exam 1 Flashcards
2 kinds of cells in nervous system
- Neurons: receive and transmit info
2. Glia: don’t transmit info, perform tasks such as support and guidance
neural doctrine
Neurons are independent, specialized functional units separated by a synaptic gap, across which information is transmitted
dendrites
branching fibers responsible for bringing info into the neuron
- Receive information and send to cell body
soma/ cell body
contains nucleus, mitochondria, ribosomes, and other structures found in other cells
axon
thin fiber that sends information from cell body to presynaptic terminal
myelin sheath
insulating material covering axons in many neurons; speeds up communication along the axon
presynaptic terminal
the end point on the axon that releases chemicals
4 zones of a neuron
- input (receives info through dendrites
- integration (cell body region where inputs are integrated)
- conduction (single axon conducts output info away from cell body as impulse)
- output (axon terminals at end communicate to other cells)
types of glia
- astrocytes
- microglia
- radial glia
- myelination:
- oligodendrocytes
- schwann cells
oligodendrocytes
located in CNS and produce myelin sheaths for axons
- One oligodendrocyte myelinates many axons
- When axon is damaged oligodendrocytes produce scar tissue and prevent healing of the axon
schwann cells
located in PNS and produce and repair myelin sheaths for axons
- One Schwann cell myelinates one axon
- When axon is damaged Schwann cell creates a tube that allows the axon to heal
electrical signals are for communication _____ a neuron
within
chemical signals are for communication ____ neuron
between
electricity
moving charged particles
ions
charged molecules
Cations +
Anions -
ions associated with a neuron
Potassium(K+) **
Sodium (Na+) **
Calcium (Ca2+)
Chloride (Cl-)
nerve impulse
the electrical message that is transmitted down the axon of a neuron
resting potential
state of the neuron prior to sending a nerve impulse
- -70 millivolts, inside of neuron is slightly more negative than fluid outside of the neuron
- There is more Na+ outside of the cell and more K+ inside of the cell
electrical gradient
a difference in the electrical charge inside and outside of the neuron
2 forces that cause ions to move
diffusion
electrostatic pressure
diffusion
ions move from areas of high concentration to areas of low concentration
- Diffusion “down” the concentration gradient
electrostatic pressure
like charges repel and opposites attract
equilibrium potential
when net movement through channels is 0
- When the chemical and electrical forces are in balance
- Electrostatic pressure draws K+ in b/c the intracellular environment is negative
- Diffusion pushes K+ out of the cell
- forces act against each other
- The equilibrium potential for K+ is –60mV
Na+
mostly extracellular; diffusion pushes it in cell; since inside of cell is negative, EP attracts Na into cell
K+
mostly intracellular; diffusion push it out of the cell, outside of the cell is positively charged so electrostatic pressure tends to force K+ inside; opposing forces balance
Cl-
mostly extracellular; diffusion pushes it in; inside of cell is negatively charged, EP pushes it out; opposing forces balance
sodium-potassium pump
continually pumps three sodium ions out of the cells while drawing two potassium ions into the cell
Helps maintain electrical gradient
hyperpolarization
increasing the polarization (difference) between the electrical charge inside and outside of cell
depolarization
decreasing the polarization towards zero
Threshold of excitement
any stimulation beyond a certain level and results in a massive depolarization
action potential
stimulation beyond a certain level crosses the threshold of excitation and produces a massive depolarization of the membrane
Rapid depolarization continues to about +30 mV and then returns rapidly to its resting potential
sodium channels
- slight depolarization, sodium channels open slightly
- Once threshold is reached, sodium channels open wide (voltage dependent) and Na + ions rush into cell
- At peak of action potential, sodium channels close and cannot be opened again for the next millisecond or so
potassium channels
Open wide as action potential approaches its peak allowing K+ ions to flow out of the cell
- Cell becomes hyperpolarized and overshoots resting membrane potential, and then returns to - 70 mV
stages of action potential
- Na+ channels open, Na+ begins to enter cell
- K+ channels open, K+ begins to leave cell
- Na+ channels become refractory, no more Na+ enters cell
- K+ continues to leave cell, causes membrane potential to return to resting level
- K+ channels close, Na+ channels reset
- Extra K+ outside diffuses away
the refractory period
Immediately after an action potential, the neuron enters a refractory period and resists producing more action potentials
- absolute
- relative
absolute refractory
(~1ms)
The sodium gates are firmly closed
The membrane cannot produce an action potential, regardless of the stimulation
relative refractory
(another 2-4 ms)
The sodium gates are reverting to their usual state, but the potassium gates remain open
A stronger than normal stimulus can result in an action potential
all or none law
the size, amplitude, and velocity are independent of the intensity of the stimulus that initiated it
saltatory conduction
word used to describe this “jumping” of the action potential from node to node.
