A&P Exam 4 Chp. 12

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

The human nervous system is separated into two major anatomical divisions:

brain and spinal cord

Central Nervous System (CNS) includes

nerves and nervous structures outside of the brain and spinal cord (sensory and motor)

Peripheral Nervous System (PNS) includes

Sensation (Sensory Input)

Detects changes and receives information about the external or internal environment

Integration

Combines sensory input with higher-level mental processes (memories, emotional state, learning, and existing perceptions) to determine an appropriate response

Response (Motor Output)

Generates physical or physiological actions based on the integrated sensory information

Somatic, Autonomic, and Enteric Nervous Systems

Control of the body by the nervous system can be separated into 3 functional divisions:

Somatic Nervous System

conscious perception and voluntary motor responses (skeletal muscle)

Autonomic Nervous System

involuntary control of the body, usually in order to maintain homeostasis (smooth muscle, cardiac muscle, glands)

Enteric Nervous System

controlling smooth muscle and glandular tissue in the digestive system

Autonomic

Enteric

_______ = involuntary functions throughout the body

_______ = Eating and digestion

gray matter

Mostly neuronal cell bodies, dendrites, and unmyelinated axons

gray matter

Appears darker due to blood supply and lack of heavy myelination

white matter

Mostly myelinated axons

white matter

Appears light due to the high lipid (fat) content of the myelin sheaths

nucleus

A collection of neuron cell bodies in the CNS

ganglion

A collection of neuron cell bodies in the PNS

tract

A bundle of nerve fibers (axons) located in the CNS

nerve

A bundle of axons located in the PNS

nucleus, tract

CNS Cluster of Cell Bodies is _______ and Bundle of Axons is _______

ganglion, nerve

PNS Cluster of Cell Bodies is _______ and Bundle of Axons is _______

Cell Body (Soma)

central portion of the neuron that houses the nucleus and organelles

Dendrites

highly branched processes that receive incoming electrical signals from other neurons at specialized contact points (synapses) and direct them toward the soma

Axon

single, elongated fiber projecting from the soma that propagates electrical nerve impulses away from the cell body toward target cells

Myelin Sheath

lipid-rich insulating cover wrapping around axons that speeds up signal conduction

Nodes of Ranvier

uninsulated gaps in the myelin sheath along the length of an axon that assist in electrical signal propagation

Axon Terminal

branching distal end of an axon that extends toward target cells

Terminal Buttons (Synaptic End Bulbs)

enlarged, tips at the end of an axon terminal branch that forms a physical junction (synapse) with a target cell

Unipolar / Pseudounipolar

1 axon splitting in 2 directions

Unipolar / Pseudounipolar

sensory neurons with cell bodies in peripheral ganglia (e.g., dorsal root ganglia)

Bipolar

1 axon, 1 dendrite

Bipolar

uncommon, found in specialized sensory organs (retina, olfactory epithelium)

Multipolar

1 axon, many dendrites

Multipolar

most common type, including almost all CNS neurons and motor neurons

Glial cells

provide a framework of tissue that supports neurons and their activities

CNS Glial cells

Astrocytes, Microglia, Ependymal cells, Oligodentrocytes are _____

PNS Glial cells

Satellite cells, Schwann cells are ______

membrane potential

The difference in electrical charge between the inside and the outside of a cell's plasma membrane

-70mV

Resting membrane potential of a neuron = ______

sodium/potassium pump

moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell and regulates ion concentration on both sides of the cell membrane

out of, into

The sodium/potassium pump moves sodium ions (Na+) ______ a cell and potassium ions (K+) ______ a cell and regulates ion concentration on both sides of the cell membrane

Na+ (sodium), K+ (potassium)

The Sodium-Potassium Pump uses energy from ATP hydrolysis to actively transport ______ ions out of the cell and ______ ions into the cell

Ligand-Gated (Ionotropic)

Open when a specific chemical ligand (e.g., ACh) binds

Mechanically-Gated

Open via physical deformation/distortion (touch, pressure, temperature receptors)

