Starting small The Neuron neuron a nerve cell

Starting small: The Neuron • neuron: a nerve cell; receives signals from other neurons or sensory organs, processes these signals, and sends signals to other neurons, muscles, or bodily organs – the basic unit of the nervous system

The Neuron • 3 types of neurons: – 1. sensory neurons: respond to input from sensory organs (skin, eyes, etc. ) – 2. motor neurons: send signals to muscles to control movement – 3. interneurons: connect the sensory neurons and motor neurons • most of the neurons in the brain = interneurons • average human brain 100 billion neurons

Structure of the Neuron

Structure of the Neuron • cell body (soma): the central part of the neuron, contains the nucleus – regulates cell functioning • dendrites: the branching part of the neuron that receives messages from other neurons and relays them to the cell body

Structure of the Neuron • axon: the long, cable-like extension that delivers messages to other neurons • myelin sheath: layer of fatty tissue that insulates the axon and helps speed up message transmission – multiple sclerosis: deterioration of myelin leads to slowed communication with muscles and impaired sensation in limbs • knobs: structure at the end of one of the axon’s branches that releases chemicals into the space between neurons, when the neuron is fired

From Neuron to Neuron • ≈100 billion neurons in a human brain, connected to an average of 10, 000 others; some up to 100, 000 • synapse: the place where an axon of one neuron meets with the dendrite/cell body of another neuron

From Neuron to Neuron

From Neuron to Neuron • neurotransmitters: a chemical that sends signals from one neuron to another over the synapse

From Neuron to Neuron • Neurotransmitters are stored in vesicles in the knobs, and bind to receptors on the cell membrane of the next neuron. – Each receptor can only bind with one kind of neurotransmitter.

(Some) Neurotransmitters Neurotransmitter Function Examples of malfunctions Acetylcholine (ACh) Enables muscle action, learning & memory Alzheimer’s disease less ACh production Dopamine Influences movement, learning, attention, & emotion Excess schizophrenia Undersupply Parkinson’s disease Serotonin Affects mood, hunger, sleep, and arousal Undersupply depression Norepinephrine Helps control alertness & arousal Undersupply depressed mood Glutamate Excitatory neurotransmitter involved in memory Excess overstimulation of brain, seizures

The Nervous System Central Nervous System (CNS) Brain Peripheral Nervous System (PNS) Spinal Cord Motor Neurons Somatic Nervous System • voluntary movements via skeletal muscles Sensory Neurons Autonomic Nervous System • organs, smooth muscles Sympathetic - “Fight-or-Flight” responses Parasympathetic - maintenance

The Nervous System • Made up of the 1. central nervous system and the 2. peripheral nervous system

The Nervous System The Central Nervous - brain and spinal cord • Peripheral Nervous System: links central nervous system to organs – comprised of the somatic nervous system and the autonomic nervous system (sympathetic and parasympatheic nerves)

CNS PNS Sensory division Sympathetic division Parasympathetic division Human Anatomy and Physiology, 7 e by Elaine Marieb & Katja Hoehn Motor division Autonomic nervous system Somatic nervous system Copyright © 2007 Pearson Education, Inc. , publishing as Benjamin Cummings.