1. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

2. Spinal Cord Extends from the medulla oblongata to the region of T12
Below L2 is the cauda equina (a collection of spinal nerves)
Enlargements occur in the cervical and lumbar regions
31 pairs of spinal nerves branch off it
Meninges follow cord all the way to the spinal hiatus of the sacrum C7
at L2
Figure 7.18

3. Lumbar Puncture vs. Epidural Space Injection1 2 3
Epidural injection (steroids, anaesthetic) into epidural space
Lumbar puncture for CSF below L2 in larger subarachnoid space

4. Spinal Cord Anatomy
Exterior white mater – conduction tracts (axons) – is myelinated
Internal gray matter - mostly cell bodies, is unmyelinated
Dorsal (posterior) horns (mostly association/interneurons)
Anterior (ventral) horns (motor nerves of somatic system)
Central canal filled with cerebrospinal fluid

5. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

6. What’s in the Gray Matter of the Spinal Cord?
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Spinal nerve
Ventral horn
(motor neurons)
Ventral root
(motor)
Somatic
motor neuron
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32

7. White Matter: Spinal Cord Information Pathways
Dorsal/posterior
Dorsal columns carry only ascending/afferent sensory tracts
Lateral and anterior columns carry both
Ascending/afferent sensory tracts
Descending/efferent motor tracts
Pathways are composed of 2-3 neurons in a chain or relay
Pathways cross from one side of the CNS to the other (decussate)
Ascending fibers add on laterally in cord as they join - they “map” in the tract based on where they enter or exit (somatotopy)
Ventral/anterior
Ascending/Afferent Sensory Tracts only in posterior columns
Ascending/ Afferent Sensory) AND Descending/Efferent Motor) Tracts in lateral and anterior columns

8. Three Ascending Pathways to Somatosensory Cortex
Spinocerebellar tracts
Dorsal column-medial lemniscal pathway
Anterolateral (spinothalmic) pathways
Conveys information about muscle or tendon stretch. Do not contribute to conscious sensation. In lateral columns.
Precise, “straight-through” transmission of inputs from single, localized body surface receptors. In dorsal columns.
Transmission of pain, temperature, and coarse touch. In anterior-ventral and lateral columns.

9. Descending Pathways and Tracts
Indirect (Extrapyramidal system), e.g. the rubrospinal tract
Direct pyramidal pathways stimulate skeletal muscles

10. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

11. Spinal Nerves
Nerve C8 emerges
Below vertebra C7
There is a pair of spinal nerves at the level of each vertebrae (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) = 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

12. Anatomy of Spinal Nerves
Spinal nerves divide soon after leaving the spinal cord
Dorsal ramus – serves the skin and muscles of the posterior trunk
Ventral ramus – forms a complex of networks (plexus) for the anterior part of the body
spinal
nerve
posterior
anterior

13. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

14. Areas of the Skin Served By Single Spinal Nerves
Dermatomes
Used to diagnose spinal cord injury
Pain in a particular skin area reflects trouble in a specific spinal nerve and spinal location
Can help to locate the site of damage in the spinal cord
Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness

15. Infects sensory skin neurons
Shingles (Herpes zoster) is a viral infection of sensory neurons to the skin
Scaly, painful blisters confined to a narrow strip of skin on one side of the body trunk
Infects sensory skin neurons
Caused by latent infection (resurgence) of chicken pox virus when immune system is weakened as an adult
Mostly in people over 50.

16. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

17. Peripheral Nervous System (The PNS)
one neuron (nerve fiber)
Nerves and ganglia outside the central nervous system
Nerve = bundle of neuron fibers
Neuron fibers are bundled by connective tissue; one fiber = 1 axon or cell
Endoneurium surrounds each fiber, just outside of Schwann cells
Groups of fibers are bound into fascicles by perineurium
Fascicles are bound together by epineurium

18. Classification of Nerves
Mixed nerves – both sensory and motor fibers present in the nerve
Afferent (sensory) nerves – carry impulses toward the CNS
Efferent (motor) nerves – carry impulses away from the CNS

