Unit 2 - Neurophysiology Flashcards
Chapter 8
what are the 3 functions of the nervous system?
- receiving info (using sensory neurons)
- integrating info (organizes and looks at already stored info)
- transduces info (send to appropriate target)
what is contained in the CNS and PNS?
CNS is purely just the brain and spinal cord and the PNS is everything else, consisting of sensory/afferent and motor/efferent neurosn
define soma
- center of chemical processes
- clusters of cell bodies in CNS is nuclei and in PNS is ganglia
define dendrites
- receive information
- transmits electrical signals towards soma
define axon
- cytoplasmic extension that sends out information
- transmits electrical signals away from soma
- bundles of axons in CND is tracts and in PNS is nerves
define axon terminal
- end of axon where it is the connection between other neurons and cells
- contains presynaptic part of connection
define nervous system
network of billions of nerve cells linked together in a highly organized manner to form the rapid control system of the body
define neurotransmitter
a chemical signal released by a neuron that influence the neuron’s target cell
what are the 2 divisions of the CNS?
The somatic motor controls skeletal muscles and the autonomic controls smooth and cardiac muscles, exocrine glands and some adipose tissues.
how is the autonomic division divided?
sympathetic is responsible for flight-or-fight response and parasympathetic is responsible for day-to-day activities (rest and digest)
define enteric nervous system
neurons in the wall of the gastrointestinal tract that are capable of sensing and integrating information and carrying out a response without input from the CNS. A possible 3rd division of the nervous system found in recent years.
What are the 3 steps in the signal pathway that go with the axon?
input signal (dendrites) –> integration (soma) –> output signal (presynaptic axon terminal)—> input signal (postsynaptic dendrite) –> and continues in this same pattern
what are the different classifications of neurons?
multipolar: many dendrites and branched axons
pseudounipolar: have a cell body located off one side of a single longaxon
bipolar: single axon and single dendrite coming from the soma
anaxonic: lack an identifiable axon but have many dendrites
define interneurons
neuron that is completely contained within the CNS, short for interconnecting neurons
what is the branch of a axon called?
collateral
define axon terminal
the distal end of a neruon where neurotransmitters are released into a synapse
define sensory neurons
carry info about temperature, pressure, light and other stimulus to the CNS
define nerve
a collection of axons running between the CNS and the peripheral target cells, both afferent and efferent peripheral neurons create this when bundled together
what are the different kinds of nerves
- afferent/sensory: receives info from receptor cell and cytoplasmic extensions and transmits it to CNS, located outside of CNS
- interneurons: inside CNS, transmits info and acts as integrating centre (gets afferent signal and send it efferent)
efferent/motor: get info from the interneurons, located in the CNS but transmit info away from CNS to effectors (muscles, glands, etc.)
define dendritic spines
projections of the dendrites membrane that increase surface area to be able to accept neural signals. can chance their size and shape in response to input from neighbouring cells
define axon hillock
the region of the axon where it joins the cell body, often contains the trigger zone
define axonal transport
movement of material between the axon terminal and the cell body
the axon is filled with cytoplasm but lacks ribosomes and ER, so proteins must be created in the soma and then moved down via vesicles to reach axon or axon terminal
what is the difference between anterograde and retrograde transport?
anterograde is moving vesicles from the cell body to the axon terminal and retrograde is going the opposite direction. this si down on microtubules with the help of motor proteins (kinesin and dynein)
define the main parts of the synapse junction
synapse: where the axon temrinal meets the target cell
presynaptic cell: delivers the signal
postsynaptic cell: receives the signal
synaptic cleft: narrow space between the cells
define neurotrophic factor
chemicals secreted by Schwann cells that keep damaged neurons alive, this is what the survival of neuronal pathways depends on, and is secrete by neruons and glial cells
define glial cells
- non-excitable support cells of the CNS
- do not carry electrical signals over long distances
- only communicate with nearby cells
what are the types of cells that glial cells create?
PNS
- Schwann cell are to support and insulate axons by creating myelin, forms of membrane around the axon
- Satellite cells are nonmyelinating Schwann cells, support cell bodies (nutrients)
CNS
- oligodendrocytes are the same thing as Schwann cells but can myelinate multiple cells at once
- AStrocytes are highly branched glial cells, some work with the synapse, some do metabolic substrates for ATP procedures and they help to maintain homeostasis in CNS, and create a blood-brain barrier to regulate the movement of material between blood and extracellular fluid
- microglia are specialised immune cells that help to remove damaged cells and foreign invaders (phagocytosis)
- ependymal are cells that create a selectively permeable epithelial layer to separate fluid compartments, produce cerebral spinal fluid
define node of Ranvier
unmyelinated regions on myelinated axons, this si where the axon memrbane remains in contact with extracellular fluid to move the transmission of the signal along the axon.
what are the 4 kinds of selective ion channels in the neuron?
