biomed neuro-muscle lecture

8/2/2019 Biomed Neuro-Muscle Lecture

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Mechanisms of Nerve Conduction

and Muscle Contraction

J. Kurantsin-Mills, Ph.D.

Department of Physiology and Biophysics


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Mechanisms of Nerve ConductionLecture Objectives List the structural and functional divisions of the nervous system, and

describe their relationship to each other. Describe the types of glial cells, their function, and location in the

nervous system.

Explain the physiological characteristics of mature neurons.

Define the terms voltage, potential difference, and current, anddescribe how electrical current travels in the body.

Name the various types of membrane channels, and the signals thatcontrol each type.

Explain the resting membrane potential and how it is generated.

Identify how changes in membrane potentials act as signals, and relateeach type of signal to the generation of action potentials.

Discuss the mechanism of generation of an action potential, and thethree phases of an action potential.


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Mechanisms of Nerve Conduction

Lecture Objectives (continued)

Describe a threshold stimulus. Discuss how it relates to thegraded potentials generated on dendrites, and the all-or-none behavior of axons.

Define the absolute and relative refractory periods, anddescribe the events that occur during each.

Identify the effects of axon diameter and myelination onconduction velocity of axons.

Define a synapse, name the two types, and describe howsynaptic transmission occurs at a chemical synapse.

List the chemical and functional classes of neuro-transmitters, members of each class, and the types ofreceptors for neurotransmitters.

Read Chapter 11: Mariebs Human Anatomy &

Physiology; Understand all Figures and Tables


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Organization of the Nervous System


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Dendrites Cell Body

Axon

Terminal

Review Figure 11.4 &

Table 11.1 functions of thecomponents of motor

neurons.

A Typical Neuron Overview


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Electrical Signals:

Ionic Concentrations and Potentials

Ionic Concemtrations and Equilibrium Potentials

Ion ECF ICF Eion@37oCK+ 5mM (3.5-5) 150mM -90mV

Na+

145mM (135-145) 15mM +60mV

Cl- 108mM (100-108) 10mM (5-15) -63mV

Ca2+ 1mM 0.0001 mM


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All or none Signal does not diminish over distance

Initiation

Depolarization

Signal peak

Repolarization

Membrane & Channel Changes during

an Action Potential


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Action Potential Stages: Overview


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Regulating the Action Potential

Positive Feedback Loop Absolute Refractory Period

Relative Refractory Period


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Regulating the Action Potential


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Frequency of Action Potentials


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Conduction of Action Potentials

Kinetic energy depolarizes ahead, and drives action potential to the terminal


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Cell to Cell Conduction: the Synapse

Electrical synapses: gap junctions Very fast conduction Example: cardiac muscle

Chemical synapses

Pre synaptic terminal Synthesis of Neurotransmitters

Ca2+ releases Neurotransmitters

Synaptic cleft Postsynaptic cell: Neurotransmitter receptors Neuromodulators

Neurohormones


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Cell to Cell Conduction: the Synapse


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Synapse Mechanism


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Inactivation of Neurotransmitters


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Presynaptic terminal

Inhibitory neuron(s) less NT released

Excitatory neuron(s) more NT released

Postsynaptic membrane and receptors

Receptor numbers

Degradation rates

Permeability

Synaptic Modulation


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Synaptic transmission

Drugs in ECF Disorders of ion balance

Too much/too little NT release

Examples: Parkinson's, schizophrenia, epilepsy,depression

Nerve injury

Limited regrowth

Parallel nerves help some

Pathologies


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Summary

Organization and role of the nervous system: CNS &

components of PNS Neuron and glial cell structure and function

Electrical signals from waves of depolarization

Graded potentials function and mechanism

Action potentials function and mechanism

Synapse: neurotransmitters, cell to cell communication

Conduction, modulation, integration of the signals

Development and pathologies of the nervous system


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Muscle Contraction

Lecture Objectives Describe the properties of the three types of muscle tissue.

Identify the functional characteristics of muscle tissue. Explain the functions of the three types of muscles.

Skeletal & Cardiac Muscles

Explore the histology and the specific arrangement all elements.

Describe the neuromuscular junction. Explain the mechanism of generation of an action potential

across the sarcolemma.

Explain the sliding filament mechanism of muscle fiber contraction.

Define a motor unit, and explain the events of a muscle twitch.

Define muscle tone, and explain isometric and isotonic contractions. Describe the sources of ATP for muscles.

