Nervous System Flashcards
objective of the nervous (and endocrine) systems
keep controlled conditions within limits that maintain life
- nervous system regulates body activities by responding rapidly using nerve impulses
- endocrine system responds by releasing hormones
four things the nervous system is responsible for
- perceptions
- behaviors
- memories
- initiating voluntary movements
TRUE OR FALSE: The nervous system is one of the smallest and yet the most complex of the 11 body systems.
TRUE.
two main subdivisions of the nervous system
- central nervous system (CNS)
2. peripheral nervous system (PNS)
_______ deals with normal functioning and disorders of the nervous system.
neurology
composition of the central nervous system (CNS)
brain and spinal cord
____ is the part of the CNS that is located in the skull and contains about 85 billion neurons
brain
____ is connected to the brain through the _____ of the _______ and is encircled by the bones of the vertebral column
spinal cord
foramen magnum
occipital bone
number of neurons that the spinal cord contains
about 100 million neurons
processes that are done by CNS
- processes incoming sensory information
- source of thoughts, emotions, and memories
- processes signals that stimulate muscles to contract
- processes signals that stimulate glands to secrete
composition of the peripheral nervous system (PNS)
all nervous tissue outside the CNS
- nerves
- sensory receptors
____ is a bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord
nerve
cranial nerves : ______ :: spinal nerves : ______
cranial nerves : 12 PAIRS :: spinal nerves : 31 PAIRS
sensory receptors
refers to a structure of the nervous system that monitors changes in the external or internal environment
examples of sensory receptors
- touch receptors in the skin
- photoreceptors in the eye
- olfactory (smell) receptors in the nose
two divisions of the PNS
- sensory
2. motor
sensory division of PNS
sensory or afferent division
- conveys input into the CNS from sensory receptors in the body
- provides the CNS with sensory information about the somatic senses (tactile, thermal, pain, and proprioceptive sensations)
- provides the CNS with sensory information about the special senses (smell, taste, vision, hearing, and equilibrium)
motor division of PNS
motor or efferent division
- conveys output from the CNS to effectors (muscles and glands)
two divisions of the motor division of PNS
- somatic nervous system
2. autonomic nervous system
somatic nervous system (SNS)
- conveys output from the CNS to skeletal muscles only
- because its motor responses can be consciously controlled, the action of this part of the PNS is voluntary
autonomic nervous system (ANS)
- conveys output from the CNS to smooth muscle, cardiac muscle, and glands
- because its motor responses are not normally under conscious control, the action of ANS is involuntary
- composed of three main branches
three branches of ANS
- sympathetic nervous system
- parasympathetic nervous system
- enteric nervous system
TRUE OR FALSE: With a few exceptions, effectors receive innervation from both of the branches of ANS, and usually the two branches have opposing actions.
TRUE.
example of the opposing actions; neurons of the sympathetic nervous system increase heart rate WHILE neurons of the parasympathetic nervous system slow it down
compare the sympathetic and parasympathetic nervous system
sympathetic nervous system helps support exercise or emergency actions such as the fight-or-flight response
parasympathetic nervous system takes care of rest-and-digest activities
enteric nervous system (ENS)
- extensive network of over 100 million neurons confined to the wall of the GI tract
- helps regulate the activity of the smooth muscles and glands of the GI tract
- ENS can function independently but communicates with and is regulated by other branches of the ANS
three main functions of the nervous system
- sensory function
- integrative function
- motor function
sensory function of the nervous system
- sensory receptors detect internal stimuli (e.g. increase in bp) or external stimuli (e.g. raindrop landing in your arms)
- sensory information is carried into the brain and spinal cord through cranial and spinal nerves
integrative function of the nervous system
- nervous system processes sensory information by analyzing it and making decisions for appropriate responses (integration)
motor function of the nervous system
- happens after integration
- nervous system may elicit an appropriate motor response by activating effectors (muscles and glands) through cranial and spinal nerves
- stimulation of the effector causes muscles to contract and glands to secrete
example of how the three basic functions of the nervous system occur
answering the cellphone after hearing it ring
- sound of the ringing cellphone stimulates sensory receptors in the ears (sensory function)
- auditory information is subsequently relayed into the brain where it is processed and the decision to answer the phone is made (integrative function)
- the brain then stimulates the contraction of specific muscles that will allow you to grab the phone and press the appropriate button to answer it (motor function)
nervous tissue comprises two types of cells: ____ and ____
neurons and neuroglia
neurons
- forming the complex processing networks within the brain and spinal cord
- connect all regions of the body to the brain and spinal cord
- provide most of the unique functions of the nervous system (i.e. sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions)
TRUE OR FALSE: Because of neurulation, most neurons have lost the ability to undergo mitotic divisions.
