Unit 3

Organ Systems that provide coordination and integration

• Chapter 7 – The Nervous System

• Chapter 9 – The Endocrine System

Chapter 7

The Nervous System

Nervous System

• Master controlling and communicating system of the body

• Works with the Endocrine System to regulate and maintain body homeostasis– Nervous system controls through nerve

impulses– Endocrine system controls through hormones

Functions of the Nervous System

• Monitor changes, stimuli, inside and outside the body– Gathered information – sensory input

• Process and interpret sensory input– Make decisions - integration

• Effect a response– Activate muscles or glands via motor output

Structural Classifications

• Nervous System organs are classified into 2 subdivisions– Central nervous system - CNS

• Brain and spinal cord• Integration center – interpret sensory information,

issue instructions

– Peripheral nervous system – PNS• Spinal nerves – carry impulses to and from spinal

cord• Cranial nerves – carry impulses to and from brain

Functional Classifications

• PNS has 2 functions, carrying impulses to the CNS, and carrying impulses away from the CNS

• Sensory (afferent) division – nerve fibers that carry impulses from sensory receptors to CNS– Somatic sensory fibers – deliver impulses

from skin, skeletal muscles, joints– Visceral sensory fibers – deliver impulses

from organs

• Motor (efferent) division – carry impulses from CNS to effector organs, muscle, glands– 2 divisions – somatic nervous system,

autonomic nervous system– Somatic – consciously control muscles– Autonomic – regulates involuntary activity

Nervous System organization

Figure 7.2

Nervous Tissue

• Nervous system is composed of 2 types of cells: supporting cells and neurons

• Supporting cells of CNS are called Neuroglial cells and include: astrocytes, microglia, ependymal cells, oligodendrocytes

• Supporting cells of PNS include Schwann cells and Satellite cells

Figure 7.3a

Nervous Tissue: Support Cells of CNS (Neuroglia)

• Astrocytes– Abundant, star-shaped cells– Brace neurons– Form barrier

between capillaries and neurons

– Control the chemical environment of the brain

CNS: Support Cells

• Microglia– Spider-like phagocytes– Dispose of debris

• Ependymal cells– Line cavities of the

brain and spinal cord– Circulate

cerebrospinal fluid

Figure 7.3b–c

CNS: Support Cells

• Oligodendrocytes– Produce myelin sheath around nerve fibers in

the central nervous system

Figure 7.3d

• Resemble neurons structurally but are not able to transmit impulses and do not lose the ability to divide– Most brain tumors are gliomas, tumors formed

by neuroglial cells

Figure 7.3e

PNS: Support Cells

• Satellite cells– Protect neuron cell bodies

• Schwann cells– Form myelin sheath in the peripheral nervous

system

Neuron Structure

• Specialized to transmit impulses from one part of the body to another

• Common structure for different types of neurons– Cell body containing a nucleus - metabolic

center– One or more processes extending from cell

body

• Cell body – contains usual organelles except for centrioles, no mitosis– Nissl substance – rough ER– Neurofibrils – filaments that maintain cell

shape

Neuron process – fibers– Vary in length – microscopic to 3 to 4 feet– Dendrites – impulses toward cell body

• Each neuron may have hundreds of branching dendrites

– Axons – generate impulses and carry them away from cell body

• Each neuron has only one axon

Neuron Anatomy

• Extensions outside the cell body– Dendrites –

conduct impulses toward the cell body

– Axons – conduct impulses away from the cell body

Figure 7.4a

Axons

Axons arise from region on cell body called axon hillock

Axons branch at terminal end forming axon terminals which contain neurotransmitters

Synaptic cleft – gap between one neuron and another neuron – junction called synapse

Myelin sheath – formed by schwann cells wrapping around axons – nerve fiber covering

• Myelin – fatty material that helps transmit impulses• Neurilemma – external part of myelin sheath

Nodes of Ranvier - gaps between schwann cells along axon

Figure 7.5

Locations of cell bodies and fibers

• Cell bodies located in the CNS– Found in clusters called nuclei– Carry out metabolic functions of cell– Well protected to avoid damage

• Cell bodies located in the PNS– Found in clusters called ganglia

• Nerve fibers located in CNS– Bundles of fibers called tracts– Myelinated fibers called white matter– Unmyelinated fibers and cell bodies called

gray matter

• Nerve fibers located in PNS– Bundles of fibers called nerves

Classification of neurons

• Neurons can be classified according to function or structure

• Functional classifications – sensory, motor, association neurons

• Structural classifications – based on the number of processes – multipolar, bipolar, unipolar

