Ch. 12 - Nervous System Cells - CLASS NOTES Flashcards
Function of the nervous system
communicate
3 things the nervous system is comprised of:
- brain
- spinal cord
- nerves
Nervous system is organized to carry out 3 functions
- detect changes in environment (internal and external)
- evaluate information
- initiate appropriate response
General organization of the nervous system includes 4 sections:
- central nervous system
- peripheral nervous system
- afferent & efferent divisions
- somatic & autonomic systems
Central nervous system consists of what 2 structures:
- brain
2. spinal cord
Central nervous system’s 3 functions:
- integrates sensory information
- evaluates it
- initiates outgoing response
Peripheral nervous system consists of what:
- nerve tissue
PNS consists of 2 types of nerves, they are:
- cranial nerves - originate from brain
2. spinal nerves - original from spinal cord
Afferent division consists of:
all INCOMING sensory pathways
Efferent division consists of:
all OUTGOING motor pathways
Somatic nervous system carries information to:
skeletal muscles
Autonomic nervous system (ANS) carries information these 2 effectors
- autonomic effectors
2. visceral effectors
Efferent pathways of the ANS can be split into 2 divisions:
- sympathetic
2. parasympathetic
Sympathetic division:
FIGHT OR FLIGHT
Parasympathetic division:
REST AND REPAIR
GLIA
- non-neuronal cells in the brain
- support the neurons
- means glue
- 5 major types
Name the 5 types of glia:
- astrocytes
- microglia
- ependymal cells
- oligodendrocytes
- schwann cells
Which of the glia are “star-shaped”?
astrocytes
Which of the glia are the most numerous and the largest
astrocytes
Which of the glia form the Blood Barrier
astrocytes
Which of the glia transfer nutrients from the blood to the neurons
astrocytes
Which of the glia are small and usually stationary?
microglia
Which of the glia carry on phagocytosis
microglia
Which of the glia form thin sheets that line fluid-filled cavities of the brain & spine
Ependymal cells
Which of the glia produce the myelin sheath?
Oligodendrocytes
Which of the glia are found only in the peripheral nervous system
Schwann cells
What are Myelin sheath gaps are called?
Nodes of Ranvier
This type of glia supports nerve fibers and forms myelin sheath
Schwann cells
This is formed by the cytoplasm of Schwann cells wrapped around the myelin sheath.
Neurilemma
What structure is essential for nerve regrowth?
Neurilemma
What is a satellite cell?
Schwann cells that cover and support cell bodies in the PNS.
What are known as excitable cells that initiate and conduct impulses and make possible all system functions?
Neurons
4 components of neurons
- cell body
- dendrites
- axon
- cytoskeleton
In the cell body, this organelle provides energy for neuron and some are transported to the end of an axon.
Mitochondria
This structure branches off from the cell body in a neuron
Dendrite
These conduct signals to the cell body of the neuron
dendrite
Single process extending from axon hillock - sometimes covered by fatty layer called myelin sheath.
axon
conducts nerve impulses away from the cell body
axon
distal tips of axon, each terminating with a synaptic knob
telodendria
End of a telodendria
synaptic knob
bundles of neurofilaments
neurofibrils
function of the neuron’s cytoskeleton
allows rapid transport of small organelles
molecule that shuttles organelles to and from the far ends of a neuron
motor molecule
4 functional regions of a neuron
- input zone
- summation zone
- conduction zone
- output zone
The _________ zone receives input from other neurons or from sensory stimuli.
input zone
The _________ zone serves as the site where the nerve impulses combine and possibly trigger an impulse that will be conducted along the axon.
summation zone
Both the _________ zone and the _________ have many voltage-gated Na and K channels imbedded in the plasma membrane
summation, conduction
the _______ zone is where the nerve impulse triggers the release of neurotransmitters
output zone
the output zone includes many voltage-gated ________ channels in the membrane
calcium
3 structural classifications of neurons
- multipolar
- bipolar
- unipolar
kind of neuron that has one axon and several dendrites
multipolar
kind of neuron that has only one axon and one dendrite
bipolar
kind of neuron that has one process comes off neuron cell body but divides almost immediately into 2 fibers: central and peripheral fiber
unipolar
3 functional classification of neurons
- afferent (toward spinal cord and brain)
- efferent (away spinal cord and brain)
- interneurons
afferent neurons are also known as ________ neurons
sensory
efferent neurons are also known as _______ neurons
motor
signal conduction route to and from the CNS with electrical signal beginning in receptors and ending in effectors
reflex arc
most common reflex arc consisting of afferent neurons, interneurons, and efferent neurons
3-neuron arc
simplest form of reflex arc consisting of afferent and efferent neurons
2-neuron arc
where nerve signals are transmitted from one neuron to another
synapse
2 types of synapse:
- chemical
2. electrical
type of synapse typical in adult
chemical
type of synapse located at the junction of the synaptic knob of one neuron and the dendrite or cell body of another neuron
chemical
bundles of nerve fibers held together by several layers of connective tissue in the PERIPHERAL NERVOUS SYSTEM
nerves
bundles of nerve fibers held together by several layers of connective tissue in the CENTRAL NERVOUS SYSTEM
called tracts instead of nerves
3 kinds of nervous connective tissue:
- endoneurium
- perineurium
- epineurium
delicate layer of fibrous connective tissue surrounding each nerve fiber
endoneurium
connective tissue holding together fascicles (bundles of fibers)
perineurium
fibrous coat surrounding numerous fascicles and blood vessels to form a complete nerve
epineurium
________ matter: myelinated nerves and tracts
WHITE
________ matter: composed of cell bodies and unmyelinated fibers
referred to as nuclei in CNS
referred to as ganglia in the PNS
GRAY
the reason that damage to nervous tissue can be permanent
mature neurons are incapable of cell division
nerve fibers can only be repaired in the _________ nervous system
peripheral
structure integral to cell repair
neurilemma
