The Nervous System

1.A bigger brain is better 2.Alcohol kills brain cells 3.Drugs destroy brain tissue 4.Humans use about 10% of their brain 5.Humans are either right or left brained 6.Intelligence is solely determined by genes

Introduction to The Nervous System A.Neurons = nerve cells that transmit signals to other nerves, tissues or cells

Basic Structure of a Neuron Dendrites - shorter, more numerous, receive information Cell Body - contains the nucleus and two extensions Axons - single, long fiber which transmits impulses away from the cell body

CNS and PNS The nervous system is divided into two parts: 1. Central Nervous System (CNS) - brain and spinal cord. Integrates sensory information to make decision. 2. Peripheral Nervous System (PNS) – nerves that originate from spine or brain, but branch off throughout the body. Nerves that initially detect external signals.

Basic Functions of Nervous System 1.Sensory Function - Gathers info, carries message to the CNS (brain). Afferent. 2.Integrative Function - Info brought together and decisions are made 3.Motor Function - Responds to stimuli, carries message away from brain. Efferent.

Sensory – Integrative - Motor 1. Sensory Function - gathers info about changes occurring within and around the body - Sensory receptors, at ends of peripheral nerves send signals (nerve impulses) to the CNS. The 3 basic functions:

Sensory – Integrative - Motor 2. Integrative Function - information is "brought together," interpreted, to create sensations, create thoughts, add to memory, make decisions, etc. Association neuron or interneuron The 3 basic functions:

Sensory – Integrative - Motor 3. Motor Function - responses to signals (impulses). Signals sent from the CNS to effectors (muscles or glands). The goal is usually to maintain stable conditions (Homeostasis). The 3 basic functions:

Motor Functions: Somatic & Autonomic -Somatic Nervous System = Signals from CNS effect skeletal muscles, voluntary. Example: talking, running, chewing, ect. -Autonomic Nervous System = Signals from CNS effect smooth muscles & glands, involuntary. Example: shaking when cold, increase saliva production when eating, slowing heart rate before bed.

-Autonomic Nervous System -Can be divided into Parasympathetic and Sympathetic Parasympathetic: Control the body's response while at rest. Sympathetic: Control the body's response during perceived threat.

(Integrative)

Neuron

Neuroglial Cells (Support cells for neurons) 1. Microglial Cells: scattered throughout, digest debris or bacteria. Immune response.

Neuroglial Cells (p 208) 2. Oligodendrocytes: makes the myelin sheath around the axon of neuron

Neuroglial Cells (p 208) 3. Astrocytes: connect blood vessels to neurons. Supplies nutrition for neuron to function. I connect to blood vessels

Neuroglial Cells (p 208) 4. Ependymal Cells: form a membrane that covers brain and spinal cord.

5. Schwann cells: form the insulating myelin sheath around the neurons

MYELIN SHEATHS - serve as insulation around the axon. Allows signal to travel long distances. The nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be course and sometimes involve the whole body. Try surprising a baby!

Supporting Cells - NEUROGLIA

Neurons

Axon - long section, transmits impulses Dendrite - small extensions from the cell body; receive information Neurofibrils - fibers within the axon neurofibrils

Chromatophilic substance (rough ER) - transport system Myelin -insulation surrounding axons Nodes of Ranvier - gaps in the insulation Axon Terminal – sends impulse to next neuron

White vs Grey Matter Grey matter – short neurons with unmyelinated axons. Also contains support cells (neuroglial cells). White matter – long myelinated axons with no dendrites or cell bodies. Function to connect gray matter. (Think of this as an extension cord)

Cannabis effects on Gray Matter - Heavy exposure to THC has been shown in many studies to reduce gray matter -This affect is drastically seen in maturing brains under the age of 25. -Researchers also have seen a decrease in IQ scores in long time cannabis users - Heavy Cannabis use (2-3 times daily) does not shrink brain as studies claim, but the brain compensates by increase the wiring of the brain (White matter)

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Interesting Facts about the Neuron Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose

Types of Neurons Functional: Sensory, Motor, Interneurons Structural: (A) Bipolar (B) Unipolar (C) Multipolar

The electrical signal (nerve impulse)is sent in this order: Dendrite  cell body  along axon  axon terminal  synapse (gap) Transmission of Nerve Impulses Nerve Impulses

How is a nerve impulse like a simple electrical circuit? If the wire is connected to a battery, then the light will illuminate. If a neuron is connected to another neuron with neurotransmitter, then the nerve will function. A neuron sending a signal down the axon.

“It’s like riding a bike, it will be easy to do it again!” Once you learn a skill (physical, emotional or academic) and you practice it enough it becomes second nature. Some call this “muscle memory” for physical activities. In reality, you have lots of gray matter neurons working at the same time. You have trained your brain to make those connections required for balance, coordination, or strength. Many top level athletes have mental trainers for this reason. Train your brain, and you can achieve more physically. “I dunno man, I haven’t skied in years. I’ll fall on my face!”

