degradation in the synaptic cleft: AChE breaks down ACh on synaptic cleft and postsynaptic membrane, then synaptic knob reabsorbs choline

3 properties of neurons

excitability: respond to stimuli conductivity: transmit electric signal to other neurons secretion: release of neurotransmitter

How do proteins and other chemicals synthesized in the soma get to the synaptic knobs?

fast or slow anterograde transport

By what process can a virus that invades a peripheral nerve fiber get to the soma of that neuron?

fast retrograde transport

What does it mean to say a local potential is graded, decremental, and reversible?

graded: a greater stimulus leads to a greater depolarization decremental: as we move down the axon, the signal loses its intensity reversible: if stimulation is ceased before threshold is reached, diffusion will reverse and RMP will be achieved again

Compare and contrast the effects of neurotransmitters and neuromodulators.

modulators: chemical signals that have long-term effects on entire groups of neurons transmitters: chemical signals that have short-term effects on a single synapse Neuromodulators adjust, or modulate, the activity of neuron groups in various ways—increasing the release of neurotransmitters by presynaptic neurons; adjusting the sensivity of postsynaptic neurons to neurotransmitters; or altering the rate of neurotransmitter reuptake or breakdown to prolong their effects.

How is a glial cell different from a neuron?

neuroglia perform supportive and protective roles for the neurons

how to classify a neuron as anaxonic, unipolar, bipolar, etc?

number of branches directly off soma body

List the types and functions of glial cells in the CNS

oligodentrocytes: from myelin in brain and spinal cord ependymal cells: line cavities of brain and spinal cord; secrete and circulate CSF microglia: phagocytize and destroy microorganisms, foreign matter, and dead tissue astrocytes: cover brain surface and non-synaptic regions of neurons so so so many things

Describe how the nervous system communicated qualitative and quantitative information.

quantitative: labeled line code qualitative: graded stimulation

3 functional classes of neurons

sensory (afferent): towards CNS interneurons: located within CNS-- majority of neurons motor (efferent): away from CNS

How does the plasma membrane at the trigger zone differ from that on the soma? How does it resemble the membrane at a node of Ranvier?

trigger zone has way more voltage-gated ion channels; membrane at nodes of Ranvier have ligand-gated Na+ channels