Chapters 9, 10, 11 | University of Florida
Difficulty: Intermediate to Advanced | Prerequisites: Modules 1 and 2 (especially cell biology, tissues, skeletal system, and joints)
Tags: muscle tissue, skeletal muscle, smooth muscle, sliding filament model, contraction, neuromuscular junction, ATP, muscle groups, origin insertion action, lever systems, nervous system, neurons, action potential, synapse, neurotransmitters, EXER 2168, UF
Module 3 bridges the skeletal and nervous systems through muscle. Chapter 9 explains what muscle tissue is, how it contracts at the molecular level, and how contraction is fuelled. Chapter 10 focuses on the muscular system as a whole: how muscles are named, how they work together in groups, and the specific muscle groups you need to know for the exam. Chapter 11 introduces the nervous system, from the structure of a neuron to the generation and propagation of action potentials and synaptic transmission. These three chapters are tightly linked: a nerve signal triggers a muscle contraction that pulls on a bone at a joint to produce movement.
Skeletal muscle contracts via the sliding filament mechanism, powered by ATP and triggered by nerve impulses at the neuromuscular junction. Muscles work in functional groups (prime movers, antagonists, synergists) and act as levers on the skeleton. The nervous system uses neurons to transmit electrical signals (action potentials) across synapses via neurotransmitters, coordinating every body function.
Tags: skeletal muscle, cardiac muscle, smooth muscle, sarcomere, myosin, actin, sliding filament, neuromuscular junction, acetylcholine, excitation-contraction coupling, isotonic, isometric, twitch, tetanus, motor unit, ATP generation, creatine phosphate, aerobic respiration, anaerobic glycolysis
Three types of muscle tissue
Skeletal: voluntary, striated, multinucleated, attached to bones; responsible for locomotion and posture
Cardiac: involuntary, striated, branching cells with intercalated discs (gap junctions for synchronised contraction); found only in the heart
Smooth: involuntary, non-striated, spindle-shaped, single nucleus; found in walls of hollow organs (blood vessels, GI tract, bladder)
Four characteristics of muscle tissue
Excitability (responsiveness): ability to receive and respond to stimuli
Contractility: ability to shorten forcefully
Extensibility: ability to stretch beyond resting length
Elasticity: ability to return to resting length after stretching
Muscle functions
Movement, maintaining posture, stabilising joints, generating heat (thermogenesis).
Connective tissue sheaths (superficial to deep)
Epimysium: surrounds the entire muscle
Perimysium: surrounds each fascicle (bundle of muscle fibres)
Endomysium: surrounds each individual muscle fibre (cell)
These sheaths converge at the ends of a muscle to form the tendon or aponeurosis that attaches the muscle to bone.
Microscopic anatomy of skeletal muscle
A single skeletal muscle fibre (cell) contains:
Sarcolemma: the plasma membrane of the muscle fibre
Sarcoplasm: the cytoplasm
Myofibrils: long rod-like structures running the length of the fibre, made of repeating units called sarcomeres
Sarcoplasmic reticulum (SR): specialised smooth ER that stores and releases calcium ions
T-tubules (transverse tubules): invaginations of the sarcolemma that carry the action potential deep into the cell
Sarcomere
The functional (contractile) unit of skeletal muscle, defined as the segment between two Z-discs (Z-lines). Contains:
Thick filaments: made of myosin, with heads that form cross-bridges
Thin filaments: made of actin (plus troponin and tropomyosin, the regulatory proteins)
A band: the full length of the thick filaments (dark band); does not change length during contraction
I band: the region of thin filaments only (light band); shortens during contraction
H zone: the region of thick filaments only (centre of the A band); shortens during contraction
Z disc: anchors the thin filaments at each end of the sarcomere
M line: anchors the thick filaments at the centre
Sliding filament model of contraction
Muscle contraction occurs when thin filaments slide past thick filaments, pulling the Z-discs closer together. The filaments themselves do not shorten. The sarcomere shortens, the I bands and H zones narrow, and the A band stays the same width.