Neuron Classification

Figure 7.6

Functional Classification

• Sensory (afferent) neurons– Cell bodies are in ganglion outside CNS– Carry impulses from receptors to CNS– Dendrite endings associated with specialized

receptors• Skin receptors – cutaneous sense organs – pain

receptors• Muscle and tendon receptors – proprioceptors –

detect stretch and tension in muscles and tendons• Figure 7.7

• Motor (efferent) neurons – Cell bodies always located in CNS– Carry impulses from CNS to organs, muscles,

glands

• Association neurons – interneurons– Connect motor and sensory neurons – Cell bodies always located in CNS

Structural Classification of Neurons

• Multipolar neurons – many extensions from the cell body – all motor and association neurons

Figure 7.8a

Structural Classification of Neurons

• Bipolar neurons – one axon and one dendrite – found in special sense organs acting as receptors

Figure 7.8b

Structural Classification of Neurons

• Unipolar neurons – have a short single process leaving the cell body – found in PNS ganglia

Figure 7.8c

Neuron Physiology

• Neurons have 2 major functions:

• Irritability – the ability to respond to a stimulus and convert it into a nerve impulse

• Conductivity – the ability to transmit the impulse to other neurons, muscles or glands

• A nerve impulse is an electrochemical event that causes a change in neuron plasma membrane permeability, allowing sodium ions to enter the cell. Once begun, the impulse continues over the entire surface of the cell.

Nerve impulses

• IRRITABILITY – generating the impulse• A resting neuron has a plasma membrane

that is polarized. – Normally there are positive ions on both sides

of the plasma membrane – Na on the outside, K on the inside.

– There are more Na on the outside of the membrane than K on the inside, which results in the inside of the membrane being more negative than the outside

• Stimuli excite neurons to generate an impulse– Many different types of stimuli can generate

an impulse– The result of the stimulation is that the cell

membrane becomes permeable to Na ions which will diffuse quickly into the cell

– The membrane becomes depolarized – the inside of the membrane is more positive

Starting a Nerve Impulse

• Depolarization – a stimulus depolarizes the neuron’s membrane

• A deploarized membrane allows sodium (Na+) to flow inside the membrane

• The exchange of ions initiates an action potential in the neuron

Figure 7.9a–c

Nerve Impulse Propagation

• The impulse continues to move toward the cell body

• Impulses travel faster when fibers have a myelin sheath

Figure 7.9d–f

• Generation of an action potential– If the local depolarization is strong enough, it

causes the polarity of the entire membrane to be completely reversed

– An action potential, or a nerve impulse is generated

– The impulse always travels the entire length of the axon, all-or-none response

• Repolarization occurs– Almost immediately after Na rushes into the

cell, the membrane again becomes impermeable to Na but permeable to K

– K ions diffuse out of the neuron– Membrane again is polarized

• Active transport restores Na/K ion concentrations– Sodium-potassium pump uses ATP to pump

excess Na out of cell and bring K ions back into cell

• If the nerve fiber is myelinated, the impulse cannot travel along the myelinated section

• Fibers that are myelinate conduct impulses much faster because the impulse jumps from node to node along the length of the fiber

• CONDUCTIVITY – transmitting the impulse

• Action potential reaches axon terminal

• Vesicles containing neurotransmitters fuse with axon membrane and are released into the synaptic cleft

• Neurotransmitters bind to receptors on the membrane of next neuron

• Membrane receptors cause a change in permeability of membrane to Na ions

• New nerve impulse is generated

• Neurotransmitter is removed from synapse

Figure 7.10

Reflexes

• Reflexes are rapid, predictable, involuntary responses to stimuli

• Reflexes occur over pathways called reflex arcs

• Reflexes involve both CNS and PNS• Somatic reflexes stimulate skeletal muscle• Autonomic reflexes regulate activity in

smooth muscle, heart and glands– Digestion, elimination, blood pressure, sweat

• Reflex arcs have 5 elements: sensory receptor, sensory neuron, integration center CNS, motor neuron, effector organ

The Reflex Arc

Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector

Figure 7.11a

• Two-neuron reflex arc – patellar reflex

• Three-neuron reflex arc – withdrawal reflex

• The more synapses in a reflex arc, the longer the reflex takes to happen

• Reflex testing is an important tool in evaluating the condition of the nervous system

Simple Reflex Arc

Figure 7.11b–c

Central Nervous SystemBrain Anatomy

• Largest and most complex mass of nervous tissue in the body

• 4 major regions– Cerebral hemispheres – cerebrum– Diencephalon– Brain stem– Cerebellum

