Lesson 13: PNS

Question 1

Define the peripheral nervous system and identify its components.

Answer 1

A portion of the nervous system consisting of nerves, ganglia, sensory receptors, and motor endings that lie outside of the brain and spinal cord.

Question 2

Identify and classify the sensory receptors.

Answer 2

Classification by stimulus:
-Mechanoreceptors: respond to touch, pressure, vibration, and stretch
-Thermoreceptors: sensitive to changes in temperature
-Nociceptors: sensitive to pain-causing stimuli(extreme heat or cold)
-Photoreceptors:respond to light energy(ex.retina)
-Chemoreceptors: respond to chemicals(ex. taste, smell, changes in blood chemistry)
-Exteroreceptors: respond to stimuli outside the body, receptors in skin for touch, pressure, pain, and temp
Classification by location:
-Interoreceptors: respond to stimuli arising in internal viscera and blood vessels
-Proprioceptors: respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles; informs brain fo one’s movements

Question 3

Describe the structure of a nerve.

Answer 3

A cord-like organ that consists of parallel bundles of peripheral axons enclosed by successive wrappings of connective tissue. Each axon is surrounded by endoneurium, nerve bundles or fascicles are surrounded by the perineurium, and the entire nerve is covered by the epineurium

Question 4

Identify the types of nerves classified by how they transmit impulses.

Answer 4

Mixed nerves: contain sensory and motor fibers and transmit impulses both to and from the CNS
Sensory(afferent) nerves: carry impulses only towards CNS
Motor(efferent) nerves: carry impulses only away CNS

Question 5

Define sensation, perception, referred pain, ganglion, plexus, dermatome.

Answer 5

Sensation: awareness of the stimulus
Perception: interpretation of the meaning of the stimulus
Referred pain: Pain felt at a site other than the area of origin
Ganglion: collections of neuron cell bodies in PNS
Plexus: a complex network of nerves
Dermatome: Portion of somite mesoderm that forms the dermis of the skin; also the area of skin innervated by the cutaneous branches of a single spinal nerve

Question 6

Name the 12 pairs of cranial nerves, identify their function name and number.

Answer 6

I: Olfactory-sensory: smell
II: Optic-sensory: vision
III: Oculomotor-motor: eye movement
IV: Trochlear-motor: eye movement
V: Trigeminal-both: touch/pain on face, chewing
VI: Abducens-motor: eye movement
VII: Facial-both: taste tongue; muscles facial expression
VIII: Vestibulocochlear-sensory: hearing and balance
IX: Glossopharyngeal-both: taste and swallowing
X: Vagus-both: regulate internal organ function
XI: Accessory-motor: muscles in head movement
XII: Hypoglossal-motor: muscles of the tongue(gag reflex)

Question 7

Identify the 31 pairs of spinal nerves and their names.

Answer 7

8 pairs of cervical nerves (C1–C8)

12 pairs of thoracic nerves (T1–T12)

5 pairs of lumbar nerves (L1–L5)

5 pairs of sacral nerves (S1–S5)

1 pair of tiny coccygeal nerves (Co1)

Question 8

Identify the major plexuses and describe the distribution and function of the nerves arising from each.

Answer 8

Cervical Plexus(C1-C5): transmit sensory impulses from the skin of the neck, the ear area, the back of the head, and the shoulder; phrenic nerve- innervates the diaphragm
Brachial Plexus(C5-T1): gives rise to virtually all the nerves that innervate the upper limb; axillary, radial, median, and ulnar nerve
Lumbar Plexus(L1-L4): Its proximal branches innervate parts of the abdominal wall muscles and the psoas muscle, but its major branches descend to innervate the anterior and medial thigh; femoral nerve
Sacral Plexus(L4-S4): innervates lower limbs, posterior thigh, leg, and feet; sciatic nerve: the thickest and longest nerve in the body. It supplies the entire lower limb, except the anteromedial thigh.