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1. Unit 7: Nervous System
NRS 237 Principles of Anatomy
Dr. Moattar Raza Rizvi

2. The Nervous system has three major functions:
Nervous System

3. Major Structures of the Nervous System
Thenervoussystem
containstwo main
divisions: thecentral
nervous system
(CNS) and the
peripheral nervous
system
(PNS).
Thecentral nervous
system consistsofthe
brainandspinalcord.
The peripheral nervous
system consists of the vast
network of nerves throughout
the body.

4. Organization of the Nervous System

5. • Somatic (voluntary) nervous system (SNS)
– neurons from cutaneous and special sensory receptors
to the CNS
– motor neurons to skeletal muscle tissue
• Autonomic (involuntary) nervous systems
– sensory neurons from visceral organs to CNS
– motor neurons to smooth & cardiac muscle and glands
• sympathetic division (speeds up heart rate)
• parasympathetic division (slow down heart rate)
• Enteric nervous system (ENS)
– involuntary sensory & motor neurons control GI tract
– neurons function independently of ANS & CNS
Subdivisions of the PNS

6. Neurons: Functional unit of nervous system
The cell body (also called the soma) is the control center of
the neuron and contains the nucleus.
Dendrites, which look like the bare branches of a tree,
receive signals from other neurons and conduct the
information to the cell body. Some neurons have only one
dendrite; others have thousands.
The axon, which carries nerve signals away from the cell
body, is longer than the dendrites and contains few branches.
Nerve cells have only one axon; however,
the length of the fiber can range from a few millimeters to as
much as a meter.
The axons of many (but not all) neurons are encased in a
myelin sheath. Consisting mostly of lipid, myelin acts to
insulate the axon. In the PNS, Schwann cells form the myelin
sheath. In the CNS, oligodendrocytes assume this role.
Gaps in the myelin sheath, called nodes of Ranvier, occur
at evenly spaced intervals
The end of the axon branches extensively, with each axon
terminal ending in a synaptic knob. Within the synaptic
knobs are vesicles containing a neurotransmitter.

7. Functional Classification of Neurons

8. Structural Classification of Neurons

9. Neuroglial Cells: support protect and nourish the neurons

10. Nerve Structure
Nerves are protected by a cloak of
connective tissue called epineurium

11. Myelination in CNS and PNS
In the CNS, the myelin sheath is formed by
oligodendrocytes. Unlike Schwann cells—which
wrap themselves completely around one
axon—one oligodendrocyte forms the myelin sheath
for several axons.
Specifically, the nucleus of the cell is located away
from the myelin sheath and outward projections from
the cell wrap around the axons of nearby nerves.
As a result, there is no neurilemma, which prevents
injured CNS neurons from regenerating. This
explains why paralysis resulting from a severed
spinal cord is currently permanent
In the PNS, the myelin sheath is formed when
Schwann cells wrap themselves around the axon,
laying down multiple layers of cell membrane.
It’s these inside layers that form the myelin
sheath.
The nucleus and most of the cytoplasm of the
Schwann cell are located in the outermost layer.
This outer layer, called the neurilemma, is
essential for an injured nerve to regenerate.

12. SPINAL CORD
Nerves from the cervical region of
the spinal cord innervate the chest,
head, neck, shoulders, arms, hands,
and diaphragm.
Nerves from the thoracic region
extend to the intercostal muscles of
the ribcage, the abdominal muscles,
and the back muscles.
The lumbar spinal nerves innervate
the lower abdominal wall and parts
of the thighs and legs.
Nerves from the sacral region extend
to the thighs, buttocks, skin of the
legs and feet, and anal and genital
regions.
Basically a bundle of nerve
fibers, the spinal cord
extends from the base of the
brain until about the first
lumbar vertebra.
Extending from the end of
the spinal cord is a bundle
of nerve roots called the
cauda equina—so named
because it looks like a
horse’s tail.

13. Structure of the Spinal Cord

14. Meninges of the Spinal Cord

15. Attachment of Spinal Nerves

16. Spinal tracts

17. Spinal Nerves
Spinal nerves(part of theperipheral nervoussystem) relay information from the
spinal cord to therest of thebody.
Most nervescontain both sensory and motor fibersand arecalled mixed nerves.
Thesenervescan transmit signalsin two directions. A few nerves(such astheoptic
nerves) aresensory nerves and contain only sensory (afferent) fibers. They
carry sensationstoward thespinal cord. Othersare motornerves and contain only
motor(efferent) fibers and carry messagesto musclesand glands.

