main components of the nervous system Flashcards
central nervous system
brain, spinal cord
peripheral nervous system
cranial veins, spinal nerves
functional classes of neurons
Motor (efferent): away from CNS
Sensory (afferent): towards CNS
Interneurons: relay/ connector neurons that connect sensory and motor neurons in the CNS (e.g. reflex circuit interneurons)
spinal nerves
mixed motor and sensory fibers
cranial nerves
mixed or purely sensory or motor
draw diagram of influence in and of the central and peripheral nervous system
nerves vs neurons
neurons: Neurons are specialized cells that transmit electrical and chemical signals in the nervous system.
nerves: Nerves are bundles of axons (from many neurons) surrounded by connective tissue.
-> act as communication highways, transmitting signals between the central nervous system (CNS) and the peripheral body parts.
cells of nervous system: neurons
Receptive component: dendrites (increase surface area), cell body
Transmission component: Axon
Effector component: Axon terminals
Information flow:
Upstream neuron -> Dendrite -> Cell body -> Axon -> Downstream cell (neuron, muscle…)
are morphologically diverse:
- multipilar, motor neuron, unipolar MN, pseudo unipolar
cells of the nervous system: glia cells
- Support cells- physically connected to neurons
- Don’t directly participate in electrical signalling
- Main types:
CNS: Astrocytes, Oligodendrocytes, Microglia
PNS: Schwann cells - Portion of glia cells increases with increased complexity of the nervous system -> glia/ neuro ratio doesn’t increase uniformly with brain size
glia cells: Astrocytes
- Structural & metabolic support to neurons
- Gray matter in CNS
- Synaptic transmission (Glu, GABA transporters)
- Ionic composition
- Neuronal repair (glia scars)
E.g. regrowth of axons following spinal cord injury
Possible involvement in dementia and AD
glia cells: myelinated glia: oligodendrocytes & schwann cells
- Insulate axons (lipid rich myelin)
- Speed of transmission
- Metabolic support of axons
- Multiple sclerosis (MS): destroys myelin/ oligodendrocytes – therapy: stimulating of OD stem cells
glia cells: Microglia
- Resident CNS immune cells
- Scavenge and remove cell debris post-injury (like macrophages)
- Mediate inflammatory reaction by secreting cytokines
- Alzheimers disease: potential for microglial-based therapeutic strategies
Synapses
Information-processing units of nervous system
= specialized structure for transmission of information between a neuron and its target cell
chemical and electrical synapses
chemical: structures that translate incoming messaage into a different signal
- complex
- slow
- one way
electrical:
- simple
- fast
- bi directional
chemical synapses: Electrical signal from the brain converted into a muscle contraction
At a chemical synapse, the electrical signal (action potential) triggers the release of neurotransmitters from the presynaptic neuron.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
This binding initiates a new electrical signal in the postsynaptic cell or a muscle contraction if the postsynaptic target is a muscle cell.
-> Unidirectional transmission.
-> Slower due to the chemical diffusion step.
-> Allows for amplification and modulation (e.g., neurotransmitter reuptake, degradation).
electrical synapses: Electrical signal from the brain converted into a muscle contraction
Electrical synapses are formed by gap junctions, where ions and small molecules pass directly between adjacent cells.
The electrical signal (ion current) flows passively from the presynaptic to the postsynaptic cell without the need for neurotransmitters.
-> Bidirectional transmission.
-> Faster due to direct ionic flow.
-> Less adaptable and modifiable compared to chemical synapses.
