1. The Nervous System
Mindy Milton, MPA, PA-C
July 15, 2010

2. Neurological Anatomy
• Neurons
– Functional units of the nervous system
• Fuel source is glucose
• Does not require insulin for cellular uptake
• Structure
– Cell body: contains nucleus, neurofilaments, and neurotubules.
Mitochondria active due to high energy needs, contain Nissl
bodies that are responsible for the grey color of the neuron
tissue
– Dendrites: fine highly branched structures that are responsible
for receiving information and transmitting to cell body
– Axon: long projection that is capable of propagating an action
potential

3. • Neurons
– Neuronal structure
• Anaxonic: small with no anatomical clues to
identify dendrite from axon
• Unipolar: single dendrite and axon that are
essentially fused with cell body that lies off to the
side
• Bipolar: two distinct processes ie axon and
dendrite
• Multipolar: have two or more dendrites and a
single axon

4. NEURON TYPES

5. Types of neuronal structure

6. Multipolar Neuron

7. Neuroglia
Oligodendrocytes
Astrocyte
Ependymal
Microglia
Cells
cells

8. Neurological Anatomy
• Synapse
– Definition: specialized site where the neuron
communicates with another cell
– Components
• Pre-synaptic cell: neuron that sends the message
• Post- synaptic cell: neuron or muscle cell that receives a
message
• Neurotransmitters: chemical substances that are released by
the pre-synaptic cell and cause a change in electrical activity
of the post-synaptic cell i.e stimulation of an impulse

9. SYNAPTIC TRANSMISSION

11. NEUROMUSCULAR
JUNCTION
• Anatomy:
– Axon terminal contains large numbers of
mitochondria that are important in the
synthesis of acetylcholine
– Acetylcholine is stored in multiple vesicles
– Synaptic cleft: area between the axon and the
muscle fiber
– Sub neural cleft: invagination of the muscle
fibers that increases surface area

13. Neurotransmitters
These have either excitatory functions, inhibitory or both
• Acetylcholine
• Norepinephrine
• Serotonin
• Dopamine
• Histamine
• Gamma aminobutyric acid (GABA)
• Glycine
• Glutamate and Aspartate
• Endorphin
• Substance P

14. Cerebral Cortex
• General Principles
– Each cerebral cortex receives information
from and sends motor commands to the
opposite side of the body
– Two hemispheres have different functions
– Assignment of specific functions to a specific
region of the brain is imprecise at this time

16. Neurological Anatomy

17. Pre-Frontal Function
• Alertness and orientation
• Mood
• Attention
• Perception
• Memory
• Thought content
• Thought process
• Insight
• Judgment
• Language

18. Examination of pre-frontal function
• Observation of alertness, dress, hygiene,
manor.
• Coma scale, e.g. Glascow
• General conversation and history-taking
• Mental status examinations
• Special scales, e.g., depression, alcohol

19. CEREBRUM
• FRONTAL LOBE • PARIETAL LOBE
– Contains somatic motor – Contains somatic sensory
areas areas
• Voluntary • Primary
• Premotor area • Association
• Eye fields – Important in the
interpretation of sensory
– Important in the control
data
of body movements
– Loss is associated with
– Loss is associated with
difficulty recognizing
inability to direct and
objects, forms, or having a
program movements
sense of body parts

20. Homunculus

22. CEREBRUM
• TEMPORAL LOBE
– Hearing and speech is located in the
dominant hemisphere
– Responsible for the interpretation and
understanding of speech
– Major area of long term memory storage
– “General Interpretative or Wernicke’s area”
– Vestibular sense

23. CEREBRUM
• OCCIPITAL LOBE
– Vision and the visual interpretative area
• CORPUS CALLOSUM
– Connects the two hemisphere’s and helps
coordinate activities between them. Transfers
learned descrimination, experiences, and
memories

24. Neurological Anatomy
• Cerebral Cortex
– Association areas: storage, analysis and
interpretation of sensory data
• Somatic association area
• Visual association area
• Auditory association area

25. Neurological Anatomy
• Integrative Areas
– Integrate information from multiple association areas
and direct complex motor activity
– General Interpretive Area: (Wernike’s Area)
• Present in the left hemisphere
• Receives information from all of the sensory association
areas
• Provides the ability to interpret what is seen and heard,
coordinates access to complex visual and auditory memories
– Broca’s area:
• Motor neurons in the general interpretative area that
coordinate the activity of the respiratory, pharyngeal, and
muscles of the tongue, cheeks, and jaws

