Ch 14, 15

Extrapyramidal (Multineuronal) Pathways

-Reticulospinal tracts - maintain balance -Rubrospinal tracts - control flexor muscles -Superior colliculi and tectospinal tracts mediate head movements

Major Ascending

1. Fasciculi gracilis and cuneatus 2. Lateral and anterior spinothalamic 3. Anterior and posterior spinocerebellar

Major Descending

1. Pyramidal - Corticospinal - control voluntary movement 2. Extrapyramidal : -Rubrospinal -Vestibulospinal -Reticulospinal -Tectospinal

Spinal Tracts

2 types Ascending sensory signals from spinal nerves to brain touch, pain, pressure, etc. -Descending motor brain to spinal nerves control movement Bilateral - member of each pair on each side Ipsilateral - same side from origin to destination Contralateral - cross from 1 side to other

Spinal Cord

31 pairs of spinal nerves attach to the cord by paired roots. Cervical and lumbar enlargements are the sites where nerves serving the upper and lower limbs emerge. The cauda equina is a collection of nerve roots at the inferior end of the vertebral canal.

Spinal nerve pathway

A preganglionic neuron synapsing in sympathetic trunk ganglion travels through gray ramus at the same "level". (synapsing in L4 ganglion for example). The postganglionic axon exits through L4 ramus and enters the spinal nerve and extends to the target organ (skin of neck, torso, and limbs, sweat glands, arrector pili muscles, and blood vessels in skin).

Nerve Plexuses

All ventral rami except T2-T12 form interlacing nerve networks called plexuses. Plexuses are found in the cervical, brachial, lumbar, and sacral regions. Each resulting branch of a plexus contains fibers from several spinal nerves.

Comparison of Neurotransmitters and Receptors of the Two Divisions: Adrenergic Receptors

Alpha receptors are typically stimulatory and may divided into subclasses. α1 receptors: located in most smooth muscle cells stimulate smooth muscle contraction found in most blood vessels (vasoconstriction) arrector pili muscle (contraction) uterus (contraction) ureters, internal urethral sphincter (closing) α2 receptors: located in pancreas inhibit insulin secretion involved with contraction of GI tract sphincters facilitate blood clotting

Interactions Between the Parasympathetic and Sympathetic Divisions: Dual Innervation

Antagonistic Effects - Parasympathetic and sympathetic effects usually antagonistic. One example is the control of heart rate. Parasympathetic stimulation slows heart rate while sympathetic stimulation increases heart rate. The same cells have both muscarinic and adrenergic receptors. Cooperative Effects are seen when both parasympathetic and sympathetic produce single result. An example is male sexual function. The penis is erect due to parasympathetic innervation. Ejaculation due is to sympathetic innervation.

Anatomy of the Spinal Cord

Anterior median fissure - separates anterior funiculi Posterior median sulcus - divides posterior funiculi

Reflexes

As we have seen many control systems in the body are related to reflexes. We are born with some and we learn some. A reflex is a rapid, predictable motor response to a stimulus. Reflexes may be inborn (intrinsic) such as the withdrawal reflex or learned (acquired) such as driving.. They involve only peripheral nerves and the spinal cord. They involve higher brain centers as well.

Autonomic Plexuses

Autonomic plexuses are collections of: sympathetic postganglionic axons, parasympathetic preganglionic axons and some visceral sensory axons. They do not synapse with each another. -The cardiac plexus consists of sympathetic postganglionic axons from the cervical and thoracic trunk as well as parasympathetic preganglionic axons from the vagus nerve. Increased sympathetic activity increases heart rate and blood pressure while increased parasympathetic decreases heart rate. -The pulmonary plexus consists of sympathetic postganglionic axons from the cervical and thoracic trunk and parasympathetic preganglionic axons from the vagus nerve. They project to the bronchi of the lungs. Increased sympathetic activity causes bronchodilation while increased parasympathetic activity causes bronchoconstriction. -The pulmonary plexus consists of sympathetic postganglionic axons from the cervical and thoracic trunk and parasympathetic preganglionic axons from the vagus nerve. They project to the bronchi of the lungs. Increased sympathetic activity causes bronchodilation while increased parasympathetic activity causes bronchoconstriction. -The abdominal aortic plexus consists of the celiac, superior mesenteric, and inferior mesenteric plexuses, sympathetic postganglionic axons from prevertebral ganglia and parasympathetic preganglionic axons from vagus or pelvic splanchnic nerves. It innervates all abdominal and some pelvic organs. -The hypogastric aortic plexus consists of sympathetic postganglionic axons from the aortic plexus and sympathetic trunk, parasympathetic preganglionic axons from pelvic splanchnic nerves. It innervates viscera within pelvic region.

