Human Physiology Exam II

Autonomic Nervous System

System that controls organs glands. Split into two subgroups: sympathetic and parasympathetic

Sympathetic nervous system

Fight or flight; prepares body for action

Parasympathetic nervous system

Rest and digest; helps body relax, reuptake, and prepare for future action

Where do preganglionic neurons originate

The spinal cord or brainstem

Where do postganglionic neurons originate?

The ganglion

Organization of preganglionic cell bodies: sympathetic

Preganglionic neurons originate in thoracic and lumbar regions of the spinal cord

Organization of preganglionic cell bodes: parasympathetic

Preganglionic neurons originate in brainstem (cranial nerves) and sacral region of the spinal cord

Organization of postganglionic cell bodies: sympathetic

Postganglionic neurons originate in sypathetic chair, running parallel to the spinal cord

Organization of postganglionic cell bodies: parasympathetic

Postganglionic neurons originate in organs they innervate

Which neurotransmitter is released by preganglionic neurons?

Acetylcholine

What neurotransmitter is released by sympathetic post-ganglionic neurons?

Norepinephrine

What neurotransmitter is released by parasympathetic post-ganglionic neurons?

Acetylcholine

Motor Unit

motor neurons and all the muscle fibers it innervates

Neuromuscular Junction

Synapse of a motor neuron and muscle

Acetylcholine

Released by motor neuron, carries messages from brain to body

Somatic Motor Disease: ALS (amyotrophic lateral sclerosis)

Degeneration of motor neurons. Not much currently known about the cause

Autonomic Motor Disease: Pandysautonomia

Severe and sudden loss of ANS function. Acquired and triggered by medications or viruses

Define reflex

An involuntary action to external stimuli

Describe each of the 4 ways to classify reflexes and provide an example of each

1) Efferent Division Controlling

• Somatic controls muscle

2) CNS Location where processing occurs

• Cranial reflexes processed in brain

3) Development of the reflex

• innate reflexes are naturally occurring

4) # of neurons in the pathway

• Monosynaptic: 2 neurons in pathway

Describe a muscle spindle and how it functions

A muscle spindle is a capsule embedded in muscle that responds to stretch. when a muscle stretches, the muscle spindle also stretches and triggers action potentials in afferent sensory nerves

Alpha motor neuron role in muscle spindles

innervates contracting fibers

Gamma motor neuron role in muscle spindles

innervates spindle muscle fibers

Spindle sensory neuron role in muscle spindles

detects stretch of muscle spindle

Define co-activation and provide its role/purpose

Coactivation refers to a simultaneous activation of both the agonist and antagonist muscles, further stabilizing the joint.

Describe the process which regulates a simple stretch reflex

A simple stretch reflex involves a single sensory neuron synapsing on a single motor neuron in the spinal cord. Ex. knee jerk reflex

Describe the process which regulates a reciprocal innervated stretch reflex

In a simple stretch reflex, interneurons are also stimulated in the spinal cord to inhibit antagonistic muscles on that limb

Stretch reflex

a contraction of a muscle in response to a stretch of that muscle

Muscle disease/disorder: Botulism

Inhibits acetylcholine release from somatic motor neurons. caused by a bacteria

Skeletal Muscle

Regular arrangement of sarcomeres attached to bone. Voluntary, ex. breathing

Cardiac Muscle

Striated, branched and intertwined. Intercalated discs, gap junctions. Involuntary.

Smooth Muscle

irregular sarcomeres, organs, circular orientation. Involuntary, ability for regulation.

Muscle

Bundle of fasicles

Muscle Fasicle

Bundle of fibers

Muscle fiber

single muscle cells

myofibril

Bundle of actin and myosin

epimysium

tissue that surrounds a muscle

perimysiun

thick membrane that covers each fascicle

endomysium

Matrix embedded with blood vessels and nerves that surrounds each muscle fiber

fascia

Connective tissue that is continuous with “mysiums” and connects to the tendon

tendon

connects muscle to bone

Sliding filament model of muscle contraction

Myosin heads bind to actin filaments and pull the filaments toward the M-band, shortening the sarcomere between Z-lines. This process is regulated by calcium binding to troponin, which shifts tropomyosin to expose binding sites, and ATP is required for myosin detachment and resetting.

