The Nervous System

Function

• The nervous system works with the endocrine system to maintain homeostasis.

– sensory receptors monitor changes in and out of the body

– process and interpret sensory input and make decisions on what should be done

– effect a response by activating (muscle, organ, glands)

Nervous System - OverviewTwo main components:

1. Central Nervous system: Brain and spinal cord

2. Peripheral nervous system: nerves that emerge from spinal cord and brain that go to other parts of the bodya. Afferent—

towards CNSb. Efferent—away

from CNS

Multipolar Neuron

Parts of a neuron

Types of neurons

Neurons in context

Neuroglia (CNS) Schwann and Satellite Cells (PNS)

ADAM-IAP modules (mount IP-10.iso before starting)

• Interactive Anatomy and Physiology Nervous I

Anatomy Review 4, 5, 6, 7, 9

Schwann CellsMyelin Sheath

How neurons communicate

• Simple animation of how neurons communicate (action potentials and neurotransmission)

• http://www.bris.ac.uk/synaptic/public/basics_ch1_2.html

• Overview of the whole system

Axon - Resting Potential

The normal voltage difference maintained across the membrane of the neuron. Excess positive charges accumulate on the outside of the cell while excess negative charges accumulate on the inside of the cell

This is results in a resting potential of about -70 mV

Gated channelsProteins that open to allow ions to flow across the membrane in response to a signal. There are two main types:--chemical (usually respond to a chemical like a neurotransmitter)--voltage (respond to a change in membrane potential voltage)

Action potential-generated at axon hillock—results in a large spike in voltage across the membrane as ions flow across the axon membrane—this spike tends to travel down the axon to the axon terminus where it triggers neurotransmitter release at the synapse-only triggered when voltage at hillock is greater than threshold potential (>~55mV)

Action Potential

• Simple animation of how neurons communicate (action potentials and neurotransmission)

Propogation of an Action Potential

Action Potential another view

Conduction VelocityIt’s all about resistance.

Axon diameter - larger the diameter, the less resistance for sodium to move along axon

Myelin sheath - prevents leakage of sodium as it moves along axon (saltatory conduction)

Note: alcohol, sedatives, anesthetics all block nerve impulses by reducing the membrane permeability to sodium ions (by blocking chemically-activated or voltage-activated channels)

ADAM-IAP Modules

Interactive Physiology and Anatomy Nervous I

The Action Potential 3, 4, 6, 7, 16

Synapses

• Junction between axon and post-synaptic cell (another neuron, muscle cell, etc)

• Action potential reaches end of axon, triggers release of neurotransmitters

• Neurotransmitters cause graded potential on post-synaptic cell

• Can cause excitatory post-synaptic potential (EPSP) or inhibitory post-synaptic potential (IPSP)

Synapse

Overview of neuron communication

• http://www.bris.ac.uk/synaptic/public/basics_ch1_3.html

• http://www.getbodysmart.com/ap/nervoussystem/neurophysiology/synapses/menu/menu.html

Synapses

Excitatory Post-Synaptic Pontentials (EPSPs) and Inhibitory Post-Synaptic Potentials (IPSPs)

Excitatory or Inhibitory?

• EPSP or IPSP?• Determined by which ion channels open up in the

postsynaptic cell.• Spatial summation • Temporal summation

• To see:• Interactive Physiology and Anatomy Nervous I• Nervous System 2 Synaptic Potentials 12• Synaptic Potentials and Cellular Integration 4, 5,

6, 7, 8, 9

Neuronal communication

http://thebrain.mcgill.ca/flash/i/i_01/i_01_cl/i_01_cl_fon/i_01_cl_fon.html

nt where action

glutamate CNS EPSPGABA CNS IPSPAcetylcholine* neuro-muscular EPSPAcetylcholine heart IPSP (parasympathetic)Norepinephrine* heart EPSP(sympathetic)Norepinephrine resp. IPSPserotonin CNS IPSPdopamine CNS EPSP

* Ach and NE are also released at other synapses in the PNS and CNS

Neurotransmitters - Actions

Drugs

cold/allergy med.- binds to all receptors non-specifically - drys mucosae, but also causes some CNS, HR, etc.

amphetamines - most increase release of NE, epinephrine, dopamine

botulism - bacterial toxin, prevents Ach release

valium - receptor for GABA is a fast Cl- channel leading to IPSPvalium binds to another site (allosteric) increasing action of receptor, thus more IPSP than nomal, relaxes anxiety, less stimulation

LSD/mescalin - bind to serotonin and some dopamine receptors - blocking and thus prevents normal nt inhibition of certain pathways

cocaine - blocks reuptake mechanism, increases nt release (dopamine, NE, serotonin synapses?)

nerve gas - inhibits Ach-esterase...problem especially in intercostal skel muscles.

