Neural and Hormonal Systems Central (brain and spinal cord) Nervous system Autonomic (controls self-regulated action of internal organs and glands) Skeletal (controls voluntary movements of skeletal muscles) Sympathetic (arousing) Parasympathetic (calming) Peripheral

Neurons and Synapses Types of Neurons Sensory/AfferentMotor/Efferent Interneurons

Spinal Cord Brain Sensory Neuron Sensory Neurons INPUT From sensory organs to the brain and spinal cord. Drawing shows a somatosensory neuron Vision, hearing, taste and smell nerves are cranial, not spinal

Spinal Cord Brain Sensory Neuron Motor Neuron Motor Neurons OUTPUT From the brain and spinal cord To the muscles and glands.

Spinal Cord Brain Sensor y Neuron Motor Neuron Interneurons Interneurons carry information between other neurons only found in the brain and spinal cord.

Structures of a neuron

The cell body –Round, centrally located structure –Contains DNA –Controls protein manufacturing –Directs metabolism –No role in neural signaling Contains the cell’s Nucleus

Dendrites Information collectors Receive inputs from neighboring neurons Inputs may number in thousands If enough inputs the cell’s AXON may generate an output

Dendritic Growth Mature neurons generally can’t divide But new dendrites can grow Provides room for more connections to other neurons New connections are basis for learning

Axon The cell’s output structure One axon per cell, 2 distinct parts –tubelike structure branches at end that connect to dendrites of other cells

Myelin sheath White fatty casing on axon Acts as an electrical insulator Not present on all cells When present increases the speed of neural signals down the axon. Myelin Sheath

How neurons communicate Neurons communicate by means of an electrical signal called the Action Potential Action Potentials are based on movements of ions between the outside and inside of the cell When an Action Potential occurs a molecular message is sent to neighboring neurons

Ion concentrations Cell Membrane in resting state K+ Na+ Cl- K+ A- Outside of Cell Inside of Cell Na + Cl-

The Cell Membrane is Semi- Permeable In a resting state – there is more negatively charged molecules on the inside than outside & more positively charged ions on the outside than inside.

Resting Potential At rest the inside of the cell is at -70 microvolts With inputs to dendrites the inside becomes more positive if resting potential rises above threshold an action potential starts to travel from cell body down the axon Figure shows resting axon being approached by an AP

Depolarization ahead of AP AP opens cell membrane to allow sodium (NA+) in inside of cell rapidly becomes more positive than outside this depolarization travels down the axon as leading edge of the AP

Repolarization follows After depolarization potassium (K+) moves out restoring the inside to a negative voltage This is called repolarization The rapid depolarization and repolarization produce a pattern called a spike discharge

Finally, Hyperpolarization Repolarization leads to a voltage below the resting potential, called hyperpolarization Now neuron cannot produce a new action potential This is the refractory period

Neuron to Neuron Axons branch out and end near dendrites of neighboring cells Axon terminals are the tips of the axon’s branches A gap separates the axon terminals from dendrites Gap is the Synapse Cell Body Dendrite Axon

Synapse axon terminals contain small storage sacs called synaptic vesicles –vesicles contain neurotransmitter molecules Sending Neuron Synapse Axon Terminal

Neurotransmitter Release Action Potential causes vesicle to open Neurotransmitter released into synapse Locks onto receptor molecule in postsynaptic membrane

Locks and Keys Neurotransmitter molecules have specific shapes positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarize When NT binds to receptor, ions enter Receptor molecules have binding sites

Some Drugs work on receptors Some drugs are shaped like neurotransmitters Antagonists : fit the receptor but poorly and block the NT –e.g. beta blockers Agonists : fit receptor well and act like the NT –e.g. nicotine. Website for neural simulations

Neural Communication Neurotransmitter molecule Receiving cell membrane Receptor site on receiving neuron Agonist mimics or enhances Neurotransmitter Antagonist blocks neurotransmitter Curare is a antagonist for Ach Caffeine increases the availability of glutamate (keeps NS aroused) Amphetamines & cocaine are agonists increasing dopamine in the brain Alcohol is an agonist by increasing sensitivity of receptor site to the inhibitory GABA Anti-psychotic drugs block dopamine in schizophrenics anti-depressants are agonists that increase the levels of norepinephrine and serotonin by blocking reuptake

Neural Communication

Some Neurotransmitters and Their Functions Neurotransmitt er FunctionProblems Caused by Imbalances Roles of Different Neurotransmitters SerotoninAffects mood, hunger, sleep, and arousal Undersupply linked to depression; some antidepressant drugs raise serotonin levels DopamineInfluences movement, learning, attention, and emotion Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility in Parkinson’s disease and ADHD Acetylcholine (ACh) Enables muscle action, learning, and memory ACh-producing neurons deteriorate as Alzheimer’s disease progresses NorepinephrineHelps control alertness and arousal Undersupply can depress mood and cause ADHD-like attention problems GABA (gamma- aminobutyric acid A major inhibitory neurotransmitter Undersupply linked to seizures, tremors, and insomnia GlutamateA major excitatory neurotransmitter; involved in memory Oversupply can overstimulate the brain, producing migraines or seizures; this is why some people avoid MSG (monosodium glutamate) in food

The Endocrine System The endocrine system refers to a set of glands that produce chemical messengers called hormones.

The Body’s “Slow but Sure” Endocrine Message System  The endocrine system sends molecules as messages, just like the nervous system, but it sends them through the bloodstream instead of across synapses.  These molecules, called hormones, are produced in various glands around the body.  The messages go to the brain and other tissues.

1.The sympathetic “fight or flight” nervous system responds to stress by sending a message to adrenal glands to release the hormones listed above. 2.Effect: increased heart rate, blood pressure, and blood sugar. These provide ENERGY for the fight or flight! Adrenal Glands produce hormones such as adrenaline/epinephrine, noradrenaline/norepinephrine, and cortisol. Pancreas Adrenal Glands

The Pituitary Gland  The pituitary gland is the “master gland” of the endocrine system.  It is controlled through the nervous system by the nearby brain area-- the hypothalamus.  The pituitary gland produces hormones that regulate other glands such as the thyroid.  It also produces growth hormone (especially during sleep) and oxytocin, the “bonding” hormone. Pituitary gland