Lecture 11 Nervous System and Senses
Overview of the Lecture
1. What is a Nervous System? (Purves p. 785-791)
key terms: Neuron, ganglion, signal transduction, central nervous system (CNS), peripheral nervous system (PNS)
Task: list examples of the nature of sensory input
Summary: a nervous system consists of afferent sensory cells that transport nerve impulses from sensory receptors to integrating neurons (e.g. in the brain) where the information gets processed. Motor neurons then send nerve signals to effectors, e.g. muscles or glands. In higher animals, the sensory and motor neurons constitute the peripheral nervous system and the spinal chord and brain constitute the central nervous system.
2. How Neurons Work (Raven p. 991-1003; Purves p. 775-791)
key terms: resting/action potential, supporting cells, saltatory conduction, Na+/K+ pump, ion channel, neurotransmitter, synapse, signal integration
Overview: electrical signals travel through an axon in a "La Ola" wave of short electric polarity reversals
2.1. Generation of a resting potential
2.2. Depolarization events
2.3. Nerve Synapses and Neurotransmitters
Overview:
Two types of small gaps connect the end of axons with the next neuron and with muscle cells. The electrical synapses simply transmit the action potential. The chemical synapse is slower and more complicated, but allows for integration of incoming information. In chemical synapses, an incoming action potential causes a neurotransmitter to be released and travel across the gap. Depending on the neurotransmitter, the effect can be excitation or inhibition of a new action potential in the downstream neuron.
3. The Human Brain
4. Sensory Organs
key terms: transduction, sensory cells, sensory organs,
Task: assign a number of sensory perception to the three classes
4.1. Various Receptors in the Skin
4.2. Chemoreception: sense of smell and taste
4.2. Mechanoreceptors (other than in the skin)
Sound is pressure waves (actual displacement of medium) that travel through the air or other media. Sound travels faster and with more energy in water than in air. Hence animals that live under water don't need an outer ear, the pressure waves travel right through the body and can be captured by a medium that is of different density than water (in fishes that can be ear stones or the gas-filled swim bladder). Terrestrial animals typically have an outer ear to transmit the sound waves better to the inner ear.
The mammalian ear has an eardrum (the tympanic membrane) that captures the sound and transfers it via a chain of three little bones bones (hammer, anvil, and stirrup) in the middle ear to another, smaller drum membrane. There, the amplified vibrations get transduced again into pressure waves in the fluid-filled cochlea ("the snail"). The sound waves travel down the upper canal, around a bend, back in the lower canal and from there "out the round window" to a connection with the throat (so that the pressure can escape). As the sound travels through the uppper canal it makes a part of a membrane at its bottom (the basilar membrane) resonate depending on the sound frequency (the pitch). High frequency sounds make the membrane resonate close to the origin of the cochlea while low frequency sounds resonate farther back. Hair cells near that resonating spot get most stimulated. The brain interpretes which pitch a sound had through the location in the brain that the stimulated sensory hair cells connect to. Louder sounds are waves with a higher amplitude that mov emore hair cells (=more action potentials).
Directional hearing is achieved through the time delay between a sound reaching the right and left ear. Because sound travels faster in water, diving humans cannot interprete where a sound comes from. Healthy humans can hear sounds with a pitch of between about 20 to 20,000 Hertz (oscillations per second). Dogs can hear up to 40,000 hertz and bats even higher.
4.4. Electromagnetic Perception
4.5. Extrasensory Perception (at least for us humans)
