Chapter 10

Nervous system

Detects changes, makes decisions, stimulates muscles and glands to respond, and maintains homeostasis.

Neurons

React to changes and send nerve impulses for communication.

Neuroglia

Surround and support neurons, nourish neurons, send & receive messages, and help maintain blood-brain barrier.

Central Nervous System (CNS)

Consists of the brain and spinal cord.

Peripheral Nervous System (PNS)

Connects CNS to other body parts, including cranial nerves and spinal nerves.

Migraine

Signs include pounding head, nausea, aura (shimmering images in visual field), light or sound sensitivity; lasts 4 - 72 hours.

Environmental triggers of migraines

Bright light, certain foods, lack of sleep, stress, high altitude, stormy weather, excess caffeine or alcohol.

Hormonal triggers of migraines

Migraine occurs just prior to menstruation.

Sensory Function

Nervous system receives information through sensory receptors that gather information by detecting changes.

Integrative Function

Nervous system coordinates sensory information to create sensations, memory, thoughts, and makes decisions on body's response.

Motor Function

Decisions are acted upon and impulses are carried to effectors (muscles or glands).

Somatic Nervous System

Transmits voluntary instructions to skeletal muscles.

Autonomic Nervous System

Transmits involuntary instructions from the CNS to smooth muscles, cardiac muscle, and glands.

Neuron Structure

Includes cell body (soma), dendrites, and axon.

Myelin Sheath

Coating formed by Schwann cells that insulate axons.

Nodes of Ranvier

Gaps in myelin sheath between Schwann cells.

Multiple Sclerosis

Destruction of myelin sheaths in CNS by an immune response, leading to symptoms like fatigue and blurred vision.

Classification of neurons by structure

Includes multipolar neurons (99% of neurons), bipolar neurons, and unipolar neurons.

Sensory Neurons

Afferent neurons that carry impulses to CNS; most are unipolar.

Interneurons

Association neurons that link neurons; typically multipolar and located in CNS.

Motor Neurons

Multipolar, efferent neurons that carry impulses away from CNS to effectors.

Astrocytes

Connect neurons to blood vessels, exchange nutrients and growth factors, and form scar tissue.

Oligodendrocytes

Myelinate CNS axons and provide structural support.

Microglia

Phagocytic cells that provide structural support.

Ependyma or ependymal cells

Line central canal of spinal cord & ventricles of brain, covering choroid plexuses.

Schwann Cells

Produce myelin sheath found on some peripheral axons and speed up nerve impulse transmission.

Satellite Cells

Support clusters of neuron cell bodies (ganglia).

Neuron Regeneration in the PNS

If a peripheral axon is injured, it may regenerate with the help of Schwann cells.

Neuron Regeneration in the CNS

CNS axons lack neurilemma, making regeneration unlikely.

Synapse

Neurons communicate with each other at synapses.

Presynaptic Neuron

Neuron that sends the nerve impulse.

Postsynaptic Neuron

Neuron that receives the nerve impulse.

Synaptic Cleft

Gap separating presynaptic and postsynaptic neurons.

Neuromuscular Junction

Connection between motor neuron and skeletal muscle.

Synaptic Vesicles

Contain neurotransmitters in synaptic terminal.

Synaptic Transmission

One-way transfer of information between neurons.

Calcium Ions (Ca+2)

Trigger neurotransmitter release during synaptic transmission.

Neurotransmitters

Chemicals affecting postsynaptic neuron activity.

Cell Membrane Potential

Electrical charge difference across a cell membrane.

Resting Membrane Potential (RMP)

Voltage difference of -70 mV in resting neurons.

Sodium/Potassium Pump

Transports Na+ out and K+ into the cell.

Hyperpolarization

Membrane potential becomes more negative.

Depolarization

Membrane potential becomes less negative.

Threshold Potential

Minimum potential of -55 mV for action potential.

Action Potential

Rapid change in membrane potential during impulse.

Voltage-Gated Sodium Channels

Open at threshold to initiate action potential.

Refractory Period

Time when neuron cannot respond to stimuli.

Ion Movements

Na+ influx and K+ efflux during action potential.

All-or-None Response

Action potential occurs fully or not at all.

Impulse Conduction

Propagation of action potentials along axon.

Local Potential Changes

Graded changes in neuron membrane potential.

Graded Potentials

Potentials that vary in magnitude with stimulus.

Mitochondria

Organelles providing energy in synaptic terminals.

Primary Synaptic Cleft

Main cleft in neuromuscular junction.

Secondary Synaptic Cleft

Junctional folds increasing surface area for transmission.

Absolute Refractory Period

No action potential can occur, Na+ channels unresponsive.

Relative Refractory Period

Only strong stimuli can generate action potentials.

Myelin

Lipid-rich insulation preventing ion movement.

Saltatory Conduction

Action potentials jump between nodes, faster transmission.

Thick Axons

Transmit impulses at 120 m/sec.

Thin Axons

Transmit impulses at 0.5 m/sec.

K+ Concentration Increase

Reduces gradient, lowers threshold for action potentials.

K+ Concentration Decrease

Hyperpolarizes neurons, prevents action potentials.

Na+ Permeability Decrease

Anesthetics block impulses, no sensation of pain.

Chemically Gated Ion Channels

Respond to neurotransmitters, altering membrane potential.

Excitatory Neurotransmitters

Increase Na+ permeability, promote action potentials.

Inhibitory Neurotransmitters

Decrease likelihood of action potentials occurring.

EPSP

Depolarization caused by Na+ channel opening.

IPSP

Hyperpolarization from K+ or Cl- channel opening.

Summation

Combining EPSPs and IPSPs for net effect.

Neurotransmitter Types

Includes monoamines, amino acids, and peptides.

Neurotransmitter Release

Occurs via exocytosis at synaptic knob.

Vesicle Trafficking

Membrane recycling during neurotransmitter release.

Neuropeptides

Act as neurotransmitters or neuromodulators.

Enkephalins

Neuropeptides that relieve pain sensations.

Beta Endorphin

Potent neuropeptide for pain relief.

Substance P

Neuropeptide involved in pain impulse transmission.

Opiate Drugs

Painkillers derived from the poppy plant.

Endogenous Opiates

Body-produced substances relieving pain naturally.

Neuronal Pools

Interneurons in CNS performing common functions.

Facilitation

Increased neurotransmitter release from repeated impulses.

Convergence

One neuron receives input from multiple sources.

Divergence

One neuron sends impulses to several neurons.

Antagonist

Blocks neurotransmitter binding at receptors.

Agonist

Activates receptor, enhancing neurotransmitter effect.

Amphetamines

Enhance norepinephrine activity, elevate mood.

Nicotine

Stimulates dopamine release, pleasurable effects.