3). Gross Anatomy: Introduction to the Nervous System and Spinal Cord

Building subunit of the nervous system:

Neuron.

The most complex system in the human body is:

The nervous system.

What does the nervous system do?

Coordinates the activity of the muscles, monitors the organs, constructs and stops input from the senses, and initiates actions.

What does the central nervous system consist of (CNS)?

Brain and spinal cord.

What does the peripheral nervous system consist of (PNS)?

Consists of the nerves going to and from the CNS.

What are the two subdivisions of the nervous system?

• Somatic part

• Visceral part

What is the somatic part of the nervous system?

Innervates structures (skin and skeletal muscle) derived from somites in the embryo.

Mainly involved with receiving and responding to information from the external environment.

What is the visceral part of the nervous system?

Innervates organ systems in the body and other visceral elements, such as smooth muscle and glands.

Concerned mainly with detecting and responding to information from the internal environment.

The visceral motor component is referred to what division of the PNS?

Autonomic division.

What does the autonomic division of the PNS do?

Regulates individual organ function and homeostasis, and for the most part is involuntary, reflexive control.

What does the ANS innervate?

*Autonomic nervous system

• Smooth muscle

• Cardiac muscle

• Secretory cells (glandular epithelium)

ANS: Motor components

Motor nerves mainly innervate smooth muscle, cardiac muscle and glands.

ANS: Sensory components

Sensory nerves monitor changes in the viscera.

When is the ANS most important?

• Emergencies; “fight or flight”

• Non-emergencies; “rest and digest”

What division of the nervous system is “fight or flight” part of?

Sympathetic nervous system.

What division of the nervous system is “rest or digest” part of?

Parasympathetic nervous system.

The ANS helps regulate structures associated with:

• Digestion

• Circulation

• Respiration

• Excretion

• Reproduction

• Body temperature

Peripheral Components of the ANS: Sympathetic

• Spinal levels: T1 - L2/L3

• Paravertebral ganglia

• Prevertebral ganglia

Peripheral Components of the ANS: Parasympathetic

• Brain stem - Cranial nerves

• Spinal levels: S2-4

• Ganglia close to target muscles

Neurons Categories:

• General somatic afferents (GSA)

• General somatic efferent (GSE)

• General visceral afferent (GVA)

• General visceral efferent (GVE)

General somatic afferents:

Somatic sensory neurons carry information from the periphery into the CNS and are also called somatic sensory afferents.

PNS → CNS

General somatic efferent:

Somatic motor fibers carry information away from the CNS to skeletal muscles and are also called somatic motor efferent.

CNS → Skeletal muscles

General visceral afferent:

Visceral sensory neurons and their processes, related to ANS and are associated primarily with chemoreception, mechanoreception, and stretch reception.

General visceral efferent:

Visceral motor neurons related to ANS.

What are Dermatomes?

A specific area of skin that sends sensory signals - like touch, temperature and pain - to your brain through a single spinal nerve root.

What is a myotome?

A group of skeletal muscles supplied by a single spinal nerve root.

CNS: Gray Matter

Aggregation of cell bodies.

• Cortex

• Nuclei

CNS: White Matter

Bundles of neuronal axons.

• Tracts

• Fibers

• Columns

PNS: Grey Matter

Ganglia.

PNS: White Matter

Fibers.

How many pairs of spinal nerves are there?

31 pairs.

The spinal nerves are distributed as:

• Cervical = 8

• Thoracic = 12

• Lumbar = 5

• Sacral = 5

• Coccygeal = 1

Spinal Cord Structure:

• Conus medullaris

• The Cauda Equina

• The Filum Terminale

• Cervical enlargement

• Lumbar enlargement

The lateral horn is only a characteristic of two segments in the spinal cord. What are they?

• Thoracic segment

• Upper lumbar segment

The amount of white matter in the spinal cord increases in a _____ direction.

Caudal-to-rostral.

Where does grey matter increase in volume for innervation of the limbs?

In the cervical and lumbosacral enlargements.

What part of the spinal cord contains the highest amount of fibers in the white matter?

Cervical spinal segments.

(The higher you go in the spinal cord, the more “traffic” is traveling through it)

Dorsal Roots

Where afferent fibers (sensory) ENTER the spinal cord.

Dorsal; afferent/sensory

Ventral Roots:

Where efferent fibers (motor) LEAVE the spinal cord.

Ventral; efferent/motor

What do the axons of alpha motor neurons do?

Innervate extrafusal skeletal muscle fibers, producing muscle contraction and force.

What do the axons of gamma motor neurons do?

Innervate intrafusal muscle spindle fibers, adjusting spindle sensitivity and helping regulate muscle tone.

Dorsal Root Ganglion:

A cluster of sensory neuron cell bodies located along the dorsal root of a spinal nerve just outside the spinal cord.

Transverse section of the spinal cord - White and Grey Matter

• Has a roughly H-shaped or butterfly outline

• Central canal is lined by ependymal epithelium

• Dorsal horns: Sensory

• Ventral horns: Motor

• Lateral horn / intermediate zone

Transverse section of the spinal cord - White Matter

Consists of 3 funiculi:

• Dorsal funiculus

• Lateral funiculus

• Ventral funiculus

And contains the dorsolateral tract of Lissauer located between the apex of the dorsal horn and the surface of the cord.

Where is Laminae I - VI located?

Posterior / dorsal horn.

Where is Laminae VII - IX located?

Anterior / ventral horn.

Intermediolateral cell column (IML):

*(T1 - L3)

Preganglionic sympathetic neurons for the ANS.

*GVE

Intermediomedial cell column (IMM):

*(S2-S4)

Preganglionic parasympathetic neurons for the ANS

*GVA

Where are long ascending fibers found?

(Sensory)

Found in all funiculi.

Where are long descending fibers found?

(Motor)

Are found primarily in the lateral and anterior funiculi.

Where are the shorter propriospinal fibers found?

In a thin shell surrounding the grey matter called the propriospinal tract (fasciculus proprius).

What is propriception?

The body’s unconscious ability to sense its own position, movement, and force in space without relying solely on vision.

Spinal Cord Injury:

Damage to the spinal cord that results in a loss of function such as mobility or feeling.

What are frequent causes of spinal cord damage?

• Trauma (gunshot, car accident, falls etc.)

• Disease (Polio, spina bifida, etc.)

Which part of the spinal cord usually results in full or partial tetraplegia?

Cervical (neck) injuries.