Describe what is “sliding” and what is “getting shorter” during a contraction

The thick and thin filaments slide past each other, and the sarcomere shortens.

Describe the two interrelated cycles mediated by calcium and ATP during muscle contraction

1) The cross bridge cycle is mediated by ATP and is the process where myosin heads bind to actin and pull it toward the M band. ATP binding causes the myosin to detach and the myosin head to re-cock for the next cycle

2) Calcium Activation Cycle: calcium binds to troponin to shift tropomyosin out of the way and expose the myosin binding sites. When calcium is repumped to the sarcoplasmic reticulum, tropomyosin shifts to re-block the binding sites.

Describe the events at the neuromuscular junction leading to muscle contraction (acetylcholine, nicotinic receptor, action potential, voltage gates sodium channels, t tubules, DHP receptor, ryanodine receptor, sarcoplasmic reticulum, calcium)

At the neuromuscular junction, acetylcholine is released from the motor neuron and binds to nicotinic receptors on the muscle fiber, triggering an action potential that spreads via voltage-gated sodium channels. The action potential travels down the T-tubules, activating the DHP receptor, which in turn stimulates the ryanodine receptor on the sarcoplasmic reticulum, causing the release of calcium into the cytoplasm. This rise in calcium enables muscle contraction by allowing actin-myosin interactions.

Describe the molecular events starting with a motor neuron being stimulated leading to a muscle contraction (neuron ap, neurotransmission, muscle ap, sliding filament model)

A neuron action potential (AP) triggers neurotransmission at the neuromuscular junction, where acetylcholine is released and binds to nicotinic receptors, generating a muscle action potential (AP). This AP travels along the T-tubules, leading to calcium release from the sarcoplasmic reticulum, which enables cross-bridge formation between actin and myosin. According to the sliding filament model, myosin heads pull actin filaments inward using ATP, causing muscle contraction.

What are the three types of muscle fibers?

Slow twitch (type I), Fast twitch IIA, Fast twitch IIB

Compare the 3 types of muscle fibers based on speed of max tension

• Slow twitch: slow

• Fast twitch IIA: fast

• Fast twitch IIB: fast

Compare the 3 types of muscle fibers based on diameter

• Slow twitch: small

• Fast twitch IIA: large

• Fast twitch IIB: large

Compare the 3 types of muscle fibers based on ability for endurance

• Slow twitch: not fatigue-able

• Fast twitch IIA: not fatigue-able

• Fast twitch IIB: fatigue-able

Compare the 3 types of muscle fibers based on types of movements/exercises used

• Slow twitch: postural/endurance

• Fast twitch IIA: short duration, high intensity

• Fast twitch IIB: short duration, high intensity

Compare the 3 types of muscle fibers based on energy use

• Slow twitch: oxidative metabolism

• Fast twitch IIA: oxidative metabolism

• Fast twitch IIB: glycolysis

Compare the 3 types of muscle fibers based on blood vessels present

• Slow twitch: high vascularization

• Fast twitch IIA: high vascularization

• Fast twitch IIB: low vascularization

Compare the 3 types of muscle fibers based on relative mitochondria present and myoglobin concentration

• Slow twitch: lots

• Fast twitch IIA: lots

• Fast twitch IIB: few

Compare skeletal and smooth muscle organization and structure

Skeletal muscle has actin and myosin arranged in regular sarcomeres, while smooth muscle is non striated and arranged in sheets and bundles.

Describe the processes of contraction in smooth muscle

1) extracellular or sarcoplasmic reticulum derived calcium enters the cell and binds to calmodulin

3) bound calmodulin activates myosin light chain kinase

4) MLCK phosphorylates myosin light chain, activating ATPase activity on myosin head

5) muscle tension increases

Describe the processes of relaxation in smooth muscle

1) myosin light chain phosphatase removed phosphate from MLC

2) As stimulation stops and calcium is removed from the muscle cell, less MLCK is activated

3) The balance of MLCP starts to dephosphorylate MLC, and ATPase activity is reduced

How is calcium released in smooth muscle?

1) voltage gated ion channels

2) ligand gated calcium channels

3) stretch activated channels