Na+, K+, Ca2+ and Cl-
what are th 3 kinds of channels on the neuron
- mechanically gated: found in sensory neruons and open in response to physical forces such as pressure
- chemically gated: responding to a ligand
- voltage-gated: responds to changes in cell membrane potential (Na and K)
define the difference between graded and action potentails
graded are varibale-strength signals that travel over short distances and lose strength as they move where action are large depolarizations that travel for long distances without losing strength. Graded can stimulate an action potential.
define trigger zone
the region of the axon where graded potentials are integrated (initial segment) an an action potentials begins if the signal is above threshold
define the all-or-none phenomena
a stimulus is either above the threshold potential or not. once above the threshold, will always create the same size in stimulus
what are the 9 main steps in ana action potential?
- at rest, -70mV
- depolarizing stimulus
- voltage gated Na and K open
- rapid entry of Na depoloarizes cell
- Na channel close and slower K channels open
- K moves fromcell to ECF
- K channel remain open and extra K leave cell, hyperpolarizaing it
- voltage gated K channel close, less K leaves cell
- cell returns to resting potential
what are the 2 kinds of gates of Na+?
activation, that opens to initiate an action potential, and inactivation gate, that closes and stops ion flow
what is the difference between absolute and relative refractory period?
absolute is when no other stimulus can be conducted and relative is when another stimulus can occur ut it has to be way above threshold to make it create another action potential
define saltatory conduction
the apparent leap-frogging of the action potential down myelinated axons. this creates faster conduction down the length of the axon
define ionotropic receptor
neurotransmitter receptor that alters ion channel function (receptor-channels)
define metabotropic receptor
neurotransmitter receptor that act through a second messenger system (GPCR)
define acetycholine
a neurotransmitter sed y neurons of the central and peripheral nervous system, the synthesis of the molecule is a simple reaction that takes place in the axon terminal
what is a majoy neurotransmitter of the PNS autonomic sympathetic division?
norepinephrine, neurons that secrete this are called adrenergic neurons
what are the 2 ways that glial cells add to the function of neurons?
- aid in nerve impulse control (the speed of the signal travelling down the axon)
- maintain the microenvironment around neurons
define membrane potential
the difference in electrical potential between the inside and outside of the cell
what kind of tissues will cause a rapid change in the membrane potential?
excitable tissues (nervous and muscle)
what are the 2 main properties of the membrane potential?
- unequal distribution of ions in ECF and ICF: Na, Ca, and Cl are high on the outside while K and anions is high inside
- selective movement of the ions across the membrane (na-K pump, passive or gate channels)
define equilibrium potential
Eion, membrane potentail that exactly opposes the concentration gradient of an ion (forces are equal and opposite), only suppose to be for when the membrane is permeable to one ion
- Nerst Equation
- K = -90mV
- Na = 60mV
define resting membrane potential
- charge difference between inside and outside of the cell (-70mV)
- ions moving down their concentration gradient move the cell away from rest
- contribution to resting membrane potential is proportional to its permeability
- Goldman-Hodgkin-Katx (GHK) equation
what is the difference between depolarization, hyperpolarization, and repolarization?
depolarize: decrease in membrane potential, LESS negative
hyperpolarize: increase in MP, MORE negative
repolarization: membrane return to rest
define graded potentials
- can de/hyperpolarize
- occur in the dendrites or cell body
- triggered by ion channels open/closing
- amplitude of the potential is proportional to the strength of the trigger
- only travel short distances
- strength is determined y how many ions enter the cell
how do graded potentials lose strength?
- current leak: positive charge leak back to where depolarization is
- cytoplasmic resistance: cytoplasm restricts flow of the current
define depolarizing graded potentials?
- membrane potential becomes less negative
- closer to threshold (-55mV)
- Excitatory postsynaptic potentials (EPSP): increases the change of exciting the neuron to fire = action potential
define hyperpolarization graded potentials?
- membrane potential becomes more negative
- further from the threshold
- inhibitory postsynaptic potentials (IPSP): decreases the change of exciting the neuron to fire = action potential
define action potential
- all identical, all-or-none law
- do not diminish in strength as they travel over long distances
- start at the trigger zone (integrating center of the neuron)
where is the trigger zone located on the different kinds of neurons?
- sensory: adjacent to the receptor
- efferent/interneurons: is the axon hillock and initial sequence of the axon
the close tot he stimulus the trigger zone is, the stronger the signal will be
how can graded potentials trigger an action potential?