Regions of the Brain

• Cerebral hemispheres

• Diencephalon

• Brain stem

• Cerebellum

Figure 7.12b

Cerebrum

• Most superior part of brain, larger than other 3 regions

• Surface contains elevated ridges called gyri separated by shallow grooves called sulci

• Deep grooves called fissures separate large regions of brain– longitudinal fissure separates brain into

hemispheres

• Separated into lobes– Parietal lobe – somatic sensory area– Occipital lobe – visual area– Temporal lobe – auditory and olfactory areas– Frontal lobe – primary motor area

• Central sulcus separates frontal and parietal lobes

Cerebral Hemispheres (Cerebrum)

Figure 7.13a

• Cerebral cortex – outermost area of cerebrum – Cell bodies – gray matter

• Parietal lobe – posterior to central sulcus– Impulses from sensory receptors are localized

and interpreted– Sensory homunculus – sensory cortex– Left side receives impulses from right side of

body

Sensory and Motor Areas of the Cerebral Cortex

Figure 7.14

• Frontal lobe – anterior to central sulcus– Motor homunculus – primary motor area

• Sends impulses to skeletal muscles• Anterior to central sulcus

– Broca’s area – specialized area involved in speech – only in one hemisphere (left)

– Anterior part of frontal lobe – higher intellectual reasoning

– Language comprehension

• Speech area – junction of temporal, parietal, occipital lobes

• Memories stored in temporal and frontal lobes

• Cerebral white matter – fiber tracts to carry impulses to and from cerebral cortex

• Corpus callosum – large fiber tract that connects two cerebral hemispheres

• Basal nuclei – “islands” of gray matter within the white matter of the cerebrum

• Visual area – posterior part of occipital lobe

• Auditory area – temporal area

• Olfactory area – deep in temporal lobe

Diencephalon

• Enclosed by cerebral hemispheres

• Above the brain stem

• Major structures include thalamus, hypothalamus, epithalamus

Thalamus

• Surrounds the third ventricle– Figure 7.17

• The relay station for sensory impulses passing up to the sensory cortex

• Transfers impulses to the correct part of the cortex for localization and interpretation

Hypothalamus

• Under the thalamus

• Important autonomic nervous system center– Helps regulate body temperature– Controls water balance– Regulates metabolism

Hypothalamus

• An important part of the limbic system (emotions)– Thirst, appetite, sex, pain, pleasure center

• The pituitary gland is attached to and regulated by the hypothalamus

• Mammillary bodies – involved in sense of smell

http://upload.wikimedia.org/wikipedia/commons/9/9f/LocationOfHypothalamus.jpg

Epithalamus

• Forms the roof of the third ventricle

• Houses the pineal body (an endocrine gland)

• Includes the choroid plexus – forms cerebrospinal fluid

Brain Stem

• Provide a pathway for ascending and descending tracts

• Contain small areas of gray matter nuclei which are part of cranial nerves

• Main structures are midbrain, pons, medulla oblongata

Midbrain

• Mostly composed of tracts of nerve fibers

• Has two bulging fiber tracts – cerebral peduncles

• Has four rounded protrusions – corpora quadrigemina– Reflex centers for vision and hearing

Pons

• The bulging center part of the brain stem

• Mostly composed of fiber tracts

• Includes nuclei involved in the control of breathing

Medulla Oblongata

• The lowest part of the brain stem• Merges into the spinal cord• Includes important fiber tracts• Contains important control centers

– Heart rate control– Blood pressure regulation– Breathing– Swallowing– Vomiting

Reticular Formation

• Diffuse mass of gray matter along the entire brain stem

• Involved in motor control of visceral organs

• Reticular activating system plays a role in awake/sleep cycles and consciousness

• Damage can result in coma

Cerebellum

• Under occipital lobe of cerebrum

• 2 hemispheres, convoluted surface

• Outer gray matter cortex. Inner region of white matter

• Provides timing for skeletal muscles

• Controls balance and equilibrium

Protection of the Central Nervous System

• Scalp and skin

• Skull and vertebral column

• Meninges and cerebrospinal fluid

Figure 7.16a

Meninges

• 3 connective tissue membranes covering the CNS structures

• Outer membrane – dura mater

• Middle membrane – arachnoid mater

• Inner membrane – pia mater

• Dura mater– Double-layered membrane– Outer layer attached to inner skull – periosteal– Inner layer forms outermost covering of brain

