Exam 3 Nervous System 3 Flashcards
what is divergence a typical property of?
motor pathways
Divergence
impulse originates on one motor neuron and it passed downstream to multiple motor neurons
what is convergence a typical property of?
sensory pathways
Convergence
multiple sensory signals originating from multiple neurons are transmitted to one target neuron
what is divergence a form of?
amplification; way that initial signals can amplify as they travel down the pathway to the effector
divergence result
recruiting more neurons –> recruit more muscle fibers –> increased force of AP
what is the internal mechanism of control for divergence?
lateral inhibition
divergent pathway setup
central core of neurons which form the most direct pathway, then you have all these lateral neurons to the side of the core; as the central neurons are stimulated, they stimulate their direct downstream neurons, and they also inhibit the lateral neurons beside them causing them to fire less frequently
how does lateral inhibition occur?
the central core neuron axons synapse directly with the downstream neurons; as the central neuron is excited, it is inhibitory on the axon hillock of the lateral neurons and excitatory on the dendrites and soma of the downstream neurons
how does one AP have an excitatory effect on downstream neurons, but an inhibitory effect on lateral neurons?
the same NT can have different effects on downstream neurons vs inhibitory neurons because there is a different distribution of receptors on the two types of neurons
what are examples of how one AP has an excitatory effect on downstream neurons and an inhibitory effect on lateral neurons?
- typical Nicotinic receptor on dendrites and soma of downstream neuron that activates sodium channel which polarizes membrane
- typical Muscarinic receptor on axon hillock of lateral neuron that activates calcium channel which hyperpolarizes membrane making it harder to generate an AP
convergent (sensory) pathways
sensory pathways going from peripheral body to CNS (afferent pathways)
what do convergent pathways usually involve?
the sorting and integration of multiple different senses (vision, touch, pressure, hearing)
what are the parts of the brains usually affected in convergent pathways?
cerebellum, thalamus, and the cerebral cortex
what do convergent sensory pathways do?
take multiple sensory input and integrate it and send it to the brain where the brain processes it resulting in a sophisticated response to a variety of stimuli
T or F: is the cerebellum part of the hindbrain?
T
what does the cerebellum act as?
a gyroscope and accomplice for motor function of the body
gyroscope
keeps you correctly oriented in your environment
accomplice
produces a smooth motor response to keep you walking in a straight line instead of zigzagging (ex)
what does the cerebellum do?
receives sensory input from multiple inputs
what sensory inputs does the cerebellum receive?
- vestibular (balance receptors in ears, keeps you oriented)
- visual (how are you oriented in your environment?)
- proprioceptive (pressure, how contracted are your muscles?)
how does a sensory target like the cerebellum know where each of the signals is coming from and which ones to give priority to?
through a form of lateral inhibition! Allows the strongest/most direct signals to come through most laterally
what does lateral inhibition look like in sensory pathways?
central neuron is located at the primary source of the stimulus; terminals branch and synapse with interneurons
what is different about lateral inhibition in sensory pathways vs motor pathways?
different arrangement; the branches of the axon of the central neuron don’t synapse with the axon hillock, but they synapse with the interneuron which then synapses with the terminals of the lateral neurons
what occurs during lateral inhibition in sensory pathways when the interneurons synapse with the terminals of the lateral neurons?
the interneurons release an inhibitory NT which binds to a receptor and activates a Cl- channel
what occurs during lateral inhibition in sensory pathways after the Cl- channel is activated via the release and binding of an inhibitory NT from interneurons?
the Cl- current hyperpolarizes the terminal membrane, preventing NT release from the lateral neuron
lateral inhibition in sensory pathways
one neuron directly stimulates downstream targets and indirectly inhibits the lateral neurons
pre-synaptic inhibition
inhibition at the terminals of the lateral neuron is done by activating Cl- ion channels; Cl- current hyperpolarizes membrane (makes more negative), making it harder for an AP to depolarize terminal and release NT
what does lateral inhibition in sensory pathways do?
increases the contrast between the direct sensory field and the surround lateral sensory field
how does lateral inhibition work for creating a visual field?
