Chapter 11: nervous system Flashcards
What are the 3 functions of the nervous system?
1) SENSORY INPUT: collection of stimuli
2) INTEGRATION: interpretation of the sensory information and decide response
3) MOTOR OUTPUT: activation of effector organs (muscles and glands) to produce a response
What type of neuron fulfills each of the three functions of the nervous system?
Sensory neurons receive stimuli
Interneurons (association neurons) interpret and decide
Motor neurons produce response
What are the 2 main divisions of the nervous system?
CNS = brain and spinal cord (integration and command)
PNS = paired spinal and cranial nerves that carry messages to and from the CNS
What are the 2 functional divisions of the PNS?
SENSORY (afferent) division
MOTOR (efferent) division
What are the 2 subdivisions under the sensory (afferent) division of the PNS?
somatic afferent fibers carry info away from skin, skeletal muscles, and joints
visceral afferent fibers carry info from visceral organs
What are the 2 subdivisions under the motor (efferent) division of the PNS?
Somatic (voluntary) nervous system:
- conscious control of skeletal muscles
Autonomic (involuntary) nervous system (ANS)
- unconscious control
- regulates smooth muscle, cardiac muscle, and glands
What are the two subdivisions of the ANS (autonomic (involuntary) nervous system)?
Sympathetic
Parasympathetic
What are the two major cell types of the nervous tissue?
NEURONS: excitable cells that carry info by transmitting electrical signals
NEUROGLIAL (accessory) cells that assist neurons
What are the 4 kinds of neuroglial cells in the CNS?
ASTROCYTES
MICROGLIA
EPENDYMAL cells
OLIGODENDROCYTES
What are astrocytes and what is there function?
They are the most abundant cell, they are star shaped and highly branched
- SUPPORT and ANCHOR the neurons to capillaries
- TRANSFER glucose from blood to neurons
- GUIDE GROWTH of young neurons - aid in synapse formation
- control ION CONTENT around neurons (remove excess K+)
- signal each other and influence neuron signals
What do microglia look like and what do they do?
Small ovoid cells with thorny processes
- MONITOR condition of neurons
- MIGRATE toward injured neurons
- convert to MACROPHAGES to phagocytize microorganisms and debris
What do ependymal cells look like and what do they do?
range in shape from squamous to columnar
- line the central cavities of the brain and spinal column
- cilia move the CSF (cerebrospinal fluid)
- form the BLOOD-BRAIN BARRIER
What do oligodendrocytes look like and what do they do?
large branched cells
- Processes wrap around several nerve fibers, FORMING insulating MYELIN SHEATHS
- Gaps between are called NODES OF RANVIER
What are the 2 types of neuroglial cells in the PNS?
SATELLITE CELLS
SCHWANN CELLS
What do satellite cells do?
- surround neuron cell bodies in the PNS
- same role as astrocytes in CNS
- support, nurture, control environment around cell bodies
What do schwann cells do?
smaller than oligodendrocytes
- surround peripheral nerve fibers and form myelin sheaths
- gaps between cells called nodes of ranvier
- vital to regeneration of peripheral nerve fibers
What are the 5 special characteristics for neurons?
1) long lived (100 yrs plus)
2) amitotic (don’t divide, with a few exceptions)
3) high metabolic rate (depends on continuous supply of oxygen and glucose b/c it can’t store its own)
4) irritable - respond to stimuli
5) plasma membrane functions in electrical signaling
What are the two other names for the cell body of a neuron?
perikaryon or soma
What organelles do neurons lack?
centrioles (do not divide)
What is the rough ER of a neuron called? what is significant about this feature?
Nissl bodies:
- they are specialized while developed rough ER and are there because the neurons need to produce large numbers of proteins/neurotransmitters.
What is a cluster of cell bodies in the CNS called?
Nucleus
What is a cluster of cell bodies in the PNS called?
Ganglion
What are the two types of neural appendages?
dendrites - receive input
axon - the cells output
How many axons are there per neuron?
1
Where are stimuli integrated?
at the axon hump.
What is longer, an axon or a dendrite?
axons
What happens to an axon if it is cut? why?
it degenerates quickly because it has no ER or Golgi bodies and depends on transport of proteins from the neuron’s body
What makes up the myelin sheath?
proteins and lipids (think of cell membranes that are wrapped around the axon)
What are the functions of the myelin sheath?
