Coordination & Regulation

Nervous Systems

Case study : Optic nerve

The optic nerve connects the eye to the brain. Damage to this nerve will result in blindness One disease that causes this is glaucoma

In the chamber between the cornea and iris, a clear fluid is formed and drained

If draining is inhibited, this can cause the intraocular pressure (IOP) to build up

Symptoms: nothing → eye pain → lose sight from corners of eye → tunnel vision → blindness

Early diagnosis can slow / prevent onset of disease

The Human Eye

The Nervous System

Central Nervous System (CNS) Brain Spinal Chord

Peripheral Nervous System Sensory (afferent): Information to the CNS

Somatic sensory neurons (from external env.) Visceral sensory neurons (from internal env.)

Motor (efferent): Information from the CNS Somatic system (mainly voluntary actions) Autonomic system (mainly involuntary actions)

Sympathetic (senses aroused – eg. fight or flight) Parasympathetic (relaxed state)

xcvb

Nerve Cells

Cell Body

Axon

Myelin sheath

Synaptic Terminals

Dendrites

Note the direction ofnerve impulse

Different Types of Neurons

a) Affector (sensory) neurons: body to CNS

b) Effector (motor) neurons: CNS to body

c) Connecting neurons (affector to effector in CNS)

Nerve Impulses

In a relaxed state, the external environment of a neuron is more positive than the interior

Stimulated receptors will cause sodium ions to be imported, enough will start an action potential

The impulse moves down the cell as sodium ions are imported, resting potential is restored as potassium ions are exported.

Myelin Sheath

Our neurons start myelinating from birth Myelination is usually complete by age 30 Works as a kind of insulation around our

neurons An impulse will move down the axon of an

unmyelinated neuron at 0.5 m/s An impulse will move down the axon of a

myelinated neuron at 200 m/s

Communication Via Neurotransmitters

Once an action potential (nerve impulse) reaches the axon terminal of the neuron it triggers the intake of calcium ions

This results in the exocytosis of a vessicle bound neurotransmitter (usually acetylcholine)

As the neurotransmitter binds to the receptor mediated proteins on the corresponding neuron, sodium ions are imported and the action potential continues

Neurotransmitter animation

More on Neurotransmitters

Vessicles containing neurotransmitters are only located at the synaptic end of the axon

The gap between the synaptic terminal of one neuron and the dendrite of another is called the “synaptic cleft”

The gap between the synaptic terminal of one neuron and a muscle is called the “nerve-muscle junction”

The action triggered by a nerve is short lasting as the recipient muscle or gland releases enzymes to inactivate the neurotransmitter substances

Neurohormones

Neurohormones involve cooperation between the nervous and endocrine system to maintain homeostasis

Neurohormones are carried on the blood Eg. the hypothalamus releases a particular

neurohormone to trigger the pituitary gland to release a corresponding hormone:

Nerve networks – converging or diverging

There can be hundreds of axon terminals synapsing with a neuron

A neuron can synapse with any number of other neurons

Hence, there are no discrete linear pathways, bat rather a network of activated or inhibited neurons contributing to the ultimate action

NOTE: The outcome is not just determined by the number of activation / inhibition messages but is also dependent on their relative strength

Nerve networks – converging or diverging

Diverging network

Converging network

Depending on signal, networks can operate in one way or the other

Impediment of Neuron Function

Can be caused by drugs or disease and have many consequences: eg. non-functioning thyroid can result in weight

loss, increased appetite, heart tremors, muscle wasting.

Can be caused by toxins contained in venom Cytotoxic – causes cell death (necrosis) Haemotoxic – effects blood cloting and ability

to carry oxygen Neurotoxic – details on following slide

Neurotoxic Venom

Venom is simply modified saliva containing toxins

Found in many Australian spiders & snakes eg. Red Back, Funnel Web eg. Inland Taipan, King Brown, Death Adder

Some bacteria produce neurotoxins

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Porcupine fish and Funnel Web spider Small toxin, fast acting, fast dispersal Interferes with movement of Na+ ions, thereby

preventing particular nerve impulses

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Red Back spider Larger toxin Causes

neurotransmitters to trickle out of neuron

Message does not reach muscle = paralysis

Parasitic tick Larger toxin Inhibits release on

neurotransmitters Message does not

reach muscle = paralysis

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Snakes Neurotoxins effect the permeability of the pre

& post synaptic membrane May results in muscle damage May result in kidney failure due to large

amounts of protein in bloodstream

The good news is that many antivenoms & antitoxins have been developed that act as antibodies, in that they will bind and interfere with toxin.