Explain the effects of exercise on muscles


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Muscle Contraction

Lecture Objectives (continued)

Smooth Muscle

Explore the histology of smooth muscle cells, and

compare to skeletal muscle cells. Describe the mechanism and regulation of smooth

muscle contraction.

Describe the types of smooth muscle and theirlocations in the body.

Read Chapter 9: Mariebs Human Anatomy &Physiology; Understand all Figures and Tables


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Muscles

Muscle types

What muscles do How muscles contract

Contraction to locomotion

Roles of smooth muscles

What do muscles do? Contract! Generate motion Generate force

Generate heat Support

Cardiac heart

Smooth internal organsSkeletal "voluntary"

Attach to boneMove appendages

Support bodyAntagonistic pairsFlexors

Extensors


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Types of Muscles


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About 40% body mass

Muscle fibers cells

Fascicle bundle

Motor unit Muscle

sheath

Attach to tendons (which attach to bone)

Skeletal Muscle Anatomy


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Multiple nuclei

Sarcolemma

T-tubules

Sarcoplasmic reticulum

Sarcoplasm

Mitochondria

Glycogen & ions

Myofibrils

Muscle Fiber Structure


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Actin "thin fibers" Tropomysin

Troponin

Myosin "thick fibers" Tinin elastic anchor

Nebulin non-elastic

Myofibrils: Site of Contraction


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Myofibrils: Site of Contraction


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Sarcomere: Organization of Fibers


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Contraction Sequence: Sliding Filament Theory


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Skeletal Muscle Contraction: Mechanisms


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Skeletal Muscle Contraction: Mechanism


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Energy for Contraction: ATP & Phosphocreatine

Aerobic Respiration

Oxygen Glucose

Fatty acids

30-32 ATPs Anaerobic Respiration

Fast but

2 ATP/glucose PhosphocreatineATPs


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Central

"Feeling"

Lactic acid

Peripheral

Glycogen depletion

Ca2+ interference

High Pi levels ECF high K+

ACh depletion

Muscle Fatigue: Causes not well known


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Rate

2-3 times faster SR uptake of Ca2+

ATP splitting

Anaerobic/Fatigue easily Power lifting

Fast/delicate

Sprint

Fiber Contraction Speed: Fast

Twitch


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Fast Twitch glycolytic muscles

Larger diameter fibers, pale color; Easily fatigued Intermediate speed

Anaerobic & aerobic

Slow Twitch: Aerobic, less fatigue Smaller diameter fibers

More mitochondria

More capillaries Dark color due to myoglobin

Endurance activities

Postural muscles

Fiber Contraction Speed: Oxidative Fast & Slow


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Length-tension relation in contracting muscle

LengthTension: Note that more crossbridges: more tension


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Coordinating the Fibers:

Summation to Tetanus


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Motor Unit: Fibers Innervated from 1 neuron

"All or none"

Fine touch

1:1 nerve to

fiber

Finger tips

Big muscles

1: 2000

Leg muscles

Motor units


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Weak stimulus Lowest threshold fibers

Slow twitch typically

Moderate: adds Fast

Oxidative

High stimulus: all fibers

Asynchronous:

Units take turns

Prevents fatigue

Recruitment of Fibers: Produce Graduated Force

Motor units


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Mechanics of Body Movement: Joints

S h M l C d


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Homeostatic role

Control fluid

Sphincters

Tonic contractions

Support tubes

Move products

Slow contractions

Little fatigue

Low O2 use

Smooth Muscles: Contrasted to

Skeletal Muscle

Duration of muscle contractionin three types of muscle


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Stimulation

Electrically coupled

Hormones

Paracrines

Various receptors

Single Unit Multiple unit

Single tapered cells

Longer actin & myosin

Smooth Muscles: Characteristics

Two Types of Smooth Muscle

(a) Single-unit smooth muscle

Connected by gap junctions

Sheet of muscle contracts a unite.g. small intestines

(b) Multi-unit smooth muscle

Cells are not electrically

connected; each cell is

stimulated independently

e.g. Iris and ciliary body of the

eye

Smooth muscle fibers are much smaller than skeletal muscle fibers


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Smooth Muscles: Characteristics


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Smooth Muscle Contraction: Mechanisms


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Smooth Muscle Relaxation: Mechanisms


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Summary: Comparison of Three Muscle Types

biomed neuro-muscle lecture

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