L4: Neurophysiology I

What three ions are higher OUTSIDE the cell?

• Na+

• Ca2+

• Cl-

What ion is higher inside the cell?

K+

What is the ratio for the ATPase pump?

3 Na+ OUT →

2 K+ IN ←

What is the purpose of the ATPase pump?

Creates a negative resting membrane potential inside the cell. (~-60 to -80mV)

Explain how voltage-gated ion channels function during action potential generation.

Voltage changes open Na+ channels (voltage gated sodium channels) causing depolarization and (voltage gated potassium channels) K+ channels that cause repolarization

Describe the sequence of events in an action potential, including depolarization and repolarization.

• depolarization: Na+ influx

• Repolarization: K+ influx

• Followed by brief hyperpolarization

Predict how changes in ion channel function (ex. blocked sodium channels) would affect nerve signaling.

Blocked Na+ channels prevent depolarization → no action potential → signal failure

How do impulses travel down myelinated axons?

Saltatory conduction: nodes of ranvier

How do impulses travel down unmyelinated axons?

Continuous, slower conduction

What are the key differences in graded potentials and action potentials?

• graded potentials: variable size, decay with distance

• Action potentials: all or none, long-distance, no decay

Analyze the effect of increased extracellular K+ on membrane potential and excitability

As the membrane becomes less negative (closer to the threshold for firing and action potential) → increased excitability

List the common neurotransmitters

• excitatory- glutamate, ACh

• Inhibitory- GABA

• Modulatory: dopamine, norepinephrine

Identify the types of neurotransmitter receptors

Nicotinic: fast ionotropic

Muscarinic, adrenergic, GABAergic: slower, metabotropic, or inhibitory

Explain the steps in neurotransmitter release, synaptic transmission, and clearance from the synaptic cleft

Ca2+ influx → vesicle fusion → neurotransmitter release → receptor binding → reuptake or breakdown

What are the three key components of the neuromuscular junction?

1- presynaptic terminal

2- synaptic cleft

3- motor end plate

Identify ACh as the neurotransmitter at the NMJ and the role of nicotinic receptors

ACh binds nicotinic receptors on muscle → triggers depolarization

Explain how action potential in a motor neuron leads to skeletal muscle contraction

AP → ACh release → endplate depolarization → Ca2+ release → muscle contracts

Describe the role of calcium in ACh release and muscle fiber activation.

Ca2+ triggers both neurotransmitter release and muscle fiber activation

Trace the sequence of events from motor neuron stimulation to muscle fiber contraction (excitation-contraction coupling)

Neuron fires → ACh release → depolarizes muscle → Ca2+ release → contraction

Predict the effects of blocking ACh receptors on muscle function

• causes muscle weakness or PARALYSIS (muscle relaxants)

Identify the hypothalamic region responsible for sensing and regulating body temperature (ex. Pre optic area)

Preoptic area of anterior hypothalamus detects and regulates temperature

List the physiological mechanisms used to conserve and dissipate heat

• conserve: vasoconstriction, shivering

• Dissipate: vasodilation, sweating

Illustrate a homeostatic feedback loop for body temperature, including sensory input, central integration, and effector response

Receptors → hypothalamus (integrator) → effectors (sweat glands, blood vessels)

Apple the concept of negative feedback to explain how the body responds to environmental temperature changes

Body opposes changes to restore normal temp

Ex. Cooling in heat, heating when cold

Describe how the brain’s energy demands are met primarily through glucose metabolism under normal physiological conditions

Brain uses glucose almost exclusively under normal condition

Explain the relationship between cerebral metabolic rate, oxygen consumption, and cerebral blood flow

Higher metabolism → more O2 use → increased blood flow

Analyze how factors such as hypothermia, hyperthermia, and anesthetic agents influence cerebral metabolic rate

Hypothermia and anesthetics: decreased CMRO2

Hyperthermia: increase CMRO2

List the normal range of cerebral blood flow in adults and the key determinants of CBF

Normal range: ~50mL/100g/min

• depends on blood pressure, ICP, and metabolic demand

Describe the principles of autoregulation of cerebral blood flow and its limits

Maintains steady flow from MAP ~50-150 mmHg

Explain how changes in arterial CO2 and O2 levels affect cerebral vessel tone and blood flow

• increased CO2 = vasodilation and increased flow

• Decreased O2 = vasodilation (protective)

Apply the concept of intracranial compliance (Monroe-Kellie doctrine) to explain how changes in blood, CSF, or brain volume influence intracranial pressure (ICP)

Total volume fixed, increase in one must be offset by a decrease in another, or else ICP increases

Analyze the physiologic consequences of impaired autoregulation (ex. In traumatic brain injury or severe hypotension)

• can lead to ischemia, hypoxia, or increased ICP

Compare the effects of anesthetic agents (volatile vs intravenous agents) on cerebral blood flow and metabolic coupling

• volatile- increased CBF and uncouple from metabolism

• IV- decreased CBF and metabolism together

Explain how cerebral perfusion pressure (CPP) is calculated and describe its role in maintaining adequate CBF

CPP= MAP - ICP

• must be adequate to sustain brain perfusion

describe the structure and function of the BBB, including how it protects the CNS from toxins and regulates molecular transport

Tight junctions- selective permeability protects brain

Explain how disruption of the BBB can alter CNS homeostasis

Leads to edema, infection, and dysregulation of CNS function

Identify the sites of CSF production, circulation, and réabsorption

Produced in choroid plexus, reabsorped via arachnoid granulations

Explain the physiological functions of CSF

Cushions the brain, removes waste, stabilizes ionic balance

Describe the normal range of intracranial pressure and the factors that influence it

• normal: 5-15 mmHg

• Influenced by volumes of brain, blood, CSF

Identify the major EEG waveforms (alpha, beta, theta, delta) and their associated states of consciousness

• alpha- relaxed

• Beta- alert

• theta- light sleep

• delta- deep sleep

Describe hoe EEG activity reflects underlying cortical function and changes in neuronal activity

Measures summed cortical electrical activity; shows brain state

Interpret basic EEG changes associated with sleep, anesthesia depth, and cerebral ischemia

Sleep- slower waves

Anesthesia- burst suppression

Ischemia- flatline or reduced activity

Describe the pathways by which peripheral sensory impulses are transmitted from receptors through peripheral nerves to the spinal cord and ultimately to the brain for processing

Receptors → peripheral nerves → spinal cord → ascending tracts → brain