Autonomic Nervous System

¥Preganglionic neuron

§cell body in brain or spinal cord

§axon is myelinated type B fiber that extends 

to autonomic ganglion

¥Postganglionic neuron

§cell body lies outside the CNS in an 

autonomic ganglion

§axon is unmyelinated type C fiber that 

terminates in a visceral effector

¥The output (efferent) part of the ANS is divided into two principal parts:

¥

§The Sympathetic division

§

§The Parasympathetic division

¥Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation.

Cholinergic neurons include:

     - All sympathetic and parasympathetic      preganglionic neurons.

     - Sympathetic postganglionic neurons that innervate sweat glands.

      - All parasympathetic postganglionic neurons.

Nicotinic receptors:

      - are present in dendrites & cell bodies of sympathetic and parasympathetic postganglionic neurons.

     - present in NMJ as well as in chromaffin cells of adrenal gland.

Muscarinic receptors:

     - are present in plasma membranes of all effectors innervated by parasympathetic postganglionic neurons.

     - are present in sympathetic postganglionic neuron that innervate sweat glands.

Activation of nicotinic receptors by Ach causes depolarization and thus excitation.

- Activation of muscarinic receptors by Ach causes depolarization (excitation) and sometimes hyperpolarization (inhibition). 

¥Adrenergic neurons release norepinephrine

(NE)

§from postganglionic sympathetic neurons only.

¥

¥Excites or inhibits organs depending on 

receptors

¥

¥The main types of adrenergic receptors are 

alpha 

and beta receptors:

§α1 and β1 receptors produce excitation

§α2 and β2 receptors cause inhibition

§β3 receptors (brown fat) increase thermogenesis

¥

¥Effects triggered by adrenergic neurons typically 

are longer lasting than those triggered by

 cholinergic neurons.

¥Most body organs receive dual innervation

§innervation by both sympathetic & parasympathetic

¥

¥Hypothalamus regulates balance (tone) between  sympathetic and parasympathetic activity levels

¥

¥Some organs have only sympathetic innervation

§sweat glands, adrenal medulla & many blood vessels

          **  Long lasting due to lingering of NE in

 synaptic gap and release of norepinephrine by the

 adrenal gland

¥Dominance by the sympathetic system is caused by physical or emotional stress - “E situations”.

§

§emergency, embarrassment, excitement, exercise

¥

¥Alarm reaction = flight or fight response

§

§dilation of pupils

§increase of heart rate, force of contraction & BP

§decrease in blood flow to nonessential organs

§increase in blood flow to skeletal & cardiac muscle

§airways dilate & respiratory rate increases

§blood glucose level increase

¥Enhance “rest-and-digest” activities

¥

¥Mechanisms that help conserve and

 restore body energy during times of rest

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¥Normally dominate over sympathetic 

impulses

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¥SLUDD type responses =

Salivation, Lacrimation, Urination, Digestion 

& Defecation

in addition to 3 “decreases”- ↓HR, ↓diameter

 of airways and ↓diameter of pupil

¥A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously.

§changes in blood pressure, digestive functions etc

§filling & emptying of bladder or defecation

¥

¥Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc:

§sensory receptor

§sensory neuron

§integrating center

§pre & postganglionic motor neurons

§visceral effectors

¥Not aware of autonomic responses because control center is in lower regions of the brain.

¥

¥Hypothalamus is major control center

¥

§input: emotions and visceral sensory information

 smell, taste, temperature, osmolarity of blood, etc.

§

§output: to nuclei in brainstem and spinal cord

§

§posterior & lateral portions control sympathetic NS: increase heart rate, inhibition GI tract, increase temperature.

§

§anterior & medial portions control parasympathetic NS: decrease heart rate, lower blood pressure, increased GI tract secretion and mobility.

Stratified Epithelial Tissue

Stratified Squamous epithelium - keratinized

§Formed of multiple layers of cells. The topmost layer is formed of squamous cells. The epithelium is covered with keratin (a non-living material).

§

§It’s found in areas that require protection:

      - Skin à Epidermis

§Function:

     1) Stratification à protection

     2) Keratin à prevent water loss

Stratified Squamous epithelium – Non-keratinized

§Formed of multiple layers of cells. The topmost layer is formed of squamous cells. The epithelium is not covered with keratin.

§

§It’s found in areas that require protection and water loss is not a problem:

      - Mouth, esophagus, anal canal

      - Vagina

§Function: protection, secretion.

Stratified Cuboidal and Columnar epithelium

qThese are rare in the body. They’re formed of several layers of cuboidal and columnar cells respectively.

§

qFound in:

      - Columnar: Conjunctiva

      - Cuboidal: Lining of large excretory ducts of salivary and sweat glands.

qFunctions: protection and secretion

Transitional epithelium (Urothelium):

vThe topmost cells of this stratified epithelium are dome-like (also called umbrella cells).

v

vFound in: Urinary bladder, ureters and renal calyces.

v

vThe umbrella cells are dome-shaped when the bladder is empty. Once it’s full, these cells will become flattened (hence the name transitional).

v

Functions: protection against the adverse effects of urine. Allow the bladder to change size

Pseudostratified columnar ciliated epithelium:

ØIn this epithelium, the cells have different heights. All cells rest on the basal lamina, but not all of them reach the surface. This makes the nuclei occupy different levels giving the epithelium a false stratified appearance.

Ø

ØFound in trachea, bronchi and nasal cavity.

Ø

ØFunctions: protection, secretion. Ciliary movement remove particles from the airway passages.

 

Simple Epithelial Tissue

• The epithelial tissue has the following characteristics:

•

1)It covers surfaces or lines cavities.

2)Rapid turn-over (time of renewal).

3)It’s formed sheets of closely packed cells.

4)The cells are polar.

5)The epithelium rests upon a sheet of extracellular matrix called the Basal Lamina. Also, most epithelia have connective tissue under them.

6)Epithelial tissues lack blood supply.

Basement Membrane

Ø Basement membrane is formed of the basal lamina and the reticular lamina. The reticular layer is the upper part of the connective tissue that’s usually located under the epithelium.

Simple Squamous epithelium

oFormed of a single layer of flattened cells.

§

oIt’s found in:

      - Capillaries à Endothelium

      - Lining of body cavities à Mesothelium

      - Lining alveoli à Pneumocytes

oFunction: Their thin cytoplasm allows various substances to pass easily across them (endothelium and pneumocytes). Mesothelial cells, also, produce a lubricating fluid.

Simple Cuboidal epithelium

§Formed of a single layer of cubical cells.

§

§It’s found in:

      - Renal collecting tubules

      - Covering the ovary

§

§Function: Covering of organs. Involved in active transport.

Simple Columnar epithelium

§Formed of a single layer of tall cells that could be ciliated or not.

§

§It’s found in:

      - Ciliated: Uterine tubes.

      - Non-ciliated: most of the GIT.

§

§Function: Secretion as in the stomach. Absorption as in the small intestine.