Reflexes and Reflex Arcs

Reflex

fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus 

What is a spinal reflex?

when integration takes place in the spinal cord gray matter

What is a cranial reflex?

integration occurs in the brain stem

What are somatic reflexes?

involves the contractions of skeletal muscles

What are autonomic reflexes?

Is it perceived/

responses of smooth and cardiac muscles, and glands 

not consciously perceived 

Reflex arc

pathway followed by nerve impulses that produce a reflex

What are the components of a spinal reflex?

sensory receptor, afferent neuron, integrating center, efferent neuron, and effector 

(SR) Sensory receptor is stimulated:

by a change in the internal/external environment and generate nerve impulses

• like pain or heat

(SR) Afferent neuron

conducts nerve impulses along its axon to its axon terminals in the spinal cord

(SR) Integrating center is one or more regions of?

What can it synapse to?

gray matter in the spinal cord

can synapse directly with motor neuron 

can also synapse with interneuron to send information to the brain (later) and motor neuron 

(SR) Efferent neuron

impulses triggered by integrating center pass out of the spinal cord along the axon of the motor neuron 

(SR) Effector 

What is it?

part of the body that responds to the fine motor impulse

can be a muscle or gland 

What type of reflex is the knee jerk reflex? 

spinal and somatic reflex 

(KJR) 1. Sensory receptor

muscle spindle in quadriceps femoris muscle senses the stretch

(KJR) 2. Afferent neuron 

sends information from muscle spindle to spinal cord 

(KJR) 3. Integration center 

single synapse in the spinal cord, sensory neuron synapses to somatic motor neuron 

• also synapses with inhibiratory interneuron

(KJR) 4. Motor neuron

carries impulse from integration center to effector, stimulating the quadriceps femoris muscle to contract

• interneuron: motor neuron to antagonistic muscles is inhibited, causing them to relax

(KJR) 5. Effector

quadriceps femoris m., contracts to move lower leg