- light hits rods and cones (photoreceptors) in the retina which are excited by the electromagnetic light stimulation and fire AP
- when a photoreceptor fires an AP, it excites bipolar cells and excites horizontal cells
- bipolar cell excites ganglion cell
- ganglion cell sends signal to optic nerve which goes to brain and tells visual cortex that light is coming in
- bipolar cell also synapses with amacrine cell
- amacrine cells inhibit lateral bipolar cells
- horizontal cells inhibit lateral bipolar cells
what two things do photoreceptors do when firing an AP?
they excite the bipolar cell downstream, but also horizontal cells which inhibit lateral neurons
what is the result of lateral inhibition in vision?
weak periphery signal and clear/sharp center image
what are the 4 ways in which you can distinguish somatic and autonomic nervous systems?
- which effectors they innervate
- way they function in relation to their effectors
- anatomy/arrangement of neurons
- mechanism in which the NT is delivered to the effector
somatic vs. autonomic NS: #1 difference: which effectors they innervate
somatic: skeletal muscle
autonomic: smooth muscle, cardiac muscle, and glands
somatic vs. autonomic NS: #2 difference:
way they function in relation to their effectors
somatic: initiate skeletal muscle contraction (skeletal muscle will atrophy without somatic neuron supply)
autonomic: regulate rate and strength of smooth and cardiac muscle; regulate frequency and amount of glandular secretions for glands
autorhythmic/myogenic
smooth muscle, cardiac muscle, and glands
they will contract at their own intrinsic rate and strength, independent of any neural input from the autonomic system
somatic vs. autonomic NS: #3 difference:
anatomy/arrangement of neurons
somatic: one long motor neuron that goes from the spinal cord to the skeletal muscle; long heavily myelinated axon
autonomic: two neurons; first from spinal cord to second neuron then to effector; synapse occurs outside the CNS; no second neuron for adrenal glands
somatic vs. autonomic NS: #4 difference: mechanism in which the NT is delivered to the effector
somatic: well-defined NMJ; delivery of NT is concentrated and precise (like a bullseye shot)
autonomic: no well-defined NMJ; nerve terminals wander around the effector and have swellings called varicosities (instead of terminal buttons) that release NT in a diffuse way (wide angle shot into glass)
what is a ganglion?
a cell body or group of cell bodies outside of the CNS
what is the first neuron called in the autonomic NS?
pre-ganglionic neuron
what is the second neuron called in the autonomic NS?
post-ganglionic neuron
why is there not a second neuron for adrenal glands?
the inside/central core of the adrenal gland (adrenal medulla) is a set of neurosecretory cells that used to be post-ganglionic neurons and have evolved to be more like glandular/endocrine cells rather than neurons; therefore, they are only innervated by the pre-ganglionic neuron
neurosecretory cells
neurons that have lost their ability to do APs and instead of secreting a NT, they become more like glandular cells and secrete hormones directly into the bloodstream
varicosities
neurons of the autonomic NS; contain synaptic vesicles that contain the NT; release NT in a diffuse mechanism when the neuron is stimulated
somatic vs autonomic NT delivery difference
autonomic = slower response by the effector because of the varicosities that release NT in a broad, diffuse mechanism
what are the three main differences between the sympathetic and parasympathetic NS?
