Somatic nervous system

Question 1

Divisions of the PNS

Answer 1

1. Somatic
   - Sensory/afferent (sensations from touch, pain, heat/cold, taste, smell and sound)
   - Motor/efferent (contraction of skeletal muscle)
2. Autonomic (visceral nervous system)
   - Sympathetic is fight or flight: increased heart rate, blood pressure, sweating, and blood flow to muscles.
   - Parasympathetic is rest and digest. Decrease heart rate and blood pressure and increase GI activities.

Question 2

Sensory stimuli can influence ___ and ___.

Answer 2

Memory and correlation coordination.

Ex: hand movements, smells

Question 3

GSA and GSE

Answer 3

General somatic afferent, general somatic efferent. (the voluntary division of the PNS)

Question 4

Examples of somatic afferent fibers

Answer 4

Sensory fibers. Can detect pain, temperature, stretch, vision, hearing.

Question 5

Examples of somatic efferent fibers

Answer 5

Most skeletal muscles, but there are always some exceptions.

Question 6

Cranial nerve pairs in the PNS

Spinal nerve pairs in the PNS

Answer 6

12 cranial nerve pairs

31 Spinal nerve pairs

• 8 cervical pairs (C1-C8) *mixed, except C1. C1 is motor only.
• 12 thoracic pairs (T1-T12) *mixed
• 5 lumbar pairs (L1-L5) *mixed
• 5 sacral pairs (S1-S5) *mixed
• 1 coccyx pair *sensory

Question 7

C1

Answer 7

Spinal nerve (cervical) that is motor/efferent only

Question 8

How impulse travels through spinal nerve segment

Answer 8

Sensory impulse travels to meningeal ramus. The meningeal ramus splits to continue onto the dorsal root ganglion, which enters the dorsal side of the spinal cord.

Motor response exits the spinal cord at the ventral side through the ventral root, then joins again with the main axon to innervate a skeletal muscle.

Question 9

What enters the dorsal root ganglion?

Answer 9

Sensory/afferent SOMATIC nerve

Question 10

What parts of the body are most sensitive/have the smallest and most touch receptors?

Answer 10

hands, lips, and face.

Question 11

How to increase skin sensitivity?

Answer 11

many small receptive fields close together and many neurons connected to each field.

Question 12

Posterior (dorsal) root ganglion is a

Answer 12

Sensory somatic and visceral/Autonomic (neurons are pseudo-unipolar and the ganglion contains cell bodies of these neurons.

Question 13

Dermatomes

Answer 13

General somatic afferent (GSA) = sensory.
30 dermatome pairs/31 spinal cord pairs. The extra spinal cord pair, C1, does not innervate dermatome because it is strictly motor. The other 30 are sensory.

This includes 
7 cervical (C2-C8) 
12Thoracic (1-12)
5 Lumbar (1-5)
5 Sacral (1-5) 
1 coccygeal 

Sensory information relayed to the CNS via spinal nerves and dorsal root ganglia. Face, scalp, and front of ears are the exception.

Question 14

Are dermatomes present in the face?

Answer 14

No. The face is innervated by cranial nerves, not spinal nerves.

Question 15

Spinal cord regions from superior to inferior

Answer 15

Cervical
Thoracic 
Lumbar 
Sacra 
Coccygeal

Question 16

Myotomes

Answer 16

General somatic efferent (GSE)= motor
Nerves leave spinal cord ventral and form the ventral root. Innervates regional muscles (except facial, a few head and neck).

Sections:
Cervical- neck, shoulder, and arm movements
Lumbar/sacral- hip and leg
Muscles are often innervated by multiple spinal nerves (plexus= overlapping fields)

Question 17

GSE vs GSA

Answer 17

General somatic efferent (motor, myotomes)
General somatic Afferent (sensory, dermatomes)

Both distributed through specific segmental regions.

Question 18

The most devastating spinal cord injury

Answer 18

The most devastating spinal cord injury is in the cervial region, especially C1 and C2. Will lose motor movement to everything except head.

Question 19

Spinal cord injury to thoracic region

Answer 19

Lose motor to legs. Arms still function normally.

Question 20

Conus or cauda equina lesion to spinal cord

Answer 20

Lesion at the termination of the spinal cord. This is not as devastation. Will use walking sticks.

Question 21

Plexus

Answer 21

Network of axons/switching yard

Question 22

Somatic plexuses (2 main divisions)

Answer 22

1. Cervical enlargement:
   - Cervical plexus (Neck, parts of trunk, diaphragm, ansa cervicalis (C1-C3))
   - Brachial plexus (upper appendages= afferent and efferent fibers)
2. Lumosacral enlargement
   - Lower appendages (lumbar and sacral plexuses)

Question 23

Autonomic plexuses

Answer 23

Cardiac, gut

Question 24

Cervical plexus of the cervical enlargement

Answer 24

The most superior. Sensory, motor, muscles, jerk, and fine movements. Info collected from C1-C4 pass through the cervical plexus. Plays a big role in neck musculature.

Question 25

Brachial plexus of the cervical enlargement

Answer 25

C5-T1.
Superior portion innervates upper arm and shoulder.
Lower innervates lower arm and hands.

Question 26

What happens if you have an injury to the superior brachial plexus

Answer 26

Since the superior portion of the brachial plexus innervates the upper arm and shoulder, that will now be damaged.

Musculature to wrist and hands will still be working, causing the hand to appear flipped back with palm up.

Question 27

What happens if you have an in injury to the inferior brachial plexus

Answer 27

Innervation to lower arm and hand are damaged. This results in a hand clench.

Can still bend arm out/flex elbow. Shoulder and upper arm still work fine.