NERVOUS SYSTEM- PART 3

Parasympathetic Division Function

In general, this system inhibits. It centers on relaxation, food processing, and energy absorption. In general, the effects of parasympathetic stimulation is the "rest and digest" response. (Think SLUDD and 3 decreases: salivation, lacrimation, urination, digestion, defecation, and decreased heart rate, decreased diameter of airways, and decreased diameter of pupils.)

There are two major parts of the PNS

Sensory (Afferent) Division and . Motor (Efferent) Division

Nerve VIII

Vestibulocochlear Nerves Function:Monitor sensations of balance, position, and movement and monitor hearing receptors. Function:Hearing; balance and posture

Peripheral nerves (or simply "nerves")

are 1000s of axons bundled together and wrapped in connective tissue

Dorsal Ramus

innervates the deep muscles of the back and the skin of the back.

Cranial Nerves

nerves that originate from the brain

Cervical Plexus Formation

(Form primarily from anterior rami of spinal nerves C1-C4) This plexus innervates the skin and diaphragm. In diaphragm it plays an essential role in breathing.

Sensory (Afferent) Division

(af = to; ferre = to carry) The afferent division brings sensory information picked up by sensory receptors throughout the body and carried by nerve fibers of the PNS and sends the information to the CNS.

Autonomic Nervous System

(auto = self; nomic = law) a. Effectors: The visceral motor system or autonomic motor system has motor neurons that convey impulses from the CNS to smooth muscle tissue (e.g. the smooth muscle around arteries), cardiac muscle tissue, and glands. b. Control Thus, the autonomic NS is involuntary

Motor (Efferent) Division

(ef = from; ferre = to carry) The efferent division carries motor commands from the CNS to muscles and glands. The efferent division is further divided into two: somatic motor system and autonomic nervous system.

Nerve IX

Glossopharyngeal Nerves Function:Mixed nerves that innervate the tongue and pharynx and control swallowing. Function:Taste, muscle sense; swallowing, secretion of saliva

Ganglia - (ganglio = knot) Function

House the cell bodies of sensory or autonomic neurons

Nerve XII

Hypoglossal Nerves Function:Provide voluntary control over tongue movements. Function:Speech, swallowing; muscle sense

Sympathetic Division Function

In general, this system stimulates tissue metabolism, increases alertness, and prepares the individual for sudden, intense physical activity ("fight or flight" response). When this entire division responds, the effects are felt as increased alertness, a feeling of energy and euphoria, increased cardiovascular and respiratory activity, and increase in muscle tone.

Autonomic Nervous System

The ANS functions in maintaining homeostasis. It coordinates cardiovascular, respiratory, digestive, excretory, and reproductive functions. It is divided into 2 divisions: Sympathetic and Parasympathetic divisions. Most of the visceral organs are innervated by nerve fibers from both systems. and both control the activities of an internal organ at any time. However, the sympathetic branch dominates during the "fight or flight" response of the body.

Nerve X

Vagus Nerves Function:Control autonomic functions some motor functions Function:Visceral sensations, taste; visceral muscles and glands

Parasympathetic Division Function Conti

a. salivation b. lacrimation c. urination Stimulates contraction of urinary bladder d. digestion Increases digestive activity e. defection f. decreases heart rate g. decreased diameter of airways (bronchioles) h. decreases diameter (Constricts) the pupils

Cervical Plexus Major Nerves

Most branches are cutaneous nerves (skin of neck, ear, shoulder). The phrenic nerve innervates the diaphragm.

As a spinal nerve approaches the cord, it branches into two points called roots:

a dorsal root and ventral root.

Cranial nerves

carry signals to and from the brain

Spinal nerves

carry signals to and from the spinal cord

Proprioception

detects the amount of stretch in muscles, tendons, and joint capsules. They inform you of the position and movement of your body space.

Lumbar Plexus Formation

Formed from anterior rami of spinal nerves L1-L4)

Somatic Sensory Receptors

(somato = body) These are receptors that monitor the outside world and our position in it (e.g. skin, skeletal, muscle, and bones-these are structures external to the ventral body cavity) These include the senses of touch, pain, pressure, vibration, temperature, and proprioception in the skin, body wall, and limbs. Somatic sensory receptors also include receptors for hearing, equilibrium, vision, and smell.