- points of origin in the CNS
- locations of ganglia, ganglionic fiber lengths, post-ganglionic branching
- NTs they use and the receptors that are on the surface of the effectors
sympathetic vs. parasympathetic NS: #1 difference: points of origin in the CNS
sympathetic: 1st thoracic through the 3rd lumbar vertebrate
parasympathetic: 3, 7, 9, 10 cranial nerves and 2, 3, 4 sacral vertebrate
what is the sympathetic NS also known as? why?
thoracolumbar system; because of it’s points of origin
what is the parasympathetic NS also known as? why?
craniosacral system; because of its points of origin
sympathetic vs. parasympathetic NS: #2 difference: locations of the ganglia, ganglionic fiber lengths, post-ganglionic branching
sympathetic: short pre-ganglionic fiber, long post-ganglionic fiber
parasympathetic: long pre-ganglionic fiber, short post-ganglionic fiber
sympathetic NS short pre-ganglionic fiber
only exits the spinal cord and travels a short way before it synapses with a series of ganglia that parallel the spinal cord called the sympathetic chain
sympathetic NS long post-ganglionic fiber
has a lot of branching going on; travels from sympathetic chain to the effector
parasympathetic NS long pre-ganglionic fiber
goes to the surface of the effector; the synapse with the post-ganglionic fiber occurs on the surface of the effector
parasympathetic NS short post-ganglionic fiber
very little branching
myelination in sympathetic and parasympathetic ganglions
pre-ganglionic neurons: much less myelinated
post-ganglionic neurons: unmyelinated (type C fibers, naked axons)
sympathetic vs. parasympathetic NS: #3 difference: NTs they use and the receptors that are on the surface of the effector
sympathetic: pre-ganglionic fibers secrete ACh, post-ganglionic fiber secretes norepinephrine and epinephrine
parasympathetic: pre-ganglionic fibers secrete ACh, post-ganglionic fibers secrete ACh
what do sympathetic post-ganglionic neurons have on them?
nicotinic receptors (N isoform)
what is the primary NT of sympathetic post-ganglionic neurons?
norepinephrine
what did norepinephrine used to be called?
noradrenaline
what did epinephrine used to be called?
adrenaline
what receptors are on the surface of sympathetic NS effectors?
alpha and beta receptors
excitatory alpha and beta receptors (numbers)
alpha 1 and beta 1
inhibitory alpha and beta receptors (numbers)
alpha 2 and beta 2
what are sympathetic receptors known as? why?
adrenergic receptors; they respond to norepinephrine and epinephrine
what is sympathetic stimulation known as?
adrenergic stimulation
what do the dendrites and soma of parasympathetic post-ganglionic fibers have on them?
nicotinic receptors (N isoform)
what receptor is on the surface of parasympathetic effectors?
muscarinic receptors
what is the parasympathetic system known as? why?
cholinergic system; exclusively uses ACh as its NT (has cholinergic receptors that respond to ACh aka muscarinic and nicotinic receptors)
what is parasympathetic stimulation known as?
cholinergic stimulation; inhibitory or excitatory depending on which muscarinic receptor is found on the effector
the sympathetic and parasympathetic NS are ___________ of each other
antagonists; they have the opposite effect on their target organisms
sympathetic vs parasympathetic: inactivation of NT at synapse
sympathetic: transmitter receptor complex is engulfed/taken up on the surface and the NT is taken back up in varicosities
parasympathetic: recycles components of ACh
function of sympathetic and parasympathetic NS: heart
SNS: excitatory (strength and speed); accelerates heart beat, gives ventricles stronger contraction
PSNS: inhibitory; slows down heart
function of sympathetic and parasympathetic NS: GI system
OPPOSING EFFECTS ARE UNEQUAL
SNS: inhibitory; little to no effect
PSNS: excitatory; simulates gastric juices, digestion, GI smooth muscle, etc.; Vagus nerve has most control over GI system (specifically GI smooth muscle)
function of sympathetic and parasympathetic NS: lungs
SNS: excitatory; dilates airways by relaxing smooth muscles (basis for why people with Asthma use epi to open up lungs)
PSNS: inhibitory; constricts smooth muscle that surrounds airways/bronchioles, making it harder to breath
what do excitatory or inhibitory effects in the autonomic NS depend on?
the distribution of receptors
SNS vs PSNS: receptors on the heart
SNS: stimulates mainly by beta 1 receptors on ventricles
PSNS: inhibits by M2 muscarinic inhibitory receptors
SNS vs PSNS: receptors on vascular smooth muscle
SNS: stimulated primarily by alpha 1 receptors (maintains vascular tone)
PSNS: almost no effect of the PSNS
what receptors are the dominant receptors in most major blood vessels and major arteries (except skeletal muscle)?
