lecture 5 behavior from the perspective of bioelectricity Flashcards
what is a reflex
a reaction in response to a stimulus not requiring conscious awareness
what to reflex exams reveal
general nervous system disorders and problems with particular parts of the nervous system
what is the latency between time of stimulus and reaction in the paterllar tendon reflex
20 milliseconds
is reflex latency faster or slower in tall people
slower; the distance the signal travels is longer
steps in myotatic reflex
1) stimulus 2) transduction 3) frequency encoding 4) sensory motor synapse 5) motor neuron action potential 6) muscle fiber activation
what is the stimulus step in the myotatic reflex
tapping patellar tendon causes quadricep muscle to stretch
what is the transduction step
converting mechanical stimulus into electrical signal
what is the transduction apparatus
a muscle spindle whos fibers are wrapped by a sensory axon called the 1a axon
what does the stretching of the spindle muscle fibers to
causes stretching of sensory axons, opening up na+ channels
what is a receptor potential
depolarization of 1a axon (na+ channels opening) in response to stretch of muscle fibers
what is frequency encoding
converting receptor potential amplitude into the frequency of action potentials
what is an action potential
large, rapid, stereotyped change in membrane potential
when is the only time an action potential can be elicited
when a receptor potential brings the membrane potential above a threshold value
what is the same and different across all action potentials
their size and shape is invariant but their frequency can vary widely
the stronger the receptor potential… (the more depolarization due to strong and long stimulus)
the greater the frequency of the action potentials (amount per second)
where does receptor potential occur
locally in 1a axon
difference between receptor and action potentials
action potentials, once started (reach threshold), dont stop but receptor potentials can die out
where do the action potentials with the 1a axon start and end
begin in 1a axon and propagate via peripheral nerve to dorsal root ganglion, then from dsg to spinal cord
where is the dorsal root ganglion and what is its function
cluster of neurons in dorsal root of spinal nerve, carries sensory information to spinal cord and enters posterior of spinal cord
what happens with sensory motor synapses after frequency encoding
action potential from 1a axon drives the axon terminal to release neurotransmitters at synaptic junction
what do neurotransmitters do once released (for myotatic reflex)
bind to receptors on motor neuron dendrite causing synaptic potential in motor neuron
what is similar between synaptic potential and receptor potential
decrease in amplitude (and power) with distance
what causes motor neuron action potential
once synaptic potentials build on top of each other and pass the threshold to trigger action potential
what is an epsp and what does it do
excitatory post synaptic potential, allows sequential synaptic potentials to piggyback on top of each other and cross threshold to elicit action potential
what happens after motor neuron action potential is triggered
muscle fiber activates (via neuromuscular junction, synapse between neuron and muscle) motor signal is sent through motor neuron axon terminal to muscle fiber
what happens when muscle fiber reaches threshold
triggers action potential that causes muscle fiber to contract which counters stretch induced from stimulus
what is strength of muscle contraction related to
number and frequency of motor axons activated
what is bells palsy
weakness of muscle supplied by facial nerve
where is the soma of the 1a axon
in the dorsal root ganglion
Frequency coding
since action potentials are unitary in size and duration, the strength of
the signal is determined by the frequency of the action potentials. A stronger signal
increases the frequency of action potentials (i.e. number of action potentials per second)
Action potential
an actively propagated impulse that conveys information across long
distances. Action potentials are considered unitary or “all or none”. Meaning that the size
and duration of each action potential remains constant. Details will be covered in later
lectures.
Graded potential
an electric signal that changes the membrane potential in a continuous
manner (oppose to unitary, or “all or none” manner) typically in a small region of a neuron.
Graded potentials can differ in size, shape, or duration, depending on the stimulus and
response properties of the responding neuron. Graded potentials are commonly found at
sensory receptors and synapses
Stimulus
an extrinsic or intrinsic signal that causes a response. In sensory systems, the
nature of the stimulus is specific to the sensory modality and the type of sensory receptors
activated
Signal transduction
converting one kind of signal or stimulus into another type (e.g.
mechanical stimulus to electrical signal or electrical signal to chemical signal)
Signal transduction
converting one kind of signal or stimulus into another type (e.g.
mechanical stimulus to electrical signal or electrical signal to chemical signal)
Excitatory neuron
a neuron, that when active and fires action potentials, increases the
probability that the neurons it connects to via synapses will also fire an action potential.
Inhibitory (often an interneuron)
a neuron, that when active (fires action potentials),
decreases the probability that the neurons it connects to via synapses will fire an action
potential. Many inhibitory neurons do not send their axons very far, making local
connections and are referred to as interneurons
Motor neuron
type of efferent neuron (a cell that carries information away the brain to the
periphery) that synapses onto skeletal muscle fibers
Sensory neuron
type of afferent neuron (a cell that carries sensory information toward the
brain from the periphery).
List the components of behavior
Describe the anatomical organization and electrical signaling that give rise to the knee jerk
reflex circuit
Explain how amplitude coding and frequency coding is used in the myotatic stretch reflex
Explain the differences between a local potential and a propagated potential
