Brain and Nervous system

The cerebrum - what makes us human

• this is the largest part of the brain
• it is divided into two cerebral hemispheres, left and right
• these are joined by corpus callosum
• the outermost layer has a surface area of 2.5m^2 and it is folded
• it consists of a thin layer of nerve cell bodies known as cerebral cortex
• this area is highly developed in humans than in any other orgnisms
• The cerebrum contols the higher brain functions such as
• concious thoughts and emotional responses
• the ability to override some reflexes
• features associated with intelligence, such as reasoning and judgement

• Two areas of the brain (most found in the left cerebral hemisphere) are associated with understanding language and speaking
• these a Broca's area and Wernicke's area. Damage to these cause problems with understanding language.
• damage to Bronca's area will result with an inability to speak
• damage to Wenicke's area causes trouble understanding language.
• they are connected by a bundle of neurones
• if broke - unable to speak but understand the language
• visual sensory and association - Wernicke's area
• hearing sensory area - Broca's area

The cerebellum - movement and postures

• the concious decision to move voluntary muscle is initiated by the cerebral hemispheres
• the fine control of muscular movements requires a significant level of non-concious operation and involves the cerebellum e.g. walking and riding a bike
• examples - responding to changes in the body position to remain balanced and upright
• judging the position of objects and limbs
• tensioning of muscles in order to manipulate tools effectively
• feedback information on muscle position, tension and fine movement
• Neurones in cerebellum carry impulses to the motor areas so that motor output the effectors can be adjusted appropriately
• often feels like we are on 'auto-pilot' some activties become programmed into the cerebellum e.g. catching  a ball
• the cerebellum contains over half of the nerve cells in the brain

Key role in balance and fine movement

• the cerebellum processes sensory information from
• the retina
• balance organs in the inner ear
• joints
• specialised fires in muscles called spindle fibres which relay information about muscle tension

Hypothalamus

• controls the body's homoeostatic mechanisms
• temperature regulations - input from thermoreceptors
• osmoregulation - input from osmoreceptors
• controls much of the endocrine function because it regulates pituitary gland

Medulla oblongata

• controls non-skeletal muscle eg. cardiac muscle, smooth muscle of the gut
• effectively in control of autonomic nervous system
• contains regulatory centres such as cardiac centre and the respiratory centre
• contains reflex centres for vomiting, coughing sneezing and swallowing

RESPONDING TO THE ENVIRONMENT

• The CNS (central nervous system) is a way of connecting sensors with effectors
• this is significant if living things are to escape predation, control balance and regulate temperature
• the nervous system is made up of the CNS and peripheral nervous system

CNS

• the central nervous system is made up of the brain and spinal cord
• it is made up of grey matter and white matter
• grey matter has billions on non-myelinated nerve cells
• white matter has longer, myelinated axons and dendrons

Peripheral nervous system

• relays impulses from sensors to the CNS
• it then relays impulses from CNS to effectors (motor neurones)
• this peripheral nervous system is divided into sensory and motor systems

Motor system

• the motor system is divided into
• somatic motor neurones - impulses from the CNS to skeletal muscle which are under voluntary concious control
• autonomic motor neurones - impulses from the CNS to cardiac muscle, smooth muscle in the gut to glands, involuntary (subconscious) control

Somatic v Autonomic

• Autonomic neurones are non-myelinated
• Somatic neurones are myelinated
• Autonomic connections to effectors consists of two neurones (connect at a ganglion)
• somatic connections to effectors consist of one
• autonomic
• independent of concious control
• controles homoeostatic mechanisms
• autonomic motor neurones occur in 2 types
• sympathetic
• dilates pupils
• no effects on tears glands
• accelerates heart, constrict arterioles
• dilates bronchi
• relaxes bladder
• most active in times of stress
• the neurones of a pathway are linked at a ganglion just outside the spinal cord. pre-ganglionic neurones are very short
• post-gaglionic neurones secrete noradrenaline t the end of the synapse etween neurone and effector 
• parasympathetic
• constricts pupil
• stimulates tear glands
• inhibits heart, dilates arterioles
• constricts bronchi
• contracts bladder
• most active in sleep and relaxation
• the neurones of a pathway are linked at a ganglion within the target tissue. pre-ganglionic neurones carry considerable in length
• post-ganglionic neurones secrete acetyl-choline at the synapses between neurone and effector

Why plants respond to the environment?

