BPOA Chapter 3

What is the basic structural unit of the nervous system?

The neuron

What are the three major regions of a neuron?

Cell body (soma), dendrites, and axon

What is the function of dendrites?

Receive impulses/stimuli from outside and carry the impulse toward the cell body

What is the role of the axon?

Conducts impulses away from the cell body

What are axon terminals filled with?

Neurotransmitters

What is a nerve impulse?

An electrical signal that communicates between the periphery and the brain

What is the resting membrane potential (RMP)?

The difference in electrical charges between the outside and inside of a cell, typically -70 mV

What causes the resting membrane potential?

Uneven separation of charged ions, leading to polarization

What ion has a high concentration outside the cell?

Sodium (Na+)

What ion has a medium concentration inside the cell?

Potassium (K+)

How do sodium-potassium pumps maintain the resting membrane potential?

By actively transporting 3 Na+ out for each 2 K+ it brings in

What happens during depolarization?

Na+ channels open, Na+ enters the cell, making the inside less negative and creating a nerve impulse

What is the threshold for action potential?

The point at which depolarization occurs, typically around 0 mV

What occurs during hyperpolarization?

K+ channels open, K+ leaves the cell, making the inside more negative

What is the effect of hyperpolarization on nerve impulse generation?

It makes it more difficult for a nerve impulse to arise

What regulates the sodium-potassium pumps?

Na+-K+-ATPase

What is the electrical potential of a resting neuron?

-70 mV

What does it mean for a neuron to be polarized?

It has a difference in electrical charge across its membrane

What is the primary role of the nervous system?

To respond to stimuli and communicate through nerve impulses

What is the significance of the axon hillock?

It is where the axon begins and where action potentials are initiated

What happens to the permeability of the cell membrane during depolarization?

It becomes more permeable to Na+

What are graded potentials (GP)?

Changes triggered by the neuron's local environment that may or may not trigger an action potential.

What is an action potential (AP)?

rapid and substantial depolarization of the neuron's membrane that passes a signal down the axon

What is the all-or-none principle in action potentials?

If the threshold is not reached, no action potential occurs.

What is the typical threshold range for generating an action potential?

From -50 mV to +55 mV, commonly using -55 mV for examples.

What two characteristics determine the speed of impulse travel along an axon?

Myelination and diameter of the axon.

How does myelination affect action potential conduction?

conduct impulses faster due to saltatory conduction

What are nodes of Ranvier?

Gaps in the myelin sheath where action potentials jump during saltatory conduction.

What is a synapse?

The junction or gap between neurons where communication occurs.

What is the direction of action potential movement across a synapse?

From presynaptic neuron to synapse to postsynaptic neuron (axon → synaptic cleft → dendrites)

What role do synaptic vesicles play in synaptic transmission?

They carry neurotransmitters that are released into the synaptic cleft.

What neurotransmitter is used at the neuromuscular junction?

Acetylcholine (ACh).

What is the function of the hypothalamus in the nervous system?

It maintains homeostasis by regulating the body's internal environment.

What are the two major divisions of the peripheral nervous system (PNS)?

Sensory (afferent) and Motor (efferent) divisions.

What does the autonomic nervous system control?

Involuntary internal functions such as smooth muscle, cardiac muscle, and glands.

What is the role of the sympathetic nervous system (SNS)?

Prepares the body for physical activity, emergency, and stressful situations.

What is the dominant player in 'quiet, relaxed situations'?

The parasympathetic nervous system (PNS).

What physiological effects does sympathetic stimulation include?

Increased heart rate, blood pressure, blood flow to muscles, and airway diameter.

What happens to blood vessels of non-essential organs during sympathetic stimulation?

They constrict to decrease blood flow.

How does the autonomic nervous system achieve dual innervation?

Most organs are innervated by both sympathetic and parasympathetic divisions.

What is the effect of parasympathetic stimulation on heart rate?

It decreases heart rate and promotes digestion and urination.

What is the primary function of the somatic nervous system?

stimulate skeletal muscle activity

What is the significance of the SA node in regulating heart rate?

It is the primary pacemaker of the heart, influencing the rate of depolarization.

What role does the parasympathetic nervous system (PNS) play in heart rate regulation?

decreases heart rate by innervating the heart at the SA and AV nodes via vagus nerve and releasing Acetylcholine, which decreases the permeability of the SA node to sodium, making depolarization more difficult

What is the effect of the sympathetic nervous system (SNS) on heart rate?

increases heart rate and force of contraction by innervating the heart at the SA node and ventricles via cardiac accelerator nerve and releasing Norepinephrine, which binds to β-receptors.

What is the intrinsic depolarization rate of the SA node?

100 beats per minute (bpm)

What is the normal resting heart rate (RHR) for a healthy adult?

60 to 80 bpm

Why is the resting heart rate kept below the intrinsic rate of the SA node?

the predominance of the parasympathetic system, which provides 'vagal tone' that decreases resting heart rate

What happens to heart rate during exercise?

an initial increase in heart rate due to the withdrawal of the PNS, allowing heart rate to rise to the intrinsic 100 bpm

How does training affect resting heart rate?

resting heart rate can drop to 30-40 bpm in highly trained endurance athletes due to increased PNS activity

Does the PNS still withdraw at the start of exercise after training?

Yes, allowing heart rate to increase to 100 bpm

What is the role of the SNS in regulating blood flow at rest?

partial constriction of blood vessels in skeletal muscle, limiting blood flow and shifting it to the kidneys and liver

What occurs to blood vessels during exercise?

dilatation in blood vessels in skeletal muscle to increase blood flow, while constricting blood vessels in the kidneys and liver

What are the five steps of sensory-motor integration?

1. Stimulus sensed by sensory receptor

2. Sensory AP sent to CNS

3. CNS interprets information and sends response

4. Motor AP sent to α-motor neurons

5. Motor AP arrives at skeletal muscle, resulting in a response

What are mechanoreceptors?

sensory receptors sensitive to mechanical stimuli, including muscle spindles and Golgi tendon organs (GTO)

What do muscle spindles detect?

muscle length and the rate of length change, sensing muscle stretch

What is the function of Golgi tendon organs (GTO)?

sensitive to tension in tendons and inhibit agonist muscles while exciting antagonist muscles to prevent excessive tension and reduce injury risk

What is the stretch reflex?

triggered when muscle spindles sense stretch, causing a reflex muscle contraction to prevent further damaging stretch

How does the SNS affect blood flow during exercise?

causes blood vessels in the kidneys and liver to constrict, decreasing blood flow to these areas while allowing increased flow to skeletal muscles

What is meant by 'vagal tone'?

the influence of the parasympathetic nervous system on heart rate, contributing to a lower resting heart rate

What happens to heart rate when the PNS is withdrawn?

heart rate increases as the brake on heart activity is removed

What is the typical resting heart rate range for trained athletes?

30-40 bpm

What is the primary role of the SNS in blood flow regulation?

regulates blood vessel size, causing constriction to limit blood flow to certain areas and redirecting it to others based on the body's demands