Peripheral Nervous System Part I Study Guide

Question 1

How is the peripheral nervous system essential to our survival?

Answer 1

Provides the links between our brains and the outside world
Consistent sensory inputs and motor outputs are essential to survival

Question 2

What anatomical structures make up the peripheral nervous system?

Answer 2

Sensory receptors, afferent nerves + efferent nerves and their associated ganglia, and motor endings

Question 3

What are sensory receptors specialized to do?

Answer 3

respond to changes in their environment

Question 4

What happens when a sensory receptor is activated?

Answer 4

results in graded potentials that trigger nerve impulses

Question 5

What happens when the generated nerve impulses reach the brain?

Answer 5

Once nerve impulses (sent along the afferent pns fibers to the cns) reach the brain, awareness of the stimulus (sensation) and interpretation of the meaning of the stimulus (perception) occurs in the brain

Question 6

What are the 5 TYPES of receptors we discussed in class? (Classification by stimulus type)

Answer 6

Mechanoreceptors
Thermoreceptors
Photoreceptors
Chemoreceptors
Nociceptors

Question 7

Mechanoreceptors

Answer 7

respond to mechanical forces such as touch, pressure, vibration, and stretch

Question 8

Thermoreceptors

Answer 8

respond to changes in temperature

Question 9

Photoreceptors

Answer 9

respond to light energy (ex-retina)

Question 10

Chemoreceptors

Answer 10

response to chemicals in solution (ex-smell, taste, changes in blood chemistry)

Question 11

Nociceptors

Answer 11

respond to pain-causing stimuli; these stimuli are potentially harmful (ex-extreme heat, cold, pressure, or inflammatory chemicals)

Question 12

exteroreceptor

Answer 12

• Classification by location
• Respond to stimuli arising outside the body

Question 13

location of exteroreceptor

Answer 13

the body’s surface
- ex. receptors in the skin for touch, pressure, pain, and temperature, and most receptors for the special sense (vision, hearing, equilibrium, smell, and taste)

Question 14

interoreceptor

Answer 14

• Classification by location
• Respond to internal stimuli such as from the internal viscera and blood vessels
• Respond to changes in stretch and body position - inform the brain of one’s movements

Question 15

location fo interoreceptors

Answer 15

Occur in skeletal muscles, tendons, joints, ligaments, and the connective tissue coverings of the bones and muscles

Question 16

2 structural classifications for receptors

Answer 16

• Simple receptors of the general senses
• Receptors of the special sense

Question 17

General sensory receptors are either _______________ or ________________

Answer 17

• nonencapsulated (free) nerve endings
• encapsulated nerve endings

Question 18

location of nonencapsulated nerve endings

Answer 18

Abundant in epithelial and connective tissues

Question 19

What type of fiber are nonencapsulated nerve endings made of

Answer 19

Most are nonmyelinated, small diameter, group C fiber; distal terminals have knoblike swellings

Question 20

what kinds of stimuli do nonencapsulated nerve endings typically respond to

Answer 20

mostly to temperature, pain, or light touch

Question 21

thermoreceptors

Answer 21

• Cold receptors are activated by temps from 50-104°F
• Located in the superficial dermis
• Average skin temperature is about 93°F
• Heat receptors are activated by temps from 89-118°F
• Located in the deeper dermis
• Outside of these temperature ranges, heat or cold trigger nociceptors and are interpreted as pain

Question 22

Nociceptors

Answer 22

pain receptors that respond to extreme temperatures, pinch, or the release of chemicals from damaged tissue

Question 23

Itch receptors

Answer 23

located in the dermis, activated by the chemical histamine

Question 24

Tactile (merkel) discs

Answer 24

lie at the junction of the epidermis and dermis; function as light touch receptors

Question 25

Hair follicle receptors

Answer 25

free nerve endings that wrap around hair follicles – act as light touch receptors that detect bending of the hairs

Question 26

What makes a nerve fiber “encapsulated”?

Answer 26

One or more fiber terminals of sensory neurons enclosed in connective tissue capsules

Question 27

Almost all encapsulated dendritic endings are ____________.

