control systems

Hormone

A chemical messenger, usually a protein, peptide or steroid, which is produced by an endocrine gland and released into the blood plasma

Protein and peptide hormones

Polar, soluble in watery blood plasma but cannot diffuse through cell surface membranes w phospholipid bilayer- hydrophobic tail and hydrophilic head, hormone cannot enter w SIMPLE diffusion, needs channel / carrier protein

Adrenaline and ADH

Steroid hormones

Lipid based so non polar nature, insoluble in blood plasma so bind to specific plasma carrier proteins produced by the liver to move through the bloodstream, hydrophobic so can diffuse across cell membrane eg oestrogen and testosterone

Endocrine gland

Ductless glands that synthesise hormones and release them into the bloodstream

Secretory cells, many capillaries- rich blood supply

Pancreas- both endocrine-insulin and glucagon and exocrine- digestive hormones

How are protein/peptide hormones made

Protein synthesis, mRNA, moves out of nuclear pore, ribosome at rough ER, tRNA, Golgi

How are steroid hormones made

Cholesterol, smooth er, made on demand as they can’t be stored in vesicles- lipid soluble so would simply diffuse out

Position of hypothalamus, pituitary gland, thyroid gland, parathyroid gland, pancreas, kidneys, ovaries, testes

Anatomy of adrenal gland

Where is adrenaline released

Adrenal medulla

Anatomy of hypothalamus and pituitary gland

Pituitary gland

Produces and releases secretions which affect most of the other endocrine glands, has an anterior and prosterior lobe, controlled mostly by hypothalamus

Anterior lobe produces six hormones- thyroid stimulating, growth, ACTH, FSH, LH, prolactin- milk in mammary glands, develops from roof of mouth

Posterior pituitary- adh, oxytocin, outgrowth of hypothalamus

Hypothalamus

Monitors blood levels, controls pituitary gland, has receptors which monitor the levels of various chemicals in blood- neurosecretory cells, nerve cells which produce secretions from end of axons to control release of hormones

Neurosecretory cells 1- stimulate or inhibit from anterior pituitary, known as releasing factors/ release inhibiting factors

Neurosecretory cells 2- produce secretions which are stored in posterior pituitary and released later as hormones

Target cells

They can only affect cells w receptors

Integral proteins- in cell surface membranes, specific hormone receptors for polar protein or peptide hormones

Intracellular receptors- in cytoplasm, non polar steroid hormones

Oestrogen Transport and effects

Steroid hormones synthesised by ovarian follicles, non polar and hydrophobic so attached to plasma proteins for transport in plasma, stimulates monthly growth of endometrium, female sexual secondary characteristic

How does oestrogen work

Non polar so can diff solve in the lipid component of the phospholipid bilayer and move into cytoplasm w simple diffusion

binds to a specific receptor in the cytoplasm to form an oestrogen-receptor complex

Complex passes through nuclear pore to enter nucleus

Acts as a transcription factor by binding to a specific promotor region of DNA switching on the relevant genes, slow process

Transcription factor

Protein that binds to DNA and either inhibits or initiates the transcription of a particular gene

Promotor region

Specific DNA base sequence to which a specific transcription factor binds

Adrenaline control of release, transport

Hypothalamus activates a sympathetic nerve which sends the impulses to the adrenal medulla stimulating the release of adrenaline, polar so dissolves in the watery plasma, faster than oestrogen

How does adrenaline work

It is polar so it is unable to dissolve in phospholipid bilayer so it cannot diffuse across cell surface membrane. Adrenaline THE FIRST MESSENGER to a specific adrenlaine receptor to form a hormone receptor complex.

This complex activates a membrane bound protein- G protein

This activates a membrane bound enzyme called adenylate cyclase

Adenylate cyclase converts ATP to cAMP THE SECONDARY MESSENGER!!

Activates futher enzymes depending on target cell

Adrenaline sets off a chain reaction / cascade effect, one enzyme forms hundreds of cAMP, many enzyme molecules millions of products

Control of hormone release- ways they are released

1. Direct stimulation by nerves- adrenaline

2. Response to another hormone- oestrogen and fsh

3. Response to the levels of a specific chemical in blood- insulin

Neurones

Individual cells specialised for the rapid transmission of electrical impulses throughout organisms- sensory, motor, relay

Gilal cells

Cells that support, protect and maintain neurones eg the schwann cells that provide myelination to certain axons

Synapses

Specialised junctions between 2 neurones across which nerve impulses are transmitted by neurotransmitter chemicals

Nerves

A bundle of neurones axons encased in connective tissue can be motor sensory or mixed

Receptor cells and sense organs

Specialised cells which can respond to changes in the internal or external environemt. May be grouped together w other tissues to form sense organs

Effectors

Cells or tissues that bring about a response when stimulated eg skeletal muscle, smooth muscle, cardiac muscle, endocrine glands, exocrine glands

