Nervous Tissue Flashcards
What provides for the generation of nerve impulses (action potentials) that communicate with a regulate most body tissues?
Nervous tissue
Who shares responsibility for maintaining homeostasis?
The nervous system and the endocrine system
The nervous system regulates?
Body activities by responding rapidly using nerve impulses
The endocrine system responds faster or slower by use of hormones to changes in homeostasis?
Slower
What is the branch of medical science that deals with the normal functioning and disorders of the nervous system?
Neurology
What comprises the central nervous system?
Brain
Spinal Cord
What comprises the peripheral nervous system?
Cranial nerves (12 pairs; 1-Xii) Spinal nerves (31 pairs) Peripheral nerves (numerous)
The nervous systems comprises?
The brain Spinal cord Spinal nerves Ganglia Enteric Plexuses Sensory receptors
Which receptors detect changes in the internal or external environment?
Sensory
Sensory neurons are afferent or efferent neurons?
Afferent neurons
Sensory nerve cells (neurons) carry the sensory information from the receptor to the?
brain and spinal cord
What do the integrative neurons do?
Analyze and store information
Make decisions
Many integrative neurons are what kind of neurons?
Interneurons
What are relatively short neurons in the brain, spinal cord, ganglia that connect to nearby neurons?
Integrative
Which neurons respond to decisions and are efferent neurons?
Motor neurons
Motor neurons carry information from the brain and spinal cord to?
Effectors (muscles or glands)
What are somatic senses? What kind of motor control?
Sensation from body wall, limbs, head, and special senses (sight, hearing, taste, balance, smell)
Motor control of skeletal muscle (voluntary control)
What are autonomic senses? What kind of motor control?
Sensation from internal organs like heart, lungs, bladder
Motor control of smooth and cardiac muscle, glands (involuntary control)
What are Enteric senses? What kind of motor control?
Sensation from gastrointestinal tract
Motor control of smooth muscle and glands of the GI tract (involuntary control)
The peripheral nervous system consists of all nervous tissue outside of the?
Central Nervous System
-SNS, ANS, ENS
Each subdivision of the PNS has both of these neurons?
Sensory and motor neurons
The motor part of the autonomic nervous system consists of what two branches?
Sympathetic division
Parasympathetic division
What is an association (a bundle) of neuronal axons in the peripheral nervous system?
Nerve
What is a group of neuronal cell bodies in the peripheral nervous system (plus associated tissue)?
Ganglion
What is an association (a bundle) of neuronal axons in the central nervous system?
Tract
What is an association (a bundle) of (unmyelinated) nerve cell bodies in the central nervous system?
Nucleus
What is an extensive network of nerves found within the peripheral nervous system (PNS)?
Plexus
The term plexus is also applied to?
A network of veins or lymphatic vessels
What are cells that have the property of electrical excitability, and are specially adapted to produce and transmit action potentials?
Neurons
What are cells of the nervous system that support, nourish, and protect the neurons?
Neuroglia
True or False
There are less neuroglia than neurons
False
There are more neuroglia
What are the basic parts of a neuron?
The cell body
Nerve Fibers
What are nerve fibers comprised of?
An Axon
Dendrites
What are the name adaptations for neurons?
Axoplasm (cytoplasm)
Axolemma (plasmalemma)
Like most cells, what structures do neurons have (think organelles)?
Nucleus
Cytoplasm
Typical organelles
What are Nissl bodies?
Specialized forms of typical organelles in the neuron which are prominent clusters of rough ER
What are dendrites?
The receiving portion of a neuron
Typically short, tapering, highly branched
(incoming)
What is an axon?
Propagates impulses to another neuron, muscle, or nerve.
Can approximate three feet long in humans.
(outgoing)
How many axons are there per neuron?
Only a single axon
Where do axons typically arise from?
An elevation in the cell body called the axon hillock (= small hill)
In the axon, where do (action potentials) generally arise?
In the trigger zone
What is the trigger zone of the axon?
The junction of hillock and initial segment
What dies if the an axon is cut?
The distal fragment dies
What does the axon contain?
Mitochondria
Microtubules
Neurofibrils
What does the axon not contain?
Rough ER so protein synthesis does not occur in the axon
What may branch off of the main axon?
Axon collaterals
Axon and collateral end by dividing into what?
Axon terminals (telodendria)
Telodendria end in either?
Synaptic end bulbs, bulb-shaped structures
Varicosities, string of swollen bumps
What is the cytoskeleton of a neuron made of?
Neurofibrils
Microtubules
What are neurofibrils of the cytoskeleton made of?
Intermediate filaments
Provide cell shape and support
What are microtubules of the cytoskeleton made of?
Tubulin
Participate in moving material between the cell body and axon
What contains only some cytosol, mitochondria, cytoskeleton, smooth endoplasmic reticulum, and synaptic vesicles?
Axon terminals
Where does synthesis of new proteins, vesicles, etc. take place in the neuron?
