BIO25 Chapter 12 Nervous System - Part 1

Flashcards about the nervous system.

Nervous System

Communication and control system.

Nervous System Function 1

Collect information via receptors that detect stimuli and send sensory signals to the spinal cord and brain.

Nervous System Function 2

Process and evaluate information in the brain and spinal cord to determine a response.

Nervous System Function 3

Initiate a response to information by sending motor output via nerves to effectors (muscles or glands).

Central Nervous System (CNS)

Brain and spinal cord.

Peripheral Nervous System (PNS)

Nerves and ganglia.

Sensory Nervous System

Afferent nervous system; receives information from receptors and transmits it to the CNS.

Somatic Sensory System

Detects stimuli we are aware of.

Visceral Sensory System

Detects stimuli we typically do not perceive (e.g., signals from the heart or kidneys).

Motor Nervous System

Efferent nervous system; initiates motor output and transmits it from the CNS to effectors.

Somatic Motor System

Sends voluntary signals to skeletal muscles.

Autonomic Motor System

Visceral motor system; sends involuntary commands to the heart, smooth muscle, and glands.

Sympathetic Division

Part of the autonomic motor system.

Parasympathetic Division

Part of the autonomic motor system.

Nerve

A bundle of parallel axons in the PNS.

Epineurium

Encloses the entire nerve; thick layer of dense irregular connective tissue.

Perineurium

Wraps fascicle (bundle of axons in nerve); layer of dense irregular connective tissue.

Endoneurium

Wraps an individual axon; delicate layer of areolar connective tissue that separates and electrically insulates each axon.

Cranial Nerves

Extend from the brain.

Spinal Nerves

Extend from the spinal cord.

Sensory Nerves

Contain sensory neurons sending signals to the CNS.

Motor Nerves

Contain motor neurons sending signals from the CNS.

Mixed Nerves

Contain both sensory and motor neurons.

Ganglion

A cluster of neuron cell bodies in the PNS.

Neuron

The structural unit of the nervous system.

Excitability

Responsiveness to a stimulus; stimulus causes change in cell’s membrane potential.

Conductivity

Ability to propagate electrical signal; voltage-gated channels along membrane open sequentially.

Secretion

Release of neurotransmitter in response to conductive activity; messenger is released from vesicle to influence target cell.

Extreme Longevity (Neurons)

Cell can live throughout a person's lifetime.

Amitotic (Neurons)

After fetal development, mitotic activity is lost in most neurons.

Dendrites

Branching off cell body, receive input and transfer it to cell body.

Cell Body (Soma)

Initiates some graded potentials, receives others from dendrites; conducts these potentials to axon.

Axon

Long process from cell body that contacts neurons, muscles, or glands.

Axon Hillock

Where the axon attaches to the cell body.

Synaptic Knobs

Contain vesicles with neurotransmitters.

Multipolar Neurons

Most common type, many dendrites, one axon.

Bipolar Neurons

One dendrite and one axon, less common, found in the retina of the eye.

Unipolar Neurons

One process extends from cell body and splits into two processes.

Anaxonic Neurons

Have dendrites but no axons.

Sensory Neurons (Afferent)

Conduct input from somatic and visceral receptors to the CNS; mostly unipolar.

Motor Neurons (Efferent)

Conduct output from CNS to somatic and visceral effectors; all are multipolar.

Interneurons (Association)

Receive, process, and integrate information from other neurons; communicate between sensory and motor neurons; located within CNS.

Synapse

Place where a neuron connects to another neuron or an effector.

Chemical Synapse

More common; presynaptic neuron's axon terminal produces a signal, postsynaptic neuron receives it.

Synaptic Cleft

Small fluid-filled gap between two neurons at a chemical synapse.

Astrocytes

Star-shaped glial cells abundant in the CNS; help form the blood-brain barrier, regulate brain chemistry, provide structural support.

Ependymal Cells

Line brain and spinal cord cavities, part of the choroid plexus which produces cerebrospinal fluid (CSF).

Microglia

Small, mobile glial cells that act as immune responders; engulf pathogens and debris.

Oligodendrocytes

Large glial cells with extensions that wrap around axons in the CNS, forming the myelin sheath.

Satellite Cells

Glial cells arranged around neuronal cell bodies in a ganglion; electrically insulate and regulate the exchange of nutrients and wastes.

Neurolemmocytes (Schwann Cells)

Elongated, flat glial cells that ensheath PNS axons with myelin.

Myelination

Wrapping an axon with myelin.

Neurofibril Nodes (Nodes of Ranvier)

Gaps between Schwann cells.

