Monday April 14, Nervous system and biological electricity IV 1. Exam 2 results 2. Lab this week 3. Review of the synapse 4. The connectome 5. Vertebrate nervous system 6. Mapping the brain

This week in Lab

Lab philosophy and Scientific literacy An example of why this is important

Lab is designed to illustrate science as: – A creative process – Challenging – An interactive and social activity Lab philosophy and Scientific literacy

Dropping grades in lab

ACTION POTENTIAL TRIGGERS RELEASE OF NEUROTRANSMITTER Na + and K + channels Presynaptic membrane (axon) Postsynaptic membrane (dendrite or cell body) Action potentials 1. Action potential arrives; triggers entry of Ca In response to Ca 2+, synaptic vesicles fuse with presynaptic membrane, then release neurotransmitter. 3. Ion channels open when neurotransmitter binds; ion flows cause change in postsynaptic cell potential. 4. Ion channels will close as neurotransmitter is broken down or taken back up by presynaptic cell (not shown).

Excitatory vs. Inhibitory Synapses Excitatory synapses cause the post-synaptic cell to become less negative triggering an excitatory post-synaptic potential (EPSP) – Increases the likelihood of firing an action potential Inhibitory synapses cause the post-synaptic cell potential to become negative triggering an inhibitory post-synaptic potential – Decreases the likelihood of firing an action potential

Postsynaptic Potentials Can Depolarize or Hyperpolarize the Postsynaptic Membrane Postsynaptic potentials can depolarize or hyperpolarize the postsynaptic membrane. Depolarization, Na + inflow Hyperpolarization, K + outflow or Cl – inflow Depolarization and hyperpolarization stimuli applied Excitatory postsynaptic potential (EPSP) Inhibitory postsynaptic potential (IPSP) EPSP  IPSP Resting potential

Neurons Integrate Information from Many Synapses Most neurons receive information from many other neurons. Axons of presynaptic neurons Dendrites of postsynaptic neuron Cell body of postsynaptic neuron Axon hillock Axon of postsynaptic cell Excitatory synapse Inhibitory synapse

Neurons Integrate Information from Many Synapses Postsynaptic potentials sum. Action potential Threshold Resting potential

Neurotransmitters More than 100 neurotransmitters are now recognized, and more will surely be discovered. Acetylcholine is important and one of the first ones discovered because its involvement in muscle movement. Dopamine and serotonin hugely important for many behaviors. The workhorses of the brain are glutamate, glycine, and γ-aminobutyric acid (GABA).

Neurotransmitter Transport Proteins/Reuptake Neurotransmitters must be stopped. They have to be broken down and recycled by the neuron. E.g., Acetylcholine is broken down by acetylcholine esterase. Drug companies often target these 'reuptake' proteins for drug therapies.

‘The Connectome’ Sebastian Seung MIT. astian_seung

Mini-Brain/Nervous System Lecture Central Nervous System = brain and spinal cord (interneurons) Peripheral Nervous System = all other parts of nervous system besides brain & spinal cord - includes motor neurons and sensory neurons

The Functions of the PNS Form a Hierarchy Central nervous system (CNS) Information processing Peripheral nervous system (PNS) Sensory information travels in afferent division Most information travels in efferent division, which includes… Somatic nervous system Autonomic nervous system Parasympathetic division Sympathetic division

Neurons vs. Nerves Neuron = a cell that is specialized for the transmission of nerve impulses. Typically has dendrites, a cell body, and a long axon that forms synapses with other neurons. Also called a nerve cell. Nerve = A long, tough strand of nervous tissue typically containing thousands of neurons wrapped in connective tissue; carries impulses between the central nervous system and some other part of the body.

Sciatic Nerve The sciatic nerve is this huge nerve that leaves your lower back (and spinal cord) and runs the length of your leg. There are many different types of neurons. Some are myelinated, some are not. Smaller nerves branch off of the sciatic nerve. The sciatic nerve responsible for innervating muscles, skin, etc. in the leg. It contains both motor neurons and sensory neurons (i.e. messages go both way). There are some neurons that originate at the top and have axons that run the whole way to your foot. In other words, there are axons that are about 1 meter long.

How Does Information Flow through the Nervous System? The brain integrates sensory information and sends signals to effector cells. Sensory neuron Sensory receptor CNS (brain  spinal cord) Interneuron Motor neuron (part of PNS) Effector cells

When reflexes occur, sensory information bypasses the brain. Sensory receptor Motor neuron Effector cells Sensory neuron Spinal cord Interneuron How Does Information Flow through the Nervous System?

Brain Parts The brain is made up of four distinct structures. Inside view Diencephalon Information relay and control of homeostasis Brain stem Information relay and center of autonomic control for heart, lungs, digestive system Cerebrum Conscious thought, memory Cerebellum Coordination of complex motor patterns

Paul Broca Studied the brain of a person who could hear and comprehend, but not speak. Found a lesion on one part of the brain. First to claim that different parts of the brain did different things. Functional Mapping

Brain Lesion

Brain Mapping – Electrical Stimulation In treating people with severe seizures, doctors electrically stimulate the brain to find the area where the seizure originates from. The idea is to remove this part of the brain with removing as little as possible from other adjoining areas. Doctors still do this today. Based on electrical stimulation of conscious patients, we know that different parts of the brain do different things.

Brain Mapping – fMRI

Mapping of Brain to Anatomical Parts

Specific Brain Areas Have Specific Functions Cross section through area responsible for sense of touch and of temperature Left hemisphere Intra-abdominal Tongue Teeth Jaw Lips Nose Eye Thumb Fingers Hand Arm Head Trunk Hip Leg Genitals