Control and Integration of Autonomic System Function: Autonomic Reflexes

Autonomic reflexes enable the ANS to control visceral function. They consist of smooth muscle contractions, cardiac muscle contractions or secretions of glands. They are mediated by autonomic reflex arcs in response to a stimulus. Cardiovascular reflex 1. stretch receptors stimulated in blood vessel walls with pressure elevation 2. signals propagated to cardiac center in medulla oblongata 3. inhibit sympathetic and activate parasympathetic output to heart 4. slows heart rate and decreases volume ejected 5. decreases blood pressure -The gastrointestinal reflex controls the proximal GI tract. It stimulates secretion of gastric glands by parasympathetic stimulation in response to sight or smell of food. It controls the rectum by a parasympathetic reflex causing contraction to aid in elimination. Stimulation is stretch of the rectum walls by fecal matter. Figure

Comparison of Neurotransmitters and Receptors of the Two Divisions: Adrenergic Receptors

Beta receptors may cause stimulation or inhibition. β1 receptors: primarily stimulatory found in heart (increase heart rate and force) found in kidney (stimulate renin secretion) β2 receptors: primarily inhibitory effects in smooth muscle of vessels to heart, liver, and skeletal muscle cause smooth muscle relaxation and vessel dilation lung (bronchodilation) uterine and GI tract smooth muscle (relaxation) detrusor muscle of bladder (relaxation)

Comparison of Neurotransmitters and Receptors of the Two Divisions: Adrenergic Receptors

Biogenic amines (monoamines) bind adrenergic receptors. One subcategory of biogenic amines is catecholamines. This subcategory includes dopamine, norepinephrine, and epinephrine. Remember that there are two subtypes of adrenergic receptors: alpha (α) and beta (β) receptors

Spinal Cord

Conus medullaris is terminal portion of the spinal cord. Filum terminale is fibrous extension of the pia mater; anchors the spinal cord to the coccyx. Denticulate ligaments are delicate shelves of pia mater; which attach the spinal cord to the vertebrae.

Innervation of Skin

Dermatome refers to the area of skin innervated by the cutaneous branches of a single spinal nerve. All spinal nerves except C1 participate in dermatomes Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness

Spinal Nerves: Roots

Each spinal nerve connects to the spinal cord via two medial roots. Each root forms a series of rootlets that attach to the spinal cord. Ventral roots arise from the anterior horn and contain motor (efferent) fibers. Dorsal roots arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers.

Stretch and Deep Tendon Reflexes

For skeletal muscles to perform normally, The Golgi tendon organs (proprioceptors) must constantly inform the brain as to the state of the muscle and stretch reflexes initiated by muscle spindles must maintain healthy muscle tone.

Parasympathetic Division: Cranial Components

Ganglia associated with parasympathetic division are terminal ganglia which are located close to an effector ganglia which are located within wall of a target organ. Cranial components are the oculomotor, facial, and glossopharyngeal nerves. These convey parasympathetic information to the head. The vagus nerve carries stimulation for the thoracic and most abdominal organs. -The Oculomotor Nerve (CN III) has cell bodies in a midbrain nucleus. Preganglionic axons extending to ciliary ganglion within the orbit Post ganglionic axons project to ciliary muscle to control focusing of the lens and go to the constrictor muscle of the iris to allow less light into the eye. -The Facial Nerve (CN VII) has cell bodies in the pons with axon branches terminating at pterygopalatine ganglion near the junction of the maxilla and palatine bones. Postganglionic axons also project to lacrimal glands, small glands of nasal cavity, oral cavity, and palate increasing secretion of the gland -Glossopharnygeal Nerve (CN IX) exits the brainstem and synapses on the ganglionic neuron in the otic ganglion. Postganglionic axons project to parotid glands increasing glandular secretion. -The Vagus Nerve (CN X) supplies parasympathetic innervation to: the thoracic organs, most abdominal organs and the gonads. It projects inferiorly through neck and splits into the anterior and posterior vagal trunks.

