Nervous System - ANS & ENS Flashcards
What are the three types of muscle tissue?
Skeletal muscle
Cardiac muscle
Smooth muscle
What gives skeletal muscles their striated appearance?
Skeletal muscles are made of repeating sarcomeres
= thin and thick filaments organized in a particular way that gives them a striated appearance
Do smooth muscles have a striated appearance? Why or why not?
In smooth muscles, there are still thin and thick filaments but they are not organized into sarcomeres for that striated appearance
Where can smooth muscle be found in the body?
- Female reproductive system
- Stomach
- Blood vessels
- Trachea
- Iris
- Bladder
How do skeletal muscles and smooth muscles differ in structure?
Skeletal Muscles are MULTINUCLEATED (many nuclei)
- striated from sarcomeres of thin and thick filaments
Smooth muscles only have ONE NUCLEUS
- have thick middles and then taper out at the ends
- have thick and thin filaments but are not arranged into sarcomeres (no striated pattern)
Skeletal muscles and smooth muscles differ by one key element: They do not have the same types of filaments: Elaborate
Skeletal muscles: thin and thick filaments
Smooth muscles: thin, thick, and intermediate filaments/microfilaments
Compare contraction in skeletal muscles and smooth muscles
Skeletal muscles
- contraction: sarcomeres shorten as muscles contract along one axis (through calcium-contraction cycle)
Smooth muscles
- contraction: contracts along many axes and bulges towards the middle
What are the two subtypes of smooth muscle tissue?
- Multi-unit smooth muscle
- Visceral smooth muscle
How does multi-unit smooth muscle differ from visceral smooth muscle?
They differ by their innervation and interconnection, affecting excitation
What is multi-unit smooth muscle?
Smooth muscle cells communicating with neurons, forming NMJs, and getting excited through communication directly from a neuron
- involves many smooth muscles cells working together with neurons
- webbing of neurons to communicate
- carry out excitation through synapses
What is visceral smooth muscle?
AKA single-unit smooth muscle
Smooth muscle cells communicating with each other (and occasionally a pacesetter cell) through gap junctions
- excitation can be spread through connecting muscle cells
- have pacesetter cells
- excitation through gap-junction coupling and pacesetter cells
- can perform excitation or inhibition through neurotransmitters
What are pacesetter cells and which type of smooth muscle tissue is it found in?
These are special types of cells in visceral smooth muscle that can depolarize on its own
- able to communicate through the gap junctions
- excitation happens through gap junctions
True or False:
Smooth muscle excitation-contraction coupling is also calcium-dependent
TRUE!
Smooth muscle excitation-contraction coupling is very similar to skeletal muscle excitation-contraction in that they both require the use of Ca2+
However, the exact use of Ca2+ is slightly different in skeletal muscle fibres compared to smooth muscle fibres
Excitation requires an increased [Ca2+]
How does smooth muscle use Ca2+ in excitation-contraction coupling?
Instead of the Ca2+ binding to troponin, Ca2+ in smooth muscle binds to another protein called CALDESMON
Ca2+ is also involved in myosin head activation, turning of the head in the contraction cycle
- Compared to the skeletal muscle contraction cycle where ATP hydrolysis was in charge of activating the myosin head
What is caldesmon?
A protein that is present in smooth muscle in placement of troponin
What are the two main differences between Ca2+ roles in excitation-contraction coupling in smooth muscles and skeletal muscles?
- Caldesmon is present in smooth muscle instead of troponin in smooth muscle
- Calcium leads to myosin head activation in smooth muscle
True or False:
Smooth muscle can be found inside the eye
TRUE
The iris is an example of smooth muscle in the eye
True or False:
Smooth muscle is non-contractile
FALSE
Smooth muscle does contract – And it does so on many axes (forming into bulges in the center)
True or False:
Smooth muscle does contain myosin and actin filaments
TRUE
Smooth muscle contains myosin and actin filaments AND INTERMEDIATE FILAMENTS, but they are not arranged into sarcomeres
True or False:
Input from the nervous system is always required for smooth muscle excitation
FALSE
ALWAYS is a very strong word, and smooth muscles (specifically visceral smooth muscle) is capable of exciting without input from the nervous system because it has PACESETTER CELLS
True or False:
Input from the nervous system is never required for smooth muscle excitation
FALSE
NEVER is also another strong word and although pacesetter cells in visceral smooth muscles don’t require input from the nervous system, multi-unit smooth muscles do require input from the nervous system through neuronal connections
True or False:
Smooth muscle cells can be directly inhibited, as well as excited
TRUE
Through single-unit smooth muscle tissue, the smooth muscle cells are capable of being directly inhibited or excited (neurotransmitters)
True or False:
Smooth muscle cells in a tissue are always interconnected by gap junctions
FALSE
Multi-unit smooth muscle cells are interconnected by neurons… Visceral smooth muscle cells are interconnected by gap junctions, but not all smooth muscle cells are interconnected by gap junctions… Some are connected by neurons!
