homeostasis 🧠

what does the human nervous system consist of

1. central nervous system

2. peripheral nervous system

what is the central nervous system

the brain and spinal chord

what is the peripheral nervous system consist of

all the nerves in the body

what does the nervous system enable

humans to react to their surroundings and to coordinate their behaviours

what is a bundle of neurones known as

a nerve

adaptions of the nervous system

1. neurones have a cell body

2. some have axons over a metre

3. axons insulated by fatty myelin sheath with small uninsulated sections

what does the receptor detect

stimuli in the environment

what is the order of the pathway through the nervous system

stimulus - receptor - coordinator - effector - response

describe the nervous system

1. very fast

2. precise electrical impulses through nerves

3. responds quickly

4. faster

describe the endocrine system

1. relies on hormones

2. travel throughout entire body

3. only affects certain cells

4. longer lasting

5. more generalised

what is negative feedback

whenever the levels of something get too high they’re brought back down, and vice verse

what does an involuntary response not involve

the conscious part of the brain as the coordinator of the reaction

the process for reflexes

1. stimulus is detected by a receptor

2. sensory neurone sends electrical impulses to the spinal cord

3. passed to a relay neurone in the spinal chord

4. a relay neurone synapses with a motor neurone

5. a motor neurone carries an impulse to a muscle

6. muscle will contract

what are the three main types of neurones in a reflex arc

1. sensory

2. relay

3. motor

what do sensory neurons do

carry impulses from sense organs to the cns

what do relay neurones do

found inside the CNS and connect sensory and motor neurones

what do motor neurones do

carry impulses from the CNS to effectors

describe a sensory neurone

1. long

2. have a cell body branching off the middle of an axon

describe a relay neurone

1. short

2. have a small cell body at one end with many dendrites

describe a motor neurone

1. long

2. have a large cell body at one end

3. long dendrites branching off it

what are neurones separated by

synapses

how small are synaptic junctions

10nm in size

what chemicals are released into the synaptic cleft and diffuse across it

neurotransmitters

what is reaction time

time taken to respond to a stimulus

what can reaction time be affected by

1. age

2. stress

3. drugs

describe the cerebral cortex

• the outer layer of the brain

• divided into two hemispheres

• highly folded

what is the cerebral cortex responsible for

1. intelligence

2. memory

3. consciousness

4. personality

describe the cerebellum

underneath the cerebral cortex

what is the cerebellum responsible for

balance, muscle coordination and movement

describe the medulla

region that controls unconscious activities such as heart rate and breathing

describe the eye

• s a sense organ containing receptors

• sensitive to light intensity and colour

purpose of the eye

1. receive light and focus it onto the retina

2. adaption to bright or dim light

3. accommodation to focus on objects

function of the retina

controls the light receptor cells that detect light intensity and colour of light

function of the optic nerve

sensory neurone that carries electrical impulses from the eye to the brain

function of the sclera

the white layer of the eye that covers the eyeball

function of the cornea

transparent covering of the front of the eye that refracts light

function of the iris

controls how much light enters the pupils

function of the ciliary muscles

ring of muscles around the lens which relaxes and contracts to change the shape of the lens

function of the suspensory ligaments

work with the ciliary muscles to change the shape of the lens

function of the lens

transparent disc that changes shape to focus light onto the retina

what does the eye do when dim light

pupil dilates so more light can enter

what does the eye do when bright light

pupil constricts so less light enters

what is accommodation

the process of changing the shape of the lens to focus on near or distant objects

what does changing the shape of the lens alter

how much light is refracted

describe the eye muscles when focusing on a near object

• ciliary muscles contract

• suspensory ligaments loosen

• the lens is then thicker and refracts light rays more strongly

describe the eye muscles when focusing on distant objects

• the ciliary muscles relax

• the suspensory ligaments are pulled tight

• the lens is then thin and only slightly refracts light rays

what is the other name for short sightedness

myopia

what is the other name for long sightedness

hyperopia

describe how laser surgery works and the risks

• can be used to change the shape of the cornea

• all surgical processes have a risk of unexpected change occurring during the procedure which could lead to worse vision or an infection

how is myopia fixed with laser eye surgery

the cornea is slimmed down, reducing the refractive power

how is hyperopia fixed with laser eye surgery

the cornea shape is changed so the refractive power is increased

ways of treating eye defects surgically

1. laser eye surgery

2. lens replacement surgery

describe how lens replacement works and the risks

• completely replaces the lens of the eye with a plastic artificial lens

• more invasive than laser surgery and carries a risk of damage occurring to the retina, leading to complete sight loss

what temperature do enzymes work best at

37 degress celcius

what is body temperature monitored and controlled by

the thermoregulatory centre in the brain

what happens if body temperature is too high

• blood vessels dilate,the and sweat is produced from teh sweat glands

• cause a transfer of energy from the skin to the environment, cooling the body down

what happens if body temperature is too low

• blood vessels constrict and sweating stops and skeletal muscles contract to shiver

• these mechanisms reduce heat loss to the surroundings

what is the endocrine system composed of

glands which secrete hormones directly into the bloodstream

describe the pituitary gland

master gland. makes hormones such as fsh and lh

describe the pancreas

produces insulin which regulates the blood glucose levels

describe the thyroid

produces thyroxine, which controls metabolic rate and affects growth

describe the adrenal glands

produces adrenaline

what do the ovaries produce

oestrogen

what do the testes produce

testosterone

what is TSH and what does it do

thyroid stimulating hormone which secrets the thyroid to release thyroxine

what is excess glucose turned into and where

in liver and muscle cells, excess glucose is converted into glycogen for storage

what happens if theres too much glucose

cells of the body losing water by osmosis

can be very dangerous

what does the pancreas do if blood glucose concentration is too high

secretes insulin to bring it back down

what is type 1 diabetes

a disorder in which the pancreas fails to produce a sufficient amount of insulin to control blood glucose levels

describe type 2 diabetes

the body cells no longer responding to insulin produced by the pancreas - the person still makes insulin but their cells are resistant to it and dont respond as well as they should

what hormone does the pancreas secrete if glucose is too high

glucagon that causes glycogen to be converted into glucose and released into the blood

when is insulin produced

when blood glucose rises and stimulates liver and muscle cells to convert excess glucose into glycogen to be stored – this reduces the blood glucose level

when is glucagon produced

when blood glucose falls too low and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the bloodstream – this increases the blood glucose level

what does too much water in the blood result in

cells swelling as water moves into them, this has a diluting effect and can lead to bursting

what does too little water in the blood result in

the cells lose water by osmosis, this has a dehydrating effect and can lead to cell death

what are the 2 sources of water in the body

1. produced by aerobic respiration

2. water in the diet

how is water lost

1. leaves the body via the lungs during exhalation

2. water, ions and urea are lost from the skin in sweat

what do the lungs mainly excrete and why

carbon dioxide as a product of aerobic respiration during exhalation

what do the kidneys mainly excrete and why

excess water, salt and urea by producing urine

what is digestion of proteins from the diet resulting in

excess amino acids which need to be excreted safely as they cant be stored in the body in the same way that glucose can

deamination definition

the process of breaking down excess protein

mostly happens in the liver

how does deamination occur

1. enzymes in the liver split up amino acid molecules, with the part containing carbon turned into glycogen and the other part containing nitrogen turned into ammonia

2. ammonia is toxic to our cells and is immediately converted to urea which can be transported around the body safely for excretion by the kidneys