18. Categories of Spinal Nerves
Thirty-one pairs of spinal nerves connect to the spinal cord. They
include:
•8 Cervical nerves (C1-C8)
•12 Thoracic nerves (T1-T12)
•5 Lumbar nerves (L1-L5)
•5 Sacral nerves (S1-S5)
•1 Coccygeal nerve (Co)
The four major plexuses are the cervical plexus, the brachial plexus,
the lumbar plexus, and the sacral plexus.
The first cervical nerve exits the spinal cord between the skull and
the axis. The other nerves pass through holes in the vertebra
(intervertebral foramina).
Once outside the spinal column, each spinal nerve forms several
large branches. Some of these branches subdivide further to form
nerve networks called plexuses.

19. Categories of Spinal Nerves
The cervical plexus contains nerves that supply the muscles
and skin of the neck, tops of the shoulders, and part of the
head. The phrenic nerve, which stimulates the diaphragm
for breathing, is located here.
Thebrachial plexus innervatesthelowerpartoftheshoulderandthearm.
Keynervestravelingintothearmfromthisregionincludetheaxillary
nerve (whichpassesclosetothearmpit,makingitsusceptibletodamagefrom
theuseofcrutches),theradial nerve,theulnar nerve,andthe
median nerve.
Thelumbar plexus—derivedfromthefibersofthefirstfourlumbar
vertebrae—suppliesthethighandleg.Akeynerveinthisregionisthelarge
femoral nerve.
Thesacral plexus isformedfromfibersfromnervesL4,L5,andS1through
S4.(Becauseoftheco-minglingoffibersofthesacralplexuswiththoseofthe
lumbarplexus,thesetwoplexusesareoftenreferredtoasthelum bo sacral
ple xus .)Thesciatic nerve,thelargestnerveinthebody,ariseshereand
runsdownthebackofthe
thigh.Irritationofthisnervecausesseverepaindownthebackoftheleg,a
conditioncalledsciatica.

20. General Structures of the Brain

21. – In the spinal cord = gray matter forms an H-shaped inner core
surrounded by white matter
– In the brain = a thin outer shell of gray matter covers the
surface & is found in clusters called nuclei inside the CNS
Gray and White Matter
– Like the spinal cord, the brain contains both gray and white
matter. Unlike the spinal cord (in which gray matter forms the
interior), in the brain, gray matter forms the surface.
– Specifically, gray matter (consisting of cell bodies and
interneurons) covers the cerebrum and cerebellum in a layer
called the cortex.
– Underneath the cortex is white matter, although gray matter
exists in patches called nuclei throughout the white matter. The
white matter contains bundles of axons that connect one part of
the brain to another.

22. Meninges of the Brain

23. Meninges of the Brain

24. The brain contains four chambers, called ventricles
Ventricles
Two lateral ventricles arch through the
cerebral hemispheres: one in the right
hemisphere and one in the left.
Each of the lateral ventricles connects to a
third ventricle
A canal then leads to the fourth ventricle.
This space narrows to form the central canal,
which extends through the spinal cord.

25. • A clear, colorless fluid called cerebrospinal fluid
(CSF) fills the ventricles and central canal;
• It also bathes the outside of the brain and spinal cord.
• CSF is formed from blood by the choroid plexus (a
network of blood vessels lining the floor or wall of
each ventricle).
Cerebrospinal Fluid

26. Formation and Flow of CSF

27. • Arterial blood supply is branches from circle of Willis
on base of brain
• Vessels on surface of brain----penetrate tissue
• Uses 20% of our bodies oxygen & glucose needs
– blood flow to an area increases with activity in that area
– deprivation of O2 for 4 min does permanent injury
• at that time, lysosome release enzymes
• Blood-brain barrier (BBB)
– protects cells from some toxins and pathogens
• proteins & antibiotics can not pass but alcohol & anesthetics do
– tight junctions seal together epithelial cells, continuous
basement membrane, astrocyte processes covering capillaries
Blood Supply to Brain

28. • The brainstem consists of the midbrain, pons, and
medulla oblongata
Divisions of the Brain: Brainstem