Oligodendrocytes Myelination in CNS

One oligodendrocyte can myelinate multiple axons at multiple spots.

Neurilemma

Not formed by oligodendrocytes in the CNS.

PNS Axon Regeneration

Regeneration is possible if the neuron cell body is intact and enough neurilemma remains.

CNS Axon Regeneration

Extremely limited; oligodendrocytes secrete growth-inhibiting molecules, regrowth obstructed by scars from astrocytes.

Multiple Sclerosis

Progressive demyelination of neurons in CNS; autoimmune disorder where oligodendrocytes are attacked by immune cells.

Guillain-Barré Syndrome

Loss of myelin from peripheral nerves due to inflammation; muscle weakness begins in distal limbs.

Neoplasms (Tumors)

Unregulated cell growth; can occur in the CNS, typically originating in supporting tissues.

Gliomas

Glial cell tumors; can be benign or malignant.

Channels (Nervous System)

Protein pores in the membrane that allow ions to move down their concentration gradients; do not require energy.

Leak (Passive) Channels

Always open for continuous diffusion.

Chemically Gated Channels

Normally closed, but open when a neurotransmitter binds.

Voltage-Gated Channels

Normally closed, but open when membrane charge changes.

Pumps (Nervous System)

Require energy; neurons have sodium-potassium pumps and calcium pumps in their membranes.

Na+/K+ Pumps Location

Entire plasma membrane of a neuron.

Ion Distribution

Higher concentration of potassium (K+) inside; higher concentrations of sodium (Na+), chloride (Cl-), and calcium (Ca2+) outside.

Resting Membrane Potential (RMP)

Typically -70 mV; inside of the neuron is relatively negative compared to the outside.

Resting Membrane Potential (RMP) Potassium role

K+ moves out of the cell to make inside the cell negative

Resting Membrane Potential (RMP) Sodium role

Na+ also leaks into the cell, this small Na+ influx makes the RMP slightly less negative, around –70 mV.

Na+/K+ Pumps Ratio

3 Na+ out and 2 K+ in, to maintain –70 mV resting membrane potential.

Plasma Membrane Segments

Receptive, Initial, Conductive and Transmissive

Receptive Segment

Chemically gated channels (For example, chemically gated Cl– channels)

Initial Segment

Voltage-gated Na+ channels and voltage-gated K+ channels

Conductive segment

Voltage-gated Na+ channels and voltage-gated K+ channels

Transmissive segment

Voltage-gated Ca2+ channels and Ca2+ pumps

Graded Potentials

Small, short-lived changes in the RMP established in the receptive segment by the opening of chemically gated ion channels.

Excitatory Postsynaptic Potential (EPSP)

Postsynaptic potential resulting in depolarization.

Inhibitory Postsynaptic Potential (IPSP)

Postsynaptic potential resulting in hyperpolarization.

EPSP Cause

Depolarizations caused by Na+ entry

IPSPs Cause

Hyperpolarization caused by K+ exit or Cl− entry

Summation (Nervous System)

Of EPSPs and IPSPs occurs at the axon hillock; voltage changes from the dendrites and soma are added.

Threshold Membrane Potential

Typically, threshold is about –55 mV

Spatial Summation

Multiple locations on cell’s receptive regions receive neurotransmitter simultaneously and generate postsynaptic potentials

Temporal Summation

A single presynaptic neuron repeatedly releases neurotransmitter and produces multiple EPSPs within a very short period of time

Action Potential

involves depolarization and repolarization

Action potential Depolarization

gain of positive charge as Na+ enters through voltage-gated Na+ channels

Repolarization

return to negative potential as K+ exits through voltage-gated K+ channels

Action potential Propagation

Voltage-gated channels open sequentially down axolemma

Nerve signal

also known as Nerve impulse

Voltage-gated Na+ channels

open as Na+ enters from adjacent region

Positive Potential

Na+ enters the axon causing the membrane to have a positive potential

Inactivation state

Na+ channels close becoming inactive (unable to open) temporarily

K+ channels Open

Depolarization slowly opens K+ channels, and K+ diffuses out, causing negative membrane potential

K+ exit

makes cell more negative than RMP (hyperpolarization)

Neuronal Pools (Neuronal Circuits)

Groups of neurons arranged in specific patterns.

Types of Neuron Circuits

Converging, diverging, reverberating, parallel-after-discharge

Converging Circuit

Input converges at a single postsynaptic neuron

Diverging Circuit

Spreads information from one presynaptic neuron to several postsynaptic neurons