26. Anatomy

27. CEREBRUM
• BASAL GANGLION
– Exerts regulating,
controlling influences
on motor integration
– Numerous pathways
from the motor cortex
– Dopamine and GABA
found here and are
responsible for
inhibition of tone

28. DIENCEPHLON
• THALAMUS
– Receives sensory
information for somatic
senses, taste, hearing, and
relays to cerebral cortex
– System of connecting
nuclei
• HYPOTHALAMUS
– Temperature regulation,
thirst center, ADH release
– Behavior: affective nature
of sensory stimuli
– Hormonal control

29. BRAIN STEM
• MIDBRAIN
– Located between the Pons
and diencephalon
– Contains both motor and
sensory pathways
– Contains the nuclei for the
third and fourth cranial
nerves
• MEDULLA
– Located between the Pons
and spinal cord
– Center for vegetative
functions
– Cranial nerve tracts for
8,9,10,11,12

30. Reticular Activating System

31. CEREBELLUM
• CEREBELLUM
– Important in
synchronization of muscle
movement
– Monitors and makes
corrective movements
– Receives information from
the motor and sensory
cortex, and peripheral
sensory receptors
– Serves as feedback
regulator
– “Damping” of movement

32. Neurological Anatomy: CSF
• Produced by the choroid
plexus in the lateral, third
and fourth ventricles
• Flow pathway
– Lateral ventricle
– Foramen of Monroe
– Third ventricle
– Aqueduct of Sylvius
– Fourth ventricle
– Foramina of Luschka,
Foramen of Magendi

33. CSF
• Allows passage of
nutrients between the
blood and extracellular
fluid of the brain
• Reabsorbed by the
arachnoid villi
• Blood brain barrier:
selective ability for
substances to enter the
brain through the
capillaries of the choroid
plexus.

34. CSF
• Cerebral Spinal Fluid
– Reabsorbed by the arachnoid villa secondary
to pressure gradient
– Arachnoid villa act as one way valve that
moves CSF fluid out into blood
– Obstruction of flow of CSF fluid will increase
pressure within cranial cavity.
– Hydrocephalus is the result of increased CSF

35. Hydrocephalus

36. MENINGES
• Dura mater: tough outer meningeal
membrane that lies directly below the
skull. The epidural space lies between the
dura and the skull
• Arachnoid: middle meningeal membrane
with tissue arranged in a web like fashion.
Cross the subdural space and reabsorb
CSF

37. MENINGES
• PIA MATER: is a vascular thin membrane
that covers the brain and the spinal cord
– Vessels pass between the pia and the
arachnoid through the subarachnoid space

38. Neurological Anatomy:Meninges

39. Spinal Cord
• Spinal Cord Nerves
– Vertebrae
• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 Sacral
• 1 coccygeal
– Divided into sensory
and motor pathways

40. MOTOR SYSTEM
• SPINAL CORD
– Automatic reflex control
– Thirty one pairs of spinal nerves with a
sensory and motor root
– Anterior Horn cells are large myelinated motor
neurons that terminate on skeletal muscle

41. Spinal Cord View

42. SENSORY SYSTEM
• Afferent transmission through posterior
(dorsal) horns of the spinal cord
• Sensory tracts
– Spinothalamic
• Small myelinated/non-myelinated fibers
• Poorly localized sensation of crude touch, pain,
temperature
• Fibers synapse quickly on entering the spinal cord
and cross over to the opposite side

43. SENSORY TRACTS
• POSTERIOR COLUMN
– Larger fibers that are myelinated with increased
degree of spatialization
– Carries fibers for touch requiring localization, vibratory
sense, and position sense
– Travels up same side of cord and synapses with
second order neuron that travels to thalamus
– Well spatialized: organized for increased ease of
sensory interpretation and localization

44. • Sensory Pathways
• Pain and temperature
• Cross at Cord level.
• Touch crosses at
• Medulla

45. Neuro Anatomy: Sensory Tracts

46. Neuro Anatomy: Sensory Tracts

47. MOTOR SYSTEM
• MOTOR CORTEX
– Initiation of the pyramidal tract in the large
Betz cells within the motor cortex
– Impulses sent down to the motor tracts with
collateral messages to the cerebellum, basal
ganglia, and reticular activating system