Structure and role of myelin sheath

A fatty layer fo/rmed from specialised glial cells called Schwann cells. Each Schwann cell is wrapped multiple times around the neurone, cell surface membrane has a high lipid content

Role of myelin sheath- protect neurone, insulates neurone increasing the spread at which nerve impulses travel along neurone fibres- saltatory conduction

Nodes of ranvier

The gaps between Schwann cells where neurone fibres are exposed to surrounding tissue fluid

Myelinated and unmyleinated

Vertebrates are myelinated and unmyelinated, invertebrates are unmyleinated

Voluntary movements- motor neurons, myleinated

Automatic- un

Sodium / potassium pumps

Active transport pumps that harness energy from ATP to pump 3Na+ out of the axon for ever 2K+ they pump in, involved in stabilising and maintaining resting potential

Potassium facilitated diffusion channels

Many of them, facilitate the diffusion of K+ ions down chemical and electrical gradients, resting potential

Sodium facilitated diffusion channels

Very few present, membrane is relatively impermeable to sodium at rest, resting potential

Sodium voltage gated channels

Diffusion of Na+ down a conc gradient when open, voltage gated means they open when membrane potential reaches a certain voltage, involved in depolarisation

Potassium voltage gated channels

Permit diffusion of K+ down a conc gradient when open, involved in repolarisation and hyperpolarisation

What is resting potential

The potential difference of around -70mV across the plasma membrane of a neurone when the neurone is not transmitting an impulse

Resting potential explanation

The sodium/potassium pump moves 3 sodium ions out of the axon for ever 2 potassium ions it moves in, requires ATP

The membrane is impermeable to Na+ so these ions cannot diffuse back into the axon

The membrane does have some K+ facilitated diffusion channels so these can move back out of the axon down their chemical gradient

The inside of the axon thus becomes more negative than the outside

This electrical gradient pulls some of the potassium ions back into the axon

There is an equilibrium between the chemical and electrical gradients at around -70mV and then no more K+ movement

Role of atp in sodium potassium pump

Needed for pump to work so for resting potential, toxins called metabolic inhibitors eg cyanide prevent the formation of ATP by respiration and so can stop the transmission of impulses

Action potential graph

Resting potential

The potential difference of around -70mV across the plasma membrane of a neurone when the neurone is not transmitting an impulse

Depolarisation

The potential difference across the membrane is reversed for about 1ms reaching a peak of around -40mV

Na+ voltage gated channels open, allowing the Na+ ions that were pumped out of the neurone by the Na+/K+ pump top rapidly diffuse into the neurone down their chemical conc gradient

This makes th inside more positive than the outside

Repolarisation

The potential difference across the neurone membrane returns to a negative resting value after the peak of depolarisation

Na+ voltage gated channels close, K+ voltage gated channel open allowing the K+ ions that were pumped into the neurone down their chemical conc gradient. This returns the inside to a more negative potential than the outside, repolarising the membrane

Hyperpolarisation

The potential difference of the neurone membrane temporarily becomes more negative than the normal resting potential

More K+ ins diffuse out than needed to reach the resting potential so the inside temporarily becomes more negative than the resting potential

Then the K+ voltage gated channels close

K+ ions diffuse back into the neurone through the K+ facilitated diffusion channels repolarising the membrane

The Na+ / K+ pump also works to maintain resting potential

Refractory period

The time taken for ionic movements to repolarise an area and then restore the resting potential so that another Acton potential can be formed

What is a synapse

The junction between two neurones or between a neurone and an effector across which nerve impulses transfer using neurotransmitters

Synapse between motor neurone and effector

Motor end plate or neuromuscular junction

What do synapses cause

Excitatory- cause excitatory post synaptic potentials (EPSPs) or be inhibitory and cause inhibitory post synaptic potentials (IPSPs)

Function of synapses

-allow neurones o inter communicate and to communicate with effectors

-allow integration of sensory inputs from many sources allowing the organism ro respond appropriately to multiple stimuli (convergence)

-increase the range of simultaneous actions that can take place in response to a stimulus (divergence)

-help to ensure one way transmission

-filter out low level stimuli

-involved in memory and learning

Synapse structure

Why can synapse only travel in one direction

Pre synaptic- post synaptic

Neurotransmitter only storied in pre synaptic neurone and receptors only present in post synaptic neurone

EPSP

Excitatory post synaptic potential

Depolarisation caused by an influx of Na+ ions into the post synaptic membrane in response to a neurotransmitter binding to a receptor

Increases likely hood of action potential forming

Inhibitory post synaptic potential

Hyperpolarisation caused by influx of Cl- ions into the post synaptic membrane in response to the binding of a neurotransmitter to a receptor

Dec liklihood of an action potential

The formation of an excitatory post synaptic potential

1. Action potential reaches the synapse