PDBIO 210 -- Lesson 11 (part 6) Dermatomes, Shingles, Plexus, Reflex Arc

From which plexus is the musculocutaneous nerve formed?

--Brachial

What are the principal plexuses? (fig. 16.1)

--Cervical --Brachial --Lumbar --Sacral (this is the order from Superior to Inferior)

What is the Lumbar Plexus? (fig 16.10a) (which spinal nerves contribute to the plexus?) (what does the plexus innervate?) (what major nerves arise from the plexus?)

--Spinal Nerves L1-L4 --Innervates: lower limb --Femoral nerve innervates anterior thigh muscles

What is the Cervical Plexus ?(fig 16.18) (which spinal nerves contribute to the plexus?) (what does the plexus innervate?) (what major nerves arise from the plexus?)

--Spinal nerves C1-C4 make up Cervical Plexus --Innervates: anterior neck and parts of head and shoulders --Phrenic nerve innervates the diaphragm

What is the Brachial Plexus? (fig 16.9b) (which spinal nerves contribute to the plexus?) (what does the plexus innervate?) (what major nerves arise from the plexus?)

--Spinal nerves C5-T1 --Innervates: pectoral girdle and upper limbs --Musculocutaneous nerve -- Median nerve --Radial nerve --Ulnar nerve

What is the Sacral Plexus? (fig 16.11a) (which spinal nerves contribute to the plexus?) (what does the plexus innervate?) (what major nerves arise from the plexus?)

--Spinal nerves L4-S4 --Innervates: lower limb --Sciatic nerve **innervates all of lower limb except anterior/medial thigh **divides into the tibial and common fibular (peroneal) nerve

What are the components of a reflex arc?

--Stimulus activates receptor --Nerve impulse travels through sensory neuron to the CNS --information from nerve impulse is processed in the integration center by interneurons --motor neuron transmits nerve impulse to effector --effector responds to nerve impulse from motor neuron

What is a nerve plexus?

--a network of interweaving spinal nerves --split into multiple "named" nerves that innervate various body structures

What is shingles? (clinical view pg 492)

--a reactivation of childhood chicken pox infection

Which nerve might you have damaged if you have difficulty abducting your arm and experience anesthesia (lack of sensation) along the superolateral arm?

--axillary nerve

What is the benefit of having an intricate nerve plexus, rather than a single nerve that innervates a structure?

--damage to a single segment of the spinal cord or to a single spinal nerve generally does not result in complete loss of innervation to a particular muscle or region of skin

Why are dermatomes clinically important?

--dermatomes are clinically important because they can indicate potential damage to one or more spinal nerves ex: if a patient experiences anesthesia (w/out sensation) along the medial side of the arm and forearm, then spinal nerve C8 may be damaged

What causes shingles?

--during the initial infection the chicken pox virus will leave the skin and invades the posterior root ganglion --there it remains latent until adulthood --can become reactivated and proliferated --travels through the sensory axons to the dermatome **psychological stress or cold/flu or sunburn, can trigger development of shingles (usually in adults after 50)

Which nerve of the lumbar plexus might you have damaged if you have trouble extending your knee?

--femoral nerve

What is a polysynaptic reflex? (fig 16.13)

--have a more complex neural pathway --more than one synapse involving interneurons w/in the reflex arc (more delay between stimulus and response) --an example is the "withdrawal reflex" (for example when you step on something painful with your left foot, you lift it up but then the muscles contract in your right leg to maintain balance, that contraction of the extensor muscles in your right leg, to maintain balance, is the polysynaptic reflex)

What is a reflex arc?

--is the neural wiring of a single reflex **always begins at a receptor in the PNS, communicates w/ the CNS, and ends at a peripheral effector such as a muscle or gland cell

What are reflexes?

--rapid, automatic, involuntary reactions of muscles or glands to a stimulus **stimulus is require to initiate a response --reflex is a survival mechanism (allows us to respond, before brain fully processes whats happening) (ex: like removing your hand from something hot)

What are the symptoms of shingles?

--rash of scaly painful blisters (**fyi--usually accompanied by intense burning and pain, patients are contagious as long as they have blisters) --usually confined to one or a few adjacent dermatomes

What are dermatomes? (fig 16.6 pg 493)

--specific segment of skin supplied by a single pair of spinal nerves ** all spinal nerves except C1 innervate a segment of skin, so all nerves are associated w/ a dermatome--the skin is divided into sensory segments that make up a dermatome map

What is a monosynaptic reflex?

--the simplest of all reflexes --no interneurons **the sensory neurons synapse directly on the motor neurons whose axons project to the effector --interneurons are not involved in this process -- an example is the "stretch reflex" (patellar or knee jerk) --goes directly from the sensory receptor to the sensory neuron to the motor neuron to the effector

What are the 5 parts of a reflex arc? (fig 16.12 pg 509)

1--receptor 2--sensory (afferent) neuron 3-- interneurons 4--motor (efferent) neuron 5--effector