PSL 310 Unit 1: Nervous System Cells

Two major divisions of neurophysiology

Central nervous system and peripheral nervous system

CNS

Brain and spinal cord

PNS

Cranial nerves, spinal nerves, sensory organs such as stretch receptors in uterus

CNS glial cells

Ependymal, astrocytes, oligodendrocytes, microglia

Microglial cells

Macrophages of CNS, immune surveillance, phagocytosis for dead neurons, fights infections in brain

Oligodendrocytes

Myelinate neurons

How do oligodendrocytes myeline neurons?

By extending the oligodendrocyte plasma membrane and wrapping it around axons 7-10 times, one oligo can wrap around several different axons but not one whole axon as it isn’t long enough, another picks up where the previous left off, creates nodes of Ranvier

Why is myelin a good insulator?

Because it is hydrophobic plasma membrane and is therefore resistant to charge going through it

Node of Ranvier

Areas of the axon with no myelin, where one oligodendrocyte stops and another begins

Internode

Area with myelin, between nodes

Astrocytes

Form blood-brain barrier with pedicels, has projections to neurons and blood vessels, scavenge for neurotransmitters and ions that are in spaces between neurons and redeliver them to neurons, adds connective tissue (scar tissue) to neuron-infarcted areas

What are the largest and most numerous of the glial cells?

Astrocytes

Infarction

Areas with dead tissue

Pedicels

Vascular feet, touch and connect to blood vessels, forms blood-brain barrier

How do pedicels keep things out of the brain from blood vessels?

As pedicels touch and connect to blood vessels, things that want to get out have to get between the pedicels and the endothelium lining the inside of blood vessels

Ependymal cells

Line spaces of brain, secrete CSF into space, ciliated to circulate CSF

Gray matter

Cell bodies of neurons, glial cells

White matter

Myelinated axons

Ventricle

CSF-filled spaces of brain

Function of CSF

Internal hydrostatic skeleton, prevents brain from being squashed

Central canal

Spinal cord’s internal hydrostatic skeleton, lined by ependymal cells that have cilia circulating fluid around

PNS cells

Satellite cells, Schwann cells

Satellite cells

Behave like astrocytes but don’t form pedicels, scavenge and redeliver neurotransmitters and ions in ISF to PNS, support/nourish cells, located around ganglia “orbiting” the cell body

Ganglion

Aggregation of nerve cell bodies in the PNS with a common specific function

Nucleus

Aggregation of nerve cell bodies in the CNS with a common specific function

Schwann cell

Myelinate axons, can only myeline one segment of one axon as the entire cell wraps around the axon segment

Dorsal root ganglion

Collection of nerve cell bodies

Structural classes of neurons

Unipolar, bbipolar, multipolar

Unipolar neurons

1 process/projection emanating from cell body

What are unipolar neurons involved in?

Sensory neurons, general senses like touch, stretch, temperature, pain, vibration; mechanoreceptors

How does a unipolar neuron transmit an AP?

Dendrites receive, nothing happens in cell body, AP transmits along axon straight to the terminals

Bipolar neuron

2 processes

What are bipolar neurons involved in?

Special senses such as the eyes, ears, nose, and mouth, equilibrium receptors in ears

How does a bipolar neuron transmit an AP?

Dendrites receive, info integrated in cell body, generate AP, transmits along axon to the terminal

Multipolar neuron

Multiple processes

What are multipolar neurons involved in?

Send out motor/efferent information, takes in info from unipolar/bipolar

How does a multipolar neuron transmit an AP?

Large dendritic tree brings in sensory info, processed, AP generated and propagated, sends efferent info to effectors

Functional classes of neurons

Sensory, interneuron, motor

Sensory neurons

Afferent, brings in info to transmit to interneuron

Motor neurons

Efferent, sends out efferent info (motor) taken in by interneuron

Interneuron

In gray matter of brain and spinal cord, most abundant in human body, multipolar, relays info between sensory and motor neuron