- PROTECT and electrically INSULATE axon
- increase SPEED of nerve impulse
How are axons myelinated in the PNS?
many schwann cells wrap many times around the axon
- myelin sheath is made of concentric layers of Schwann cell membrane
- NEURILEMMA: peripheral bulge of Schwann cell cytoplasm (outer layer)
What is the neurilemma?
the peripheral bulge of schwann cell cytoplasm; the outer layer.
(because schwann cell, only in the PNS not CNS)
How is nerve tissue myelinated in the CNS?
formed by oligodendrocytes
- much larger than schwann cells
- each cell may myelinate multiple axons
- formed by the processes of oligodendrocytes, not the whole cell
contains nodes of ranvier, but no neurilemma
What makes up grey matter?
non-myelinated fibers
What makes up white matter?
myelinated fibers
What are the three structural classifications of neurons?
MULTIPOLAR: 3 + processes
- most common
- ex somatic neurons
BIPOLAR: 2 processes
- very rare
- ex specialized receptors in sensory organs
UNIPOLAR: 1 short process which branches into 2
(structure like 0-I) where O is the body.
- peripheral process often associated with a sensory receptor
- central process - branch entering CNS
ex most sensory neurons
What are the three functional classifications of neurons?
SENSORY (afferent): carry info from receptors to CNS
- most are unipolar. cell bodies in ganglia outside cns
MOTOR (efferent): carry info from cns to effectors
- multipolar, cell bodies insided cns
INTERNEURONS (association): connect sensory and motor neurons
- receive and integrate info and decide response
- mostly multipolar
- inside cns
What percentage of neurons are interneurons?
99%
Define voltage.
the measure of potential energy generated by separated charges
What is potential difference?
voltage measured between two points
What are the two main types of ion channels?
1) PASSIVE channels - always open, also called leakage
2) GATED channels - open in response to stimulus
What are the two types of gated ion channels?
CHEMICALLY gated - open with binding of a specific neurotransmitter
VOLTAGE gated - open and close in response to changes in membrane potential
What is a graded potential?
a potential change that occurs when a stimulus causes gated ion channels to open
What are the characteristics of a graded potential?
- amplitude varies directly with stimulus str
- they are short-lived, localized changes in membrane potential
- dec in magnitude with distance
What are the characteristics of an action potential?
is large with amplitude of approx 100 mV
- moves along whole axon of neuron
- does not dec in magnitude with distance
- is all or nothing
- produced from the sum of many graded potentials
- used for long-distance signalling
What is the value of the resting potential?
-70 mV
How is the resting potential maintained?
by the Na/K pump which keeps NA low and K high inside, and the opposite outside
What is the value of threshold potential?
-50 to -55 mV
What happens if threshold is reached by graded potentials?
an action potential is generated
How do action potentials code for strength of a stimulus?
with frequency, NOT amplitude
it is always the same
What are the two types of graded potentials?
Excitatory graded potentials (EP)
- rise in potential toward threshold (depolarizes)
Inhibitory graded potentials (IP)
- movement away from potential (hyperpolarizationg)
What determines how a neuron responds to stimuli?
the sum of all the graded potential inputs
- if the graded potentials add up to reach threshold
To what voltage does the membrane depolarize to during an AP?
+ 30 mV
What causes the absolute refractory period? What does this ensure that each action potential will be?
Na gates are still open so no new AP can be generated
- ensures each AP is a separate event and keeps transaction unidirectional.
Describe what the relative refractory is and what causes it.
relative refractory period is when the period during hyperpolarization when the Na channels are closed, but the membrane potential is more neg b/c the Na/K pumps haven’t restored normal resting conditions.
Therefore it can be stimulated to generate a new AP, but requires a stronger stimulus
what are the two types of conduction of an AP?
CONTINUOUS conduction in unmyelinated
SALTATORY conduction in myelinated axons
- signal jumps from node to node
- approx 30x faster
What 4 factors contribute to the speed of transmission of impulses?
1) axon diameter - larger = less resistance
2) Myelinated or not
3) presence of chems - (ex from drugs, usually slows transmission)
4) physical conditions around axon - ex low temp
What are the two types of synapses?
ELECTRICAL SYNAPSE: rare in adult, common in embryo
- like a gap junction, very fast.
- used to synchronize actions of neurons in a single area (ex controlling eye muscles)
CHEMICAL SYNAPSE: most common
- neurotransmitter carries message across synaptic cleft
How is transmission kept unidirectional in chemical synapses?