Excitation-contraction coupling (step by step)
A nerve impulse reaches the neuromuscular junction.
Acetylcholine (ACh) is released from the motor neuron into the synaptic cleft.
ACh binds to receptors on the sarcolemma, triggering an action potential.
The action potential travels along the sarcolemma and down the T-tubules.
The SR releases stored Ca²⁺ into the sarcoplasm.
Ca²⁺ binds to troponin, which shifts tropomyosin away from the active sites on actin.
Myosin heads bind to actin, forming cross-bridges.
The power stroke occurs: myosin heads pivot, pulling the thin filaments toward the M line.
ATP binds to myosin, causing it to detach from actin. ATP is hydrolysed, re-cocking the myosin head for another cycle.
This cycle repeats as long as Ca²⁺ and ATP are available.
When the nerve signal stops, Ca²⁺ is pumped back into the SR, tropomyosin re-covers the binding sites, and the muscle relaxes.
Neuromuscular junction (NMJ)
The synapse between a motor neuron and a skeletal muscle fibre. The motor neuron releases ACh, which binds to nicotinic receptors on the motor end plate (the specialised region of the sarcolemma). Acetylcholinesterase (AChE) in the synaptic cleft quickly breaks down ACh to prevent continuous stimulation.
Types of muscle contractions
Isotonic: muscle changes length, producing movement. Concentric (muscle shortens), eccentric (muscle lengthens while under tension).
Isometric: muscle generates tension but does not change length (e.g., holding a heavy object stationary).
Motor unit
One motor neuron and all the muscle fibres it innervates. Small motor units (few fibres per neuron) allow fine control (eye muscles). Large motor units (many fibres per neuron) produce powerful but less precise movements (quadriceps).
Graded muscle responses
Muscles do not operate on a simple on/off basis. The force of contraction is graded by:
Recruitment (multiple motor unit summation): activating more motor units increases force
Wave (temporal) summation: increasing the frequency of stimulation increases force. If stimulation frequency is high enough, individual twitches fuse into sustained contraction: unfused tetanus (incomplete fusion) → fused tetanus (smooth, sustained contraction).
Muscle twitch
A single contraction-relaxation cycle in response to one stimulus. Three phases: latent period (no visible contraction, excitation-contraction coupling occurring), contraction period (cross-bridges cycling, tension increasing), relaxation period (Ca²⁺ returning to SR, tension declining).
ATP generation for muscle contraction
Three systems, used sequentially as demand increases:
Creatine phosphate (CP) system: immediate energy source, lasts about 10 to 15 seconds. CP donates a phosphate to ADP to regenerate ATP. Fast but limited supply.
Anaerobic glycolysis: glucose is broken down without oxygen, producing 2 ATP per glucose and lactic acid as a byproduct. Sustains activity for 30 to 60 seconds at high intensity.
Aerobic respiration (oxidative phosphorylation): glucose, fatty acids, or amino acids broken down with oxygen in the mitochondria, producing ~36 ATP per glucose. Slower to kick in but sustains prolonged activity.
Adaptation to exercise
Aerobic (endurance) exercise: increases mitochondria, capillary density, and myoglobin content; improves cardiovascular efficiency
Resistance (strength) exercise: causes muscle hypertrophy (increase in fibre size, not number) via increased myofibril synthesis
Smooth vs. skeletal muscle
Smooth muscle: no sarcomeres (hence non-striated), uses dense bodies instead of Z-discs, contracts more slowly but can sustain contraction longer, does not require nerve stimulation for every contraction (some is autorhythmic), uses calmodulin rather than troponin for calcium-mediated regulation.
