ch 6

What is the difference between electrical and chemical signals?

Electrical signals are changes in membrane potential; chemical signals are molecules secreted into the ECF that communicate with other cells.

What are gap junctions?

Direct cytoplasmic connections between adjacent cells that allow rapid transfer of electrical and chemical signals.

What are contact-dependent signals?

Signals that require direct interaction between membrane molecules of adjacent cells using cell adhesion molecules (CAMs).

What is an autocrine signal?

A chemical signal that acts on the same cell that secreted it.

What is a paracrine signal?

A chemical signal that diffuses through interstitial fluid and acts on nearby cells.

How do endocrine hormones communicate over long distances?

They are released into the blood and travel through the cardiovascular system to distant target cells with specific receptors.

What is a neurotransmitter?

A chemical signal released by a neuron that crosses a small synaptic gap to affect a target cell.

What is a neurohormone?

A chemical signal released by a neuron directly into the bloodstream to act on distant target cells.

What is the basic sequence of a physiological signal pathway?

Ligand → receptor → protein transduction → intracellular change → cellular response.

Where are receptors for lipophilic ligands located?

Inside the cell, usually in the cytosol or nucleus.

Where are receptors for lipophobic ligands located?

On the cell membrane, where they trigger rapid intracellular signaling cascades.

What are the four major types of cell membrane receptors?

Receptor-channels, receptor-enzymes, G protein-coupled receptors (GPCRs), and integrin receptors.

What is a receptor-channel?

A ligand-gated channel that opens or closes to change membrane permeability.

What is a receptor-enzyme?

A membrane receptor with cytoplasmic enzymatic activity, such as tyrosine kinase.

What is a G protein-coupled receptor (GPCR)?

A membrane receptor linked to a G protein that activates intracellular signaling pathways.

What is an integrin receptor?

A receptor linked to the cytoskeleton through anchor proteins that can alter cell shape and movement.

What is the tyrosine kinase receptor pathway?

Ligand binds receptor → tyrosine kinase activates → ATP provides a phosphate group → target proteins are phosphorylated → cell response occurs.

What is the GPCR-adenylyl cyclase-cAMP pathway?

Ligand → GPCR → G protein → adenylyl cyclase → cAMP → PKA → protein phosphorylation → cellular response.

What does adenylyl cyclase do?

Converts ATP into cyclic AMP (cAMP).

What is cAMP?

A second messenger produced from ATP that activates Protein Kinase A.

What does Protein Kinase A (PKA) do?

Phosphorylates target proteins to produce a cellular response.

What is an agonist?

A substance that mimics the primary ligand and activates a receptor.

What is an antagonist?

A substance that binds to a receptor and blocks the primary ligand from activating it.

Why can the same ligand cause different effects in different tissues?

Different tissues may have different receptor isoforms, which produce different responses.

What does epinephrine do when it binds to α-receptors on intestinal blood vessels?

It causes vasoconstriction.

What does epinephrine do when it binds to β2-receptors on skeletal muscle blood vessels?

It causes vasodilation.

What is antagonistic control?

Use of opposing neural inputs to regulate a target and maintain homeostasis.

How do sympathetic and parasympathetic stimulation affect heart rate?

Sympathetic stimulation increases heart rate; parasympathetic stimulation decreases heart rate.

What is the main relay center for almost all sensory information?

The thalamus.

Which major sensory pathway is the exception to thalamic relay?

Olfaction (smell).

What are the major cognitive functions of the cerebral cortex?

Memory formation, prediction, language, complex thought, and analysis.

What is the main homeostatic role of the hypothalamus?

It regulates autonomic and endocrine functions, including water balance, osmolarity, and body temperature.

What does the limbic system regulate?

Emotion, memory, and learning.

Where are the three vital centers of the CNS located?

In the medulla oblongata.

Which brain regions regulate ventilation?

The pons and medulla oblongata.

What happens if the pons and medulla are severely damaged?

Regulation of ventilation can be completely lost.

What are the five brain divisions in order from lowest to highest information processing?

Medulla oblongata → pons → hypothalamus → cerebellum → cerebrum.

What tissues are controlled involuntarily by the autonomic nervous system (ANS)?

Cardiac muscle, smooth muscle, and glandular tissue.

Which receptors are found between preganglionic and postganglionic parasympathetic neurons?

Nicotinic receptors.

Which receptors are found on parasympathetic target tissues?

Muscarinic receptors.

What neurotransmitter does the sympathetic division use at its ganglia?

Acetylcholine (ACh).

What neurotransmitter does the sympathetic division typically use at its target organs?

Norepinephrine (NE).

What are adrenergic receptors?

Receptors with α and β subtypes found at sympathetic target effectors.

What happens if the sympathetic division is impaired?

Fight-or-flight responses and physical excitement are impaired; parasympathetic functions such as digestion, urination, defecation, and salivation are still promoted.

Which division of the efferent nervous system typically provides antagonistic control?

The autonomic nervous system.

What structure produces cerebrospinal fluid (CSF)?

The choroid plexus.

Which glial cells are important for the blood-brain barrier (BBB)?

Astrocytes.

What does the enteric nervous system regulate?

Local visceral activities and reflexes within the digestive system.

What is the adequate stimulus for a mechanoreceptor?

Cell stretch or mechanical deformation.

What are phasic receptors?

Receptors that rapidly adapt to a constant stimulus and decrease their action potential frequency.

What is a receptive field?

The specific physical area monitored by a single sensory receptor.

Which vestibular structure detects rotational acceleration?

The crista ampullaris in the semicircular canals.

What happens if the hair cells of the crista are damaged?

The ability to detect rotational acceleration is impaired, causing problems with balance during turns or spins.

Which tongue papillae help detect texture?

Filiform papillae.

Do filiform papillae contain taste buds?

No. They provide friction and tactile sensory feedback.

Which part of the eye provides the highest-acuity vision for fine details?

The fovea.

Why is the fovea important for reading and fine-detail vision?

It contains the highest density of cone photoreceptors.

What is habituation?

A decrease in perception of a stimulus even though the stimulus intensity remains unchanged.

What causes habituation?

Inhibition by higher neural pathways in the central nervous system.

What is a simple endocrine reflex pathway?

Change → endocrine sensor-integrating center → efferent hormone → effector → response.

What is a simple neural reflex pathway?

Change → receptor → afferent sensory neuron → CNS integrating center → efferent neuron → effector → response.

What is a complex neuroendocrine pathway?

Change → receptor → afferent neuron → CNS integrating center → efferent neuron/neurohormone → endocrine integrating center → hormone → effector → response.

What is the difference between central and peripheral sensory receptors?

Central receptors are located in or near the brain; peripheral receptors are located outside the brain.

What do chemoreceptors detect?

Chemicals and changes in pH.

What do osmoreceptors detect?

Changes in osmolarity.

What do thermoreceptors detect?

Temperature.

What do baroreceptors detect?

Pressure.

What do proprioceptors detect?

Body position.

What do mechanoreceptors detect?

Mechanical stimuli such as touch, vibration, pressure, or stretch.