Peripheral nervous system overview: The PNS is the communication network between the CNS and the rest of the body.
Organization and function: The peripheral nervous system (PNS) includes all neural tissue excluding the brain and the spinal cord.
- PNS specific neurons: Unipolar Sensory Neurons: large myelinated neurons with the cell body off to one side of the single dendritic-axon process. Multipolar Motor Neurons: large myelinated neurons that have many dendrites off the cell body and an axon that may branch to effect many effectors.
- Signal transmission: electrical signals are transmitted in 3 steps: (1) Neurotransmitters released from one neuron bind to and activate the dendrites of the next neuron. (2) If the signal is strong enough, an action potential is propagated down the axon. (3) Which causes the release of neurotransmitters from that neuron.
- Action potential: When another neuron sends a sufficiently strong signal to the next neuron, the neuron excites to a threshold potential. Transporters on the cell membrane let positive ions into the cell, causing a change in potential, which spreads down the axon. This electrical propagation is called the action potential.
Glial cells of the PNS
- Satellite Cells: The cell bodies of several sensory neurons form structures called Ganglia. Satellite cells are the glial cells that surround each ganglion.
- Schwann Cells: Like Oligodendrocytes in the CNS, Schwann cells wrap themselves around neurons in the PNS to form the myelin sheath. Unlike Oligodendrocytes, which myelinate several neurons, a single Schwann cell forms a segment of myelin sheath.
Proprioception: involve sensors that keep track of where the body is in space.
The five senses: The sensory nervous system includes sensory organs, which receive information from the environment, and sends it to the CNS.
- Skin: detects temperature, touch, and painful stimuli. Three separate kinds of nerves detect sensation on the skin
- Mechanoreceptors: Detect pressure and tension on the skin
- Thermoreceptors: Detect the temperature of the
- Nociceptors: Detect painful stimuli.
- Nose: detects aromatic molecules. Thousands of chemicals can be detected by our olfactory and taste receptors and sorted into “pleasant, toxic, etc.”
- Tongue: taste buds detect salty, bitter, sweet, and sour information.
- Ears: detect sound waves with mechanical receptors. Fluctuations in air pressure move a membrane attached to hair cells in the Organ of Corti. These motions open ion channels in neurons, sending the signal to the CNS.
- Eyes: detect photons or light. The retina is the neural portion of the eye. Photons (light) activate receptors on the retina and the signal is transported to the CNS via the optic nerve.
Motor nervous system
- Spinal Nerve Anatomy: There are 31 nerves exiting the spinal cord, dorsal connections bring sensory information to the CNS, ventral motor connections send commands to the periphery.
- Reflexes: For painful stimuli, involuntary withdrawal (like a hand from a flame) occurs without input from the brain. This very simple nervous pathway is called a reflex arc.
- Autonomic nervous system: directly controls automatic body functions (involuntary movements). The autonomic system has two opposing parts: the sympathetic and parasympathetic nervous systems.