bio 201 exam 3 flashcards

What is a sarcomere?

The contractile unit of striated muscle between two Z discs.

What does endomysium surround?

An individual muscle fiber.

What does perimysium surround?

A fascicle (bundle of muscle fibers).

What does epimysium surround?

The entire skeletal muscle.

What are intercalated discs?

Cardiac muscle junctions that connect cells mechanically and electrically.

What is a motor unit?

One motor neuron and all muscle fibers it innervates.

What are T-tubules?

Invaginations of the sarcolemma that carry action potentials into muscle fibers.

What are myofibrils?

Contractile structures in muscle fibers made of repeating sarcomeres.

What do actin and myosin do?

Actin forms thin filaments; myosin forms thick filaments that pull actin.

What is the sarcoplasmic reticulum?

A specialized smooth ER that stores and releases Ca2+ in muscle.

What is a cross-bridge?

A myosin head bound to an actin filament during contraction.

What is muscle tone?

Low-level ongoing muscle activity that helps maintain posture.

What is an isometric contraction?

Muscle produces tension without changing length.

What is an isotonic contraction?

Muscle changes length while moving a load.

What is a muscle agonist or prime mover?

The muscle chiefly responsible for producing a movement.

What is an antagonist muscle?

A muscle that opposes or reverses an agonist’s movement.

What is muscle origin?

The attachment that is usually more fixed during a movement.

What is muscle insertion?

The attachment that usually moves toward the origin.

How is skeletal muscle identified?

Striated, long cylindrical, multinucleated, usually voluntary.

How is cardiac muscle identified?

Striated, branching cells with intercalated discs; involuntary.

How is smooth muscle identified?

Nonstriated, spindle-shaped cells with one nucleus; involuntary.

What is a muscle twitch?

A brief contraction-relaxation response to one stimulus.

What is wave summation in muscle?

Greater tension from stimuli arriving before full relaxation.

What is tetanus in muscle physiology?

Sustained contraction caused by rapid repeated stimulation.

Slow oxidative fibers: key traits?

Slow, fatigue-resistant fibers rich in mitochondria and myoglobin.

Fast glycolytic fibers: key traits?

Fast, powerful fibers relying mainly on glycolysis; fatigue faster.

What does acetylcholine (ACh) do at the NMJ?

Binds motor end-plate receptors and initiates muscle excitation.

What ends ACh signaling at the NMJ?

Acetylcholinesterase breaks down acetylcholine.

What happens when Ca2+ binds troponin?

Tropomyosin shifts, exposing myosin-binding sites on actin.

What does tropomyosin do at rest?

Covers the myosin-binding sites on actin.

What powers myosin cross-bridge cycling?

ATP binding and hydrolysis by myosin.

What causes the power stroke?

Myosin pivots and pulls actin after releasing phosphate.

What lets myosin detach from actin?

A new ATP molecule binds to myosin.

How does muscle relax after stimulation ends?

Ca2+ is pumped into the SR; tropomyosin blocks actin sites.

What happens first in excitation-contraction coupling?

A motor neuron releases ACh, initiating a muscle action potential.

How do T-tubules and SR coordinate contraction?

The action potential travels down T-tubules, triggering SR Ca2+ release.

What are the four rotator cuff muscles (SITS)?

Supraspinatus, infraspinatus, teres minor, subscapularis.

What is the rotator cuff’s main job?

Stabilizes the shoulder joint and helps rotate/abduct the arm.

What are the hamstring muscles?

Biceps femoris, semitendinosus, and semimembranosus.

What do the hamstrings do?

Flex the knee and extend the hip.

What does the quadriceps group do?

Extends the knee; rectus femoris also flexes the hip.

What does gastrocnemius do?

Plantar flexes the foot and helps flex the knee.

What does tibialis anterior do?

Dorsiflexes and inverts the foot.

What does sternocleidomastoid do?

Flexes the neck bilaterally; rotates head oppositely unilaterally.

What does brachioradialis do?

Flexes the elbow, especially with forearm in neutral position.

What does masseter do?

Elevates the mandible to close the jaw when chewing.

What does temporalis do?

Elevates and retracts the mandible.

What does orbicularis oculi do?

Closes the eyelids.

What does orbicularis oris do?

Closes and protrudes the lips.

What is resting membrane potential?

Voltage across a resting cell membrane; neurons are typically near -70 mV.

What is depolarization during an action potential?

