Somatic nervous system Flashcards
Divisions of the PNS
- Somatic
- Sensory/afferent (sensations from touch, pain, heat/cold, taste, smell and sound)
- Motor/efferent (contraction of skeletal muscle) - 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.
Sensory stimuli can influence ___ and ___.
Memory and correlation coordination.
Ex: hand movements, smells
GSA and GSE
General somatic afferent, general somatic efferent. (the voluntary division of the PNS)
Examples of somatic afferent fibers
Sensory fibers. Can detect pain, temperature, stretch, vision, hearing.
Examples of somatic efferent fibers
Most skeletal muscles, but there are always some exceptions.
Cranial nerve pairs in the PNS
Spinal nerve pairs in the PNS
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
C1
Spinal nerve (cervical) that is motor/efferent only
How impulse travels through spinal nerve segment
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.
What enters the dorsal root ganglion?
Sensory/afferent SOMATIC nerve
What parts of the body are most sensitive/have the smallest and most touch receptors?
hands, lips, and face.
How to increase skin sensitivity?
many small receptive fields close together and many neurons connected to each field.
Posterior (dorsal) root ganglion is a
Sensory somatic and visceral/Autonomic (neurons are pseudo-unipolar and the ganglion contains cell bodies of these neurons.
Dermatomes
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.
Are dermatomes present in the face?
No. The face is innervated by cranial nerves, not spinal nerves.
Spinal cord regions from superior to inferior
Cervical Thoracic Lumbar Sacra Coccygeal
Myotomes
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)
GSE vs GSA
General somatic efferent (motor, myotomes)
General somatic Afferent (sensory, dermatomes)
Both distributed through specific segmental regions.
The most devastating spinal cord injury
The most devastating spinal cord injury is in the cervial region, especially C1 and C2. Will lose motor movement to everything except head.
Spinal cord injury to thoracic region
Lose motor to legs. Arms still function normally.
Conus or cauda equina lesion to spinal cord
Lesion at the termination of the spinal cord. This is not as devastation. Will use walking sticks.
Plexus
Network of axons/switching yard
Somatic plexuses (2 main divisions)
- Cervical enlargement:
- Cervical plexus (Neck, parts of trunk, diaphragm, ansa cervicalis (C1-C3))
- Brachial plexus (upper appendages= afferent and efferent fibers) - Lumosacral enlargement
- Lower appendages (lumbar and sacral plexuses)
Autonomic plexuses
Cardiac, gut
Cervical plexus of the cervical enlargement
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.
Brachial plexus of the cervical enlargement
C5-T1.
Superior portion innervates upper arm and shoulder.
Lower innervates lower arm and hands.
What happens if you have an injury to the superior brachial plexus
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.
What happens if you have an in injury to the inferior brachial plexus
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.