Only the presynaptic neuron contains neurotransmitter vesicles and only postsynaptic neuron has the appropriate receptors
Describe what an EPSP is.
Excitatory post synaptic potentials (a type of graded)
- binding of neurotransmitter causes Na and K channels to open, more Na moves in then K moves out (depolarizes slightly)
- travel to the axon hillock where they are integgrated
Describe what an IPSP is.
Inhibitory post synaptic potential
- binding of neurotransmitter changes permeability so K moves out or Cl moves in -> hyperpolarization and less likely to generate an AP
What two factors contribute to the strength of the post synaptic potential?
amount of neurotransmitter released
time the neurotransmitter is in area
What are the two types of summation of graded potentials?
TEMPORAL summation: over time
- mult. EPSPs over a short time interval at same point on membrane
SPATIAL summation: over space
- mult EPSPs occurring at different places on membrane at same time
- the closer to hillock, the greater the effect
What is synaptic potentiation?
the more often a synapse is used, the stronger its effect on the post synaptic neuron becomes
the ability of a neuron to learn
- presynaptic neuron contains more Ca -> more NT released -> more effect
What is multiple sclerosis?
an autoimmune disease that mainly affects young adults
- immune system attacks the myelin sheaths of the CNS
- results in shunting and short-circuiting of impulses
- conduction slows and eventually ceases
What are 6 common neurotransmitters?
Acetylcholine Biogenic amines Amino acids Peptides Gasotransmitters Purines
where is ACH found?
in all neuromuscular junctions, in CNS, and some autonomic synapses
What are biogenic amines synthesized from?
from amino acids
from tyrosine -> dopamine -> norepinephrine -> epinephrine
from tryptophan -> serotonin
from histidine -> histamine
Where are biogenic amines commonly found?
in CNS and autonomic
- play a role in emotions
Where are amino acid NT found? give some examples.
only in CNS
ex GABA, glutamate, glycine, aspartate
give some examples of peptide NT
substance P - causes pain
endorphins - pleasure chems, reduce pain
gut brain peptides - somatostatin, CCK
give a few examples of gasotransmitters
NO - involved in learning and memory, excess release causes brain damage in stroke patients
CO - regulates cGMP in brain
H2S - not much known
Give a few examples of purine NT
ATP
Adenosine
What are the three functional classifications of neurons?
EXCITATORY (depolarizing) ex glutamate
INHIBITORY (hyperpolarizing) ex GABA
NEURMODULATOR
What does the neuromodulator class of neurotransmitter do?
it is a NT that is released by a neuron that doesn’t directly cause EPSPs or IPSPs, but affects the strength of synaptic transmission
ex. controlling synthesis, release or reuptake, changing of sensitivity of post synaptic membrane to NT
What are the two mechanisms of action neurotransmitters can have?
DIRECT - binds to receptor which then opens channels to change permeability
INDIRECT - binds to G receptor which activates cAMP to exert its effects
What is a neuronal pool?
a functional grouping of neurons that integrate information from receptors or other neuronal pools
- forward process information to the next level of the nervous system
What are the 4 types of neural circuits?
DIVERGING
CONVERGING
REVERBERATING
PARALLEL after discharge
What is a diverging circuit?
it is an amplifying circuit
one fiber stimulates many others
- common for motor and sensory circuits
- ex one motor neuron in the brain stimulates hundreds to the skeletal muscles
What is a converging circuit?
the opposite of diverging
- many different impulses funneled into a single receiving area
- produces strong inhibition/stimulation
- common in motor and sensory systems
What is a reverberating circuit?
it is an oscillating circuit
-> 0 -> 0 -> 0
I I
0<- 0
used in control of rhythmic activities
- sleep/wake cycles, breathing
What is a parallel after discharge circuit?
- one incoming fibers stimulates many parallel neurons which then stimulate a single output cell.
- signals arrive at different times at the output cell
- involved in complex mental activities
What are the two patterns of processing?
SERIAL processing
PARALLEL processing
What is serial processing?
input travels along a single pathway to specific destination
- much faster, but takes longer to get a complete picture
What is parallel processing?
input travels along several different pathways to integration points in CNS
- allows for the brain to process many different aspects at same time
- much faster at determining connections than with serial
- important for higher mental functioning
