B3.1 Nervous System OCR Gateway GCSE

Stimulus

Change in the environment

Receptor

Cell that detects a stimulus

Central Nervous System

Brain and Spinal Cord

Effector

Muscle or gland that carries out a response

Coordinated Response

Several effectors working together

Sensory Neurone

Carries impulses from receptor to CNS

Relay Neurone

Neurone in CNS

Motor neurone

Carries impulses from CNS to effector

Synapse

Gap between neurones

Axon

Long extension of cell body

Myelin Sheath

Fatty layer that insulates axon and speeds up impulse

Reflex

Fast, innate, automatic, involuntary response

Cornea Function

Refracts Light

Accommodation

Focusing on objects near and far away

Diverging Lens

Used to correct short sightedness

Converging Lens

Used to correct long sightedness

Cone Cell

Receptors in eye that detect colour

fMRI

Functional MRI, Detects blood flow to parts of brain to help show function

Peripheral Nervous System

The neurones that connect the CNS to the rest of the body.

What does the CNS help do?

Make decisions

Stage 1 of Nervous Response

Stimulus

Stage 2 of Nervous response

to Receptor

Intermediate stage between 2 and 3

An electrical impulse is sent from the receptor to the CNS through the sensory neurone

Stage 3

at CNS

Intermediate stage between 3 and 4 (of a nervous response)

An electrical impulse is sent from the CNS to the effector through the motor neurone.

Stage 4

to Effectors

Stage 5

Response

Sense organ: Eye

Receptor Cells: Rod and Cone, Stimulus: Light

Sense Organ: Tongue

Receptor Cells: Taste Buds, Stimulus: Chemical

Sense organ: Skin

Receptor Cells: Ruffini Capsule and Merkel Disks, Stimulus: Touch, heat and pain

Sense organ: Nose (receptor cells, stimulus)

Receptor Cells: Smell receptors, stimulus: chemical (smells and odours)

Brain is protected by…

skull

What does a muscle effector do?

Contracts to make a movement (and relaxes as well)

What does a gland effector do?

secretes a substance

“to secrete” Meaning

discharges/produces a substance

Neurones

Cells that transmit electrical impulses as part of the nervous response, there are 3 types of them.

Part of neurone: Cell body

Where the nucleus is found

Part of neurone: Dendrites

small branches at the end of the neurone which join to other neurones to form networks or to work as an effector

Structure of Sensory Neurone (from left to right)

Receptor, dendron, cell body, axon (myelin sheath (formed by schwann cells) around axon and dendron), dendrites (at the end of the sensory neurones which connects to CNS

Structure of Motor Neurone (from Left to right)

(end next to CNS) Cell body, axon (with myelin sheath wrapped around), dendrites (end next to effector)

Structure of Relay Neurone

Why are reflexes quick?

to help us survive

Reflexes are automatic which means…

they are involuntary, you don’t think about it

Reflexes are innate, meaning that:

You don’t learn them, you’re born with them

Reflex example: Pupil reflex

Pupils constrict in bright light to protect retina.

Reflex example: Rooting reflex in babies

helps baby to feed

Reflex example: Salivating

You produce saliva when smelling food

What does a reflex arc diagram show?

How a reflex works

Reflex arc diagram structure

Receptors —> Sensory Neurone —> CNS (almost junction maybe) —> Relay Neurone (Synapse between neurones) —> Motor Neurone —> Effector

Reflex arc shape

like a backwards C

Stage 1 of how electrical impulses cross a synapse gap

They arrive at the synapse, this causes neurotransmitter to be released

Stage 2 of how electrical impulses cross a synapse gap

the neurotransmitter diffuses across the synapse extremely quickly

Stage 3 of how electrical impulses cross a synapse gap

It is detected by receptors on the other neurone which causes a new electrical impulse to start

Ciliary Muscle

Controls the shape of the lens

Cornea

forms the outer protective membrane of the eye and bends the light in towards the pupil

Iris

Gives the eye its colour and controls the amount of light entering the eye by controlling the diameter of the pupil

Lens

Changes shape in order to focus the light on the retina (especially on the fovea at the back of the eye)

Retina

Made of light receptors (rod and cone cells). These receptors turn light into nerve impulses.

Optic Nerve

Carries nerve impulses to the brain

Suspensory Ligament

Connects ciliary muscle to lens

Blind Spot

The point where the optic nerve meets the retina

Which 2 parts of the eye refract light?

Cornea and the Lens

If an object is near, what do the ciliary muscles and suspensory ligaments do and what shape is the lens?

Ciliary muscles contract, suspensory ligaments slacken and the lens shape is fat and round.

If an object is far away what do the ciliary muscles and suspensory ligaments do and what shape is the lens?

Ciliary muscles relax, suspensory ligaments stretch and the lens shape is thinner and flatter.

Common Problems with eyesight

Red-green colour blindness and short and light sightnedness

The Retina is made up of:

rod and cone cells, (cone cells are less sensitive)

Rod cells

Very sensitive cells, can see in low light and only detect/see black and white

Problem with cone cells:

Can lead to red green colour blindness (where a person can’t tell the difference between red and green, it’s inherited usually and more common in men)

Test for colour blindness

Ishihara test

Long Sightedness Symptoms

Hard to focus on objects close up

Causes of Long Sightedness (in terms of lens and eye shape)

Lens is too thin and/or eye is too flat

When you have long sightedness…

Light is focused behind the retina when you look at close up objects

Short sightedness symptoms

Hard to focus on things further away

Causes of Short Sightedness (in terms of lens and eye shape)

Lens too fat and round, eye shape is like a rugby ball and too long

How is light focused when someone has short-sightedness?

In front of the retina (especially when things are far away)

The Cerebrum is also known as…

the cerebral cortex

Cerebrum

controls complex behaviour (conscious movement and thought, personality, memory, emotion and learning

Hypothalamus

Maintains body temperature and water levels in blood

Pituitary gland

Releases hormones into bloodstream

Medulla

Controls breathing and heart rate

Cerebellum

Where muscle memory is and controls your balance

Brain damage studies

studying effects of damage to the brain caused by things such as strokes (blockage in a blood vessel which stops oxygen to the brain tissue).

CT Scans

An X-Ray scan that can produce a 3D image of the brain to identify abnormalities.

Electrode Stimulation

Studying the response of a patient when a part of the brain is stimulated with an electrode. This is often done during “awake surgery”.

Damage to the nervous system can be caused by

injury (e.g. a cut), disease (e.g. measles, diabetes) and genetic conditions (e.g. huntingdon’s disease).

Damage to the Peripheral Nervous System can cause:

inability to detect pain, numbness and loss of coordination.

Damage to the Central Nervous System can cause:

a loss of control of body systems, partial or complete paralysis, memory loss or processing difficulties