Exam 3 study guide

What are the types of neurons?

• Motor Neurons (Efferent)

• Sensory Neurons (Afferent)

• Interneurons

Motor Neurons (Efferent)

• Takes nerve impulses from the CNS to the muscles or glands

• Multipolar because they have many dendrites and a single axon

• They cause muscle fibers to contract or glands to secrete

Sensory Neurons (Afferent)

• Neurons take nerve impulses form sensory receptors to the CNS

• Unipolar

• The sensory receptor is as simple as a naked nerve ending ( a pain receptor), or it may be a part of a highly complex organ, such as the eye or ear

Interneurons

• Association neurons, occur entirely within the CNS

• Multipolar, they convey nerve impulses between various parts of the CNS

• Some lie between sensory neurons and motor neurons, and some take messages from one side of the spinal cord to the other or from the brrain to the cord, and vice versa

What are synapses?

• Junction between the dendrites of one neuron and the axon of a second neuron

• Nerves communicate by releasing chemical messenger at synapse

Important neurotransmitters:

• Monoamines

• Neuropeptides

• Nitric oxide

Resting membrane potential:

• Sodium in greater concentration outside

• Potassium in greater concentration inside

• Anions in greater concentration inside

• Membrane permeability greater for potassium than sodium

• Na+/K+ pump moves sodium out, potassium in

  • Utilizes ATP

Generating action potentials:

• Voltage gated ion channels

  • Sodium channels open- sodium rushes in

  • Sodium channels close- stops inward flow of sodium

  • Potassium channels open- potassium rushes out

• Net effect- Depolarization and then Repolarization

  • electrical flow created by ionic flow, not electron flow

Neuromuscular junction:

• Motor neuron cell body and dendrites in gray matter of spinal cord

• Axons extend to muscle

• Axon’s terminal end contains a synaptic knob

• Synaptic know has synaptic vesicles containing acetylcholine

Motor end plate:

• Area beneath the terminal branches of the axons

• Contains acetylcholine receptor complexes

• Acetylcholine binding opens the receptor complex

• Cholinesterase degrades acetylcholine into acetate and cholie

Proprioreceptors:

• Muscle Spindles:

  • Encapsulated fibers within the muscle belly

  • Monitor changes in muscle length

  • Monitor the rate of change in muscle length

  • Respond by causing muscle contraction

• Golgi Tendon Organs:

  • Encapsulated receptors

  • Located at the musculotendinous junction

  • Monitor tension within the tendon

  • Respond by causing the muscle to relax

• Pacinian Corpuscles & Ruffini Endings:

  • Encapsulated receptors

  • Located near joints, in muscle, tendon, and bone

What are Chemical Synapses?

One way conduction mechanism that allows signals to directed toward specific goals. Allows the nervous system to perform its myriad function of sensation, motor control, memory etc.

What are Electrical Synapses?

An electrical synapse, also known as a gap junction, is a mechanical link between two neurons that allows for the conduction of electricity. Electrical synapses contain channels that allow charges (ions) to flow from one cell to another.

What is the Autonomic Nervous System?

Sympathetic and Parasympathetic Neurotransmitters and their regulatory organ system functions (excitatory and inhibitory)

Sympathetic:

• Responsible for increasing activity (excitatory) in most systems (except GI)

• Adrenergic fibers release epinephrine

• Each sympathetic pathway from the cord to the stimulated tissue is composed of two neurons, a preganglionic neuron a postganglionic neuron, in contract to only a single neuron in the skeletal motor pathway

• Sympathetic nerve fibers: T1-L2

  • T1: head

  • T2: neck

  • T3-T6: thorax

  • T7-T11: abdomen

  • T12-L2: legs

    • About 75% of all parasympathetic nerve fibers are in the vagus nerves (cranial nerve X), passing to the entire thoracic and abdominal regions of the body

Parasympathetic:

• Responsible for slowing activity (inhibitory) in most systems (except GI)

• Cholinergic fibers release acetylcholine

Somatic afferent (sensory):

Carries sensations from the periphery to the spinal cord. Includes exteroceptive (pain, temperature, touch) & proprioceptive.

Somatic efferent (motor):

Communicates from spinal cord to skeletal muscles.

What is the Central Nervous System composed of?

