1. The Nervous System: The Spinal Cord & Spinal Nerves
Chapter 9
Anatomy & Physiology I

2. Outline ROLE OF THE NERVOUS SYSTEM
Structural divisions—anatomic (CNS and PNS)
Functional divisions—physiologic (somatic and autonomic)
NEURONS AND THEIR FUNCTIONS
Structure of a neuron (cell body, cell fibers, myelin sheath)
Types of neurons (afferent, efferent, interneuron)
Nerves and tracts—bundles of neuron fibers
NEUROGLIA
Nonconducting cells
Protect and support nervous tissue
THE NERVOUS SYSTEM AT WORK
Nerve impulse (action potential)
Synapse—junction between neurons (neurotransmitter, presynaptic, postsynaptic, receptors)
SPINAL CORD
Location
Structure of the spinal cord
Reflex arc—pathway through the nervous system
Medical procedures involving the spinal cord
Diseases and other disorders of the spinal cord
SPINAL NERVES—31 PAIRS
Roots
Mixed nerves—combine sensory and motor fibers
Branches of the spinal nerves
Disorders of the spinal nerves—peripheral neuritis, sciatica, herpes zoster, Guillain-Barré
AUTONOMIC NERVOUS SYSTEM (VISCERAL NERVOUS SYSTEM)
Characteristics
Divisions of the autonomic nervous system
Cellular receptors
Functions of the autonomic nervous system

3. I. Role of the Nervous System
Chief coordinating center for all body systems
Conditions internally & externally are constantly changing. These changes stimuli.
Nervous system detects & responds to changes (stimuli) so the body can adapt & maintain homeostasis >> nerves carry message to and from Centers (Brain and the spinal cords)
Sensors- Nerves that detect stimuli
Effector – any tissue that carries out a command from the NS; they are muscles or glands

4. Anatomic Divisions of the Nervous System
1. Structural Division
Central nervous system(CNS)
Brain &
Spinal cord
Peripheral nervous system (PNS)
Cranial nerves
Spinal nerves
Nerves carrying messages to & from the body

5. Somatic nervous system
2. Functional Division
Somatic nervous system
Controlled voluntarily
Effectors are skeletal muscles
No further subdivision
Autonomic nervous system
involuntarily controlled
Effectors: smooth muscle, cardiac muscle, glands
Subdivided into:
Sympathetic nervous system and
Parasympathetic nervous system

7. Neurons and Their Functions
Neurons: Functional cell of the nervous system

8. Neuron Structure Cell body: Cell fibres: Contains nucleus & organelles
Ganglion – a collection of nerve cell bodies that are located outside
Cell fibres:
Dendrite – fibers that conduct nerve impulses to the nerve body
Highly branched, tree-like appearance
Receptors of the NS – receive stimuli to NS
Axon - fibers that conduct nerve impulses away from the nerve body
Deliver impulses to another neuron, a muscle or a gland
Single long fiber

10. Myelin Sheath
Covering of fatty material over some axons that acts as an insulator
Schwann cell – a glial cell that produces myelin in the PNS in layers
Nodes of Ranvier – spaces between the myelin sheath
Nerve impulses jump from node to node, increasing their speed of conduction along an axon

13. Myelin Sheath - Neurilemma
Neurilemma – outer membrane of a Schwann cell that allows some peripheral nerves to repair themselves if injured
Neurilemma creates a sleeve into which a nerve can regenerate
CNS is not myelinated by Schwann cells so have no mechanism by which to repair themselves

14. Myelination & Axon Regeneration

15. White Matter vs Gray Matter
White matter – myelinated part of the NS
Gray matter – unmyelinated part of the NS

16. Types of Neurons Sensory neurons (afferent neurons)
relay information to the CNS
Motor neurons (efferent neurons)
relay information from the CNS; efferent neurons
Interneurons
relay information within the CNS

17. Nerves & Tracts Nerve – a bundle of nerve fibers within the PNS
Tract – a bundle of nerve fibers within the CNS
Fascicles – a bundle of nerve fibers within a nerve or tract
Endoneurium – connective tissue surrounding an individual nerve fiber
Perineurium – connective tissue surrounding a neural fascicle
Epineurium – connective tissue surrounding an entire nerve

20. Neuroglia aka Glial Cells
Support nervous tissue & bind it to other structures (i.e. Schwann cells)
Aid in repair of cells
Act as phagocytes to remove pathogens & impurities (i.e. astrocytes)
Regulate the composition of fluids around cells
Can reproduce