19. The Twelve Cranial Nerves (I-V)
I Olfactory nerve – purely sensory for smell; ask patient to identify oil of cloves and vanilla
II Optic nerve – purely sensory for vision; observe eye, test patient with eye chart
III Oculomotor nerve – mostly motor fibers to eye muscles, some proprioreceptive afferents; examine pupil size and reflex, ability to follow objects with the eye
IV Trochlear – mostly motor fibers to extrinsic eye muscles; test patient’s ability to follow objects with eye
V Trigeminal nerve – 3 divisions:
Opthalmic (tested by corneal reflex) carrying sensory for skin of anterior scalp, eyelid, nose
Maxillary (tested with pain, touch temperature using safety pin) carrying sensory from nasal cavity, palate, upper lip, cheek
Mandibular (test by teeth clenching, move jaw) carrying sensory from lower teeth, masseter, temporalis
On Old Olympus' Towering Top a Frisky Virile Gymnast Vaults And Hops
Oh, Oh, Oh, To Touch And Feel Very Good Velvet: AH!
Oh, Oh, Oh, To Touch And Feel And Grip Vegas' Slot Handles!
On Occasion, Our Trusty Truck Acts Funny - Very Good Vehicle Anyhow.

20. The Twelve Cranial Nerves (Vi-XIII)
VI Abducens nerve – motor fibers to eye muscles (lateral rectus); test by having patient follow object side-to-side
VII Facial nerve – sensory for taste; motor fibers to the face (test with ability to taste sweet salt, sour, bitter and close eyes, smile, whistle, make tears); five major branches: temporal, zygomatic, buccal, mandibular, cervical
VIII Vestibulocochlear nerve – sensory for balance (semicircular canals) and hearing; test with air and bone conduction with tuning fork
IX Glossopharyngeal nerve – sensory for taste and touch, pressure, pain from posterior tongue; motor fibers to the swallowing muscles in pharynx; test for gag and swallowing reflex, cough, taste, uvula position
X Vagus nerves – sensory (including aortic arch baroreceptors, respiration) and motor fibers for pharynx, larynx, and viscera (heart rate, breathing, digestive activity); test by gag, swallowing reflexes
XI Accessory nerve – mostly motor fibers to neck and upper back (trapezius, sternocleidomastoid); test for head rotation strength and shrugging against resistance
XII Hypoglossal nerve – mostly motor fibers to tongue allowing food manipulation; test by tongue protraction and retraction)
On Old Olympus' Towering Top a Frisky Virile Gymnast Vaults And Hops
Oh, Oh, Oh, To Touch And Feel Very Good Velvet: AH!
Oh, Oh, Oh, To Touch And Feel And Grip Vegas' Slot Handles!
On Occasion, Our Trusty Truck Acts Funny - Very Good Vehicle Anyhow.

21. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

22. Reflexes Classification by Acquisition
Inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response to a stimulus
E.g. withdrawing your arm when fingers burned
Learned (acquired) reflexes result from practice or repetition
Example: driving skills, knitting
Classification by Function
Somatic (drives skeletal muscle)
Autonomic/visceral if activates visceral effectors in glands or smooth and cardiac muscle
Classification by Number of Synapses
Monosynaptic - e.g. any stretch reflex like knee-jerk reflex
Polysynaptic - e.g.
Golgi tendon reflex causing muscle relaxation and lengthening
Flexor/withdrawal reflexes causing flexion of muscles to pull limb away
Crossed-extensor reflexes casuing withdrawal and opposing extensor activity like sudden pain in the foot and shifting of weight

23. Basic Reflex Arc 1 2 3 4 5 Stimulus Skin Interneuron Receptor
Sensory neuron 3
Integration center 4
Motor neuron 5
Effector
Spinal cord
(in cross section)
Figure 13.14

24. Stretch Reflexes are Monosynaptic Pathways Triggered By Muscle Stretching
Stretched muscle spindles initiate a stretch reflex,causing contraction of the stretched muscle and inhibition of its antagonist.
The events by which muscle stretch is damped
Sensory neuron
Cell body of sensory neuron
Initial stimulus (muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Figure (1 of 2), step1

25. Stretch Reflexes are Monosynaptic Pathways Triggered By Muscle Stretching
Stretched muscle spindles initiate a stretch reflex,causing contraction of the stretched muscle and inhibition of its antagonist.
The events by which muscle stretch is damped 1
When muscle spindles are activated by stretch, the associated sensory neurons (blue) transmit afferent impulses at higher frequency to the spinal cord.
Sensory neuron
Cell body of sensory neuron
Initial stimulus (muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Figure (1 of 2), step1

