Nervous System - Objectives Only
Functions of the Nervous System: SIM
Sensory Input: Collects information from sensory receptors.
Integration: Processes and interprets sensory information.
Motor Output: Sends signals to muscles and glands for responses.
______ Potentials: Rapid changes in membrane potential that travel along the axon
Action Potentials
_________: Local changes in membrane potential that vary in strength and can initiate action potentials.
Graded Potentials
Differences in ion concentrations (e.g., sodium and potassium) across the membrane
Ion Concentration Gradients
Opening and closing of voltage-gated and ligand-gated channels
Ion Channels
Movement of action potentials along axons and across synapses.
Signal Transmission
Process by which multiple graded potentials combine to reach the threshold for an action potential.
Summation
Chemicals released at synapses that transmit signals between neurons.
Neurotransmitters
________ Neurotransmitters: Promote action potentials (e.g., glutamate)
Excitatory
________ Neurotransmitters: Prevent action potentials (e.g., gamma-aminobutyric acid, GABA)
Inhibitory
___________ Neurotransmitters: Influence the effects of other neurotransmitters (e.g., dopamine)
Modulatory
Breakdown of the axon and myelin sheath after injury.
Wallerian Degeneration
Growth of new axon sprouts from the damaged neuron.
Axonal Regeneration
Reformation of the myelin sheath around regenerated axons.
Remyelination
CNS is composed of:
Brain and Spinal Cord
The PNS is composed of: SAMS
Sensory Division
Autonomic Nervous System
Motor Division
Somatic Nervous System
Neuron classification by type:
Sensory, Motor, Interneurons
Neuron classification by structure:
Unipolar, bipolar, multipolar, pseudopolar
Astrocytes, Microglia, Oligodendrocytes, Schwann Cells
Neuroglia types
Bundles of axons in the PNS
Nerves
Clusters of neuron cell bodies in the PNS
Ganglia
Clusters of neuron cell bodies in the CNS
Nuclei
Ion channel types:
Voltage-gated, Ligand-gated
Resting membrane potential is typically:
Typically -70 mV; established by ion distribution
Examples: Acetycholine, dopamine, serotonin
Small-Molecule Neurotransmitters
Small proteins in brain that help trasmit signals to regulate mood and pain. Examples: Substance P, endorphins
Neuropeptides
Motor vs Sensory
Motor functions = transmission of signals initiating movement & control muscle activity
Sensory = reception and processing of external stimuli
Components of a neuron:
Cell body, dendrites, axon, myelin sheath, nodes of ranvier, axon terminals,
Gaps in the myelin sheath that facilitate rapid conduction of impulses through saltatory conduction.
Nodes of Ranvier
A long, slender projection that transmits electrical impulses away from the cell body to other neurons or muscles
Axon
_______ (Soma): Contains the nucleus and organelles, responsible for maintaining the cell's functions.
Cell body
These have a single process that extends from the cell body, which then branches into two parts; dendrite & axon.
- They are primarily found in sensory neurons
Unipolar Neurons
These have two processes—one axon and one dendrite—extending from opposite ends of the cell body. They are typically found in specialized sensory organs (retina)
Bipolar Neurons
These possess multiple processes, 1 axon & several dendrites, most common type of neuron in the nervous system.
- Involved in motor functions and complex processing and are found throughout the brain and spinal cord.
Multipolar Neurons
Transports sodium ions out of the cell and potassium ions into the cell, maintaining the resting membrane potential
Sodium-Potassium Pump
______ is the point a neuron needs to reach to trigger an action potential
- Once it hits this level, sodium channels open, allowing sodium ions to flow in & send an electrical signal down the neuron.
Threshold
Saltatory conduction advantages:
Speed - Axon potentials jump between nodes of Ranvier
Energy efficient - Fewer ions needed
Space efficient - Myelination = thinner axons
Saltatory conduction disadvantages:
Nodes of Ranvier Exposed - susceptible to damage
Limited Ability of Repair
Immature neurons cannot conduct, need more timr to develop
Plasticity vs. Repair
Plasticity - brain's ability to adapt/reorganize itself in response to injury
Repair - restoration of damaged neural structures/functions
Supportive cells in the peripheral nervous system
- Wrap around nerve fibers to create myelin
- Help signals travel faster
Schwaan Cells
Star-shaped cells in the brain & spinal cord that support neurons by:
- providing nutrients
- maintaining the environment
- helping with the repair of nervous tissue.
Astrocytes
Ganglion vs Neuron
Ganglion - cluster of nerves outside brain
Neuron - single nerve cell that sends messages
This type of ion channel is a gate in the cell membrane that opens when a special molecule attaches to it, letting ions pass through
A ligand-gated ion channel (or chemical-gated)
A type of ion channel that opens or closes in response to changes in electrical voltage, allowing specific ions to flow in or out of the cell
A voltage-gated ion channel
Repair process of peripheral nerve:
1. Wallerian Degeneration: The damaged part of the nerve breaks down and is cleaned up.
2. Axonal Regeneration: The nerve cell starts to heal, and the axon grows back toward its target.
3. Schwann Cell Support: Supporting cells help guide the growing axon and create a protective layer around it.
4. Reinnervation: The growing axon connects to the target tissue, helping restore its function.
Randomly open and close, ions move across cell membrane.
Leak Ion Channels
Gates open and close in response to stimulation (touch, pressure, vibration), example is the eardrum
Mechanically-Gated Ion Channel
Process by which nerve impulses jump between gaps in the myelin sheath covering the axon
- Transmits signals across the nerve
Saltatory Conduction