Voltage-Gated

Open/close in response to changes in local membrane voltage

Graded Potential

short-range, local voltage changes in dendrites/soma whose amplitude matches stimulus intensity

EPSPs (Excitatory Postsynaptic Potentials)

Depolarize membrane (Na+ or Ca2+ influx) toward threshold

IPSPs (Inhibitory Postsynaptic Potentials)

Hyperpolarize membrane (K+ efflux or Cl- influx) away from threshold

spatial and temporal

two types of Summation at Axon Hillock:

spatial summation

Adding together Postsynaptic Potentials (PSPs) that arrive at the same time at different locations across the dendrites/soma

temporal summation

Adding together Postsynaptic Potentials (PSPs) generated in rapid succession from a single presynaptic terminal

-55 mV

Action Potentials (APs) Threshold = ______

All-or-None Principle

Reaching -55 mV triggers a uniform AP peaking around +30 mV; sub- threshold stimuli fail to fire

action potential frequency

Stimulus strength is determined by _______, not amplitude

Depolarization, Repolarization, Hyperpolarization, Restoration of Resting State

four steps of action potential:

Depolarization

An incoming stimulus opens Na+ channels, letting positively charged Na+ rush into the cell and shifting the membrane voltage from negative toward positive

Repolarization

Voltage-gated Na+ channels close and voltage-gated K+ channels open, allowing K+ to rush out of the cell and driving the internal voltage back down toward -70 mV

Hyperpolarization

Voltage-gated K+ channels close slowly, leading to a brief overshoot where the membrane potential becomes slightly more negative than -70 m

Restoration of Resting State

Leakage channels and active Na+/K+ pumps move ions back to their resting concentrations, returning the cell to -70 mV

Repolarization

Restoration of Resting State

Depolarization

Hyperpolarization

_______ = K+ leaves the cell, making the inside more negative again

_______ = Na+/K+ pumps and leakage channels restore the cell to its normal resting potential of -70 mV

_______ = Na+ enters the cell, making the inside more positive

_______ = Too much K+ leaves the cell, making the inside more negative than its resting state

Absolute Refractory Period

Time during which all Na+ channels are either already open or inactive and another AP cannot fire regardless of stimulus strength

Relative Refractory Period

Time during which Na+ channels have reset, but K+ efflux hyperpolarizes the membrane, requiring a much stronger stimulus to reach threshold

Absolute

Relative

_______ = can not fire again

_______ = can fire again, but needs a stronger stimulus

Continuous Conduction

Slow, step-by-step propagation along unmyelinated axons

Saltatory Conduction

Fast propagation along myelinated axons as current "jumps" between Nodes of Ranvier

increase

Thicker axon diameters _______ speed by lowering internal resistance

Electrical Synapses

direct connection (gap junction) between cells; rare

Chemical Synapses

presynaptic terminal releases neurotransmitter across the synaptic cleft to postsynaptic receptors; more common type of synapse

Ionotropic Receptors and Metabotropic Receptors

two types of postsynaptic receptors:

Ionotropic Receptors

Ligand-gated ion channels causing immediate, localized ion flow (e.g., nicotinic ACh receptors)

Metabotropic Receptors

Transmembrane receptor ("first messenger") activates a G-protein → effector enzyme produces intracellular "second messengers" (e.g., cAMP) for prolonged, amplified effects or gene-expression (e.g., muscarinic ACh receptors)

Neurotransmitters

Molecules that carry messages or signals from one nerve cell to the next target cell

Cholinergic, Amino Acids, Biogenic Amines, Neuropeptides

types of neurotransmitters:

Cholinergic

Operates at neuromuscular junctions and throughout the central and autonomic nervous systems

Amino Acids

CNS excitation and inhibition

Biogenic Amines

Synthesized from enzymatic breakdown of amino acids

Neuropeptides

Chains of amino acids that can be very short or very long and function as neuromodulators or hormones

Cholinergic

Amino Acids

Biogenic Amines

Neuropeptides

Acetylcholine is an example of ______

Glutamate, GABA, Glycine is an example of ______

Serotonin is an example of ______

Met-enkephalin, Beta-endorphin is an example of ______