Muscular disorders
Muscular dystrophy: genetic, progressive degeneration of skeletal muscle (most common is Duchenne, caused by lack of dystrophin)
Myasthenia gravis: autoimmune, antibodies attack ACh receptors at the NMJ, leading to muscle weakness
Fibromyalgia: chronic widespread muscle pain of unknown cause
The filaments do not shorten during contraction. They slide past each other. The sarcomere shortens, but the thick and thin filaments remain the same length.
The A band does not change width during contraction. The I band and H zone narrow. This is one of the most commonly tested details.
ATP is needed for both contraction (power stroke) and relaxation (detaching myosin from actin). Without ATP, the muscle cannot relax, which is why rigor mortis occurs after death.
Lactic acid (lactate) does not directly cause the "burn" during intense exercise. It is a fuel source, not a waste product in the traditional sense. The burn is more closely related to hydrogen ion accumulation and metabolic acidosis.
⚠️ Know the steps of the sliding filament model and excitation-contraction coupling in sequence.
⚠️ Understand what happens to the A band, I band, and H zone during contraction.
⚠️ Be able to explain the role of calcium, troponin, tropomyosin, and ATP in contraction and relaxation.
⚠️ Know the three ATP-generating systems and when each is primarily used.
⚠️ Distinguish isotonic from isometric contractions and give examples.
True or False: The A band shortens during contraction. (False, the I band and H zone shorten; the A band stays the same)
Fill in the blank: The neurotransmitter at the neuromuscular junction is _______. (Acetylcholine / ACh)
True or False: Smooth muscle is striated. (False)
Fill in the blank: The immediate energy source for muscle contraction, lasting about 10 to 15 seconds, is the _______ system. (Creatine phosphate / CP)
True or False: Rigor mortis occurs because there is too much ATP available after death. (False, it occurs because there is no ATP to detach myosin from actin)
Tags: prime mover, antagonist, synergist, fixator, origin, insertion, action, fascicle arrangement, lever systems, muscle naming criteria, muscle groups, rotator cuff, quadriceps, hamstrings, abdominals, erector spinae
Prime mover (agonist)
The muscle primarily responsible for producing a specific movement.
Antagonist
A muscle that opposes the prime mover. It relaxes and stretches while the prime mover contracts. Example: triceps brachii is the antagonist to the biceps brachii during elbow flexion.
Synergist
A muscle that assists the prime mover, often by stabilising the joint or preventing unwanted movement.
Fixator
A synergist that stabilises the origin of the prime mover so all the force goes to the insertion. Example: muscles that stabilise the scapula during arm movements.
Origin and insertion
Origin: the more stationary attachment, usually proximal
Insertion: the more movable attachment, usually distal
A muscle's action is determined by the movement that occurs at the joint(s) it crosses when it contracts, pulling the insertion toward the origin.
Criteria used in naming muscles
Location (e.g., temporalis, over the temporal bone)
Shape (e.g., deltoid, triangular)
Size (e.g., gluteus maximus vs. minimus)
Direction of fibres (e.g., rectus = straight, oblique = angled, transversus = across)
Number of origins (e.g., biceps = two heads, triceps = three)
Action (e.g., flexor, extensor, adductor)
Origin and insertion (e.g., sternocleidomastoid: origin on sternum and clavicle, insertion on mastoid process)
Fascicle arrangements
Parallel: fibres run parallel to the long axis (e.g., sartorius). Good endurance, moderate power.
Convergent: broad origin converging to a narrow insertion (e.g., pectoralis major). Versatile.
Pennate: fibres attach obliquely to a tendon. Unipennate (extensor digitorum longus), bipennate (rectus femoris), multipennate (deltoid). More fibres per unit area, so greater power.
Circular (sphincter): fibres arranged in concentric rings (e.g., orbicularis oris). Controls opening/closing.
Lever systems
A lever is a rigid bar (bone) that moves on a fulcrum (joint) when effort (muscle force) is applied to move a load (resistance).
