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