True or False:
Increases in intracellular calcium are required for smooth muscle contraction
TRUE
Just like skeletal muscle, smooth muscle also requires an increase in intracellular calcium for contraction!
What are the 3 anatomical divisions of the nervous system?
- Central Nervous System
- Peripheral Nervous System
- Enteric Nervous System
What are the 2 subdivisions of the peripheral nervous system?
- Autonomic Nervous System
- Somatic Nervous System
What are the 2 subdivisions of the autonomic nervous system?
- ANS - Parasympathetic division
- ANS - Sympathetic division
What is the peripheral nervous system?
Outside of the skull and spine, but directly connected to the CNS
- still forms synapses with the CNS
What is the autonomic nervous system?
Central and peripheral components of the neural circuits that control non-somatic organs
- division of the PNS that is in charge of forming neural circuits to visceral organs
- mostly involuntary
What is the somatic nervous system?
Central and peripheral components of the neural circuits that skeletal muscles
- division of the PNS that is in charge of forming neural circuits to skeletal muscles
- mostly voluntary BUT not completely
- involves INVOLUNTARY SPINAL REFLEXES
What is the enteric nervous system?
Associated with the digestive tract, and only indirectly connected to the CNS
- indirect connection to CNS through ANS
How do you distinguish of the division is autonomic or somatic?
Look at the efferent neurons
If the efferent neurons go to skeletal muscles then it is SOMATIC (not necessarily voluntary because there are also reflexes that are involuntary)
If the efferent neurons go to visceral organs then it is AUTONOMIC
The autonomic system’s efferent pathways control what kind of effectors? Visceral or skeletal?
VISCERAL!
What does it mean for efferent pathways to be monosynaptic? Disynaptic?
Monosynaptic = efferent neurons forming single synapses (one NMJ) directly on the effector cell
Disynaptic = efferent neurons forming two synapses, extra stop in the circuit because one cell has to talk to a ganglion then another cell before it talks to the effector cell
In the PNS, are somatic efferent pathways monosynaptic or disynaptic?
Somatic efferent pathways are MONOSYNAPTIC
In the PNS, are autonomic efferent pathways monosynaptic or disynaptic?
Autonomic efferent pathways are DISYNAPTIC
What are the two autonomic neurons called?
Preganglionic and postganglionic
What is the preganglionic neuron?
The autonomic neuron leading to the autonomic ganglion, forms a synapse with the autonomic ganglion
What is the postganglionic neuron?
The autonomic neuron leaving the autonomic ganglion to form a synapse with the effector cell
True or False:
ANS efferent neurons often synapse onto neurons of the ENS rather than onto effector cells
TRUE!
Possible to see disynaptic pathways, but usually it goes
presynaptic < autonomic ganglion < postsynaptic < ANS < ENS < effector cell
What kind of receptors do visceral effector cells use?
Visceral effector cells usually use metabotropic neurotransmitter receptors, which produce diverse, long-lasting cellular effects through biochemical cascades
Features of using metabotropic receptors:
1. longer-lasting responses
2. diverse biochemical effects (not just changes in membrane potential)
3. stimulatory or inhibitory responses to the same neurotransmitter
What is the meaning of “dual innervation of target organs”?
Dual = two
Innervation = communication
Target organs = same organs
Parasympathetic and sympathetic divisions can talk to the same organs
And ** MOST OF THE TIME ** the parasympathetic and sympathetic divisions do opposite things (BUT NOT ALL THE TIME) They just usually stimulate opposite effects
What physiological state correlates to parasympathetic activity?
High parasympathetic activity = REST AND DIGEST
In general, if one division becomes more active, the other will usually become less active
What physiological state correlates to sympathetic activity?
High sympathetic activity = FIGHT OR FLIGHT
In general, if one division becomes more active, the other will usually become less active
Parasympathetic
REST AND DIGEST
Sympathetic
FIGHT OR FLIGHT
Give two examples of when the two divisions of the ANS are not antagonistic
AKA They are not working in opposition to one another
- Male sexual response
- parasympathetic neurons mediate arousal responses in erectile tissue
- sympathetic neurons stimulate contractile ejaculatory/orgasmic reflexes - Eye dilation/contraction
- two divisions supposedly have opposite effects on pupil size
- decreased light = implied increased sympathetic stimulation (DILATION)
- increased light = implied increased parasympathetic stimulation (CONTRACTION)
- pupillary reflexes are actually driven by light intensity, not stressful or reflexing situations
Describe the chain structure of sympathetic ganglia
Sympathetic ganglia = fight or flight response
- form an interconnected chain, which means the entire division can be activated at once
- sympathetic activation refers to a situation where sympathetic ganglia are activated together, amplifying each others’ activity
Compare and contrast the structure / activation of sympathetic vs parasympathetic ganglia
Sympathetic
- can spread to other ganglia
- become activated at one time because of the way the sympathetic ganglia are connected in a long chain
Parasympathetic
- do not see this in parasympathetic ganglia because they are separated (not communicating with each other or activating each other)
The location of the preganglionic neuron cell bodies differ between the two ANS divisions:
Sympathetic division
Parasympathetic division
Sympathetic Division:
- preganglionic neurons are found in the lateral gray matter/ventral horn in the thoracic and superior lumbar spinal cord (very specific location)
Parasympathetic Division:
- preganglionic neurons are found in the brainstem and lateral gray matter in sacral spinal cord
Differentiate the length of pre- and post-ganglionic axons between the ANS divisions
Sympathetic
- preganglionic neuron is located somewhere in the CNS
- preganglionic fiber is average length(?)