Parasympathetic and Sympathetic Interactions: Systems Controlled Only by Sympathetic Division

In some ANS effectors opposing effects are achieved without dual innervation. For example, many blood vessels are innervated by sympathetic axons only. Increased smooth muscle contraction increases blood vessel. This results in an increase in blood pressure. Vasodilation is achieved by decreasing stimulation below autonomic tone.

Comparison of the Somatic and Autonomic Nervous Systems: Motor Neurons

In the somatic nervous system, single lower motor neurons extend from CNS to skeletal muscle fibers. The cell body is in the brainstem or spinal cord and exits the CNS in a cranial nerve or a spinal nerve. These myelinated axons have a large diameter for fastest conduction and always release acetylcholine (ACh) from synaptic knob. The motor neurons of ANS consist of a chain of two motor neurons. The first neuron is the preganglionic neuron. Its cell body is within the brainstem or spinal cord and it exits the CNS in a cranial nerve or spinal nerve projecting to an autonomic ganglion in peripheral nervous system. This system has myelinated axons with a small diameter and slower conduction. It releases ACh from the synaptic knob. Remember that this is a chain of two motor neurons. The second neuron, the postganglionic neuron has a cell body within and autonomic ganglion and exits the ganglion to an effector (cardiac muscle, smooth muscle, gland). The unmyelinated axons with even smaller diameter and have the slowest conduction. It releases ACh or norepinephrine (NE) from synaptic knob. The chain of two motor neurons allows for increasing communication and control. It has neuronal convergence. Multiple preganglionic neurons synapse with a single cell. We also see has neuronal divergence in which axons from one preganglionic cell synapse with numerous cells. See Table 15.1: Comparison of Somatic and Autonomic Motor Nervous Systems

Sympathetic Division: Organization and Anatomy

In the sympathetic division preganglionic cell bodies housed in lateral horn of T1-L2. From there, they travel with somatic motor axons. They then enter T1-L2 spinal nerves and shortly exit. -Sympathetic trunks are located on the left and right anterior to the spinal nerves and lateral to the vertebral column. This resembles a string of pearls. The "string" is composed of axons and "pearls" are the sympathetic trunk ganglia. -Superior cervical ganglion have axons distributed to structures in head and neck and thoracic viscera. Postganglionic axons innervate: sweat glands; smooth muscles in blood vessels; the dilator pupillae muscle of the eye; and the superior tarsal muscle of the eye. Middle and inferior cervical ganglion postganglionic axons innervate thoracic viscera. -White and Gray Rami connect spinal nerves to each sympathetic trunk. White rami communicantes carry preganglionic sympathetic axons from T1-L2 nerves to trunk. They are associated with T1-L2 spinal nerves and myelination provides a whitish appearance. Gray rami communicantes carry postganglionic sympathetic axons from the trunk to the spinal nerve and connect to all spinal nerves. They are unmyelinated , so they have a grayish appearance and are similar to similar to highway "exit ramps".

White Matter in the Spinal Cord

In the white matter, fibers run in three directions :up, down and crosswise. White matter is divided into three funiculi or columns: posterior, lateral, and anterior. Each funiculus contains several fiber tracts composed of axons with similar functions. Fiber tracts are named to reflect their beginning and destination.

Control and Integration of Autonomic System Function: CNS Control of the ANS

Involvement of the CNS: ANS is a regulated nervous system, not independent. It is influenced by four CNS regions: the cerebrum, hypothalamus, brainstem, and spinal cord 1. Cerebrum - ANS is affected by conscious activities here. 2. Hypothalamus is an integration and command center for autonomic functions. It communicates with the association areas of the cortex and is affected by sensory processing in the thalamus and by emotional states in the limbic system. It also communicates with the brainstem, cerebellum, and spinal cord. 3. Brainstem nuclei -mediate major ANS reflexes -control changes in blood pressure, blood vessel diameter, and digestion -control changes in heart rate, pupil size, and eye lens shape for focusing 4. Spinal cord -some autonomic responses controlled at level of spinal cord -e.g., defecation and urination (in children) -may be inhibited by higher centers

Interactions Between the Parasympathetic and Sympathetic Divisions: Autonomic Tone

Most organs are innervated by both divisions of the ANS. This is termed dual innervation Both divisions stimulate continuously to varying degrees. This process is referred to as autonomic tone. For example, most blood vessels are kept in a partially constricted state due to sympathetic tone. A decrease in stimulation below tone causes vessel dilation while an increase above sympathetic tone causes greater vessel constriction. See Table 15.5: Effects of the Parasympathetic and Sympathetic Divisions See Figure 15.11: Comparison of the Parasympathetic and Sympathetic Divisions of the ANS