21. Glial Cells

22. The Nervous System at Work
The NS works by means of electrical impulses sent along neuron fibers and transmitted between cells at junctions

23. Nerve Impulse Resting state a neuron at rest; polarized Depolarization
a neuron being stimulated, causing an electrical charge
Repolarization
the electrical charge
leaves and the neuron
returns to its resting state

24. Nerve Impulse – Resting State
Resting state – a neuron at rest
Neurons at rest are polarized with a separation of + & - ions on either side of its plasma membrane (like a battery)
- ions are on the inside of the plasma membrane
Resting neuron has a negative charge
The separation of ions creates the potential for creating energy

25. Nerve Impulse - Depolarization
Depolarization – a neuron being stimulated, causing an electrical charge
An electrical, chemical or mechanical force stimulates the neuron
+ ions (Na+ ions) rush into the neuron, causing the neuron to suddenly change from negative to positive
The nerve impulse starts

26. Nerve Impulse - Repolarization
Repolarization – the electrical charge leaves and the neuron returns to its resting state
The neuron cannot be stimulated until it returns to a negative state
The neuron must pump all of the + ions out; pumps out K+
The Na+/K+ pump describes the action of the neuron pumping + ions Na+ & K+ back out of the cell
Requires energy (ATP)

27. Nerve Impulse
Action potential – the traveling of an electric charge along the plasma membrane of a neuron - < 1/1000 of a second

28. Synapse
Point of junction for transmitting a nerve impulse from one nerve axon to
Another nerve dendrite
A muscle at the neuromuscular junction
A gland
Synaptic cleft – the space between one cell & another
Information must cross this cleft for the nerve impulse to continue or create action
Can do this chemically, through neurotransmitters
Can also do this electrically, as in cardiac muscle, CNS, smooth muscle

31. Neurotransmitters
Chemical that crosses the synaptic cleft from the axon of one neuron to signal the receiving cell
Receptors – on the receiving dendrite, motor end plate or gland that respond to specific neurotransmitters

32. Neurotransmitters Epinephrine aka adrenaline
Norepinephrine aka noradrenaline
Acetylcholine –
Acts between neurons & muscles at the neuromuscular junction

33. Spinal Cord The link between the brain & the peripheral nervous system
Spinal cord ends
around T12 and then
a tail of spinal nerves called the cauda
equina travels the
rest of the way down
the spinal canal

34. Spinal Cord Structure
Composed of both white (myelinated) & gray (unmyelinated) matter
White matter – outer layer
Gray matter – H shaped middle section
Dorsal horn – back part of H
Ventral horn – front part of H
Gray commissure – the middle bar of the H, connecting the dorsal & ventral horn
Central canal: Contains cerebrospinal fluid
Posterior median sulcus: divides the right and left portions of the posterior white matter
Anterior median fissure : separates the right and left portions of the anterior white
matter.

35. Spinal Cord Structure

38. Spinal Cord Structure
Ascending tracts – sensory (afferent) impulses entering the spinal cord carrying information to the brain
Descending tracts – motor (efferent) impulses traveling from the brain to the body

39. Reflex Arc The complete pathway through the nervous system from the
stimulus to the body’s response
Five parts to the reflex arc
1. Receptor
End of dendrite,receives stimulus
2. Sensory neuron
afferent; carries messages
to CNS from body
3. CNS
processes the information
& coordinates response
4. Motor neuron
efferent; message sent from
CNS to body
5. Effector
a muscle or gland outside the
CNS that carries out a response

40. Reflex Activities Simple reflex – rapid automatic response
Involves very few neurons
a given stimulus always produces same response
Spinal reflex – reflex arc passes through the spinal cord & does not travel to the brain
Stretch reflex – muscle is stretched & responds by contracting
A simple spinal reflex

41. Reflex Arc

42. Spinal Nerves
31 pair of nerves that attach directly to the spinal cord; all spinal nerves are mixed nerves
First part of the peripheral nervous system
Attach to spinal cord by 2 branches
Dorsal root – receives sensory information
Dorsal root ganglion – contains all sensory (afferent) neuron cell bodies
Ventral root – send motor information (efferent) to muscles and glands

43. Branches of the Spinal Nerves
Plexus – branches off the spinal nerves that intertwine into a network
Cervical plexus – supplies head & neck
phrenic nerve to diaphragm
Brachial plexus – shoulder and upper extremities
Lumbosacral plexus – pelvis & legs
Sciatic nerve – largest nerve in body; to legs