FALSE. Because of SPECIALIZATION, most neurons have lost the ability to undergo mitotic divisions.
neuroglia
- smaller cells but outnumber neurons by appx. 25 times
- support, nourish, and protect neurons, and maintain the interstitial fluid that bathes them
- continue to divide throughout an individual’s lifetime
TRUE OR FALSE: Only neuroglia differ structurally depending on whether they are located in the CNS or PNS.
TRUE OR FALSE: BOTH neurons and neuroglia differ structurally depending on whether they are located in the CNS or PNS.
the differences in structure correlate with the differences in the function of the CNS and the PNS
neurons (nerve cells) possess ______, the ability to respond to a stimulus and convert it into an action potential
electrical excitability
stimulus
any change in the environment that is strong enough to initiate an action potential
action potential (nerve impulse)
- an electrical signal that propagates (travels) along the surface of the membrane of a neuron
- begins and travels due to the movement of ions (i.e. sodium and potassium) between interstitial fluid and the inside of a neuron through specific ion channels in its plasma membrane
- once begun, a nerve impulse travels rapidly and at a constant strength
three parts of most neurons
- cell body
- dendrites
- axon
cell body in the neuron
- aka perikaryon or soma
- contains a nucleus surrounded by cytoplasm that includes typical cellular organelles (lysosomes, mitochondria, a Golgi complex)
- also contain free ribosomes and prominent clusters of endoplasmic reticulum called Nissl bodies
what happens to the newly synthesized proteins produced by Nissl bodies?
- used to replace cellular components as material for the growth of neurons
- used to regenerate damaged axons in the PNS
the cytoskeleton includes both ____ and ____
- neurofibrils composed of bundles of intermediate filaments that provide the cell shape and support
- microtubules that assist in moving materials between the cell body and axon
lipofuscin
- contained in aging neurons
- a pigment that occurs as clumps of yellowish-brown granules in the cytoplasm
- product of neuronal lysosomes that accumulates as the neuron ages, but does not seem to harm the neuron
ganglion
- collection of neuron cell bodies outside the CNS
nerve fiber
- general term for any neuronal process (extension) that emerges from the cell body of a neuron
two kinds of processes of neurons
- multiple dendrites
2. single axon
dendrites
- receiving or input portions of a neuron
- plasma membranes of dendrites (and cell bodies) contain numerous receptor sites for binding chemical messengers from other cells
- usually short, tapering, and highly branched
- form a tree-shaped array of processes extending from the cell body
- cytoplasm contains Nissl bodies, mitochondria, and other organelles
axon
- propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell
- long, thin, cylindrical projection that often joins to the cell body a cone-shaped elevation called the axon hillock
the part of the axon closest to the axon hillock is the __________
initial segment
trigger zone
junction of the axon hillock and the initial segment that is arisen by the nerve impulses
components of the axon
- mitochondria
- microtubules
- neurofibrils
TRUE OR FALSE: Protein synthesis occurs in the axon.
FALSE: Because rough endoplasmic reticulum is NOT present, protein synthesis DOES NOT occur in the axon.
