Definition of a reflex

a stereotyped behavior to a give stimulus

Do reflexes operate with cortical influence? 

No - they can operate with out cortical influence

however, cortex can/often modifies them (precious coffee)

Components of the Reflex Arc

Sensory Input - the receptor and primary afferent

Central Integration - interneurons

Motor Output - motor neuron (LMN) and target (skeletal muscle)

What is the function of reflexes?

they provide rapid motor response for posture (stabilization - vestibular senses), protection, and homeostatis (autonomic nervous system)

the response often counteracts the stimulus that elicits the reflex

Reflexes are constently working ...

muscle tone which is set by a reflex

posture - constently being corrected by reflexes

adapts gait disturbances 

Types of Reflexes

Myotatic Reflex - stretch/tendon tap reflex

Cutaneous - Withdrawl reflex (stimulates skin)

Pathologic - Crossed extensor, Babinski response (only appear under abnormal circumstances) 

Function of the Myotatic Reflex

cuases muscle contractions that oppose the stretch of the muscke to help oppose unexpected loads

How the myotatic reflex is observed

Observed as muscle contracting during testing

is responsible for setting muscle tone (passive, residual tone/motion)

is the rapid correction for unexpected loads 

extrafusal muscle fibers

cells of the skeletal muscles that lie outside of the muscle spindle

intrafusal muscle fibers

striated muscle fibers insice the muscle spindle that can shorten

gamma motor neuron 

motor neuron that innervates the intrafusal muscle fibers

alpha-gamma co-activation

when gamma lower motor neurons and alpha lower motor neruons fire at the same time to keep the muscle spindle from being fully unloaded

gamma LMN's take up the slack in the muscle spindle to keep it taut

Gamma bias

the amount of tone in the muscle based on the gamma LMN

baseline activity in gamma LMN = resting tention in spindles

gamma bias is affected by psychological states (dentist example) and by pathology 

What does and increased activity in gamma LMN's cause

An increase in tension

an increase in gamma bias = increase in resting tone of the muscles (and their responsiveness to stretch)

Function of the Withdrawl Reflex

to protect from injury (or noxious stimuli)

it is operational all the time

Withdrawl Reflex Arch

Sensory Limb - receptor (generally a noceiceptor) and a primary afferent

Contains Multiple interneurons

Motor Limb - Lower Motor Neurons (alpha LMN's) innervating muscles that pull back the receptive field

Crossed Effects

these are generally observed within the the Withdrawl Reflex

Their function is to maintain a standing position/posture while the receptive field is being retracted

Reciprocal Inhibition

process by which an inhibitory interneuron branches off of the primary afferent and synapses onto a LMN to inhibit the antagonist muscle

Pathologic Reflexes

show an abnormal response to a particular reflex

Babinski Response/sign

-Is a pathologic reflex

-is a classic sign of UMN (upper motor neuron) damage

-is demonstrated by abnormal plant reflex response

- Normal response: flex toes/ plantar flextion

- Babinski sign: exted/flare toes out, dorsi flex and abduct

Crossed Extensor Reflex

- is normal in standing position

- is suppressed by laying down (recumbency)

- abnormal when response is visible when person is lying down

Damage to the reflex arc 

- will reduce (hyporefluxia) or eliminate (arefluxia) the function of the arc

Damage to descending pathways affect on reflex arch

- does not eliminate the relfex

- can change the behavior of the arch

- can cause excessive response (hyperreflexia)