BIO 132 Neurophysiology Lecture 2 Neurons

Lecture Goals: Understanding the basic function of the nervous system. Understanding the basic function of the nervous system. Understanding the parts of a neuron. Understanding the parts of a neuron.

Neuron – A specialized cell of the body that can communicate information quickly by using ionic currents and chemical signals called neurotransmitters. Neuron – A specialized cell of the body that can communicate information quickly by using ionic currents and chemical signals called neurotransmitters. Nerve - Many neurons that are bundled together and covered by a connective tissue sheath. Nerve - Many neurons that are bundled together and covered by a connective tissue sheath. Nervous System – The entire network of interconnecting neurons. Nervous System – The entire network of interconnecting neurons.

Overall function of the nervous system: To control motor output of the body based on sensory information it detects from both the internal and external environments of the body.

There are ~100 billion neurons in the brain. There are ~100 billion neurons in the brain. (Current population is less than 7 billion people.) Each neuron can make one to thousands of connections with other neurons. Each neuron can make one to thousands of connections with other neurons. Glial cells are support cells of the nervous system Glial cells are support cells of the nervous system There are ~10 times as many glial cells as there are neurons. There are ~10 times as many glial cells as there are neurons. Used to nourish, insulate, direct growth of neurons. Used to nourish, insulate, direct growth of neurons.

Parts of a typical neuron: Parts of a typical neuron: Neuron Morphology Cell body Axon Dendrites Axon terminal

Contains most of the cellular machinery of the neuron (nucleus, ER, mitochondria, golgi complex, etc). Contains most of the cellular machinery of the neuron (nucleus, ER, mitochondria, golgi complex, etc). Is where most the synthesis of new cellular products occurs. Is where most the synthesis of new cellular products occurs. Cell Body (soma) Cell body

Means “tree” in Latin. Means “tree” in Latin. Main site where input is received from other neurons. Main site where input is received from other neurons. Dendrites

Long projection from cell body that carries an ionic signal, called an action potential, to other neurons. Long projection from cell body that carries an ionic signal, called an action potential, to other neurons. Can be very short or very long (up to 6 feet in humans). Can be very short or very long (up to 6 feet in humans). Can send off many branches (collaterals). Can send off many branches (collaterals). Axon

Is at the end of each axon. Is at the end of each axon. Contains vesicles filled with neurotransmitter. Contains vesicles filled with neurotransmitter. Forms a connection with another neuron, called a synapse. Forms a connection with another neuron, called a synapse. Axon Terminal Axon terminal

There are several conventions for classifying neurons: There are several conventions for classifying neurons: By neurites (projections from the cell body). By neurites (projections from the cell body). By dendrite shape. By dendrite shape. By connections. By connections. By neurotransmitter released By neurotransmitter released Classifying Neurons

Unipolar neuron - A single neurite (projection from cell body: Unipolar neuron - A single neurite (projection from cell body: Bipolar – Two neurites (both part of the axon) Bipolar – Two neurites (both part of the axon) Multipolar – Many neurites (usually one axon and many denrites) Multipolar – Many neurites (usually one axon and many denrites) Classification By Neurites

Primary sensory – dendrites detect external stimuli. Primary sensory – dendrites detect external stimuli. Motor - makes a direct connection with skeletal muscle. Motor - makes a direct connection with skeletal muscle. Interneuron - only makes connections with other neurons. (Most numerous type) Interneuron - only makes connections with other neurons. (Most numerous type) Classification By Connections Stimuli

Based on the type of neurotransmitter released. Based on the type of neurotransmitter released. Examples: Examples: Cholinergic Cholinergic Noradrenergic Noradrenergic GABAergic GABAergic Glutamatergic Glutamatergic Dopaminergic Dopaminergic Classification By Neurotransmitter Acetylcholine (ACh) Norepinephrine (NE) GABA Glutamate (Glu) Dopamine (DA)

Astrocytes Astrocytes Most numerous Most numerous Fill the space between neurons Fill the space between neurons Envelope synapses to limit the spread of neurotransmitters Envelope synapses to limit the spread of neurotransmitters Regulate chemical content of extracellular fluid Regulate chemical content of extracellular fluid Remove neurotransmitters from synapse Remove neurotransmitters from synapse Myelinating glia – insulate axons from ion leakage Myelinating glia – insulate axons from ion leakage Oligodentrites Oligodentrites Found in Central NS and spinal cord Found in Central NS and spinal cord Can wrap around several axons Can wrap around several axons Schwann cells Schwann cells Found in peripheral NS Found in peripheral NS Wrap around a single axon Wrap around a single axon Classifying Glia