Plants responds to a stimuli

• When a plant responds to a directional stimulus by a growth movement it is known as tropism
• If growth is towards the stimulus it is known as positive tropism
• if growth is away from the stimulus it is described negative tropism

Tropisms

• Light
• response: phototropism: eg. shoots grow towards a light source (positively phototropic)
• Gravity
• Geotropism: e.g. shoots grow away from gravity (negatively geotropic) but roots grow in the direction of gravity (positively geotropic)
• Chemicals
• Chemotropisim: e.g. pollen tubes grow down style attracted by chemicals
• Water
• hydrotropism: e.g. roots grow towards water (positive hydrotropic)

Hormones

• Auxins e.g. IAA
• promote cell elongation
• inhibit growth of side shoots
• inhibit lead abscission (leaf fall)
• Cytokinins
• promotes cell division
• Gibberellins
• promotes seed germination and growth of stems
• Abscissic acid
• inhibits seed germinationa nd growth
• causes stomatal closure when plant is stressed due to low water availibility
• ethene
• promotes fruit ripening

Growing regions

• Growth only happens in particular places in plants called meristems
• where there a groups of immature cells capable of dividing
• apical meristems - located at the tip/apex of roots and shoots, lengthening growth
• lateral bud meristems - found in the buds, could give rise to side shoots
• lateral meristems - found in a cylinder near the outside of roots and shoots widening growth

voluntary muscle - skeletal muscle brief notes

• muscles attach to bones by tendons - which are made of collagen
• bones to bones = ligaments
• muscles work in pars - oppose each other - antagonistic 

complex joing e.g. wrist has whole range of movement you need a complex series of muscles = synergist
if a join does a lot of movement it needs to be lubricated - use synonial fluid - made by the synorial membrane

skeletal of voluntary muscle

muscle is made up of bundles of muscle fibre and each muscle fibre is a giant cell with many nuclei

each muscle fibre is made up of bundles of myofibrils each myofibril is made off bundles of myofilaments which are proteins, myosim and actin

became myofils are inside giant fibre they can be called organelles

how muscles contracts - sliding filament theory and power stroke

Actin = globular protein which join together like string of heads

2 actins twist around each other - they have binding sites to the myosin head

troponin has 3 binding sites: 1 to troponin and actin and ca^++

POWER STROKE

• nervous impulse arrives at the neuromuscular junction an releases acetyl-choline 
•  DEPOLARISES 
• sarcolemma going into the centre of cells to T tubes - releases calcium ions from sarcoplasmic reticulum
• calcium ions binds to the troponin 
• troponin moves tropomyosin exposing thebinding sites on the actin
• myosin head flips through 45 degrees = power stroke
• pulling the actin
• ATP binds to the head - head = ATPase - ATP > ADP + phosphate > eergy
• energy unbinds the head to the binding site in ATP - head flips back to bind to next binding site
• this continues to happen power stroke is the flipping of the head
• actin is made to slide over myosin
• sarcomere - Z - Z shortens from 2.5 um to 2 um
• after contraction calcium ions move back to sarcoplasmic reticulum by active transport

• when myosin head binds to the actin band is known as cross link
• as the muscle contracts the A band always stays at thesame length
• H band gets shorter and may disappear
• I band - actin on its own will get shorter
• Z-Z = sarcomere shortens

Fight - flight - scared

• e.g. heart rate increase, breathing rate increases, depth increases, pupils dilate
• release endorphins in brain (natural pain killers)
• stressor - stimulus that causes stress
• humans are intelligent - so we can percieve stress e.g. when OFSTED come we know theyre not going to kill you
• percieve by cererum
• sends mpulse to the hypathalamus
• sympathetic nervous system stimulated release of adrenaline from adrennal medulla
• hypathtlamus releases a hormone aka CORTICOTROPHIN RELEASING FACTOR into the pitutitary - pituitury release adrenocorticotrophic hormone
• this makes adrenal cortex release more corticotrophic hormones

