PHIS 206 Lecture Notes - Lecture 12: The Heart Beats, Pacemaker Current, Cardiac Muscle

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blueskunk578

2 May 2018

School

VCU

Department

Physiology and Biophysics

Course

PHIS 206

Professor

Charles Anderson; Steven Price

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Lecture 12: Cardiac Electrophysiology and Cardiac Cycle

Good Connections

• SKM is made of fibers, each runs from bone to bone

• Cardiac muscle cells are connected end-to-end and side-by-side

• Specialized connections allow for force and APs to be passed easily from cell-to-cell

• The heart beats like its a single cell

Electrical Aspects

• Heart has specialized cellular connections... ...but even those are not enough to insure

proper timing

• Internal wiring system distributes AP throughout muscle

• Cells within that system generate AP (no nerve commands the heart to contract like in

SKM)

• Want to make sure that the heart doesn’t waste blood

• Great connections between cells (Gap junctions)

• Heart does not require neural input to beat → heart can bring itself up to threshold

Conduction System

• Specialized muscle fibers (that do not contract) move AP rapidly through heart muscle

• Gap junctions between ordinary muscle cells then take over

• SA node is where heartbeat originates and spreads throughout the heart (look at diagram

and familiarize with the different nodes)

• Heart needs to beat from apex to base so can squeeze blood up

Sino-Atrial Node

• SA Node

o Is intended ”pacemaker” of the heart

o Made of specialized self-depolarizing cells that generate the AP necessary for

contraction

• Little piece of the heart where the action potential starts, brings itself up to threshold

• Never electrically quiet

• Action potential still goes up and down but there is no wait like normal action potentials

→ depolarization happens immediately

Automaticity

• Ha Ha

o “Funny” Channels depolarize the cell from resting to threshold potential

• Turned on when the cell becomes negative (which is funny because most currents don’t

do that)

• This is a specialized current that opens when cell becomes negative → responsible to

bringing up the cell back to threshold potential

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Document Summary

Electrical aspects: heart has specialized cellular connections but even those are not enough to insure proper timing. Internal wiring system distributes ap throughout muscle: cells within that system generate ap (no nerve commands the heart to contract like in. Skm: want to make sure that the heart doesn"t waste blood, great connections between cells (gap junctions, heart does not require neural input to beat heart can bring itself up to threshold. Conduction system: starts at sa node internodal pathway av node bundle of his bundle. Branches purkinje fibers contracting muscle cells: picks up speed after passing apex, his purkinje system, blood can begin to clot if heart doesn"t beat correctly. If av node is gone, you now have 2 pacemakers. Sa node controls atria and purkinje fibers control ventricles but they run at different paces. Electrocardiogram: ekg (or ecg, a global way to view the rhythm and conduction of electrical signals throughout the heart, don"t have to know in detail.

Related Questions

Select 30 medical terms from the articles.

Complete the table in this document, like the Summary Tables in your textbook.

In the first column list the medical term.

In the second column, list any prefixes and define them.

In the third column, list the root and define it.

In the fourth column, list any suffixes and define them.

In the fifth column list the exact definition of the term.

NOTE: You many not use any medical terms that appear in any of the summary tables in your textbook.

Make sure to include references to the articles your terms come from.

1: Facelift Anatomy

With age, characteristic changes occur in the central third of the face. ^[¹^] A youthful midface is characterized by prominent cheeks and a smooth transition between the lower eyelid and cheek. Structural, soft tissue, and skin changes develop as wrinkles and creases, progressive ptosis, and general atrophy of the structures.

Pessa confirmed the changes seen in the bony structures of the face, and these include a downward migration of cephalometric points. ^[²^] The downward migration manifests as a change in soft tissue volume. The effects of gravity and repeated animation of the face also directly affect the soft tissue that overlies the mimetic musculature.

The results of magnetic resonance imaging (MRI) evaluations have helped to determine that the mimetic muscles themselves remain intact; however, the attachment to the overlying soft tissue and skin changes. The repeated action of smiling results in deepening of the nasolabial fold at the point at which the superficial musculoaponeurotic system (SMAS) inserts into the dermis.

2: Pancreas Anatomy

Embryology

The pancreas develops as 2 buds (outpouchings) of endoderm from the primitive duodenum at the junction of the foregut and the midgut. A small ventral bud (pouch) forms the lower (inferior) part of the head and the uncinate process of pancreas, whereas a large dorsal bud (pouch) forms the upper (0) part of the head as well as the body and tail of the pancreas. The ventral bud rotates behind the duodenum dorsally from right to left and fuses with the dorsal bud, and the duct of the distal part (body and tail) of the dorsal bud unites with the duct of the ventral bud to form the main pancreatic duct (of Wirsung). Because the common bile duct (CBD) also arises from the ventral bud, it forms a common channel with the main pancreatic duct. The remaining proximal part (head) of the duct of the dorsal bud remains as the accessory pancreatic duct (of Santorini).

3: Conduction System of the Heart

The conducting system of the heart consists of cardiac muscle cells and conducting fibers (not nervous tissue) that are specialized for initiating impulses and conducting them rapidly through the heart (see the image below). They initiate the normal cardiac cycle and coordinate the contractions of cardiac chambers. Both atria contract together, as do the ventricles, but atrial contraction occurs first.

The conducting system provides the heart its automatic rhythmic beat. For the heart to pump efficiently and the systemic and pulmonary circulations to operate in synchrony, the events in the cardiac cycle must be coordinated.

4:Spleen Anatomy

Overview

The spleen is an organ shaped like a shoe that lies relative to the 9th and 11th ribs and is located in the left hypochondrium and partly in the epigastrium. Thus, the spleen is situated between the fundus of the stomach and the diaphragm. The spleen is very vascular and reddish purple in color; its size and weight vary. A healthy spleen is not palpable.

Development

The spleen develops in the cephalic part of dorsal mesogastrium (from its left layer; during the sixth week of intrauterine life) into a number of nodules that fuse and form a lobulated spleen. Notching of the superior border of the adult spleen is evidence of its multiple origin (see the image below)

5:Lung Anatomy

Development

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PHIS 206 Lecture Notes - Lecture 12: The Heart Beats, Pacemaker Current, Cardiac Muscle

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