- summation of the graded potentials, if reached the threshold, can trigger an action potential
- combo of EPSP and IPSP added together create action potentials
spatial summation: over space, all of the signals happening simultaneity being added
temporal summation: over time, looking at one synapse and adding the graded potential up
define electrical synapses
- the electrical signal passes directly from cell to cell through gap junctions
- mostly occurs in the CNS and uncommon
- info can flow in both directions
- exist between neruons and between neurons and glial cells
- important for nervous system development and transmission in adult brain
define chemical synapses
- use neurotransmitters to pass information to the target cell (neurocrines)
- vast majority
- peripheral neurons
- exist between neurons or between neuron and effect (neuroeffector junction)
what are the different kinds of neurocrine receptors?
ionotropic: mediate rapid response by altering ion flow across the membrane
metabotropic: these receptors act as a second messenger system
what are the 7 classes of neuroscrines?
acetylcholine, amines, amino acids, peptides, purines, gases, and lipids
define synaptic vesicle
small secretory vesicle that releases NT into the synapse
how are NT released from the synapse?
- action potential depolarizes
- Ca chaneels open and Ca comes into the cell
- Ca triggers exocytosis of vesicles
- NT diffuse across synaptic cleft
- NT binding to receptors initiates a response in psotsynaptic cell
define fusion pore
when synaptic vesciles fuse to the presynaptic membrane it forms a pore, and it is just big enough to let NT pass through.
what are the 2 pathways neural info can take?
divergence:few presynaptic neurons branch to affect a large number of post
divergence: number of pre neurons provide input to a smaller number of post neurons
define slow synaptic potential
slower onset and longer lasting response of post cells to certain NT
define fast synaptic potentials
graded potentials in post cell that begin quickly and last only a few milliseconds
define long-term potentiation
physical changes in a synapse that allow the response of the post cell to a constant stimulus be enhanced
what are the 2 types of neurons responsible in the PNS?
somatic motor neurons: efferent neurons that control skeletal muscles
autonomic neurons: efferent neurons that control smooth muscles, cardia muscle, and glands
what are the 2 branches of the autonomic division fo the PNS?
sympathetic: flight or flight responses
parasympathetic: responsible for day to day activities, rest and digest
- can differ from where they oringiate and what chemical transporters they use
do the symp/parasympathetic braches display the 4 characteristics of homeostasis?
YES
preservation of the fitness of internal environment, up-down regulation by tonic control, antagonistic control, chemical signals with different effects in different tissues
what are the 2 neuronal pathways in the autonomic division?
preganglionic neuron: originates in the CNS and ends in autonomic ganglion
postganglionic neuron: has its cell body in the ganglion and send its axon to the target tissue
define vagus nerve
cranial nerve that caries sensory info and efferent signals to many internal organs including heart and GI tract
what chemicals do the sympathetic and parasym use?
sym: acetylcholine and norepinephrine
para: acetylcholine
define neuroeffector junction
this is the synapse between the postganglionic autonomic neuron and its target muscle/gland
define somatic pathway
- only have 1 neuron kind
- originates in CNS
- projects its axon to the target tissue (always skeletal muscles)
what is the synapse called of a somatic motor neuron?
neuromuscular junction, and it has 3 things:
1. presynaptic axon filled with blisters and mito
2. synaptic cleft
3. post synaptic membrane of skeletal muscle fiber
What are the 2 kinds of gates on the voltage-gated Na channel?
activation: closed at resting membrane potentail to stop Na from going in at large amounts
inactivation: ball and chain mechanism of amino acids that lie on the cytoplasmic side of the membrane and is open at resting membrane (cause activation is already closed and in the way)
How does the voltage-gated Na Chanell work when an action potential occurs?
- resting potential: activation is closed, inactive is open
- reaches -55mV and whole channel becomes active (Na channel is completely open)
- The activation gate opens to allow Na to enter (open state)
- Na further depolarizes
- more Na channels open (creates a positive feedback loop, need external stimulus to stop the cycle from reoccurring)
- inactivation gate closes (this gate takes longer to move even when still stimualted in step 2, inactivation state, ends positive feedback loop, peak of action potential)
*think of it as people who wake up to their alarm right away but go to bed earlier
how does the membrane return to resting membrane potential?
K ions leave the cell, this is the falling phase of the action potential (repolarization)
- voltage gated K channels take a lot more time to open than Na channels
- depolarization to threshold will trigger the opening of the K channels just takes a long time
- gate will become fully open at +30mV
*think of it as people who take longer to get up/hit snooze and they go to bed later in the day
does the concentration gradient change?
per action potential, only a few ions will move, causing no significant change in the concentration gradient
why cant an action potential be activated during the absolute refractory period?
because the Na channel is in its active state
- Na is the ion to depolarize the neuron so without Na entering the neuron, no depolarization can occur
- Memraben must repolarize before the Na channel can return to its normal resting state (activation is closed and inactivation is open)
what is the importance of the refractory period?
- it sets the direction of current flow
- prevents temporal summation
- prevents the action potential from going backwards
How does an action potential not lose its strength as it travels?