48. Motor pathways
• Lower motor
• Upper motor
– Pyramidal
• Fine discrete
– Extrapyramidal
• Coordination- cerebellar
• Tone- mid-brain

49. MOTOR TRACTS
• CORTICOSPINAL -
PYRAMIDAL
– UMN Fibers pass from the
cell body of the Betz cell in
the motor cortex through
the brain stem down the
opposite side of the cord
– Responsible for fine
discrete motor movement
– Synapse with inter-neurons
or anterior horn cells in the
spinal cord
– Necessary for voluntary
movement
– Excitatory in nature

50. MOTOR TRACTS
• BASAL GANGLIA -
EXTRAPYRAMIDAL
– All tracts outside the
corticospinal system
– Controls body tone and
gross body movements
• Cerebellum
– Sensory and motor input
– Controls posture and
coordination

51. Motor Pathways
• Most cross at Medulla
in pyramid-shaped pathways.
– Some don’t cross
So whole tract is called
Pyramidal tract.

52. Neuro Anatomy: Motor Tracts

53. Cerebellar Function

54. Test Motor pathways
• DTRs
• Active range of motion
(include CN III, IV, VI, VII, XI, XII)
• Gait
• Romberg
• Coordination

55. Blood Supply: CNS
• General Concepts
– 20% of cardiac output per minute
– Blood supply controlled largely by changes in the
level of carbon dioxide
• Arterial Blood Flow
– Internal carotids enter through the skull, branch into
the anterior and middle cerebral arteries
– Vertebral arteries: originate from the subclavian, enter
the skull through the foramen magnum, join to form
the basilar artery, that will then divide and form the
posterior cerebral arteries

56. Blood Supply: CNS
• Circle of Willis
– Formed by posterior cerebral arteries,
posterior communicating arteries, internal
carotid arteries, anterior cerebral arteries, and
anterior communicating arteries
– Ring shaped anastomosis allows for
protection of blood flow interruption from the
vertebral or carotid arteries

57. Blood Supply: CNS

59. Blood Supply: CNS

60. Peripheral Nervous System
• Two Components
– Spinal and cranial nerves
– Autonomic Nervous system
• Spinal Nerves
– Mixed nerves as they contain both sensory and motor neurons
– Divide and form posterior and anterior rami
– Anterior rami then form plexuses
• Brachial plexus: C 5-8 and T1 innervates the nerves of the arm, wrist, and
hand
• Lumbar plexus: L2-4 and sacral plexus: L5-S5 innervate the anterior and
posterior portions of the lower body
– Posterior rami form dermatomes that are distributed to specific areas of
the body
– Cranial Nerves: Most are mixed nerves that arrive from nuclei in the
brain or brain stem

61. Neurological Anatomy
• Peripheral Nervous System
– All nervous tissue outside of the central nervous
system
– Important in the delivery of sensory data to the CNS
and transmission of motor commands from the CNS
– Two divisions
• Afferent: brings sensory data into CNS
• Efferent: transmits motor information from CNS
– Somatic nervous system: skeletal muscles
– Autonomic nervous system: visceral motor system

62. Sensory System
• Smell
• Vision
• Hearing
• Taste
• Touch
• Pain
• Temperature
• Pressure
• Position
• Vibration

63. Testing the Sensory System
• Cranial nerves I, II, V, VII, VIII, IX, X
• Body sensory touch, pain, temperature
• DTRs
• Vibratory
• Position
• Romberg

64. Cranial Nerve: Olfactory

65. Cranial Nerve: Optic

66. Optic Nerve
• The visual signals
of the right half of
both eyes goes
to left visual cortex

67. Cranial Nerve: Trigeminal

68. Cranial Nerve: Facial

69. Cranial Nerve: Acoustic

70. Cranial Nerve: Glossopharyngeal

71. Cranial Nerve: Vagus

73. • Dermatome
Distribution

74. • Peripheral Nerve
Distribution

75. Lower Motor Neuron Pathway

76. Reflexes
• Test sensory
perception
• Sensory pathway
• Sensory-motor
connection
• Motor nuclei
• Motor pathway
• Muscle function
• Neurotransmitters.
• Flexible joint

77. Autonomic system
• Sympathetic
• Parasympathetic
• Test largely by history
• Note skin temp, moisture,
• Vital signs
• Pupillary response to light,
accommodation

80. The End