B10 - The human nervous system

Homeostasis

regulation of conditions inside the body to maintain a stable internal environment, in response to internal and external conditions

What things need to be controlled?

Core body temperature (enzymes)
pH (enzymes)
Blood glucose concentration (respiration)
Water and ion content (osmosis)

What is a reflex?

involuntary response to a stimulus

Receptors

specialised cells that detect stimuli - changes in environment

Coordination centres

process the information received from receptors and coordinate response eg. brain, spinal cord

Effectors

muscles or glands that carry out response to stimuli

Function of the nervous system

enables humans to react to their surroundings and coordinate their behaviour

Central Nervous System (CNS)

Coordination centre consisting of brain and spinal cord which contains relay neurones that coordinate the response of the effectors

Sensory neurones

carry impulses from receptors to CNS

Relay neurones

carry impulses through spinal cord

Motor neurones

carry impulses from the CNS to effectors

Synapses

junctions between connected neurones

How neurones pass impulses

When an impulse arrives at a synapse with a neurone a chemical is released which diffuses across the synapse and sets off a new electrical impulse at the next type of neurone

Order of response of nervous system

Stimulus -> Receptor -> Coordinator (CNS) -> Effector -> Response

Cerebral cortex

concerned with consciousness, memory, intelligence, language

Cerebellum

concerned with coordination of muscle activity

Medulla

concerned with unconscious activity eg. heart beating, breathing

Pituitary gland

produces hormones

Hypothalamus

regulating centre for temperature and water balance in body

3 ways scientists can study the brain

Studying people with brain damage
Electrically stimulating the brain
Scanning the brain: CT, MRI

Electrical stimulation (studying brain)

expose the brain by removing too of skull, stimulate different areas and see what effect it has

MRI scans (studying brain)

enables scientists to see exactly which area of the brain is affected and link behaviours to it

CT scans

X rays to produce cross sectional images of brain

Why is it so difficult to study the brain?

Wide range of things that could go wrong
Difficult to access and fix as it is well protected by skull an surrounding fragile brain tissue
Difficult to target with medications as it is so complex

Retina

contains light sensitive cells

Optic nerve

transmits impulses to brain, so we can see what we're looking at

Sclera

tough, white protective layer of eye

Cornea

refracts light

Iris

controls amount of light entering eye

Ciliary muscles

alters thickness of lens for focus

Suspenseful ligaments

attach lens to CM

Fovea (Yellow Spot)

most sensitive part of the retina where we sense colour

Pupil

lets light into eye

How our brain receives information about light entering eye

Retina contains light sensitive cells that pass impulses along neurone to the optic nerve, which can then be interpreted in the brain

Iris reflex - Bright light

circular muscles contract, radial muscles relax
pupil constricts, less light in eye

Iris reflex - Dim light

circular muscles relax, radial muscles contract
pupils dilate
more light enters the eye

Accommodation of the eye - Distant objects

ciliary muscle relax (outwards away from lens), suspension ligaments pulled tight
lens more rounded and pulled thin, less convex
lens refracts light less

Accommodation of the eye - Near objects

ciliary muscles contract (inwards towards lens), suspension ligaments slack
lens more rounded and relatively thick, more convex
lens refracts more light - light rays focus on retina

Myopia

shortsighted
near objects yes
distant objects no (light focused in front of retina)

Myopia treatment

Wear glasses with a concave lens - spread light from distant objects before it reaches the eye

Hyperopia

long sighted
distant objects yes
near objects no
(lens cannot refract rays of light strong enough)

Hyperopia treatment

Wear glasses with convex lens - bring rays of light together before they reach the eye

Reaction time practical - Method

1. Person 1 sits on a stool with good upright posture and places the forearm of their non-dominant arm across the table with their hand overhanging the edge
2. Person 2 holds a ruler vertically. The 0cm mark should be between person 1's thumb and first finger
3. Person 2 tells person 1 to prepare the catch the ruler and drops it at a random time. Person 1 has to catch the ruler with their thumb and first finger as quickly s possible when it drops
4. Person 2 records the measurement on the ruler that is level with the top of person 1's thumb
5. Test is repeated a number of times and a mean is calculated.

Reaction time variable

Independent variable - person having RT tested
Dependent variable - reaction time
Control variable - starting distance between thumb and first finger, room conditions eg lighting, background noise, where you measure from.