The Nervous System Nervous System Three basic functions

The Nervous System

Nervous System • Three basic functions – Sensation • gather information – Integration • process information • use of multiple sources of information. – Response • coordinated action appropriate to environment

EK 3 E 2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. a. The neuron is the basic structure of the nervous system that reflects function. 1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator. 2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information. 3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.

The neuron is the basic structure of the nervous system that reflects function. 1. A typical neuron has a cell body, axon and dendrites. Many axons have a myelin sheath that acts as an electrical insulator. 2. The structure of the neuron allows for the detection, generation, transmission and integration of signal information. 3. Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron. Rat Cortical Neuron Primary rat hippocampal neurons Hippocampal Neuron

Neurons are similar to other cells in the body because: 1. Neurons are surrounded by a cell membrane. 2. Neurons have a nucleus that contains genes. 3. Neurons contain cytoplasm with organelles 4. Neurons carry out basic cellular processes such as protein synthesis and energy production. However, neurons differ from other cells in the body because: 1. Neurons have specialized extensions called dendrites and axons. Dendrites bring information to the cell body and axons take information away from the cell body. 2. Neurons communicate with each other through an electrochemical process. 3. Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters).

Neuron Trivia Neurons are the oldest and longest cells in the body! You have many of the same neurons for your whole life. Although other cells die and are replaced, many neurons are never replaced when they die. In fact, you have fewer neurons when you are old compared to when you are young. On the other hand, data published in November 1998 show that in one area of the brain (the hippocampus), new neurons CAN grow in adult humans. Neurons can be quite large - in some neurons, such as corticospinal neurons (from motor cortex to spinal cord) or primary afferent neurons (neurons that extend from the skin into the spinal cord and up to the brain stem), can be several feet long!

Neuron Anatomy • Soma/Cell Body: is the metabolic center of the neuron, contains the Nucleus and Mitochondrion. • Dendrites: convey incoming messages to the cell body. • Axon: generates nerve impulses and topically conduct them away from the cell body myelinated by either oligodendroglia in CNS or Schwann cells in PNS. Each neuron has only one axon. • Axon Hillock: a cone like region from where an axon arises. • Presynaptic terminals: The swollen, distal end of an axon; contains a neurotransmitter substance within synaptic vesicles. Also called synaptic ending or synaptic bouton. • Synapse: Specialized junctions with other cells that are along the length or at end of an axon.

• • • Axons Take information away from the cell body Smooth Surface Generally only 1 axon per cell No ribosomes Can have myelin Branch further from the cell body n n n Dendrites Bring information to the cell body Rough Surface (dendritic spines) Usually many dendrites per cell Have ribosomes No myelin insulation Branch near the cell body

Neuron Anatomy

Neurons can also be classified by the direction that they send information: • Sensory (or afferent) neurons: send information from sensory receptors (e. g. , in skin, eyes, nose, tongue, ears) TOWARD the central nervous system. • Motor (or efferent) neurons: send information AWAY from the central nervous system to muscles or glands. • Interneurons: send information between sensory neurons and motor neurons. Most interneurons are located in the central nervous system.

EK 3 E 2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. b. Action potentials propagate impulses along neurons. 1. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. 2. In response to a stimulus, Na+ and K+ gated channels sequentially open and cause the membrane to become locally depolarized. 3. Na+/K+ pumps, powered by ATP, work to maintain membrane potential.

How neurons conduct impulses: • Membrane potential (as seen in muscle cells) • K+ diffuses out of neurons faster than Na+ diffuses in, • Na-K pump moves 3 Na+ back out for 2 K+ back in • Cl-, phosphate, protein anions balance cations • “Resting potential” ~ -70 m. V • Nerve Impulse • Action Potential Exercise

Voltage Gated Channels and the Action Potential

Rate of conduction • Unmyelinated axons – Action potential propagates at 2 -3 meters per second (m/sec) • Saltatory Conduction • Action Potential occurs only in nodes, – "leaps" from node to node – Ion attraction and diffusion stimulate new A. P. in each node – Saltatory conduction much faster than continuous conduction in unmyelinated fibers. • up to 100 m/sec

EK 3 E 2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. c. Transmission of information between neurons occurs across synapses. 1. In most animals, transmission across synapses involves chemical messengers called neurotransmitters. – – – Acetylcholine Epinephrine Norepinephrine Dopamine Serotonin GABA 2. Transmission of information along neurons and synapses results in a response. 3. The response can be stimulatory or inhibitory.

How does impulse get from cell to cell? Chemical synapses, 2 • Axon (& A. P. ) ends short of next – “Gap junctions, ” tiny holes connect cytoplasm of adjacent cell, cells • Synaptic knob (axon end) – A. P. continuous from cell to cell releases chemical transmitter Electrical synapses

Neurotransmission • When Action Potential reaches synaptic knob, – Synaptic vesicles unite with membrane, – Release neurotransmitter, – Neurotransmitter diffuses across synaptic cleft, – Neurotransmitter binds to receptors in postsynaptic membrane, – Chemically gated channels open • Chemical Signals • Mouse Party

Synapse • Neurotransmitter can't remain in cleft (would continue to stimulate uncontrollably) – ACh removed by acetylcholinesterase (ACh. E) – Acetate & choline reabsorbed by axon end, resynthesized to ACh – Other neurotransmitters taken back by axon or diffuse away

Neurotransmitters may be … • Excitatory – depolarize postsynaptic membrane – Excitatory Postsynaptic Potential (EPSP) • Inhibitory – hyperpolarize postsynaptic membrane – Inhibitory Postsynaptic Potential (IPSP)

• Reward Pathway • Reflex Arc

EK 3 E 2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. d. Different regions of the vertebrate brain have different functions.

LO 3. 43 The student is able to construct an explanation, based on scientific theories and models, about how nervous systems detect external and internal signals, transmit and integrate information, and produce responses. LO 3. 44 The student is able to describe how nervous systems detect external and internal signals. LO 3. 45 The student is able to describe how nervous systems transmit information. LO 3. 46 The student is able to describe how the vertebrate brain integrates information to produce a response. LO 3. 47 The student is able to create a visual representation of complex nervous systems to describe/explain how these systems detect external and internal signals, transmit and integrate information, and produce responses. LO 3. 48 The student is able to create a visual representation to describe how nervous systems detect external and internal signals. LO 3. 49 The student is able to create a visual representation to describe how nervous systems transmit information. LO 3. 50 The student is able to create a visual representation to describe how the vertebrate brain integrates information to produce a response.

Resources • • • • • Action Potential Tutorial A&P Text, 2 Essential Study partner Links Parts of a Neuron Review Anatomy Drill Body Smart Nervous System Campbell’s Activity Quiz Human A&P Lessons Cerebral Commando Synaptic Transmission Tutorial Drugs, Brains & Behavior Parts of the Brain, 2 Video Quiz - Making Brain Cells Video Quiz - ALS Lost Nerve Power Video Quiz - Wild Young Brains Video Quiz - Vanishing Brain Video Quiz - Meth and the Brain Video Quiz - Paralysis Push Resting Membrane Potential Action Potential (Biological Psychology) A&P Chapter 8 A&P Chapter 14 Function of the Neuromuscular Junction