Divisions of the Autonomic Nervous Systems: Anatomic Differences

Parasympathetic -Preganglionic neuron in brainstem or S2-S4 spinal cord -Termed craniosacral division -Ganglionic neuron innervating muscles or glands -Preganglionic axons longer -Postganglionic axons shorter -Few preganglionic axons -Ganglia close to or within effector Sympathetic -Preganglionic neuron in lateral horns of T1-L2 -Termed thoracolumbar division -Ganglionic neuron innervating muscles or glands -Preganglionic axons shorter -Postganglionic axons longer -Many preganglionic axons -Ganglia relatively close to spinal cord (in sympathetic trunk ganglia or prevertebral ganglia)

Divisions of the Autonomic Nervous Systems: Degree of Response

Parasympathetic activation results in a local response due to long preganglionic neurons with limited branches. -Sympathetic activation usually involves activation of many structures simultaneously. This is termed mass activation. Sometimes only a single effector activated due to short preganglionic neurons with many branches. This especially important in the response to stress when we need rapid changes in activity in many structure are needed at the same time. See Table 15.2: Comparison of Parasympathetic and Sympathetic Divisions

he Splanchnic nerve pathway uses splanchnic nerves

Preganglionic axons pass through sympathetic trunk without synapsing and extend to prevertebral ganglia. They synapse with a ganglionic neuron and travel to an effector organ such as the abdominal and pelvic organs.

Postganglionic sympathetic nerve pathway

Preganglionic neurons synapses in the sympathetic trunk ganglion. The postganglionic axon does not leave trunk via grey ramus. It extends from ganglion and goes to target organ (esophagus, heart, lungs, and thoracic blood vessels) and structures in the head (blood vessels, sweat glands, dilator pupillae, superior tarsal muscles).

Sympathetic Division: Sympathetic Splanchnic Nerves

Preganglionic sympathetic axons not synapsing in sympathetic trunk run anteriorly from the sympathetic trunk to most viscera. The greater thoracic splanchnic nerve extends from T5-T9 trunk ganglia. The lesser thoracic splanchnic nerve extends from T10-T11 trunk ganglia. The least thoracic splanchnic nerve extends from T12 trunk ganglia. The lumbar splanchnic nerves extend from L1 and L2 trunk ganglia and the small sacral splanchnic nerves extend from the sacral sympathetic ganglia. -Prevertebral ganglia are the termination site of the splanchnic nerves. Immediately anterior to vertebral column they cluster around the origins of major abdominal arteries. Postganglionic axons extend away and innervate many abdominal organs.

Sympathetic Division: Types of Prevertebral Ganglia

Prevertebral ganglia are located only in the abdominopelvic cavity. Celiac ganglia are adjacent to the origin of the celiac artery. The greater thoracic splanchnic nerve synapse here. Postganglionic axons innervate the stomach, spleen, and liver The gallbladder, proximal duodenum, and part of pancreas. -The superior mesenteric ganglia are adjacent to the origin of the superior mesenteric artery. The lesser and least thoracic splanchnic nerve synapse here. Postganglionic axons innervate: the distal half of duodenum: the remainder of the small intestine; the proximal large intestine, part of pancreas, the kidneys, and the proximal ureters. -Inferior mesenteric ganglia are adjacent to the origin of the inferior mesenteric artery The lumbar splanchnic nerve synapses here. Postganglionic axons innervate the distal large intestine, rectum, bladder, distal ureters and most reproductive organs.

Comparison of the Somatic and Autonomic Nervous Systems: Functional Organization

Somatic nervous system (SNS) includes processes that are perceived or controlled consciously. The somatic sensory portion detects stimuli from special senses, skin, and proprioceptors and sends information to CNS. The somatic motor portion transmits nerve signals from CNS to control skeletal muscles. The autonomic nervous system (ANS) includes processes regulated below conscious level. The visceral sensory portion detects stimuli from blood vessels and internal organs. The autonomic motor portion (visceral motor) transmits nerve signals to cardiac muscle, smooth muscle, and glands. Autonomic nervous system functions to maintain homeostasis (a constant internal environment). It regulates: heart rate and blood pressure, respiratory rate, sweating, and digestion keeping these variables within optimal ranges.