axoplasm
- cytoplasm of an axon
- surrounded by a plasma membrane known as the axolemma
axon collaterals
- side branches along the length of an axon
- typically at a right angle to the axon
- axon and its collaterals end by dividing into many fine processes called axon terminals or axon telondendria
synapse
site of communication between two neurons or between a neurons and an effector cell
synaptic end bulbs
tips of some axon terminals that swell into bulb-shaped structures
varicosities
a string of swollen bumps
synaptic vesicles
tiny membrane-enclosed sacs contained in the synaptic end bulbs and varicosities
neurotransmitter
- stored in the synaptic vesicles
- molecule released from a synaptic vesicle that excites or inhibits another neuron, muscle fiber, or gland cell
- many neurons contain two or even three types of neurotransmitters each with different effects on the postsynaptic cells
two types of transport system that carry materials from the cell body to the axon terminals and back
- slow axonal transport
2. fast axonal transport
slow axonal transport
- slowers system
- moves materials about 1-5mm per day
- conveys axoplasm in one direction only: from the cell body toward the axon terminal
- supplies new axoplasm to developing or regenerating axons and replenishes axoplasm in growing and mature axons
fast axonal transport
- capable of moving materials a distance of 200-400mm per day
- uses proteins that function as motors to move materials along the surfaces of microtubules of the neuron’s cytoskeleton
- moves materials in both directions: away from and toward the cell body (anterograde and retrograde)
anterograde fast axonal transport
- forward direction
- moves organelles and synaptic vesicles from the cell body to the axon terminals
retrograde fast axonal transport
- backward direction
- moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled
- also moves substances that enter the neuron at the axon terminals (trophic chemicals such as nerve growth factor and harmful agents such as tetanus toxin and the viruses that cause rabies, herpes simplex, and polio)
two classifications of neurons
- structural classification
2. functional classification
structural classification of neurons
according to the number of processes extending from the cell body
- multipolar neurons
- bipolar neurons
- unipolar neurons
multipolar neurons
- structural classifications
- usually have several dendrites and one axon
- most neurons in the brain and spinal cord are of this type, as well as all motor neurons
bipolar neurons
- structural classification
- have one main dendrite and one axon
- found in the retina of the eye, the inner ear, and the olfactory area of the brain
unipolar neurons
- structural classification
- have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body
- more appropriately called pseudounipolar neurons because they begin in the embryo as bipolar neurons
- dendrites of most function as sensory receptors that detect a stimulus such as touch, pain, pressure, or thermal stimuli
pseudounipolar neurons
- begin in the embryo as bipolar neurons
- during development, the dendrites and axon fuse together and become a single process
trigger zone in a unipolar neuron
located at the junction of the dendrites and axon
the cell bodies of most unipolar neurons are located in…
the ganglia of spinal and cranial nerves
named neurons
Purkinje cells in the cerebellum and pyramidal cells in the cerebral cortex of the brain which have pyramid-shaped cell bodies
functional classification of neurons
according to the direction n which the nerve impulse (action potential) is conveyed with respect to the CNS
- sensory neurons
- motor neurons
- interneurons
sensory neurons
- functional classification, afferent neurons
- either contain sensory receptors at their distal ends (dendrites) or are located just after sensory receptors that are separate cells
- most are unipolar in structure
once an appropriate stimulus activates a sensory receptor, the sensory neuron forms an action potential in its axon and the axon potential is conveyed into the CNS through cranial or spinal nerves
motor neurons
- functional classification, efferent neurons
- convey action potentials away from the CNS to effectors (muscles and glands) in the PNS through the cranial or spinal nerves
- most are multipolar in structure
interneurons
- functional classification, association neurons
- mainly located within the CNS between sensory and motor neurons
- most are multipolar in structure
interneurons integrate (process) incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neurons
this make up about half the volume of the CNS
neuroglia
what happens to neuroglia in cases of injury or disease?
neuroglia multiply to fill in the spaces formerly occupied by neurons
glioma
- brain tumors derived from glia
- tend to be highly malignant and to grow rapidly
six types of neuroglia? which four are found in the CNS?
found in the PNS
- Schwann cells
- satellite cells
found in the CNS
- astrocytes
- oligodendrocytes
- microglia
- ependymal cells
how are the neuroglia of the CNS classified?
