The Neuron Quick Nervous System Breakdown 1 Central

The Neuron

Quick Nervous System Breakdown 1. Central nervous system (CNS): • Brain • Spinal cord 2. Peripheral nervous system (PNS): • Sensory neurons • Motor neurons (both Somatic and Autonomic) • Interneurons (aka Relay Neurons)

The Nervous System consists of 2 main types of cells: 1. Neurons - Sensory Neurons - Motor Neurons - Interneurons (Relay)

The Nervous System consists of 2 main types of cells: 2. Glial cells • Astrocyte - numerous functions; most abundant type of Glial cell • Ependymal cells - line cavities; secrete CSF • Microglia - phagocytes • Oligodendrocytes - form multiple myelin sheaths around up to ~50 axons • Schwann cells - located in PNS; form singular axon myelin sheaths

Neurons § Basic units of the Nervous System § Receive, integrate and transmit information § Operate through the use of electrical impulses § Communicate with other neurons through chemical signaling

Glial cells • There are ~100 billion neurons but 10 x more glial cells • Glial cells: – Support neurons (literally, provide physical support, as well as nutrients) – Cover neurons with myelin – Clean up debris around the Neurons – Remove neurotransmitter from synaptic cleft

Astrocytes • Regulate external environment (ions, etc. ) • Most abundant type of Glial Cell • May contribute to Blood-Brain barrier and to ensuring the proper functioning of synapses

3 types of Neurons • Sensory Neurons • Interneurons • Motor Neurons

Sensory (Afferent) vs. Motor (Efferent) Sensory (afferent) neurons e. g. , skin Neurons that send signals from the senses, skin, muscles, and internal organs via the PNS to the CNS. Motor (efferent) neurons e. g. , muscle Neurons that transmit commands from the CNS to the muscles, glands, and organs via the PNS

The Reflex

Neural Anatomy Dendrite s Axon of another neuron Cell Body Myelin Sheath Axon Dendrites of another neuron

Neural Anatomy § Dendrite § branching extensions of a neuron that receive messages and conduct impulses toward the cell body. § Axon § the extension of a neuron, ending in branching terminal fibers, through which messages are sent to other neurons, muscles or glands

Neural Anatomy cont… §Synapse §junction between the axon tip of the sending neuron and the dendrite of the receiving neuron §tiny gap at this junction is called the synaptic cleft (or gap)

Specific Parts: The Neuron Function 1. 3. 2. Neurons = 3 functions: Reception, Conduction, Transmission

Action Potentials • Action potentials occur when ions (Na+, K+) cross the neuron’s membrane. • A stimulus first causes sodium channels to open. • Sodium ions rush into the neuron reversing the polarity of the neuron.

W. W. Norton

Threshold • The threshold is the minimum stimulus needed to cause an Action Potential to fire. • Usually occurs at about -55 m. V

Relay Race • Action Potential path starts at dendrite; Travels through the cell body; Down the axon via the Nodes of Ranvier; To the axon terminals; Then across the synapse. (Synapse is ~ a millionth of an inch gap) – Vesicles with neurotransmitters inside are released from the axon terminal into the synaptic cleft » Neurotransmitters are chemical messengers that transmit info for the Nervous System.

• Communication between Neurons Impulse releases neurotransmitters from vesicles at the axon terminal • Neurotransmitter enters synaptic cleft • Neurotransmitter binds to receptors on the receiving neuron’s dendrites

Myelin Sheath – Fatty material made by glial cells – Insulates the axon – Allows for rapid movement of electrical impulses along axon

Nodes of Ranvier: - gaps in myelin sheath that action potentials are transmitted across - Speed of neural impulse ranges from ~2 -200 mph ØMultiple Sclerosis is a breakdown of the myelin sheath that leads to jerky movements due to the interruption of the impulses along the axon.

Resting Potential • The difference in electrical charge for a neuron when it is NOT firing an Action Potential. • Usually Resting Potential is -70 m. V, with the inside more negative than the outside.

Neurotransmitters § chemical messengers that cross the synaptic cleft between neurons