29. Medulla Oblongata

30. Cerebellum

31. Diencephalon: Thalamus & Hypothalamus

32. Diencephalon: Thalamus & Hypothalamus

33. Cerebrum
Frontal Lobe
Parietal Lobe
Occipital Lobe
Temporal Lobe

34. Cerebrum
Frontal Lobe
•Central sulcus forms the
posterior boundary
•Governs voluntary movements,
memory, emotion, social
judgment, decision making,
reasoning, and aggression;
•is also the site for certain aspects
of one’s personality
Parietal Lobe
Temporal Lobe
•Separated from the parietal lobe
by the lateral sulcus
•Governs hearing, smell, learning,
memory, emotional behavior, and
visual recognition
Temporal Lobe
•Concerned
with analyzing
and interpreting
visual
information

35. Cerebrum
Frontal Lobe
Parietal Lobe
•Central sulcus forms the anterior
boundary
•Concerned with receiving and
interpreting bodily sensations (such as
touch, temperature, pressure, and pain);
•also governs proprioception (the
awareness of one’s body and body parts
in space and in relation to each other)
Occipital Lobe
Temporal Lobe

36. Cerebrum
Frontal Lobe
Parietal Lobe
•Central sulcus forms the anterior
boundary
•Concerned with receiving and
interpreting bodily sensations (such as
touch, temperature, pressure, and pain);
•also governs proprioception (the
awareness of one’s body and body parts
in space and in relation to each other)
Occipital Lobe
Temporal Lobe

37. Insula
• Hidden behind the lateral
sulcus
• Plays a role in many
different functions,
including perception,
motor control, self
awareness, and cognitive
functioning

38. Inside the Cerebrum

39. Inside the Cerebrum

40. Limbic System: Two key structures the hippocampus and amygdala.
Sometimes called the “emotional brain,” the limbic system is the seat of
emotion and learning. It’s formed by a complex set of structures that encircle
the corpus callosum and thalamus. In brief, it links areas of the lower brainstem
(which control automatic functions) with areas in the cerebral cortex associated
with higher mental functions.

41. Functions of the Cerebral Cortex
Motor Functions
of the Cerebral
Cortex
Theprimary somatic
motor areaisthe
precentral gyrus.

42. Functions of the Cerebral Cortex
Sensory
Functions of the
Cerebral Cortex
Sensory nervefibers
transmit signalsup the
spinal cord to
thethalamus, which
forwardsthem to the
postcentral gyrus.

43. Functions of the Cerebral Cortex

44. Language
Each aspect of language—which includestheability to read, write, speak, and
understand—ishandled by adifferent region of thecerebral cortex.

45. Cranial Nerves
Thebrain has12 pairsof cranial nervesto relay messagesto therest of thebody

46. Cranial Nerves

47. Cranial Nerves

48. Cranial Nerves

49. Cranial Nerves

50. Cranial Nerves

51. Afferent and efferent neurons
They conduct impulses from
the receptors to CNS
They conduct impulses from
CNS to the effector
The terminals of dendrites
become modified to form
receptors
The axon terminals come in
contact with the motor end
plate to form neuromotor
junction
They are sensory in nature They are motor in nature

52. Grey and white matter
Greyish in color White in color due to
present of fatty myelin
sheath
Comprises of cell bodies,
dendrites and synpases of
neurons
Consists of nerve fibres
(axons) arising from or to the
nerve cells in grey matter
Grey matter is situated on the
surface, while white matter is
located deeper
In the spinal cord, white
matter forms the outer layer
and grey matter is located
deep into the core

53. Cranial Nerves
Cranial Nerve: Major Functions:
I Olfactory • smell
II Optic • vision
III Oculomotor • eyelid and eyeball movement
IV Trochlear
• innervates superior oblique
turns eye downward and laterally
V Trigeminal
• chewing
face & mouth touch & pain
VI Abducens • turns eye laterally
VII Facial
• controls most facial expressions
secretion of tears & saliva
taste
VIII Vestibulocochlear
(auditory)
• hearing
equillibrium sensation
IX Glossopharyngeal
• taste
senses carotid blood pressure
X Vagus
• senses aortic blood pressure
slows heart rate
stimulates digestive organs
taste
XI Spinal Accessory
• controls trapezius & sternocleidomastoid
controls swallowing movements
XII Hypoglossal • controls tongue movements