The cell body
About how far apart might the cell body and axon terminals be?
Over a meter apart
Things made in the cell body must be transported along the?
Interior of the axon to reach the axon terminal
What is one-way only transport from cell body to axon terminals?
Slow axonal transport
What is two-way transport, both toward and away from the cell body?
Fast axonal transport
What transports axoplasm to growing or regenerating axons?
Slow axonal transport
What uses microtubules as tracks and motors?
Fast axonal transport
What transports organelles and materials that are used to form axolemma membranes, synaptic end bulbs, and synaptic vesicles?
Fast axonal transport
What is structural classification of a neuron based on?
The number of processes extending from the cell body
Which class of neurons have several dendrites and only one axon and are located throughout the brain and spinal cord?
Multipolar neurons
The vast majority of the neurons in the human body are?
Multipolar neurons
Which class of neurons have one main dendrite and one axon?
Bipolar neurons
Which class of neurons are used to convey the special senses of sight, smell, hearing and balance?
Bipolar neurons
Where are Bipolar neurons found?
In the retina of the eye, the inner ear, and the olfactory area of the brain.
Which class contain one process which extends from the body and divides into a central branch that functions as an axon?
Unipolar (pseudounipolar) neuron
When is the unipolar structure often employed for?
Sensory neurons that convey touch and stretching information from the extremities.
In cases of injury or disease, what can multiply to fill in the spaces formerly occupied by neurons?
Neuroglia
What are characteristics of neuroglia?
Not excitable cells
Smaller, more numerous than neurons
Make up about half the volume of the CNS
What are Neuroglia of the CNS?
Astrocytes
Oligodendrocytes
Microglia
Ependymal Cells
What are the neuroglia of the PNS?
Schwann Cells (neurolemmocytes) Satellite cells
The neuroglia of the PNS is completely surround the what?
Axons and cell bodies of neurons
These do not typically undergo mitosis, meaning if a neuron dies there is no reservoir of cells to replace it…
Neurons
Mitosis of nervous system cells
These do undergo mitosis
Neuroglial cells
Myelin is produced by?
Schwann cells and oligodendrocytes
What is multi-layered complex of lipids and proteins, layers of plasma membrane?
Myelin
What does myelin do?
Insulate axons: myelin prevents loss of electrical signal; speeds up conduction of nerve impulses
Myelination requires the glial cell to have?
wrapped its plasma membrane around the axon many times
A schwann cell myelinates a 1 mm-long segment of an
axon
Migrates around the axon multiple times and multiple layers of the schwann cell plasma membrane surround the axon
What is the neurolemma?
The outer nucleated cytoplasmic layer of the schwann cell, which encloses the myelin sheath
Which axons have no myelin sheath and no neurolemma?
Unmyelinated axons
Can be associated with schwann cells, but the axons simply lay in grooves on the surface of the schwann cell.
What inner portion successively encircles the axon, forming many layers that comprise the myelin sheath?
Schwann cell (neurolemmocyte)
What comes to reside in neurolemma, which is the outer nucleated cytoplasmic layer of the schwann cell?
The nucleus of the neurolemmocyte
What is the neurolemma?
- Outer layer of a myelinating schwann cell
- Contains the nucleus and virtually all the cytoplasm
- Not to the axolemma
- Found only around axons in the PNS
What are the Nodes of Ranvier?
- Only on nerve fibers supplied by potentially myelin-producing cells
- Gaps between myelinating cells
- Found in PNS and CNS
A nerve fiber consists of?
an axon plus myelin sheath (if present)
What surrounds the nerve fiber?
The endoneurium
What overlies the schwann cell?
Endoneurium
What are the schwann cells of the CNS?
Oligodendrocytes
Each process of a oligodendrocytes can form a?
Myelinated segement
- can myelinate several segments
- can participate in myelination of several axons
Why is a neurolemma not present in the CNS?
Because oligodendrocyte cell body and nucleus do not envelop the axon.
One oligodendrocyte can myelinate how many times?
Multiple
There is no neurolemma
There are nodes of Ranvier
A region of the brain predominantly filled with myelinated tract fibers, The appearance is due to the whitish color of myelin.
White matter
A region of the brain predominantly filled with neuronal cell bodies. There is little or no myelin in these areas, and the Nissl bodies impart gray color.
Gray matter
Nerve cells are highly adapted for using ________ potentials, and changes in _______ potentials, to initiate and transmit nerve impulses
Membrane potential
What are the two types of electrical signals neurons communicate with?
Action Potentials (nerve impulses) Graded Potentials (localized)
What is for both short and long distance communication within the body? “all or none”
Action potentials
What neuronal signals are for short-distance communication only?
Graded potentials
What is the physiological role of graded potentials?
Is to affect (and effect) the generation of action potentials.
Both types of neuronal signals depend on two features of the plasma membrane of excitable cell, which are?
