nerve reflexes

Reflex arc

— is an often-used model of nerve pathways

reflex arc

is a way of visualizing the direction of transmission of nerve signals or action potentials.

receptor

The reflex arc begins with a —, a specialized cell or cell projection, which is stimulated by a change in its environment.

central nervous system

If stimulation of the receptor was significant enough to initiate an action potential in the afferent neuron, the signal is transmitted toward the —

afferent, sensory

The —, or —, neuron brings the signal into the brain or spinal cord.

peak

At the — of the arc, where the signal is “turned around”, the afferent neuron may synapse directly with an efferent neuron, forming a two-neuron arc

two-neuron arc

At the peak of the arc, where the signal is “turned around”, the afferent neuron may synapse directly with an efferent neuron, forming a —.

three-neuron arc

Often an interneuron synapses with the afferent neuron and transmits the signal to an efferent neuron, thereby making a —

effector

An — is a muscle or gland innervated by a motor nerve

contracting, secreting a chemical

The effector responds in some way to nerve signals, perhaps by — or —

reflex arc

If the reflex shows an abnormal reaction or no reaction at all, damage to some component of the — is suspected.

Hyperreflexia, hyporeflexia

— and — are the two possible abnormal spinal reflex results.

hyperreflexia 

also referred to as exaggerated response, results from damaged or diseased motor areas in the central nervous system.

hyporeflexia 

also referred to as inhibited response, results from degeneration of nerve pathways, voluntary motor control, and other factors.

patellar, biceps, triceps. achille reflex

The following activities demonstrates several reflexes that are categorized as stretch reflexes.

patellar reflex

also known as knee-jerk reflex

patellar reflex

is mediated by a two-neuron arc centered in the spinal cord.

two-neuron spinal reflex

What type of reflex is the patellar reflex?

L3, L4 nerves

Which spinal nerves are involved in the patellar reflex?

patellar reflex 

a reflex performed by having the subject sit on a table/chair with the legs dangling above the floor

tap the ligament just below the patella while the legs dangle freely 

How is the patellar reflex performed?

quadriceps muscle is stretched

What happens when the patellar ligament is tapped?

they trigger the muscle to contract and extend the lower leg 

What do stretch receptors in the quadriceps do during the patellar reflex?

it helps the quadriceps reflexively increase contraction strength when load increases 

What is the function of the patellar reflex in normal circumstances?

spinal reflex

What type of reflex is the biceps reflex?

c5, c6 nerves

Which spinal nerves are involved in the biceps reflex?

sit with the elbow flexed at about 90* and palm facing downward 

How should the subject be positioned for the biceps reflex test?

on the biceps tendon at the inside angle of the elbow 

Where should the thumb be placed during the biceps reflex test?

press the biceps tendon gently with your thumb and tap your thumb with a reflex mallet

How is the biceps reflex test performed?

flexion of the elbow

What is the normal response in the biceps reflex?

a spinal reflex 

What type of reflex is the triceps reflex?

c6, c7 nerves 

Which spinal nerves are involved in the triceps reflex?

lie on a table with one arm across the abdomen 

How should the subject be positioned for the triceps reflex test?

with the elbow flexed at a 90* angle

How should the arm be supported during the triceps reflex test?

posterior surface of the upper arm just above the olecranon 

Where should you tap to elicit the triceps reflex?

extension of the lower arm as the triceps branchii contracts

What is the normal response in the triceps reflex?

ankle-jerk reflex

What is another name for the Achilles reflex?

spial reflex 

What type of reflex is the Achilles reflex?

s1, s2 nerves

Which spinal nerves are involved in the Achilles reflex

plantar flexion of the foot 

What is the normal response in the Achilles reflex?

kneel on a chair facing away, with toes pointing toward the floor

How should the subject be positioned for the Achilles reflex test?

middle of the achilles tendon

Where should you tap to elicit the Achilles reflex?

cutaneous reflex 

reflexes that result from the stimulation of cutaneous or skin receptors

cutaneous receptors

What type of receptors are involved in the plantar reflex?

bare foot with the lateral surface resting on a table or chair 

How should the subject’s foot be positioned for the plantar reflex test?

firmly sweep the handle of a rubber malt along the lateral region of the sole

How is the plantar reflex performed?

toes flex

What is the normal response in the plantar reflex?

toes extend and move apart

What is a Babinski response

infants up to 18 months old

In whom is the Babinski response considered normal?

abnormal neurological condition

What does a Babinski response indicate in adults?

pupillary reflexes

A reflex can also be mediated by the brain such in the case of —  which involves cranial nerves and autonomic reflex centers

brainstem

Where is the pupillary reflex centered?

in a dimly lit area, staring straight ahead with a hand held vertically between the eyes 

How should the subject be positioned for the pupillary reflex test?

shine a penlight into one eye from bout 5 to 7 cm away

How is the pupillary reflex performed?

light receptors detect bright light and signal the iris muscles 

What triggers the pupillary reflex?

pupil decreases in diameter (constricts)

What happens to the pupil when light is shone into it?

protects the retina from excessive light and improves visual clarity 

What is the advantage of pupil constriction in bright light?

right pupil decreases in diameter 

What is the response of the opposite (right) pupil when light is shone in the left eye?

ensures balanced light response in both eyes for better vision and eye protection 

What is the advantage of the consensual pupillary reflex?