54. Cranial Nerves
Which cranial nerve is the largest?
CN V (Trigeminal)
Which cranial nerve is the only one that exits the "posterior" side of the brainstem?
CN IV (Trochlear)
How many cranial nerves are responsible for eye movements?
Three: CN III (Oculomotor), IV (Trochlear), and VI (Abducens).
What does "abducens" refer to?
The abducens nerve carries motor impulses to the lateral rectus eye muscle which
moves the eye laterally causing abduction of the eye.
Which cranial nerves carry gustatory (taste) information?
CN VII (Facial), CN IX (Glossopharyngeal) and CN X (Vagus).
Which cranial nerve is the longest?
CN X (Vagus) which reaches from the medulla to the digestive and urinary
organs.
What two cranial nerves carry sensory information about blood pressure to the brain?
CN IX (Glossopharyngeal) and CN X (Vagus).
Which cranial nerve is responsible for pupillary constriction?
CN III (Oculomotor).

55. AUTONOMIC NERVOUS SYSTEM
• Maintain homeostasis
• include such things as the secretion of digestive
enzymes, the constriction and dilation of blood vessels
for the maintenance of blood pressure, and the
secretion of hormones.
• Most of these activities happen independently, or
autonomously.
• The ANS sends motor impulses to cardiac muscle,
glands, and smooth muscle (as opposed to skeletal
muscle, which is innervated by the peripheral nervous
system).
• Because the ANS targets organs, it’s sometimes called
the visceral motor system.

56. Visceral Reflexes
The ANS asserts control through visceral reflexes—similar to somatic
reflexes discussed earlier, but, instead of affecting a skeletal muscle,
these reflexes affect an organ.

57. Structure of the Autonomic Nervous System
Autonomic motorpathways (both sympathetic and parasympathetic)
Somatic motorpathways

58. Comparison of Somatic and Autonomic Nervous Systems
Somatic Autonomic
Innervates skeletal muscle Innervates glands, smooth muscle,
and cardiac muscle
Consists of one nerve fiber
leading from CNS to target
(no ganglia)
Consists of two nerve fibers that
synapse at a ganglion before
reaching target
Secretes neurotransmitter
acetylcholine
Secretes both acetylcholine and
norepinephrine as neurotransmitters
Has an excitatory effect on
target cells
May excite or inhibit target cells
Operates under voluntary
control
Operates involuntarily

59. Divisions of the Autonomic Nervous System
Sympathetic Division Parasympathetic Division
Increases alertness Has a calming effect
Increases heart rate Decreases heart rate
Dilates bronchial tubes to increase air flow in
the lungs
Constricts bronchial tubes to decrease air flow
in lungs
Dilates blood vessels of skeletal muscles to
increase blood flow
Has no effect on blood vessels of skeletal
muscles
Inhibits intestinal motility Stimulates intestinal motility and secretion to
promote digestion
Stimulates secretion of thick salivary mucus Stimulates secretion of thin salivary mucus
Stimulates sweat glands Has no effect on sweat glands
Stimulates adrenal medulla to secrete
epinephrine
Has no effect on adrenal medulla
Has no effect on the urinary bladder or
internal sphincter
Stimulates the bladder wall to contract and the
internal sphincter to relax to cause urination
Causes “fight or flight” response Causes the “resting and digesting” state

60. Receptors
Cholinergic
Receptors
Acetylcholine
may bind to one
of two different
typesof
receptors:

61. Receptors
Adrenergic Receptors
There are also two basic types of adrenergic receptors:
alpha-(-)adrenergic receptors and beta-(-)adrenergic
receptors. The following principles are true most of the
time:
● Cells with a-adrenergic receptors are excited by NE.
● Cells with b-adrenergic receptors are inhibited by NE.

62. Neurotransmitters and Receptors
Sympathetic Division

63. Neurotransmitters and Receptors
Parasympathetic Division

64. Impulse Conduction

65. Impulse Conduction

66. Synapse

67. Synapse

68. Continuous propagation
(continuous conduction)
• Involves entire membrane
surface
• Proceeds in series of small
steps (slower)
• Occurs in unmyelinated
axons (& in muscle cells)
Continuous vs Saltatory propagation

69. Saltatory propagation
(saltatory conduction)
 Involves patches of
membrane exposed at
nodes of Ranvier
 Proceeds in series of
large steps (faster)
 Occurs in myelinated
axons
Continuous vs Saltatory propagation