Nervous System Nerve Cells Neuron  designed to respond to surrounding environment Axons and Dendrites Small branches called dendrites receive chemical or electrical input from the body. Neurons have many dendritesSmall branches called dendrites receive chemical or electrical input from the body. Neurons have many dendrites Large branches are called axons, or nerve fibers, which carry information away from the cell in the form of a nerve impulse. Neurons commonly have only 1 axonLarge branches are called axons, or nerve fibers, which carry information away from the cell in the form of a nerve impulse. Neurons commonly have only 1 axon Nerves are simply bundles of axons. Axons are surrounded by a “Band-Aid” of cells called Schwann Cells. Multiple layers of these cells create a sheath, or covering, around the axon called a myelin sheath.Nerves are simply bundles of axons. Axons are surrounded by a “Band-Aid” of cells called Schwann Cells. Multiple layers of these cells create a sheath, or covering, around the axon called a myelin sheath. The myelin sheath, allows for the super-fast conduction of nerve impulses. Nerves that are mylenated appear white. Mylenated nerves are used to send signals over long distances.The myelin sheath, allows for the super-fast conduction of nerve impulses. Nerves that are mylenated appear white. Mylenated nerves are used to send signals over long distances. Unmylenated nerves appear gray (like gray matter in the brain) and are often used for processing nerve informationUnmylenated nerves appear gray (like gray matter in the brain) and are often used for processing nerve information

Typical Nerve Cell (Neuron)

Neurons in 3 dimensional space

Nerve Communication Neurons communicate to each other by sending chemical signals to one another. These chemicals are called neurotransmitters.Neurons communicate to each other by sending chemical signals to one another. These chemicals are called neurotransmitters. Neurotransmitters leave one neuron, travel through a small intercellular space, to another neuron. That space is called a synapse.Neurotransmitters leave one neuron, travel through a small intercellular space, to another neuron. That space is called a synapse. At the end of each neuron is a receptor that monitors the internal condition of the bodyAt the end of each neuron is a receptor that monitors the internal condition of the body Receptors transmit information down the dendrite, to the cell body. Information is processed and sent out of the axon, away from the neuronReceptors transmit information down the dendrite, to the cell body. Information is processed and sent out of the axon, away from the neuron The nervous system consists of millions of communicating neurons, neurotransmitters, receptors, and synapses. The nervous system consists of millions of communicating neurons, neurotransmitters, receptors, and synapses.

Neuron Clusters Neurotransmitter Release

Conduction of a Nerve Impulse Nerve impulse in a human travels more than 600 feet per secondNerve impulse in a human travels more than 600 feet per second Resting nerve cells tend to have lots of negatively charged proteins in them, and therefore have a negative charge to them (-65mv). Resting nerve cells tend to have lots of negatively charged proteins in them, and therefore have a negative charge to them (-65mv). Resting nerve cells also have lots of potassium inside the cell.Resting nerve cells also have lots of potassium inside the cell. They also have lots of Sodium just outside the cellThey also have lots of Sodium just outside the cell

Action Potential 1.Action Potentials describe how a nerve impulse is generated and conducted throughout the body 2.The nerve cell is stimulated by an electric current, change in pH, or a pinch, causing an action potential 3.Upon stimulation, Sodium gates in the nerve cell membrane open and sodium rushes into the cell. This rush of positive ions causes the cell’s charge to rise and spike (from -65mv to +40mv). This process is called depolarization. 4.After the initial rush, the sodium gates close (stopping sodium movement) and potassium gates open. Potassium then rushes out of the cell. The loss of these positive ions causes the cell to return to its resting charge (-65mv). This is called repolarization. 5.Eventually, the sodium which rushed into the cell and the potassium which rushed out of the cell are pumped out of the cell (Na) and into the cell (K). This is done by the sodium potassium pump. 6.During this time the nerve is in its refractory period.

Action Potential

Divisions of the Nervous System Central Nervous System  Brain and spinal cord Peripheral Nervous System  All other parts of the body Somatic Nervous System  Nerves that are controlled voluntarily Autonomic Nervous System  Nerves that are controlled involuntarily

Types of Neurons Sensory Neuron  Neurons with receptors on the end. Send signals to the brain.Sensory Neuron  Neurons with receptors on the end. Send signals to the brain. Motor Neurons  Carry nerve impulses to from the brain to your musclesMotor Neurons  Carry nerve impulses to from the brain to your muscles Interneurons  Reside in the brain and spinal cord. Connect sensory neurons to motor neuronsInterneurons  Reside in the brain and spinal cord. Connect sensory neurons to motor neurons

Parts of the Brain Brain Stem  contains the medulla oblongata and the pons. Located at junction of brain and spinal cordBrain Stem  contains the medulla oblongata and the pons. Located at junction of brain and spinal cord Medulla Oblongata  contains clusters of neurons that control heartbeat, respiration, and blood pressure. Also contains neurons that control reflexes like swallowing, coughing, hiccups, and vomitingMedulla Oblongata  contains clusters of neurons that control heartbeat, respiration, and blood pressure. Also contains neurons that control reflexes like swallowing, coughing, hiccups, and vomiting Pons  Means “bridge”. Mostly aids in sending messages from MO to spinal cord. Also has limited tactile, visual, and auditory functionPons  Means “bridge”. Mostly aids in sending messages from MO to spinal cord. Also has limited tactile, visual, and auditory function

Diencephalon Hypothalamus  Maintains Homeostasis; Regulates hunger, thirst, body temperature, and sleep. Hypothalamus also controls the pituitary gland (growth)Hypothalamus  Maintains Homeostasis; Regulates hunger, thirst, body temperature, and sleep. Hypothalamus also controls the pituitary gland (growth) Thalamus: Post office of the brain. Receives incoming messages from the spinal cord and processes the information, sends the information to the appropriate part of the brainThalamus: Post office of the brain. Receives incoming messages from the spinal cord and processes the information, sends the information to the appropriate part of the brain

Cerebellum and Cerebrum Cerebellum 2 portions separated by the brain stem Cerebellum functions in skeletal muscle coordination; maintaining balance and posture. Receives information from the inner ear Cerebrum Surface area of the brain Area of the brain devoted to consciousness. 4 surface areas: Frontal, Parietal, Temporal, and Occipital Frontal Lobe: formation of conscious thought; thinking Parietal Lobe: Sensations: Pain, pressure, touch Temporal Lobe: Hearing and smelling Occipital Lobe: Visual Processing

Other Interesting Parts of the Brain Corpus callosum  Part of the frontal lobe that splits into right and left sides. Over excitation of CC can cause epileptic seizures. Limbic System  Lies below the cerebrum in the frontal lobe. Controls emotions such as love, anger, sadness, guilt, etc... Also controls sense of memory (long and short term) Destruction of neurons in the limbic system leads to Alzheimer’s disease Most hallucinogenic drugs affect neurons in the limbic system