NERVOUS SYSTEM QUIZLET

The Nervous System

A highly complex physiological system that conveys information and regulates homeostasis.

Central Nervous System (CNS)

Comprises the brain and spinal cord.

Peripheral Nervous System (PNS)

Links the CNS to the body.

Afferent Nerves

Carry sensory information from the body to the brain.

Efferent Nerves

Transmit motor commands from the brain to the body.

Mechanoreceptors

Respond to mechanical stimuli.

Thermoreceptors

Respond to changes in temperature.

Nociceptors

Respond to damaging/possibly damaging stimuli.

Photoreceptors

Respond to light.

Chemoreceptors

Respond to chemical stimuli.

Autonomic Nervous System

Sympathetic: Activates the 'fight or flight' response.

Parasympathetic Nervous System

Responsible for the body's housekeeping functions.

Somatic Nervous System

Involves motor neurons that act on skeletal muscles.

Neurons

The functional units of the nervous system.

Cell Body

Central operational hub of the neuron.

Dendrites

Receptive area that conducts electrical impulses toward the cell body.

Axon

Carries action potentials away from the cell body to other neurons or effector organs.

Myelin Sheath

Insulating layer that increases conductivity of the neuron.

Nodes of Ranvier

Gaps in the myelin sheath that facilitate fast signal transmission.

Resting Membrane Potential

The inside of a neuron is negatively charged (-70 mV), while the outside is positively charged, resulting in polarization.

Ion Movement

Drive changes in electrical charge through permeability of the cell membrane to certain ions (e.g., Na+, K+).

Resting Condition

K+ channels are mostly open, allowing positive charge to leak out, maintaining the negative charge inside.

Process of Action Potential

Initiated when a sufficient stimulus reaches the neuron membrane, opening Na+ gates, causing depolarization.

Phases of Action Potential

Depolarization: The cell becomes more positive as Na+ rushes in. Repolarization: K+ exits the cell to restore the negative interior charge.

Na/K Pump

Maintains ion concentrations and resting potential, allowing for continued neuron excitability and action potential generation.

How Neurons Communicate

Nerve impulses reaching the end of an axon trigger neurotransmitter release into the synapse.

Excitatory Neurotransmitters

Promote depolarization through mechanisms like temporal and spatial summation.

Inhibitory Neurotransmitters

Cause hyperpolarization, making it harder for a neuron to depolarize and generate an action potential.

Proprioceptors

Sensors that inform the CNS about body position.

Joint Receptors

Monitor the position and movement of joints.

Muscle Spindles

Located within muscles, they detect changes in muscle length and provide information about stretch.

Golgi Tendon Organs

Found at the junction between muscles and tendons, they sense tension and prevent excessive force.

Free Nerve Endings

Most abundant type of joint proprioceptors; sensitive to touch and pressure; initially strongly stimulated, then adapt.

Golgi-type Receptors

Found in ligaments and around joints; functionally similar to free nerve endings.

Pacinian Corpuscles

Located in tissues around joints; detect rate of joint rotation.

Mechanoreceptors

Sensitive to mechanical changes such as length and pressure.

Muscle Spindles

Indicate the relative length of the muscle.

Golgi Tendon Organs

Monitor the tension developed by the muscle.

Fibrous Capsules

Located within the muscle belly.

Signal Transmission

When stretch is sensed, a signal is sent through the CNS (spinal cord).

Neuronal Interaction

Sensory neurons synapse with alpha motor neurons.

Outcome

Action potential.

Muscle Spindles

Sensitive to changes in muscle LENGTH.

Signal Transmission

Sends impulses to the spinal cord, synapses with motor neurons to facilitate muscle contraction.

protective mechanism

Protects the body from injury caused by overstretching and maintains muscle tone.

Encapsulated Sensory Organs

Located within muscle tendons.

Function

Sense small changes in tension and monitor force development in muscle.

Reflex Stimulation

Stimulates a reflex in which the muscle relaxes.

Injury Prevention

Can prevent muscle injury when there is excessive force.

Activation of Muscles

Arrival of the action potential at the nerve terminal causes release of acetylcholine.

Action potential

is generated across the sarcolemma.

Fiber contracts

Control of a Muscle: Depends on the number of muscle fibers within each motor unit.

