Monday April 14, 2014.

Nervous system and biological electricity IV

1. Exam 2 results 2. Lab this week3. Review of the synapse4. The connectome5. Vertebrate nervous system6. 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

Presynapticmembrane(axon)

Postsynapticmembrane(dendrite orcell body)

Actionpotentials

1. Action potential arrives;triggers entry of Ca2+.

2. In response to Ca2+, synapticvesicles fuse with presynapticmembrane, then releaseneurotransmitter.

3. Ion channels open whenneurotransmitter binds; ionflows cause change inpostsynaptic cell potential.

4. Ion channels will close asneurotransmitter is brokendown or taken back up bypresynaptic 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 thepostsynaptic membrane.

Depolarization,Na+ inflow

Hyperpolarization, K+

outflow or Cl– inflowDepolarization andhyperpolarizationstimuli applied

Excitatorypostsynapticpotential(EPSP)

Inhibitorypostsynapticpotential(IPSP)

EPSP IPSP

Resting potential

Neurons Integrate Information from Many Synapses

Most neurons receive information from many other neurons.

Axons ofpresynaptic neurons

Dendrites ofpostsynaptic neuron

Cell body ofpostsynaptic neuron

Axonhillock Axon of postsynaptic cell

Excitatory synapseInhibitory synapse

Neurons Integrate Information from Many Synapses

Postsynaptic potentials sum.

Action potential

ThresholdRestingpotential

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• Biophysicist/neurophysiologist

@ MIT.• http://www.ted.com/talks/

sebastian_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 HierarchyCentral nervous system (CNS)

Information processing

Peripheral nervous system (PNS)

Sensoryinformation

travels inafferent division

Most informationtravels in

efferent division,which includes…

Somaticnervoussystem

Autonomicnervous system

Parasympatheticdivision

Sympatheticdivision

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 NerveThe 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 signalsto effector cells.

Sensory neuron

Sensory receptor

CNS (brain spinal cord)

Interneuron

Motor neuron(part of PNS)

Effector cells

When reflexes occur, sensory information bypasses thebrain.

Sensoryreceptor

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

DiencephalonInformationrelay and controlof homeostasis

Brain stem Information relayand center of autonomic controlfor heart, lungs, digestive system

CerebrumConsciousthought,memory

CerebellumCoordinationof complexmotor 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 touchand of temperature

Lefthemisphere

Intra-abdominal

Tongue

TeethJaw

Lips

NoseE

yeThum

bFingers

Hand

Arm

Head

Trun

k

Hip

Le

gG

enita

ls