26. Cell body of sensory neuron
Stretched muscle spindles initiate a stretch reflex, causing contraction of the stretched muscle and inhibition of its antagonist.
The events by which muscle stretch is damped 2
The sensory neurons synapse directly with alpha motor neurons (red), which excite extrafusal fibers of the stretched muscle. Afferent fibers also synapse with interneurons (green) that inhibit motor neurons (purple) controlling antagonistic muscles. 1
When muscle spindles are activated by stretch, the associated sensory neurons (blue) transmit afferent impulses at higher frequency to the spinal cord.
Sensory neuron
Cell body of sensory neuron
Initial stimulus (muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Figure (1 of 2), step 2

27. Cell body of sensory neuron
Stretched muscle spindles initiate a stretch reflex, causing contraction of the stretched muscle and inhibition of its antagonist.
The events by which muscle stretch is damped 2
The sensory neurons synapse directly with alpha motor neurons (red), which excite extrafusal fibers of the stretched muscle. Afferent fibers also synapse with interneurons (green) that inhibit motor neurons (purple) controlling antagonistic muscles. 1
When muscle spindles are activated by stretch, the associated sensory neurons (blue) transmit afferent impulses at higher frequency to the spinal cord.
Sensory neuron
Cell body of sensory neuron
Initial stimulus (muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle 3a
Efferent impulses of alpha motor neurons cause the stretched muscle to contract, which resists or reverses the stretch.
Figure (1 of 2), step 3a

28. Cell body of sensory neuron
Stretched muscle spindles initiate a stretch reflex, causing contraction of the stretched muscle and inhibition of its antagonist.
The events by which muscle stretch is damped 2
The sensory neurons synapse directly with alpha motor neurons (red), which excite extrafusal fibers of the stretched muscle. Afferent fibers also synapse with interneurons (green) that inhibit motor neurons (purple) controlling antagonistic muscles. 1
When muscle spindles are activated by stretch, the associated sensory neurons (blue) transmit afferent impulses at higher frequency to the spinal cord.
Sensory neuron
Cell body of sensory neuron
Initial stimulus (muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Efferent impulses of alpha motor neurons cause the stretched muscle to contract, which resists or reverses the stretch. 3a 3b
Efferent impulses of alpha motor neurons to antagonist muscles are reduced (reciprocal inhibition).
Figure (1 of 2), step 3b

29. The patellar (knee-jerk) reflex—a specific example of a stretch reflex2
Quadriceps (extensors) 3a 3b 3b 1
Patella
Muscle spindle
Spinal cord (L2–L4) 1
Tapping the patellar ligament excites muscle spindles in the quadriceps.
Hamstrings (flexors)
Patellar ligament 2
Afferent impulses (blue) travel to the spinal cord, where synapses occur with motor neurons and interneurons.
The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending the knee. 3a
+ –
Excitatory synapse Inhibitory synapse
The interneurons (green) make inhibitory synapses with ventral horn
neurons (purple) that prevent the antagonist muscles (hamstrings) from resisting the contraction of the quadriceps. 3b
Figure (2 of 2)

30. Golgi Tendon Reflex: A Polysynaptic Reflex1
Quadriceps strongly
contracts. Golgi tendon
organs are activated. 2
Afferent fibers synapse
with interneurons in the
spinal cord.
Interneurons
Quadriceps
(extensors)
Spinal cord
Golgi
tendon
organ
Hamstrings
(flexors) 3a
Efferent impulses
to muscle with
stretched tendon are
damped. Muscle
relaxes, reducing
tension. 3b
Efferent
impulses to
antagonist
muscle cause
it to contract. +
Excitatory synapse –
Inhibitory synapse
Figure 13.18

31. Crossed Extensor Reflex: A Polysynaptic Reflex
+ Excitatory synapse
– Inhibitory synapse
Interneurons
Efferent
fibers
Afferent
fiber
Efferent
fibers
Extensor
inhibited
Flexor
inhibited
Arm
movements
Flexor
stimulated
Extensor
stimulated
Site of reciprocal
activation: At the
same time, the
extensor muscles
on the opposite
side are activated.
Site of stimulus: a noxious
stimulus causes a flexor
reflex on the same side,
withdrawing that limb.
Figure 13.19

32. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

33. Autonomic Nervous System
The involuntary branch of the nervous system
Consists of only motor nerves
Innervate smooth and cardiac muscle and glands
Make adjustments to ensure optimal support for body activities
Operate via subconscious control
Divided into two divisions
Sympathetic division
Parasympathetic division
somatic sensory fibers
Skin, muscle, and joint sensors
visceral sensory fibers (visceral afferents)
and reflexes
Visceral organ sensors
inhibitory stimulatory