- meningeal

• Arachnoid mater– Cobweb looking membrane– Threadlike extensions pass through

subarachnoid space to attach to pia mater

• Pia mater– Delicate membrane, clings to surface of brain

and spinal cord

Cerebrospinal Fluid

• Similar to blood plasma composition

• Formed by the choroid plexus

• Forms a watery cushion to protect the brain

• Circulated in arachnoid space, ventricles, and central canal of the spinal cord

• Changes in CSF composition can indicate meningitis

Blood Brain Barrier

• Brain is dependent on constant internal environment

• Barrier includes the least permeable capillaries of the body

• Excludes many potentially harmful substances• Useless against some substances

– Fats and fat soluble molecules– Respiratory gases– Alcohol– Nicotine– Anesthesia

Traumatic Brain Injuries

• Concussion– Slight brain injury– No permanent brain damage

• Contusion– Nervous tissue destruction occurs– Nervous tissue does not regenerate

• Cerebral edema– Swelling from the inflammatory response– May compress and kill brain tissue

Cerebrovascular Accident (CVA)

• Commonly called a stroke

• The result of a ruptured blood vessel supplying a region of the brain

• Brain tissue supplied with oxygen from that blood source dies

• Loss of some functions or death may result

Central Nervous SystemSpinal cord

• Continuation of brain stem• Two way conduction to and from the brain• Major reflex center• Extends from foramen magnum to first or

second lumbar vertebra• Protected by meninges• Enlargements at cervical and lumbar regions• Cauda equina – spinal nerves at inferior end of

vertebral column

Central Nervous System Spinal Cord Anatomy

• Figure 7.19

• Gray matter looks like a butterfly in the white matter

• Gray matter surrounds the central canal which contains CSF

• Gray matter is divided into dorsal or posterior horns, lateral horns, ventral or anterior horns

• Dorsal root – contains sensory nerve fibers that enter the dorsal horn of the spinal cord – Dorsal root ganglion – contain the cell bodies

of the sensory neurons whose fibers enter into the dorsal horn

• Dorsal horn – contains association neurons

• Ventral horns – contain cell bodies of motor neurons of the somatic nervous system

• Dorsal and ventral roots fuse to form spinal nerves

• White matter is composed of myelinated fiber tracts

• White matter is divided into posterior, lateral and anterior columns

• Tracts in the posterior column are ascending tracts and contain sensory tracts

• Lateral and anterior columns contain both ascending and descending, or motor, tracts

Peripheral Nervous System

• Consists of spinal and cranial nerves and some groups of cell bodies, ganglia, found outside the Central Nervous System

• Classified into sensory and motor functions figure 7.2

• Motor functions can be somatic or autonomic

• Autonomic system can be sympathetic or parasympathetic

Nervous System organization

Figure 7.2

Nerve structure

• A nerve is a bundle of neuron fibers found outside the CNS

• Nerve fibers are wrapped in connective tissue

• Endoneurium covers each fiber• Bundles of fibers are called fasicles and

are covered by perineurium• Many fascicles are covered with

epineurium

Structure of a Nerve

• Endoneurium surrounds each fiber

• Groups of fibers are bound into fascicles by perineurium

• Fascicles are bound together by epineurium

Figure 7.20

Connective Tissue Wrappings of Skeletal Muscle

• Epimysium – covers the entire skeletal muscle

• Fascia – on the outside of the epimysium

Figure 6.1

• Nerves can be considered mixed nerves – carry both sensory and motor fibers

• Sensory or afferent nerves – carry impulses to the CNS

• Motor or efferent nerves – carry impulses away from CNS

Cranial Nerves

• 12 pairs of nerves that mostly serve the head and neck

• Numbered in order, front to back

• Most are mixed nerves, but three are sensory only

• Table 7.1

• Oh, oh, oh, to touch and feel very good velvet, ah

Cranial Nerves

• I Olfactory nerve – sensory for smell

• II Optic nerve – sensory for vision

• III Oculomotor nerve – motor fibers to eye muscles

• IV Trochlear – motor fiber to eye muscles

Cranial Nerves

• V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles

• VI Abducens nerve – motor fibers to eye muscles

• VII Facial nerve – sensory for taste; motor fibers to the face

• VIII Vestibulocochlear nerve – sensory for balance and hearing

Cranial Nerves

• IX Glossopharyngeal nerve – sensory for taste; motor fibers to the pharynx

• X Vagus nerves – sensory and motor fibers for pharynx, larynx, and viscera

• XI Accessory nerve – motor fibers to neck and upper back

• XII Hypoglossal nerve – motor fibers to tongue

Spinal Nerves

• There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs

• Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord

• Spinal nerves are named for the region from which they arise – cervical, thoracic, lumbar, sacral – figure 7.22

Anatomy of Spinal Nerves

• Spinal nerves divide soon after leaving the spinal cord– Dorsal rami – serve the

skin and muscles of the posterior trunk

– Ventral rami – forms a complex of networks (plexus) for the anterior

Figure 7.22b

• Rami contain both motor and sensory fibers

• Dorsal rami are smaller and serve the skin and muscles of posterior body trunk

• Ventral rami of spinal nerves T1 through T12 form the intercostal nerves which service the muscles between the ribs and the muscles of the anterior and lateral trunk

• Ventral rami of cervical, lumbar and sacral nerves form a complex network of nerves called plexuses which serve the motor and sensory needs of the limbs

• Cervical plexus, brachial plexus, lumbar plexus, sacral plexus

• Table 7.2, figures 7.22 and 7.23

Autonomic Nervous System

• The involuntary branch of the nervous system– Controls body activities automatically– Controls the stability of internal body

environment

• Consists of only motor nerves• Divided into two divisions

– Sympathetic division– Parasympathetic division

Differences Between Somatic and Autonomic Nervous Systems

• Nerves– Somatic – one motor neuron– Autonomic – preganglionic and postganglionic

nerves

• Effector organs– Somatic – skeletal muscle– Autonomic – smooth muscle, cardiac muscle,

and glands

Differences Between Somatic and Autonomic Nervous Systems

• Neurotransmitters– Somatic – always use acetylcholine– Autonominic – use acetylcholine, epinephrine,

or norepinephrine

Differences Between Somatic and Autonomic Nervous Systems

• Pathways – figure 7.24– Somatic – cell bodies of motor neurons are

inside CNS and axons extend all the way to the skeletal muscle

– Autonomic – chain of 2 motor neurons• 1st neuron cell bodies inside CNS and axons

(preganglionic axon) synapse with 2nd neuron in a ganglion outside CNS

• Axon of 2nd neuron (postganglionic axon) extends to effector organ

Anatomy of Parasympathetic Division

• Neurons originate in brain nuclei of several cranial nerves– Serve head and neck organs– Original neurons synapse with 2nd neuron at

terminal ganglion– Postganglionic axon extends sort distance to

organ it serves

Anatomy of Parasympathetic Division

• Neurons originate S2 through S4

– Preganglionic axons leave spinal cord and form pelvic splanchnic (pelvic) nerves which travel to pelvic cavity

– Synapse with 2nd axons in terminal ganglion near organs they serve

Anatomy of Sympathetic Division

• Neurons originate in spinal cord gray matter from T1 through L2

• Preganglionic axons leave spinal cord through the ventral root, enter the spinal nerve, pass through a ramus communicans and enter a sympathetic chain ganglion (sympathetic trunk) – figure 7.26

• After leaving the sympathetic chain, the postganglionic axon can reenter the spinal nerve and travel to skin or synapse with splanchnic nerves and travel to viscera via another collateral ganglion

• Ganglia are at the sympathetic trunk (near the spinal cord)

• Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector

Autonomic Functioning

• Organs served by autonomic system receive fibers from both parasympathetic and sympathetic divisions– Antagonistic effects– Postganglionic axons of each division release

different neurotransmitters• Para. fibers release acetylcholine, sympa. fibers

release norepinephrine

– Preganglionic fibers both releases acetylcholine

Sympathetic Functions

• “fight-or-flight” system• Response to unusual situations like

emotional upset and physical stress• Increases heart rate, blood pressure,

blood glucose levels, dilates bronchioles, blood vessels

• Enables body to cope rapidly and vigorously with situations that threaten homeostasis

Parasympathetic Functions

• “resting-and-digesting” system

• Concerned with normal digestion and elimination of feces and urine

• Decreases demands on cardiovascular system

Development Aspects of the Nervous System

• The nervous system is formed during the first month of embryonic development

• Any maternal infection can have extremely harmful effects

• Lack of oxygen can lead to death of neurons

• The hypothalamus is one of the last areas of the brain to develop– Body heat of premature babies

• No more neurons are formed after birth, but growth and maturation continues for several years– Myelination of axons

• The brain reaches maximum weight as a young adult

• With age sympathetic system becomes less effective

• Gradual lack of oxygen due to aging leads to senility– Circulatory system problems cause lack of

oxygen to neurons