Muscle Physiology and Contraction Types: Motor Units, Fatigue, and Cell Types, Nervous System: Structure, Function, and Cell Types

Motor unit

Neuron (Nerve cell) and all of the skeletal muscle cells that it is wired to.

Motor unit composition

Neuron, all of its branches, and all of the skeletal muscle cells its branches are wired to.

Number of skeletal muscle cells per motor unit

~100 skeletal muscle cells per motor unit.

Isometric contractions

When a Skeletal muscle contracts but does not change in length (stays the same).

Isotonic contractions

When a skeletal muscle contracts and the muscle changes length.

Concentric contractions

The sk. Muscle shortens; Myosin heads pull on the thin filaments + thin filaments move w/ them.

Eccentric contractions

The sk. Muscle lengthens; Myosin heads pull on thin filaments + thin filaments slide in the opposite direction.

Muscle twitch

Quick/brief contraction stimulated by a single impulse of electricity.

Wave summation

An extended contraction resulting in gradual increase in contraction strength due to an increased frequency of electrical stimulation to a skeletal muscle.

Unfused Tetanus

Results from a moderate frequency of electrical stimulation; There's brief periods of partial relaxation before the next electrical impulse stimulates the muscle.

Fused Tetanus

Results from a high frequency of electrical stimulation; No periods of relaxation between electrical stimuli.

Spatial summation

An increase in the force of contraction due to the number of motor units activated for a given muscle.

ATP in muscle cells

ATP is required by muscle cell to sustain contractions/exercise.

Creatine phosphate system

First system that kicks in to regenerate ATP; CP + ADP -> CP + ATP.

Glycolysis

2nd system that kicks in to regenerate ATP; Series of ten reactions that breaks down glucose.

Aerobic Respiration

3rd process that kicks in; Uses oxygen, carbs, amino acids, and fat molecule breakdown to generate ATP.

Muscle fatigue

When a muscle is unable to sustain contractions/contract w/ enough force to perform intended movements.

Causes of muscle fatigue

Lack of ATP, buildup of acid (H+), electrolyte imbalances, buildup of phosphate.

Fast glycolytic cells/fibers (FG cells)

Fast twitch cells; Efficient at generating ATP via glycolysis; Appear pale/white colored. break down ATP fast.

Slow oxidative cells/fibers (SO cells)

Slow twitch cells; Efficient at aerobic respiration; Appear dark red. Breaks down ATP slowly/recharges slowly

Fast oxidative glycolytic cells/fibers (FOG cells)

Intermediate type; Efficient at glycolysis + aerobic respiration; Appear pink colored. Fast type of myosin

Weight training

Converts FOG cells into FG cells; Stimulates skeletal muscle cells to produce more myofibrils.

Endurance training

Converts FG cells into FOG cells; Stimulates cells to increase production of myoglobin and mitochondria.

Anabolic steroids

Drugs that mimic the hormone testosterone; Stimulate skeletal muscle cells to produce more myofibrils.

Side effects of anabolic steroids

Causes acne, hair loss/growth, liver/kidney damage, increased risk of certain cancers/heart disease, personality changes.

Motor (efferent) Functioning

Controls muscle contractions and gland secretions

Sensory (afferent) functioning

detects changes in the body's environment

Entegrative (Associative)

Gives rise to emotions, memory, creativity, language, interpretation, and logic

Peripheral Nervous System

Nerves, sensory organs, and sensory receptors outside the brain and spinal cord.

Sensory (afferent)

Sensory organs + receptors and the nerves wired to them.

Central Nervous System

Brain + spinal cord

Motor (efferent)

Nerves wired to/controlling muscles/glands.

Somatic Nervous System

Nerves wired to skeletal muscles (Motor unit neurons) control skeletal muscle contractions and can be controlled consciously.

Autonomic Nervous System

Nerves wired to the heart, smooth muscle, and glands. Controls heart + smooth muscle contractions and gland secretions. Only controlled unconsciously.

Cells of the nervous system

Neuroglia and neurons

Neuroglia - "Glial cells"

Surround neurons and support neuron functioning.

Monitor and maintain the environment surrounding neurons.

6 types.

What shape are astrocytes?

Star-shaped

Where are astrocytes found?

In the central nervous system

What is the most abundant type of neuroglia in the central nervous system?

Astrocytes

What do astrocytes use to bind and hold neurons and capillaries in place?

ARM-like extensions

What role do astrocytes play in capillary walls?

They plug up leaks

What do astrocytes regulate between the blood and the central nervous tissue fluid?

What chemicals pass

What barrier do astrocytes help form?

The blood-brain barrier

What is the function of the blood-brain barrier?