Answer 27

mechanoreceptors

Question 28

Tactile (Meissner’s) Corpuscles

Answer 28

small receptors involved in discriminative touch – found just below the epidermis, mostly in sensitive and hairless areas

Question 29

Lamellar (Pacinian) Corpuscles

Answer 29

large receptors that respond to 1st application of deep pressure and vibration – located deep in the dermis and subcutaneous tissue

Question 30

Bulbous Corpuscles (Ruffini Endings)

Answer 30

a spray of nerve endings, respond to deep and continuous pressure – located in the dermis, subcutaneous tissue, and joint capsules

Question 31

Muscle Spindles

Answer 31

spindle-shaped proprioceptors that respond to muscle stretch; found in the perimysium; initiate the stretch reflex

Question 32

Tendon Organ

Answer 32

proprioceptors located in tendons; detect stretch; initiate the stretch/relax reflex

Question 33

Joint Kinesthetic Receptors

Answer 33

proprioceptors that monitor stretch in the articular capsules; provide information on joint position and motion

Question 34

nerve

Answer 34

Cordlike organ of the pns – a bundle of myelinated and nonmyelinated peripheral axons enclosed by connective tissue

Question 35

2 types of nerves

Answer 35

cranial and spinal

Question 36

connective tissue coverings for the different layers of the nerve

Answer 36

Endoneurium Perineurium Epineurium

Question 37

Endoneurium

Answer 37

loose connective tissue that encloses individual axons + their myelin sheaths

Question 38

Perineurium

Answer 38

coarse connective tissue that bundles fibers into fascicles

Question 39

Epineurium

Answer 39

tough, fibrous sheath that encloses all fascicles and blood + lymphatic vessels to form a nerve

Question 40

Most nerves contain a mixture of what 4 things?

Answer 40

- Afferent + Efferent fibers - Somatic + Autonomic (visceral) fibers

Question 41

Mixed Nerves

Answer 41

contain both sensory and motor fibers – impulses travel both to and from the CNS

Question 42

Sensory (Afferent) Nerves

Answer 42

impulses only move toward the CNS

Question 43

Motor (Efferent) Nerves

Answer 43

impulses only move away from the CNS

Question 44

Are sensory nerves efferent or afferent? What about motor nerves?

Answer 44

- Sensory nerves are afferent - Motor nerves are efferent

Question 45

What happens if damage to a neuron is close to the cell body

Answer 45

the whole neuron may die – other neurons typically stimulated by its axons may also die

Question 46

what if there is damage is further from the cell body?

Answer 46

axons in the pns can regenerate – axons in the cns cannot regenerate

Question 47

Compare/contrast nerve regeneration in the central and peripheral nervous systems. Which system has more regeneration capacity? Be sure to understand the respective roles played by oligodendrocytes and Schwann cells.

Answer 47

- Pns has more regenerative capacity – axons of the cns do not regenerate - Oligodendrocytes of the cns bear growth inhibiting proteins that prevent cns fiber regeneration - Schwann cells are stimulated to divide in order to regenerate axons of the pns very slowly

Question 48

wallerian degeneration

Answer 48

Pns only – axon fragments and myelin sheaths distal to the injury degenerate

Question 49

peripheral motor ending

Answer 49

Pns elements that activate effectors by releasing neurotransmitters

Question 50

examples of effectors activated by the PNS

Answer 50

skeletal muscles (neuromuscular junction), visceral muscles, and glands

Question 51

3 levels of motor control in the PNS

Answer 51

Segmental level Projection level Precommand level

Question 52

movements are controlled by the segmental level

Answer 52

Reflexes and automatic movements

Question 53

CPGs

Answer 53

circuits that control locomotion and specific, often repeated motor activities

Question 54

What happens at the projection level of control? Reminder this is your middle manager role!

Answer 54

- Projection level consists of neurons acting through direct and indirect motor pathways - Upper motor neurons of the motor cortex initiate direct (pyramidal) pathways to produce voluntary skeletal muscle movements - Brain stem motor nuclei oversee indirect (extrapyramidal) pathways to control and modify reflex and CPG-controlled motor areas - Projection motor pathways send information to lower motor neurons and keep the higher command levels informed

Question 55

2 anatomical areas are responsible for the precommand level of control

Answer 55

Cerebellum Basal nuclei

Question 56

List the specific functions of the precommand level of control.

Answer 56

- Regulating motor activity - Precisely start and stop movements - Coordinating movements with posture - Blocking unwanted movements - Monitoring muscle tone - Performing unconscious planning and discharge in advance of willed movements

Question 57

Inborn (Intrinsic) Reflex

Answer 57

rapid, involuntary, predictable motor response to a stimulus - Regulated by the subconscious lower regions of the CNS – the brain stem and spinal cord - Ex: maintain posture, control visceral activities - Inborn reflexes are unlearned, but they can be modified by learning and conscious effort - ex. When we are holding something hot but instead of dropping it we burn ourselves and put the hot thing down in a safe place (like food)

Question 58

Learned (Acquired) Reflex

Answer 58

results from practice and repetition Ex: driving a car

Question 59

effectors in a somatic reflex

Answer 59

skeletal muscles

Question 60

effectors in a autonomic reflex

Answer 60

visceral effectors (smooth/cardiac muscles, glands)