A&P Chp. 13: The Peripheral Nervous System and Reflex Activity

Question 1

Modality

Answer 1

Mode
Each input is a specific type of sensation
Individual sensory neurons generally carry only one modality

Question 2

Selectivity of Receptors

Answer 2

Sensory neurons respond strongly to one type of stimulus and weakly or not at all to other types
Some respond accidentally to other types of stimuli: rubbing your eye mechanically stimulates the eyes’ light receptors in the retina

Question 3

Stimulation

Answer 3

1st Component of Sensation

Stimulus or change in the environment

Question 4

Transduction

Answer 4

2nd Component of Sensation
Requires a sensory receptor cell or organd which responds to specific stimuli and converts them into receptor/generator potentials

Question 5

Impulse generation and conduction

Answer 5

3rd Component of Sensation
If a receptor/generator potential (graded potential) reaches a threshold, then the neuron’s action potential will be send to the CNS

Question 6

Integration

Answer 6

4th Component of Sensation
Some region of the CNS must receive and translate nerve impulses into sensations and perceptions
Generally occurs in the cerebral cortex

Question 7

Mechanoreceptors

Answer 7

type of sensory receptor classification
classification by the type of stimulus
mechanical pressure or stretching
generate action potentials when deformed

Question 8

Thermoreceptors

Answer 8

type of sensory receptor classification
classification by the type of stimulus
changes in temperature

Question 9

Nociceptors

Answer 9

type of sensory receptor classification
classification by the type of stimulus
pain due to physical or chemical damage to nearby tissue

Question 10

Photoreceptors

Answer 10

type of sensory receptor classification
classification by the type of stimulus
light strikes retinal receptor cells
generates action potentials in response to light energy

Question 11

Chemoreceptors

Answer 11

type of sensory receptor classification
classification by the type of stimulus
certain specific chemical molecules are detected in the mucous fluids of the GI & respiratory tracts or in the blood or other body fluids

Question 12

Exteroceptors

Answer 12

type of sensory receptor classification
classification by location
located at or near the body’s surface
provide information about the external environment

Question 13

Interoceptors (visceroceptors)

Answer 13

type of sensory receptor classification
classification by location
found in blood vessels, connective tissues, and organs
provide information about the internal environment

Question 14

Proprioceptors

Answer 14

type of sensory receptor classification
classification by location
located in muscles, tendons, joints and the internal ear
provide information about gravity, body and limb positions and skeletal muscle movements

Question 15

Sensory Receptor Classification

Answer 15

1. by the type of stimulus

2. by location

Question 16

Adaptation by Sensory Receptors

Answer 16

A change in sensitivity to a long-lasting stimulus
Primarily by rapidly-adapting phasic receptors
1. pressure, touch, hearing, smell
2. adapt very quickly, respond less if the stimulus remains constant
3. allows us to shut out background “noise”
Little adaptation by slowly adapting tonic receptors
1. pain, body position, chemicals in the blood of CSF
2. adapt slowly, continue to respond even when the stimulus remains constant
3. continuous input is useful for some modalities because the body needs to make continuous responses to that kind of information

Question 17

Anesthesia

Answer 17

Partial or complete loss of sensation

Question 18

General Anesthesia

Answer 18

gas agents act in the CNS through poorly understood mechanisms

Question 19

Local Anesthesia

Answer 19

drugs injected near peripheral nerves inhibit the opening of gated sodium channels, preventing local transmission of action potentials

Question 20

Analgesia

Answer 20

reduced perception of pain without loss of other sensory information or loss of consciousness: biochemical interference with local stimulus (NSAIDs) or mimic endogenous endorphins in CNS (opiates)

Question 21

Paresthesias

Answer 21

abnormal sensations (burning, tingling, numbness) not related to normal stimulation
mechanical pressure on nerves in your legs puts your foot to sleep