44. Dermatome
Dermatome
the area of skin
supplied by
a single spinal
nerve

45. Autonomic Nervous System
Regulates glands, smooth muscle & cardiac muscle
Automatic and without conscious awareness
Motor Pathway (efferent) different in ANS than in somatic NS (voluntary) because has 2 motor nerves
Spinal cord to ganglion via preganglionic neuron
Ganglion to effector via postganglionic neuron
Somatic NS has a single motor neuron that travels from spinal cord directly to effector

46. Autonomic vs. Somatic Motor Neurons

47. Divisions of the Autonomic NS
Sympathetic – “fight or flight” responses of organs
Accelerates organs that are needed for flight or fight
Brakes organs that are not needed for flight or fight
Parasympathetic
Brings organs back into balance after stress or danger has been alleviated
Reverses fight or flight effects
Most organs are innervated by both sympathetic & parasympathetic fibers

48. Parasympathetic vs Sympathetic ANS

49. Sympathetic NS Structure
Thoracolumbar – preganglionic efferent motor fibers begin in spinal cord at around T1 and continue to about L2
Synapse with sympathetic ganglia near the spinal cord
Sympathetic chain – close to spinal cord from lower neck to upper abdomen
Collateral ganglia – farther from spinal cord in lower abdomen & pelvis
Celiac ganglion – digestive organs
Superior mesenteric ganglion – small intestine
Inferior mesenteric ganglion – large intestine, urinary & reproductive organs
Postganglionic fibers continue from ganglia to effector organs & glands
Act on effector organs by releasing epinephrine & norepinephrine

50. Parasympathetic NS Structure
Craniosacral – preganglionic efferent motor fibers begin at the brainstem & then begin again at the sacrum
Synapse with ganglia near the effector organs
Terminal ganglia
Postganglionic efferent motor fibers from ganglia to effector organs
Act on effector organs by releasing acetylcholine

52. Diseases and Other Disorders of the Spinal Cord
Multiple sclerosis (MS)
a disease in which the myelin sheath around axons is damaged and the neuron fibers themselves degenerate.
slows the speed of nerve impulse conduction and disrupts nervous system communication
evidence that it involves an attack on the myelin sheath by a person's own immune system, a situation described as autoimmunity. Genetic makeup, in combination with environmental factors, may trigger MS.
At this point, no cure has been found for MS, but drugs that stop the autoimmune response and drugs that relieve MS symptoms are currently under study.
Amyotrophic lateral sclerosis
motor neurons are destroyed
The progressive destruction causes muscle atrophy and loss of motor control until finally the affected person is unable to swallow or talk.
Poliomyelitis
is a viral disease
Infection of the gastrointestinal tract leads to passage of the virus into the blood, from which it spreads to the CNS. Poliovirus tends to multiply in the spinal cord's motor neurons, leading to paralysis, including paralysis of the breathing muscles.
Tumors
Injuries: root -plegia, meaning “paralysis,”
Monoplegia: paralysis of one limb
Diplegia: paralysis of both upper or both lower limbs
Paraplegia: paralysis of both lower limbs
Hemiplegia: paralysis of one side of the body
Tetraplegia: paralysis of all four limbs

53. Disorders of the Spinal Nerves
Peripheral neuritis
Sciatica
Herpes zoster
Guillain-Barré syndrome

54. Disorders of the Spinal Nerves
Peripheral neuritis or peripheral neuropathy: is the degeneration of nerves supplying the distal areas of the extremities. Causing symptoms of pain and paralysis. Causes include chronic intoxication (alcohol, lead, drugs), infectious diseases (meningitis), metabolic diseases (diabetes, gout), or nutritional diseases (vitamin deficiency, starvation).
Sciatica: form of ^. pain along the sciatic nerve and its branches. The most common causes of this disorder are rupture of a disk between the lower lumbar vertebrae and arthritis of the lower spinal column.
Herpes zoster (shingles): characterized by numerous blisters along the course of certain nerves (eg. Intercostal). Shingles is caused by a reactivation of a prior chickenpox virus infection and involves an attack on the sensory cell bodies inside the spinal ganglia.
Guillain-Barré syndrome: polyneuropathy (disorder involving many nerves) muscle weakness caused by loss of myelin, with numbness and paralysis