Term 1 - Physiology - Nerve and Muscle Unit
What type of synapse are muscarinic receptors found in?
All effector synapses (postganglionic)
Describe a graded potential and the function of the trigger zone (axon hillock) in an axon
- A graded potential is signal that can be of different strengths that travels over short distances and loses strength as it travels through the cell - The trigger zone (axon hillock) in an axon is where a graded potential can initiate an action potential if it is strong enough when reaching the area.
Define and give examples of sympatholytic agents
- Agents targeting the parasympathetic division by inhibiting the neurotransmitters - Example: Atropine
First Order Neurons
- aka Sensory-Afferent - carry information towards the brain and spinal cord; respond to external stimuli then generate and propagate action potentials
Identify the mechanisms for primary active transport and the driving forces
- concentration gradient of a molecule that uses energy influences the movement of other molecules Ex: [Na+] drives the movement of K+
What is the location of nicotinic receptors?
ANS, ganglion synapses (postganglionic), skeletal muscle (motor end plates)
List the neurotransmitters of the sympathetic nerves
Acetylcholine, Epinephrine, Norepinephrine
Ion conductance
Affinity of ions towards something (e.g. axon)
Define synapse
End of a neuron cell that modulate electrical or chemical signals to other cells
Bulk Flow
Lots of flow that creates pressure to "push" molecules through pores
List the properties of membrane channels
Membrane channels are selective and driven by electro-chemical gradient
Identify the mechanisms for osmosis and the driving forces
Osmosis (transport of water) moves from high concentration to low concentration Osmosis is affected by osmotic pressure, tonicity, and osmolarity Driving forces: concentration gradient and electrical gradient
Solvent drag
Paracellular water flow drags molecules
Explain the functions of a reflex arc
Transmit action potentials from sensory input to motor neurons at the origin???
Define monosynpatic reflex
Two neurons and a single synapse (muscle is the source AND target organ)
Depolarization
When the membrane potential is less negative aka more positive
Explain the function of excitatory synapses
facilitate the generation of action potentials
Define Isometric Contraction
length stays constant as tension changes
Resting membrane potential
the electrical difference in membrane potential when the cell membrane is at normal activity
Describe the effects of adrenergic nerves and their receptors in the target cells
- Adrenergic nerves target norepinephrine and epinephrine receptors - Affects fight or flight responses (sympathetic)
Define and give examples of parasympathomimetic agents
- Agents target the parasympathetic division by mimicking neurotransmitters - Example: Nicotine, muscarine
Describe the effects of cholinergic nerves and their receptors in the target cells
- Cholinergic nerves target nicotinic and muscarinic receptors - Affect smooth and cardiac muscles, endocrine and exocrine glands, and some adipose tissue
Explain the function of the Na/K pump (=ATPasE)
- Create [Na+] in the cell - ATPase moves Na+ out of cell and K+ into the cell which generates high Na+ concentration outside and high K+ concentration inside - 3 Na+ : 2 K+ → creates concentration difference intracellularly
Describe which factors determine the rate of conduction
- Diameter of axon: larger diameter = lower electrical resistance = higher current = faster depolarization = higher conduction rate - Myelination of axon: allows for higher conductance of axon = more energy efficient = lower electrical resistance = etc
Contrast the characteristics of electrical and chemical synapses
- Electrical synapses do not require a neurotransmitter to deliver signals - Chemical synapses require the use of a neurotransmitter and calcium
Compare the rate of diffusion (speed) of Na and K channels
- Na+ channels are automatic and fast - K+ channels are slow to act and leak
Describe the structure and function of the neuron
- Neurons = nerve cell with the property of electrical excitability - Function: generate, propagate and respond to action potential - Dendrites receive incoming messages; axons send outgoing messages - Dendrites surround the nucleus; Schwann cells surround the axon with Nodes of Ranvier in between each Schwann cell; dendrites on terminal end
Explain the differences between active and passive transport
- Passive transport occurs without additional Energy - Active transport requires additional energy in order to occur
Describe the properties of the cell membrane
- Phosopholipid leaflets determines membrane polarity - highly permeable to small moelcules - less permeable to large, uncharge molecules and ions
Describe the role of phosphate and proteins in the generation of an electric potential across a cell membrane
- Phosphate and other proteins from the intracellular fluid are attracted to the cell membrane and move closer to it. - These anions and proteins are non-diffusible yet affect the distribution of other ions. - The imbalance of other ions from this association drives the need for diffusible molecules to move in and out of the cell due to concentration gradient, creating an electric potential.