in repair of nerve fibers, remaining ________ and endoneurium form a tunnel from point of injury to the effector
neurilemma
in nerve fiber, axon “_______” appear
sprouts
slight excess of positively charged ions on the outside of the membrane and slight deficiency of positively charged ions on the inside of the membrane
membrane potential
membrane that exhibits a membrane potential
polarized membrane
membrane potential maintained by a nonconducting neuron’s plasma membrane is typically -70mV is known as:
resting membrane potential
membrane’s selective ________ characteristic help maintain a slight excess of positive ions on the outer surface of the membrane
permability
active transport mechanism in plasma membrane that transports sodium and potassium ions in opposite directions at different rates
sodium-potassium pump
this mechanism actively pumps sodium ions out of the neuron and potassium ions into neuron
sodium-potassium pump
slight shift away from resting membrane in a specific region of the plasma membrane
local potentials
when a stimulus triggers the opening of additional sodium channels, allowing the membrane potential to move toward zero (depolarization)
excitation
when a stimulus triggers the opening of addition potassium channels, increasing the membrane potential (hyperpolarization)
inhibition
local potentials are called _______ ________ because the magnitude of deviation from the resting membrane potential is proportional to the magnitude of the stimulus
grade potentials
membrane potential of a neuron conducting an impulse
action potential
also known as a nerve impulse
action potential
an all-or-none response
action potential
order of action potential
-70 mV (stimulus)
1. stimulus gated Na+ channels open
2. voltage gated Na+ channels open
3. voltage-gated Na+ channels close
30+ mV
4. voltage-gated K+ channels open
5. voltage-gated K+ channels close
- 70 mV
voltage-gated Na+ channels stay open for only about 1 ____ before they automatically close
milisecond
after action potential peaks, membrane begins to move back toward the resting membrane potential when K+ channels open, allowing outward diffusion of K+
repolarization
brief period during which a local area of a neuron’s membrane resists restimulation and will not respond to a stimulus, no matter how strong
absolute refractory period
time when the membrane is repolarized and restoring the resting membrane potential and will respond only to a very strong stimulus
relative refractory period
action potential never moves backwards because of the
refractory period
in myelinated fibers, action potentials only occur at the nodes of Ranvier - a type of impulse conduction called:
saltatory
speed of nerve conduction depends on 2 things:
- diameter
2. presence or absence of myelin sheath
2 types of synapses (junctions)
- electrical
2. chemical
type of synapse that occurs where cells joined by GAP JUNCTIONS allow an action potential to simply continue along postsynaptic membrane
electrical synapse
occurs where presynaptic cells release chemical transmitters - NEUROTRANSMITTERS - across a tiny gap to the postsynaptic cell
chemical
2 key structures of chemical synapse:
- synaptic knob
2. synaptic cleft
tiny bulge at the end of a terminal branch of a presynaptic neuron’s axon that contains vesicles housing neurotransmitters
synaptic knob
space between synaptic knob and plasma membrane of postsynaptic neuron
synaptic cleft
3 types of synapses:
- Axodendritic: axon signals postsynaptic dendrite; common
- Axosomatic: axon signals postsynaptic soma; common
- Axoaxonic: axon signals postsynaptic axon; may regulate action potential of postsynaptic axon
Plasma membrane of a postsynaptic neuron has _______ ________ that serve as receptors for the neurotransmitters
protein molecules
Mechanism of synaptic transmission
- Action potential reaches a synaptic knob, causing Ca+ ions to diffuse into the knob rapidly
- Increased Ca+ concentration triggers the release of neurotransmitter by way of exocytosis
- Neurotransmitter molecules diffuse across the synaptic cleft and bind to receptor molecules, causing ion channels to open
- Opening of ion channels produces a postsynaptic potential, either an excitatory postsynaptic potential or an inhibitory postsynaptic potential
- The neurotransmitter’s action is quickly terminated by neurotransmitter molecules being transported back into the synaptic knob (reuptake) and/or metabolize into inactive compounds by enzymes and/or diffused and taken up by nearby glia
2 kinds of summation
- spatial summation
2. temporal summation
adding together the effects of several knobs being activated simultaneously and stimulating different locations on the postsynaptic membrane, producing an action potential
spatial summation
when synaptic knobs stimulate a postsynaptic neuron in rapid succession, their effects can summate over a brief period to produce an action potential
temporal summation
means by which neurons communicate with one another; more than 30 compounds are known to be neurotransmitters, and dozens of others are suspected
neurotransmitters
2 major functional classifications of neurotransmitters
- excitatory
2. inhibitory
Functional classification of neurotransmitters can also be according to whether the receptor directly opens a channel or whether a second messenger involving _____ proteins and intracellular proteins
G
mechanism by which neurotransmitters cause a change
chemical structure
4 kinds of small-molecule neurotransmitters
- acetylcholine (acetate with choline)
- amines (synthesized from amino acids)
- amino acids (most common)
- other small-molecule transmitters
large-molecule neurotransmitters are also called
neuropeptides
2 Theories of Role of Nervous System Cells
- neuron doctrine
- proposes that the neuron is the basic structural and functional unit of nervous system - reticular theory
- proposes the nervous system is best understood as a large integrated network
neurons act as the “wiring” that connects structures needed to maintain _______
homeostasis
sensory neurons act as ________ to detect changes in the internal and external environment
receptors
information is process and a response is relayed to the appropriate effectors the the ________ neurons
motor
neurons released into the bloodstream are called _________
hormones
