Polysynaptic Reflexes: Withdrawal Reflex

 POLYSYNAPTIC REFLEXES: WITHDRAWAL REFLEX

In this type of reflex, one or more (or even hundreds) of neurons are involved. One example is the with-drawal reflex, in which a painful stimulus causes the stimulated part to withdraw. This reaction even hap-pens in individuals who have had a spinal cord injury above the level of the segments supplying the limb tested. This is an important protective reflex and su-persedes other activities.


Comments

Post a Comment

Popular posts from this blog

Microorganisms on the Skin

  Microorganisms on the Skin On the integumentary system would not be complete without considering the invisible layer of microorganisms that inhabit the surface of the skin. This huge colony of organisms is the  “normal mi-crobial flora.”  Similar to residents and tourists in acity, there are resident microorganisms (resident flora) that are regularly found in a specific area at a specific age and transient flora that inhabit the skin for hours, days, or weeks. The resident flora play an important part in maintaining health and normal function. Resident flora prevent harmful bacteria from thriving on the skin by directly inhibiting them or competing with them for nutrients. However, resi-dent bacteria can be infective and harmful if they are introduced in large amounts into the bloodstream, which can occur when the skin is injured or when surgery is performed without adequately cleansing the skin surface before incision. They may also be harmful in individuals whose immu...
Read more

Neuroglia

Image
  NEUROGLIA Neuroglias are the supporting cells. They are five times more abundant than neurons. There are four types of glial cells in the CNS: the  ependymal cells, astro-cytes, microglia,  and  oligodendrocytes  and twotypes in the PNS:  Schwann cells,  or  neurolemmo-cytes, and  satellite cells,  or  ganglionic gliocytes. The ependymal cells line the cavities in the brain and spinal cord and are responsible for producing, circulating, and monitoring the cerebrospinal fluid—the fluid inside and around the CNS that cushions and protects the brain. The astrocytes, as the name suggests, are star-shaped. They are present between the blood capillaries and the brain and spinal cord, monitoring the sub-stances that enter and leave the brain and preventing sudden changes in the environment around the CNS. This is the  blood-brain barrier,  and the astrocytes are responsible for its creation. The astrocytes also help at the time...
Read more

Movement in the Colon and Defecation

Image
  Movement in the Colon and Defecation The movement in the colon is similar to the small in-testine in that peristalsis and a segmentation type of contraction are present. In addition, there is a third type of contraction,  mass action  contraction, in which there is simultaneous contraction of the smooth muscle over a large area. This movement pushes material from one portion of the colon to an-other and into the rectum. When the rectum is dis-tended, it initiates the  defecation reflex.  When the pressure increases a little, there is a desire to defe-cate. Beyond a pressure of 55 mm Hg, both the inter-nal and external sphincters relax and the contents of the rectum are expelled. This is the reason for the in-voluntary expulsion seen in infants and individuals with spinal cord injury. In humans, sympathetic stimulation causes contrac-tion of the internal anal sphincter and parasympathetic stimulation relaxation. The external anal sphincter, which is comprised o...
Read more