Chapter 12 The Nervous System

The Nervous System Central Nervous System Peripheral Nervous System

Peripheral Nervous System Somatic Autonomic Enteric

Central Nervous System Brain 100 billion neurons 12 pairs of cranial nerves Spinal Cord Connected to the brain 100 million neurons 31 pairs of spinal nerves Ganglia

Peripheral Nervous System All nerves outside the CNS Somatic- Sensory neurons from somatic receptors in head, body wall, limbs, and from special sense organs (vision, hearing, taste and smell) to the CNS. Autonomic- Sensory neurons from autonomic sensory receptors (visceral organs-e.g. stomach, lungs) Motor neurons from CNS to smooth muscle, cardiac muscle, and glands. ANS=involuntary. Sympathetic vs Parasympathetic Enteric- Enteric plexus extends through the GI tract. Monitor GI tract. Contraction of GI smooth muscle as well as secretion (e.g. stomach acid)

Parts of a Neuron

Neuron

Multipolar Neuron Most neurons of the CNS are multipolar

Unipolar Neuron Most neurons of ganglia are unipolar

Bipolar Neuron Some neurons of the retina, the ear, and the olfactory bulb are bipolar

Neurons do not all look the same-why?

Glia-Astrocyte Largest type of glial cell Processes make contact with blood capillaries, neurons, and the pia matter Function to support neurons, create blood-brain barrier, secrete and takeup ions, neurotransmitters, and nutrients

Glia-Oligodendrocyte Smaller than astrocytes, form myelin sheaths around CNS axons

Microglia Small cells act primarily as phagocytes

Neuroglial cells in the PNS Schwann Cells wrap around PNS axons (like oligos in CNS) except that each schwann cell myelinates a single axon Satellite Cells Flat cells that surround cell bodies of neurons in PNS ganglia Help to regulate exchange between cells and interstitial fluid

Myelination In CNS and PNS Gaps-nodes of Ranvier

Ion Channels Leak channels-randomly open and close at rest providing a measure of permeability Voltage-gated channels-open and close in response to a change in membrane potential (voltage). Ligand-gated channels-open and close in response to binding chemicals (e.g. ACh binding to its receptors opens a cation channel) Mechanically-gated channels-open and close in response to mechanical stimulation (e.g. vibration, touch, pressure, stretch). Auditory receptors in the ear are channels that open in response to movement of inner ear bones).

Voltage-gated channels

Ligand-gated channels

Resting membrane potential-charge distribution

Resting membrane potential-ion distribution

Ion Permeability-resting membrane potential (Buildup of negative ions in cytosol and positive ions on outside of membrane causes charge difference acrosss membrane) Na permeability is low Few leak channels and Na/K pumps (pump 3 Na2+ out and 2 K+ in).

Graded potentials Hyperpolarizing Depolarizing

Phases of the action potential

Phases of the action potential

Action potential propagation-non myelinated

Action potential propagation-myelinated

Neurotransmission

Neurotransmission-spatial summation

Neurotransmission-temporal summation

Channel locations on neurons

Neural Circuits

Circuit example There are three basic parts of a neural circuit: the sensory input-the sensory neuron detects the stretching of the muscle the information processing-this circuit has only a few synapses and is very short, which is why it acts so quickly. It also functions with no intervention by the conscious brain, which has better things to do than constantly remind the body to stay upright. the motor output- stmulation of a motor neuron responsible for contracting the extensor muscle.

End of Chapter 12