Peripheral Nervous System

peripheral nervous system

peripheral nervous system

• nervous system located outside the brain and spinal cord

• provides vital links to the body and outside world

• provides communication between the central nervous system (CNS) and the rest of the body

• contains cranial and spinal nerves

somatic sensory system

General: includes touch, pain, pressure, vibration, temperature, and proprioception in skin, body wall, and limbs

Special includes hearing, equilibrium, and vision.

visceral sensory system

General: includes stretch, pain, temperature, chemical changes, and irritation in viscera; nausea and hunger

Special includes taste and smell.

somatic nervous system

a voluntary somatic (muscle) motor system that conducts impulses from the CNS to skeletal muscles.

autonomic nervous system

an involuntary visceral (organ) motor system that conducts impulses from the CNS to cardiac muscles, smooth muscles and glands. It is further divided into the sympathetic and parasympathetic divisions.

sympathetic

mobilizes body systems during activity

• responsible for the fight or fight response, an activity that is evident during vigorous exercise, excitement or emergency dangerous situations

  Examples:

• pounding heart

• fast and deep breathing

• dilated pupils

• cold/sweaty skin

parasympathetic

conserves energy by promoting housekeeping functions during rest such as digestion and elimination of feces and urine

Example:

• a person relaxing after dinner and reading the newspaper because the heart rate are at low-normal levels, and the gastrointestinal tract is digesting food

• pupils are constricted as the eyes focus for close vision.

sensory receptors

pick up stimuli (environmental changes) from inside and outside the body and then initiate impulses in sensory axons, which carry the impulse to the CNS

nerves

bundles of peripheral axons, can be sensory only, motor only or sensory and motor (called a mixed nerve, most common)

ganglia

clusters of peripheral cell bodies

motor endings

axon terminals of motor neurons that innervate the effector organs, muscles and glands

CN I: Olfactory

contain special sensory nerves of smell

CN II: Optic

contain special sensory nerves of vision, since it develops as an outgrowth of brain is is not a true nerve, but a brain tract. 

CN III: Oculomotor

innervates four of the extrinsic eye muscles (muscles that move the eyeball in the orbit, oculomotor means "eye mover").

CN IV: Trochlear 

innervates an extrinsic eye muscle that hooks through a pulley-shaped ligament in the orbit (trochlear means "pulley").

CV V: Trigeminal

provides general sensory innervation to the face and motor innervation to the chewing muscles (trigeminal means "threefold" which refers to the nerves three major branches), called the great sensory nerve of the face.

CN VI: Abducens

innervates the muscle that abducts (turns laterally) the eye

CN VII: Facial

nerve that innervates the muscles of facial expression, taste,  as well as other structures

CN VIII: Vestibulocochlear

contain special sensory nerves of hearing and equilibrium

CN IX: Glossopharyngeal 

helps innervate the tongue and pharynx, taste (glossopharyngeal means "tongue" and "pharynx").

CN X: Vagus

a nerves that wanders beyond the head into the thorax and abdomen (vagus means "wanderer").

CN XI : Accessory

it originates from the cervical region of the spinal cord, enters the skull through an opening and exits the skull to carry motor innervation to the trapezius and sternocleidomastoid muscles.

XII: Hypoglossal

runs below the tongue and innervates the tongue muscles (hypoglossal means "below the tongue".

spinal nerves

31 pairs, exit from the spinal cord through spaces between the vertebrae called intervertebral foramina
- Nerves are named according to their point of issue from the vertebral column

Cervical (8)

C1-C8

Thoracic (12)

T1-T12

Lumbar (5)

 L1-L5

Sacral (5)

S1-S5

Coccygeal (1)

Co1

dorsal roots

contain axonal processes of sensory neurons arising from cell bodies in the dorsal root ganglion

• meets the ventral root to form a spinal nerve

ventral roots

contain axonal processes of motor neurons whose cell bodies are located in ventral gray column of the spinal cord

spinal nerve

connects to the spinal cord by a dorsal (posterior) root and a ventral (anterior) root 

• exits the intervertebral foramina and divides into two branches

dorsal (posterior) ramus 

(smaller branch) going to the posterior part of the body, area behind the transverse processes of the vertebral column

ventral (anterior) ramus 

(much larger branch) going to the anterolateral part of the body

ventral (anterior) rami

_ of all the spinal nerves (except T2-T12 branch) join one another lateral to the vertebral column, forming nerve plexuses

cervical nerve plexus

• formed by the ventral rami of C1 through C4

• an important nerve of the cervical plexus is the phrenic nerve that originates from spinal cord segments C3, C4 and C5

• the phrenic nerve travels through the thorax passing along sides of the pericardial sac to innervate the diaphragm

brachial nerve plexus

• formed by the ventral rami of C5 through T1 and are responsible for innervation to the arm, forearm and hand

• Important nerve is the median nerve, innervates most muscles of the anterior forearm and lateral palm.

lumbar nerve plexus

• formed by the ventral rami of L1 through L4 and lies within the muscles of the posterior abdominal wall

• main branches innervate the anterior region of the thigh, important nerve of the plexus is the femoral nerve.

sacral nerve plexus

• formed by the ventral rami of L4 through S4, because some fibers from the lumbar plexus contribute to the sacral plexus we can refer to these two plexuses as the lumbosacral plexus

• innervates the lower limb and buttocks

• An important nerve of the plexus is the sciatic nerve which is the thickest and longest nerve in the body

• The sciatic nerve supplies all of the lower limb except the anterior and lateral region of the thigh.

thoracic region

• each ventral ramus (branches) travels along the lower border of the rib and form the intercostal nerves (not a plexus)

• they travel with an intercostal artery and vein forming the neurovascularbundle to supply the corresponding rib space. 

dermatomes

• area of skin that is mainly supplied by one spinal nerve 

• area of skin is innervated by cutaneous (skin) sensory branches from a single spinal nerve.

• all spinal nerves except C1 participate in dermatomes

Examples

• C3 supplies the skin around the neck

• S1/S2 supply the skin on back of lower limb

autonomic nervous sytem

• system of motor neurons that innervate smooth muscle, cardiac muscle and glands of the body (effectors).

• by controlling these effectors, the ANS regulates such visceral (organ) functions as heart rate, blood pressure, digestion, and urination, which are essential for maintaining the stability of the body's internal environment.

• general visceral (organ) motor division of the peripheral nervous system

somatic motor system

focuses on the motor innervation of skeletal muscle (targets the skeletal muscle) and is a one-neuron pathway

autonomic motor system

targets smooth muscle, cardiac, smooth, and glands and isa two-neuron pathway with a synapse in an autonomic ganglion

preganglionic neuron

axon of the_ synapses with the cell body of the second postganglionic neuron in a peripheral autonomic ganglion (motor ganglia)