BIO 132 Neurophysiology Lecture 2 Neurons Lecture Goals

BIO 132 Neurophysiology Lecture 2 Neurons

Lecture Goals: n Understanding the basic function of the nervous system. n 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. n Nerve - Many neurons that are bundled together and covered by a connective tissue sheath. n Nervous System – The entire network of interconnecting neurons. n

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.

n 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. n Glial cells are support cells of the nervous system n There are ~10 times as many glial cells as there are neurons. n Used to nourish, insulate, direct growth of neurons. n

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

Cell Body (soma) n n 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. Cell body

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

Axon n 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 send off many branches (collaterals). Axon

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

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

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

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

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

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