Bio11 schedule Lecture Nervous system and senses Lab Current events reports (10 pts) Urinalysis Lecture exam 2 Thursday Feb 24 Same format as before Study guide will be posted Your total points so far (your grade in class) will be posted in lecture on Thur Chapter 13 and 14 Nervous and Sensory Systems The Nervous System Neurons are nerve cells specialized for carrying electrical signals from one part of the body to another The Nervous System Supporting cells Outnumber neurons by as many as 50 to 1 Protect, insulate, and reinforce the neurons Organization of Nervous Systems Two main divisions: The central nervous system (CNS) brain and spinal cord The peripheral nervous system (PNS) nerves that carry signals into and out of the CNS Nerves A nerve is a communication line made from cablelike bundles of neuron fibers.
Organization of the nervous system Sensory receptor Effector cells SENSORY INPUT Sensory neuron MOTOR OUTPUT Motor neuron Peripheral nervous system (PNS) INTEGRATION Interneuron Brain and spinal cord Central nervous system (CNS) Organization of the nervous system The three interconnected functions are carried out by three types of neurons: Sensory neurons function in sensory input Interneurons integrate information Motor neurons function in motor output Signal direction Structure of a motor neuron Dendrites Cell body Direction of electrical signal: Dendrite cell body axon Signal direction Dendrites Cell body An axon ends in a cluster of branches, each with a bulb-like synaptic terminal that relays signals to Another neuron or An effector Axon Supporting cell Signal pathway terminals Axon Supporting cell Signal pathway terminals Nucleus Nucleus Myelin sheath Forms insulating material around an axon Helps increase the speed of the electrical signal Myelin sheath Figure 27.2 Sending a Signal through a Neuron Resting potential when the axon is not conducting a nerve impulse Difference in charge (voltage) across the plasma membrane More positive ions outside than inside the membrane There is a negative charge inside the axon Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. axonal membrane inside axon recording electrode inside axon outside axon - - - - - - - - - - - - - - - - - - - - reference electrode outside axon K Na gated K channel gated Na channel a. Resting potential: Separation of charges polarizes the cell and causes the resting potential. The nerve impulse: action potential A stimulus causes the inside of the axon to lose its negative charge. Sodium gates open letting Na in Depolarization - - - - - - - - - - direction of signal - - - - - - - - - - b. Stimulus causes the axon to reach its threshold; the axon potential increases from -65 to -40. The action potential has begun. open Na channel
The nerve impulse: action potential Propagation of the Signal Repolarization Interior of axon regains negative charge K gates open and K moves outside the axon Wave of depolarization/ repolarization travels down the axon - - - - - - - - - direction of signal - - - - - - - - - - open K channel An action potential is a local electrical event. To function as a nerve signal over a distance, this local event must be passed along the neuron. Action potential ends Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Action potential Axon Passing a Signal from a Neuron to a Receiving Cell Wave of depolarization/ repolarization travels down the axon Action potential Action potential A synapse is a relay point Between two neurons or Between a neuron and an effector cell Transmission is accomplished across this gap by a neurotransmitter ACh, dopamine and serotonin http://www.youtube.com/watch?v=r0tdxkxboke&nr=1 terminal of sending neuron Dendrite of receiving neuron Neurotransmitters SYNAPSE Sending neuron Vesicles terminal Vesicle fuses with plasma membrane. Action potential arrives. Neurotransmitter is released into synaptic cleft. Neurotransmitter Receptor Ions More than 100 small molecules act as neurotransmitters Most widely studied Acetylcholine, norepinephrine, dopamine, serotonin, and GABA cleft Receiving neuron Ion channels Neurotransmitter molecules Neurotransmitter binds to receptor. Ion channel opens and triggers or inhibits a new action potential. Ion channel closes. Neurotransmitter is broken down and released. http://www.youtube.com/watch?v=32aercwkls8&feature=related Figure 27.5
Drugs and the Brain Caffeine Many drugs, such as caffeine, nicotine, and alcohol, act at synapses by increasing or decreasing the normal effect of neurotransmitters. Prescription drugs used to treat psychological disorders alter the effects of neurotransmitters. Counters the effects of inhibitory neurotransmitters, ones that suppress nerve signals That s why caffeine tends to stimulate you Nicotine Nicotine acts as a stimulant by mimicking acetylcholine it binds to and activates ACh receptors Amphetamines and cocaine Increase the release and availability of dopamine (DA) at synapses Dopamine is the reward neurotransmitter that is highly active in numerous pathways of the brain How do drugs work? The Central Nervous System The brain and spinal cord Protected by bone; wrapped in protective membranes called the meninges Spaces filled with cerebrospinal fluid Cushions the CNS Supplies nutrients, hormones http://learn.genetics.utah.edu/content/addiction/drugs/mouse.html