Hypathalaus - nervous tissues - release hormones

• lots of ways to animal deals with threats/stress
• animals deal w/ stress in different ways
• e.g. snakes place dead so they wont be eaten by the eagle
• some reptiles camouflage
• stress/hurting/digestion - are interlinkes
• stress-stomach ulcer

a2 biology: muscles

Muscles - three types

1. cardiac muscle cell
2. skeletal muscle cell
3. smooth muscle cell

Structure

• they are made up of elongated cels called fibres
• contraction is possible because the fibres contain filaments
• these filaments are made up of the proteins actin and myosin.

Involuntary muscle (smooth)

• this muscle is innervated (distrubution of nerves to an organ or body part) with neurones
• these neurones are from the autonomic nervous system
• as a result they are not under voluntary (concious) control

Types of smooth muscles

• Walls of intestines
• arranged in circular and longitudinal bundles
• Peristalsis - moves food along the intestines
• Iris of the eye
• circular and radial bundles
• controls the intensity of the light entering
• contraction of radial muscles dilates the pupil
• contraction of circular muscle constricts the pupil
• Walls of arteries and around arterioles' wall and cervix of uterus
• circular bundles
• important in temperature regulation, regulation of BP and redirecting blood flow
• contraction narrows vessel diameter
• relaxation causes dilation

Smooth muscle cells

• They are not striated like voluntary and cardiac muscle
• they are described as being 'spindle shaped'
• they contain small bundles of actin and myosin and a single nucleus
• when relaxed they are 500 µm and 5µm wide
• contraction is slow but the muscle tires very slowly

CARDIAC MUSCLE

• these are three types of cardiac muscle
• atrial
• ventricular
• specialised excitatory and conductive muscle fibres
• it contracts continuously, powerfully and without fatigue
• contraction of atrial and ventricular muscle is similar to skeletal muscle but for longer
• the excitatory and conductive fibred contract feebly
• they conduct electrical impulses and control the rhythmic heartbeat
• some cardiac muscle is myogenic
• capable of stimulating contraction without a nerve impulse
• cardiac cycle
• initiation of this rhythm comes from a patch of specialised excitatory and conductive muscle fibres in a small part of the right atrium
• this is called sino-atrial node (S.A.N)
• waves of electrical activity spread out rapidly over oth atria.
• the atrioventricular septum between the atria and the ventricles does not conduct the cardiac impulse from SAN
• another node made of specialised excitatory and conductive muscle fibres, the atrioventricular node (AVN) and t picks up atrial impulse
• this is transmitted along a bundle of modified cardiac fibre in the inerventricular septum
• this bundle of fibres is called the bindle of His
• when the impulse reaches the apex of the heart it spreads rapidly up the ventricular walls in a network of conductive fibred called the purkyne fibre

Role of autonomic nervous system

• neurones of the autonomic nervous system can carry impulses to the heart and regulate the rate of contraction
• sympathetic stimulates an increase
• parasympathetic stimulates a decrease
• Intercalated discs
• these are areas where adjacent cardiac muscle cells meet
• they are cell membranes with gap junctions with free diffusion ions
• this allow action potentials to pass easily and quickly

Voluntary (skeletal/striated) muscle

• Result in the movement of the skeleton at joins
• muscle cells form fibred about 100µm in diameter
• these contains several nuclei
• Each fibre is surrounded by a cell surface membrane called sarcolemma
• muscle cell cytoplasm is called sarcoplasm
• contains following organelles
• many mitochondria
• extensive sarcoplasmic reticulum
• a numer of myofibrils
• Myofibrils
• these are contractile elements
• each consists of a chain of smaller contractile units called sarcomeres
• this is the smallest contractile unit of a muscle
• within myofibrils there are two types of myofilaments
• thin actin
• thick myosin

The sarcomere

• the span from Z-line to the next is the sarcomere
• relaxed its around 2.5µm and shorter when contracted
• Z line gets closer durig contraction

Actin

• thin filaments are two strands
• mainly actin couled around each other
• each strand is made up of actin sub units
• tropomysin coils around actin to reinforce it
• a troponin complex is attached to the tropomyosin
• each troponin consist of 3 polypeptides (binding sites) for
• actin
• tropomyosin
• calcium ions