Central Nervous System

Protection Bone (skull / vertebrae) Meninges (membrane) Fluid (between membrane & tissue) –

cushioning NB – If a problem is suspected, diagnosis is often

possible through analysis of cerebrospinal fluid

The Brain

The Brain

Cerebrum - Largest part of the brain is the The 2 hemispheres are joined by many axons Folded surface is called the cerebral cortex

Thalamus - receives impulses from sensory organs and directs these for processing

Hypothalamus – responsible for hormone production and many aspects of homeostasis

Brain Stem (midbrain, pons and medulla oblongata) – essential for survival as it controlls breathing and heart rate.

Mapping the Brain

Most easily done by observing the effect on the person after they have damaged a certain part of their brain.

More complex functions require more neurons, therefore a larger part of the brain is dedicated to this task

Neck

Hands and fingers

Mapping the Brain

Neural energy is electrical and can be measured via an EEG (electroencephalogram)

There is an EEG range considered as normal Values outside the

normal range may indicate brain damage

Flat EEG indicates that brain / person is dead

Sensory detectors from body go via spinal chord to brain

Grey matter (cell bodies)

White matter (axons) Surrounded by bone

(vertebral column) Cartilaginous discs

between vertebrae provide shock absorption and flexibility

The Spinal Chord

Brain Scanning

PET (positron emission tomography) detects amount of glucose being used by cells Damaged sections need glucose for repair Tumours have very high glucose requirements

CAT (computerised axial tomography) emits very density sensitive x-rays from multiple positions Images appear as “slices” of the brain Tumour cells are much denser than normal

cells

Comparison between nerves and hormones

Hormones Slower acting Longer lasting

Nerves Faster acting Faster dissipating

Both Rely on chemical messengers

Hormones (in bloodstream) Nerves (over synaptic cleft)

Comparison between nerves and hormones (continued)

Nerves - inactivation of neurotransmitters almost instantaneous

Hormones Adrenaline can dissipate in minutes Insulin can persist in bloodstream for hours Thyroxin can remain active for up to a week

What is the control mechanism?

Melanin is a cell pigment that if spread evenly causes the cell to be dark in colour. If melanin clumps toward the centre, the cell will appear light in colour.

Arctic hares are brown in summer and white in winter

HORMONAL Chamelions can change

colour in seconds

NERVOUS

Neurons and Homeostasis

1 neuron = 1 type of neurotransmitter = 1 action Activation or inhibition determined by individual neurons. Neurons maintain homeostasis through their actions on

glands or muscles

NothingActivate

Homeostasis – Nerves & Hormones Acting Together

Just like hormones, homeostatic systems relying on the nervous system also uses negative feedback loops

Blood glucose is not all hormonally controlled. Sensory nerves in the intestines will

stimulate insulin production due to the amount of glucose entering the system as a result of digestion

Control of Blood Pressure

Maintaining Core Temperature

Maintaining Water Balance Osmoreceptors in hypothalamus detect high solute

concentration in blood This triggers the posterior pituitary gland to produce

vasopressin Vasopressin increases permeability of distal tubules &

collecting ducts in nephrons Therefore more water is reabsorbed

Osmoreceptors also trigger nerves that generate a sensation of thirst More water is consumed

Pressure-sensitive detectors in kidneys detect drop in blood pressure Renin is released in the kidneys This triggers the release of aldosterone which encourages

greater reabsorption of Na+ from filtrate Water follows the passage of Na+ via osmosis

Neuron

Neurotransmitter

Neuron

Neurohormone

Homework!!!

Chapter review questions: 2-7 & 9 Biozones: