1. Chapter 7 The Nervous System
Biology 112
Tri-County Technical College
Pendleton, SC

2. Structural Organization
Structural Classification which includes ALL nervous system organs has two subdivisions:
CNS-consists of brain and spinal cord
PNS(peripheral)-is part outside CNS consisting mainly of nerves that from CNS
Spinal nerves carry info to and from spinal cord
Cranial nerves carry info to and from brain

3. Functional Organization
Concerned ONLY with PNS structures
Sensory/Afferent division conducts impulses to CNS
Sensory fibers from skin, skeletal muscles, and joints are called somatic sensory (afferent) fibers
SFs from visceral organs called visceral sensory fibers (visceral afferents)
Sensory division keeps CNS informed of events going on outside/inside body

4. Functional Organization, cont.
Motor/Efferent division carries impulses from CNS to effector organs, muscles, and glands
Impulses activate muscles/glands
They EFFECT (bring about) a motor response
MOTOR division has two subdivisions
SOMATIC NERVOUS SYSTEM
AUTONOMIC NERVOUS SYSTEM

5. Autonomic Nervous System
ANS is motor subdivision of PNS that controls body activities automatically (involuntary)
Composed of special group of neurons that regulate cardiac muscle, smooth muscle, and glands
ANS also called involuntary nervous system
ANS has two distinct subdivisions
Sympathetic and Parasympathetic
Serve same organs but cause essentially opposite effects
Counterbalance each other to keep body systems running smoothly

6. Organization of Nervous System

7. ANS, continued
Preganglionic axons of sympathetic div. release acetylcholine; Postganglionic fibers release noreeinephrine and/or epinephrine (adrenergic fibers)
Pre- and Postganglionic axons of parasympathetic division release acetylcholine (cholinergic fibers)
Sympathetic part mobilizes body during extreme situations (fear, exercise, rage)
E for exercise/emergency/embarrassment
Parasympathetic part allows body to “unwind” and conserve energy
D for digesting/defecation/diuresis

8. Somatic Motor Division
Somatic system allows conscious/voluntary control of skeletal muscles
Often called “voluntary nervous system”
Cell bodies of motor neurons are inside CNS and their axons (in spinal nerves) extend all way to skeletal muscles served
Skeletal muscles are effectors of somatic nervous system
Neurotransmitter is acetylcholine

9. Cells of Nerve Tissue Two principal types of cells
Neurons and supporting cells
Supporting cells of CNS lumped together as neuroglia (nerve glue)
Neuroglia (Glia) support, insulate, and protect delicate neurons
There are different types of “supporting cells” in the CNS

10. Supporting Cells, cont.
Astrocytes account for nearly ½ of neural tissue
Brace/anchor neurons to blood capillaries
Form living barrier between capillaries and neurons & play role in making exchanges between the two
Help protect neurons from harmful stuff in blood
Help control chemical environment by picking up excess ions and recapturing released neurotransmitters

11. Supporting Cells, cont.
Microglia are phagocytes that dispose of debris-dead brain cells, bacteria, etc.
Ependymal Cells line cavities of brain and spinal cord
beating of their cilia help circulate cerebrospinal fluid that fills those cavities and forms protective cushion around CNS
Oligodendrocytes wrap their flat extensions around nerve fibers producing fatty insulating coverings called myelin sheaths

12. FYI
Neuroglia are NOT able to transmit nerve impulses and they NEVER lose their ability to divide
Most brain tumors are GLIOMAS or tumors formed by glial cells

13. He ain’t heavy…he’s my brother
Supporting cells in PNS come in two major varieties
Schwann cells form myelin sheaths around nerve fibers that are found in PNS
Satellite cells act as protective, cushioning cells

14. Supporting cells, Visual

15. You’re getting on my nerve..
Neurons are highly specialized to carry impulses (transmit messages)
All neurons have CELL BODY (SOMA) and one or more slender processes extending from cell body
Dendrites conduct electrical impulses TOWARD the cell body
Axons conduct electrical impulses AWAY from cell body
May be 100s of dendrites but only 1 axon
Axons may branch at terminal end forming 100s to 1000s of axonal terminals

16. Neuron, Visual

17. Neuron Part Functions Cell body = nucleus and metabolic center
Dendrites = impulses to the cell body
Axon = impulses away from cell body to either another neuron or the effector
Most long neurons covered with whitish, fatty material called MYELIN
Myelin protects and insulates fiber and > the transmission rate of nerve impulses

18. Parts, cont. Axons outside CNS insulated by Schwann cells
wrap tightly around axon jelly-roll style
wrapping done, tight coil of wrapped membranes called myelin sheath encloses axon
most of Schwann cell cytoplasm ends up just beneath outermost part of its plasma membrane
this part of Schwann cell, external to myelin sheath is called the neurilemma

19. Parts, cont. Myelin sheath formed by many individual Schwann cells
Gaps or indentations called NODES OF RANVIER occur at regular intervals
Myelin sheaths in CNS are formed by the oligodendrocytes
CNS myelin sheath lacks a neurilemma
Neurilemma plays vital role in fiber regeneration of injured fiber
Regeneration of damaged fibers largely lacking in CNS

20. Schwann cells, Visual

21. Nuclei, Ganglia, and more…
In CNS, cell bodies found in clusters called nuclei
This well protected location essential to well-being of nervous tissue
Small collections of cell bodies called ganglia are found outside CNS in the PNS
Bundles of nerve fibers running through CNS are called tracts
Bundles of nerve fibers running though PNS are called nerves

22. Nuclei and Ganglia, cont.
Terms white matter and gray matter refer to myelinated versus unmyelinated reions of the CNS
As a general rule, white matter consists of dense collections of myelinated fibers (tracts)
Gray matter contains mostly unmyelinated fibers and cell bodies

23. Classification of Neurons
Can be classified according to HOW they function or according to their STRUCTURE
FUNCTIONAL classification based on direction impulse traveling relative to CNS
Sensory (afferent) neurons carry impulses from sensory receptors (internal organs/skin) to CNS
Cell bodies of sensory neurons always found in ganglion outside the CNS
Inform about what is happening in/out of body

24. Classification, cont.
Motor neurons (efferent) carry impulses away from CNS to viscera/muscles/glands
Cell bodies of motor neurons always located in CNS
Association (interneurons) neurons connect sensory and motor neurons in a neural pathway
Cell bodies of association neurons always located in CNS

25. Functional Classification, Visual

26. Structural Classification
Based on number of processes extending from cell body
Multipolar neuron has several processes
all motor and association neurons are multipolar
most common structural type
Bipolar neuron has 2 processes—dendrite and axon
Rare in adults; found only in some special sense organs (eye, ear) where act as sensory receptor cells

27. Structural Classification, cont.
Unipolar neuron has single process emerging from cell body
Very short and divides into proximal (central) and distal (peripheral) fibers
Unique in that only small branches at end of peripheral process are dendrites
Remainder of peripheral process and central process function as axon
In unipolar neuron, axon conducts impulse both toward and away from cell body
Sensory neurons found in PNS ganglia are unipolar

28. Structural Classification, Visual

29. Resting State…I wish
Plasma membrane of resting (inactive) neuron is polarized
fewer positive charges on inner surface of membrane that on its outer face in tissue fluid
Major positive ions on inside are K+
Major positive ions on outside are Na+
As long as inside remains more negative as compared to outside, neuron will stay inactive (resting)
Resting potential of neuron is about –70 millivolts

30. Action, cameras, and more…
Action potential = nerve impulse
Stimulus changes permeability of patch of membrane and sodium ions diffuse rapidly into cell
Changes polarity of membrane at that location
Inside becomes more +, outside more –
Event called depolarization
If stimulus strong enough (at or > threshold) action potential is initiated

31. Action Potential, cont.
Depolarization of first membrane patch causes permeability changes in adjacent membrane and event is repeated
Membrane potential goes from –70 mv to +30 mv
Action potential propagates rapidly along entire length of membrane
Don’t want to waste space on this slide..so, IS THIS FUN, OR WHAT????

32. Action Potential, Visual

33. Repolarization After patch of membrane depolarizes, it repolarizes
Membrane permeability changes and K+ ions diffuse OUT of cell
Restores negative charge inside cell and positive charge outside
Sodium-potassium pump used to restore ionic conditions of resting neuron
Resting potential of –70 mv restored
Until repolarization occurs, neuron CANNOT conduct another impulse

34. Reflex Defined and More…
Reflex is rapid, predictable and involuntary response to a stimulus
Reflexes occur over neural pathway called reflex arc
SOMATIC = reflexes that stimulate skeletal muscles
Dendrite of sensory neuron carries impulse to CNS
Processing of info may/may not occur in CNS
Axon of motor neuron carries impulse to effector
pull hand away from hot object = somatic reflex

35. Reflex, cont.
Autonomic reflexes regulate activity of smooth muscles, heart, and glands
saliva secretion and size of eye pupils two examples of autonomic reflexes
ALL reflex arcs have minimum of 5 elements
Sensory receptor which reacts to stimulus
Afferent neuron
Integration center located in CNS
Efferent neuron
Effector organ (muscle or gland to be stimulated)
Two-neuron (patellar knee-jerk) most simple
Three-neuron (flexor/withdrawal) more complex

36. Somatic reflexes Patellar knee-jerk somatic reflex
receptors in patellar tendon
effectors are upper leg muscles that cause leg extension
Withdrawal somatic reflex
receptors located in epidermis/dermis
touching a hot object or finger stick
effectors are the appropriate muscles
can be used as a diagnostic tool
Whenever reflexes are exaggerated, distorted, or absent, nervous system disorders indicated

37. Reflexes, Visual

38. Cerebrum Functions Speech Memory Logic Emotional Responses
Consciousness
Interpretation of sensation
Voluntary movements

39. Basal Nuclei (ganglion)
Modify instructions from cerebrum to skeletal muscles
Problems with basal nuclei lead to inability to carry out movements in normal way
Huntington’s disease=inability to control muscles; individual exhibits abrupt, jerky, almost continuous movements
helped by drugs that block dopamine’s effect
Parkinson’s disease=trouble initiating movement or in getting muscles going
Persistent hand tremor with thumb and index finger making continuous circles with one another
Due to deficit of neurotransmitter dopamine

40. Functions of the Thalamus
Thalamus is part of diencephalon (innerbrain) that sits atop brain stem & enclosed by cerebral hemispheres
Encloses third ventricle of the brain
Relay station for sensory impulses > cerebrum
Provides “crude” recognition of whether sensation about to have is pleasant or unpleasant
Actual interpretation occurs in neurons of cerebral cortex

41. Functions of the Hypothalamus
Part of the diencephalon & important autonomic nervous system center
Plays role in regulation of body temp, water balance, and metabolism
Center for many drives and emotions
Important part of limbic system (emotional-visceral brain)
Thirst, appetite, sex, pain, and pleasure centers located in hypothalamus
Regulates pituitary gland and produces two hormones: ADH and oxytocin

42. Functions of the Midbrain
Midbrain is small part of the brain stem
Anteriorly composed of two bulging fiber tracts called cerebral peduncles that convey > and < impulses
Dorsally composed of four rounded protrusions called corpora quadrigemina which are reflex centers involved with vision and hearing

43. Functions of the Pons
PONS is rounded structure that protrudes just below midbrain
Functions as “bridge” for ascending and descending impulses through this area
Contains important nuclei involved with BREATHING

44. Functions of Medulla Oblongata
Most inferior part of the brain stem
Merges into spinal cord (no obvious change in structure)
Like pons, is important fiber tract area
Contains many nuclei that regulate vital visceral activities
Heart rate, blood pressure, breathing, swallowing, and vomiting

45. Functions of the Cerebellum
Has two hemispheres & convoluted surface
Outer cortex of gray matter and inner region of white matter
Provides precise timing for skeletal muscle activity, controls balance and equilibrium
It’s activity = smooth and coordinated body movements
Continually monitors brain’s intentions with action body performance by monitoring body position and amount of tension in various body parts

46. Protection for the CNS
CNS protected by enclosure within bone (skull and vertebral column); by watery cushion (cerebrospinal fluid) and by enclosure within membranes (meninges)
Also protected from harmful substances in blood by the blood-brain barrier
Three connective tissue membranes covering and protecting CNS structures are called meninges

47. CNS protection, cont. Dura mater is leathery outermost layer
double layer membrane where surround brain
periosteal layer attached to inner surface of brain
meningeal layer forms outermost covering of brain and continues as dura mater of spinal cord
Arachnoid mater is weblike middle layer
Its threadlike extensions span subarachnoid space to attach it to innermost membrane, the pia mater
Pia mater (gentle mother) clings tightly to surface of brain and spinal cord by following every fold

48. CNS protection, cont.
Meningitis is inflammation of the meninges and is serious threat to brain because bacterial/viral meningitis may spread to nervous tissue of CNS
Meningitis usually diagnosed by taking sample of CSF from subarachnoid space
Brain inflammation called encephalitis

49. Meninges, Visual

50. Cerebrospinal Fluid
CSF continually formed from blood by choroid plexuses (clusters of capillaries that hang from roof in each brain ventricle
Forms watery cushion in and around brain and spinal cord
Moves from lateral hemispheres 3rd ventriclecerebral aqueduct of midbrain  4th ventricle dorsalpons/medulla
Some fluid reaching 4th ventricle continues down central spinal canal of spinal cord

51. CSF, cont.
MOST CSF circulates into subarachnoid space through three openings in wall of 4th ventricle
CSF returned to blood through subarachnoid space
CSF contains water, glucose, proteins, and sodium chloride ions
Lumbar spinal tap used to collect sample of CSF for testing
Something affects CSF drainage—begins to collect and exert pressure on brain
Results in hydrocephalus (water on the brain)
Risks and treatments

52. CSF, Visual

53. Selected Traumatic Brain Injuries
Head injuries leading cause of accidental death in US
Brain injury at site of bloweffect of ricocheting brain hitting opposite end of skull
Concussion occurs when brain injury slight
dizzy, brief unconsciousness/no permanent brain damage
Contusion result of marked tissue damage
brain stem contusion results in coma (hours to lifetime)

54. Injuries, cont.
Cerebral edema is swelling of brain due to inflammatory response to injury
Intracranial hemmorhage is bleeding from ruptured vessels
CARDIOVASCULAR ACCIDENTS commonly called “strokes”
3rd leading cause of death in US
CVAs occur when blood circulation to brain area blocked by blood clot/ruptured vessel
Vital brain tissue begins to die

55. CVAs, cont.
After CVA, often possible to determine area of brain damage by patient’s symptoms
Left-side paralysis=right motor cortex damaged
Aphasias common result of damage to left cerebral hemisphere where language areas located
Motor aphasia involves damage to “Broca’s area” and loss of ability to speak

56. CVAs, cont.
Sensory aphasia—person loses ability to understand written or spoken language
Temporary brain ischemic (transient ichemic attack or TIA) is uncompleted stroke
Lasts from 5 to 50 minutes
Numbness, temporary paralysis, and impaired speech
Symptoms NOT permanent but RED FLAG warning of serious impending CVAs

57. Alzheimer’s Disease
Degenerative disease of brain that results in dementia (mental deterioration)
May begin in middle age with memory loss (recent events), becomes moody, irritable, confused, and sometimes violent…then hallucinations
Abnormal protein deposits (plagues) and twisted fibers appear within neurons with local brain atrophy
Influx of calcium into brain implicated

58. Spinal Cord Cylindrical spinal cord is continuation of brain stem
Provides 2-way conduction pathway to & from brain
It is the major reflex center (spinal reflexes completed at this level)
Enclosed within vertebral column and extends from foramen magnum of skull to 1st or 2nd lumbar vertebra (just below ribs)

59. Spinal Cord, cont.
Meningeal coverings do NOT end at L2 but extend well beyond end of spinal cord in vertebral column
NOT possible to damage cord below L2 so good place to draw CVS
Collection of spinal nerves at inferior end called cauda equina (horse’s tail)
31 pairs of spinal nerves arise from the cord

60. Spinal Cord, Visual

61. Gray matter of spinal cord
Gray matter of spinal cord looks like “H” in xs
Surrounds central canal of cord which contains CVS
2 Dorsal (posterior) and 2 Ventral (anterior) horns
Dorsal horns contain association neurons so is sensory in nature
Ventral horns contain cell bodies of motor neurons of somatic (voluntary) nervous system

62. Gray matter, cont.
Damage of dorsal root results in loss of sensation from body area served
Damage to ventral root results in flaccid paralysis of muscles served
nerve impulses DO NOT reach muscles affected so no voluntary movement possible
muscles begin to atrophy (waste away) because they are no longer being stimulated

63. White matter of the spinal cord
Composed of myelinated fiber tracts
Organized into columns (regions) by irregular shape of gray matter
Posterior, lateral, and anterior columns
Each column contains number of fiber tracts made up of axons with same destination and function
Descending tracts are motor (efferent)
Ascending tracts are sensory (afferent)
Posterior column has ONLY ascending tracts
Anterior and lateral columns contain both ascending and descending tracts

64. Spinal Cord XS, Visual

65. Spinal Transection
Spinal cord transected (cut crosswise) or crushed, spastic paralysis results
Muscles stay healthy—still stimulated by spinal reflex arcs and movement of muscles occurs
However, all movements are involuntary
Cord carries both sensory and motor impulses, loss of feeling or sensory input occurs in body areas below point of cord destruction
Quadriplegic=injury high enough in cord and affects all four limbs
Paraplegic=injury low enough that ONLY legs are affected

66. Anatomy of Typical Nerve
Nerve is bundle of neuron fibers found outside CNS
Within nerve, neuron fibers (processes) are wrapped in protective connective tissue
Each fiber surrounded by endoneurium  groups of fibers surrounded by perineurium to form fiber bundles or FASCICLESall fascicles bound together by tough fibrous sheath called epineurium to form cordlike nerve
Nerves carrying both sensory/motor fibers called MIXED NERVES
ALL SPINAL NERVES ARE MIXED NERVES

67. Nerve Anatomy, Visual

68. Cranial Nerves 12 PAIRS of cranial nerves that serve head and neck
Only one pair, the VAGUS, extends to thoracic and abdominal cavities
Most are mixed except for optic, olfactory, and vestibulocochlear nerves which are purely sensory
“Oh, oh, oh, to touch and feel very good velvet, ah”

69. Cranial Nerves, Visual

70. Spinal Nerves
31 Pairs of spinal nerves formed by combination of ventral & dorsal roots of spinal cord
Named for region of cord from which they arise
Cervical (8); Thoracic (12); Lumbar (5); Sacral (5); Coccygeal (1)
Almost immediately after being formed, each divides into dorsal & ventral RAMI

71. Getting on who’s nerves

72. Spinal Nerves, cont. RAMI contain both sensory & motor fibers
Smaller dorsal rami serve skin & muscles of posterior trunk
Ventral rami form complex networks of nerves called plexuses which serve motor and sensory needs of limbs
Ventral rami of T1-T12 form intercostal nerves which supply muscles between ribs/skin and muscles of anterior and lateral trunk

73. Plexuses
Ventral rami form nerve complexes that serve sensory/motor needs of limbs
Formed by ventral rami of spinal nerves OTHER than T1-T12
Cervical (C1-C5)
Brachial (C5-C8; T1)
Lumbar (L1-L4)
Sacral (L4-L5; S1-S4)
Major nerves of body emanate from a plexus

74. Four Major Nerves of Body
Phrenic = breathing; damage results in respiratory paralysis and death if not treated promptly
Radial = triceps/extensor muscles of forearm; damage results in wristdrop—the inability to extend hand at wrist
Ulnar = wrist and many hand muscles; damage results in clawhand—inability to spread fingers apart
Sciatic = largest nerve in body; splits to form fibular/tibial nerves; damage results in sciatica (pain along peripheral distribution of nerve; inability to extend hip and flex knee

75. Autonomic Nervous System
ANS is motor subdivision of PNS that controls body activities automatically
Composed of special group of neurons that regulate cardiac muscle, smooth muscles (walls of visceral organs/blood vessels) and glands
Relative stability of homeostasis depends on workings of ANS
ANS called “involuntary nervous system”
Sympathetic and Parasympathetic Divisions

76. Comparing…and more
Somatic motor division cell bodies are INSIDE CNS and axons extend to skeletal muscles they serve
ANS has chain of two motor neurons
FIRST is in the brain or spinal cord
Its axon (preganglionic axon) leaves CNS to synapse with second motor neuron in ganglion outside CNS
Axon of second neuron (postganglionic) extends to organ it serves

77. Parasympathetic Division
Most active when body at rest
Often called “resting and digesting system”
Concerned with normal digestion and elimination of urine and feces; and with conserving energy by decreasing demands on CV system
Acetylcholine is neurotransmitter PRE- and POSTGANGLIONIC

78. Sympathetic Division
Acetylcholine as PREganglionic; norepinephrine and epinephrine as POSTganglionic
Called “fight or flight” system
Increases heart rate, BP, blood glucose levels, dilates bronchioles of lungs, dilation of skeletal blood vessels and withdrawal of blood from digestive organs
**ONLY sympathetic division controls blood vessels

79. Nervous System, Visual