1. intro to the nervous system + spinal cord

The nervous system

the most complex system in the human body.

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

what is the building subunit of the nervous system?

Neuron

Neurons → Circuits

afferent neuron

1st neuron that receives info from the environment

Structural subdivisions of the Nervous System

CNS + PNS

CNS central nervous system

brain and the spinal cord

PNS peripheral nervous system

consists of the nerves going to and from the central nervous system.

Functional subdivisions of the Nervous System

Somatic part

Visceral part

Somatic part

innervates structures (skin and most skeletal muscle) derived from somites in the embryo

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

Visceral

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

involuntary

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

Autonomic Nervous System-ANS)

The visceral motor component is commonly referred to as the autonomic division of the PNS

regulates individual organ function and homeostasis

for the most part is involuntary, reflexive control

ANS innervates:

smooth muscle

cardiac muscle

secretory cells (glandular epithelium)

motor and sensory components of ANS

1. sensory nerves monitor changes in the viscera

2. motor nerves mainly innervate smooth muscle, cardiac muscle, and glands.

Visceral part of the nervous system (Autonomic Nervous System)

The ANS is most important in two situations:
1. The Sympathetic Nervous System

• In emergencies that cause stress and require us to "fight" or take "flight" (run away)

2. The Parasympathetic Nervous System

• In non-emergencies that allow us to "rest" and "digest."
  
  

ANS regulates 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

1. General somatic afferents (GSA)

2. General somatic efferent (GSE)

3. General visceral afferent (GVA)

4. General visceral efferent (GVE)

Neurons categories: General somatic afferents (GSA)

Somatic sensory neurons carry information from the periphery into the CNS

also called somatic sensory afferents.

Neurons categories: General somatic efferent (GSE)

Somatic motor fibers carry information away from the CNS to skeletal muscles

also called somatic motor efferent

Neurons categories: General visceral afferent (GVA)

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

Neurons categories: General visceral efferent (GVE)

visceral motor neurons related to ANS.

spinal nerves what should we know abt this?

Dermatomes

the area of skin supplied by a single spinal cord level, or on one side, by a single spinal nerve.

Each dorsal root fibers from all spinal cord segments will supply the sensory innervation to a skin segment in the human body.

Somatic sensory fibers originally associated with that somite enter the posterior region of the spinal cord at a specific level and become part of one specific spinal nerve

Myotome

the portion of a skeletal muscle innervated by a single spinal cord level or, on one side, by a single spinal nerve

each spinal nerve carries somatic motor fibers to muscles that originally
developed from the related somite.

The spinal cord is responsible for

Motor reflexes

Conduct sensory information from the environment to the brain.

Contain pathways for motor impulses going out to the peripheral muscles

contains autonomic efferents

Organization of neurons: Central Nervous system

Grey matter: aggregation of cell bodies ~ Cortex, Nuclei

White matter: Bundles of neuronal axons~ Tracts, Fibers, Columns

Organization of neurons: Peripheral Nervous system

Grey Matter: Ganglia

White Matter: Fibers

The spinal nerves are distributed as:

31 pairs of spinal nerves.

 8 Cervical

12 Thoracic

5 Lumbar

5 Sacral

1 Coccygeal

Spinal Cord Structure

Spinal Cord Structure

Subarachnoid space

Conus medullaris

The Cauda Equina

The Filum Terminale

Cervical enlargement

Lumbar enlargement

Meninges

An outer dura mater, middle arachnoid and pia mate.

Subarachnoid space has:

Cerebrospinal fluid

The amount of white matter _______ in a ________ direction.

The amount of white matter increases in a caudal-to-rostral direction.

A(n) ______ of grey matter volume in the __________ enlargements for _________________

An increase of grey matter volume in the cervical and lumbosacral enlargements for innervation of the limbs.

The lateral horn of grey matter is characteristic of the ____________.

The lateral horn of grey matter is characteristic of the thoracic and upper lumbar segments only.

Cervical spinal segments contain the largest number of fibers in the _______

Cervical spinal segments contain the largest number of fibers in the white matter

Cervical enlargement to innervate

the arms

Lumbar enlargement to innervate

the legs

where do Afferent fibers (sensory) enter the spinal cord?

Dorsal roots

dorsal root ganglia

has cell bodies of afferent fibers

where do Efferent fibers (motor) leave the spinal cord? 

Ventral roots

• axons of alpha motor neurons.

• axons of gamma motor neurons.

Transverse section of the spinal cord- White and Grey Matter

has a roughly H-shaped or butterfly outline.

The central canal is lined by ependymal epithelium.

The dorsal horns: Sensory

The ventral horns: Motor

The lateral horn/intermediate zone : containing sympathetic efferent neurons is added in the thoracic and upper lumbar segments.

structural classes of neurons

1. multipolar neuron

2. bipolar neuron

3. unipolar neuron

structural classes of neurons: multipolar neuron 

has many dendrites + one axon 

motor + interneurons 

ex: motor neuron at ventral horn

structural classes of neurons: bipolar neuron

one dendrite and one axon attached to the cell body 

only found in the eyes and ears

structural classes of neurons: unipolar neuron

have one process from the cell body to an axon

dendrites branches at the receptors + axon leads to the spinal cord or brain 

most of the bodys sensory neurons

ex: cell of the dorsal root ganglion

white matter consists of 3 funiculi

1. The dorsal funiculus

• Medial Fasciculus Gracilis

•  Lateral Fasciculus Cuneatus

2. The lateral funiculus.

3. The ventral funiculus

The dorsolateral tract (of Lissauer) located between 

the apex of the dorsal horn and the surface of the cord

Rexed's Laminae

Laminae I-VI: Posterior/dorsal horn

Laminae VII-IX: Anterior/ventral horn

SPINAL GRAY MATTER: Lateral gray horn or intermediate area know fs

1. Intermediolateral cell column (IML)

2. Intermediomedial cell column (IMM) 

1. Intermediolateral cell column (IML)

T1-L3

preganglionic sympathetic neurons for the ANS (GVE)

2. Intermediomedial cell column (IMM)

S2-S4

preganglionic parasympathetic neurons for the ANS (GVA)

Long ascending fibers

sensory

found in all funiculi

(white matter)

Long descending fibers

(white matter)

motor

found primarily in the lateral and anterior funiculi.

Shorter propriospinal fibers

(white matter)

in a thin shell surrounding the grey matter called the propriospinal tract.

Proprioception

Proprioception

sensing stimuli arising within the body regarding position, motion, and equilibrium.

Spinal Cord Injury

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

Frequent causes of damage are trauma
(car accident, gunshot, falls, etc.) or disease (polio, spina bifida.. etc.).