Myosin

• thick filaments arranged as bundles of protein
• each molecule is made up of a tail and two heads
• each filament consists of many myosin molecules with heads sticking out from opp ends

Succession

• Primary succession
• Begins in a place without soil
• sand dunes
• sides of volcanoes
• landslides
• flooding/land left after glaciation
• Starts with the arrival of living things such as LICHENS that do  not need soil to survive (called PIONEER SPECIES)
• Lichens - mutualistic relationship between algae and fungus
• algae photosynthesis - fungus absorbs water and minerals and cling onto rocks
• Soil starts to form as lichens and the forces of weather and erosion help break rocks into smaller pieces
• when lichens die, they decompose, adding small amounts of organic matter to the rock to make soil
• simple plants like mosses and ferns can grow in the new soil
• the simple plants die adding ore organic material
• the soil layer thickens and grasses and windflowers and other plants begin to take over
• these plants die thus more nutrients added to the soil
• shrubs and trees can survive
• insects smalls birds and mammals have begun to move in
• what was once a bare rock now supports a variety of life
• Secondary succession
• begins ina place that already has soil and was once a home of living organisms
• occurs faster and has different pioneers species than primary successin
• eg. after forest fires
• Climax community
• a stable group of plants and animals that is the end result of succession pricess
• does not always mean big trees
• grasses in prairies
• cacti in deserts

Galapagos islands - effects of human activities

• Charles Darwin visited the Galapagos island in 1835
• Native species of Galapagos
• Darwin's finches
• Giant tortoises
• Land iguanas
• Galapagos are the best conserved and have the highest number of native species.
• For these reasons, they are a world heritage site since 1978.
• Unfortunately, 50% of vertebrates and 25% of plant species are endangered.
• The population of Galapagos has grown in response to developing tourist trade
• Effect of human activities on the animal and plant population in the Galapagos Islands
• Habitat disturbance
• increased population has place demands on water, energy and sanitation
• more waste pollution
• demand for oil has increased
• an oil spill in 2001 had adverse effect on marine and coastal ecosystems
• increased pollution, building and conversion of land to agriculture have caused destruction. (Forests of scalesia trees and shrubs has been eradicated for agriculture)
• Over exploitation of resources
• harvesting whales and seals to sell internationally
• giant tortoises een killed and eaten (200, 000 tortoises taken in less than half a century)
• fishing for exotic species in 1990s have depleted population
• depletion of sea cucumber population has a drastic effect on under water ecology
• demand for shark fin had led to death of 150 000 sharks each year
• introducing new species
• deliberately brought in
• humans
• goats
• one of the most damaging species
• eats Galapagos rock purslane
• out competes tortoise for grazing and trampling on their food supply
• changes habitat reduced tortoise nesting sites
• cats
• fruits and veg
• unintentionally brought in
• insects
• diseases (malaria, bird flu etc)
• Charles Darwin research centre adopted strategies to prevent the introduction and dispersion of introduced species
• they have instigated a quarantine system, they search boats for foreign species
• natural predators have been exploited e.g. ladybirds to control a scale insect
• culling wild goats and pigs
• educating local people
• 
  

A2 biology: Ecosystem

Ecosystem - an interacting community of organisms, and the environment in which they live and with which they interact.  (Can be larger, e.g. African grassland, or small, e.g. pond)

Habitat - a place where an organism lives (e.g. an oak tree)

Population - a group of organisms of the same species which live in the same place at the same time and can interbreed with each other.

Community - all the populations of different species wo live in the same place at the same time and can interact with each other e.g. the woodland made up of a community with different trees, plants and animals etc.

Niche - the role o the organism in the ecoystsem. e.g. oak tree, produces O2, provides food a shelter for organisms, takes in CO2

Ecosystems are dynamic

• Ecosystems are constantly changing
• physical changes e.g. temperature
• changes in population due to predation disease etc
• human interferance
• pollution
• changes in soil condition
• Biotic and abiotic factors are constantly chnaging, a change in one factor can affect others