Exercise 7: Somatic Reflex Arcs

identify the components of a reflex arc

receptor, afferent neuron (sensory), integration (CNS), efferent neuron (motor), and an effector. 

Define Afferent Neuron.

Also known as the sensory neuron, carries the information regarding the stimulus from the nerves to the integration center / CNS.

Define Receptor.

a specialized sensory cell or the modified dendrite of a sensory neuron that detects some type of stimulus 

Define Integration.

Assesses the information from the CNS and directs the response to the effector cells

Define Efferent Neuron.

Also known as the motor neuron, carries information from the brain and spinal cord to muscle fibers throughout the body.

Somatic Nervous System

The part of the peripheral nervous system responsible for carrying sensory and motor information to and from the CNS. Responsible for transmitting sensory information as well as for voluntary movement. Contains two major types of neurons. 

What is the function of Effector cells ?

To Respond

Spinal Reflex

Allows a rapid, automatic response to a stimulus to be carried to the spinal cord for integration. 

Monosynaptic Reflex

One synapse between the sensory neuron axon and the motor neuron dendrite, both located within the CNS.

Multisynaptic Reflex

More than one synapse within the CNS. More than two neurons (sensory and motor neuron) located totally within the CNS.

Ipsilateral Reflex

Stimulus and the response are on the same side of the body. (can be mono or multi)

Contralateral Reflex

Stimulus and Response are on the opposite sides of the body (multisynaptic)

Consensual and Bilateral Response

Response occurs on both sides of the body

How are somatic reflexes categorized ?

1. number of synapses

2. side of stimulation

Extrafusal Fibers

Innervated by alpha motor neurons and are responsible for the development of force by skeletal muscles

Intrafuslal Fibers

Innervated by gamma motor neurons, used as a stretch detector, and are located in the muscle spindles

Define Alpha Motor Neurons

• Large motor neurons

• Generate muscle force and movement

• Directly control muscle contraction by innervating the main muscle fibers (extra-fusal fibers)

• Initiate Movement 

Define Gamma Motor Neurons

• Small motor neurons

• Regulate muscle tone and proprioception by adjusting the sensitivity of the muscle spindle

• Adjust muscle tension during movement 

• innervate intrafusal muscle fibers within the muscle spindle 

Proprioception

The body's ability to sense movement, action, and location

Spastic Paralysis

When upper motor neurons are damaged and a person can no longer perform movements directed by the cerebral motor cortex. Muscles then can only be stimulated to move reflexively 

Flaccid Paralysis

When lower motor neurons are damaged, a condition marked by severe muscle weakness and loss of muscle tone, often developing suddenly