alpha 1
what receptors are in abundance on skeletal muscle?
blood vessels that go to skeletal muscle have an abundance of beta 2 receptors (inhibitory); when stimulated they relax the blood vessels and allow more blood flow to skeletal muscle
SNS vs PSNS: receptors on smooth muscle in GI tract
SNS: little to no effect (alpha 1, alpha 2, beta 2 receptors)
PSNS: muscarinic 3 receptors; increases motility of smooth muscle and aids with digestion
SNS vs PSNS: receptors on bronchioles
SNS: excites beta 2 receptors in smooth muscle that surround the bronchioles; dilates, making it easier to breathe
PSNS: action on M3 muscarinic receptors; tightens down/constricts smooth muscle surrounding bronchioles
Mass discharge
a result of specific adaptations of the SNS that allows it to fire as a coordinated unit
what does the complete firing of all units of the SNS prime the body for?
periods of intense bursts of speed, strength, and endurance
what are the three features/adaptations of the SNS that allow mass discharge?
- organization
- very highly divergent system
- stimulates adrenal medulla
first feature/adaptation of the SNS: organization
- has control centers in the brain (specifically medulla oblongata) and spinal cord
- all the neurons that go along the spinal cord act as a master switch of the SNS
what causes massive stimulation to all the effectors in the SNS during mass discharge?
intense, potentially life-threatening stimuli (rage, fear, anger, extreme cold, blood loss, extreme pain)
what are the intense, potentially life-threatening stimuli in the SNS during mass discharge received by?
hypothalamus (part of midbrain); control center for all of these strong emotions
where does the hypothalamus send the intense, life-threatening stimuli signals during mass discharge in the SNS?
sends signals to medulla and spinal cord; that is what lights up the SNS
second feature/adaptation of the SNS: highly divergent system
as the control center fires and recruits more neurons, it hits the sympathetic chain and branches even further resulting in a huge amplification of neural signals in the SNS which gives a very strong final signal to all the effectors
divergence
property of motor pathways that is used to amplify neural signals and the strength of neural signals
third feature/adaptation of the SNS: stimulates the adrenal medulla
the SNS stimulates the adrenal medulla, then these modified post-ganglionic neurons that are now endocrine glands excrete epinephrine and norepinephrine into the blood at a ratio of 80:20
how does the SNS stimulating the adrenal medulla contribute to mass discharge?
effector organs get hit two ways:
1. direct stimulation by sympathetic neurons (stimulated neurally)
2. stimulated by circulating epinephrine and norepinephrine which primes the body
what are the 3 main physiological effects/results of mass discharge?
- increased HR and strength of contraction
- increased BP
- increased blood glucose
physiological result of mass discharge #1: increased HR and strength of contraction
epi/norepi affects the beta 1 receptors on the ventricles; ventricles pump blood harder and faster
physiological result of mass discharge #2: increased BP
result of peripheral vasoconstriction (and partly increased HR)
alpha 1 receptors on arteries that lead to peripheral parts of body: clamp down on smooth muscle and arteries, shutting off blood flow to peripheral parts of body…. this begins to redistribute blood flow —> decreased blood flow to peripheral parts of body and increased blood flow to skeletal muscle
beta 2 receptors on blood vessels that feed skeletal muscles: activated by epi/norepi; blood vessels dilate resulting in more blood flow to skeletal muscle (primes muscle by delivering O2 and glucose)
physiological result of mass discharge #3: increased blood glucose
- norepinephrine primarily on the liver mobilizes stored glycogen into glucose
- glucose = dumped into bloodstream and circulates to the muscles, priming the muscles for work
you’re splitting a lot of ATP during mass discharge (chemical to mechanical work), so your body heats up!
this causes your cooling mechanisms to increase via sweating and panting