Membrane becomes less negative as voltage-gated Na+ channels open.

What is repolarization during an action potential?

Membrane returns toward resting voltage, mainly as K+ leaves.

What is after-hyperpolarization?

Membrane briefly becomes more negative than resting potential.

What is the absolute refractory period?

No second action potential can start because Na+ channels are unavailable.

What is the relative refractory period?

A stronger-than-usual stimulus can trigger an action potential.

What is an ion leak channel?

An ion channel that is typically open and helps set resting voltage.

What is a ligand-gated (chemical) channel?

Opens or closes in response to a chemical messenger.

What is a voltage-gated (electrical) channel?

Opens or closes in response to membrane voltage changes.

What does the Na+/K+ ATPase pump do?

Uses ATP to pump 3 Na+ out and 2 K+ in.

What is an action potential?

An all-or-none electrical signal regenerated along an axon.

What is a graded potential?

A local voltage change that varies in size and can fade with distance.

Graded potential vs. action potential?

Graded: variable and local. Action potential: all-or-none and propagated.

What is saltatory conduction?

Action potentials regenerate at nodes of Ranvier in myelinated axons.

How does myelin change signal conduction?

Insulates axons and greatly speeds impulse transmission.

What are nodes of Ranvier?

Gaps between myelin segments rich in voltage-gated channels.

What is a synapse?

A junction where one neuron signals another cell.

What is the synaptic cleft?

The narrow gap between a presynaptic cell and postsynaptic cell.

What triggers neurotransmitter release?

Ca2+ enters the presynaptic terminal and triggers vesicle fusion.

What happens at a chemical synapse?

Neurotransmitter crosses the cleft and binds postsynaptic receptors.

How are neurotransmitters cleared from synapses?

Reuptake, enzymatic breakdown, and diffusion away.

What is an EPSP?

An excitatory postsynaptic potential that brings voltage toward threshold.

What is an IPSP?

An inhibitory postsynaptic potential that makes firing less likely.

What is temporal summation?

Repeated inputs from one synapse add together over time.

What is spatial summation?

Inputs from different synapses add together at the same time.

What does the axon hillock/initial segment do?

Integrates inputs; action potentials typically initiate nearby.

What is a multipolar neuron?

A neuron with one axon and multiple dendrites; most common type.

What is a bipolar neuron?

A neuron with one axon and one dendrite; found in special senses.

What is a unipolar (pseudounipolar) neuron?

A sensory neuron with one process dividing into two branches.

What is the role of dendrites?

Receive signals from other cells.

What do astrocytes do?

Support CNS neurons and help maintain the blood-brain barrier.

What do oligodendrocytes do?

Form myelin around axons in the CNS.

What do Schwann cells do?

Form myelin around axons in the PNS.

What do microglia do?

Act as immune/phagocytic cells in the CNS.

What do ependymal cells do?

Line ventricles; specialized cells of the choroid plexus produce CSF.

What do satellite cells do?

Support neuron cell bodies in PNS ganglia.

What is the CNS?

Brain and spinal cord; integrates and processes information.

What is the PNS?

Nerves and ganglia outside the brain and spinal cord.

What is the somatic motor nervous system?

Controls skeletal muscle activity, including voluntary movement.

What is the autonomic nervous system?

Regulates cardiac muscle, smooth muscle, and glands involuntarily.

What is the sympathetic division?

Autonomic fight-or-flight response that mobilizes energy.

What is the parasympathetic division?

Autonomic rest-and-digest functions that conserve energy.

What is the enteric nervous system?

Neural networks in the digestive tract controlling GI activity.

What is gray matter?

Nervous tissue rich in neuronal cell bodies, dendrites, and synapses.

What is white matter?

Nervous tissue with many myelinated axons.

Nerve versus tract?

Nerve: bundle of axons in PNS. Tract: bundle of axons in CNS.

Nucleus versus ganglion in neuroanatomy?

Nucleus: CNS neuron cell-body cluster. Ganglion: PNS cluster.

What is epineurium?

The outer connective-tissue sheath surrounding an entire peripheral nerve.

What are the meninges from outermost to innermost?

Dura mater, arachnoid mater, pia mater.

Where is cerebrospinal fluid (CSF) produced?

Primarily by choroid plexuses within brain ventricles.

What ventricles contain CSF and why is it helpful?

Two lateral, third, and fourth ventricles; CSF cushions, supports, and circulates.