The Nervous System

1. The Nervous System Chapter 48-49

2. What you need to know! • The anatomy of a neuron. • The mechanisms of impulse transmission in a neuron. • The process that leads to release of neurotransmitter, and what happens at the synapse. • The components of a reflex arc and how they work. • The organization and function of the major parts of the nervous system. • One function for each major brain region. • The location and function of several types of sensory receptors. • How skeletal muscle contracts. • Cellular events that lead to muscle contratction

3. The Neuron • Functional unit of the nervous system • Dendrites: cell extensions that receive incoming messages from other cells • Axon: transmit messages to other cells • Covered in myelin sheath (Schwann cells or oligodendrocytes) to speed up transmission • Synapse: is the junction between axons and dendrites • Neurotransmitters (NT): chemical messengers (drugs) released from the synaptic terminals of the axon which bind to receptors of the receiver (another neuron, muscle cell, or gland) • Acetylcholine, dopamine, serotonin, GABA, etc.

4. Nervous System • Central nervous system (CNS) = brain & spinal cord • Peripheral nervous system (PNS) = everything else including motor and sensory neurons • Nerves are clusters of neurons Types of neurons: • Sensory receptors: receive information from the environment • Sensory neurons: send signals from receptors to CNS • Interneurons: brain and parts of the spinal cord • Motor neurons: transmit signals to effectors (muscles, glands)

5. Action Potential (nerve impulse) • Membrane potential: difference in electrical charge across the cell membrane • Resting potential: neuron at rest (-70mV)

6. Action Potential (AP) • All or none response to stimulus • If membrane potential reaches threshold (-55mV) AP will fire • Resting state • Depolarization • Depolarization >= threshold  AP • Repolarization • Undershoot

7. Axon • APs propagate down the axon • It jumps from one node of Ranvier to the next (saltatory conduction) • The signal is revitalized at every node • At the synapse the signal continues via electrical or chemical (NT) stimulus • Stimulus can be inhibitory or excitatory

8. Reflex Arc • Simplest response to stimulus • Receptor  sensory neuron  interneuron (spinal cord)  motor neuron  effector (reaction) • The brain finds out later

9. Central Nervous System • Brain and spinal cord • Cells bathed in cerebrospinal fluid (CSF) for nutrients and cleansing • Grey matter = neuron cell bodies and unmyelinated axons • White matter = myelinated axons • Neural glial cells (glia) support neurons: • Astrocytes provide nutrients for neurons • Oligodendrocytes make myelin sheath in the CNS (Schwann cells in the PNS)

10. Peripheral Nervous System • Divided into two subdivisions: • Somatic nervous system: muscles you control • Autonomic nervous system: automatic muscle and organ control subdivided into two more categories • Sympathetic division: fight or flight mechanism • Parasympathetic division: rest and digest

11. Brain • Compartmentalized: • Brainstem = medulla oblongata, pons, and midbrain • Primitive brain = primitive functions like homeostasisand breathing • Cerebellum: coordinated motor movement • Thalamus: main center for all sensory and motor information • Hypothalamus: regulates homeostasis and basic survival behaviors • Cerebrum: two hemispheres with grey over white matter • Cerebral cortex: Higher order thinking occurs here (largest in mammals) and voluntary movement • Corpus callosum: white matter enabling communications of the two hemispheres

12. Sensory Receptors Perception: brain recognition of stimulus Reception: receptor detects a stimulus • Mechanoreceptors: stimulated by physical stimuli • Thermoreceptors: stimulated by temperature • Chemoreceptors: chemical stimulation (taste and smell) • Electromagnetic receptors (photoreceptors): detect various forms of energy (light, electricity, or magnetism) • Pain receptors: detect too much heat or chemicals released from dying cells

13. Movement