All-or-None Principle

All muscle fibers in a motor unit contract and develop force at the same time.

Strength of Contraction

A stronger action potential does NOT produce a stronger contraction.

Muscle Fiber Types

Type I (Slow-Twitch): Designed for endurance and are fatigue-resistant.

Type IIa (Fast-Twitch)

Intermediate fibers that can use both aerobic and anaerobic metabolism.

Type IIx (Fast-Twitch)

Primarily anaerobic, designed for quick bursts of power but fatigue quickly.

Motor Units

Muscle fibers with specific characteristics that determine functional capacity.

Force Output of Muscle

Depends on frequency of activation and changes in the number of activated fibers.

Motor Neuron (Alpha Motor Neuron)

Leaves the spine and reaches all the way out to the muscle.

Motor Unit

Motor neuron and all the muscle fibers it innervates.

Motor Unit Composition

A motor unit consists of an alpha motor neuron and ALL of the muscle fibers that it innervates.

Whole Muscle Composition

Multiple motor units (sometimes thousands) comprise a whole muscle (e.g. biceps).

All-or-NONE Principle

Motor units operate on an ALL-or-NONE principle, meaning that the firing of a motor unit is either full or none at all.

Biceps Usage Example

I can use my biceps to pick up a pen or the desk that the pen is sitting on by activating the appropriate motor units to control the force required for each task.

Types of Motor Units

Motor units are NOT all the same and can be categorized into three types.

Slow (Type I) Motor Unit

Small, with high aerobic capacity. Also referred to as 'aerobic,' 'red,' or 'slow oxidative'.

Fast Fatigue Resistant (FR; Type IIa)

Intermediate size, sometimes called 'mixed' or 'fast oxidative'.

Fast Fatigable (FF; Type IIx, IIb)

Larger size with significant anaerobic power. Also known as 'glycolytic' or 'white'.

Motor Unit Type Determination

The type of motor unit is dictated by the muscle and the nerve, NOT just the muscle.

Size Principle of Motor Unit Recruitment

Motor Units are recruited to complete a task from smallest (usually Type I) to largest (Type IIx, if necessary).

GXT (Graded Exercise Test)

A test that measures the response of the body to increasing levels of exercise.

Stage I of GXT

Easy work -> mostly Type S-fibers (slow twitch, Type I).

Stage III of GXT

Harder work -> Type FR (fast-twitch resistant, Type IIa).

Stage V of GXT

Heavy work -> Type FF (fast-twitch fatigable, Type IIx).

Purpose of Motor Unit Recruitment System

This recruitment system allows for the delay of fatigue.

Short Term Explosive Movements

In movements such as an Olympic lift, Fast Fatigue Resistant (FR) and Fast Fatigable (FF) motor units are recruited first.

Type S (slow-twitch) Motor Units

Inhibited during explosive activities.

Variation in Contraction Strength

Choice between slow (Type I) or fast (Type II) motor units can vary strength.

Number of Motor Units

Increasing the number of motor units activated can also vary strength.

Autonomic Nervous System (ANS)

Plays an important role in homeostasis.

Effector Organs of ANS

Innervates organs that are not under voluntary control, such as cardiac, digestive, and respiratory organs.

Sympathetic Nervous System (SNS)

Activates the 'fight or flight' response.

Parasympathetic Nervous System (PNS)

Responsible for the body's housekeeping functions.

Sympathetic Portion Neurotransmitter

Releases norepinephrine to excite an organ.

Parasympathetic Portion Neurotransmitter

Releases acetylcholine to inhibit the same organ.

Sympathetic System Function

Works to activate an organ (e.g., increases heart rate).

Parasympathetic System Function

Works to inhibit an organ (e.g., decreases heart rate).

Homeostasis

At rest, the sympathetic and parasympathetic systems are in balance.

Exercise Effect on ANS

During exercise, the activity of the parasympathetic system decreases, leading to an increase in sympathetic system activity.

Post-Exercise ANS Activity

After exercise stops, the sympathetic system activity diminishes, allowing the parasympathetic system to regain balance and restore normal function.

Blood Flow During Exercise

Sympathetic Nervous System (SNS) increases cardiac output (Q) and redistributes blood to working muscles.

Post-Exercise Blood Flow

After exercise ends, SNS activity decreases and PNS activity increases, allowing the body to return to resting state.