Identify the mechanisms for secondary active transport and the driving forces
- Substrate and carrier move in different directions - Energy is used to create substrate concentration gradient which drives molecules to move
Describe the synthesis and degradation of Acetylcholine (ACh)
- Synthesis: ACh released into the synaptic cleft and attaches to ACh receptors then detaches from the receptor. - Degradation: In the synaptic cleft, Acetylcholinesterase (AChE) breaks down ACh into choline and acetate.
Describe the synthesis and degradation of norepinephrine
- Synthesized from Tyrosine - Degraded by mitochondrial monoamine oxidase (MAO) and intracellular catechol-O-methyltransferase (COMT)
Define and give examples of sympathomimetic agents
- Targeting the sympathetic division by mimicking neurotransmitters - Example: Clenbuterol
Describe the importance of the difference in the membrane permeability to Na+ and K+ to generate the resting membrane potential
- The difference in how many of a certain molecule that moves creates the resting membrane potential - Both molecules are positively charged ions... if the same amount of each molecule moved in and out, there would be no charge difference. 3 Na+ : 2 K+ → creates concentration difference intracellularly
Describe the structure of the cell membrane
- phospholipid bilayer structure with various transmembrane proteins throughout - Bilayer is composed of phospholipids with a hydrophilic polar head and hydrophobic fatty acid tail - selectively permeable
Define and give examples of parasympatholytic agents
-Agents targeting the sympathetic division by inhibiting the neurotransmitters - Example: Acepromazine (ACP), Atenolol
Explain the filament sliding cycle and the role of ATP, ATPase, Ca++, and Mg++
> Ca2+ binds to troponin C, exciting troponin T to bind to tropomyosin; this exposes myosin-binding site on actin > ADP + P attaches to myosin head, exciting myosin head to attach to actin myofilament, forming cross bridge > ADP + P is released; myosin head pivots and bends to low-energy state, pulling actin toward the M-line in the sarcomere > ATP attaches to myosin, weakening the link between actin and myosin to where myosin head can detach > ATP is hydrolyzed to > > ADP + P in the ATPase; Myosin head returns to previous high-energy, upright position > Mg2+ is a catalytic cofactor in this process (needed for enzyme activation)
Explain the mechanical events that occur during excitation-contraction coupling
> Ca2+ released from terminal cisterns of sarcoplasmic reticulum and diffuses to thin and thick filaments > Ca2+ binds to troponin C, which reveals myosin binding sites on actin filaments > Myosin heads attach to binding sites on actin filament, forming cross bridges > Sliding of myosin and actin filaments produces movement
Describe the electrical events that occur during excitation-contraction coupling
> Discharge motor neuron > Acetylcholine (ACh) released at motor endplate and binds to nicotinic ACh receptors > Na+ and K+ conductance increases in endplate membrane > Endplate potential generated > Action potential generated in muscle fibers > T-tubules allow for inward spread of depolarization in muscle fibers
Describe the relaxation of the smooth muscle
> Free Ca2+ in cytosol decreases with its pumped out of the cell, back into the sarcoplasmic reticulum > Ca2+ unbinds from calmodulin = MLCK activity decreases > Myosin phosphatase (MLCP) removes phosphate from MLCK = decreases myosin ATPase activity > Less myosin ATPase activity results in decreased muscle tension
Major functional characteristics of skeletal muscle
> Has motor end plates > Cylindrical, long fibers > Few mitochondria > Multiple nuclei per fiber > Has sarcomeres > Highly developed sarcoplasmic reticulum > Troponin = Ca2+ switch > Pacemaker: No, nerve stimulus needed > Response to stimulus: Graded
List the components of a sarcomere
> I-band > H-zone > A-band > Z-disc/line
Describe the contraction of the smooth muscle
> Intracellular [Ca2+] increases when Ca2+ is released from sarcoplasmic reticulum into the cell > Calcium ion binds to calmodulin > Ca2+-calmodulin activates myosin light chain kinase (MLCK) > MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity > Myosin crossbridges slide along actin and create muscle tension
Major functional characteristics of cardiac muscle
> No motor end plates > Branched fibers > Many mitochondria > 1 nucleus per fiber > Has sarcomeres > Moderately-developed sarcoplasmic reticulum > Troponin = Ca2+ switch > Pacemaker: sinus nodes > Response to stimuli: all or none
