Ch. 14 PNS

Question 1

Peripheral nervous system (PNS)

Answer 1

Composed of nerves found outside the brain and spinal cord. The PNS can be divided into two subdivisions the sensory (afferent) and motor (efferent) divisions.

There are three major components to the PNS
Sensory receptors
Nerves
Motor endings

Question 2

Explain sensory receptors in the different types based on “ classification by stimulus detected”

Answer 2

Mechanoreceptors - respond to touch pressure vibration and stretch
Thermoreceptors - sensitive to changes in temperature
Photoreceptors - respond to light energy
Chemoreceptors - respond to chemicals (eg. smell taste, changes in blood chemistry)
***Chem detectors in the aorta and carotid artery sense in increased CO2 (low PH) and transmit this information to breathing centers of the brainstem
Nociceptors - sensitive to pain-causing stimuli or damage to tissues (eg. extreme heat or cold, excessive pressure, inflammatory chemicals)

Question 3

Explain sensory receptors and the different types based on “classification by location”

Answer 3

Exteroceptors
-respond to stimuli arising outside body
-receptors in skin for touch, pressure, pain, and temperature
-Most special sense organs (vision, hearing, taste and smell)
Interoceptors (visceroceptors)
-respond to stimuli arising in internal viscera and blood vessels
-sensitive to chemical changes, tissue stretch, and temperature changes
-Sometimes causes discomfort, but usually unaware of their workings
Proprioceptors
-respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue covering of bones and muscles
-inform brain of one’s movement, help with spatial orientation

Question 4

Explain sensory receptors and different types based on “classification by structural complexity”

Answer 4

Majority of sensory receptors in the PNS belong to the general senses (pressure stretch, vibration, temperature, pain, and muscle sense)
Most of the receptors are modified dendritic endings of sensory neurons
-these type of receptors are found throughout the body
-Receptors associated with general senses may be free or encapsulated
-the main difference between the two is that free nerve endings do not have complex sensory structures while the encapsulated nerve endings have either a brush border or fluid filled sacks at the end

Question 5

Describe the three levels of neural integration in the sensory system

Answer 5

Survival depends upon sensation and perception
-Sensation is the awareness of changes in the internal and external environment
-Perception is the conscious interpretation of those stimuli
There are three basic levels of neural integration and sensory systems
Receptor level -sensory receptor
Circuit level -processing in ascending pathways
Perceptual level -cortical sensory areas (cerebral cortex)

Question 6

Identify and describe the anatomical structure of a nerve ending

Answer 6

Question 7

Define ganglia and where they are located

Answer 7

• The PNS doesn’t just contain nerve fibers(axons)-there are also cell bodies of neurons found in the PNS collections of these nerve cell bodies are called ganglia
• ganglia are associated with both sensory and motor neurons
• ganglia associated with century nerve fiber contains cell bodies of sensory neurons
  (ex. Dorsal root ganglia-contains sensory neurons cell bodies; these are unipolar neurons- one process extends to receptors the other process extends to the spinal cord
  -ganglia associated with motor nerves contain autonomic motor neuron cell bodies
  (ex. Autonomic ganglia, which are associated with the visceral organs)
  * there are no somatic motor ganglia*

Question 8

Describe how nerves can be classified by the direction in which they carry impulses (what is the most common type?)

Answer 8

Sensory nerves-carry sensory input to the brain or spinal cold from the environment (afferent)
Motor nerves - Carrie motor impulses from the brain or spinal cord, muscle or glands (efferent)
Mixed nerves - have a combination of sensory and motor neurons in one nerve

***** most nerves are mixtures of motor and sensory fibers as well as somatic and autonomic (visceral) fibers

Question 9

Differentiate between the major types of peripheral nerves
Cranial vs Spinal

Answer 9

There are 12 pairs of cranial nerves
-to arise from the cerebrum (optic and olfactory) the rest from the brainstem
- Other than vagus nerves which extended into the abdomen, the other 10 cranial nerves, serve only head and neck structures
- Most are mixed nerves (that is they have both sensory and fiber) 2 pairs are purely sensory
- each numbered ( I - XII )

There are 31 pairs of spinal nerves
-Each are mixed nerves (Carry motor and sensory fibers or outgoing and incoming signals)
-Spinal nerves in all parts of the body except the head and part of the neck
-spinal nerves are named point of issue from the spinal cord

Question 10

Differentiate between the major types of peripheral nerves
somatic vs autonomic

Answer 10

Somatic nerves are those that innervate skeletal muscles, they are part of the voluntary or somatic nervous system

Autonomic are nerves that innervate the internal organs, glands, smooth and cardiac muscle, they are part of the involuntary or autonomic nervous system

Question 11

Differentiate between the major types of peripheral nerves
sensory vs. motor

Answer 11

sensory nerves carry sensory input to the brain or spinal cord from the environment

motor nerves carry motor impulses from the brain or spinal cord to muscles or glands

Question 12

explain how many pairs of cranial nerves there are

Answer 12

there are 12 pairs
10 from the brainstem
2 pairs (optic and olfactory) from cerebrum

