Chapter 12 Flashcards
Two kind of cells of neural tissue
- Neurons
2. Neuroglia
Cells that send and receive signals
Neurons
Cells that support and protect neurons
Neuroglia (glial cells)
Functions of neuroglia
- Maintain physical structure of tissues
- Repair tissue framework after injury
- Perform phagocytosis
- Regulate the composition of the interstitial fluid surrounding neurons
Anatomical Divisions of the Nervous System
- Central nervous system (CNS)
* Peripheral nervous system (PNS)
division of the nervous system that consists of the spinal cord and brain and functions to process and coordinate sensory data, motor commands, and higher functions of brain intelligence, memory, learning, and emotion
Central Nervous System (CNS)
Functional Divisions of the PNS
- Afferent division
* Efferent division
Division of the PNS that carries sensory information from PNS sensory receptors to CNS
Afferent division
Division of the PNS that carries motor commands from CNS to PNS muscles and glands
Efferent division
These detect changes or respond to stimuli and consists of neurons and specialized cells
Receptors
These respond to efferent signals
Effectors
Part of the efferent division that controls voluntary and involuntary (reflexes)
muscle skeletal contractions
Somatic nervous system (SNS)
Part of the efferent division that controls subconscious actions, contractions of
smooth muscle and cardiac muscle, and
glandular secretions
Autonomic nervous system (ANS)
Part of the ANS division that has a stimulating effect
Sympathetic division
Part of the ANS division that has a relaxing effect
Parasympathetic division
What structures are found in the cytoskeleton of a neuron?
Neurofibrils, neurofilaments and neurotubules
bundles of neurofilaments that provide support for dendrites and axon
Neurofibrils
Dense areas of RER and ribosomes that make neural tissue appear gray (gray matter)
Nissl bodies
Area where a neuron
communicates with another cell
synapse
expanded area of axon of presynaptic neuron that contains synaptic vesicles of neurotransmitters
synaptic terminal
chemical messengers that are released at presynaptic membrane that affect receptors of postsynaptic membrane; they are broken down by enzymes and are reassembled at synaptic terminal
Neurotransmitters
Neurotubules within the axon that transport raw materials between cell body and synaptic terminal, and are powered by mitochondria, kinesin, and dynein
Axoplasmic transport
Type of synapse between neuron and muscle
Neuromuscular junction
Type of synapse between neuron and gland
Neuroglandular junction
Type of neuron found in brain and sense organs (small)
Anaxonic neurons
Type of neuron found in special sensory organs (sight, smell, hearing, one axon and one dentrite)
Bipolar neurons
Type of neuron found in sensory neurons of PNS (Fused dendrites and axon)
Unipolar neurons
Type of neuron common in the CNS and include all skeletal muscle motor neurons (Multiple dendrites, one axon)
Multipolar neurons
Afferent neurons of PNS
Sensory neurons
Efferent neurons of PNS
Motor neurons
Association neurons that are responsible for distribution of sensory information, coordination of motor activity, and are involved in higher functions such as memory, planning, and learning
Interneurons
Functions of Sensory Neurons
- Monitor internal environment (visceral sensory neurons)
* Monitor effects of external environment (somatic sensory neurons)
Three Types of Sensory Receptors
- Interoceptors
- Exteroceptors
- Proprioceptors
Type of sensory receptors that monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) and internal senses (taste, deep pressure, pain)
Interoceptors
Type of sensory receptors that monitor external senses (touch, temperature, pressure) and distance senses (sight, smell, hearing)
Exteroceptors
Type of sensory receptors that monitor position and movement (skeletal muscles and joints)
Proprioceptors
Four Types of Neuroglia
- Ependymal cells
- Astrocytes
- Oligodendrocytes
- Microglia
Cells with highly branched processes and contact neuroglia directly; they secrete cerebrospinal fluid (CSF)
Ependymal cells
Type of neuroglia that have large cell bodies with many processes
Astrocytes
Type of neuroglia that have smaller cell bodies with fewer processes
Oligodendrocytes
Type of neuroglia that has the smallest and least numerous neuroglia with many fine-branched
processes
Microglia
Functions of astrocytes
- Maintain blood–brain barrier (isolates CNS)
- Create three-dimensional framework for CNS
- Repair damaged neural tissue
- Guide neuron development
- Control interstitial environment
Function of oligodendrocytes
responsible for myelination
What are the benefits of myelination?
- Increases speed of action potentials
* Myelin insulates myelinated axons
Regions of CNS with many myelinated nerves
White matter
Unmyelinated areas of CNS
Gray matter
Masses of neuron cell bodies surrounded by neuroglia and are found in the PNS
Ganglia
Also called amphicytes, they surround ganglia and regulate environment around neuron
Satellite cells
Also called neurilemma cells, they form myelin sheath (neurilemma) around
peripheral axons
Schwann cells
The transmembrane potential of resting cell and ranges from –10 mV to –100 mV,
depending on cell type
Resting potential
Temporary, localized change in resting potential, caused by stimulus
Graded potential
an electrical impulse produced by graded potential and propagates along surface of axon to synapse
Action potential
resting potential of the neuron
70mV difference between the inside and
the outside
powered by ATP and carries 3 Na+ out and 2 K+ in, balances passive forces of diffusion and maintains resting potential (–70 mV)
Sodium–potassium ATPase (exchange pump)
Channels that are always open and their permeability changes with conditions
Passive Channels (Leak Channels)
Channels that open and close in response to stimuli
Active Channels (Gated Channels)
How does an action potential fire?
• The action potential is a rapid depolarization
of the membrane.