- Provides rapid conduction of impulses
- Conserves energy for the cell
synapse
space between axon of one neuron and the dendrite (or axon or soma) of another
synaptic transmission
the way neurons communicate with each other
- message carried by NT
- When electrical signal reaches axon, the synaptic vessicles release NT into synapse
- NT cross the synapse and bind with receptors
neurotransmitters
chemicals that affect electrical signal of receiving neuron
excitatory NT
increases chance neuron will fire
inhibitory NT
decreases chance neuron will fire
Steps of NT release
- Action potentials reach presynaptic terminal
- Ca2+ channels open and Ca2+ rushes in
- Vesicles release NT into synapse
- NT binds to receptors on postsynaptic membrane
- Receptors open channels and admit ions
- Receptor deactivation and desensitization shuts down postsynaptic response
- Clearance of NT from synaptic cleft: degradation or reuptake
reuptake
NT taken back up by presynaptic cell
enzymatic deactivation
enzyme breaks apart NT inactivating it
EPSP
Na+ influx depolarizes dendrite
- Increased probability of action potential firing
IPSP
Cl- influx locally hyperpolarizes dendrite
- Less probability of action potential firing
temporal summation
occurs when 2 EPSP are produced in rapid succession
- Potentials sum if close enough in time
spatial summation
occurs when different synapses produce EPSPs on the same postsynaptic neuron simultaneously
- Potentials sum if close enough inspace
endogenous substances
internal substances that are released by the presynaptic cell and bind to the receptors on the postsynaptic cell
exdogenous substances
external substances that are mimic neurotransmitters
Drugs
2 types of NT receptors
ionotropic and metabotropic
ionotropic
quickly change shape and open or close an ion channel when the transmitter molecule binds
metabotropic
Do not contain ion channels
- Usually activate G- proteins (affect ion channels directly through enzymes and second messengers)
- When activated, they activate second messengers that change excitability of postsynaptic cell or make other slower, large-scale changes to cell
- Receptor and ion channel functions are NOT a single protein
- “Metabotropic” = (delayed) movement of ions through the channel requires metabolic steps
criteria for NT classification
- Synthesized in presynaptic neurons and stored in axon terminals
- Released when action potentials reach axon terminals
- Recognized by receptors on postsynaptic membrane
- Causes changes in postsynaptic cell
- Blocking its release interferes with a cell’s ability to affect a postsynaptic cell
amino acid NT
most common in brain
- glutamate: most widespread excitatory NT
- GABA: most widespread inhibitory NT
amine NT
basic nitrogen compounds
- Acetylcholine: plays a major role in transmission in the forebrain
- dopamine: important for many aspects of behavior
- norepinephrine: is important in control of many behaviors ranging from alertness to mood to sexual behavior, Fight or flight response
- serotonin: participates in the control of many aspects of behavior (mood, vision, anxiety, sleep,etc)
peptide NT
compound made of two or more amino acids
- Opioid peptides: mimic opiate drugs such as morphine and reduces the perception of pain
- Substance P: a peptide NT important in perception of pain
gas NT and how it differs
nitric oxide, carbon monoxide
- Differs from other transmitters in 3 ways:
1. Produced outside of axon terminals and diffuses out of neuron as soon as it is produced
2. No receptors are involved; diffuses into the target cell and activates second messengers
3. It can function as a retrograde transmitter by diffusing from postsynaptic neuron back to presynaptic neuron
ventral
toward stomach
dorsal
toward back
lateral
toward side
medial
toward midline
CNS
brain and spinal cord
PNS
all other parts besides brain and spinal cord
- consists of nerves
- somatic
- autonomic
- —- sympathetic
- —- parasympathetic
motor nerves
transmit info from the spinal cord and brain to muscles and glands
sensory nerves
convey info from the body to the CNS
somatic sys
part of PNS
nerves that convey messages from sense organs to the CNS and from the CNS to the muscles and glands
- has cranial and spinal nerves
cranial nerves
innervate the head, neck, and visceral organs directly from the brain
- 12 pairs that control much of the motor and sensory functions of the head and neck
spinal nerves
connect to spinal cord - 31 pairs, each nerve consists of a group of motor fibers that project from spinal cord and a group of sensory fibers that enter the spinal cord Cervical (neck) Thoracic (trunk) Lumbar (lower back) Sacral (pelvic) Coccygeal (bottom)
autonomic sys
set of neurons that control the heart, the intestines, and other internal organs (visceral)
sympathetic
parasympathetic
sympathetic
arousal, “fight or flight”, emergency
- Increased breathing, heart rate, decreased digestive activity
parasympathetic
“relax and digest”, nonemergency