on the basis of size, cytoplasmic processes, and intracellular organization
astrocytes
- neuroglia present in the CNS
- star-shaped cells which have many processes
- largest and most numerous of the neuroglia
two types of astrocytes
- protoplasmic astrocytes that have many short branching processes and are found in gray matter
- fibrous astrocytes that have many long unbranched processes and are located mainly in the white matter
the process of astrocytes make contact with ____, ____, and _____
blood capillaries, neurons, and the pia matter (a thin membrane around the brain and spinal cord)
functions of astrocytes
- contain microfilaments that give them considerable strength and enables them to support neurons
- processes of astrocytes wrapped around blood capillaries isolate neurons of the CNS from various potentially harmful substances in blood by secreting chemicals that maintain the unique selective permeability characteristics of the endothelial cells of the capillaries –> endothelial cells create a blood-brain barrier restricting movement of substances between the blood and interstitial fluid of CNS
- (in embryo) secrete chemicals that appear to regulate growth, migration, and interconnection among neurons in the brain
- help maintain the appropriate chemical environment for the generation of nerve impulses (ex. regulating concentration of important ions like K+; take up excess neurotransmitters; serve as conduit for the passage of nutrients and other substances between blood capillaries and neurons
- play a role in learning and memory by influencing the formation of neural synapses
oligodendrocytes
resemble astrocytes but are smaller and contain fewer processes
process of oligodendrocytes
responsible for forming and maintaining the myelin sheath around CNS axon
myelin sheath
multilayered lipid and protein covering around some axons that insulates them and increases the speed of nerve impulse conduction (–> myelinated axons)
microglial cells or microglia
- small cells with slender processes that give off numerous spinelike projections
- function as phagocytes
- mimic tissue macrophages by removing cellular debris formed during normal development of the nervous system and phagocytize microbes and damage nerve tissues
ependymal cells
- cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia
- line the ventricles of the brain and central canal of the spinal cord (spaces filled with cerebrospinal fluid, which protects and nourishes the brain and spinal cord)
- produce, possibly monitor, and assist in the circulation of cerebrospinal fluid
- form the blood-cerebrospinal fluid barrier
neuroglia of the PNS
- Schwann cells and satellite cells
- completely surround axons and cell bodies
Schwann cells
- cells encircle PNS axons
- form the myelin sheath around axons
- myelinates a single axon
- can enclose as many as 20 or more unmyelinated axons
- participate in axon regeneration, which is more easily accomplished in PNS than CNS
satellite cells
- flat cells that surround the cell bodies of neurons of PNS ganglia
- provides structural support
- regulates the exchanges of materials between neuronal cell bodies and interstitial fluid
explain the process of myelination
https://www.youtube.com/watch?v=5V7RZwDpmXE
important characteristic of myelin sheath
myelinated
what does the myelin sheath do?
electrically insulates the axon of a neuron and increases the speed of nerve impulse conduction
what type of axon does the myelin sheath electrically insulate?
axons without covering, unmyelinated
two types of neuroglia that produce myelin sheaths
- Schwann cells (in the PNS)
2. oligodendrocytes (in the CNS)
how do Schwann cells produce myelin sheath?
- begin to form myelin sheaths around axons during fetal development
- each Schwann cell wraps about 1 mm (or 0.04 in) of a single axon’s length by spiraling many times around the axon
- eventually, multiple layers of glial plasma membrane surround the axon, with the Schwann cell’s cytoplasm and nucleus forming the outermost layer
what is found in the inner portion of the cytoplasmic layer of the Schwann layer that consists of up to 100 layers of Schwann cell membrane?
myelin sheath
neurolemma
- the outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath
- sheath of Schwann
- found only around axons in the PNS
what does the neurolemma do when an axon is injured?
neurolemma aids regeneration by forming a regeneration tube that guides and stimulates regrowth of the axon
nodes of Ranvier
- gaps in the myelin sheath
- appear at intervals along the axon
how does the Schwann cell wrap each axon?
each Schwann cell wraps one axon segment between two nodes
TRUE OR FALSE: In the PNS, an oligodendrocyte myelinates parts of several axons.
FALSE: In the CNS, an oligodendrocyte myelinates parts of several axons.
how do the oligodendrocytes produce myelin sheath?
each oligodendrocyte puts forth about 15 broad, flat processes that spiral around CNS axons, forming a myelin sheath
is a neurolemma present in the oligodendrocyte?
a neurolemma is NOT present because the oligodendrocyte cell body and nucleus do not envelop the axon
are nodes of Ranvier present in the oligodendrocytes?
yes they are present but they are fewer in number compared to Schwann cells
TRUE OR FALSE: Axons in the CNS display significant regrowth after injury. Why?
FALSE: Axons in the CNS display LITTLE regrowth after injury.
thought to be due, in part, to the absence of a neurolemma, and in part to an inhibitory influence exerted by oligodendrocytes on axon regrowth
does the amount of myelin increase from birth to maturity?
yes. its presence greatly increases the speed of nerve impulse conduction.
an infant’s responses to stimuli are neither as rapid nor as coordinated as those of an older child or an adult, in part because myelination is still in progress during infancy