Visceral Sensory Receptors

(visceral = organ) These are receptors that monitor internal conditions and that status of the organ systems (heart, lungs, digestive tract, etc) These include receptors for stretch, pain, temperature, chemical changes, and irritation in the viscera; it also includes nausea and hunger. Taste is a special visceral sense

There are 3 large plexuses:

1. Cervical Plexus 2. Brachial Plexus 3. Lumbar Plexus 4. Sacral Plexus

Autonomic Nervous System has Two major divisions

1. Sympathetic Division 2. Parasympathetic Division

Spinal Nerves Structure

31 pairs of spinal nerves originate on the spinal cord from posterior and anterior roots. Each spinal nerve is formed from the union of 1000's of both motor axons (from anterior gray horn cell bodies) and sensory axons (from cell bodies in posterior root ganglion). Note that the spinal nerves are part of the PNS but the spinal cord is part of the CNS.

There are 31 pairs of spinal nerves:

8 cervical (C1-C8), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral, (S1-S5) 1 coccygeal (Co1). (Laura: The first cervical pair of spinal nerves emerges between the atlas (C1) and occipital bone. All others leave the vertebral column from the intervertebral foramina between vertebrae.)

Ganglia - (ganglio = knot) Structure

A ganglion (plural, ganglia) is a collection of nerve cell bodies located outside the CNS. Also contain neuroglia and are covered by a connective tissue capsule.

Sacral plexus major nerves

A major nerve is the sciatic nerve (the longest and thickest nerve in the body). It leaves the pelvis via the greater sciatic notch, passes along the back of the femur and divides into 2 branches posterior to the knee. The sciatic nerve controls flexion of the knee, plantar flexion of the foot, and flexion of the toes.

Brachial Plexus Major Nerves

A major nerve is the ulnar nerve which controls flexor muscles and pronator muscles of the forearm. The ulnar nerve travels across the olecranon process; when you hit your "funny bone" you are really compressing this nerve.

Sacral Plexus Formation

Formed from the anterior rami of spinal nerves L4-S4) This plexus innervates the gluteal region, pelvis, perineum, posterior thigh and leg and foot.

Cranial Nerves Struction

Cranial nerves are any of 12 pairs of nerves connected to the base of the brain and passing through foramina of the cranium. They originate from the nose, eyes, inner ear, brainstem, and spinal cord.

Brachial Plexus Formation

Form primarly from anterior rami of spinal nerves C5-T1) This innervates the muscles of the shoulder and upper limb.

Nerve VI

Abducens Nerves Function:Innervate the six extrinsic eye muscle Function:Movement of eye; muscle sense

Nerve XI

Accesssory Nerves Function:Innervates voluntary swallowing muscles of the soft palate and pharynx and muscles associated with the pectoral girdle. Function:Head and shoulder movement; muscle sense

Distal Branches

After leaving the intervertebral foramen, a typical spinal nerve almost immediately splits into branches, termed rami.

Cranial Nerves Function

Cranial nerves supply sensory and motor neurons to the head, neck, part of the trunk and viscera of the thorax and abdomen. Most are mixed nerves (consist of both sensory and motor fibers and thus transmit signals in two directions), some are totally sensory nerves (carry signals from sensory receptors to the CNS), and others are primarily motor nerves (carry signals from the CNS to muscles and glands). The names of the cranial nerves indicate their primary functions or their general distribution. The Roman numerals indicate their order of appearance from the brain, from front to back. There are 12 pairs of cranial nerves which connect to the brain (not to the spinal cord).

Nerve VII

Facial Nerves Function:Control muscles of the scalp and face. They receive taste information from the tongue. Function:Taste; movement of face; secretion of saliva and tears

Nerve III

Oculomotor Nerves Function:Innervate four of the six muscles that move the eyeball. Function:Movement of eye and eyelid; focusing; change in pupil size; muscle sense

Nerve I

Olfactory Nerves Function: Carry sensory information responsible for the sense of smell Function: Smell

Nerve II

Optic Nerves Function:Carry visual information from special sensory receptors (rods and cones) in the eyes Function:Sight

Peripheral Nervous System (Cranial Nerves, Spinal Nerves, and Ganglia)

The PNS is the part of the nervous system that lies outside the CNS. It consists of ganglia, cranial nerves arising from the brain, the spinal nerves arising from the spinal cord. They connect the brain and spinal cord with receptors, muscles, and glands.

Dorsal root gangion

The cell bodies of these sensory nerve axons are located in the posterior root ganglion which is attached to the posterior root. The cell bodies are so large that is causes the swelling of ganglion.

Dorsal Root (Posterior Root) Structure:

The dorsal root carries sensory nerve axons only. (Sensory in the back) They enter the dorsal horn of the cord and sometimes synapse with an interneuron there.

Lumbar Plexus Major Nerves

The femoral nerve is supplies the anterior thigh muscles (ex: quadriceps femoris and sartorius) and receives sensory info from anterior and medial aspects of the thigh.