• It starts at the axon hillock and passes quickly
along the axon.
• The membrane is quickly repolarized to allow
subsequent firing.
Four Steps in the Generation of Action Potentials
• Step 1: Depolarization to threshold • Step 2: Activation of Na+ channels • Step 3: Inactivation of Na+ channels and activation of K+ channels • Step 4: Return to normal permeability
What happens during rapid depolarization?
• When partial depolarization reaches the activation
threshold, voltage-gated sodium ion channels open.
• Sodium ions rush in.
• The membrane potential changes from -70mV to +40mV.
What happens during activation of Na+ channels (Step 2)?
- Rapid depolarization
- Na+ ions rush into cytoplasm
- Inner membrane changes from negative to positive
The time period from beginning of action potential to return to resting state, during which membrane will not respond normally to additional stimuli
Refractory Period
Moves action potentials generated in axon hillock along entire length of axon
Propagation
Two methods of propagating action potentials
- Continuous propagation (unmyelinated axons)
2. Saltatory propagation (myelinated axons)
Steps in propagation
- Step 1: Action potential in segment 1
- Step 2: Depolarizes second segment to threshold
- Step 3: First segment enters refractory period
- Step 4: Local current depolarizes next segment
Method of propagating action potentials that occur along myelinated axon, and is faster and uses less energy than continuous
propagation; Myelin insulates axon which prevents continuous
propagation, so local current “jumps” from node to node and depolarization occurs only at nodes
Saltatory Propagation
The larger the diameter of an axon, the ________ the resistance
lower
Three Groups of Axons
- Type A fibers
- Type B fibers
- Type C fibers
A group of axon that are myelinated, has a large diameter and high speed, and carry rapid information to/from CNS (ex: position, balance, touch, and motor
impulses)
Type A Fibers
A group of axon that are myelinated, has a medium diameter medium speed (18 m/sec) and carry intermediate signals (ex: sensory information, peripheral
effectors)
Type B Fibers
A group of axon that are unmyelinated, has a small diameter, slow speed (1 m/sec), and carry slower information (ex: involuntary muscle, gland controls)
Type C Fibers
Two Types of Synapses
- Electrical synapses
2. Chemical synapses
Type of synapse involving direct physical contact between cells
Electrical synapses
Type of synapse involving signal transmission across a gap by chemical
neurotransmitters
Chemical synapses
Two Classes of Neurotransmitters
- Excitatory neurotransmitters
2. Inhibitory neurotransmitters
Type of neurotransmitteres that cause depolarization of postsynaptic membranes and promote action potentials
Excitatory neurotransmitters
Type of neurotransmitteres that cause hyperpolarization of postsynaptic membranes and suppress action potentials
Inhibitory neurotransmitters
A type of neurotransmitter that usually promotes action potentials, but inhibits cardiac neuromuscular junctions
acetylcholine (ACh)
What are cholinergic synapses?
Any synapse that releases ACh at:
1. All neuromuscular junctions with skeletal muscle
fibers
2. Many synapses in CNS
3. All neuron-to-neuron synapses in PNS
4. All neuromuscular and neuroglandular junctions of
ANS parasympathetic division
Occurs when neurotransmitter cannot recycle fast
enough to meet demands of intense stimuli and synapse inactive until ACh is replenished
Synaptic Fatigue
Neurotransmitters that are released by adrenergic synapses, and have an excitatory and depolarizing effect
Norepinephrine (NE)
CNS neurotransmitter that may be excitatory or inhibitory and is involved in Parkinson’s disease and cocaine use
Dopamine
A CNS neurotransmitter that affects attention and emotional states
Serotonin
A neurotransmitter that has an inhibitory effect and functions in CNS
Gamma Aminobutyric Acid (GABA)
Characteristics of neuromodulators
• Effects are long term, slow to appear
• Responses involve multiple steps, intermediary compounds
• Affect presynaptic membrane, postsynaptic membrane, or
both
• Released alone or with a neurotransmitter
Neuromodulators that bind to receptors and activate
enzymes
Neuropeptides
Neuromodulators in the CNS that bind to the same receptors as opium or morphine and relieve pain
Opioids
Four Classes of Opioids
- Endorphins
- Enkephalins
- Endomorphins
- Dynorphins
Work through second messengers, and are enzyme complex that bind GTP; they are the link between neurotransmitter (first messenger) and
second messenger and they activate enzyme adenylate cyclase
G Proteins
Which activated enzyme produces messenger cyclic-AMP (cAMP)?
adenylate cyclase
Graded potentials developed in a postsynaptic cell in response to neurotransmitters
Postsynaptic Potentials
Two Types of Postsynaptic Potentials
- Excitatory postsynaptic potential (EPSP)
2. Inhibitory postsynaptic potential (IPSP)
Graded depolarization of postsynaptic membrane
Excitatory postsynaptic potential (EPSP)
Graded hyperpolarization of postsynaptic membrane
Inhibitory postsynaptic potential (IPSP)
Two types of summations
- Temporal summation
2. Spatial summation
Type of summation that occurs multiple times as rapid, repeated stimuli at one synapse
Temporal Summation
Type of summation that occurs in multiple locations and the stimuli arrive at multiple synapses
Spatial Summation
Action of an axoaxonic synapse at a synaptic terminal
that decreases the neurotransmitter released by
presynaptic membrane
Presynaptic inhibition
Action of an axoaxonic synapse at a synaptic terminal
that increases the neurotransmitter released by
presynaptic membrane
Presynaptic facilitation
Can alter either the rate of neurotransmitter release or
the response of a postsynaptic neuron to specific
neurotransmitters
Neuromodulators