Major functional characteristics of smooth muscle
> No motor end plates > Fusiform fibers (short) > Few mitochondria > 1 Nucleus per fiber > No sarcomeres > Little developed sarcoplasmic reticulum > Calmodulin/caldesmon = Ca2+ switch > Pacemaker: spontaneous rhythmic activity > Response to stimulus: change in tone or rhythm frequency
Analyze the action potentials in the smooth muscle
> Slow wave potential developed and initiates action potential if they reach threshold > They develop pacemaker potentials > Tension can develop with little or no change in membrane potential (Can decrease/increase tension without changing membrane potential)
Explain how the Na/K pump generates an electric potential across a cell membrane
ATPase moves Na+ out of cell and K+ into the cell which generates high [Na+] outside and high [K+] inside; this difference in positive charges is the basis of the membrane potential
Describe the clinical importance of ANS antagonists - use clinically relevant examples
Acepromazine (ACP) is a ɑ-adrenoceptor nonselective antagonist that is used for preanesthetic and tranquilizing.
List the neurotransmitters of the parasympathetic nerves
Acetylcholine
Define components of a reflex arc
Afferent and efferent neurons; integrating center, effector, receptor
Where is the motor endplate located?
At the end terminal end of a motor neuron before the "connection" to a skeletal muscle fiber
Efferent Neurons
Carry information out of the brain or spinal cord to the effector cells (e.g. muscle cells, gland cells)
Describe the clinical importance of ANS agonists - use clinically relevant examples
Clenbuterol is a β2-adrenoceptor and is a selective agonist for bronchodilation.
Interneurons
Connect two neurons and transmit information between the two
Explain the function of the sarcotubular system
Contains T-system (transverse tubules) and L-system (sarcoplasmic rectiulum) which allows for impulse conduction in all parts of the muscle fiber
What is the function of smooth muscle cells?
Contraction stimulated by neuron signals, depolarization, hormones, stretch, and more
Describes the release of Ca++ from the L-system during the excitation-contraction coupling.
Depolarization of the cell membrane triggered the release of Ca2+ from L-system (sarcoplasmic reticulum)
Define a primary active transport
Energy comes from concentration gradient directly! Ex: Na+/K+ pump ([gradient] of Na+ effects [K+] which affects molecule movement)
Define a secondary active transport
Energy comes from concentration gradient to move molecules in and out of the cell Ex: Energy to create [Na+] and the Na+ influx drives glucose influx ([glucose] indirectly affected)
Give examples of inhibitory neurotransmitter
Gabapentin
Analyze what happens to the neighboring areas if a small area of an axon is artificially depolarized
If a small area of an axon is artificially depolarized, an action potential will be started in both directions in the neuron. The areas next to this one will be in a relative refractory period, allowing for depolarization of both areas. Depolarization and repolarization will start and continue down the axon in opposite directions.
Exocytosis
Incorporated vesicles fuse with cell membrane then released outside the cell
Phagocytosis
Intake of large particles by surrounding it in membrane projections until they are fully covered, put into a vesicle, and broken down by lysosomes
Define a reflex
Involuntary sequential process as the result of an adequate stimulus to an effector organ; Fast, predictable, automatic response to changes (always same sequence and response)
Where is Ca2+ stored during muscle relaxation?
L-system (sarcoplasmic reticulum)
What are the components of a monosynaptic reflex arc?
Monosynaptic reflex has sensory and efferent neurons directly communicate
Define the motor endplate
Motor endplate is the synapse connecting a motor neuron and the skeletal muscle fiber
Explain the relationship between sarcomere length and muscle tension of the striated muscle
Muscle tension increases with sarcomere length up to a certain point then decreases as sarcomere length increases
Describe the advantage of myelination of axons for the conduction of the action potential
Myelination of axons allows for more conduction of the action potential, meaning the electric signal travels faster and more energy-efficient (requires less energy). The conduction localizes the electric current closer around the axon, depending on the type of insulation.