Question 13

Describe in general where the cranial nerves go and what they innervate

Answer 13

in general, cranial nerves innervate the head and neck and are involved with activities that our there (sight, hearing, chewing, talking, swallowing etc. )

Question 14

what’s special about the vagus nerve

Answer 14

the vagus nerve is unique in that it’s motor fibers travel to the abdomen where they innervate with the heart, lungs, and abdominal viscera. Sensory fibers in the vagus nerve carry impulses from the thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

Question 15

How many pairs of spinal nerves

Answer 15

31

Question 16

how many spinal nerves are in each section of the spinal cord

Answer 16

8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Question 17

Identify and describe an anatomy of spinal nerves

Answer 17

Question 18

Explain the type of fibers carried in the ventral and dorsal roots and rami

Answer 18

Each spinal nerve arises from the spinal cord via two roots, the ventral root, and the dorsal root
* ventral roots- contains somatic motor fibers from ventral horn motor neurons and autonomic motor fibers from the lateral horn motor neurons
*** dorsal roots- contain sensory fibers from sensory neuron cell bodies located in the dorsal root ganglia. They are conducting impulses from peripheral receptors
- dorsal root (spinal) ganglia -cell bodies of sensory neurons….. these connect with neurons in the dorsal horn (or elsewhere in the spinal cord)
***rami- Carrie, both sensory and motor fibers
- dorsal and ventral rami and their main branches supply the entire somatic region of the body (skeletal muscle and skin) from the neck down
- the dorsal rami supply the posterior body trunk
- the ventral rami supply the rest of the trunk and limbs
- the rami communicants contain autonomic nerves that carry Vistro motor and sensor information to and from the visceral organs

Question 19

Peripheral motor endings and neuromuscular junction on skeletal muscle
Motor endings are PNS elements that activate effectors (skeletal, smooth or cardiac muscle and glands) by releasing neurotransmitters

Answer 19

• innervation of skeletal muscle takes place at the neuromuscular junction
  -neurotransmitter acetylcholine (ACh) released when nerve impulses reach axon terminal
• ACh binds to receptors resulting in
  * movement of Na+ and K+ across membrane
  *** depolarization of muscle cell
  *** an end plate, potential triggers, and action potential —-> muscle contraction

Question 20

Define what a reflex and reflex arc are

Answer 20

reflex: is an involuntary and nearly instantaneous movement in response toa stimulus.

reflex arc: is a neural pathway that allows the body to act on a stimulus before it reaches the brain

A reflex can be described as an automatic response to a stimulus that does not receive or need conscious thought

Question 21

The 4 characteristics of reflexes

Answer 21

1) reflexes require stimulation - they are not spontaneous action, but responses to sensory input
2) reflexes are quick - they involve few if any interneurons and minimum synaptic delay
3) reflexes are voluntary - they occur without intent and are difficult to suppress
4) reflexes are stereotyped - they occur essentially the same way every time

Question 22

Differentiate between monosynaptic and polysynaptic reflexes

Answer 22

monosynaptic reflex involves only one synapse between the afferent and efferent (incoming) and efferent (outgoing) neuron

polysynaptic reflex involves more than one synapse between the afferent and efferent neurons are connected by interneurons

Question 23

Briefly describe the components of a reflex arc

Answer 23

1. somatic receptor - skin muscles or tendons
2. Afferent nerve fiber - carries information from receptor to posterior horn of spinal cord or to the brainstem
3. Intergration center - point of synaptic contact between neurons in gray matter of spinal cord or brainstem (determines whether efferent neurons issue signal to muscles
4. Efferent nerve fiber - carries motor impulse to muscles
5. Effectors- the muscle that carries out the response

Question 24

Chemoreceptor

Answer 24

You are enjoying the taste of an ice cream cone
You smell a skunk on the drive-in into CNM

Question 25

Mechanoreceptor

Answer 25

Mechanoreceptors enable us to interact with our environment by providing critical information about physical forces acting on the body

Question 26

Nociceptor

Answer 26

You just scalded your hand from a hot coffee cup

Question 27

Photoreceptor

Answer 27

Retinas of your eyes are stimulated to “see”

Question 28

Thermoreceptor

Answer 28

You feel hot and sweaty after sitting for 20 minutes in an enclosed car in the summer

Question 29

Exteroceptors

Answer 29

Respond to stimuli arising outside the body
Receptors are in the skin for touch, pressure, pain and temperature. Also special sense organs vision, hearing taste and smell.

Question 30

Interoceptors

Answer 30

Respond to stimuli arising an initial viscera and blood vessels
Sensitive to chemical changes, tissue stretch, and temperature changes

Question 31

Proprioceptors

Answer 31

Respond to stretch and skeletal muscles, tendons joints, ligaments, and connective, tissue coverings of bones and muscles

Question 32

Types of fiber carried in the ventral roots

Answer 32

Carry motor fibers from ventral horn motor neurons. These fibers innervate, skeletal muscles

Question 33

Types of fibers carried in the dorsal roots

Answer 33

Contains sensory fibers from sensory neurons and dorsal root ganglia and conduct impulses from peripheral receptors

Question 34

Types of fibers in rami

Answer 34

Grammy Carrie mix sensory, and motor fibers. Fibers from both of ventral and dorsal roots are mixed within rami.