It seals between blood and the central nervous system tissue fluid, allowing only certain chemicals to cross.

How do astrocytes help the chemical environment of neurons?

They help regulate it.

What are microglia?

Immune cells in the central nervous system.

What process do microglia undergo to eliminate microbes and tissue debris?

Phagocytosis.

What do microglia clear from the central nervous system?

Infections, damaged tissue, and wastes.

What is the function of ependymal cells?

They filter blood and form new cerebral spinal fluid.

Where do ependymal cells line?

They line the inside walls of the brain and the central canal of the spinal cord.

What are oligodendrocytes?

Cells that wrap around axons of neurons in the central nervous system.

What do oligodendrocytes form?

Myelin sheaths.

What is the function of myelin sheaths?

To electrically insulate axons and speed up the flow of electricity down an axon.

What are satellite cells?

Cells in the peripheral nervous system that support neurons.

How do satellite cells function in relation to neurons?

They hold neurons in place and help regenerate their chemical environment.

What are Schwann cells?

-Like oligodendrocytes, but in the peripheral nervous system

-Form Myelin sheaths.

What is cerebrospinal fluid?

A clear fluid generated by the ependymal cells in the ventricles.

How much cerebrospinal fluid is present in the body at any given time?

Around 150mL.

How much cerebrospinal fluid is produced per day?

500mL.

How does cerebrospinal fluid flow in the body?

It flows down from the ventricles and down the central canal of the spinal cord, then up and around the surface of the spine and the brain.

Where is cerebrospinal fluid absorbed?

Into the blood vessels on the surface of the brain.

What is one function of cerebrospinal fluid?

It floats the brain and spinal cord in the skull and vertebral column.

How does cerebrospinal fluid help protect the brain and spinal cord?

It helps absorb shock from blows to the head or spine.

What role does cerebrospinal fluid play in the central nervous system?

It helps flush waste and deliver nutrients.

Cell body

Central region where the nucleus is located

Dendrites

Receive signals that control whether or not the neuron generates electricity

Axon

Arm like structure that conducts electricity down its length

Axon terminal

Contains vesicles filled with neurotransmitters

Axon Hillock

Where the Axon joins the cell body

Synapse

Space just outside the Axon terminal

Where neurotransmitters are released by the Axon terminal

Post synaptic cell

Cell on the other side of the synapse

Neurotransmitters

nerve/neuron signaling molecules

Electricity stimulates release of neurotransmitters into the synapse

Myelin sheets

Formed by the oligodendrocytes of Schwann cells

motor neurons - Efferent neurons

Wired to muscle and gland cells

Sensory neurons - Afferent neurons

Wired to sensory receptors

Integrative neurons - association neurons

-Found in the central nervous system

Give rise to integrative functions

-Wire motor and sensory neurons together

Multipolar neurons

-Multiple dendrites connected directly to the cell body

-most common type

Unipolar neuron

-Single dendrite connected directly to the Axon

-Most sensory neurons of the peripheral nervous system

Bipolar neurons

-Single dendrite is connected to the cell body

-Rare

-Certain sensory neurons for smell, vision, and hearing

Gray matter

Mostly made up of dendrites, cell bodies, and short/unmyelinated axons

Nuclei

Pockets of Gray matter in the central nervous system

Ganglia

Pockets of gray matter in the peripheral nervous system

White matter

Mostly made up of myelinated axons

Tracts

White matter in the central nervous system

Nerves

White matter in the peripheral nervous system

What is the electrical charge inside of neurons?

-70mV (Millivolts)

Why is the electrical charge inside cells negative?

There are more negative ions than positive within cells.

What are the main negatively charged components in cells?

Phosphate (PO4^-2), proteins, and nucleic acids (DNA, RNA, ATP).

What is the most abundant positive ion in our cells?

Potassium.

What are the most abundant positive ions outside our cells?

Sodium (Na+) and Chloride (Cl-).

How do cells maintain high potassium and low sodium levels?

By continuously pumping potassium in and sodium out via pumps.

How can ions cross the plasma membrane freely?

Through ion channels.

How many types of ion channels are there?

Three types.

What are ligand-gated ion channels?

Channels that open when a specific ligand binds to them.

What do ligand-gated ion channels allow to pass through?

A specific ion.

What types of molecules do ligand-gated ion channels bind to?

Specific neurotransmitters, hormones, or drugs.

Where are ligand-gated ion channels typically found?

In the plasma membrane of dendrites, and sometimes in the plasma membrane of cell bodies or axons.

What do mechanically gated ion channels open in response to?

Pressure or stretch

What do mechanically gated ion channels allow to pass through?

A specific ion

Where are mechanically gated ion channels specifically found?

In the plasma membrane of dendrites of sensory neurons