A&P Exam 3 study guide

Common properties of muscle tissue:

 excitability, contractility, extensibility, elasticity

Functions of skeletal muscle:

movement, posture/position, support, guarding body entrances and exits, maintaining body temperature, storing nutrients

Describe the organization of skeletal muscle- Epimysium

dense irregular connective tissue surrounding muscle

Describe the organization of skeletal muscle- Perimysium

dense irregular connective tissue surrounding fascicles

Describe the organization of skeletal muscle- Endomysium

areolar connective tissue surrounding fibers, contains capillaries, nerves, myosatellite cells

Three connective tissue layers come together to form

tendons/aponeuroses

Describe the characteristics of skeletal muscle fibers

Large, multinucleated, striated; special terms for plasma membrane and cytoplasm

Arrangement of thick and thin filaments within myofibrils create striations

Transverse tubules transmit electrical signal from sarcolemma to sarcoplasmic reticulum

Sarcomere

thin filaments (actin), thick filaments (myosin). Z line, M line, A band, I band, H band, Zone of Overlap. Accessory proteins: titin, nebulin, tropomyosin, troponin

Neuromuscular Junction

axon terminal of motor neuron, synaptic cleft, motor end plate

summarize the events involved in the neural control of skeletal muscle contraction and relaxation

Action potential in motor neuron results in release of Ach from axon terminal. Ach diffuses across synaptic cleft and binds to receptors in the motor end plate, causing an action potential to be produced in the sarcolemma. This travels along the T tubules to the sarcoplasmic reticulum and triggers the release of calcium ions. Calcium ions bind to troponin, this causes it to move tropomyosin away from active sites on the thin filaments. Myosin heads bind to active sites, form cross bridges, repeatedly detach and reattach, using ATP to power the pulling of actin filaments towards the M line and cause shortening of the sarcomere.

Increased frequency of stimulation: treppe

likely due to accumulation of calcium ions

wave summation

successive stimuli arrive before the relaxation phase has been completed

incomplete tetanus

very brief periods of relaxation

complete tetanus

relaxation phase eliminated, maximum tension

Recruitment of additional motor units- Motor unit

motor neuron and all muscle fibers it innervates. Motor units vary in size. Some are always active. Muscle fibers of different motor units are intermingled.

muscle fibers obtain the energy to power contractions: Glycolysis

in cytoplasm, generates net 2 ATP per glucose, generates pyruvate that is converted to lactic acid if not used as substrate by aerobic metabolism

muscle fibers obtain the energy to power contractions: Aerobic respiration

in mitochondria, requires oxygen, generates 28-30 additional glucose. Provides 95% of ATP in resting muscle.

Describe the mechanisms by which muscle fibers obtain the energy to power contractions.

Resting muscle stores glycogen and high energy phosphate reserves. At high activity if ATP must be generated by glycolysis, pyruvate builds up and is converted to lactic acid. Muscle pH becomes acidic and muscles fatigue.

Recovery requires

lactate removal, oxygen debt repayment, heat loss

Slow (slow oxidative)

small diameter, slow ATPase/slow contraction, high oxygen supply, many mitochondria, store oxygen in myoglobin, low glycogen

              Burn more fat, resist fatigue, postural muscles

Intermediate (fast oxidative)

intermediate in most things, resemble fast fibers and have fast ATPase

Fast (fast glycolytic)

large diameter, fast ATPase/fast contraction, few mitochondria, low myoglobin, high glycogen

Fatigue quickly but provide quick movement and powerful contraction

Skeletal muscle fibers

are voluntary, large, multinucleated cells with long, cylindrical shapes. They have narrow T tubules, rely on intracellular calcium, and can produce wave summation and tetanic contractions.

Cardiac muscle cells

are involuntary, small, one nucleus. Short, broad T tubules, intercalated discs with gap junctions. Dependent on extracellular calcium and aerobic metabolism. Automaticity. No wave summation or tetanic contractions.

Skeletal muscle fibers

Voluntary, striated, multinucleated cells with long cylindrical shapes. Have narrow T tubules. Thick and thin filaments arranged in sarcomeres. Myosin activated by direct calcium binding to troponin. No gap junctions.

Smooth muscle

are nonstriated involuntary. No T tubules. Single nucleus. Connected by gap junctions. Can have automaticity. Thick filaments scattered, thin filaments bound to dense bodies. Myosin activated by phosphorylation by myosin light chain kinase. MLCK activated by calmodulin after interaction with calcium.

Parallel

fascicles parallel to long axis, most skeletal muscles

Convergent

fascicles converge on a common attachment, can change direction of pull

Pennate

fascicles form an angle with the tendon, generate more tension than parallel muscles, do not pull tendon as far

Circular muscles (sphincters)

fascicles are concentrically arranged around an opening. Guard openings to body.

How do muscles contract in relation to their origin and insertion?

:Muscles contract by drawing the insertion (more movable end) toward the origin (fixed, less movable end). Muscles can only contract, not push.

Agonist (prime mover)

muscle contracting to cause an action

Antagonist

action opposes the agonist

Muscles operate in pairs, because they can only contract

one muscle opposes the other to return a body part to the starting position

Synergist

Assist the agonist

Fixator

Stabilizes the origin of the agonist during the movement

What are common bases for naming muscles, and how can muscle terms help identify muscles?

Muscles are named based on location, shape, size, fiber direction, number of origins, origin/insertion points, or action

Identify major muscles and muscle groups

Those muscles and muscle groups presented in the colouring sheets and gone over   in class.

