Kaap428 - Section 3 (1.1)

Reflex Behavior

Stimulus-Elicited Behavior

involuntary and immediate response that is produced as a result of sensory stimulation

What does it mean to be stimulus elicited? (2)

• only a short amt of time elapses between the stimulus and response

• the response CANNOT be delayed

Therefore, time between stimulus and response must be SHORT and NON MODIFIABLE

Difference between reaction time and response latency

when you measure the time between a stimulus response…

Reaction time : VOLUNTARY (ex: green light)

Response Latency : INVOLUNTARY (ex: reflex)

how do we know that a response is a reflex and not a response? (time)

100-200ms

reflex distinguishing characteristics (2)

• the response to a discrete stimulus is a discrete action

• the response results from the stimulation of a specific group of sensory receptors where recognition of the stimulus is not necessary (ex: you can be startled by a noise without knowing the source of it)

skeletomotor reflexes

• produced by activity of skeletal muscles (acoustic startle reflex, withdrawal reflex, eye-blink reflex)

sensory stimulus —> spinal cord —> muscles

alpha motor neurons

innervate EXTRAfusal muscle fibers, which cause muscle contractions

gamma motor neurons

innervate INTRAfusal muscle fibers (muscle spindles)

motor unit

a single alpha motor neuron and the group of extrafusal muscle fibers that it innervates

(can range from around 5 to thousands!!)

motor neuron pool

all of the alpha motor neurons that innervate the fibers of a single skeletal muscle

• consists of MANY motor neurons each innervates a motor unit within the muscle

principles of motor unit organization (2)

• ratio principle

• size principle

ratio principle

the number of fibers in a muscle divided by the number of motor neurons innervating it

gross motor : one neuron innervates many muscle fibers (bc you do not need precise mvmts)

fine motor : one neuron innervates few muscle fibers (high level of control —> more precice mvmts)

size principle

the order that motor neurons are recruited into force production is determined by the size of the associated motor neuron

size principle order of firing

smallest motor neurons fire first —> then slightly larger —> then large

as excitation of the pool increases, the motor units are recruited in order of size

why is the size principle important? (2)

• small motor neurons innervate fatique resistant fibers (recruits fibers that do not get tired first ; ex: we can type for a very long time without our fingers getting tired)

• large motor neurons innervate fatigueable muscle fibers (only active in tasks with high force production —> held in reserve for things like rapid production of large forces)

purpose of spinal cord (3)

• provides protection from painful or damaging stimuli (spinal reflexes)

• can adjust for unexpected perturbations (ex: catching yourself when you trip)

• can organize patterns of coordination

stretch reflex

• monosynaptic reflex pathway (quick)