CHAPTER THIRTEEN: PERIPHERAL NERVOUS SYSTEM

Question 1

CLASSIFY SENSORY RECEPTORS ACCORDING TO STIMULUS TYPE, LOCATION, AND RECEPTOR STRUCTURE

Answer 1

→ stimulus type:
Mechanoreceptors (respond to pressure, vibrations, stretch, etc)
Thermoreceptors (respond to changes in temperature)
Photoreceptors (respond to light)
Chemoreceptors (responds to chemical changes like smell and taste)
Nociceptors (respond to pain)

→ location
Exteroceptor (responds to outside stimuli)
Interoceptor (also known as visceroceptors, respond to internal stimuli)
Proprioceptor (detect stretch in skeletal muscles and alert brain of movement)

→ receptor structure
General senses: located throughout the body and can detect multiple stimuli
Special senses: detect only within special senses and are located in special sense organs

Receptors can either be nonencapsulated (located all around body and detect pain, temp and touch), or encapsulated (are all basically mechanoreceptors that can also detect pain, temp and touch)

Question 2

BRIEFLY DESCRIBE THE THREE LEVELS OF SENSORY INTEGRATION

Answer 2

1. Receptor level: detects stimulus and sends electrical impulse to the central nervous system. Transduction: electrical signal converted into a graded potential or receptor potential (special senses)
2. Circuit level: is the ascending pathway, 1st order neuron either goes to 2nd order neuron or spinal reflexes.
3. Perceptual level: integration of sensory information depends on the target neurons in the somatosensory cortex.

Question 3

LIST SEVERAL STIMULI THAT ACTIVATE NOCICEPTORS, BRIEFLY DESCRIBE PATHWAYS THAT CARRY SHARP AND BURNING PAIN, AND DESCRIBE THE ROLE OF ENDOGENOUS OPIOIDS IN PAIN SUPPRESSION.

Answer 3

→ stimuli: extreme pressure, temperature, k+, atp, acids, and more
→ sharp pain: is carried from nociceptor onto small myelinated neurons
→ burning pain: is carried from nociceptor on small unmyelinated neurons
Both are carried on 2md order neurons that go to the brain via the spinothalamic tract
→ endogenous opioids: are inhibitory and block pain impulses from nociceptors.

Question 4

DESCRIBE THE GENERAL STRUCTURE OF A NERVE

Answer 4

→ epineurium: covers the entire nerve
→ perineurium: bundles nerve fibers into fascicles
→ endoneurium: covers individual nerve fiber and myelin sheath

Question 5

DESCRIBE THE ROLE OF SCHWANN CELLS IN NERVE REGENERATION

Answer 5

Schwann cells will clean up debris distal to axon injury, release growth factor and cell adhesion molecules to promote regeneration, line up and form a regeneration tube, and overall support and regenerate the axon as well as make a new myelin sheath.

Question 6

DESCRIBE SPINAL NERVES, DISTINGUISH BETWEEN SPINAL ROOTS AND RAMI.

Answer 6

→ spinal nerves: are bundles of nerves that are named from the point of tissue from the spinal cord, they are connected to the spinal cord by dorsal (sensory) roots and ventral (motor) roots.

→ spinal roots lie medial and exclusively carry either motor or sensory information, Rami however can carry both motor and sensory information, they also lie distal and are lateral branches of spinal nerves

Question 7

NAME THE MAJOR PLEXUSES, NAME THE MAJOR PERIPHERAL NERVES THAT COME FROM THERE AND THEIR FUNCTIONS.

Answer 7

→ cervical plexus
Phrenic nerve: controls the diaphragm

→ brachial plexus
Axillary nerve: controls the deltoid and teres minor, as well as shoulder surface region
Radial nerve: controls posterior muscles of the arm, and posterolateral surface of the entire limb
Median nerve: controls anterior flexor group of forearm, intrinsic muscles of the lateral hand, and distal branches of fingers, also controls ventrolateral surface of hand and dorsum of fingers 2-3
Ulnar nerve: also controls flexor form of anterior forearm, most intrinsic muscles of hand, and postero- and ventromedial third of hand.

→ lumbar plexus
Femoral nerve: controls ventromedial thigh, medial leg and foot, and hip and knee joints , as well as anterior muscles of thigh.

→ sacral plexus
Sciatic nerve: controls thigh flexors and leg extensors, and entire lower limb except for ventromedial thigh. Also controls posterior thigh region. This nerve is formed by the tibial and common fibular nerve. It is also the longest and thickest nerve.

Question 8

LIST THE FIVE COMPONENTS OF A REFLEX ARC, ALSO COMPARE STRETCH REFLEXES, FLEXOR, AND CROSSED EXTENSOR REFLEXES.

Answer 8

→reflex arc: sensory receptor → sensory neuron → integration center (mono or polysynaptic), → motor neuron → effector

→ stretch reflex: works to maintain a muscle length set by the brain, the biggest example is the knee jerk reflex. How it works is: stretch activates muscle spindle → sensory neurons synapse with alpha motor neurons in the spinal cord → alpha motor neurons then cause stretched muscle to contract. Reflex is monosynaptic and ipsilateral.

→ flexor (withdrawal) reflex: is caused by painful stimuli which causes the affected arm to withdraw. It is a protected measure and the brain can override it when it knows a painful stimulus is about to be present. It is ipsilateral and polysynaptic (Bc of many different muscles at play).

→ crossed- extensor reflex: has to do with keeping the body at balance when one limb flexes. It involves ipsilateral withdrawal and contralateral extensor reflexes. It is polysynaptic.