Brain (including retinas) and spinal cord

Which Organs are innervated by adrenergic (sympathetic) transmission?

• Skeletal muscle → increases blood flow

• Ventilation → increase

• Sweat glands → increase perspiration

• Heart → increase force and contraction rate

• GI tract motility → Decrease

• Eyes → dilate pupils

• Secretion of digestive juices → decrease

• Blood pressure → increase mean pressure

• Airways → increase diameter

Which Organs are innervated by cholinergic (parasympathetic) transmission?

• Skeletal muscle → decreases blood flow

• Ventilation → decrease

• Sweat glands → no effect

• Heart → decrease force and contraction rate

• GI tract motility → increase

• Eyes → constrict pupils

• Secretion of digestive juices → increase

• Blood pressure → decrease mean pressure

• Airways → decrease diameter

What is the Peripheral Nervous System composed of?

• Spinal nerves and Cranial Nerves III-XII

• Somatic Nervous System:

  • Afferent

  • Efferent

• Autonomic Nervous System:

  • Sympathetic

  • Parasympathetic

What are the 3 major areas of the brain?

• Cerebrum (telencephalon-(cerebral cortex), diencephalon)

• Cerebellum

• Brainstem (midbrain, pons, medulla oblongata)

What are the 2 major parts of the Diencephalon?

• Thalamus

  • relays stimuli received from all sensory neurons to cortex for interpretation

  • relays signals from the cerebral cortex to the proper area for further processing

• Hypothalamus

  • monitors many parameters

    • temperature, blood glucose levels, various hormone levels

  • helps maintain homeostasis

  • signals the pituitary via releasing factors

  • signals the lower neural centers

Cerebellum:

• located behind the brainstem

• helps monitor and regulate movement

• integrates postural adjustments, maintenance of equilibrium, perception of speed, and other reflexes related to fine tuning of movement

Descending Nerve Tracts:

• Ascending: dorsal

• Descending: lateral, ventromedial tracts

What is Myelin?

• Schwann cells wrapped around the axon of some neurons

  • appear as multiple lipid-protein layers

  • are a continuous cell

  • increase the speed of action potential production

White Matter:

• Contains tracts or pathways made up of myelinated nerves

  • Carries ascending and descending signals

Brainstem:

Helps us with our reflexes

What are the Nodes of Ranvier?

• Gaps between Schwann Cells

  • Impulse jumps from node to node

  • Saltatory conduction

What are Dendrites?

Receives stimuli and carry it to the cell body

What is the Cell body?

Site of cellular activity

Endocrine diseases can be classified either as diseases of ____ or ____ or as conditions involving the development of mass lesions- which themselves may be associated with underproduction or overproduction

underproduction or overproduction

Endocrine:

Produces internal secretions that are transported around the body by the bloodstream

Paracrine:

Describes a hormone or other secretion released from endocrine cells into the surrounding tissue rather than into the bloodstream. Insulin, secreted by pancreatic ß-cells affects secretion of glucagon by pancreatic a-cells

Exocrine:

Produces external secretions that are released through a duct

Negative feedback:

A system that prevents deviation from a mean value.

Ex. Blood sugar regulation

Positive feedback:

A system that promotes deviation from a mean value.

Ex. Childbirth, which the release of Oxytocin during labor triggers uterine contractions

Pituitary gland:

An endocrine gland, about the size of a pea, that sits in a small, bony cavity at the base of the brain whose secretions control the other endocrine glands and influence growth, metabolism, and maturation.

Hypothalamus:

A region of the forebrain located below the thalamus, forming the basal portion of the diencephalon, that regulates body temperature, some metabolic processes, and governs the autonomic nervous system.

Hypophyseal portal system:

The system of blood vessels that link the hypothalamus and the anterior pituitary in the brain.

Thyroid-stimulating hormone (TSH):

• Produced by the anterior pituitary

• Stimulates the release of thyroxine (T4) from the thyroid gland

• It is regulated by thyrotropin-releasing hormone (TRH)

Thyrotropin-releasing hormone (TRH):

• Produced by the hypothalamus

• Stimulates cells in the anterior pituitary to secrete thyroid-stimulating hormone (TSH)

What is the term for an enlarged thyroid?

