Module 19: The Reflex Arc

Five Components of the Reflex Arc:

1. receptor 2. afferent pathway (sensory neurons) 3. integration center 4. efferent pathway (motor neurons) 5. effector

Example of a polysynaptic reflex:

Accidentally placing one's hand on a nail

Example of spinal reflex:

Knee-jerk reflex

Example of cranial reflex:

Pupillary light reflex

What type of grey matter is involved in a contralateral reflex, but NOT an ipsilateral reflex? Why?

The gray commissure (of the spinal cord) because the sensory signal is being sent to other side of the body rather than the same side

Example of contralateral reflex:

cross-extension (ex: standing on one leg; the standing leg contracting is the responder)

innate reflex

a reflex you are born with

Reflex

an involuntary response to a stimulus

autonomic (visceral) reflex

autonomic neurons to *smooth muscle and glands*

Efferent Pathway (reflex arc component)

consists of a MOTOR NEURON that carries a transmit an impulse (command) from integrating center to effector cell (*moves away from* the CNS)

Receptor (reflex arc component)

detects the stimulus

somatic reflex

motor neurons activate stimulation of *skeletal muscles*

Effector (reflex arc component)

muscle or gland cell that responds to efferent impulses; either contracts or secretes

simple reflex arc

reflex arc in which the sensory neuron directly connects to the motor neuron in the spinal cord

learned reflex

reflex developed based on experiences

contralateral reflex

reflex that occurs on the opposite side of the body

ipsilateral reflex

reflex that occurs on the same side of the body that is stimulated

Integrating Center (reflex arc component)

region of CNS where afferent neuron synapses with one or more neurons (interneurons and/or motor neurons); usually the spinal cord

When the receptor detects the stimulus, it excites a __________ neuron.

sensory

Reflex Arc

the pathway through which a stimulus can directly cause a response involuntarily

integration

the right kind of connections made among neurons within a reflex arc

Name the 4 types of reflexes that describe the pupillary reflex:

1) Cranial 2) Autonomic (pupil is made of smooth muscle) 3) Polysynaptic 4) Ipsilateral AND Contralateral

Reflex Classification (4 types):

1) Monosynaptic or polysynaptic 2) Spinal or cranial 3) Somatic or autonomic 4) Innate or learned

Name the 4 types of reflexes that describe the knee-jerk reflex (patellar reflex):

1) Spinal 2) Somatic 3) Monosynaptic 4) Ipsilateral

Name these things based on the pupillary light reflex: 1) stimulus 2) receptor 3) afferent pathway 4) integration center 5) efferent pathway 6) effector

1) bright light shined in eye 2) receptor cells of eyes are stimulated by light 3) sensory message from neurons to brain (integration center); interneurons activated 4) brain 5) motor (efferent) neuron excited, sends message to effector organ 6) pupil muscle contracts (shrinks)

Polysynaptic reflex (3 points)

-more common type of reflex -most have a single interneuron (the circle) between the sensory and motor neuron -*multiple (usually two) upside down Ys in the nerve impulse picture*

Monosynaptic reflex (4 points):

-simplest of all reflexes -a reflex that only involves one synapse -the fastest of all reflexes -*only one upside down Y in the nerve impulse picture*

Name the 4 types of reflexes that describe the cross-extensor reflex:

1) Spinal 2) Somatic 3) Polysynaptic 4) Contralateral

Name the 4 types of reflexes that describe the pain reflex (withdrawal reflex):

1) Spinal 2) Somatic 3) Polysynaptic 4) Ipsilateral

Name these things based on the knee-jerk reflex: 1) stimulus 2) receptor 3) afferent pathway 4) integration center 5) efferent pathway 6) effector (response)

1) shape change of the tendon, due to hammer hitting tendon 2) sensory (stretch) receptor (send message to muscle) 3) sensory message from neuron to spinal cord (CNS) 4) spinal cord 5) motor (efferent) neuron to effector organ 6) tendon (front) contracts and relaxes (back), causing foot to kick up

Name these things based on the pain reflex: 1) stimulus 2) receptor 3) afferent pathway 4) integration center 5) efferent pathway 6) effector (response)

1) something painful (ex: stepping on a nail) 2) pain (sensory) receptors in the bottom of your foot alert your foot 3) sensory message from neuron to spinal cord (integration center); interneurons activated 4) spinal cord 5) motor (efferent) neuron excited, sends message to effector organ 6) flexor muscles contract and move your foot away from nail

What's the main difference between a cranial and spinal reflex?

Cranial reflex: the brain is the integration center Spinal reflex: the spinal cord is the integration center

Example of somatic reflex:

Knee-jerk reflex (only involves effector of skeletal muscles)

Example of innate reflex:

Knee-jerk reflex, pupillary reflex

Example of learned reflex:

Pavlov's dogs salivation in response to bell

Example of autonomic reflex:

Pupillary light reflex

In a knee-jerk reflex arc the sensory neuron _________ connects to the motor neuron in the spinal cord.

directly

In most reflex arcs the sensory neuron connects to motor neurons through _______________ in the central nervous system (spinal cord).

interneurons

Example of a monosynaptic reflex:

knee-jerk response

Afferent Pathway (reflex arc component)

sensory neurons that transmit impulses from receptor to CNS (*approaches* the CNS)