Lecture 1: Cellular Structure of the Nervous System.

Central nervous system (CNS)

The brain and spinal cord

Peripheral nervous system (PNS)

All nervous tissue outside the brain and spinal cord

Somatic nervous system

Subdivision of the PNS involved in voluntary movement and sensory input

Autonomic (visceral) nervous system

Subdivision of the PNS involved in involuntary control of organs

Afferent neurons

Sensory neurons that carry information toward the CNS

Efferent neurons

Motor neurons that carry information away from the CNS

Mnemonic for afferent vs efferent

SAME: Sensory Afferent, Motor Efferent

Neuron

An electrically excitable cell and the basic functional unit of the nervous system

Glial cells

Non-neuronal cells that support, regulate, and interact with neurons

Other names for glial cells

Neuroglia or glia

Electrical excitability

The ability of neurons to generate and propagate electrical signals

Main structural components of a neuron

Cell body (soma), dendrites, axon, axon terminal

Primary input zone of a neuron

Dendrites

Primary output zone of a neuron

Axon

Cell body (soma)

The metabolic and genetic center of the neuron

Function of the neuronal nucleus

Contains most nuclear DNA and is the site of gene transcription

Gene transcription

Process of converting DNA into mRNA

Mitochondrial DNA

DNA located within mitochondria

Importance of genetics in neuroscience

Disease-causing mutations and transgenic model creation

Rough endoplasmic reticulum

Protein synthesis via ribosomes

Smooth endoplasmic reticulum

Lipid synthesis and intracellular signalling

Golgi apparatus

Modifies, sorts, and packages proteins

Role of ER and Golgi in neurons

Synthesise, fold, and sort proteins

Neuronal cytoskeleton components

Microtubules, neurofilaments, microfilaments

Largest cytoskeletal element

Microtubules

Intermediate filaments in neurons

Neurofilaments

Function of the cytoskeleton

Maintains structure and enables intracellular transport

Dynamic cytoskeleton regulation

Allows changes in neuronal structure and organisation

Tau protein

Binds to and stabilises microtubules

Tau abundance

Highly abundant in neurons

Tau in Alzheimer’s disease

Hyperphosphorylated and dissociates from microtubules

Neurofibrillary tangles (NFTs)

Aggregates of tau protein

Effect of tau dysfunction

Reduced axonal transport and neuronal dysfunction

Mitochondria

Site of cellular respiration

ATP

Adenosine triphosphate, the cell’s energy currency

Role of ATP in neurons

Maintains ion gradients and supports neuronal activity

Cells vulnerable in mitochondrial disease

Cells with high mitochondrial density such as neurons

Dendrites

Branched extensions that receive synaptic input

Meaning of dendron

Greek for “tree”

Function of dendritic branching

Increases surface area for synaptic input

Dendritic spines

Small protrusions that further increase synaptic surface area

Dendritic spine plasticity

Dynamic changes in spine number and morphology

Dendritic spine density in schizophrenia

Commonly decreased

Brain region affected in schizophrenia

Prefrontal cortex

Functional consequence of reduced spine density

Cognitive deficits and executive dysfunction

Axon

Long projection transmitting action potentials away from the soma

Number of axons per neuron

One

Axon collaterals

Branches of an axon

Myelin

Fatty insulating sheath around axons

Myelinated axons

Conduct action potentials faster

Anterograde axonal transport

Movement from soma to axon terminal

Retrograde axonal transport

Movement from axon terminal to soma

Motor protein kinesin

Transports cargo along microtubules

Axonal cargo

Vesicles, proteins, mitochondria

Charcot-Marie-Tooth disease (CMT)

Inherited progressive motor and sensory neuropathy

CMT type 2 (CMT2)

Primarily causes axonal degeneration

Cause of some CMT2 mutations

Impaired axonal transport and organelle interactions

Mitofusin 2

Protein regulating mitochondrial transport and mito-ER contact

Axon terminal

Presynaptic ending that communicates with another cell

Synaptic cleft

Gap between presynaptic and postsynaptic cells

Neurotransmitter vesicles

Vesicles containing chemical messengers

Postsynaptic density (PSD)

Region rich in neurotransmitter receptors

Chemical synapse

Signal transmission via neurotransmitters

Electrical synapse

Direct electrical coupling between cells

Botulinum toxin

Blocks neurotransmitter release at neuromuscular junctions

Primary effect of botulinum toxin

Paralysis

Clinical uses of botulinum toxin

Cosmetics and some pain conditions

Neuronal diversity

Neurons vary greatly in structure and size

Purkinje cells

Highly branched cerebellar neurons

Pyramidal neurons

Common excitatory neurons in cortex and hippocampus

Spinal motor neurons

Large multipolar neurons controlling muscle

Anaxonic neurons

Neurons without a clearly defined axon

Grey matter

High concentration of neuronal cell bodies

White matter

High concentration of myelinated axons

CNS cluster of cell bodies

Nucleus (plural: nuclei)

PNS cluster of cell bodies

Ganglion (plural: ganglia)

CNS axon bundle

Tract

PNS axon bundle

Nerve

Original view of glial cells

Passive “glue” holding neurons together

Modern view of glial cells

Active and essential regulators of nervous system function

Neuron-to-glia ratio

Approximately 1:1

Ependymal cells

Ciliated epithelial glial cells lining ventricles and central canal

Function of ependymal cells

Control production and flow of cerebrospinal fluid

Cerebrospinal fluid (CSF)

Fluid that cushions and maintains CNS homeostasis

Functions of CSF

Shock absorption, buoyancy, transport, waste removal

Hydrocephalus

Accumulation of CSF causing increased intracranial pressure

Cause of hydrocephalus

Ependymal dysfunction and impaired ciliary movement

Astrocytes

CNS glial cells with extensive support roles

Tripartite synapse

Synapse involving presynaptic neuron, postsynaptic neuron, and astrocyte

Astrocyte functions

Metabolic support, neurotransmitter recycling, activity modulation

Reactive astrogliosis

Astrocyte response involving proliferation or morphological change

Astrogliosis relevance

Linked to epilepsy and other CNS disorders

Satellite glial cells

Glial cells surrounding neuronal cell bodies in the PNS

Location of satellite glial cells

Sensory ganglia such as dorsal root ganglia

Function of satellite cells

Support and modulation of sensory neurons

Satellite cells in pain modulation

Regulate communication between sensory neurons

Diazepam binding inhibitor (DBI)

Protein in satellite cells affecting pain signalling

Myelinating glial cells

Produce myelin to increase conduction velocity

CNS myelinating cell

Oligodendrocyte

PNS myelinating cell

Schwann cell