The document discusses somatic motor pathways in the central nervous system. It describes how motor impulses are conducted from motor areas to skeletal muscles via neurons forming somatic motor pathways. These pathways can be classified as pyramidal or extrapyramidal tracts, or as facilitatory or inhibitory. The document also discusses spinal nerves, nerve plexuses, dermatomes and myotomes, cranial nerves, the afferent and efferent divisions of the nervous system, and the sympathetic and parasympathetic divisions of the autonomic nervous system.

1. Somatic Motor Pathways in
the Central Nervous System
 Impulses must be conducted from its motor areas to
skeletal muscles by relays of neurons referred to as
somatic motor pathways. Consist of motor neurons that
conduct impulses from the central nervous system to
somatic effectors such as skeletal muscles.
 There are two methods used to classify somatic motor
pathways: one- divides them into pyramidal and
extrapyramidal tracts. Two- classifies them as
facilitatory and inhibitory.
 Pyramidal tracts are those whose fibers come together
in the medulla to form the pyramids.
 Extrapyramidal tracts are much more complex, they
consist of all motor tracts from the brain to the spinal
cord anterior horn motor neurons except the
corticospinal tracts. (1)

2. (9 ©) (8 ©)

3. Structure of Spinal Nerves
 Each spinal nerve attaches to the spinal cord by
means of two short roots, ventral and dorsal.
 The dorsal is easily recognized by a swelling called
the dorsal root ganglion, or spinal ganglion. The
roots and dorsal ganglia lie within the spinal
cavity.
 Each spinal nerve splits into a distinct dorsal
ramus and ventral ramus. (1)

4. Nerve Plexuses
 The ventral rami of most spinal nerves subdivide to form
complex networks called plexuses.
Four Major Pairs:
 1. The Cervical Plexus – found deep within the neck;
innervates muscles and skin of the neck, upper shoulder,
and part of the head
 2. The Brachial Plexus – plexus located deep in the
shoulder that innervates the lower part of the shoulder
and the entire arm
3. The Lumbar Plexus - spinal nerve plexus located in the
lower back
 4. The Sacral Plexus – plexus formed by fibers from the
fourth the fourth and fifth lumbar nerves and the first four
sacral nerves

5.  (10 ©)

6. Dermatomes and Myotomes
 At first glance of the distribution of spinal nerves does
not appear to follow an ordered arrangement, but
detailed mapping of the skin surface has revealed a
close relationship between the spinal origin of each
spinal nerve and the region of the body it innervates.
 Dermatomes – skin surface areas supplied by a single
spinal nerve
 Myotomes – skeletal muscle or group of muscles that
receives motor axons from a given spinal nerve.
 There is some overlap among myotomes also, thus some
skeletal muscle organs may be innervated by motor
axons from more than one spinal nerve

7.  (11 ©)

8. Cranial Nerves
 (2 ©)

9. Afferent and efferent
 Afferent division of the nervous system consists of all of
the incoming sensory or afferent pathways.
 Efferent division of the nervous system consists of all
the outgoing motor or efferent pathways.

10. Vagus nerve
Phrenic nerve
The autonomic nervous system is influenced by the conscious mind, its
autonomous of voluntary control.

11. Sympathetic and
Parasympathetic
 Sympathetic division prepares the body to deal with
immediate threats to the internal environment. It
produces the “fight-or-flight” response.
 Parasympathetic division coordinates the body’s normal
resting activities. Sometimes called the “rest-and-repair”
division.