Transcript neuron
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 • comprised of the central nervous system and the peripheral nervous system • central nervous system: brain and spinal cord – reflex: an automatic response to an event • e.g. sensory neuron detects pain, send signal to spinal cord signal to interneurons signal to motor neurons The Nervous System • Peripheral Nervous System: links central nervous system to organs –comprised of the skeletal nervous system and the autonomic nervous system –skeletal nervous system: controls voluntary movements of our skeletal muscles The Nervous System • autonomic nervous system: controls many of the self-regulatory functions of the body (e.g. digestion, circulation) – comprised of the sympathetic and parasympathetic nervous systems – sympathetic: prepares us for defensive actions against threats (e.g. faster heartrate, increased breathing rate, inhibits digestion, dilates pupils to allow greater light sensitivity) – parasympathetic: counteracts effects of sympathetic nervous system, calms us down Structure of the Brain • The human brain is comprised of “older” and “newer” parts. – “older”: lower level structures, responsible for basic survival mechanisms – “newer”: higher level structures, responsible for more advanced human faculties Structure of the Brain • brainstem: the set of neural structures at the base of the brain, including the medulla, the reticular formation, and the pons – facilitates communication between the brain and spinal cord The Brainstem • medulla: controls heartbeat, breathing, and swallowing • pons: bridge from brainstem to cerebellum; controls a variety of functions, including sleep and control of facial muscles The Cerebellum • “little brain” extending from rear of brainstem – coordinates physical movement – contributes to estimating time and paying attention • cerebellum + other lower level brain structures occur without conscious effort – Much of our brain’s activity occurs outside of our awareness The Brainstem • thalamus: the brain’s sensory switchboard; receives signals from the sensory and motor systems, and relays them to the appropriate parts of the brain – also receives signals from higher brain structures, relays them to medulla and cerebellum The Limbic System • limbic system: doughnutshaped system of neural structures at the border of the brainstem and cerebral hemispheres – involved in the basics of emotion and motivation: fighting, fleeing, feeding, and sex – comprised primarily of the hypothalamus, the hippocampus, and the amygdala The Limbic System • hypothalamus: brain structure that sits under the thalamus and plays a central role in controlling eating and drinking, and in regulating the body’s temperature, blood pressure, and heart rate The Limbic System • hippocampus: brain structure that plays a key role in allowing new information to be stored in memory hippocampus does not contain memories itself, but does trigger processes that store memories elsewhere in the brain The Visible Brain • cerebral cortex: the convoluted pinkish-gray surface of the brain, where most mental processes take place • The brain is divided into two halves (cerebral hemispheres), separated by a deep fissure – hemispheres control opposite side of body (e.g. right-handers’ writing is controlled by the left hemisphere) Our Divided Brains • cerebral hemispheres connected by the corpus callosum, a large band of neural fibers that transmits messages between hemispheres – contains more than 200 million nerve fibers, can transfer more than 1 billion bits of information per second Structure of the Cortex • cerebral cortex divided into lobes, or regions of the brain – Each lobe is (roughly) responsible for different higherlevel functions, but remember that they do not work merely in isolation. Structure of the Cortex • occipital lobe: brain lobe at the back of the head – responsible primarily for vision; separate areas specify visual properties such as shape, color, and motion Structure of the Cortex • temporal lobe: the brain lobe under the temples, in front of the ears – many functions, including processing sounds, committing information to memory, and comprehending language Structure of the Cortex • parietal lobe: brain lobe at the top and center/rear of the head – involved in registering spatial location, attention, and motor control Structure of the Cortex • frontal lobe: the brain lobe located behind the forehead – the seat of planning, memory search, motor control, reasoning, emotions, and many other functions – In many ways, the frontal lobe is what makes us uniquely human.