Goiter

A lack of thyroid hormone will lead to _____

decreased negative feedback on the pituitary, which in turn will lead to increased production of thyroid-stimulating hormone.

What are pancreatic islets?

They are small islands of cells that produce hormones that regulate blood glucose levels.

Insulin is produced by ____ in the pancreas and acts to lower blood sugar levels.

beta cells

Glucagon and insulin are _____ secreted by the pancreas that plays a key role in maintaining a stable blood glucose level.

peptide hormones

Glucagon is produced by ____ in the pancreas and acts to raise blood sugar levels.

alpha cells

Insulin:

A polypeptide hormone that regulates carbohydrate metabolism

Glycogen:

A polysaccharide that is the main form of carbohydrate storage in animals and also converts to glucose as needed

Glucagon:

A hormone, produced by the pancreas, that opposes the action of insulin by stimulating the production of sugar

Blood Sugar Chart:

Fasting for person without diabetes:

70-99 mg/dl (3.8-5.5 mmol/L)

Blood Sugar Chart:

Fasting for someone with diabetes:

80-130 mg/dl (4.4-7.2 mmol/L)

Blood Sugar Chart:

2 hours after meals for person without diabetes:

less than 140 mg/dl (7.8mmol/L)

Blood Sugar Chart:

2 hours after meals for someone with diabetes:

less than 180 mg/dl (10.0 mmol/L)

Blood Sugar Chart:

HBA1C for person without diabetes:

Less than 5.7%

Blood Sugar Chart:

HBA1C for someone with diabetes:

7.0% or less

Mechanical digestion:

Physical breakdown (chewing, churning, segmentation)

Chemical digestion:

To further degrade the molecular structure of the ingested compounds by digestive enzymes into a form that is absorbable into the bloodstream

Absorption:

Nutrients, water, and electrolytes are taken up into the bloodstream or lymph

Functions of the GIT organs?

• Mouth: Chewing and initial breakdown of food with saliva containing enzymes, facilitating swallowing

• Esophagus: Muscular tube that propels food to the stomach through peristalsis (muscle contractions)

• Small intestine: Primary site of nutrient absorption, where food is mixed with digestive enzymes from the pancreas and bile from the liver, allowing for absorption of carbohydrates, proteins, fats and water

• Liver: Produces bile, which helps with digestion of fats

• Gallbladder: Stores and releases bile into the small intestine when needed

• Pancreas: Secretes digestive enzymes into the small intestine to break down proteins, fats, and carbohydrates, as well as produces hormones like insulin to regulate blood sugar

• Large intestine: Absorbs water from digested food, forming stool, and stores waste until defecation

What is the Neural Control of the Gut Wall?

The Enteric Nervous System (SNS)

What is the Neural regulation of the GIT?

Different types of reflexes

What is the Enteric Nervous System (ENS)?

• Called the “gut brain” because it can control many aspects of digestion on its own, without input from the brain

• Consists of 2 major plexuses (nerve networks) within the wall of the GI tract:

  • Myenteric Plexus (Auerbach’s plexus)

  • Submucosal Plexus (Meissner’s plexus)

Myenteric Plexus (Auerbach’s plexus):

• Located between the muscle layers of the GI tract

• Main function:

  • Controls GI movements (motility)- peristalsis (the wave-like muscle contractions that move food along)

Submucosal Plexus (Meissner’s plexus):

• Located in the submucosa layer of the GI tract

• Main function:

  • Controls GI secretion (e.g., digestive enzymes, mucus)

  • Controls local blood flow to the GI organs

• Parasympathetic regulation- increases the activity of the enteric nervous system

  • Stimulation of PSP causes a general increase in the activity of the entire enteric nervous system, which enhances the activity of most GIT functions

• Sympathetic regulation- inhibits GIT activity. Exterts this effect in 2 ways:

  • secretes norepinephrine to inhibit GIT smooth muscle

  • inhibitory effect of norepinephrine on neurons of the entire enteric nervous system

  • strong stimulation of the sympathetic nervous system can inhibit motor movements of the gut so greatly that it can literally block movements of food

What are the type of reflexes of the Enteric Nervous System (ENS)?

