RESPONDING TO THE ENVIRONMENT (HUMANS)

• nervous system (involving nerves) • endocrine system (involving hormones)

• reaction to stimuli (stimuli can be external and internal) • coordination of the various activities of the body

nerves send and carry signals to and from all parts of the body and are made up of neurons

SENSORY: * conduct nerve impulses from the receptors to the CNS and are mostly unipolar MOTOR: * conduct nerve impulses from the CNS to the effectors and are multipolar

CELL BODY: * consists of cytoplasm and a prominent nucleus. * cytoplasm contains dark granules which are rich in RNA and involved in protein synthesis DENDRITES: * conducts nerve impulses towards the cell body AXONS: * conducts nerve impusles away from cell body MYELIN SHEATH: * the myelin sheath insulates the nerve fibres and accelerates the transmission of nerve impulses

• largest part of the brain, folds and grooves that enlarge the brain surface • controls voluntary actions • receives and interprets sensations from sense organs • higher thought processes

• c-shaped structure between the two hemispheres of the cerebrum • connects the left and right hemispheres of the brain - allowing communication between both hemispheres

• situated behind and below the cerebellum • coordinates all voluntary movements • controls muscle tension to maintain balance

• an extension of the spinal cord and has the same structure • transmits nerve impulses between the spinal cord and the brain • controls involuntary actions

• starts just below the foramen magnum and extends through the vertebral canal of the vertebral column of the lumbar region • provides a pathway for nerve impulses to and from the brain. nerve impulses from receptors enter the spinal cord via spinal nerves. impulses are then transmitted along ascending tracts in the spinal cord to the brain. the impulses are transmitted from the brain, via motor neurons in descending tracts, back down the spinal cord • the spinal cord contains reflex centres that initiate reflex

• starts just below the foramen magnum and extends through the vertebral canal of the vertebral column of the lumbar region • provides a pathway for nerve impulses to and from the brain. nerve impulses from receptors enter the spinal cord via spinal nerves. impulses are then transmitted along ascending tracts in the spinal cord to the brain. the impulses are transmitted from the brain, via motor neurons in descending tracts, back down the spinal cord • the spinal cord contains reflex centres that initiate reflex actions.

• 12 pairs of cranial nerves to/from the brain • 31 pairs of spinal nerves to/from the spinal cord • conducts nerve impulses from the receptors to the CNS via the sensory neurons • conducts nerve impulses from the CNS to the effectors via the motor neurons

• heart - increases heart rate, decreases heart rate • blood vessels in skin - blood vessels constrict, blood vessels dilate • blood vessels of the heart, lungs and skeletal muscles - blood vessels dilate, blood vessels constrict • digestive system - decreases peristalsis and digestion, increases peristalsis and digestion • muscles of the bronchioles - muscles relax and bronchioles dilate, muscles contract and bronchioles constrict • muscle of the eye - radial muscles contract, circular muscles relax, pupils dilate , radial muscles relax, circular muscles contract, pupils constrict • sweat glands - stimulates sweat production • liver - stimulates conversion of glycogen to glucose • adrenal medulla - stimulates the release of adrenalin

• a reflex action is a rapid, involuntary response of an effector to a stimulus received by a receptor • a reflex arc is the pathway along which nerve impulses are transmitted from a receptor to an effector to bring about a response to a stimulus during a reflex action

• the SNS prepares the body for an emergency • the PSNS allows the body to return to normal after stimulation by the SNS

• receptor: detects a stimulus and converts it into a nerve impulse • sensory neuron: conducts the nerve impulse from the receptor to the grey matter of the CNS • interneuron: carries the impulse from sensory neuron to the motor neuron in the spinal cord • motor neuron: conducts the nerve impulse from the CNS to the effector • effector: muscle or gland that responds to the original stimulus

• the heat stimulus is detected by the receptors in the skin of the hand and converted into a nerve impulse • the nerve impulse is conducted along a sensory neuron through the dorsal root of the spinal nerve to the grey matter of the spinal cord • the sensory neuron is in synaptic contact with the interneuron in the grey matter of the spinal cord. the nerve impulse is conducted across the synapse to the interneuron, which serves as the reflex centre • the interneuron is in synaptic contact with the motor neuron in the grey matter of the spinal cord. the nerve impulse is conducted across the synapse to the motor neuron • the nerve impulse exits the spinal cord through the ventral root of the spinal nerve and is conducted along the axon of the motor neuron to the effector

• reflex actions protect the body from injury • it allows for faster reactions since higher centres of the brain are not immediately involved, and it is not always a conscious response

CAUSES: * develops very slowly as a result of a complex series of changes in the brain * plaque is formed between the neurons * tiny fibres become tangled inside the cell bodies of the neurons * a shortage of the neurotransmitter acetylcholine, occurs at the synapses * these changes cause healthy neurons to become less and less efficient because the transmission of nerve impulses between neurons is restricted. the neurons decay and the affected parts of the brain shrink SYMPTOMS: * memory loss and confusion increases * cant recognise family and friends * the ability to learn new things or handle new situations decreases. * tasks involving multiple steps become impossible * increasing aggression, irritability and mood swings * ability to speak decreases * when the brain has shrunk considerately, the sufferer cannot communicate any longer and is completely dependent on others for care. a loss of body functions ultimately leads to death.

CAUSES: * more common in colder countries * viral infections act as a possible trigger * genetic factors seem to play a role * exposure to various environmental stresses may also trigger the onset of MS SYMTOMS: * loss of speech * inability to walk * numbness in arms or legs * loss of vision * tingling sensation or pain * fatigue or weakness * loss of memory, emotional instability and mood swings

the body responds to a variety of different stimuli, such as: * light * sound * touch * temperature * pressure * pain * chemicals

• sclera - protects the eye against damage. gives shape to eyeball. its a tough membrane • choroid - supply the eye with nutrients and oxygen. prevents internal reflection of light. a dark coloured layer, rich in blood vessels • retina - converts light stimuli into verse impulses. contains the light-sensitive receptor cells, i.e. the rods and cones • optic nerve - transmit impulses from the retina to the cerebrum (sensory neuron) • ciliary muscle - contracts and relax to change the shape of the lens • suspensory ligaments - holds the lens in position. it is elastic • lens - changes shape for near and distant vision/refract light to fall on the retina. bi convex: refracts light. transparent membrane: allows light through • pupil - allow light to enter the eye • iris - controls the amount of light entering the eye/changes the size of the pupil • cornea - responsible for the refraction of light rays. convex in shape: allows refraction. transparent: allows light to pass through. • conjunctiva - protective function: protects the eye from dust and infection-causing microorganisms • yellow spot - area containing lots of cones. best image formed here • blind spot - no images formed here. optic nerve leaves the eye at the blind spot • vitreous humour - gives shape to the eye • aqueous humour - supports cornea and the front chamber of the eye

• the ability to maintain visual focus on an object with both eyes open • it allows a person to judge distance and depth

accommodation is the adjustment of the shape of the lens to see objects clearly whether they are far away or close by. DISTANT VISION: * ciliary muscles relaxes * suspensory ligaments become taut * tension on the lens increase * lens becomes less convex NEAR VISION: * ciliary muscles contract * suspensory ligaments slackens * tension on lens decreases * lens become more convex