Tying your shoes or riding a bike is now easy because of Neuronal pools. Neuronal pool - groups of neurons that make hundreds of synaptic connections and work together to perform a common function.

Types of Neurotransmitters Acetylcholine – naturally stimulates muscle contraction Monoamines - Norepinephrine & Dopamine (sense of feeling good, low levels = depression) Serotonin - sleepiness and positive mood

Endorphins Produced during exercise, excitement, pain, love and they resemble the opiates (opium) in their abilities to produce a feeling of well-being. The name “endorphin” comes from endo- and -orphin; intended to mean "a morphine-like substance originating from within the body.

Drugs that Affect Synapses and Neurotransmitters Curare – Poison made from frog skin and causes paralysis by blocking Acetylcholine receptors at the neuromuscular junction.

Drugs that Affect Synapses and Neurotransmitters Strychnine Poisoning can be fatal to humans and animals and can occur by inhalation, swallowing or absorption through eyes or mouth Allows motor neurons to be more easily activated. Spastic muscle contractions occur that eventually lead to respiratory failure and death.

Drugs that Affect Synapses and Neurotransmitters Cocaine, morphine, alcohol, ether and chloroform Anaesthetize (lose consciousness or feeling) nerve fibers. Cocaine specifically keeps dopamine (good mood hormone) in one place and user feels pleasurable for longer periods of time.

Dangers of Ecstasy (MDMA) The most common cause of Ecstasy-related death is overheating (hyperthermia). MDMA interferes with the body's ability to regulate its own body temperature and to see other warning signs allowing the body to overheat without discomfort especially when dancing for hours in hot clubs. The neurotransmitter serotonin is vital in regulating many of our basic functions. Serotonin is, among other things, the feel good neurotransmitter and helps to regulate body temp.serotonin Our brain cells are constantly trying to bring some amount of serotonin back into the cells and out of the synapse using serotonin reuptake transporters. Ecstasy essentially takes these upkeep transporters and reverses their roles. This causes a massive flood of serotonin from the brain cells into the synapse.

LSD; lysergic acid diethylamide Actions/Effects: LSD alters the action of the neurotransmitters serotonin, norepinephrine, and dopamine, triggering extreme changes in brain function. Physical effects include increased body temperature, heart rate, and blood pressure. Psychological effects include perceptual and thought distortions, hallucinations, delusions, and rapid mood swings. Produce their hallucinatory effect by interfering with Adrenaline & serotonin

Antidepressants Zoloft is part of a class of drugs called selective serotonin reuptake inhibitors, or SSRIs for short. SSRIs act on a specific chemical within the brain known as serotonin. This is one of several chemicals used to send messages from one nerve cell to another.

Cell Membrane Potential What is it? Different ions (charged atoms) are allowed to enter the neuron cell. This causes neurotransmitters to be released and the neuron to communicate with the next.

Nerve Impulse A: 1 st Neuron (Presynaptic) B: 2 nd Neuron (Postsynaptic) 1.Mitochondria 2.Neurotransmitter 3.Calcium Pump 4.Synaptic cleft 5.Neurotransmitter receptor 6.Sodium/Potassium Pump 7.Fused vesicle releasing neurotransmitter 8.Neurotransmitter re-uptake pump

The Steps of Neurotransmission 1. Electrical impulse called an action potential travels down the axon of 1 st neuron (A). 2. This action potential opens a Na/K pump (6) in the cell membrane. Na+ ions enter neuron. 3. Build up of Na+ ions signals the opening of another channel, a Ca 2+ (3). 4. The Calcium ions bond to the neurotransmitters (2) and force them to release their contents into the synaptic gap. (7) 5. The neurotransmitters then stimulate the dendrite of the second neuron. (5)

Speed of an impulse is proportionate to the DIAMETER of the AXON. Practicing a skill increases this diameter. Greater diameter = faster speed Myelinated Axons conduct faster than unmyelinated ones Nerve impulse speed

The Synapse Synapse - junction between two communicating neurons Nerve pathway - nerve impulse travels from neuron to neuron Dendrite → cell body → along axon -> synapse (gap) → dendrite

The Synapse To complete the signal, a NEUROTRANSMITTER is released at the gap to signal the next neuron. Receptors on the dendrite receive the chemical message

Neurotransmitters Excitatory - increase membrane permeability, increases chance for threshold to be achieved Inhibitory - decrease membrane permeability, decrease chance for threshold to be achieved

9.9 Types of Nerves Sensory Nerves - conduct impulses into the brain or spinal cord (afferent) Motor Nerves - carry impulses to muscles of glands (efferent) Mixed Nerves - contain both sensory and motor nerves

Neurons Classified by Function: Sensory vs. Motor Neurons Figure 12.11

9.10 Nerve Pathways Reflex arc - only includes a few neurons Reflex Behavior - automatic, subconscious responses Knee-jerk reflex - maintains uprighted-ness Withdrawal reflex - avoidance of painful stimuli