The N channels postive feedback allow it to keep putting Na into the neuron keeping it at its same strength
- wave of depolarization down the axon (one depolarization causes the next depolarization, domino effect)
- once an action potential is generated, the new AP next to it is identical
what are the 2 factors that determine the speed of conduction of an axon?
- diameter of the axon: bigger diameter = faster conduction
- resistance of the axon membrane to ion leakage out of the cell: insulating the ions with myelin sheath prevents ions from leaving the cell = fasting conduction (Schwann in CNS, node of Ranvier create saltatory conduction)
what are the 3 parts of the synapse?
- presynaptic cell: axon terminal
- synaptic cleft: space between cells
- postsynaptic cell: membrane (not always another neuron, can be tissue)
define presynaptic cell
- contains many vesicles filled with neurotransmitters
- vesicles fuse with presynaptic membrane (triggered by Ca2+)
- vesicles releases NT into synaptic cleft and they diffuse
what are the events that occur at the synapse?
- AP depolarizes the axon terminal
- depolarization trigggers opening of voltage-gated Ca chennal
- Ca sends signal to make exocytosis occur for NT to get released
- NT diffuse into cleft and bind with specific receptors on membrane
- binding of NT initiates a response
what are 2 kinds of responses that can be created in the postsynaptic cell?
- direct: fast, iontropic, quick and short lived, interaction with ion channel
- indirect: slow, metabotropic, long lasting, USes G protein and 2nd messenger system
what are the types of neurotransmitters
amino acids, purines, gases and neuropeptides
define acetylcholine
- synthesized from cholin and acetly CoA, that is catalyzed by CAT
- created in axon terminal and put into vesicles
- neurons that bind with ACh are cholinergic
what are the 2 types of cholinergic receptors?
- muscarinic: coupled with G protein (slow response and indirect)
- nicotinic: receptor-operated channels (faster and direct)
define amines
- derived from single amino acids
- ex. tyrosine created dopamine, norepinephrine, and epinephrine (catecholamine)
- synthesized in acon terminals and into vesicles
- neurons that secrete norepinephrine are adrenergic
how do neurons become inactive?
- can be taken up by glial cells
- enzymes inactive them
- diffuse out of the synaptic cleft
ex. ACh is degraded by acetylcholinesterase
what are the 2 branches in the PNS and the NT used?
afferent and efferent (exiting CNS) branches, ACh, norepinephrine, and epinephrine
What does the PNS divide into?
- autonomic: 2 neuronal chain, smooth and cardia muscles, glands and adipose tissues, involuntary
- somatic: single neuron, skeletal muscles, voluntary
what are the branches of the autonomic division?
- sympathetic: fight or flight
- parasymapthetic: rest and digest
present of different receptors on different tissues is critical for the regulation of body systems (same tissues, opposing functions)
what is the structure of the autonomic division?
- two neuron chain between CNS and effector
- synapse is called autonomic ganglia
- Cell from CNS to ganglia is preganglionic
- cell from ganlia to effector is postganglionic
what are the primary NT of the autonomic system?
preganglionic: ACh with nicotonic receptors
post ganglionic: sympathetic is norepinephrine in adrenergic and parasympathetic is ACh in muscarinic
how is the synapse structure different in autonomic pathways?
- axon ends with swollen area at distal ends called varicosity
- contains vesicles with NT to be released into tissue fluid
define adrenergic receptors
- for E and NE
- alpha 1: most tissues, NE
- beta 1: heart muscle and kidney, NE=E
- beta 2: blood vessesl and smooth muscle, E>NE
*act as G proteins (indirect and slow)
Betas release cAMP and alpha increase Ca in cytoplasm
define cholinergic receptors
- nicotinic: on motor plates, stimulate ACh and nicotine, preganglionic neurons (para and sym), act via ion channel (Na goes into channel to depolarize), always excitatory
- muscarinic: only postganglionic parasympathetic, act via G protein, can be excitatory and inhibitory
*both are agonist where they are mimicking the ligand (ACh)
what are teh 2 parts of the adrenal gland?
- adrenal cortex: secretes steriod hormones
- adrenal medulla: with sympathetic division (modified sym ganglion)
- special cells called chromaffin secrete epinephrine that travels in the blood
what is the structure of the somatic division?
- controls only skeletal muscles
- single neuron
- causes only muscle excitation
define neruomuscular junction
- synpase between somatic motor neuron and skeltal muscle fiber
- schwann cell sheath around terminal boutons at synapse
what are the 3 components of the neuromuscular junction?
- presynaptic axon terminal: has ACh in vesicles
- synaptic cleft
- postsynaptic membrane of skeletal muscle cells: modified membrane is a motor end plate, contains nicotinic ACh receptors channels