Question 22

Mixed Nerve

Answer 22

Functional Type of Nerve

contains both sensory and motor nerves

Question 23

Motor (efferent) nerves

Answer 23

Functional Type of Nerve
also carry proprioceptive sensory signals back to the CNS from the skeletal muscles, joints, and tendons being served by that nerve

Question 24

Sensory (afferent) nerves

Answer 24

Functional Types of Nerves

Question 25

Anatomy of Nerves

Answer 25

Bundles/fasicles of axons and dendrites Endoneurium: around individual processes Perineurium: around fasicles/ individual nerve fibers with their endoneurium Epineurium: outermost covering around entire peripheral nerve

Question 26

Cranial Nerves

Answer 26

12 pairs of nerves which originate from the brain and exit through foramina of the skull First 2 pairs originate from the forebrain (olefactory, optic) Remainaing 10 pairs originate from the brain stem OhOhOhToTouchAndFeelVeryGreenVegatablesAH

Question 27

Cranial Nerve I

Answer 27

Olfactory Passes through the cribriform plate of the ethmoid bone Purely sensory Carries afferent impulses associated with sense of smell

Question 28

Cranial Nerve II

Answer 28

Optic Arises from the retina of the eye and passes through the optic canals and converge at the optic chiasm Purely sensory Carries afferent impulses associated with vision

Question 29

Cranial Nerve III

Answer 29

Oculomotor Fibers extedn from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles Primarily motor Somatic motor fibers to inferior oblique and superior, inferior, and medial rectus muscles, which direct eyeball, and to levator palpebrae muscles of the superior eyelid Parasympathetic fibers to iris and smooth muscle controlling lens shape (reflex responses to varying light intensity and focusing of eye for near vision)

Question 30

Cranial Nerve IV

Answer 30

Trochlear Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle Primarily motor Provides somatic motor fibers to superior oblique muscle that moves the eyeball

Question 31

Cranial Nerve V

Answer 31

Trigeminal Composed of three divisions: ophthalmic, maxillary, and mandibular Runs from face to pons via the superior orbital fissure, the foramen rotundum and the foramen ovale Mixed: major sensory nerve of face; conducts sensory impulses from skin of face and anterior scalp, from mucosae of mouth and nose, and from surface of eyes; mandibular division also contains motor fibers that innervate muscles of mastication and muscles of floor of mouth

Question 32

Cranial Nerve VI

Answer 32

Abducens Fibers leave the inferior pons and enter the orbit via the superior orbital fissure Carries somatic motor fibers to lateral rectus muscle that moves the eyeball

Question 33

Cranial Nerve VII

Answer 33

Facial Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face Mixed: supplies somatic motor fibers to muscles of facial expression and parasympathetic motor fibers to lacrimal and salivary glands; carries sensory fibers from taste of receptors of anterior portion of tongue

Question 34

Cranial Nerve VII

Answer 34

Vestibulocochlear Two divisions: cochlear (hearing) and vestibular (balance) Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border Purely sensory: vestibular branch transmits impulses associated with sense of equilibrium from vestibular apparatus and semicircular canals; cochlear branch transmits impulses associated with hearing from cochlea

Question 35

Cranial Nerve IX

Answer 35

Glossopharyngeal Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat Mixed: somatic motor fibers serve pharyngeal muscles, and parasympathetic motor fibers serve salivary glands; sensory fibers carry impulses from pharynx, tonsils, posterior tongue (taste buds), and from chemoreceptors and pressure receptors of carotid artery

Question 36

Cranial Nerve X

Answer 36

Vagus The only cranial nerve that extends beyond the head and neck Fibers emerge from the medulla via the jugular foramen Most important: only cranial nerve that extends down into the body to abdomen Mixed: fibers carry somatic motor impulses to pharynx and larynx and sensory fibers from same structures; very large portion is composed of parasympathetic motor fibers, which supply heart and smooth muscles of abdominal visceral organs; transmits sensory impulses from viscera

Question 37

Cranial Nerve XI

Answer 37

Accessory Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord Mixed (but primarily motor in function) Provides somatic motor fibers to sternocleidomastoid and trapezius muscles and to muscles of soft palate, pharynx, and larynx (spinal and medullary fibers respectively)

Question 38

Cranial Nerve XII

Answer 38

Hypoglossal Fibers arise from the medulla and exit the skull via the hypoglossal canal Mixed (but primarily motor in function) Carries somatic motor fibers to muscles of tongue.

