exam 3- nervous system 3 Flashcards
divergence is a typical property of ___ pathways
motor
convergence is a typical property of ___ pathways
sensory
convergent pathways
multiple sensory signals originating from multiple motor neurons are transmitted to a few or one target neuron
- more typical with cerebral cortex
divergent pathways
impulse that originates on one motor neuron is passed downstream to more motor neurons (transmits one signal to multiple places)
- with each synaptic connection, more and more motor neurons are stimulated in that pathway (can be transferred up to 100’s of neurons)
divergent pathways can be a form of ___
explain
amplification
how initial signals are amplified downstream to their effector (with each synapse, pathway recruits more and more neurons to fire)
divergence allows you to recruit more neurons –> recruit more muscle fibers –> larger force of contraction
how is the amplification process controlled in divergent pathways?
by an internal mechanism called lateral inhibition
in a web, there is a central core of neurons that is the most direct pathway (the neurons are the side are the lateral neurons, on side of central core)
- as central neurons are stimulated, they stimulate their direct downstream neurons, but they also inhibit the lateral neurons beside them and cause them to fire less frequently (so signal is strongest down central core and weaker down lateral edges of pathway)
describe how lateral inhibition exactly works
branches of axon of the central neuron synapse with other downstream neurons, also synapse with the axon hillock of lateral neurons (as central neuron excited, it is excitatory on downstream neurons, but inhibitory of axon hillocks of lateral neurons –> causes them to fire less frequently b/c harder for them to generate APs at their axon hillock)
it has both excitatory and inhibitory effects because of diff distribution of receptors on the 2 diff types of neurons
- nicotinic receptor on dendrites and soma of the lower neurons to depolarize the membrane
- on axon hillock of lateral neurons, could have muscarinic receptor –> sodium channel to hyperpolarize membrane
–> same neurotransmitter has diff effects due to distribution of receptors
convergent pathways have what function and send signals where?
sensory pathways (afferent), take from peripheral parts of body to CNS
- sensory neurons take multiple signals, integrate them and sends to brain –> cerebellum, thalamus, and cerebral cortex
describe the function of cerebellum involving sensory paths and convergence
cerebellum acts as a gyroscope and compass for the motor function of your body
- gyroscope: keeps you correctly oriented in environment- standing upright
- compass: produced smooth motor responses, keeps you walking in a straight line instead of zig zagging
does this by receiving sensory signals from multiple inputs (input comes in from various areas and converges on cerebellum –> output is smooth motor response)
how does the cerebellum know where each signal is coming from and which ones to give priority to?
through a form of lateral inhibition- allows strongest/most direct signals to come through with most clarity
describe pre-synaptic inhibition
central neuron located at primary source of stimulus (if poked with pin, central neuron is where pin sticked u)
- central neuron synapses with downstream target to excite
- the terminals of the central neuron branch laterally and synapse with interneurons –> interneurons synapse at terminals of the lateral neurons –> interneurons release inhibitory neurotransmitter that binds to a receptor and activates a Cl channel (Cl is negative, Cl current crosses membrane and makes more neg, hyperpolarizes, makes it harder to generate AP and release neurotransmitter from lateral neuron
called pre-synaptic inhibition
lateral inhibition increases ___ between direct sensory field and lateral sensory field
contrast
this is the key concept in pain reception
- direct gives strongest signal when gets to brain, lateral neurons give weaker signal
virtually every sensory pathway, when excited, gives rise simultaneously to ___ signals
lateral inhibitory
describe lateral inhibition to enhance visual contrast
cone in center fires AP (directly connected to bipolar cell –> excites bipolar –> excites ganglion cell –> sends signal to optic nerve –> goes to brain to register light
when excite bipolar cell, also excite horizontal cells (horizontal cells are always inhibitory) –> horizontal cells travel laterally and inhibits adjacent/lateral bipolar cells –> this makes signal weaker the farther away it gets from the central photo cells
- amacrine cells also travel laterally and inhibit bipolar cells, making signal weaker
- so overall, get clear light signal from central rods and cones and weak signal from periphery (clear pic of what u are looking at and not distracting things to the side)
the motor/efferent NS is divided into ___ and ___
somatic and autonomic
name 4 ways to distinguish b/w somatic and autonomic branches
1- which effectors (muscle) they innervate