34. Efferent Pathways Somatic nervous system
A, thick, heavily myelinated somatic motor fiber makes up each pathway from the CNS to the muscle
ANS pathway is a two-neuron chain
Preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon
Ganglionic neuron in autonomic ganglion has an unmyelinated postganglionic axon that extends to the effector organ

35. Differences Between Somatic and Autonomic Nervous Systems
Nerves
one motor neuron, always stimulatory
preganglionic and postganglionic nerves
(two neurons connected end to end); stimulatory and inhibitory types
Effector organs
skeletal muscle
smooth muscle, cardiac muscle, and glands
Nerurotransmitters
always uses acetylcholine
uses ACh in pre-ganglionic neurons; either ACh or norepinephrine in post-ganglionic fibers

36. Comparison of Somatic and Autonomic Nervous Systems
Closer to spinal cord than target
Closer to target than spinal cord

37. Anatomy of the Sympathetic Division
Originates from T1 through L2
Short pre-ganglionic neuron and long postganglionic neuron transmit impulses from CNS to the effector
Ganglia are closer to the spinal cord than the target
Norepinephrine and epinephrine are neurotransmitters to the effector organs

38. Anatomy of the Parasympathetic Division
Originates from the brain stem (cranial nerves III,VII, IX, X) and S1 through S4
Long pre-ganglionic neuron and short postganglionic neuron transmit impulses from CNS to the effector
Terminal ganglia are at the effector organs (closer to target than spinal cord)
Always uses acetylcholine as a neurotransmitter

39. Autonomic Functioning
Sympathetic – “fight-or-flight”
Response to unusual stimulus
Takes over to increase activities
Remember as the “E” division = exercise, excitement, emergency, and embarrassment
Parasympathetic – housekeeping activites
Conserves energy
Maintains daily necessary body functions
Remember as the “D” division - digestion, defecation, and diuresis

40. Sympathetic and Parasympathetic Compared
Sympathetic Division
Parasympathetic Division

41. Neurotransmitters and Receptor Types
Cholinergic fibers release the neurotransmitter acetylcholine (Ach)
All ANS preganglionic axons
All parasympathetic postganglionic axons
Post synaptic membranes have cholinergic receptors
Adrenergic fibers release the neurotransmitter norepinephrine (NE)
Most sympathetic postganglionic axons
Post synaptic membranes have adrenergic receptors
Two general class types
Alpha (), e.g. 1: constricts blood vessels & sphincter, dilates pupils
Beta (), e.g. 1: increases heart rate, stimulates renin release (BP)
2: inhibitory; dilates blood vessels and bronchioles, relaxes smooth muscle walls of GI tract, bladder, uterus

42. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System

43. Interactions of the Autonomic Divisions
Most visceral organs have dual innervation
Dynamic antagonism allows for precise control of visceral activity
Sympathetic division increases heart and respiratory rates, and inhibits digestion and elimination
Parasympathetic division decreases heart and respiratory rates, and allows for digestion and the discarding of wastes

44. Four Steps of Regeneration of Peripheral Nerves
Axon sprouts or filaments grow through a regeneration tube formed by Schwann cells
Axon becomes fragmented at injury site
Axon regenerated and a new myelin sheath forms
Macrophages clean off the dead axon distal to the injury

45. Developmental Aspects of Fetal Nervous System
Measles (rubella)
Lack of oxygen
Radiation and drugs
Lack of folic acid
Premature birth problems

46. Aging of the Brain and Nervous System
No more neurons are formed after birth, but growth and maturation continues for several years; brain atrophies in old age
Loss of sympathetic nervous activity and slowing of vasoconstriction (e.g. headrushes, dizziness)
Circulatory problems
Dry eyes, constipation
Need for regular checkups when elderly
Enlargement of the subarachnoid space (left) and loss of white matter (right)
Shrinkage of hippocampus (left) and enlargement of ventricles (right)

47. The Spinal Cord (CNS) and Peripheral Nervous System
Meninges and Injections/Punctures
Tracts and Information Pathways
Spinal nerves
Medical conditions: Spinal cord injury, shingles
Peripheral Nervous System
Structure of a Nerve and Its Wrappings
The Twelve Cranial Nerves
Reflexes: Monosynaptic and Polysynaptic
Branches of the Peripheral System
Comparison between autonomic and somatic
Sympathetic division
Parasymphathetic division
Developmental Aspects of the Nervous System