B3.1 - The Nervous System Flashcards
3 main stages to a nervous response:
- change in environment (stimulus)
- groups of cells detect stimulus (sensory receptors)
- response occurs from (effectors)
What are the different types of effectors and how to they respond?
- muscles (contracting, causes movement)
- glands (releasing hormones)
Where are receptor cells found, what do they do?
- in sense organs
- change stimulus into electrical impulse that will travel along neurones (nerve cells)
Central Nervous System:
What bones protect these delicate nervous tissue?
- brain (skull)
- spinal cord (vertebral column/backbone)
Name the types of neurone:
- sensory neurones
- relay neurones
- motor neurones
Sensory neurones:
Carry electrical impulses from receptor cells to CNS
- dendron transmits impulse to cell body
Relay neurones
Carry electrical impulses sensory neurones to motor neurones
- direction of impulse: dendrites to axon
- only found within CNS
Motor neurones
Carry electrical impulses from CNS to effectors
- axon transmits impulse away from cell body
Nerves:
Bundles of hundreds or thousands of neurones (nerve cells)
Flow diagram for nervous reaction steps:
Stimulus -> receptor cells -> sensory neurone -> spinal cord -> brain -> spinal cord -> motor neurone -> effector -> response
(0.7 seconds)
Why is the nervous system a coordinated response
- the brain processes the info from sensory respecters and sends series of impulses to part of body, controlling what happens
Reflex action:
= automatic/involuntary reactions
How long do reflex actions take compared to nervous reaction, why?
Reflex action = 0.2s
Nervous reaction = 0.7s
As reflex action misses out brain
Reflex actions that take care of basic bodily functions:
- breathing
- heart rate
- digestion
Reflex arc (flow diagram for reflex action)
Stimulus -> receptor cells -> sensory neurone -> spinal cord -> motor neurone -> effector -> response
Withdrawal reflex:
Body reacts before brain registers you are in danger
Parts of eye:
- cornea
- pupil
- iris
- lens
- ciliary body
- suspensory ligaments
- optic nerve
- retina
Cornea
- transparent coating on front of eye
- protects eye, refracts light entering eye
Pupil
- central hole in iris
- allow light to enter eye
Iris
- coloured ring of muscle tissue
- alters pupil size by contracting or relaxing
Lens
- transparent biconvex lens
- focuses light clearly onto retina
Ciliary body
- ring of muscle tissue
- alters shape of lens
Suspensory ligaments
- ligament tissue
- connects ciliary muscle to lens
Optic nerve
- nervous tissue
- carries nerve impulses to brain
How are images formed
- cornea refracts incoming light rays (provides focus)
- light passes through pupil
- further refracted by lens (creates sharp image on retina)
- photoreceptors in retina produce nervous impulse when exposed to light
- impulse travels down optic nerve to brain, interprets impulse as visual image
What are photoreceptors
Light sensitive cells found in the retina (tissue at back of eye)
How can you focus on nearby objects:
- ciliary muscle contracts
- lens becomes more convex (fatter)
How can you focus on distant objects:
- ciliary muscle relaxes
- lens becomes less convex (thinner)
Short sightedness:
= distant objects appear blurry
- lens too strong/eyeball too long
(Light rays meet in front of retina, image blurred)
Long sightedness:
= cant focus on nearby objects
- lens too weak/eyeball too short
(Light rays meet after retina, image blurred)
How to correct short sightedness:
Concave lens bends light rays outwards before they enter eye
Light rays now meet on retina, image focused
How to correct longsightedness:
Convex lens bends light rays inwards before they enter eye
Light rays meet on retina, image focuses
Types of photoreceptors:
- rods: respond to light, allow you to see in low light levels
- cones: respond to different colours
Most common form of colour blindness:
- red-green, cant distinguish between red & green light
- genetically inherited condition, affects males
Main areas of brain:
- cerebrum
- cerebellum
- medulla
- hypothalamus
- pituitary gland
(Contains approx 86 billion neurones)
Cerebrum:
= controls complex behaviour
learning, memory, personality, conscious thought
Cerebellum
= controls posture, balance, involuntary movement
Medulla
= controls automatic actions (heart rate, breathing rate)
Hypothalamus
= regulates temperature & water balance
Pituitary gland
= stores & releases hormones that regulate many body functions
How did scientists work out function of different regions of brain?
- Used evidence from stroke victims
- analysed damaged region & its effects
How did scientists link areas of brain to region of body it controls
- placed electrodes inside animal/human brains
- electrodes transmit electrical impulses, result in movement in different parts of animals body
Computed Tomography (CT) scans:
- use x-rays to create 3D image of inside of body
- position of abnormalities linked to changes in patients behaviour
Can’t be used regularly as X-ray radiation increases risk of cancer
Magnetic resonance imaging (MRI) scans:
- use powerful magnets to identify brain abnormalities
- fMRI (functional) produces images in real time
- scientist identify areas of brain with increased blood flow (active when carrying out specific activity)
Peripheral nervous system (PNS)
= all neurones that connect CNS to rest of body (sensory & motor neurones)
Damage to PNS/CNS could occur from:
- injury
- disease
- genetic condition
- ingesting a toxic substance
Effects of damage to PNS
- an inability to detect pain
- numbness
- loss of coordination
Can the PNS regenerate?
- minor nerve damage self-heals, symptoms gradually decrease
- sever nerve damage treated through surgery
Effects of damage to CNS:
- loss of control of body systems
- partial/complete paralysis
- memory loss & processing difficulties
Can the CNS regenerate?
No
damage permanent unless corrected by surgery
Why is damage to CNS often impossible to repair
- spine cord: difficult to identify & repair damage to an individual nerve fibre without damaging others
- brain: damage difficult to diagnose, MRI/CT scans may be used
Treatments available for some brain conditions:
- radiotherapy/chemotherapy: treats brain tumour
- surgery: removes damaged brain tissue
- deep brain stimulation: inserting electrode to stimulate brain function
