A&P 1 EXAM 3 🌟

Three types of muscles

Skeletal, Cardiac, and Smooth

Skeletal Muscle

Striated, Voluntary, Multinucleated, Attached to skeleton for bone movement

Cardiac Muscle

Striated, Involuntary, Single nucleus, Located in the Heart wall

Smooth Muscle

Non-striated, Involuntary, Single nucleus, Located in Viscera (GI tract, blood vessels, bronchi)

Functions of the Muscles

Muscles move the body and help hold posture. They store energy as glycogen and make heat when they work or shiver. They can respond to signals, tighten, stretch, and spring back.

Movement and Posture: Produces body movement via contraction and stabilizes joint positions.

Storage and Heat: Stores glucose as glycogen in liver and muscle tissue; shivering produces metabolic heat.

Tissue Properties: Features electrical excitability (via neuromuscular junction), contractility, extensibility, and rubber-band-like elasticity.

Concentric contraction🌟

The muscle shortens as it works.

Example: lifting a book.

Eccentric contraction🌟

The muscle stays active while getting longer.

Example: slowly lowering a book.

Isometric contraction🌟

The muscle makes force but does not change length.

Example: holding a book still or doing a wall sit.

Origin🌟

• Usually proximal, stationary attachment

• Attachment that usually stays still.

Insertion🌟

• Usually distal/moving anchor point

• Attachment that usually moves

Agonist🌟

• Prime mover

• Main muscle doing the movement.

Example: biceps when bending the elbow.

Antagonist🌟

Muscle that opposes the movement (agonist)

Example: triceps when the biceps bends the elbow.

Synergist 🌟

Helps the main muscle (assist)

Four muscle properties

Excitability

Contractility

Extensibility

Elasticity

Excitability

Respond

Contractility

Make tension

Extensibility

Streches

Elasticity

Recoil

Muscle Structure

Whole muscle → fascicle → muscle fiber → myofibril → sarcomere → myofilaments.

Epimysium🌟

Covers entire muscle

Perimysium 🌟

Surrounds one fascicle

Endomysium🌟

Surrounds each (one) muscle fiber

Sacrolemma

Muscle cell membrane

Sarcoplasm

Muscle cell cytoplasm

Sarcoplasmic reticulum

Stores and releases calcium Ca²⁺

T-tuble

 Carry electrical signals deep into the muscle fiber.

Triad

One T-tubule + two terminal cisternae

NMJ & Contraction

1. Acetylcholine (ACH) released

2. Sodium (Na⁺) enters muscle fiber

3. Action potential travels along sarcolemma

4. Impulse travels down T-tubules

5. Sarcoplasmic reticulum releases Ca²⁺

6. Ca²⁺ binds to troponin

7. Tropomyosin moves, exposing binding sites

8. Myosin binds to actin (cross-brridge)

9. Power strokes pulls actin; ATP supports cycling

10. Ca²⁺ returns to SR → muscle relaxes

Sarcomere

Basic functional contractile unit between two Z lines.

Contractile Protein 🌟

• Actin, Myosin

• Thin filaments contain binding sites; thick filaments form cross-bridges

• Force

Regulatory Protein🌟

• Troponin, Tropomyosin

• Tropomyosin covers active sites; troponin binds calcium as the on/off switch

Structural Protein 🌟

• Titin, Dystrophin, Nebulin, Myomesin

• Maintain alignment, structural integrity, extensibility, and membrane stability

Z disc/line

Sarcomere boundary

M line

Middle of sarcomere

A band

Entire length of thick (myosin) filament

I band

Thin-only area near Z line

H zone

Thick-only central region

Actin

Thin contractile filament

Myosin

Thick contractile filament

Creatine phosphate (CP)

CP transfers phosphate to ADP through creatine kinase (CK/CPK)

Lecture focus: Rapid ATP; ≈ 15 seconds

Anaerobic glycolysis

• Glucose → pyruvate → lactate when needed; cytosol

Lecture focus: Net 2 ATP per glucose; short activity

Cori cycle

Lactate from muscle → blood → liver → glucose

Lecture focus: Liver-muscle recycling

Aerobic respiration

• What happens: Krebs cycle + ETC in mitochondria

  Lecture focus: Oxygen involved; ≈ 30–32 ATP/glucose on slides

Hypertrophy

Increases muscle fiber size / myofibrils.