2- ways they function in relationship to their effectors
3- physical arrangement of the neurons
4- mechanism by which the neurotransmitter is delivered to the effector
describe how somatic and autonomic branches differ in terms of which effectors they innervate
somatic: motor neurons innervate skeletal muscle
autonomic: innervates smooth muscle, cardiac muscle and glands
describe how somatic and autonomic branches differ in terms of the way they function in relationship to their effectors
somatic: initiates skeletal muscle contraction (skeletal doesn’t contract on its own without neural stimulation from somatic motor neuron), so if you cut the somatic motor neuron supply to skeletal muscle: it won’t contract & it will begin to atropy (lose mass) - so somatic involved in maintaining proper nutritional state of skeletal muscle
autonomic: smooth, cardiac, and glands are autorhythmic/myogenic- they will contract at their own intrinsic rate and strength independent of any neural input from autonomic NS (they self-regulate)
- for glands: autonomic regulates the amt of glandular secretions
describe how somatic and autonomic branches differ in terms of physical arrangement of neurons
somatic: one long motor axon that goes from spinal cord to skeletal muscle (axon is heavily myelinated- fast)
autonomic: has 2 neurons - the first goes from spinal cord to certain distance and synapses with second neuron which eventually hits effector (synapse occurs outside CNS, cell body of 2nd neuron is defined as a ganglion- so synapse occurs at a ganglion)
- 1st neuron is a pre-ganglionic neuron and 2nd is a post-ganglionic neuron
- for adrenal glands: no second neuron b/c instead, adrenal gland (adrenal medulla) is a set of neurosecretory cells, these cells used to be post-ganglionic neurons that have evolved to be glandular endocrine cells
describe how somatic and autonomic branches differ in terms of mechanism by which neurotransmitter is delivered to the effector
somatic: has NMJ, well-defined, delivery of neurotransmitter is concentrated and precise
autonomic: no well-defined NMJ; instead of nerve terminal ending at well-defined terminal button, the nerve terminals wander around the effector in web-like arrangement (swellings called varicosities all along nerve terminal, they contain synaptic vesicles that contain neurotransmitter) –> when stimulated, neurotransmitters released from varicosities in a more broad and wide mechanism –> results in a slower response by the effector
name 4 differences between the sympathetic and para branches
1- difference b/w points of origin in CNS
2- differing locations of ganglia
3- differing lengths of ganglionic fibers
4- postganglionic branching
where do sympathetic and para originate from in CNS
sympathetic originates from 1st thoracic and 3rd lumbar vertebrae –> sympathetic aka thoracolumbar system
para originates from cranial nerves 3,7,9,10 and sacral vertebrae 2,3,4 –> para aka craniosacral system
describe differences in pre and post-ganglionic fibers in sympathetic and para
sympathetic:
- short pre-ganglionic neuron is a series of ganglia called the sympathetic chain
- long post-ganglionic neuron has lots of branching, long fibers that travel from sympathetic chain to effector
parasympathetic:
- long pre-ganglionic fiber that goes to surface of effector and synapses with short post-ganglionic fiber right on surface of effector
- short post-ganglionic and very little branching
describe myelination of pre- and post-ganglionic neurons of the autonomic NS
all pre-ganglionic neurons in autonomic NS (para and sympathetic) are very lightly myelinated
most post-ganglionic neurons are naked axons
referring to the receptors and neurotransmitters that branches of the autonomic NS use…
the parasympathetic NS is called the ___ system
the sympathetic NS is called the ___ system
cholinergic
adrenergic
what neurotransmitters do parasympathetic and sympathetic branches secrete on their pre-ganglionic fibers
both secrete Ach
what neurotransmitters do sympathetic post-ganglionic fibers secrete
epinephrine and norepinephrine
what neurotransmitters do parasympathetic post-ganglionic fibers secrete
Ach
what receptors are on the effectors that the neurotransmitter of the sympathetic post-ganglionic fiber binds to
alpha 1 and beta 1 (excitatory)
alpha 2 and beta 2 (inhibitory)
what receptors are on the effectors that the neurotransmitter of the parasympathetic post-ganglionic fiber binds to
muscarinic receptors (excitatory and inhibitory)
describe the parasympathetic NS and its pre- & post-ganglionic fibers and the neurotransmitters and receptors involved
pre-ganglionic fiber secretes Ach - dendrites & soma of post-ganglionic fiber have excitatory nicotinic receptors – post-ganglionic fiber also secreted Ach –> muscarinic receptors on surface of the effectors
- b/c para only uses Ach as its neurotransmitter, it is called the cholinergic system and it has cholinergic receptors (nicotinic & muscarinic) that respond to Ach