Question 39

Spinal Nerves

Answer 39

31 pairs of spinal nerves originate in the spinal cord all are mixed nerves thousands of fibers per spinal nerve Each pair serves a particular region of the body Each pair also provides some service to the region supplied by the spinal nerve above it and the spinal nerve below it (redundancy)

Question 40

Dorsal Ramus

Answer 40

Spinal Nerve | Supplies posterior body trunk

Question 41

Ventral Ramus

Answer 41

Spinal Nerve | Supples the rest of the body trunk and the limbs

Question 42

Mningeal branch

Answer 42

spinal nerve | supplies the meninges and blood vessels within meninges

Question 43

Dermatones

Answer 43

Areas of the skin innervated by the cutaneous branches of each pair of spinal nerves Each pair also provides some service to the region of the spinal nerve above and the spinal nerve below (redundancy)

Question 44

Reflex

Answer 44

rapid, predictable, automatic response to a stimulus | involved in homeostasis

Question 45

Inborn Reflex

Answer 45

unlearned, unpremeditated, and involuntary

Question 46

Two Fundamental Types of Reflexes

Answer 46

1. Somatic Reflexes: produce contraction of skeletal muscle One is conscious of somatic reflexes only after they occur Politely informed you are touching a hot stove 2. Autonomic (visceral) reflexes: generally they are not perceived consciously Produce responses by smooth muscle, cardiac muscle, glands to adjust conditions of the internal environment

Question 47

Components of a Reflex Arc

Answer 47

1. Receptor: dendrites or other sensory structures respond to changes in the environment 2. Sensory Neuron: conducts an impulse from a receptor to its axon terminals 3. Integrating center (some region within the CNS) simple: monosynaptic (2 cells only: sensory and motor neurons) complex: polysynaptic (> 2 cells: interneurons involved) 4. Motor Neuron: impulses from integrating center to an effector 5. Effector: body part (muscle or gland) which responds to the motor nerve impulse

Question 48

Spinal Reflexes

Answer 48

1. Receptors: muscle spindles and Golgi tendon organs Sensory mechanorecptors which respond to stretching Increased tension (stretching) stimulates the receptors Sends proprioceptive inputs to spinal cord 2. Contraction of the skeletal muscle reduces tension on the muscle spindle Lowers the rate of action potential generation Decreases input to the spinal cord and higher centers: cortex and cerebellum

Question 49

Stretch Reflexes

Answer 49

If a muscle is being stretched, the strech is caused by the contraction of its antagonist This sensory proprioception information contributes to maintaining proper muscle tone

Question 50

Patellar Reflex

Answer 50

Monosynaptic Ipsilateral (same side) Segmental (at one level of the spinal cord) Polysynaptic component: for reciprocal inhibition of the antagonist

Question 51

Golgi (deep) tendon reflex

Answer 51

An increase in muscle tension activates receptors (Golgi tendon organ) in the tendon The muscle relaxes and lengthens in response to its agonist's contraction D-T reflex inhibits the agonist D-T reflex excites antagonist Helps to regulate a smooth start and stop for a contraction Input from the Golgi tendon organs are sent to the cerebellum and the cortex Polysynaptic, ipsilateral, and segmental

Question 52

Flexor Reflex

Answer 52

A pull on the limb, extending it, will trigger the reflex Also, a painful stimulus: a burn, pin, prick, toe stub, etc. F-R causes an automatic withdrawal from the (dangerous) stimulus Polysynaptic, ipsilateral, and segmental

Question 53

Crossed Extensor Reflex

Answer 53

Flexion of a body part is often balanced by extension of the same body part on the opposite side of the body Polysynaptic, contralateral, segmental