Peripheral Nervous System

Question 1

What are exteroceptive endings and where are they located?

Answer 1

Sensory receptors that serves to acquaint the individual with their environment. They respond to stimuli of pain, temperature, touch and pressure

Located superficially such as the skin

Question 2

What are proprioceptove endings and where are they located?

Answer 2

Sensory endings providing information concerning movement and position of parts of the body (reflex adjustments)

Located in muscles, tendon, joints.

Question 3

Where are signals from the exteroceptors and proprioceptors conducted?

Answer 3

Conducted centrally by the primary sensory neurons, whose cell bodies are located in the spinal ganglia, which are located on the dorsal roots.

Question 4

What are interoceptors?

Answer 4

Sensory end organs within the viscera

Question 5

What are the two broad categories of sensory endings and afferent neurons?

Answer 5

1. Somatic afferent - skin, bones, muscles, and connective tissue that makes up most of the mass in the body
2. Visceral afferent - internal organs of the circulatory, respiratory, alimentary, excretory, and reproductive systems.

Question 6

What are the two categories of efferent neurons?

Answer 6

1. Somatic (motor) efferent - are in the ventral gray horns of the spinal cord and motor nuclei of cranial nerves.
2. Visceral efferent (autonomic system) - participate in the transmission from the CNS to smooth muscle, cardiac muscle or secretory cells.

Question 7

On a structural basis, what are the two classes of cutaneous and other sensory endings recognised?

Answer 7

1. Nonencapsulated endings - are terminal branches of the axon that may either be closely applied to cells or lie freely in the extracellular spaces of connective tissue
2. Encapsulated endings - have distinctive arrangements of non neuronal cells that completely enclose the terminal parts of the axons.

Question 8

Define glabrous skin

Answer 8

Lacks hair

Question 9

What are the three plexus in the skin?

Answer 9

1. Subcutaneous plexus - lies in the loose connective tissue deep to the skin
2. Dermal plexus - within the densely collagenous reticular layer that constitutes the deeper part of the dermis
3. Papillary plexus - lies in the papillary layer of the dermis immediately beneath the epidermis.

Question 10

What are free nerve endings and provide three structural/functional facts

Answer 10

Free nerve endings occur in subcutaneous tissue and dermis , and some extend among the cells of the epidermis.

1. Axons are always invested in Schwann cells and do not contact the extracellular fluid directly.
2. It is impossible to identify the exact point of termination of an axon within the skin.
3. The existence of free nerve endings is inferred from the the functional sensitivity of regions of skin in which no other types of sensory ending can be recognised.

Question 11

What are Merkel cells and where are Merkel endings located?

Answer 11

Merkel cells are a small cell that differs from the other epidermal cells in having an indented nucleus and electron-dense cytoplasmic granules.

Merkel cells and endings are found in the terminal layer (stratum basale) of the epidermis. More specifically in glabrous skin and in the outer root sheaths of hairs.

Question 12

Describe peritrichial nerve endings

Answer 12

• cavelike formations of axons that surround hair follicles
• each follicle is supplied by 2 to 20 axons
• axons attach to sebaceous gland and branch in the connective tissue outside of the outer root sheath.
• some branches encircle follicle, others run parallel to its axis, and some end on Merkel cells in the outer root sheath.

Question 13

What encapsulated endings are contained in the skin?

Answer 13

1. Ruffini ending
2. Pacinian corpuscle
3. Meissner’s tactile corpuscle
4. End bulbs

Question 14

What are Ruffini endings?

Answer 14

An encapsulated ending that is an array of terminal branches of a myelinated axon surrounded by capsular cells.

Typically 1mm long and 20-30um wide

Found in the subcutaneous tissue and dermis of both hairy and glabrous skin.

Question 15

What are Pacinian corpuscles?

Answer 15

An encapsulated ending that consists of a single axon that loses its myelin sheath and is encapsulated by several layers of flattened cells with greatly attenuated cytoplasm

Ellipsoidal corpuscles that are bout 1mm long and 0.7mm wide.

Found in the subcutaneous tissue and dermis of both hairy and glabrous skin

Question 16

What are Meissner’s tactile corpuscles and where are they located?

Answer 16

An encapsulated ending that is supplied by three or four myelinated axons whose terminal branches form a complicated knot that is enclosed in a cellular and collagenous capsule.

80 microns x 30 microns in size and are oriented with their long axes perpendicular to the skins surface

Occur in large numbers in the dermal papillary ridges of the fingertips and are less abundant in other hairless regions.

Question 17

What are end bulbs and where are they located?

Answer 17

An encapsulated ending that are commonly spherical (approx 50 microns in length) with each containing a coiled, branching axons, terminal in a thin cellular capsule.

Occur in mucous membranes (mouth, conjunctiva, anal canal) and in the dermis of glabrous skin close to orifices (lips and external genitalia)

Question 18

Define modalities and state the recognised five in clinical examination

Answer 18

Modalities - the types of sensation consciously perceived from the skin

1. Fine (discriminative) touch
2. Vibration
3. Light touch
4. Temperature
5. Pain

Question 19

What is an important physiology property of any receptor?

Answer 19

Adaptation- reduced response to continued stimulation.

Question 20

Explain the difference between a slow and rapid adapting receptor

Answer 20

A slowly adapting receptor reports continuously on the stimulus that activates it

A rapidly adapting receptor reports changes in the stimuli it receives.

Example - Meissner’s corpuscles are sensitive to mechanical deformation, and they report rapidly (they do not continue to respond to sustained stimuli)