-Existence of a resting membrane potential
_presence of specific ion channels
Voltage is measured across the __________, and is relative to the outside of the cell (cell’s environment)
plasma membrane
Membrane Potential
Potential means?
potential energy that can cause a flow of electrical current
- attractive force is the potential measure in volts
An electrical current is what?
The flow of electrons
Current means flow of ions- sodium (Na+), potassium, calcium.
When current flows through a membrane charges are _____ across the membrane and potential changes
redistributed
What gives the cells the property of electrical excitability?
Ion channels
When ion channels are opn, specific ions are allowed to do what?
Move across the plasmalemma, down their electrochemical gradient
The flow of ions comprise a flow of electrical current that can change the ________.
membrane potential
Ion channels open and close due to the presence of?
Gates
A gate is the part of a channel protein that does what?
Opens or closes to allow or prevent the passage of ions
T or F
All membrane channels have gates
F
Are leakage channels gated?
No, they randomly open and close
Between K+ and Na+ there are more specific leakage channels for? The resting membrane is more permeable to?
K+
K+
Is the voltage difference measured across the plasma membrane when the neuron isn’t signaling?
Resting membrane potential
Varies from cell to cell
Is the resting membrane potential polarized or unpolarized?
Polarized
All membrane potentials are reported as the potential of the
Inside of the membrane relative to the outside of the membrane
What is the resting membrane potential due to?
A small buildup of anions in the cytosol just inside the membrane.
Equal buildup of cations in the ECF just outside the membrane
The relative permeability of the resting membrane is 50 to 100 times more permeable to?
K+ than to Na+
Cl- is in between
What is the membrane impermeable to?
Nearly all of the negatively charged intracellular molecules
Explain the steps of establishing the resting membrane potential
- K+ moves out of cell
- IC negatively charged ions cant get through membrane
- The interior of the membrane becomes negatively charged; the exterior becomes positively charged; net diffusion of K+ stops
-Na+ goes into cell but slower rate than K+ existing
A little Cl- leave the cell, interior of cell more negative - net result= resting membrane potential
What produces graded potentials in response to stimuli?
Ligand-gated or mechanically gated ion channels
What means the size of the change in the membrane potential varies in proportion to the strength of the stimulus (all or none)?
Graded
What are local effects only of the graded potentials?
Channels open, current flows through the membrane and along the membrane, and travels only a short distance before diminishing to zero.
A graded potential can either do what to the membrane since the membrane is polarized?
Depolarize or hyperpolarize
A membrane becomes more polarized
Hyperpolarization
A membrane becomes less polarized (less negative or more positive)
Depolarization
The positive charges of the calcium ions alter the what of the channel protein?
Electrical state
Increasing the voltage level required to open the gate.
Calcium ion deficit in the extracellular fluids, what becomes activated by very little change of the membrane potential from its normal resting level?
Sodium channels
What becomes highly excitable, sometimes discharging repetitively without provocation, rather than remaining in the resting state?
Calcium ion deficit
Propagation depends on what?
Positive feedback
The movement of nerve impulses are called?
Propagation
Nerve impulses must travel from the ________ down the neuron to the axon _____.
Trigger zone
Axon terminal
Step-by-step depolarization and repolarization of adjacent segments is termed?
Continuous conduction
This is a special mode of impulse propagation that occurs along myelinated axons
Saltatory conduction
Saltatory conduction happens on what type of axons?
Only myelinated
In saltatory conduction, voltage-gated channels are concentrated at the _______, with few regions where the myelin sheath covers the _______.
Nodes of Ranvier
Axolemma
In saltatory conduction, electric current is carried by extracellular and intracellular ions from one node to the next…..?
the nodes depolarize and repolarize.
Saltatory or continuous, which one is faster?
Saltatory
It is also more energy efficient, requiring less ATP to repolarize
What do neurons produce virtually all their ATP from?
Aerobic metabolism of glucose
Metabolism requires large amounts of oxygen, the nervous system requires?
High blood flow, and is consequently highly vascularized.
Most of the brains energy consumption goes into?
Sustaining the electric charges of neurons.
Who devotes more basal metabolism to the brain, vertebrates or primates?
Primates
The great the diameter of the axon, the _____ the conduction will be.
Faster
Describe the three different fibers of the effect of axon diameter.
A fibers -large diameter -myelinated B fibers -Medium fibers -myelinated C fibers -small diamerter -unmyelinated
What are the two mechanisms that enable stimuli of differing intensities to be registered as such?
Frequency of impulses
Number of sensory neurons activated (recruited)
What are the characteristics of frequency of impulses?
- A light touch generates a low frequency of widely spaced nerve impulses
- A firm pressure causes nerve impulses to go down the axon closer together
What the characteristics of number of sensory neurons recruited?
- A light touch stimulates only a few pressure sensitive neurons
- A firm pressure stimulates more pressure sensitive neurons
T or F
No action potential is generated by a subthreshold stimulus.
T
Several action potentials result from what kind of stimulus?
Suprathreshold
All have the same amplitude. This is perceived as a stronger stimulus
