Lecture Test 5
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. What would you like to do?
monitor the internal environment
monitor the exterior environment
Leak (passive) channels
are always open and allow specific ions to flow across.
resting membrane potential
is the maintenance of this separation of electrical charge across the membrane while the cell is at rest (or not conducting an action potential).
allow for the control of ion flow across the membrane
What are the three types of gated or regulated channels?
- 1. Chemically gated channels
- 2. Voltage gated channels
- 3. Mechanically gated channels
chemically gated channels
open and close in response to the presence of specific chemicals like neurotransmitters and drugs (ie. nicotine, caffeine).
Think of a locked door as the channel and the key as the drug or NT.
Voltage gated channels
open at specific voltages and close at specific voltages.
Think of pass keys to electrical gates at an apartment complex.
Mechanically gated channels
open in response to mechanical or physical distortions of the cell membrane.
Think of the air nozzle on a child's arm floats.
Channel type: Leak channel
stimulus to open/close: always open
comment: establish RMP
channel type: chemically gated NA+ channel
stimulus to open/close: excititory Neurotransmitter
comment: they can depolarize neurons
channel type: chemically gated K+ channel
stimulus to open/close: inhibitory neurotransmitters
comment: they hyperpolarize neurons
channel type: voltage gated Na+ channel
stimulus to open/close: -60 mv open / +30mv close
comment: they cause action potentials
channel type: voltage gated K+ channel
stimulus to open/close: +30mv open / -70mv close
comment: they are part of the action potential
channel type: voltage gated Ca++ channel
stimulus to open/close: open with action potential and close with action potential is gone.
comment: they are at the synaptic knob
channel type: mechanically gated channel
stimulus to open/close: open in response to mechanical or physical distortions of the cell membrane.
the voltage necessary to begin opening voltage gated channels
a small localized change in the RMP
depolarizing/excitatory post-synaptic potentials (EPSP)
if the NT opens a sodium channel, sodium ions will enter the cell, the neuron will become more positive inside and is said to excite or become depolarized or have an EPSP
hyperpolarizing/inhibitory post-synaptic potentials (IPSP)
if the NT opens potassium channels, potassium ions will exit the cell; the neuron will become more negative and is said to hyperpolarize or have an ISP.
adding several graded potentials together to increase the strength
What are the two types of summation?
one synapse, over a period of time, can continually release NT, holding chemically gated channels open for extended periods.
results from simultaneous stimulation of numerous synapses to add either EPSP's or IPSP's together
occurs when a chemical (drug or NT) raises the RMP closer to threshold for a period of time.
anything that alters resting membrane potential
is a self-propagating (pushing) wave of voltage that will pass down the entire length of the neuron.
threshold potential (or threshold)
is the level of depolarization (millivoltage) necessary to cause an action potential
any stimulus that brings the neuron to threshold will cause an action potential.
there is no turning back
What are the 5 steps for the generation of an action potential?
- 1. depolarized to threshold
- 2. rapid depolarization
- 3. repolarization
- 4. hyperpolarization
- 5. return to RMP
depolarized to threshold
a chemical stimulus opens chemically gated sodium channels to open, causing a depolarizing graded potential. If the graded potential reaches threshold (-60mV), voltage gated sodium channels begin to open.
sodium ions enter the cell making it more positively charged inside. The depolarizing continues to +30mV, the voltage at which all voltage gated sodium channels are closed.
at +30mV potassium channels are opening and potassium ions are flowing out of the cell making it less positively charged inside. This continues until the cell reaches -70mV.
at -70mV potassium channels begin to close, but do so very slowly, allowing excess potassium ions to leak out of the cell causing it to hyperpolarize to -90mV.
return to RMP
the sodium/potassium pump restores resting membrane potential
absolute refactory period
the period immediately following the firing of a nerve fiber when it cannot be stimulated no matter how great a stimulus is applied
relative refactory period
the period shortly after the firing of a nerve fiber when partial repolarization has occurred and a greater than normal stimulus can stimulate a second response
is when enough voltage spreads it can cause the next patch of membrane (floor tile) to reach threshold potential and fire an action potential identical to the last one. This will then cause the next patch (tile) and the next and the next to spread this action potential across the entire cell (floor).
propagation (to propel)
is the spreading of the action potential across the cell
once an action potential is started in one patch of membrane it will automatically spread down the entire axon, and there is no turning back or stoppig it until it reaches the synaptic knob
action potential velocity is dependent upon the flow of ions (voltage) through the axon.
the larger the axon diameter, the faster the action potential can travel down the axon.
Schwann cells or neurilemma cells
form a sheath around peripheral axon. And are filled with a fatty substance called myelin
node of Ranvier
a small gap between the Schwann cells
is when the action potential jumps from one node of Ranvier to another
What are the 4 steps of synaptic transmission?
