Chapter 13 - The PNS and Reflex Activity

Question 1

Sensory Receptors

Answer 1

Specialized to respond to changes in their environment (stimuli)
A. Function – respond to stimuli, when stimulated they trigger nerve impulses along the afferent PNS fibers though the CNS

Question 2

Sensory Receptors: Classification - Activating Stimulus

Answer 2

a. Mechanoreceptors – respond to mechanical forces (touch, pressure, vibrations and stretch)
b. Thermoreceptors – sensitive to temperature changes
c. Photoreceptors – respond to light found in the retina
d. Chemoreceptors – responds to chemicals in solutions (nose and mouth) nose – smell; mouth – taste. Also respond to changes in blood or interstitial changes
e. Nociceptors – respond to damaging stimuli that results in pain (burn, excessive pressure, and tissue damage)

Question 3

Sensory Receptors: Classification - Location

Answer 3

a. Exteroreceptors – sensitive to stimuli from the outside of the body or near the body surface (touch, pressure, pain and temperature; skin and special senses)
b. Interoreceptors – aka viscera receptors, respond to stimuli within the body (blood vessels)
c. Proprioceptors – responds to internal stimuli in skeletal muscles, tendons, joints, ligaments and connective tissue

Question 4

Sensory Receptors: Classification - Receptor Structure - Unencapsulated Dendritic Endings

Answer 4

A. Free nerve endings – are present nearly everywhere in the body and they’re abundant in epithelia and connective tissue; most are unmilinated, with a small diameter, C fibers, with small knob like distal endings
B. Merkel discs – found in basal layer of epidermis, they’re free nerve endings associated with enlarged disc shape epidermal cells, function as light touch receptors
C. Hair follicle receptors – free nerve endings that wrap around hair follicles, light touch receptors that detect the bending of hair

Question 5

Sensory Receptors: Classification - Receptor Structure - Encapsulated Dendritic Endings

Answer 5

Encapsulated dendritic endings – endings consist of 1 or more fiber terminals of sensory neurons with are enclosed in a connective tissue capsule
A. Meissner’s corpuscles – tactile corpuscles, small receptors in which a few spiraling sensory terminals are surround by Schwann cells and then by a thin egg shaped connective tissue capsule. They’re found beneath the epidermis (dermal papa lay); found in numerous in sensitive and hairless skin (nipples, finger tips and soles of feet)
B. Pacinian corpuscles – lamellated corpuscles – found deep in the dermis and in subcutaneous tissue under the skin; they respond only to pressure is first applied (vibrations); the dendrite is covered by a capsule of about 60 layers of collagen fibers and cells
C. Ruffini endings – bulbous corpuscles; found in the dermis, in subcutaneous tissue and in joint capsules. They’re receptor endings are enclosed by a flattened capsule, they respond to deep continues pressure
D. Muscle spindles, Golgi tendon organs, and joint kinesthetic receptors

Question 6

Sensory Receptors: Classification - Receptor Structure - Simple and Complex

Answer 6

a. Simple receptors – mortified dendritic endings of sensory neurons; found throughout the body, these types of receptors monitor most types of general information
b. Complex receptors – receptors for the special senses, which are housed in complex organs (ears, eyes, tongue) collection of specialized cells

Question 7

Nerves: General Structure

Answer 7

1. Nerves
   a. Epineurium – tough fibrous sheath that encloses all the fascicules of the nerve to from the nerve
2. Fascicles
   a. Perineurium –connective tissue wrapping that binds fibers or axons into bundles or fascicles
3. Axons
   a. Endoneurium – delicate layer of connective tissue that encloses the axon and its associated myelin and it surrounds each axon within a nerve

Question 8

Nerves: General Classification

Answer 8

1. Sensory nerves/ afferent nerves – nerves that carry impulse only TOWARDS the CNS
2. Motor nerves/ efferent nerves – nerves that carry impulses only AWAY from the CNS
3. Mixed nerves – contains both sensory and motor fibers and they transmit impulses both to and from CNS

Question 9

CN I - Olfactory

Answer 9

a. Location – found on the cribiform plate on the ethmoid bone
b. Function – sensory nerve that carries smell impulses

Question 10

CN II - Optic

Answer 10

a. Location – optic nerve to thalamus (optic tract – optic chiasma)
b. Function – sensory nerve that carries vision impulses

Question 11

CN III - Oculmotor

Answer 11

a. Location - LR6SO4R3
b. Function – motor nerve – supplies nervous supply to the extrinsic eye muscles (outside) (4 – inferior oblique muscle, superior rectus muscle, inferior rectus muscle, medial rectus muscle

Question 12

CN IV - Trochlear

Answer 12

a. Location - LR6SO4R3

b. Function – motor nerve – supplies motor function to the superior oblique muscle (in the eye)

Question 13

CN V - Trigeminal

Answer 13

a. Location - LR6SO4R3
b. Function – branches into 3; V1 – ophthalmic nerve, V2 – maxillary nerve, V3 – mandibular nerve – anterior 2/3rds of the tongue for normal sensory. Major sensory nerve of the face both sensory and motor – provides motor to the chewing muscles