describe the sympathetic NS and its pre- & post-ganglionic fibers and the neurotransmitters and receptors involved
pre-ganglionic fiber secretes Ach - nicotinic neuronal isoform on dendrites and soma of post-ganglionic fiber - post-ganglionic fiber secretes diff neurotransmitters (its primary is norepinephrine, can also secrete epinephrine) …epinephrine used to be called adrenaline and nor called noradrenaline –> receptors are alpha and beta receptors
- receptors are called adrenergic receptors b/c of the adrenaline naming
- sympathetic system called adrenergic system
describe the opposing functions of para and sympathetic on the heart, GI, and lungs
heart: sympathetic is excitatory (accelerates heartbeat and gives ventricle a stronger contraction)
- para is inhibitory, slows down heart rate
GI (stomach & intestines): para is excitatory- stimulates muscle to digest food, para through the vagus nerve controls most of the GI system and GI smooth muscle, so opposing effects are unequal in this case
- sympathetic is inhibitory, but has very little control
lungs: para constricts smooth muscle that surrounds bronchioles, closes them off - making it harder to breathe
- sympathetic dilates lungs airways by relaxing smooth muscle
the basis of excitatory and inhibitory effects of para and sympathetic on diff organs is due to ____
distribution of receptors
para and sympathetic effects on heart rate due to what receptors
sympathetic increases heart rate through beta 1 excitatory receptors
para decreases heart rate through M2 muscarinic receptors
para and sympathetic effects on vascular smooth muscle due to what receptors
sympathetic maintains the vascular tone, tightens arteries and blood pressure – sympathetic has most control, para has little effect
sympathetic alpha1 receptors constricts blood vessels in skin
sympathetic- blood vessels that go to skeletal muscle have abundance of beta2 receptors (inhibitory), when stimulated –> relax blood vessels and allow more blood flow to skeletal muscle
para and sympathetic effects on bronchioles due to what receptors
sympathetic with beta2 dilates/relaxes, makes it easier to breathe
para through M3 constrict and tighten them
what is the basis of the fight or flight reaction
mass discharge of the sympathetic NS
- mass discharge- allows sympathetic NS to fire as a coordinated unit (turns on in its entirety- bursts of speed, strength, and endurance)
what are the control centers of the sympathetic NS that allow for mass discharge
medulla oblongata in brain
spinal cord
what causes mass discharge in sympathetic NS?
stimuli: fear, anger/rage, extreme cold, blood loss, and extreme pain
intense, life-threatening stimuli
describe how the medulla oblongata allows for mass discharge of sympathetic NS
neurons act as a master switch- medulla is the swollen part at top of spinal cord, has lots of control neurons that are part of sympathetic outflow- all the neurons are interconnected –> when fire, all fire at once- light up entire sympathetic NS at once
- the intense, life-threatening stimuli are received by the hypothalamus (small, but control center of all strong emotions- center of anger, monitors blood pressure, and is the bodys thermostat) –> sends signal to medulla oblongata, which lights up sympathetic NS
name 3 adaptations that allow mass discharge of sympathetic NS
1- control centers in medulla oblongata & spine
2- highly divergent motor pathways
3- sympathetic NS stimulates the adrenal medulla
describe how sympathetic system being divergent pathway helps with mass discharge
divergence pathway of motor pathways used to amplify strength of neural signals – as control center neurons fire and travel down spinal cord –> huge amplification of signals in sympathetic NS, gives strong final signal to all the effectors
describe how the adrenal medulla helps sympathetic NS have mass discharge
sympathetic NS stimulates the adrenal gland (outer layer called cortex and inner layer called medulla)
adrenal medulla secretes epinephrine and norepinephrine in a ratio of 80 epi to 20 norepinephrine
–> effector organs are directly stimulated neurally by neurons and pumped up by circulating epi
what are the physiological effects of mass discharge?
1- increased heart rate and strength of contraction- beta1 receptors on ventricle make it pump harder and faster
2- increase blood pressure- mostly a result of peripheral vasoconstriction (constriction of blood vessels going to your periphery/skin to prevent blood loss b/c alpha1 receptors shut down blood flow to periphery, this increases blood flow to skeletal muscle
3- beta2 receptors respond to the increase in blood circulation on blood vessels that feed skeletal muscle (beta2 responds to epi and norepi) – primes muscle by delivering oxygen and glucose, gets it ready for activity
4- increase blood glucose- effects of norepinephrine on liver, mobilize stored glycogen –> turns to glucose –> circulates to muscles and primes them to work
5- body heats up b/c splitting a lot of ATP (so increasing body’s cooling mechanisms: sweating & panting)