Central Nervous System (CNS):

Consists of the brain and spinal cord. It processes information and coordinates activity.

Peripheral Nervous System (PNS

Includes all nerves outside the CNS. It connects the CNS to limbs and organs.

Afferent (Sensory) Division:

Carries sensory information from receptors to the CNS.

Efferent (Moter) Division

Transmits motor commands from the CNS to muscles and glands.

Communication

Sensing, integrating, responding

Sensation

Detects changes inside and outside the body through sensory receptors

Integration

Processes and interprets sensory input to make decisions.

Responses

Sends motor commands to muscles and glands to react appropriately.

Homeostasis

Helps maintain stable internal conditions by regulating body functions.

collaterals

Branches off the main axon that allow the neuron to communicate with multiple cells.

Perikaryon

Soma (Cell Body): Contains the nucleus and organelles; also called ___

axon hillock

Cone-shaped region where the axon joins the soma; initiates the nerve impulse.

Functional

sensory carry information to the CNS (afferent) and motor carry information from CNS to effectors (efferent)

Anaxonic Neurons

• No distinct axon, many dendrites

• Found in brain and retina

Rare, involved in local processing

Unipolar Neurons

• Single process that splits into two branches (axon and dendrite)

• Found mostly in sensory neurons of the peripheral nervous system (PNS)

• Common in sensory pathways

Bipolar Neurons

• One axon and one dendrite

• Found in special sensory organs (retina, olfactory epithelium)

• Rare

Multipolar Neurons

• One axon, multiple dendrites

• Most common neuron type

• Found in central nervous system (CNS) and motor neurons

Sensory (Afferent) Neurons

• Carry information to the CNS from sensory receptors

• Mostly unipolar

Motor (Efferent) Neurons

• Carry commands from the CNS to muscles or glands

• Mostly multipolar

Interneurons

• Connect sensory and motor neurons within the CNS

• Mostly multipolar

Neuroglia cell- Astrocytes (CNS)

• Star-shaped cells

• Maintain blood-brain barrier

• Provide structural support

• Regulate ion and nutrient balance

• Repair damaged tissue

Neuroglia cell- Oligodendrocytes (CNS)

• Produce myelin sheath around CNS axons

• One oligodendrocyte can myelinate multiple axons

Neuroglia cell- Microglia (CNS)

• Act as immune cells of the CNS

• Remove debris and pathogens by phagocytosis

Neuroglia cell- Ependymal Cells (CNS)

• Line ventricles of the brain and central canal of the spinal cord

• Produce and circulate cerebrospinal fluid (CSF)

• Have cilia to help move CSF

Neuroglia cell- Schwann Cells (PNS)

• Form myelin sheath around PNS axons

• One Schwann cell myelinates one segment of an axon

• Aid in axon regeneration

Neuroglia cell- Satellite Cells (PNS)

• Surround neuron cell bodies in ganglia

• Regulate nutrient and waste exchange

• Provide structural support

Graded potential

Small, variable changes in membrane potential; localized; can summate; triggered by ligand-gated channels.

Action Potentials

Large, uniform, all-or-none changes; propagate along axon; triggered by voltage-gated channels.

Depolarization

• Membrane potential becomes less negative (more positive).

• Caused by opening of voltage-gated Na⁺ channels, allowing Na⁺ influx.

Repolarization

• Membrane potential returns toward resting negative value.

• Caused by closing of Na⁺ channels and opening of voltage-gated K⁺ channels, allowing K⁺ efflux.

Hyperpolarization

• Membrane potential becomes more negative than resting potential.

• Due to delayed closing of K⁺ channels (excess K⁺ efflux).

Voltage-Gated Channels

Open/close in response to changes in membrane potential (e.g., Na⁺ and K⁺ channels in action potentials).

Ligand-gated channels

Open in response to chemical signals neurotransmitters)

Leak channels

Always open, maintain resting potential

Absolute refractory period

• Time during which no new action potential can be initiated.

• Corresponds to Na⁺ channel activation and inactivation phases.

Relative refractory period

• Time during which a stronger-than-normal stimulus can trigger an action potential.

• Corresponds to the period of hyperpolarization when K⁺ channels are still open.

Axon Diameter and Signal Speed

Thicker axons transmit signals faster than thinner axons.

Myelin and Signal Speed

increases the speed of signal propagation along an axon.

Continuous Propagation

Without myelin, an action potential moves along the axon by continuous propagation.

Saltatory Propagation

With myelin, the action potential jumps from node to node, a process called saltatory propagation.

1. Describe the structure and function of a synapse.

another neuron). Presynaptic cell sends the signal and the postsynaptic cell receives the signal. A synaptic cleft separates the two cells in a chemical synapse. An electrical synapse requires direct physical contact between cells.

Cholinergic synapses involve release of acetylcholine from the presynaptic cell after depolarization of the axon terminal by the opening of voltage gated calcium channels. Acetylcholine binds to chemically gated sodium channel to initiate a graded depolarization of the postsynaptic cell. Acetylcholine is then broken down by acetylcholinesterase and the choline component is reabsorbed by the presynaptic cell.

1. Explain how multiple inputs can be processed by the postsynaptic neuron and how presynaptic regulation occurs.

Inputs on a postsynaptic neuron can be summed temporally and spatially. Opposing       inputs can cancel each other out. Release of neurotransmitter from the axon terminals of presynaptic cells can be facilitated or inhibited by inputs from axoaxonic (axon to axon) synapses