Neurophysiology Lecture 2

Overview of Neurophysiology

Minimal function “unit” of nervous system is…

This is the “Neuron Doctrine” produced by…

The Neuron

Ramon y Cajal, 1800s

Why is physiology so intimately associated with anatomy in the nervous system?

Because neurons have action potentials and neurotransmitters so where these end up in the body matters

Interneuron/Association Neuron

• Only in CNS - circuitry

• Connect between sensory/motor neurons

• Allow for complex NSs (emotions, thoughts, behavior)

Motor Neuron

• Control of movement and some functions

• Goes to muscle, contracts or relaxes

Sensory Neuron

• Detection of external stimuli

• Picks up signal and takes it to CNS

What projects off of the neuron cell body?

Axons and dendrites project

What do dendrites do?

Receive information from sensory receptors and send to cell body

What do axons do?

Deliver electric signals from cell body to another neuron or organ (muscle)

Action Potentials

• How a neuron moves information rapidly from one location to another

• Converts AP to a chemical signal at synapse

Dendrite Description

• Tapered, extension of cell body

• Cylindrical process often with spine

• Many extensions or branches

Dendrite Primary Function

Reception

• Stimuli

• Graded potentials after “handoff” from other neurons

Cell Body Description

• 1 or more processes typically

• One axon, many dendrites

Cell Body Primary Functions

• Synthesize and sort proteins

• Integrate signals

Axon Description

• Single, thin, cylindrical process

• Myelinated/unmyelinated

• Often long

Axon Primary Functions

• Conduction

• AP propagation

Terminal Description

• Vesicle filled apposition with another neuron

• Highly specialized with many different zones

Terminal Primary Function

• Neurotransmission

How do we classify neurons?

• Function (mainly)

• Structure

Structural Classification: Anaxonic

No obvious axon

• Some CNS neurons

Structural Classification: Bipolar

2 Distinct process from cell body

• Some special sensory neurons

Structural Classification: Unipolar

Dendrite and axon continuous

• Most sensory neurons

Structural Classification: Multipolar

1 axon, 2+ dendrites

• Motor neurons and CNS neurons

Functional Classification: Sensory

AKA Afferent

• Carry signals to CNS

Functional Classification: Motor

AKA Efferent

• Carry signals from CNS

Functional Classification: Interneurons

Send signals from one neuron to another

Neuron Function Structure: Sensory Receptors

Structures that receive an environmental stimuli and produce a nerve impulse (AP)

• Pacinian corpuscles

• Golgi tendon organs

• Meissner’s corpuscles

• Photoreceptors

• Taste and smell receptors

Neuron Function Structure: Synapse

Specialized points of contact between neurons and target cells; allow circuits to occur

• NMJ is a synapse

• Chemical synapses release NTs

Glial Cell Functions (6)

• Support

  • Metabolic, structural

• Development, migration of neurons

• Uptake of NTs

  • GABA, glutamate

• Damage control after injury

  • Phagocytosis

• Cerebral blood flow control

• Blood-brain barrier

Glial cell: Oligodendrocytes

Formation of myelin within CNS

Glial cell: Schwann Cells

Formation of myelin in PNS

Protects unmyelinated axons within PNS (wraps)

Glial cell: Astrocytes

Found in CNS

Structural support

Regulate K+

Reabsorb GABA, glutamate

Constrict blood vessels, blood-brain barrier

Glial cell: Microglia

Innate immune cell in CNS

Tissue macrophages

• Made from bone marrow, migrate into brain

Divide in situ to increase amount

Activated in injection and injury thru release of:

• Phagocytosis

• Cytokine

• Prostaglandin

Normally clear and clean, can cause neuron damage when overactive

Myelin

Lipid-rich, non-conductive lipid/protein comp.

Surrounds axons of some neurons

• in node (mye) internode (nonmye) pattern

Facilitates rapid conduction of AP

• Saltatory conduction

Myelination is ______ and ____ __________ in the CNS due to more cell ________

Faster; more efficient; wrapping

NOTE: makes axon more susceptible to damage; larger target

GABA Reabsorption Importance

Can deplete neurons of NTs without astrocytes with this

• Many nervous system disorders (schizophrenia?)

Blood-brain Barrier and the Astrocyte Foot

Very tight (non leaky) junction between circ. and brain (NS)

• Large, charged, lipid-soluble molecules cannot pass

Astrocyte foot sticks to outside vessel and blocks

Pro: Pathogens/toxins can’t reach brain

Con: drug targeting is reduced to the brain

Neuron: The Review (6)

• Function unit of NS

• Found in CNS and PNS

• Have processes

  • Axons, dendrites

• Communicate through synapses

• Several structural types

• 3 Function types

  • Motor

  • Sensory

  • Interneuron

Glia: The Review (2)

4 Types

• Astrocytes

• Oligodendrocytes

• Schwann cells

• Microglia

Multiple, specific functions

• Structural support

• NT metabolism

• Immune/inflammation responses

• Blood brain barrier

• Nerve conduction