- Increases digestive activity, activates opposing sympathetic system
Bell-magendie law
The entering dorsal roots carry sensory information to the brain and
The existing ventral roots carry motor info to the muscles and glands
cerebral cortex
outermost, convoluted layer of brain
gyri
ridged or raised portions of brain
sulci
furrows or divots in brain
grey matter
outer surface of cerebral hemispheres
white matter
formed by axons extending inward from cortex
corpus callosum
how neurons from each hemisphere communicate
- bundle of axons
4 lobes of each hemisphere
- frontal
- parietal
- occipital
- temporal
frontal lobe
most anterior (front) region - Motor functions, executive functions, attention, aspects of personality
parietal lobe
lies between frontal and occipital lobes (top middle)
- Touch and spatial information
occipital lobe
posterior (back of cortex) region
- visual processing
temporal lobe
lateral (sides) region
- auditory processing
sylvian fissure
boundary of the temporal lobe
central sulcus
divides frontal lobe from parietal lobe
postcentral gyrus
a strip of cortex behind the central cortex, important for touch
precentral gyrus
in the frontal lobe, important for motor control
hindbrain
our “old” brain; certain vital body functions are controlled by brainstem
- cerebellum
- pons
- medulla
cerebellum
controls movement, balance and coordination; participates in some types of learning
pons
integrates movement between right and left side of the body, regulates sleep
medulla
marks transition from brain to spinal cord; controls vital reflexes, e.g., breathing, heart beat
midbrain
systems of tectum: (Sensory) - superior colliculi - inferior colliculi Motor sys: - substancia nigra other: - reticular formation - periaqueductal gray
superior colliculi
visual processing
inferior colliculi
auditory processing
substancia nigra
part of basal ganglia (important in motor control)
reticular formation
wakes you up; can immediately activate other parts of the brain to produce arousal, allows you to filter important information while you are sleeping
Damage can cause irreversible coma
periaqueductal gray
pain perception and reduction
limbic sys
important for emotions, pleasure, anxiety, and aggression amygdala hippocampus cingulate gyrus olfactory bulb thalamus hypothalamus
amygdala
emotional regulation
hippocampus
critical for formation of new memory
thalamus
sensory relay station information to/from cerebral cortex (except olfactory)
hypothalamus
regulates vital, survival behavior
Feeding, fighting, reproducing
meninges
three protective membranes that surround brain and spinal cord
dura mater
pia mater
arachnoid membrane
dura mater
tough outermost layer of meninges
pia mater
delicate innermost layer of meninges
arachnoid membrane
between dura and pia
filled with CNS
ventricular sys
a series of chambers filled with CSF
- Lateral ventricle: in each hemisphere extends into all four lobes and is lined with the choroid plexus (a membrane that produces CSF)
- Hydrocephalus: blockage of flow of CSF (Increases pressure on brain)
cerebral arteries
supply oxygenated blood to brain
- Stroke: caused by rupture or blockage of blood vessels, leading to insufficient oxygen supply
CNS prenatal development
- begins to form at 2 weeks
- neurolation
neurolation
formation of neural tube
Dorsal surface thickens → neural tube and fluid filled cavity.
Forward end → brain
Rest of neural tube → spinal cord
what does the neural tube develop into?
the forebrain, midbrain, and hindbrain
what does the forebrain develop into?
telencephalon and diencephalon.
telencephalon
the anterior part of the forebrain mostly consisting of the cerebral hemispheres
diencephalon
the posterior part of the forebrain including thalamus and hypothalamus
brainstem
refers to the midbrain, pons, and medulla combined.
prenatal development stages
- Proliferation: production of new cells
- Migration: neurons move towards their destination in the brain
- Differentiation: begin to form distinctive neuron shape
postnatal development stages
- Synaptogenesis: (creation of synapses) increase of synaptic and dendritic density
- Synaptic retraction: pruning synapses
“Use it or lose it” - Cell death (the ones you don’t lose)
determinants of neuronal survival
- nerve growth factor (NGF)
- neuronal darwinism
- experience (enriched vs. deprived environment)
NGF
a neurotrophin that is produced when a neuron forms a synapse on a muscle
- If neuron does not get enough NGF it dies (apoptosis)
- Activity independent survival: without contacting an appropriate cell, a neuron will die
plasticity
he brain is constantly changing throughout the lifetime.
- Experience and physical maturation → brain development
- After childhood, brain is less plastic
- Damage early on: brain is able to compensate
spilkins research
Challenged belief that brain was “hardwired”
Behavioral resiliency seen following early focal brain injury (stroke)
Children acquire functioning following brain injury that might leave adults permanently impaired
