copyright © 2010 pearson education, inc. the nervous system chapter 12, 13 and 14 central nervous...

Copyright © 2010 Pearson Education, Inc.

The nervous system chapter 12, 13 and 14

Central Nervous System (CNS)Central Nervous System (CNS)

BrainBrain Spinal CordSpinal Cord

Peripheral Nervous System (PNS)Peripheral Nervous System (PNS)

Sensory NeuronsSensory NeuronsMotor NeuronsMotor Neurons

Somatic Nervous SystemSomatic Nervous System Autonomic Nervous SystemAutonomic Nervous System

SympatheticSympathetic Parasympathetic Parasympathetic

The Nervous SystemThe Nervous System


Subjects we will cover

• Our approach will be to cover functional systems:

• Somatic nervous system – sensory and motor

• Autonomic nervous system

• Special senses

• All system will cover both the central and peripheral nervous systems


• Neurons in the nervous system link together to form circuits with specific functions.

http://www.thefullwiki.org/Nervous_System


Nervous system functions

• Motor functions

• Control contraction of skeletal muscles – somatic nervous system

• Control contractions of smooth and cardiac muscle – autonomic nervous system

• Control of glands function – autonomic nervous system

• Sensory and integrative functions

• Process incoming information to ensure appropriate motor response

• More than 99% of the incoming information is classified as irrelevant and unimportant


3 Major levels of the CNS

• Spinal cord

• involved in walking movement, reflexes of both skeletal muscles and the autonomic nervous system effectors

• Lower brain/subcortical level

• Subconscious activities of both the autonomic and somatic nervous system. Involved in several emotional patterns

• Higher brain/cortical level

• Very large memory storage, place of higher functions like thoughts, awareness


Peripheral nervous system components

• Includes nerves and ganglia

• Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers

• Pure sensory (afferent) or motor (efferent) nerves are rare

• Peripheral nerves classified as cranial or spinal nerves

• Ganglia contain neuron cell bodies associated with nerves

• Dorsal root ganglia (sensory, somatic) (Chapter 12)

• Autonomic ganglia (motor, visceral) (Chapter 14)


CNS protection

• Bony protection by the skeleton – brain by skull and spinal cord by vertebrae

• 3 layers of membrane collectively called meninges that are found between the bone and the CNS tissue

• Cerebro-spinal fluid – CSF - found in the ventricles, central canal and subarachnoid space

• Blood brain barrier - BBB


http://tle.westone.wa.gov.au/content/items/969144ed-0d3b-fa04-2e88-8b23de2a630c/1/human_bio_science_3b.zip/content/002_nervous_control/page_06.htm


Choroid Plexuses and CSF

• Clusters of capillaries and the ependymal cells

http://www.sci.uidaho.edu/med532/choroid.htm


CSF production

• The choroid plexus forms tissue fluid filters

• Have ion pumps that selectively pump ions from the plasma into the ventricles.

• The ions pumps create osmotic pressure that draws water to the CSF

• the choroid plexus of the lateral ventricles producing the most.

• The rate of formation is approximately 0.35 ml/min or 500 ml/day; a rate which replaces the total volume of CSF approximately 2-3 times over in 24 hours.


CSF – cerebrospinal fluid functions

• Liquid cushion for brain and spinal cord

• Nourishes brain

• Removes waste

• Conducts chemical signals between parts of CNS


Why are the capillaries in the BBB less permeable?

• Endothelial cells form tight junctions that prevent solutes movement between cells

• Astrocytes

• Selective transport properties of the endothelial cells

• The BBB

• Helps maintain a stable environment for the brain

• Separates neurons from some bloodborne substances


Blood-Brain Barrier: Functions• Selective barrier that allows nutrients to pass freely

• Is ineffective against substances that can diffuse through plasma membranes (ex. Ethanol, caffeine)

• Absent in some areas:

• Ex. - hormones generally do not penetrate the brain from the blood, so in order to control the rate of hormone secretion effectively, there are specialized sites where neurons can "sample" the composition of the circulating blood. At these sites, the blood-brain barrier is 'leaky‘ (pituitary gland)

• Capillaries of the choroid plexus

• The BBB can break down under certain conditions:

• hypertension, radiation, infection and brain trauma


Spinal Cord

• Because the cord does not reach the end of the vertebral column, the lumbar and sacral spinal nerve roots angle sharply downward and travel inferiorly before reaching their intervertebral foramina

• This collection of nerve roots at the inferior end of the vertebral canal is called the cauda equina

Copyright © 2010 Pearson Education, Inc. Figure 12.32

Somaticsensoryneuron

Dorsal root (sensory)

Dorsal root ganglion

Visceralsensory neuron

Somaticmotor neuron

Spinal nerve

Ventral root(motor)

Ventral horn(motor neurons)

Dorsal horn (interneurons)

Visceralmotorneuron

Interneurons receiving input from somatic sensory neurons

Interneurons receiving input from visceral sensory neurons

Visceral motor (autonomic) neurons

Somatic motor neurons

Gray Matter: Organization


White Matter in the Spinal Cord• Composed of both myelinated and unmyelinated fibers that run

in three directions

• Ascending – to higher centers; sensory

• Descending – to lower levels from brain or higher places in the cord; motor

• Transversely – from one side of the cord to the other

• Divided into three funiculi (columns) – posterior, lateral, and anterior

• Each funiculus contains several fiber tracks with similar destination and function

• Fiber tract names reveal their origin and destination

• Fiber tracts are composed of axons with similar functions


Structure of a Nerve• Nerve – cordlike organ of the

PNS consisting of peripheral axons enclosed by connective tissue

• Connective tissue coverings include:

• Endoneurium – loose connective tissue that surrounds axons

• Perineurium – coarse connective tissue that bundles fibers into fascicles

• Epineurium – tough fibrous sheath around a nerve


Spinal Nerves: Rami

• The short spinal nerves branch into three or four mixed, distal rami

• Small dorsal ramus

• Larger ventral ramus

• Tiny meningeal branch – innervate the meninges and blood vessels within the vertebral canal

• Rami communicantes at the base of the ventral rami in the thoracic region that contain autonomic nerve fibers


Nerve Plexuses• All ventral rami except T2-T12 form 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

• Fibers travel to the periphery via several different routes

• Each muscle receives a nerve supply from more than one spinal nerve

• Damage to one spinal segment cannot completely paralyze a muscle


Plexus Main spinal nerves Regions innervated Major nerves

Cervical C1-C5 Skin and muscles of head & neck. Superior chest and shoulder

Phrenic (diaphragm)

Brachial C5-C8, T1 Shoulder and upper limbs Axillary Musculocutaneous Radial

Median

Ulnar

Lumbar L1-L4 Antero-lateral abdominal wall, external genitalia, part of lower limbs

Femoral

Sacral L4-L5, S1-S4 Buttocks, perineum, lower limbs

Sciatic

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