Spinal cord The human brain Conducts signals to and from the brain Gray matter contains neuron cell bodies White matter contains myelinated axons that run together in bundles called tracts White matter Cerebrum largest portion of the brain Responsible for reasoning, learning and memory, language The cerebral cortex Spinal nerve Gray matter Cerebrum Is a highly folded layer of tissue that forms the surface of the cerebrum Cerebrum - divided into four lobes Frontal lobe The Cerebral Cortex Parietal lobe Moto rco rte x Somat ose ns orcy or te x Primary motor area and conscious thought Frontal association area Somatosensory and taste area Speech Somatosensory association area Reading Taste Speech Smell Hearing association area Hearing, smell and speech Temporal lobe Visual association area The cerebrum consists of right and left cerebral hemispheres interconnected by the corpus callosum. Vision Vision Occipital lobe Figure 27.12 The brain: Cerebellum Functions: Maintains posture Coordinates body movement Learns and remembers new motor skills (i.e. playing the piano or hitting a baseball) The brain stem Regulates breathing, heartbeat and blood pressure Brain stem
The Peripheral Nervous System Peripheral nervous system Contains the nerves Cranial nerves carry signals to and from the brain Spinal nerves carry signals to and from the spinal cord Two components: The somatic nervous system The autonomic nervous system The somatic nervous system (voluntary) Carries signals to and from skeletal muscles Mainly responds to external stimuli The autonomic nervous system (involuntary) Regulates the internal environment Controls Smooth and cardiac muscles Organs and glands Autonomic nervous system Two sets of neurons with opposing effects on most organs: The parasympathetic division primes the body for digesting food and resting. The sympathetic division prepares the body for intense, energy-consuming activities. Fight or flight Ch 14: THE SENSES Vision and hearing Sensory Input How does a taste bud detect sugar molecules? SENSORY INPUT Sensory receptors Sense the environment Detect a stimulus Send information about it to the CNS Example: Sensory receptors in the taste buds detect chemicals dissolved in saliva Taste bud Sugar molecule Sensory receptor cells And send this signal to the brain? Sensory neuron
Sensory Transduction Sensory receptor cells convert one type of signal to an electrical signal change the membrane potential of the receptor cell Sensory receptors in human skin are somewhat specialized Epidermis Heat Light Pain Cold touch (Hair) Dermis Nerve to CNS Hair movement Strong pressure Vision Human eyes are able to Detect a multitude of colors Form images of faraway objects Respond to minute amounts of light energy Structure of the Human Eye A tough outer covering, the sclera A transparent cornea in front of the lens An iris with a center opening, the pupil The retina, at the back of the eyeball, where photoreceptors respond to light The optic nerve connects the retina to the brain Photoreceptors Photoreceptors rods The human retina contains two types of photoreceptors. Rods: Are extremely sensitive to light Perceive only shades of gray Are distributed at the outer edges of the retina cones The human retina contains two types of photoreceptors. Cones: Perceive colors Are distributed at the center of focus on the retina
Hearing Photoreceptors Rods and cones are stimulus transducers that The Structure of the Human Ear Outer ear Absorb light Generate receptor potentials Integrate these receptor potentials Generate action potentials that travel along the optic nerve to the brain Pinna Eardrum canal Eustachian tube (a) Ear structure The outer ear Outer ear Inner ear Middle ear The middle ear canal (a) Ear structure Eardrum Eustachian tube Consists of the pinna and the auditory canal Collects sound waves Passes sound waves to the eardrum, a sheet of tissue that separates the outer ear from the middle ear The vibrating eardrum passes the sound waves to three small bones that relay the sound to the inner ear. The Eustachian tube The inner ear Fluid-filled channels in the bones of the skull. One of the channels, the cochlea, contains the organ of Corti Inner ear Other retinal neurons Pinna Middle ear Is the actual hearing organ Includes hair cells, the receptor cells of the ear Allows air pressure to stay equal on either side of the eardrum Stirrup Skull bones Hammer Anvil Eardrum Eustachian tube How do we hear? Stirrup Skull bones Hammer Anvil nerve, to brain Sound waves are collected by the outer ear Vibrate the eardrum Are transmitted to the cochlea, which causes Eardrum Eustachian tube Cochlea Hair cells in the organ of Corti to bend Nerve cells to send signals to the brain nerve, to brain Cochlea