Atrophy

Loss of muscle size, strength, tone with disuse or disease.

Slow-Twitch Muscle Fibers (Type I) 🌟

• Contract slowly.

• Resist fatigue (don't get tired easily).

• Use oxygen to produce energy (aerobic).

• Have lots of mitochondria.

• Have a rich blood supply.

• Contain lots of myoglobin, making them appear red.

Fast-Twitch Muscle Fibers (Type II)🌟

• Contract quickly.

• Produce powerful contractions.

• Fatigue more quickly.

• Rely more heavily on anaerobic energy production (especially Type IIx).

• Have fewer mitochondria than slow-twitch fibers.

• Generally have less myoglobin, making them appear lighter.

CNS🌟

Brain + spinal cord

PNS🌟

Cranial + spinal nerves and related ganglia

Afferent / sensory🌟

Carries information TOWARD the CNS

Efferent / motor🌟

Carries commands AWAY from CNS

Somatic (SNS)🌟

Voluntary skeletal muscle motor pathway

Autonomic (ANS)🌟

Involuntary smooth/cardiac muscle and glands

Sympathetic🌟

Fight or flight; T1–L2 (thoracolumbar)

Parasympathetic🌟

Rest and digest; CN III, VII, IX, X, S2–S4 (craniosacral)

Nucleus🌟

Cluster of neuronal cell bodies in CNS

Ganglion🌟

cluster of cell bodies in PNS.

Tract

bundle of axons in CNS

Nerve

bundle in PNS

Dendrites🌟

RECEIVE signals

Cell body (Soma)🌟

Contains nucleus and organelles; maintains the neuron

Axon hillock🌟

Integrates signals and is near the action potential initiation site

Axon🌟

Carries impulses/signals away from the cell body

Axon terminal🌟

End or Final Branches of the axon that communicate with another cell

Synaptic end bulbs🌟

Release neurotransmitters.

Multipolar neurons🌟

• Many extensions; Multiple dendrites and one axon

• Most common type of neuron.

• Motor neurons and interneurons

Bipolar neurons🌟

• Two extensions: one dendrite, one axon

• Found in special senses

Unipolar neurons🌟

One extension; mostly sensory neurons

Astrocyte🌟

• Support neurons and help form the blood-brain barrier

• Forms blood-brain barrier via perivascular feet; buffers extracellular potassium

• CNS

Oligodendrocyte🌟

• Make myelin in the CNS

• Wraps multiple axons to form central myelin sheaths

Microglia🌟

• Clean up germs and dead cells

• Acts as resident phagocyte clearing damaged tissue (monocyte/macrophage lineage)

• CNS

Ependymal Cell🌟

• Help produce and circulate CSF

• Lines brain ventricles and central canal; produces and circulates cerebrospinal fluid

• CNS

Schwann Cell🌟

• Make myelin in the PNS

• Ensheathes and myelinates individual peripheral motor and sensory axons

Satellite Cell🌟

• Support neuron cell bodies in PNS ganglia

• Surrounds neuron cell bodies in ganglia; provides structural and metabolic support

Vagus nerve (CN X)

Controls digestion, heart rate, and breathing; helps with swallowing and speaking.

• provides 80%-90% of all preganglionic parasympathetic fibers to thoracic and abdominal viscera

Glossopharyngeal nerve (CN IX)

Helps with swallowing, taste from the back of the tongue, and saliva production.

Oculomotor nerve (CN III)

Controls most eye movements, raises the eyelid, and controls pupil constriction.

Facial nerve (CN VII)

Controls facial expressions, taste from the front of the tongue, and tear and saliva production.

During contraction, Z lines get__

Closer

During contraction, I band and H zone__

Shrink

During contraction, A band stays__

The same length

During contraction, Filaments__

Slide; they do not shorten

Post-exercise higher oxygen use helps restore

CP and oxygen

Nissl bodies

Dark-staining structures representing rough ER and free ribosomes active in neuronal protein synthesis

• Aggregations of rough endoplasmic reticulum and ribosomes synthesizing structural proteins and enzymes

Precentral

Motor

Postcentral

Somatosensory