1.6 Nervous System and Hormones

Nervous system

network of nerve cells and fibres to transmits nerve impulses between parts of the body

Stages of electrical impulses mnemonic

• Simon- Stimulus

• Receives- Receptor

• Scented- Sensory Neurone

• Red- Relay Neurone

• Motors- Motor Neurone

• Every- Effector

• Rest day- Response

Neurones

transmit electrical impulses quickly

Central nervous system (CNS)

brain and the spinal cord

Stimulus

change in our surroundings/ environment

Receptors

structures that are sensitive specific stimuli

Coordinator (CNS)

formulates and decides a response before impulses are sent to an effector

Sensory neurone

carries impulses from the receptor to the coordinator

Relay/ Association neurone

connects the sensory neurone to the motor neurone via synapses

Motor neurone

sends impulses from the coordinator to effector

Effector

produces a response to stimulus e.g muscles contracting or glands secreting

Reflex arc

fast and short nerve pathway for reflex actions

Voluntary responses

require conscious thought and involve brain but are a lot slower due to thinking

Reflex responses

happen quickly without thinking (involuntary), usually protecting the body from harm

Nervous system communications

• Speed- fast and short lived

• Nature of response- electrical/ nerve impulses

• Pathway- travels by neurone

• Target- effector

• Type of response- involuntary or voluntary

Hormonal system communications

• Speed- slow and lasting

• Nature of response- hormones/ chemicals

• Pathway- travels in blood

• Target- organ

• Type of response- always involuntary

Similarities in the nervous and hormonal systems

• send messages around our body

• enable the body to respond to stimuli

Eye

specialised sense organs that contains receptors sensitive to light

Conjunctiva

thin and transparent protective outer covering that prevents entry of microorganisms

Cornea

transparent part at front of eye allowing light to enter and causes slight bending/ refraction

Pupil

opening in the iris that allows light into the eye

Iris

coloured part behind cornea that regulates size of the pupil to control how much light enters

Lens

transparent to bend/ refract light so focuses towards the retina

Ciliary muscles

muscles which relax or tighten to adjust the suspensory ligaments and change the shape of the lens

Suspensory ligaments

ligaments to adjust the shape of the lens when focusing

Aqueous humour

watery fluid in the front to maintain shape of the eyeball and lens

Vitreous humour

jelly-like substance to maintain shape of the eye and push the retina against the wall

Retina

surface at the back of the eye containing light sensitive receptor cells

Optic nerve

carries neural impulses from the receptor cells to the brain

Reflex response to dim light

pupil dilates so more light can enter

Reflex response to bright light

pupil constricts so less light can enter

Accommodation

ciliary muscles and suspensory ligaments change shape of the lens to focus different distances

Focusing on a near object

• ciliary muscles contract

• suspensory ligaments loosen

• lens is thicker and refracts light rays strongly

Focusing on a distant object

• ciliary muscles relax

• suspensory ligaments pull tight

• lens is pulled thin and only slightly refracts light rays

Synapse

junction between two neurones creating a link to allow impulses to pass between

Neurotransmitter

chemical released from ends of active neurone to diffuse across synapses

How are neurones transmitted across synapses

• When impulses reach the end of axon, transmitter chemical is released

• Chemical diffuses across the gap

• If in high enough concentration an electrical impulse triggers in the next neurone, allowing the signal to continue

Adaptations of neurones

• cell body contains cytoplasm and nucleus

• long extension (axon) of cytoplasm allows nerve impulses to travel over long distances

• myelin sheath is a fatty layer surrounding axon and acts as an insulator to speed up impulses

• dendrite (branched ends) of axon allow many connections with other neurones

Homeostasis

maintaining a constant internal environment for proper functioning of cells and enzymes in response to internal/ external change

Hormones`

chemical messengers produced by glands and released into the blood, carrying them to target organ where they act

Examples of hormones

• Insulin

• ADH

Pancreas

monitors blood glucose concentration and produces insulin in response to an increase

How does insulin lower blood glucose levels

• increases glucose absorption from the blood by the liver and muscles

• respiring absorbed glucose

• converting excess to glycogen which is stored

Glycogen

carbohydrate that acts as an energy and glucose store in animals

Diabetes

condition in which blood glucose level control fails

Type 1 diabetes

• develops usually early in life

• pancreas stops producing insulin

• treated through insulin injections

Type 2 diabetes

• progressive disease linked to lifestyle factors

• pancreas gradually produces less insulin

• treated in early stages by controlling diet/ exercise but may require insulin injections

Symptoms of diabetes

• glucose in urine as high concentration is filtered out by kidneys

• high blood glucose levels

• being thirsty

• excessive urination

• lethargy (feeling tired/ low energy)

Increase in type 2 diabetes

• poor diet leads to weight gain and obesity, which raises the risk

• aging population where older people are more likely to develop it

• modern, less active lifestyles with less exercise contributes

• better awareness and improved medical testing so more are diagnosed

• family history makes some people more likely to inherit it

• increased access to foods such as sugars and lipids

Long-term effects of diabetes

• eye damage

• kidney failure

• heart disease

• strokes

Glucagon

released by the pancreas to convert glycogen in liver back into glucose to raise blood levels

Negative feedback cycle

change brings about a process that causes the opposite effect, keeping levels constant

Purpose of negative feedback

ensure concentration does not deviate too far from normal, maintaining homeostasis

Negative feedback via insulin

• High concentrations of glucose can be detrimental so should be controlled

• Body detects if levels are too high and signals pancreas to release insulin

• Reduces levels of glucose back to normal

Osmoregulation

controls water levels in the body to bring volumes back to balance as poor control can damage cells

Function of the kidneys

• removing waste from body through urination (excretion)

• controlling water balance in the body by osmoregulation

How water is gained

• drinking

• eating

• product of respiration

How water is lost

• evaporation in breathing

• evaporation of sweat by skin

• production of urine by kidneys

Filtration

separation of molecules depending on blood concentration, if too dilute less water is reabsorbed producing more urine

Selective reabsorption

reabsorbing only key molecules while leaving waste to be excreted

Excretion

molecules not reabsorbed are removed from the body through urination

How the kidney works

• Blood enters kidney via the renal artery

• Substances are filtered out in the cortex

• In medulla some substances are reabsorbed back into the blood until normal concentrations reached

• Substances left over pass into urine, which collects in the pelvis

• Urine passes into the ureter and is stored in the bladder

• Urine is passed out the body via the urethra

Anti-diuretic hormone (ADH)

• if brain detects lower water levels ADH is produced in pituitary gland

• causes kidneys to reabsorb more water into the blood

• produces lower volume of concentrated urine

• returns blood water levels to normal

Auxins

plant hormone that controls cell growth in response to light

Phototropism

change in the direction of a plant in response to light meaning it receives more light, more photosynthesis and more growth

Effect of auxins in shoots

1. Auxin is produced at the tip of the shoot and moves down

2. Light coming from one side causes uneven distribution through diffusion (more on shaded side)

3. Auxin causes cells on shaded side to elongate faster, known as differential growth

4. Causes stem to bend towards light

Foil covering plant shoot tips

shoots grow upwards but not towards light, suggesting the tips are sensitive to light