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