Compare the functions of the Nernst Equation and the Goldman-Hodgkin-Katz Equation
Nernst Equation is for calculating the electrical potential generated by ONE kind of ion while the Goldman-Hodgkin-Katz Equation is for calculating the electrical potential generated by ALL diffusible ions
Explain the condition "Rigor Mortis"
No ATP is able to be produced in order to cause myosin and actin to unbind from each other. Myosin and actin keep bound together and cause the stiffening of the muscles seen in rigor mortis.
Saltatory Conduction
Nodes of Ranvier only get depolarized and repolarized along the axon, allowing for faster, energetically-efficient action potential; Electric signal "jumps" between Schwann cells; more efficient in long distances
Differentiate non-grated and grated channels
Non-gated channels: open all the time Gated channels: ligand-gated, mechanically-gated, voltage-gated
Give examples of excitatory neurotransmitter
Norepinephrine; Acetylcholine
Define absolute refractory
Period of an on-going action potential during which no stimulus can initiate another action potential
Define relative refractory period
Period of time following the absolute refractory period during which a stimulus initiates another action potential
What are the components of a polysynaptic reflex arc?
Polysynaptic reflex includes an interneuron between the sensory and efferent neurons
Describe the general function of the autonomic nervous system
Regulations the internal organs and adapts them to the needs of the body in the moment
Continuous Conduction
Requires the depolarization of the entire axon; Action potential decreases as it travels along the axon; more efficient in short distances
Overshoot
Reversing of the membrane's polarity (due to inactivation of Na+ channels and early repolarization of K+ channels
Graded potential
Signals of various strengths that travel over short distances and lose strength as they travel through the cell
Identify the mechanisms for simple diffusion and the driving forces
Simple diffusion is affected by: concentration gradient, temperature, surface area, particle size, lipid solubility, and diffusion medium Driving forces: concentration gradient and electrical gradient
What is the classification of smooth muscle cells?
Single-Unit and Multi-unit
What is summation?
Summation occurs when there isn't enough time for the muscle fiber to relax due to another AP arriving during the twitch, and results in further shortening of the muscle fiber
What is tetanus
Tetanus occurs when twitches fuse and cause a maximum contraction due to the frequency of APs increasing to where the intervals between APs become less than ⅓ of the time required for a single twitch
Define "resting membrane potential"
The "base" level of electrical potential in the cell membrane
Identify which organ(s) is/are the effector(s) of monosynaptic reflexes
The origin organ(s) is/are the effector(s)
Pinocytosis
Tiny droplets of extracellular fluid surrounded by pseudopods and incorporated as vesicles
Action potential
Very brief, large depolarizations that travel for long distances through a neuron without loosing strength
Hyperpolarization
When the membrane potential is more negative aka less positive
Temporal summation occurs when ...
a second postsynaptic potential arrives before the membrane has returned to its resting level
Electrical stimulus
an electrical pulse that causes an electric signal (e.g. action potential) to occur
Define sarcomere
basic functional unit of the striated muscle
What is an A-fiber?
contain myelin for fast conduction; motor functions, proprioception, and pain
What is a B-fiber?
contain myelin for fast conduction; preganglionic autonomic function
Explain the function of inhibitory synapses
inhibit the generation of action potentials
Define Auxotonic Contraction
length and tension changes
Define Isotonic Contraction
length changes as tension stays constant
neurotransmitters
molecules that have a pivotal role in carrying signals between neurons
Spatial summation occurs when ...
multiple local potentials occur at different places on the same cell at the same time
Define polysynaptic reflex
multiple neurons and synapses (source and target organ can differ)
What is/are the target cells of muscarinic recpetors?
smooth muscle, cardiac muscle, glands
Threshold
the point at which depolarization occurs and repolarization ends; when a graded potential reaches a point to become an action potential
What is a C-fiber?
unmyelinated so slower conduction; mechano-reception, pain, temperature, and postganglionic sympathetic function