Sympathetic Division Structure

The preganglionic neuron cell bodies originate in the lateral gray horns fo the T1-L2 spinal cord regions. This branch includes fibers of thoracic and lumbar spinal nerves (T1-T12 and L1-L2). The postganglionic nerves release a neurotransmitter called norepinephrine at the synapses meeting internal organs. This branch includes only motor nerves. Visualize changes that occur during "E" situations: exercise, emergency, excitement, and embarassment.

Parasympathetic Division Structure

The preganglionic neurons originate in either the brainstem or the lateral gray matter of the S2-S4 spinal cord regions. This division includes fibers of cranial and sacral spinal nerves (originating in cranial nerves II, VII, and IX, and sacral nerves S2-S4). The preganglionic axons are loner and the postganglionic axons are shorter when compared to those of the sympathetic division The parasympathetic autonomic ganglia are clos to or within the wall of the effector organ (in sympathetic division they are close to the vertebral column) The postganglionic cells discharge acetylcholine as the neurotransmitter at the synapses meeting internal organs.

Somatic Nervous System

The somatic motor system consists of nerve cells (motor neurons) that convey information from the CNS to the skeletal muscles. 1. Effectors: Skeletal Muscles 2. Control: It is under conscious or voluntary control.

Spinal Nerves Funtion

The spinal nerves connect the CNS to muscles, glands, and sensory receptors. The motor axons send commands to the muscles (skeletal, smooth and cardiac) and the sensory axons send somatic or visceral sensory information to the spinal cord. Each pair of spinal nerves serves a specific region of the body surface known as dermatomes (DERM mah tōm). A dermatome is a specific segment of skin supplied by a single spinal nerve. Dermatomes are clinically important because damage of a spinal nerve will produce a characteristic loss of sensation in the skin.

Ventral Root (Anterior Root) Structure:

The ventral horns contain motor axons only. These motor axons arise from cell bodies in the anterior and lateral gray horns of the spinal cord. Axons from these neurons exit by way of the ventral root of the spinal nerve and lead to the skeletal muscles or to smooth muscle, cardiac muscle, or glands.

Spinal Nerve Plexuses

The ventral rami form networks on both sides of the spinal cord called plexuses (singular, plexus). A plexus is a network of nerves. (plexus = a network) These nerve plexuses then split into multiple "named" nerves that innervate various body structures. Most of the thoracic spinal nerves (intercostal nerves) do not form plexuses.

Ventral Root (Anterior Root) Function:

The ventral root receives motor signals from the ventral horn.

Gray Ramus Communicantes

These are additional rami which contain axons associated with the autonomic nervous system.

Nerve Fasicles

These are bundles of nerve fibers (axons).

Nerve Fibers

These are individual axons. It can be surrounded by a myelin sheath and then, like muscle, it can have 3 connective tissue wrappings

Dorsal Root (Posterior Root) Function:

They carry sensory signals to the dorsal gray horn of the spinal cord.

Endoneurium

This is a layer of areolar connective tissues with capillaries that supply each axon. The endoneurium surrounds each nerve fiber (axon) within a nerve It surrounds a myelin sheath if the axon has a myelin sheath.

Epineurium

This is a layer of dense irregular connective tissue that binds the fascicles together into a nerve. Blood vessels and lymphatic vesels for the nerve lie within the epineurium.

Perineurium

This is a layer of epithelium and collagen fibers that surrounds each fascicle.

Ventral Ramus

This splits into multiple other branches, which innervate the anterior and lateral portions of the trunk, the upper limbs, and the lower limbs. Many of the anterior rami go on to form nerve plexuses. innervates the ventral and lateral skin and trunk muscles and gives rise to limb nerves

Nerve V

Trigeminal Nerves Function:Are mixed nerves with branches going to the eyes, maxilla, and mandibles. Function:General sensation from Skin of face; chewing of food

Nerve IV

Trochlear Nerves Function:Innervate the superior oblique muscles of the eyes Function:Movement of eye; muscle sense

Sympathetic Division Function Conti.

a. Increases heart rate and strength of contraction b. Increases blood pressure c. Dilates the bronchioles d. Stimulates sweat glands e. Increases blood glucose level f. Decreases digestive activity g. Reduces circulation to the skin and body wall h. Accelerates blood flow to skeletal muscles i. Restores stored lipids from adipose tissue j. Dilates the pupils

Each anterior root and its corresponding posterior root unite within the

intervertebral foramen to become a spinal nerve. Thus, a spinal nerve contains both motor axons (from the anterior root) and sensory axons (from the posterior root)