First-class lever: fulcrum between effort and load (like a seesaw). Example: head nodding on the atlas. Can operate at mechanical advantage or disadvantage depending on relative distances.
Second-class lever: load between fulcrum and effort. Always operates at mechanical advantage (effort arm is longer than load arm). Example: standing on tiptoe (fulcrum at the toes, load is body weight at the ankle, effort from the calf muscles at the heel).
Third-class lever: effort between fulcrum and load. Always operates at mechanical disadvantage (load arm is longer than effort arm), but produces speed and range of motion. Most common in the body. Example: biceps flexing the forearm (fulcrum at the elbow, effort at the radial tuberosity, load in the hand).
You are expected to know the origin, insertion, and action (O, I, A) for each muscle in the following groups. A chart is the best way to organise this information. Below is a summary of each group.
Primary muscles of facial expression (7)
Frontalis, orbicularis oculi, orbicularis oris, buccinator, zygomaticus major, zygomaticus minor, platysma. These insert into skin or other muscles (rather than bone), which is how they move the face. Innervated by the facial nerve (CN VII).
Muscles of mastication (5)
Temporalis, masseter, medial pterygoid, lateral pterygoid, (plus buccinator, which assists by keeping food between the teeth). The masseter and temporalis are the primary jaw closers (elevators of the mandible). The lateral pterygoid opens the jaw (depresses and protracts the mandible).
Triceps surae group (3)
The muscles of the posterior calf: gastrocnemius (two heads), soleus, and plantaris. All contribute to plantar flexion of the foot. The gastrocnemius and soleus share the calcaneal (Achilles) tendon, inserting on the calcaneus.
Hamstrings group (3)
Posterior thigh muscles: biceps femoris, semitendinosus, semimembranosus. All originate from the ischial tuberosity. They flex the knee and extend the hip.
Quadriceps group (4)
Anterior thigh muscles: rectus femoris, vastus lateralis, vastus medialis, vastus intermedius. All insert via the patellar ligament on the tibial tuberosity. They extend the knee. The rectus femoris also crosses the hip joint and flexes the hip.
Rotator cuff group (4) – "SITS" muscles
Supraspinatus, infraspinatus, teres minor, subscapularis. All originate from the scapula and insert on the greater or lesser tubercle of the humerus. They stabilise the glenohumeral joint and assist with rotation and abduction.
Supraspinatus: abducts the arm (initiates the first 15 degrees)
Infraspinatus: laterally rotates the arm
Teres minor: laterally rotates the arm
Subscapularis: medially rotates the arm
Abdominal group (4)
Rectus abdominis, external oblique, internal oblique, transversus abdominis. They flex and rotate the trunk, compress the abdomen, and support the abdominal viscera. Fibres run in different directions, providing strength like plywood.
Erector spinae group (3)
Iliocostalis, longissimus, spinalis. These are the primary extensors of the vertebral column, running vertically along the back. They maintain posture and control trunk flexion (eccentric contraction when bending forward).
Students often confuse the hamstrings and quadriceps. A simple way to keep them straight: the quadriceps are on the front of the thigh and extend the knee; the hamstrings are on the back and flex the knee.
The rectus femoris is the only quadriceps muscle that crosses both the hip and the knee. The other three vastus muscles act only on the knee.
Third-class levers are the most common in the body but operate at a mechanical disadvantage. This trades force for speed and range of motion, not efficiency.
⚠️ Know the O, I, A for every muscle in the eight named groups. Expect matching or fill-in-the-blank questions.
⚠️ Understand the three types of lever systems and be able to identify examples in the body.
⚠️ Know the naming criteria and be able to work out what a muscle does from its name (e.g., "extensor carpi radialis longus" extends the wrist, is on the radial side, and is a long muscle).
⚠️ Be able to identify the prime mover, antagonist, and synergist for a given movement.
