human nervous system- CNS,the brain, the eye

Nervous System

Coordinates body activities through electrical signals.

receptors

Special structures that allow living organisms to sense the stimuli i.e sound receptors in ear

central nervous system

The brain and spinal cord

Transmits & receives messages

sensory neurones

nerve cells that carry messages from cells in the sense organs to the CNS

motor neurones

nerve cells that carry messages from the CNS to effectors

effectors

muscles and glands that respond to nervous impulses

Information Transmission

Signals travel via neurons and synapses.

Reflex Action

Automatic response to stimuli, bypassing brain.

Importance of Reflex Actions

Protects body from harm through quick responses.

i.e if someone shines a bright light in your eye, your pupil automatically gets smaller

so less light gets into the eye

Reflex Arc

Pathway of neurons involved in reflex actions.

reflex arc steps

stimuli→ Receptor → sensory neurone → relay neurone → CNS → motor neurone → effector→ response

example of journey of reflex arc

1. bee stings finger

2.stimulation of pain receptors

3.impulses travel along sensory neurone

4.impulses passed along relay neurone, via synapse

5.impulse travels along motor neurone

6.when impulse reaches muscle, it contracts

Types of Neurons

Sensory, motor and relay

Synapse

connection between two neurones

required practical 7- reaction time with ruler

1)arm resting on edge of table

2)hold at zero end and drop

3)measure where caught to determine reaction time

4)repeat

required practical 7- reaction time computer

simple computer games i.e clicking the mouse

Brain Function

Controls thoughts, movements, and homeostasis.

labelled brain

Cerebral Cortex

wrinkly bit

Responsible for consciousness, intelligence and memory

Cerebellum

at the back, star like

Coordinates muscle movement

Medulla

controls unconsciousness activities like breathing and heart rate.

Hypothalamus

regulating body functions

pituary gland

releases hormones that control body actions

how do scientists study the brain

1) Studying patients with brain damage

2) Electrically stimulating the brain

3) MRI scans

1) Studying patients with brain damage

if small part of brain is damaged, the effect on patient tells you the role of the area damaged

2) Electrically stimulating the brain

brain can be stimulated electrically to observe what different parts of the brain does

3) MRI scans

produces very detailed picture of the brain structure

used to find out which areas are active when people are doing normal things like listening to music

Eye Function

Receives light and enables vision.

Labelled eye diagram:

Sclera

white of the eye

supports wall of eye

cornea

The clear tissue that covers the front of the eye

refracts light into the eye

iris

contains muscle that allows it to control the diameter of the pupil and therefore how much light enters

lens

Focuses light onto retina

retina

Contains sensory receptors that process visual information and sends it to the brain

focusing on near object

Ciliary muscles contract

suspensory ligaments loosen

lens is thicker and refracts light rays strongly

focusing on far object

ciliary muscles relax

suspensory ligaments tightened

lens flattens

slightly refracts light

bright light

Circular muscles contract

Radial muscles relax

Pupil constricts

dim light

Circular muscles relax

Radial muscles contract

Pupil dilates

Accommodation

Eye's adjustment for focusing on objects.

Myopia

Nearsightedness- can see close objects in clear focus

light is focused at front of retina

lens too curvy

eyeball is too long

Short sighted treatment

glasses with concave lens (curves inwards) so light can focus on the retina

Hyperopia

Farsightedness- an focus clearly on far objects

light focused behind retina

lens too flat

eyeball too short

long sighted treatment

glasses with convex lens (curves outwards) so light can focus on the retina

Temperature Regulation

thermoregulatory centre in brain which contains receptors that are sensitive to temp of blood flowing through brain

how body temp is regulated via negative feedback

too high- thermoregulatory centre receives info from temp receptors and triggers effectors i.e sweat glands to counteract change

too low-thermoregulatory centre receives info from temp receptors and triggers effectors i.e muscles to produce a response

too hot

1)hair lies flat

2)sweat is produced via glands and evaporates into skin. this transfers energy to environment

3)blood vessels dilate so more blood flows close to surface of skin-vasodilation

too cold

1)hairs stand up to trap insulating layer of air

2)no sweat produced

3)blood vessels constrict to close off skins blood supply- vasconstriction

4)when cold, you shiver too which need respiration that transfers energy to warm up body