- 1. an action potential arrives at a synaptic knob and opens voltage gated Ca+ channel.
- 2. Ca+ ions diffuse into the synaptic knob and cause synaptic vesicles filled with neurotransmitter to bind to the cell membrane, releasing NT into the clef.
- 3. the NT diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane, altering RMP of the postsynaptic cell.
- 4. the postssynaptic membrane releases an enzyme to break down the NT, ending the signal. The postsynaptic cell returns to RMP.
- mechanism of action:
- excitatory in Sk Muscle (opens Na+ channels)
- inhibitory in cardiac muscle (opens K+ channels)
distribution (CNS, PNS):
CNS & PNS
norepinephrine (adrenergic, adrenalin)
mechanism of action:
usually excitatory (opens Na+ channels)
distribution (CNS, PNS):
CNS & PNS (sympathetic)
mechanism of action:
- inhibitory to motor neurons (low- Parkinson's)
- excitatory in emotional & pleasure centers (feel good NT)
distribution (CNS, PNS)
form blood/brain barrier
monitor and alter (form) CNF (cerebrospinal fluid). found lining ventricles & central canal of the spinal cord
myelinate axons in central nervous system
modified immune cells that remove debris, toxins, and pathogens from the central nervous system
satellite cells or amphicytes
surround neuron cell bodies in ganglia
What is a collection of somata (cell bodies) that perform a specific function called?
nucleus or center
What is the PNS that same collection of somata would be called?
is made up of somata (cell bodies of neurons) and unmyelinated axons. it appears darker or gray in color due to the lack of myelination.
is made up of myelinated axons
cantains nuclei and centers that control basic vital functions like breathing, heart rate, and digestive functions
is a bridge to the cerebellum. houses to centers that are involved in regulating respiratory rhythms
it coordinates somatic motor patterns and muscle memory like dancing, juggling, shooting a basketball, playing a musical instrument, etc. it also controls posture and balance and make rapid adjustments in body position to maintain balance for standing and walking.
What are the 5 structures that make up the Brain Stem?
- 1. Medulla
- 2. Pons
- 3. Cerebellum
- 4. Midbrain
- 5. Diencephalon
contains the corpora quadrigemina
midbrain-2 superior colliculi
coordinate visual reflexes (this would include turning your head when something moves in the periphery to see if it is possible mate or predator)
midbrain-2 inferior colliculi
coordinate auditory reflexes (this would include turning your head toward a loud noise to see what caused it)
What does the diencephalon consists mostly of?
hypothalamus and thalamus
contains numerous center or nuclei that regulate the internal environment including body temperature, hunger, sex drives, and hormones. it secretes several hormones (endocrine secretions) and therefore coordinates the activities of the nervous and endocrine systems.
filtering and relaying sensory information to the cerebral cortex
it secretes a hormone called melatonin that helps regulate circadian (day/night) rythms
What are the 4 functions of the limbic system?
- 1. establish out emotional state
- 2. facilitate conversion of short term memory into long-term memory
- 3. storage of long-term memory
- 4. retrieval of memory
converts short-term memories into long-term memories also, stores long-term memories and functions in memory recall
performs intellectual functions like thinking and problem solving and is cered by the outer gray matter (the "thinking" neurons
contains the primary motor cortex and control voluntary (somatic) motor movements.
is the primary sensory cortex and receives sensory information
interprets smells, and auditory cortex that interprets sounds
visual cortex that interprets what we see
speech area (Broca's brain)
area that lies just anterior to the precentral gyrus called the premotor cortex and coordinates contractions of muscles necessary to vocalize (speak)
sequential events (what happens first, next, and then last) and cause and effect situations (if I do this, then that happens)
left hemisphere / categorical hehisphere
interpreting speech, reading, and writing, as well as analytical tasks like math, logic, and science.
right hemisphere / representational hemisphere
interpreting non-verval sounds (music, bird chirps, barking dogs) and visual information (shapes, colors, forms)
What are the 3 functions of the Cerebrospinal fluid?
- 1. deliver nutrients, ions, and oxygen to neurons and glia
- 2. removes waste and toxins
- 3. acts as a shock absorber
What is the first step of the circulation of CSF?
CSF is filtered out of the blood at a special network of capillaries called the choroid plexus and then circulates in the two latteral ventricles.
What is the second step of the circulation of CSF?
it then drains through the interventricular foramen into the third ventricle.
What is the third step of the circulation of CSF?
from the third ventricle it drains through the cerebral aqueduct (also called the mesencephalic aqueduct) into the fourth ventricle.
What is the fourth step of the circulation of CSF?
when CSF leaves the fourth ventricle it flows into the central canal and through openings called apertures into the subarachnoid space.
What is the fifth step of the circulation of CSF?
CSF is reabsorbed into veins surrounding the brain and then into the superior sagittal sinus.
What would you like to do?
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