Operation of the Muscle Spindles

Stretching the muscles activates the muscle spindle and there is an increased rate of action potential in certain fibers. Contracting the muscle reduces tension on the muscle spindle and there is a decreased rate of action potential on certain fibers.

Superficial Reflexes

Superficial reflexes are started by gentle stimulation of the skin. They involve cord level reflex arcs and corticospinal tracts. Example: Plantar reflex is initiated by stimulating the lateral sole of the foot. The response is downward flexion of the toes. This is used to indirectly test for proper corticospinal tract functioning. Damage to the primary motor cortex or the corticospinal tracts would be indicated by Babinski's sign. This is an abnormal plantar reflex indicating corticospinal damage where the great toe dorsiflexes and the smaller toes fan laterally. Babies exhibit Babinski's sign until they are about one year old because myelination of the nervous system is incomplete.

Sympathetic Division: Shared Pathways

Sympathetic preganglionic neurons all originate in lateral gray horns of T1-L2 spinal cord. Preganglionic axons travel with T1-L2 spinal nerves, leave spinal nerve and travel through white rami to enter sympathetic trunk. They remain at the same level or travel superiorly or inferiorly in trunk. They exit the trunk by four pathways:

Golgi Tendon Reflex

The Golgi Tendon Reflex produces The opposite effect of the stretch reflex. It produces muscle relaxation and lengthening in response to tension. 1. Contracting the muscle activates the Golgi tendon organs. 2. Afferent Golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated 3. As a result, the contracting muscle relaxes and the antagonist contracts

Adrenal medulla pathway

The adrenal medulla pathway is directly innervated by preganglionic sympathetic axons. The preganglionic neuron extends through the sympathetic trunk and prevertebral ganglia. Upon stimulation, epinephrine and norepinephrine produced in medulla circulate within blood helping prolong fight-or-flight response and prolong the effects of sympathetic stimulation.

Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall

The back is innervated by dorsal rami .The thorax is innervated by ventral rami T1-T12 in the form of intercostal nerves which supply muscles of the ribs, anterolateral thorax, and abdominal wall. The ventral rami of the rest form plexuses.

Cervical Plexus

The cervical plexus is formed by ventral rami of C1-C4. Most branches are cutaneous nerves of the neck, ear, back of head, and shoulders. The most important nerve of this plexus is the phrenic nerve which is the major motor and sensory nerve of the diaphragm. Irritation of the phrenic nerve may be responsible for "hiccups".

Flexor and Crossed Extensor Reflexes

The flexor reflex is initiated by a painful stimulus (actual or perceived) that causes automatic withdrawal of the threatened body part. The crossed extensor reflex has two parts: The stimulated side is withdrawn and the contralateral side is extended.

Gray Matter

The gray matter consists of soma, unmyelinated processes, and neuroglia. The gray commissure connects masses of gray matter and encloses the central canal. Posterior (dorsal) horns contain interneurons. Anterior (ventral) horns contain interneurons and somatic motor neurons. Lateral horns contain sympathetic nerve fibers.

Lumbar Plexus

The lumbar plexus arises from L1-L4 and innervates the thigh, abdominal wall, and psoas muscle. The major nerves are the femoral and the obturator.

Divisions of the Autonomic Nervous Systems: Functional Differences

The motor component of theANS is subdivided into parasympathetic and sympathetic divisions. The parasympathetic division functions to maintain homeostasis at rest. This is an energy conservation and replenishing stage so we call this the "rest-and-digest" division. The motor component of the sympathetic division prepares the body for emergencies. We call this the "fight-or-flight" division. I will cause increased alertness and metabolic activity ("three E's": emergency, exercise, or excitement).

Comparison of Neurotransmitters and Receptors of the Two Divisions: Overview of ANS Neurotransmitters

The neurotransmitters Acetylcholine (ACh) and norepinephrine (NE) bind to specific receptors on the postsynaptic cell causing stimulation or inhibition, depending on the receptor. Acetylcholine is synthesized and released by cholinergic neurons. They include the following: All sympathetic and parasympathetic preganglionic neurons, all parasympathetic ganglionic neurons and the specific neurons innervating sweat glands and blood vessels of skeletal muscle. Receptors that bind ACH are cholinergic receptors (two types). Norepinephrine is bound by adrenergic receptors. It is synthesized and released by adrenergic neurons. Most other sympathetic ganglionic neurons are adrenergic. They form network of swellings at a target organ termed varicosities. These contain stored NE. NE is released along length of axon