Tags: neurons, neuroglia, CNS, PNS, sensory, motor, afferent, efferent, action potential, resting membrane potential, depolarisation, repolarisation, threshold, synapse, neurotransmitter, saltatory conduction, refractory period
Functions of the nervous system
Sensory input: gathering information from sensory receptors
Integration: processing and interpreting sensory input (primarily in the CNS)
Motor output: activating effectors (muscles and glands)
Divisions of the nervous system
Central nervous system (CNS): brain and spinal cord; integration and command centre
Peripheral nervous system (PNS): cranial and spinal nerves; communication lines between the CNS and the body
Sensory (afferent) division: carries impulses toward the CNS
Motor (efferent) division: carries impulses away from the CNS
Somatic nervous system: voluntary control of skeletal muscles
Autonomic nervous system (ANS): involuntary control of smooth muscle, cardiac muscle, and glands (sympathetic and parasympathetic divisions)
Histology of nervous tissue
Two cell types: neurons (excitable cells that transmit electrical signals) and neuroglia (supporting cells).
Neuroglia (glial cells) of the CNS:
Astrocytes: most abundant; support neurons, maintain the blood-brain barrier, regulate the extracellular environment
Microglia: immune cells of the CNS, phagocytise debris
Ependymal cells: line brain ventricles and spinal cord central canal; assist in circulating cerebrospinal fluid
Oligodendrocytes: form myelin sheaths around CNS axons
Neuroglia of the PNS:
Schwann cells: form myelin sheaths around PNS axons (one Schwann cell per internode)
Satellite cells: surround neuron cell bodies in PNS ganglia; support and regulate the environment
Structural classification of neurons
Multipolar: many dendrites, one axon (most common; motor neurons, interneurons)
Bipolar: one dendrite, one axon (rare; found in retina, olfactory mucosa)
Unipolar (pseudounipolar): single process that splits into a peripheral and central branch (sensory neurons in dorsal root ganglia)
Functional classification of neurons
Sensory (afferent): transmit impulses from receptors to the CNS
Motor (efferent): transmit impulses from the CNS to effectors
Interneurons (association neurons): connect sensory and motor neurons within the CNS; most numerous
Resting membrane potential
Approximately -70 mV. The inside of the neuron is negative relative to the outside, due to the unequal distribution of ions (more K⁺ inside, more Na⁺ outside) and the activity of the Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in per cycle). K⁺ leak channels also contribute, as K⁺ diffuses out of the cell down its concentration gradient, leaving the interior more negative.
Membrane ion channels
Leak (passive) channels: always open, allow ions to move down their concentration gradient
Gated channels: open or close in response to a stimulus
Voltage-gated: respond to changes in membrane potential (critical for action potentials)
Chemically (ligand)-gated: respond to binding of a neurotransmitter or chemical
Mechanically gated: respond to physical deformation (touch, pressure)
Depolarisation
A shift in membrane potential toward zero (less negative, e.g., from -70 mV toward -55 mV). Caused by Na⁺ entering the cell.
Repolarisation
A return to resting membrane potential (becoming more negative again). Caused by K⁺ leaving the cell.
Hyperpolarisation
A shift below resting potential (more negative than -70 mV), caused by K⁺ continuing to leave the cell briefly after repolarisation.
Threshold
The membrane potential (approximately -55 mV) that must be reached to trigger an action potential. Subthreshold stimuli do not produce an action potential.
Action potential
A brief, self-propagating reversal of membrane polarity. All-or-none: once threshold is reached, the action potential always fires at full strength.
Steps:
Resting state: voltage-gated Na⁺ and K⁺ channels are closed
Depolarisation: a stimulus reaches threshold; voltage-gated Na⁺ channels open rapidly, Na⁺ rushes in, membrane potential shoots toward +30 mV
Repolarisation: Na⁺ channels inactivate (close), voltage-gated K⁺ channels open (slightly delayed), K⁺ rushes out, membrane potential drops back toward resting
Hyperpolarisation: K⁺ channels are slow to close, so K⁺ briefly overshoots, dipping below -70 mV
Return to resting: Na⁺/K⁺ pump restores the original ion distribution
Refractory periods
Absolute refractory period: no new action potential can be generated regardless of stimulus strength (Na⁺ channels are inactivated). Ensures one-way propagation.