• local reflex

• short reflex

• long reflex

Local reflex:

• local reflex- integrates within the gut wall enteric nervous system

  • controls secretion, peristalsis, mixing contractions, local inhibitory effects

Short reflex:

• short reflex- from gut to pre-vertebral sympathetic ganglia then back to GIT:

• These reflexes transmit signals long distances to other areas of the GIT

  • Gastrocolic (Gastroileal) reflex- stomach activity leads to ileocecal relaxation, and increased mass movement in colon

  • Enterogastric reflex- fat or protein chyme reaches duodenum and send impulses to enteric nerves of the stomach that in turn causes the inhibition of stomachal motility and secretion. Delays emptying.

  • Coloileal reflex- inhibits emptying of ileal contents into colon

  • Ileogastric reflex- ileum is distended, reflex inhibits gastric motility preventing more chyme from entering intestine

Long reflex:

• Long reflex- from gut to the prevertebral sympathetic ganglia (brain) then back to GIT

• Vaso vagal reflex- from stomach and duodenum to brain stem and back to stomach via vagus nerve to control gastric motor and secretory activity

• pain reflexes that cause inhibition of entire GIT

• Defecation reflexes- travel from colon and rectum to spinal cord and back to produce powerful colonic, rectal, and abdominal contractions required for defecation

Whats the Blood flow of the GIT?

• Splanchnic circulation involves blood flow to the GIT, spleen, pancreas and liver

• Blood from the GIT travels through the portal vein to the liver, where it is filtered and processed

• The liver’s sinusoids filter out harmful substances and store nutrients like carbohydrates and proteins

• The mesenteric arteries supply blood to the intestines, branching into smaller vessels that reach the muscle layers, intestinal villi, and submucosal areas

  • These arteries are crucial for supporting the motility, absorption, and secretion process in the gut

• The arterial and venous vessels in the villi flow in opposite directions in a countercurrent arrangement

• This setup allows oxygen from the arterioles to diffuse directly into the venules, bypassing the villus tissue

  • As much as 80% of oxygen is “short-circuited,” meaning it is not used by the villi for local metabolic functions

  • increase gut activity, such as absorption or muscle contractions, leads to increased blood flow to the gut, especially to the villi and submucosa

• After a meal, blood flow increases to support digestion and absorption, but it gradually returns to normal after a few hours

Secretory activity is___

digestive or endocrine secretions (hormones, enzymes, etc.) of the organs of the GIT

Secretory activity of the cells in the Stomach

• Stomach:

  • mucus- viscous and alkaline protects from acid and enzyme

  • intrinsic factor- secreted by parietal cells. Binds with vitamin b12 to help absorb

  • HCl- parietal cells- kills bacteria, stops carbohydrate digestion, denatures proteins, converts pepsinogen to pepsin

Secretory activity of the cells in the Small Intestine :

• Small intestine:

  • goblet cells- produce protective mucus

  • endocrine cells- produce regulatory hormones

  • digestive enzymes, disaccaharidases, peptidases, nucleases

  • brunner’s glands- stimulates by vagus, secretes secretin

Secretory activity of the cells in the Large Intestine :

• Large intestine:

  • mucus

Secretory activity of the cells in the Liver :

• Liver:

  • bile, cholesterol, fats, fat-soluble hormones, lecithin

Secretory activity of the cells in the Gallblader :

• Gallbladder:

  • stores and concentrates bile, DOES NOT PRODUCE BILE, it is stimulated by cholecystokinin to release bile

Secretory activity of the cells in the Pancreas :

• Pancreas:

  • pancreatic lipase- digests fat

  • pancreatic amylase- digests carbs

  • trypsin- digests proteins

  • chymotrypsin

  • carboxypeptidase

The chyme composition:

Ingested food + stomach secretions

Examples of Acid Base Balance disorders:

1. Proteins- HCI denatures proteins. Trypsin, chymotrypsin, and carboxypeptidase digest proteins

2. Carbohydrates- salivary amylase digests carbohydrates. Stomach acid inactivates salivary amylase, so no carbohydrate digestion in the stomach. Pancreatic amylase continues to digest carbs.

3. Lipids- bile emulsifies lipids allowing pancreatic lipase to digest lipids

What is the function unit of the liver?

The liver lobule

What is the liver lobule?