Prozac - blocks re-uptake of serotonin, relieves anxiety/depression in some

caffeine - shaped like adenosine, an IPSP nt in brain, blocks receptors, but no action

ecstasy - broken down into HMMA which stimulates ADH release...alters kidney function , water conserved...problem with solute dilution in the brain, etc.

opium - mimics endorphins

Viagra - a different kind of neurotransmitter....NO is a gas released by some neurons locally in erectile tissue, causes vasodilation. Viagra blocks an enzyme that slows NO’s effects....so vasodilation at a max.

Neuronal circuits

Spinal Cord

Components of a Reflex Arc

Reflex Circuit

Stretch Reflex

A reflex arc also involves inhibiting muscles that oppose reflex action

The main parts of the human brain

Human brain (another view)

3D Brain (Genes to Cognition)

Brain functions

• Cerebral Cortex—– “higher” functions, consciousness, creativity, thought,

etc– Sensory integration and interpretation– Motor control

• Diencephalon (includes limbic system)– Limbic system—

• Amygdala: responsible for emotion, emotional learning• Hippocampus: memory formation• Hypothalamus—hormonal regulation, thirst, hunger, body

temp, fatigue, anger, circadian rhythms

– Thalamus—relay station for sensory impulses, impulses to and from cerebral motor cortex and cerebellum

• Brain stem– Pons—relay station for neurons entering and

leaving brain– Medulla Oblongata—regulate essential bodily

functions

• Cerebellum– Coordination of movement– Physical equilibrium

Human Brain - Superior view

Human Brain - Lateral view

Human Brain - Sectional view

Sheep Brain - ventral and dorsal views

Sheep Brain - Sagittal section

Structure and functional areas of the cerebrum

Localization of brain functionalities: TMS—DVD: “How Does the Brain Work” Chapter: Magnetic Simulation

Primary motor and somatosensory areas of the human cerebral cortex

Motor Cortex Somatosensory Cortex

Hemispheric Lateralization

Mapping language areas of the cerebral cortex

Brain circuitry

A more recent view of brain circuitry (diffusion tensor imaging)

Credit: M. D. Van Wedeen, Martinos Center and Dept. of Radiology/Massachusetts General Hospital/Harvard U. Medical School

Male (left)/female (right) brain wiring differences (Diffusion tensor imaging)

Sex differences in the structural connectome of the human brain http://www.pnas.org/content/early/2013/11/27/1316909110

Circuitry used in reading out loud

From: http://thebrain.mcgill.ca/flash/i/i_01/i_01_cr/i_01_cr_fon/i_01_cr_fon.html

Eyes to Thalamus first(Understanding words)

Syntax

Brain function while listening to music

Memory formation

http://www.stanford.edu/group/memorylab/Research/Research.html

Brain MRI

Localization of Brain Functions

Case studies of patients with brain damage or congenital defects reveal information about the various functions of the brain

The tale of Phineas Gage

• Premature explosion under a tamping rod resulted in the meter long rod (4-5 centimeters in diameter) entering under his left orbit, destroying much of his frontal lobe as it was propelled out of the top of his head (landing 300 feet away). Additional tissue was destroyed by subsequent infection.

Impact of this injury on Gage’s personality

• Gage was] fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operations, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. A child in his intellectual capacity and manifestations, he has the animal passions of a strong man. Previous to his injury, although untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart businessman, very energetic and persistent in executing all his plans of operation. In this regard his mind was radically changed, so decidedly that his friends and acquaintances said he was ‘no longer Gage'.

• J. M. Harlow, 1868 (Publications of the Massachusetts Medical Society 2: pp. 339–340)

Published by AAAS

N. H. Naqvi et al., Science 315, 531 -534 (2007)

Fig. 3. Whole-brain region-by-region logistic regression analysis

Insula involved in addiction (red/orange area in this image)

The limbic system

The Amygdala—seat of emotion in the brain?

Emotions

Fear: S.M. has damaged amygdala—can no longer recognize the emotion of fear

Associative learning of emotion in the amygdala

Affective (mood) disorders

Blood flow in the brain of a patient suffering from unipolar clinical depression, compared to non-depressed patients

Memory formation—case studies that shed light on location in the brain where new meories are formed

• The case of H.M.—After surgery to treat seizures, in which the amygdala, uncus, hippocampal gyrus and anterior two-thirds of the hippocampus were removed, H.M. could not form long-term memories

• The case of N.A.—a fencing foil poked into his right nostril damaged part of his thalamus and the medial temporal lobe on the right side as well as the mammilary bodies. N.A. has lost much of his ability to form long-term memories (retaining excellent memory of events prior to 1960)

• The case of R.B.—Suffered damage to the hippocampus (bilaterally) during cardiac surgery. Also impaired in his ability to form long-term memories

Brain areas associated with memory formation

Causes of amnesia

(Cerebral cortex?)

Religion and the brain

Increased activity in the frontal lobe, decreased in parietal lobe

Embryonic development of the brain

Brain Comparison

Reflex

• A reflex is a rapid, automatic response to a stimulus, in which a particular stimulus always causes the same motor response.

• Reflexes happen over neural pathways called reflex arcs. Essential components:– Receptor– Sensory neuron– Integration center– Motor neuron– Effector

Somatic & Autonomic: The Plumbing