- sympathetic ganglia are located far from the target organ (mostly in the sympathetic chain)
- postganglionic fiber is long-ish to target organ
Parasympathetic
- preganglionic neuron is located somewhere in the CNS
- preganglionic fiber is long and far from the parasympathetic ganglia
- parasympathetic ganglia are located within or near the target organ
- very short postganglionic fiber because it is already so close to the target organ
BOTH sympathetic and parasympathetic preganglionic axons are located somewhere in the __________
Central Nervous System (CNS)
All preganglionic neurons (both sympathetic and parasympathetic divisions) release __________ just like somatic motor neurons (in the somatic nervous division)
All preganglionic neurons release ACETYLCHOLINE
The neurotransmitters released by POSTganglionic neurons differ between the parasympathetic and sympathetic divisions:
What does each division release?
- Sympathetic division
- releases ACh at preganglionic neurons
- forms synapses in ANS
- releases NOREPINEPHRINE at postganglionic neurons - Parasympathetic division
- releases ACh at preganglionic neurons
- forms synapses in ANS
- releases ACETYLCHOLINE at postganglionic neurons
Each neurotransmitter can activate a different suite of neurotransmitter receptors, what effect does this have on its metabotropic effects?
Each neurotransmitter can activate a different suite of neurotransmitter receptors, which produces DIFFERENT METABOTROPIC EFFECTS
- slightly different receptors can interact with the same neurotransmitter and have different effects
- either inhibitory or excitatory
How can one neurotransmitter be excitatory and/or inhibitory?
The same neurotransmitter can be excitatory or inhibitory depending on the subtype of receptor protein expressed by the postsynaptic cell (the effector organ)
Parasympathetic postganglionic cells ALWAYS release ______________
Acetylcholine
Sympathetic postganglionic cells ALWAYS release ______________
Norepinephrine
Parasympathetic preganglionic cells ALWAYS release ______________________
Acetylcholine
Sympathetic preganglionic cells ALWAYS release _____________________
Acetylcholine
Visceral functions are mostly controlled by visceral reflexes, but do not ALWAYS involve the CNS
True or False
True!
Long visceral reflexes involve the CNS as it passes from the stimulus/receptors to the CNS then to the ANS (preganglionic and postganglionic neurons)/peripheral effector
Short visceral reflexes do not involve the CNS as they are still able to stimulate a response without passing through the CNS (found in the digestive system and associated with the ENS)
Do long visceral reflexes involve the CNS?
YES!
Ex: The consensual pupillary light response involving the parasympathetic division
- in response to bright light, both pupils constrict
Do short visceral reflexes involve the CNS?
NO!
Ex: gastroenteric reflex and gastroileal reflex
- stretching of the stomach wall if detected by mechanoreceptive visceral afferent neurons
- these synapse onto parasympathetic post-ganglionic neurons (and ENS neurons) enhancing smooth muscle contractions in the small/large intestine
True or False:
Smooth muscle does not use actin or myosin filaments to generate tension
False!
Smooth muscles also have actin and myosin filaments (Thick and thin filaments) but they just aren’t arranged into sarcomeres
True or False:
Smooth muscle does not have sarcomeres
True!
Smooth muscles do not have sarcomeres, they have thin and thick filaments but they are not arranged into sarcomeres
Thus smooth muscle does not have the striated appearance that skeletal muscles have
True or False:
Smooth muscle contraction does not require intracellular calcium elevations
False!
Smooth muscle and skeletal muscle contraction both require intracellular calcium elevations = MUSCLE CONTRACTIONS ALL REQUIRE INCREASED CALCIUM LEVELS TO ACTIVATE
True or False:
The ANS makes synapses on smooth muscle but not skeletal muscle
True!
The ANS works on making synapses with smooth muscles/visceral organs, whereas the somatic nervous system makes synapses on skeletal muscles
True or False:
The ANS has both sensory and motor components
True!
The ANS has both afferent and efferent neurons, therefore having both a sensory and motor component to it
True or False:
The parasymapthetic division of the ANS will be more active if you are lying down quietly than if you are exercising
True!
Parasympathetic = rest and digest
Sympathetic = fight or flight
True or False:
The sympathetic and parasympathetic divisions of the ANS always act in opposition to each other
False!
In the case of the male sexual response, the sympathetic and parasympathetic divisions actually work together (same with the iris dilation/contraction)
True or False:
Both divisions of the ANS make synapses in autonomic ganglia outside the CNS
True!
Have presynaptic neurons < autonomic ganglia < postsynaptic neurons
