Chapter 12 Flashcards
(34 cards)
Overview of the Nervous System
Nervous system carries out its task in three basic steps
Sense organs receive information about changes in the body and the external environment, and transmit coded messages to the spinal cord and the brain. Brain and spinal cord process this information, relate it to past experiences, and determine what response is appropriate to the circumstances. Brain and spinal cord issue commands to muscles and gland cells to carry out such a response.
Major Anatomical Subdivisions of Nervous System
Nervous system has two major anatomical subdivisions
Central nervous system (CNS) includes the brain and spinal cord enclosed in bony coverings. Peripheral nervous system (PNS) includes all the nervous system except the brain and spinal cord; composed of nerves and ganglia.
Functional Organization: Sensory vs Motor
Sensory nervous system = afferent nervous system
Receives sensory information from receptors and transmits it to CNS. Motor nervous system = efferent nervous system. Initiates motor output and transmits it from CNS to effectors.
Universal Properties of neurons
Universal Properties of neurons: Excitability (irritability), Conductivity, Secretion
Neurons respond to environmental changes called stimuli, produce electrical signals conducted to other cells, and secrete chemical neurotransmitters when the signal reaches the end of a nerve fiber.
Structure of a Neuron: what is the soma?
Soma—the control center of the neuron
Also called neurosoma, cell body. Contains a single, centrally located nucleus with large nucleolus, mitochondria, lysosomes, Golgi complex, rough ER, cytoskeleton, and Nissl bodies.
Structure of a Neuron: what are Dendrites?
Dendrites: primary site for receiving signals from other neurons
Vast number of branches coming from thick branches of the soma, provide precise pathway for receiving and processing neural information.
Structure of a Neuron: what is an Axon?
Axon (nerve fiber)—originates from the axon hillock on one side of the soma
Cylindrical, relatively unbranched for most of its length, with axon collaterals branching on distal end for rapid conduction of nerve signals.
What are the components of the axon?
Axoplasm: cytoplasm of axon
Axolemma: plasma membrane of axon
Only one axon per neuron
Schwann cells and myelin sheath enclose axon
Distal end, axon has terminal arborization: extensive complex of fine branches
Synaptic knob (terminal button)—little swelling that forms a junction (synapse) with the next cell
Contains synaptic vesicles full of neurotransmitter
Example sentence: The axon of a neuron transmits electrical impulses to other cells.
What is axonal transport?
Axonal transport is the two-way passage of proteins, organelles, and other material along an axon
Anterograde transport: movement down the axon away from soma; Moves newly synthesized material
Retrograde transport: movement up the axon toward the soma; Moves used materials for breakdown and recycling
Fast axonal transport—occurs at a rate of 20 to 400 mm/day
Slow axonal transport or axoplasmic flow—0.5 to 10 mm/day
Additional information: Always anterograde
What are the structural classifications of neurons?
Multipolar neuron: One axon and multiple dendrites
Bipolar neuron: One axon and one dendrite
Unipolar neuron: Single process leading away from the soma
Anaxonic neuron: Many dendrites but no axon
Example sentence: The structural classification of neurons helps in understanding the different types of nerve cells.
What are the functional classifications of neurons?
Sensory (afferent) neurons: Specialized to detect stimuli
Interneurons (association neurons): Receive signals from many neurons and carry out the integrative function
Motor (efferent) neuron: Send signals out to muscles and gland cells (the effectors)
Additional information: Efferent neurons conduct signals away from the CNS
What is the myelin sheath?
Myelin sheath is an insulating layer around a nerve fiber
Formed by oligodendrocytes in CNS and neurolemmocytes in PNS
Consists of the plasma membrane of glial cells
20% protein and 80% lipid
Myelin sheath is segmented with neurofibril nodes and internodes
Example sentence: The myelin sheath plays a crucial role in speeding up nerve impulses.
What conditions are necessary for PNS axon regeneration?
Neuron cell body is intact
Enough neurilemma remains
Regeneration is possible if the neuron cell body is intact and enough neurilemma remains.
What factors increase the likelihood of successful PNS axon regeneration?
Amount of damage is less extensive
Distance between site of damage and structure it innervates is shorter
Regeneration success is more likely if the amount of damage is less extensive and the distance between the site of damage and the structure it innervates is shorter.
What is Velocity of Action Potential Propagation?
Speed at which a nerve signal travels along a nerve fiber depends on two factors: Diameter of fiber and Presence or absence of myelin
Example sentence: Larger fibers have more surface area and conduct signals more rapidly.
Electrical Potentials and Currents
Electrical current—a flow of charged particles from one point to another
Example sentence: In the body, currents are movements of ions, such as Na+ or K+, through gated channels in the plasma membrane.
The Resting Membrane Potential
Resting membrane potential (RMP)—charge difference across the plasma membrane
Negative value means there are more negatively charged particles on the inside of the membrane than on the outside.
Potassium ions and RMP
Potassium ions (K+) have the greatest influence on RMP
Example sentence: K+ is about 40 times as concentrated in the ICF as in the ECF.
Sodium ions and RMP
Membrane much less permeable to high concentration of sodium (Na+) found outside the cell
Example sentence: Na+ is about 12 times as concentrated in the ECF as in the ICF.
Na+/K+ pumps
Na+/K+ pumps out 3 Na+ for every 2 K+ it brings in
Example sentence: Pump contributes about −3 mV to the cell’s resting membrane potential of −70 mV.
Local (Graded) Potentials
Differences of local potentials from action potentials
Example sentence: Graded potentials vary in magnitude with stimulus strength.
Hyperpolarized/Depolarized Graded Potential
Hyperpolarized/Depolarized Graded Potential
Action Potentials
Action potential—more dramatic change produced by voltage-regulated ion gates in the plasma membrane
Example sentence: Only occur where there is a high enough density of voltage-regulated gates.
Membrane polarity during depolarization
Membrane now positive on the inside and negative on the outside
