Homeostasis + neurophysiology

Who coined the term "homeostasis" and what does it mean?

Walter Cannon coined "homeostasis" to describe the relative constancy of the blood’s chemical composition despite external changes.

• : Multiple systems integrate and use sensors to monitor levels (e.g., glucose), triggering corrective responses when values stray from normal ranges.

Claude Bernard's contribution to homeostasis?

He proposed the concept of internal vs. external environments, separated by integuments like skin or mucous membranes.

How does the skin help maintain body temperature in mammals?

It insulates with fat, dermis, and fur to limit heat loss, blocks heat from external sources, and cools the blood through sweat evaporation.

Liver’s role in thermoregulation

The liver produces heat during cellular metabolism, which contributes to maintaining core body temperature.

What role does the musculoskeletal system play in homeostasis?

Indirectly supports homeostasis by enabling food and water acquisition, predator avoidance, climate protection, and reproduction.

What two systems primarily regulate homeostasis?

The nervous system and the endocrine system.

What are the main features of the nervous system’s role in homeostasis?

It provides rapid sensory processing and responses (in seconds to minutes), and it helps regulate reproductive and behavioral functions.

What are the main features of the endocrine system’s role in homeostasis?

It regulates metabolism, tissue growth, and reproduction using hormones that act locally or systemically over short or long durations.

How can hormones affect the body even after levels return to normal?

Some hormones have residual effects that alter tissue function long after hormone levels have changed.

There are two main cell types in the nervous system:

1. Neurons: which conduct electrical signals and release chemical signals to other cells (neurotransmitters, across synapses, or neurohormones in circulation) but cannot divide. 

2. Glias: which act as support cells for neurons and neuronal processes and they CAN divide. 

How are neurons orgnaized?

 into circuits throughout the nervous system, controlling almost every activity of the body including the endocrine system via neuroendocrine secretions. 

What are the three main functional classifications of neurons?

1. Sensory neurons: conduct impulses from sensory receptors → CNS

2. Motor neurons: conduct impulses from the CNS → target organs 

3. Association/interneurons: located completely within the CNS and integrate functions of the nervous system.

How are motor neurons subsequently classified?

1. somatic motor neurons: responsible for reflexes and voluntary control of skeletal muscles

2. Autonomic neurons: innervate (supply body part with nerves) involuntary targets such as smooth muscle, cardiac muscle and glands.  

What are the five structural classifications of neurons?

1. Anaxonic (with no obvious axon; in the CNS primarily)

2. Unipolar (one axon)

3. Pseudouniolar  (one axon that branches into two)

4. Bipolar (two axons)

5. Multipolar (typically with a large “dendritic tree” receiving info and one main output axon)

What is the function of neurons in terms of information processing?

Neurons receive information from sensory receptors or other neurons, integrate that information, and pass it to other neurons or effector organs (like muscles) through synapses using action potentials.

Synapse

A junction between two neurons or a neuron and an effector organ where information is transmitted via action potentials.

What is the role of sensory receptors in the nervous system?

Sensory receptors detect stimuli like light, sound, heat, taste, or touch and convert them into action potentials in neurons.

• example fp sensory receptors (Rods and cones in the retina, which convert light into neural signals.)

What are glial cells in the peripheral nervous system (PNS)?

What are glial cells in the central nervous system (CNS)?

There are approx 100 billion neurons in adult human CNS, and even more glial cells.

What do neurons use to transmit signals?

Electrical potentials (voltage differences across the cell membrane).

Electroencephalography (EEG)

A technique that detects electrical activity in the brain by placing electrodes on the scalp.

What makes neurons unique among cells?

All healthy cells have a membrane potential, but only neurons use it to transmit information by generating short-lived changes called action potentials.

Membrane Potential

The voltage difference between the inside and outside of a cell, caused by the unequal distribution of ions across the membrane.

What is the typical resting membrane potential of a neuron?

About -70 millivolts (mV).

What causes the inside of a neuron to be more negative than the outside?

Fixed negatively charged molecules (like proteins, phosphate groups from ATP, and other organic anions) that cannot leave the cell.

• the fixed negative charges attract positively charged ions (cations) like sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺) from the extracellular fluid

How does the cell maintain the membrane potential?

: Using the Na⁺/K⁺ pump, which creates and maintains steep gradients of sodium and potassium ions across the membrane.

Why is potassium (K⁺) more concentrated inside neurons than outside?

Because the plasma membrane is more permeable to K⁺ than other cations, and K⁺ is attracted to fixed negatively charged ions inside the cell, it accumulates inside, creating a high intracellular concentration.

What is the intracellular and extracellular concentration of potassium (K⁺) in the human body?

Intracellular: 150 mEq/L
Extracellular: 5 mEq/L
(mEq = milliequivalents = mmol × ion valence)

What role does ion distribution play in membrane potential?

The unequal distribution of ions—especially K⁺—across the plasma membrane leads to a voltage difference, with the inside of the cell negatively charged and the outside positively charged.