Question 14

CN VI - Abducens

Answer 14

a. Location - LR6SO4R3

b. Function – motor – innervating the lateral rectus muscle

Question 15

CN VII - Facial

Answer 15

a. Location
b. Function – both sensory and motor; chief motor nerve to the muscles of the face. Sensory – provides innervations to the taste buds to the anterior 2/3rd of the tongue, this nerve branches off into 5. VII1 – temporal VII2 - zygomatic VII3 – buccal VII 4 – mandibular VII5 – cervical

Question 16

CN VIII - Vestibulocochlear

Answer 16

a. Location

b. Function – purely sensory, provides sensation to the vestibular apparatus (vestibulual and cholea) ear

Question 17

CN IX - Glossopharyngeal

Answer 17

a. Location
b. Function – both sensory and motor. Motor – some muscles to the tongue and pharynx; sensory – to the taste buds of the posterior 1/3rd of the tongue and also to the posterior part of the tongue

Question 18

CN X - Vagus

Answer 18

a. Location

b. Function – both motor and sensory to visceral organs

Question 19

CN XI - Accessory

Answer 19

a. Location

b. Function – motor nerve, trapezius and sternoclidomastiod

Question 20

CN XII - Hypoglossal

Answer 20

a. Location

b. Function – motor for the tongue

Question 21

Spinal Nerves: Regions

Answer 21

a. Cervical nerves C1-C8 though C7exit the superior canal though which their named. C8 – exits inferior C7
b. Thoracic nerves T1-T12
c. Lumbar nerves – L1-L5
d. Sacral nerves – S1- S5
e. Coccygeal nerve – C0

Question 22

Spinal Nerves: General Structure

Answer 22

a. Dorsal roots – found on both sides, contains sensory fibers that arise from sensory neurons in the dorsal root ganglia and they conduct impulses from peripheral receptors to the spinal cord
b. Ventral roots – contain motor fibers which arise from ventral horn motor neurons and they extend skeletal muscles
c. Rootlets – give rise to the roots regardless of ventral or dorsal and they attach along the length of the corresponding spinal cord segment
d. Dorsal ramus – found on the posterior side, very short; it’s a small division of the spinal nerve almost immediately after emerging from its foreman
e. Ventral ramus – larger division found more ventrally located;
f. Rami commnicantes – found joining the bases of ventral rami
g. Nerve plexuses – complicated interlacing of the ventral rami of spinal nerves except T2-T12 join lateral to the vertebral column

Question 23

Spinal Nerves: Innervation of the Back

Answer 23

Done via the dorsal rami and it follows a neat segmented plan and the nerves innervate in line with their emergence point with the spinal column

Question 24

Spinal Nerves: Innervation of the Thorax

Answer 24

a. Intercostal nerves – ventral rami from T1-T12 which coarse anteriorly deep to each rib in the costal groove, they supply the intercostals muscles. Also muscles and skin of the anterior lateral region of the thorax and abdomen

Question 25

Spinal Nerves: Cervical Plexus

Answer 25

a. Location – deep in the neck buried under the sternoclidomastiod; formed by the ventral rami of the first 4 cervical nerves
b. Phrenic nerve – 1 nerve, most important nerve from this plexus – C3-5 keeps diaphragm alive

Question 26

Spinal Nerves: Brachial Plexus

Answer 26

a. Location – formed by the ventral rami C5-C8 and T1; gives rise to the nerves that innervate the upper limbs. RTDCB – roots, trunks, division, cords, branches. It’s large and situated partially in the neck and in the axilla
b. Axillary nerve – branches off of the posterior cord to the surgical neck
c. Musculocutaneous nerve – major end branch of the lateral cord; it coarse inferiorly in the anterior arm and it supplies motor fibers of the biceps and brachialii muscles. Distal to the elbow it provides coetaneous sensation to the lateral forearm
d. Median nerve – descends though the arm to the anterior forearm; it branches to supply the skin and the flexor muscles, it supplies the 5 intrinsic muscles of the palm, the pronator muscles and helps with the flexion of the wrist and finger and the muscles that oppose the thumb.
e. Ulnar nerve – branches off the medial cord and it descends along the medial aspect of the arm towards the elbow, once it reaches the elbow it swings behind the medial epicondyle then it follows the ulna around the medial forearm (funny bone)
f. Radial nerve – largest, it’s a continuation of the posterior cord, it raps around the radial groove. It’s runs anterior around the lateral epicondyle and gives off 2 branches

Question 27

Spinal Nerves: Lumbar Plexus

Answer 27

a. Location – arises from spinal nerves L1-L4, it’s found lying within the soas major muscle
b. Femoral nerve – largest terminal of the lumbar plexus
c. Obturator nerve – enters the medial thigh via obturator foreman, it activates adductor muscles

Question 28

Spinal Nerves: Sacral Plexus

Answer 28

a. Location – arise from spinal nerves L4-S4 – it lies immediately inferior to the lumbar plexus
b. Sciatic nerve – largest, thickest and longest nerve in the body. It supplies the entire lower limb except the anterior medial thigh
c. Tibial nerve – coarse posterior to the knee joint
d. Common fibular nerve – aka common peroneal nerve – descends from its origin and it wraps around the neck of the fibula and it divides itself into the superficial and deep branches

Question 29

Motor Endings

Answer 29

A. Neuromuscular junctions – junction where the terminals of the somatic motor fibers innervate voluntary muscles and effecter cells
B. Innervation of cardiac muscle, smooth muscle, and glands – under automatic control and is much simpler to the junctions than the skeletal muscles