Neuroscience: Nervous System Functions, Cells, and Synaptic Processes

Nervous system function: Sensory input

Detects stimuli and converts them into electrical signals

Nervous system function: Integration

Process and interpret sensory information inside CNS

Nervous system function: Motor output

Send response signals to muscles or glands

Neuron

Excitable cell that sends and receives electrical and chemical signals

Neuroglia

Support cells that nourish, protect, insulate neurons

Synapse

Junction where neurons communicate

Presynaptic neuron

Neuron that releases neurotransmitter

Postsynaptic neuron

Neuron that receives neurotransmitter

Sensory neuron

Transmits signals from receptors to CNS

Interneuron

Processes information within CNS; connects sensory and motor neurons

Motor neuron

Sends signals from CNS to effectors (muscles/glands)

Astrocytes

CNS glial cell; support, nourishment, blood-brain barrier, cleanup

Ependymal cells

CNS glial cells that produce cerebrospinal fluid (CSF)

Microglia

CNS immune cells; remove pathogens and debris

Oligodendrocytes

CNS glial cells that myelinate axons

Satellite cells

PNS glial cells supporting neuron cell bodies in ganglia

Schwann cells

PNS glial cells that myelinate axons

Steps of chemical synapse: AP arrives

Action potential reaches axon terminal

Steps of chemical synapse: Ca2+ enters

Calcium ions enter presynaptic neuron

Steps of chemical synapse: NT released

Neurotransmitter released into synaptic cleft

Steps of chemical synapse: Receptors

Neurotransmitter binds receptors on postsynaptic neuron

Steps of chemical synapse: Na+ enters

Sodium enters → graded potential

Steps of chemical synapse: AP triggered

If threshold reached → action potential in postsynaptic neuron

Synapse signal end

Neurotransmitter broken down or reabsorbed

EPSP

Excitatory signal that depolarizes the cell

IPSP

Inhibitory signal that hyperpolarizes the cell

Summation

Adding EPSPs/IPSPs to reach threshold

Ganglion

Cluster of neuron cell bodies in PNS

Brain

Highly organized center with mostly interneurons

Nerve

Bundles of axons

Cnidarian nervous system

Nerve net with no brain

Planarian nervous system

Ladder-like system with cerebral ganglion; cephalization

Echinoderm nervous system

Ring nerve + radial nerves; no brain

Arthropod/Annelid nervous system

Brain + paired ventral nerve cords + segmental ganglia

Molluscan nervous system

Three pairs of ganglia around esophagus + paired nerve cords

Vertebrate nervous system

Forebrain, midbrain, hindbrain; dorsal spinal cord

CNS

Brain and spinal cord; integration and processing

PNS

Cranial and spinal nerves; communication pathways

Membrane potential

Charge difference across neuron membrane

Resting potential

−70 mV

Na+/K+ pump

Moves 3 Na+ out and 2 K+ in; maintains resting potential

Graded potential

Small change from ligand-gated channels; varies in strength

Threshold potential

−55 mV; required to fire an action potential

Action potential

Rapid, self-propagating electrical signal along axon

Voltage-gated Na+ channels

Open when threshold is reached; start action potential

Voltage-gated K+ channels

Open later to repolarize neuron

Myelination

Insulates axons and speeds conduction

Nodes of Ranvier

Gaps in myelin; allow saltatory conduction

Saltatory conduction

Action potential jumps node to node for faster speed

Electrical synapse

Direct ion flow via gap junctions; no neurotransmitter

Forebrain

Includes cerebrum and diencephalon

Midbrain

Relay region between forebrain and hindbrain

Hindbrain

Includes pons, medulla, cerebellum

Vertebrate brain regions

Forebrain, midbrain, hindbrain

Dorsal hollow nerve cord

Embryonic origin of CNS