Relative refractory period: a stronger-than-normal stimulus can trigger a new action potential (some K⁺ channels still open, membrane is hyperpolarised).
Saltatory conduction
In myelinated fibres, the action potential "jumps" from one node of Ranvier (gap in the myelin sheath) to the next, greatly increasing conduction speed. Unmyelinated fibres conduct more slowly via continuous conduction.
Anatomy of the synapse
Presynaptic neuron: contains synaptic vesicles filled with neurotransmitter
Synaptic cleft: the tiny gap between the two neurons
Postsynaptic neuron: contains receptors for the neurotransmitter on its membrane
Synaptic transmission
Action potential arrives at the axon terminal of the presynaptic neuron
Voltage-gated Ca²⁺ channels open, Ca²⁺ enters the terminal
Ca²⁺ triggers exocytosis of synaptic vesicles, releasing neurotransmitter into the cleft
Neurotransmitter binds to receptors on the postsynaptic membrane
Ligand-gated ion channels open, producing a graded potential (EPSP or IPSP)
Neurotransmitter is removed from the cleft (enzymatic degradation, reuptake, or diffusion)
Key neurotransmitters
Acetylcholine (ACh): used at NMJs and in the PNS; excitatory at NMJs
Norepinephrine (NE): sympathetic nervous system neurotransmitter
Dopamine: involved in motivation, pleasure, motor control
Serotonin: mood regulation, sleep
GABA (gamma-aminobutyric acid): main inhibitory neurotransmitter of the CNS
Glutamate: main excitatory neurotransmitter of the CNS
Patterns of neural processing
Divergence: one presynaptic neuron stimulates many postsynaptic neurons (amplifies the signal)
Convergence: many presynaptic neurons synapse on one postsynaptic neuron (integrates input)
Serial processing: neurons fire in a specific sequence (reflexes)
Parallel processing: sensory input is processed simultaneously along multiple pathways (complex thought)
An action potential is all-or-none. A stronger stimulus does not produce a bigger action potential. Instead, it increases the frequency of action potentials (how often they fire).
Myelin does not conduct the impulse. It insulates the axon so the signal "jumps" between nodes of Ranvier, making conduction faster and more energy-efficient.
EPSP (excitatory postsynaptic potential) and IPSP (inhibitory postsynaptic potential) are graded potentials, not action potentials. They can summate, and if the sum reaches threshold at the axon hillock, an action potential is generated.
The Na⁺/K⁺ pump does not directly generate the action potential. It maintains the concentration gradients that make the action potential possible.
⚠️ Know the sequence of events in an action potential and be able to explain what is happening to Na⁺ and K⁺ at each stage.
⚠️ Understand the difference between graded potentials and action potentials.
⚠️ Be able to explain saltatory conduction and why myelinated fibres conduct faster.
⚠️ Know the events at a chemical synapse in order.
⚠️ The main neurotransmitters and whether they are excitatory or inhibitory is commonly tested.
⚠️ Distinguish absolute from relative refractory periods.
True or False: A stronger stimulus produces a larger action potential. (False, action potentials are all-or-none; a stronger stimulus increases the frequency of firing)
Fill in the blank: The resting membrane potential of a typical neuron is approximately _______ mV. (-70 mV)
True or False: Oligodendrocytes form myelin in the PNS. (False, Schwann cells form myelin in the PNS; oligodendrocytes form myelin in the CNS)
Fill in the blank: The main inhibitory neurotransmitter of the CNS is _______. (GABA)
True or False: During the absolute refractory period, a very strong stimulus can trigger a new action potential. (False, no stimulus can trigger a new action potential during the absolute refractory period)
Q: Describe the sliding filament model of muscle contraction. What changes in the sarcomere, and what stays the same?
