April 3rd 2014 What were neurons again? The Neuron https://www.youtube.com/watch? v=W4N-7AlzK7s&list=UUX6b17PVsYBQ0ip5 gyeme-Q The Neuron dendrites: short branches that conduct impulse towards cell body cell body/soma: contains the nucleus and other organelles axon: long projection that conduct impulse away from cell body axoplasm: electrically-conductive cytoplasm within the axon that transmits impulses axomembrane: plasma membrane of neurons that is responsible for maintaining the axon's membrane potential The Neuron Neuron axons are packed together into nerves nerves can contain a mixture of neurons (sensory & motor) that send info in both directions to different places not all neurons form nerves ganglion: neuron cell body cluster in the PNS The Neuron - Myelin Sheath Myelin Sheath: fatty layer composed of Schwann Cells that wrap around the axon The Neuron - Myelin Sheath Functions: a) insulates the neurons from each other as they are tightly packed together within a nerve b) accelerates impulse transmission Myelin Sheath Degeneration Myelin Sheath Degeneration Multiple Sclerosis - autoimmune attack on myelin sheath https://www.youtube.com/watch? v=VIoDr8ugbqI The Neuron - Axon Node of Ranvier: points between Schwann Cells Saltatory transmission: the "jumping" transmission of impulses from one node of Ranvier to the next The Neuron The Neuron 3 Types of Neurons Sensory Neurons Interneurons Motor Neurons Connecting PNS & CNS Reflex Arc 1. Sensory Receptor 2. Sensory (afferent) neuron 3. Interneuron 4. Motor (efferent) neuron 5. Effector (muscle/ gland) Reflex Arc Reflex Arc http://youtu.be/wLrhYzdbbpE 1. Receptor Detects stimuli - if stimuli are strong enough past a certain threshold, an impulse is initiated in the sensory neuron stretch receptors in blood vessels pain receptors in skin photoreceptors in eyes chemoreceptors in heart & brain Some people are born without pain receptors = dangerous 2. Sensory Neuron contain sensory receptors that detect stimuli long myelinated dendrites & short axon cell body is outside of the spinal cord in the ganglion function: carry sensory impulses toward the CNS 3. Interneuron entirely in the spinal cord/CNS short dendrites & axon function: connect the sensory and motor neurons 4. Motor Neuron short dendrites & long myelinated axon dendrites are in the spinal cord, axon is outside of spinal cord axon endings attached to effector (muscles) function: carry impulses from the CNS to effector (muscle/ gland) 5. Effector Muscles or glands When stimulated by the motor neuron: muscles will contract glands will release a hormone Inherent vs. Conditioned Reflexes.