Nervous system

structure of nervous system

Central nervous system→ spinal chord and brain

Peripheral Nervous system→ all nerves that take info from our sense organs into CNS & from CNS to effector (muscles/glands)

label motor neurone

relay neurone

A = dendrites

B = cell body

C = axon

D = axon terminals

sensory neuron

A = dendrites

C = axon

D = nucleus

E = cell body

F = Myelin sheath

H = axon terminals

what is a nerve

a bundle of neurones

adaptation of neurones

long fibre (axon) can carry messages up and down the body over long distances

electrical nerve impulse passes along axon

axon insulated by a fatty (myelin) sheath → increases the speed of the nerve impulses along the neurone

fine branches (dendrites) at their tips to communicate with other neurones

Process of synaptic transmission

1. nerve impulses arrives at the synapse

2. chemical messages (neurotransmitters) are released into synapse

3. neurotransmitter diffuses across the synapse

4. they bind to receptors on the membrane of the post synaptic neurons

5. binding of neurotransmitter to receptor stimulates in post synaptic neurone

reflex arc

does not involve the conscious part of the brain

involuntary response to a stimuli (throughout evolution humans have needed to respond to a variety of different situations)

they protect us from harm

reflex arc process

1. stimulus detected by receptor cell eg in finger

2. impulse passed on to sensory neurone

3. sensory neurone passes impulse to spinal chord

4. impulse transmitted to relay neurone in spinal chord

5. impulse carried along nerve cell (motor neurone to effector organ)

6. effector brings response eg finger moving away from hot object

reflex arc including synaptic transmission (6marks)

receptor detects a stimulus

impulse sent to sensory neurone which is sent to spinal cord across synapse

relay neurone in spinal cord carries impulse to motor neurone across synapse

motor neurone carries impulse to effector organ

effector organ brings response

eg muscles of arm contract

reaction time

time taken between the presentation of a stimulus and the initiation of the muscular response to that stimulus

factors that affect reaction time

age

tiredness

depressant & stimulant drugs

distractions

sex

physical fitness

measuring reaction time practical

1. Person A holds out their hand with a gap between their thumb and first finger.

2. Person B holds the ruler with the zero at the top of person A's thumb

3. Person B drops the ruler without telling Person A and they must catch it.

4. The number level with the top of person A's thumb is recorded in a suitable table. Repeat this ten times.

5. Swap places, and record another ten attempts.

6. You can use the conversion table to help convert your ruler measurements into reaction time or just record the catch distance in cm.

Why is using a computer program to measure reaction times likely to be more valid than using the ruler method?

no indicator before hand when colour change

• able to get more accurate answer an answer has a higher resolution

Structure of brain

cerebral cortex

cerebellum

medulla

cerebral cortex

outer most layer

concerned with consciousness, intelligence, memory and language

folded → greater surface area

composed of grey matter consisting mainly of cell bodies and capillaries

cerebellum

• mainly coordination of muscular activity

• doesn’t initiate movement→ contributes to precision and accurate timing

• receives input from sensory system of spinal chord and other parts of the brain → integrates input to fine-tune activity

• damages produces disorders in fine movement, equilibrium, posture and motor learning

medulla

unconscious activity → heartbeat & breathing

studying the brain

neuroscientists have been able to map the regions of the brain by…

studying patients with brain damage

electrically stimulating different parts of the brain

using MRI

though the complexity of the brain makes investigating and treating the brain difficult

Magnetic resonance imaging (MRI)

shows exactly which areas of the brain are affected by a stroke or tumour

so scientists can link loss of function by the brain area

How is information transmitted from light receptors in the retina to the brain?

• electrical impulses sent

• via sensors neurones

• from eye to the brain by optic nerve to process information

the eye

sense organ containing receptors sensitive to light intensity and colour

compound eye

have more than one lens

common in nature

complex eye

eyes with a single lens

eg mammals

how do we see?

• rays of light are refracted (bent) first by the cornea and then by the lens → they focus on the retina to converge to the fovea

• light rays converge towards the retina

• the lens is able to precisely focus the image because of its ability to change shape

• focusing on a distant object → the lens becomes thinner

• focusing on a near object → the lens becomes fatter

accommodation

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

to focus on near object

• the ciliary muscles contract

• suspensory ligaments loosen

• the lens is then thicker and refracts light ray strongly

• Close, Ciliary, Contract

to focus on distant object

ciliary muscles relax

suspensory ligaments are pulled tight

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

• How does a dim/dark room cause iris to change shape of a pupil?

circular muscles dilate

radial muscles constrict

more light through pupil (dilates)

How does a bright light cause iris to change shape of a pupil?

• circular muscles in iris contract

• radial muscles dilate (relax)

• allows less light through pupil (contricts)

What is short sightedness (myopia) due to ?

a very curved lens

eyeball is too big

description of short sightedness

distant objects are blurry whilst nearby objects are in focus

light focuses in front of retina so images on retina are out of focus/blurry

ways to treat short sightedness

wear glasses with concave lens

spreads out light from distant object before it meets eye

results in light being brought into perfect focus on the retina

What is long sightedness (hyperopia) due to?

a lens that is too flat

the eye ball is to short

description of long sightedness

distant object are in focus while nearby objects objects are blurry

light focuses behind retina so images on retina are out of focus/blurry

ways to treat long sightedness

to wear glasses with convex lens

brings light rays together more before they reach the eye itself

now the thinner lens brings rays of light together to the retina perfectly

adv and disadv of replacing lenses

• + permanently corrects visual impairment ( add or replace lens)

• - can cause damage to retina, infection, & cataracts developing if natural one is left in place

adv and disadv of contact lenses

• + lasts a long time (hard lens)

• + more flexible & comfortable to wear (soft lens)

• - have to be removed overnight, kept sterile, possible baad environmental impact

adv and disadv of laser eye surgery

• - only available for adults

• + used to change curve of cornea so it refracts light more effectively (hyperopia)

• + thickness of lens is reduced so cornea reflects light less strongly (myopia)

• + fixes permanently

• - expensive

label eye

B = lens

C = cornea

D = pupil

E = iris

F= retina

G = opotic nerve

H = scalera

retina

contains light receptors

optic nerve

carries electrical impulses from eye to brain

scalera

tough white layer that protects eye

cornea

first responsible for refracting/ bending light

iris

contracts to allow less light or relaxes to allow more light to the pupil

ciliary muscles

involved in accommodation of lens → can contract/ relax to change shape of lense

suspensory ligaments

also involved in control of lens accommodation ( keeps lens in place)

lens

refracts light further

blind spot

where there are no light receptors

pupil

hole that can get bigger or smaller to let light in

fovea

densely packed light receptors

How can a persons eye adjust to form a clear image of a nearer object?

ciliary muscles contract

smaller diameter

suspensory ligaments loosen

lens becomes thick

once light hits lens its further refracted

converges on fovea at the retina

Why does a long sighted person that has difficulty seeing near objects clearly?

they may have eyes that are too short

therefore light focuses behind the retina so close objects appear blurry

describe how spectacles can correct long-sightedness

can wear glasses with a convex lens

this refracts light more so it can not spread out

this allows the light to converge perfectly on the retina