Three Ascending Pathways

The nonspecific and specific ascending pathways send impulses to the sensory cortex. These pathways are responsible for discriminative touch and conscious proprioception. The spinocerebellar tracts send impulses to the cerebellum and do not contribute to sensory perception

Parasympathetic Division: Pelvic Splanchnic Nerves

The pelvic splanchnic nerves originate from preganglionic cell bodies housed in the lateral gray regions of S2-S4. They contribute to the superior and inferior hypogastric plexus bilaterally and project to ganglionic neurons within terminal or intramural ganglion. These postganglionic axons extend to the effector. Target organs include the distal portion of large intestine, the rectum. The bladder, the distal ureter and most reproductive organs. They cause smooth muscle motility, secretory activity in digestive tract, contraction in the bladder wall, and erection of clitoris and penis. See Table 15.3: Parasympathetic Division Outflow

Sacral Plexus

The sacral plexus rises from L4-S4 and serves the buttock, lower limb, pelvic structures, and the perineum. The major nerve is the sciatic which is the longest and thickest nerve of the body.

Nervous System: Spinal Cord and Spinal Nerves

The spinal cord provides a vital link between the brain and the rest of the body. It exhibits some functional independence from the brain. The spinal cord and spinal nerves provide a pathway for sensory and motor nerve signals and are responsible for reflexes, which are the quickest reactions to stimulus. The spinal cord is enclosed within the vertebral column from the foramen magnum to L1. It provides two-way communication to and from the brain and is protected by bone, meninges, and CSF. The epidural space between the vertebrae and the dural sheath (dura mater) is filled with fat and a network of veins.

Stretch Reflex

The stretch reflex makes sure that a muscle stays at the proper length set by the brain: -Stretching the muscle activates the muscle spindle -Excited motor neurons of the spindle cause the stretched muscle to contract -Afferent impulses from the spindle result in inhibition of the antagonist Example: patellar reflex Tapping the patellar tendon stretches the quadriceps and starts the reflex action. The quadriceps contract and the antagonistic hamstrings relax.

Reflex Arc

There are five components of a reflex arc: 1. Receptor which is the site of stimulus. 2. Sensory neuron which transmits the afferent impulse to the CNS. 3. Integration center which is either a monosynaptic or polysynaptic region within the CNS. 4. Motor neuron which conducts efferent impulses from the integration center to an effector 5. Effector or muscle fiber or gland that responds to the efferent impulse

Comparison of Neurotransmitters and Receptors of the Two Divisions: Cholinergic Receptors There

There are two categories of cholinergic receptors: nicotinic and muscarinic. -Nicotinic receptors are found on all ganglionic neurons and the adrenal medulla. When bound, they open ion channels causing a greater movement of Na+ into cell than K+ out of cell. This produces an excitatory postsynaptic potential. -Muscarinic receptors are found in all target membranes in the parasympathetic division and selected sympathetic cells such as sweat glands in skin, and blood vessels in skeletal muscle. There are different subtypes of muscarinic receptors with different effects. They are either stimulated or inhibited by binding Ach. For example binding of ACh in GI tract results in stimulation and increased motility. However, binding on cardiac muscle decreases heartbeat rate.

Spinal Nerves: Rami

These roots come together and form short spinal nerves which exit through intervertebral foramina. After emerging they branch into three or four mixed, distal rami: -Small dorsal ramus - supplies the back -Larger ventral ramus - supplies the anterior body trunk and limbs -Tiny meningeal branch- reenters the vertebral canal to innervate the meninges -Rami communicantes - at the base of the ventral rami in the thoracic region- contain autonomic fibers.

Spinal Nerves

Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head. They are named according to their point of issue: 8 cervical (C1-C8) 12 thoracic (T1-T12) 5 Lumbar (L1-L5) 5 Sacral (S1-S5) 1 Coccygeal (C0)

Indirect (Extrapyramidal) System

This system includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal system as well as the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts. These motor pathways regulate: -Axial muscles that maintain balance and posture -Muscles controlling coarse movements of the proximal portions of limbs -Head, neck, and eye movement

ch 15 Nervous System: Autonomic Nervous System

the autonomic system is a system of nerves mediating involuntary actions. It regulates body organ activity and maintains normal internal functions. Divided into sympathetic and parasympathetic divisions, the autonomic nervous system allows for varied nervous system responses in times of stress and rest.

Brachial Plexus

the brachial plexus gives rise to the nerves that innervate the upper limb.