• The liver lobule is the functional unit of the liver, consisting of hepatocytes arranged in a hexagonal structure around a central vein

  • portal triad: composed of a branch of the hepatic artery, portal vein, and bile duct

  • hepatocytes: responsible for functions like bile production, detoxification, nutrient metabolism (e.g. glucose and fat), and protein synthesis (e.g. albumin, clotting factors)

  • sinusoids: capillary-like vessels that allow for the exchange of substances between blood and hepatocytes

What are the 5 GI hormones that qualify as endocrine?

• Gastrin

• Cholecystokinin (CCK)

• Secretin

• Glucose-dependent insulinotropic peptide (GIP)

• Motilin

What are the 2 example of paracrine hormones?

• Somatostatin

• Histamine

Which hormones operate as a combination of Endocrine and Paracrine mechanisms?

• Glucagon-like peptide-1 (GLP-1)

• Pancreatic polypeptide

• Peptide YY

The alimentary tract provides the body with a continual supply of ___

water, electrolytes, vitamins, and nutrients

Order of food digestion:

Ingestion → mechanical digestion (chewing)→ propulsion (swallowing, and peristalsis)→ chemical digestion → absorption → defecation

Motility physiological anatomy of the gastrointestinal wall:

A typical cross section of the intestinal wall:

1. The serosa

2. a longitudinal smooth muscle layer

3. a circular smooth muscle layer

4. the subucosa

5. the mucosa

When the RMP becomes less negative, which is call depolarization of the membrane, the muscle fibers before _____

more excitable

When the RMP becomes more negative, which is called hyperpolarization, the fibers become ___

less excitable

Factors that depolarize the membrane (make it more excitable):

1. Stretching of the muscle

2. Stimulation by Ach (Acetylcholine) released from the endings of parasympathetic nerves

3. Stimulation by several specific GI hormones

Factors that make the membrane potential more negative (make the muscle fibers less excitable):

1. The effect of NE or Ep on the fiber membrane

2. Stimulation of the sympathetic nerves that secrete mainly NE at their endings

Types of neurotransmitters secreted by the enteric neurons:

Different neurotransmitter substance that are released by the nerve ending of different types of enteric neurons including:

1. Acetylcholine (most often excited gastrointestinal activity)

2. Norepinephrine (almost always inhibits gastrointestinal activity)

3. Adenosine triphosphate

4. Serotonin

5. Dopamine

6. Cholecystokinin (CCK)

7. substance P

8. vasoactive intestinal polypeptide

9. somatostastin

10. leu-enkephalin

11. met-enkephalin

12. bombesin

Hormone- Gastrin

• Stimuli for secretion:

  • Protein

  • Distention

  • Nerve (acid inhibits release)

• Site of Secretion:

  • G cells of the antrum, duodenum, and jejunum

• Actions:

  • Stimulates:

    • Gastric acid secretion

    • Mucosal growth

Hormone- Cholecystokinin (CCK)

• Stimuli for secretion:

  • Protein

  • Fat

  • Acid

• Site of Secretion:

  • I cells of the duodenum, jejunum, and ileum

• Actions:

  • Stimulates:

    • Pancreatic enzyme secretion

    • Pancreatic bicarbonate secretion

    • Gallbladder contraction

    • Growth of exocrine pancreas

  • Inhibits:

    • Gastric emptying

Hormone- Secretin

• Stimuli for secretion:

  • Acid

  • Fat

• Site of Secretion:

  • S cells of the duodenum, jejunum, and ileum

• Actions:

  • Stimulates:

    • Pepsin secretion

    • Pancreatic bicarbonate secretion

    • Biliary bicarbonate

    • Growth of exocrine pancreas

  • Inhibits:

    • Gastric acid secretion

Hormone- Gastric inhibitory peptide (GIP)

• Stimuli for secretion:

  • Protein

  • Fat

  • Carbohydrate

• Site of Secretion:

  • K cells of the duodenum, jejunum, and ileum

• Actions:

  • Stimulates:

    • Insulin release

  • Inhibits:

    • Gastric acid secretion

Gastric inhibitory peptide (GIP):

Glucose-dependent insulinotropic peptide

Functional types of movements in the GIT:

• Propulsive movements (Peristalsis), which cause food to move forward along the tract at an appropriate rate to accommodate digestion and absorption

• Mixing movements, which always keeps the intestinal contents thoroughly mixed