A: Thin (actin) filaments slide past thick (myosin) filaments, pulling the Z-discs closer together. The sarcomere shortens, the I band narrows, and the H zone narrows or disappears. The A band remains the same width because the thick filaments do not change length.
Q: What role does calcium play in skeletal muscle contraction?
A: Calcium ions released from the sarcoplasmic reticulum bind to troponin on the thin filaments. This causes tropomyosin to shift, exposing the active (binding) sites on actin so that myosin heads can attach and form cross-bridges.
Q: A student is holding a heavy box still in front of them. What type of contraction are the biceps brachii performing?
A: Isometric contraction. The muscle is generating tension but not changing length; the box is not moving.
Q: What is a motor unit, and how does motor unit size relate to precision of movement?
A: A motor unit is one motor neuron and all the muscle fibres it innervates. Smaller motor units (fewer fibres per neuron) allow finer, more precise control (e.g., eye muscles). Larger motor units allow powerful but less precise movements (e.g., thigh muscles).
Q: Trace the events from the arrival of a nerve impulse at the neuromuscular junction to the start of muscle contraction.
A: The action potential arrives at the axon terminal → ACh is released into the synaptic cleft → ACh binds to receptors on the sarcolemma → an action potential is generated on the muscle fibre → the action potential travels down T-tubules → the SR releases Ca²⁺ → Ca²⁺ binds troponin → tropomyosin shifts → myosin binds actin → cross-bridge cycling (contraction) begins.
Q: Name the four rotator cuff muscles and state their collective function.
A: Supraspinatus, infraspinatus, teres minor, subscapularis (SITS). They stabilise the glenohumeral (shoulder) joint by holding the head of the humerus in the glenoid cavity and assist with rotation and abduction of the arm.
Q: What is the difference between convergence and divergence in neural processing?
A: In convergence, many presynaptic neurons synapse on a single postsynaptic neuron, allowing integration of input from multiple sources. In divergence, one presynaptic neuron stimulates many postsynaptic neurons, amplifying and distributing the signal.
Q: A muscle is named "extensor carpi radialis longus." Using the naming criteria, what can you deduce about it?
A: "Extensor" indicates it extends; "carpi" indicates it acts on the wrist (carpus); "radialis" indicates it is on the radial (lateral/thumb) side; "longus" indicates it is the longer of two similarly named muscles. So it is a long muscle on the radial side of the forearm that extends the wrist.
The neuromuscular junction introduced in Chapter 9 is your first synapse, and the same basic mechanism (neurotransmitter release, receptor binding, ion channel opening) reappears throughout the nervous system chapters (Chapters 11 to 14). The action potential from Chapter 11 is the same electrical event that triggers muscle contraction in Chapter 9, that propagates along sensory and motor nerves in Chapter 13, and that operates within the brain and spinal cord in Chapter 12. The muscle groups from Chapter 10 connect directly back to the skeletal system (Chapter 7, bone markings serving as origins and insertions) and to joints (Chapter 8, muscles crossing joints to produce movement). ATP generation in muscle ties back to mitochondria and cellular metabolism from Chapter 3.
Muscle tissue study guide, EXER 2168 module 3, skeletal muscle anatomy, sarcomere structure, sliding filament model, excitation contraction coupling, neuromuscular junction acetylcholine, isotonic isometric contractions, motor unit recruitment, ATP creatine phosphate anaerobic aerobic, muscle groups origin insertion action, rotator cuff SITS muscles, quadriceps hamstrings, erector spinae, lever systems first second third class, nervous system divisions CNS PNS, neuron structure, neuroglia glial cells, action potential steps, resting membrane potential, depolarisation repolarisation, refractory period, saltatory conduction myelin, synapse neurotransmitter, GABA glutamate serotonin dopamine